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PD-1 blockade enhances the function of antitumor T cells and antibody-dependent, cell-mediated cytotoxicity (ADCC) of NK cells. In a single-center, open-label, phase 2 trial, we tested the combination of pembrolizumab, an anti-PD-1 monoclonal antibody, and rituximab, an anti-CD20 monoclonal antibody that induces ADCC, in 30 patients with follicular lymphoma (FL) with rituximab-sensitive disease who had relapsed after ≥1 prior therapy. Pembrolizumab was administered at 200 mg IV every 3 weeks for up to 16 cycles, and rituximab was given at 375 mg/m2 IV weekly for 4 weeks in cycle 1 only. The most common grade 3/4 adverse events (AEs) were liver enzyme abnormalities (3%), diarrhea (3%), nausea (3%), aseptic meningitis (3%), and pancreatitis (3%). Low-grade immune-related AEs were reported in 80% of patients, including diarrhea (43%), liver enzyme abnormalities (33%), thyroid dysfunction (27%), and rash (23%). Grade 3 or 4 immune-related AEs occurred in 13% of the patients. Treatment-related AEs led to discontinuation in 6 (20%) patients. The overall response rate (primary end point) was 67%, and the complete response (CR) rate was 50%. Median progression-free survival (PFS) was 12.6 months (95% confidence interval, 8.2-27.6), the 3-year overall survival rate was 97%, and 23% of patients were in remission at a median follow-up of 35 months. The presence of a high CD8+ T-effector score at baseline in the tumor was associated with induction of a CR and improved PFS. In this single-arm, phase 2 study, the combination of pembrolizumab and rituximab demonstrates favorable efficacy and safety profile in relapsed FL. This trial is registered at www.clinicaltrials.gov as #NCT02446457.

CXCR5 mediates homing of both B and follicular helper T (TFH) cells into follicles of secondary lymphoid organs. We found that CXCR5+CD8+ T cells are present in human tonsils and follicular lymphoma, inhibit TFH-mediated B cell differentiation, and exhibit strong cytotoxic activity. Consistent with these findings, adoptive transfer of CXCR5+CD8+ T cells into an animal model of lymphoma resulted in significantly greater antitumor activity than CXCR5-CD8+ T cells. Furthermore, RNA-Seq-based transcriptional profiling revealed 77 differentially expressed genes unique to CXCR5+CD8+ T cells. Among these, a signature comprised of 33 upregulated genes correlated with improved survival in follicular lymphoma patients. We also showed that CXCR5+CD8+ T cells could be induced and expanded ex vivo using IL-23 plus TGF-β, suggesting a possible strategy to generate these cells for clinical application. In summary, our study identified CXCR5+CD8+ T cells as a distinct T cell subset with ability to suppress TFH-mediated B cell differentiation, exert strong antitumor activity, and confer favorable prognosis in follicular lymphoma patients.

Chimeric antigen receptor (CAR) T-cell therapy has been clinically proven to efficiently combat haematological malignancies. However, continuous efforts are required to increase the specificity of CAR T-cells against tumour versus normal tissues, and are essential to improve their antitumour activity in solid tumours. This review summarises the structure of major CAR designs, and strategies to overcome immunosuppressive tumour microenvironment, and reduce toxicities. Along with reviewing currently available techniques that allow the elimination of CAR T-cells after they fulfil their desired functions, using suicide genes, drug elimination strategies are also introduced. A better understanding of the strengths and pitfalls of CAR T-cell therapy will provide fundamental knowledge for the improvement of engineered T-cell therapy in the near future.

// Fei Mao 1,* , Qiang Tu 2,* , Li Wang 1 , Fuliang Chu 3 , Xia Li 4 , Haiyan S. Li 5 and Wenrong Xu 1 1 Key Laboratory of Medical Science and Laboratory Medicine of Jiangsu Province, School of Medicine, Jiangsu University, Zhenjiang, Jiangsu, P.R. China 2 Jiangning Hospital of Nanjing, Nanjing, Jiangsu, P.R. China 3 Department of Lymphoma and Myeloma, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA 4 Department of Gastroenterology, Binzhou Medical University Yantai Affiliated Hospital, Yantai, Shandong, P.R. China 5 Department of Immunology, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA * These authors have contributed equally to this work Correspondence to: Wenrong Xu, email: // Haiyan S. Li, email: // Keywords : mesenchymal stem cell, inflammatory bowel disease, cell therapy, pericyte, tissue repair Received : January 05, 2017 Accepted : March 06, 2017 Published : March 29, 2017 Abstract Mesenchymal stem or stromal cells (MSCs) are non-hematopoietic stem cells that facilitate tissue regeneration through mechanisms involving self-renewal and differentiation, supporting angiogenesis and tissue cell survival, and limiting inflammation. MSCs were originally identified and expanded in long-term cultures of cells from bone marrow and other organs; and their native identity was recently confined into pericytes and adventitial cells in vascularized tissue. The multipotency, as well as the trophic and immunosuppressive effects, of MSCs have prompted the rapid development of clinical applications for many diseases involving tissue inflammation and immune disorders, including inflammatory bowel disease. Although standard criteria have been established to define MSCs, their therapeutic efficacy has varied significantly among studies due to their natural heterogenicity. Thus, understanding the biological and immunological features of MSCs is critical to standardize and optimize MSCs-based therapy. In this review, we highlight the cellular and molecular mechanisms involved in MSCs-mediated tissue repair and immunosuppression. We also provide an update on the current development of MSCs-based clinical trials, with a detailed discussion of MSC-based cell therapy in inflammatory bowel disease.

Immunotherapeutic strategies are promising approaches for the treatment of follicular lymphoma (FL). However, their efficacy may be limited by immunosuppressive elements in the immune system and tumor microenvironment. Therefore, strategies to reverse the effects of the immunosuppressive elements are needed. We observed that regulatory T cells (Tregs) were increased in the peripheral blood at diagnosis and persisted in high numbers after induction of clinical remission with a cyclophosphamide and doxorubicin-containing chemotherapy regimen in FL patients. High levels of peripheral blood Tregs prior to therapy were associated with decreased progression-free survival in FL patients treated with either chemotherapy or combination immunotherapy that targeted CD20 and PD-1 with monoclonal antibodies rituximab and pidilizumab, respectively. Intratumoral and peripheral blood Tregs potently suppressed autologous antitumor effector T cells in FL. However, the effects of FL Tregs could be reversed by triggering Toll-like receptors (TLR) with TLR ligands Pam3 CSK4 (TLR 1/2), flagellin (TLR 5), and CpG-B (TLR 9), and/or OX40. The TLR ligands synergized with each other as well as OX40 signaling to inhibit Tregs. Furthermore, they restored the function of FL tumor-specific effector T cells. Our results suggest that a state of tolerance exists in FL patients at diagnosis and after induction of clinical remission, and agents that activate TLRs 1/2, 5, and 9, and OX40 may serve as adjuvants to enhance the efficacy of antitumor immunotherapeutic strategies and preventive vaccines against infectious diseases in these patients.

In immune responses, activated T cells migrate to B-cell follicles and develop into follicular T-helper (TFH) cells, a recently identified subset of CD4(+) T cells specialized in providing help to B lymphocytes in the induction of germinal centres. Although Bcl6 has been shown to be essential in TFH-cell function, it may not regulate the initial migration of T cells or the induction of the TFH program, as exemplified by C-X-C chemokine receptor type 5 (CXCR5) upregulation. Here we show that expression of achaete-scute homologue 2 (Ascl2)--a basic helix-loop-helix (bHLH) transcription factor--is selectively upregulated in TFH cells. Ectopic expression of Ascl2 upregulates CXCR5 but not Bcl6, and downregulates C-C chemokine receptor 7 (CCR7) expression in T cells in vitro, as well as accelerating T-cell migration to the follicles and TFH-cell development in vivo in mice. Genome-wide analysis indicates that Ascl2 directly regulates TFH-related genes whereas it inhibits expression of T-helper cell 1 (TH1) and TH17 signature genes. Acute deletion of Ascl2, as well as blockade of its function with the Id3 protein in CD4(+) T cells, results in impaired TFH-cell development and germinal centre response. Conversely, mutation of Id3, known to cause antibody-mediated autoimmunity, greatly enhances TFH-cell generation. Thus, Ascl2 directly initiates TFH-cell development.

Optimal expansion protocols for adoptive human T-cell therapy often include interleukin (IL)-15; however, the mechanism by which IL-15 improves the in vivo antitumor effect of T cells remains to be elucidated. Using human T cells generated from HLA-A2+ donors against novel T-cell epitopes derived from the human U266 myeloma cell line Ig light chain V-region (idiotype) as a model, we found that T cells cultured with IL-15 provided superior resistance to tumor growth in vivo, compared with IL-2, after adoptive transfer into immunodeficient hosts. This effect of IL-15 was associated with delayed/reversed senescence in tumor antigen-specific memory CD8+ T cells mediated through downregulation of P21WAF1, P16INK4a, and P53 expression. Compared to IL-2, IL-15 stimulation dramatically activated JAK3-STAT5 signaling and inhibited the expression of DNA damage genes. Thus, our study elucidates a new mechanism for IL-15 in the regulation of STAT signaling pathways and CD8+ T-cell senescence.

Targeting CAR T resistance due to CD19 loss with CD79b-specific CAR T cells in B-cell malignancies Fuliang Chu, JingJing Cao, Jingwei Liu, Xiaoyun Cheng, Swathi Karri, Adithi Reddy, Shao Qing Kuang, Jinsheng Weng, Sattva S. Neelapu Department of Lymphoma and Myeloma, The University of Texas M. D. Anderson Cancer Center. Houston, TX 77030 USA Chimeric antigen receptor (CAR) T cells targeting CD19 are highly effective in B-cell malignancies and two CD19-targteing CAR T-cell therapy products were recently approved by the US FDA for relapsed or refractory B-cell acute lymphoblastic leukemia and/or large B cell lymphoma. In pivotal trials, durable remissions lasting more than 1 year have been observed in ~40-50% of these patients. However, relapse or progression occurs in ~50-60% and a major cause of resistance appears to be due to CD19 antigen loss. Thus, there is an urgent need to develop CAR T-cell therapies against novel targets to further improve outcomes in these patients. CD79b is a pan B-cell linage marker and an important component of the B-cell receptor complex. CD79b is broadly expressed in normal B cells and B-cell malignancies and its expression is usually retained in CD19 negative tumors progressing after CD19-specific CAR T-cell therapy. Here, we report our results with a novel CD79b-specific CAR T cell product in in vitro and in vivo models. We generated five murine monoclonal antibodies against human CD79b by hybridoma technology and demonstrated that they bind specifically to recombinant human CD79b, have high affinity (Kd range of 1.44-18.1 nM), and stain multiple B-cell lymphoma cell lines comparable to the commercial CD79b fluorochrome-labeled antibodies. Next, we cloned the variable regions of the heavy and light chains of the CD79b antibodies, and developed lentiviral constructs for CD79b-specific CARs with CD3z and CD28 costimulatory domains. We demonstrated that the CD79b-CAR lentiviral constructs can be transduced into primary CD4+ and CD8+ T cells from healthy donors to >85% transduction efficiency. We observed that the CD79b-specific CAR T cells but not untransduced T cells had significant cytotoxic activity that was comparable to control CD19-specific CAR T cells against Daudi Burkitt lymphoma and Mino mantle cell lymphoma cell lines. More importantly, CD79b- but not CD19-specific CAR T cells lysed CD19-CD79b+ lymphoma cells. Significant CD107a/b degranulation was also observed in both CD4+ and CD8+ CD79b-specific CAR T cells when they were co-cultured with lymphoma cell lines. Multiplex cytokine analysis of co-culture supernatants revealed predominantly release of IFN-γ. The efficacy of CD79b-specific CAR T cells was also examined in vivo against Mino xenograft models in NSG mice. Luciferase-labeledMino mantle cell lymphoma cell line was injected IV into NSG mice at 2x106 tumor cells/mouse. After 18 days, mice were treated with untransduced primary T cells, CD19-specific CAR, or CD79b-specific CAR T cells via tail vein at 10x106 T cells/mouse. Bioluminescence imaging was used to assess tumor burden. Tumor growth was inhibited and survival was markedly improved in mice treated with CD19- and CD79b-specific CAR T cells but progressive tumor growth was observed in the control group treated with untransduced T cells. Additional studies using CD19-CD79b+ lymphoma cell line xenograft model are ongoing and will be presented at the meeting. In conclusion, these preclinical results indicate that CD79b is a novel target for CAR T-cell therapy and support its evaluation in patients with B-cell malignancies. Importantly, our results suggest that targeting CD79b could be a novel strategy to overcome resistance due to CD19 loss after CD19-specific CAR T-cell therapy. Disclosures No relevant conflicts of interest to declare.

Chimeric antigen receptor (CAR)-modified T-cell therapy targeting CD19 induces high response rates in patients with relapsed or refractory B-cell lymphomas. However, about 60% of patients experience primary or secondary resistance after CD19-targeted CAR T-cell therapy and a major of cause of failure appears to be due to loss of CD19 expression on the tumor. Therefore, novel targets for adoptive T-cell therapeutic approaches are needed to further improve clinical outcome in these patients. T-cell leukemia/lymphoma antigen1 (TCL1) is an oncoprotein that is overexpressed in multiple B-cell malignancies including follicular lymphoma (FL), mantle cell lymphoma (MCL), diffuse large B-cell lymphoma (DLBCL), and chronic lymphocytic leukemia (CLL). Importantly, it has restricted expression in only a subset of B cells among normal tissues. We previously identified a TCL1-derived HLA-A2-binding epitope (TCL170-79 SLLPIMWQLY) that can be used to generate TCL1-specific CD8+ T cells from peripheral blood mononuclear cells of both HLA-A2+ normal donors and lymphoma patients. More importantly, we showed that the TCL1-specific CD8+ T cells lysed autologous primary lymphoma cells but not normal B cells (Weng et al. Blood 2012). To translate the above discovery into clinic, we cloned the T-cell receptor (TCR) alpha and beta chains from a TCL1-specific CD8+ T-cell clone and showed that this TCL1-TCR could be transduced into polyclonal donor T cells using a lentiviral system with a transduction efficiency of >40% as determined by TCL170-79 tetramer positive T cells. Furthermore, we demonstrated that the TCL1-TCR-transduced T cells recognized T2 cells pulsed with TCL170-79 peptide producing IFN- γ >8 ng/ml and IL-2 >350 ng/ml but were not reactive to control HIV-Gag peptide (IFN- γ 10 ng/ml) suggesting it has moderate to high avidity. Importantly, TCL1-TCR-transduced T cells lysed HLA-A2+ (up to 43% lysis of Mino and 25% lysis of Jeko-1 at 40:1 Effector:Target ratio) but not HLA-A2- lymphoma cell lines (5.5% lysis of HLA A2- Raji and 2.3% lysis of Daudi at 40:1 Effector:Target ratio). TCL1-TCR-transduced T cells were also cytotoxic to HLA-A2+ primary lymphoma tumor cells (up to 48% lysis of CLL, 43% lysis of FL, 41% lysis of DLBCL, 46% lysis of splenic marginal zone lymphoma, and 11% lysis of MCL at 40:1 Effector:Target ratio) but not normal B cells derived from the same patients. Lastly, TCL1-TCR transduced T cells showed high efficacy in in vivo models. Adoptive transfer of the TCL1-TCR-tranduced T cells significantly reduced lymphoma tumor growth and extended survival in Mino mantle cell lymphoma cell line xenograft model (48% survival in TCL1-TCR-T treated group vs. 12.5% survival in control group at 10 weeks n=7-8 mice/group; P=0.02). Collectively, our data suggest that the high expression in B-cell tumors, restricted expression in normal tissues, and presence of an immunogenic CD8 T-cell epitope, make TCL1 a target for T cell-based therapeutic approaches in multiple B-cell malignancies. Our results also demonstrate that the TCL1-specific TCR-transduced T cells may serve as a novel adoptive immunotherapy approach for the treatment of patients with various B-cell malignancies (including FL, MCL, DLBCL, CLL). Acknowledgments: This study is supported by MD Anderson Moon Shot Program and CPRIT and the National Natural Science Foundation of China Grant (No. 81570189) Disclosures Neelapu: Kite/Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Cellectis: Research Funding; Poseida: Research Funding; Merck: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Acerta: Research Funding; Karus: Research Funding; Bristol-Myers Squibb: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; Unum Therapeutics: Membership on an entity's Board of Directors or advisory committees.

The microenvironment of human follicular lymphoma (FL), an incurable B cell non-Hodgkin’s lymphoma, is thought to play a major role in its pathogenesis and course. Microenvironmental cells of likely importance include follicular Th cells (TFH) and regulatory T cells (Tregs), and understanding their interactions with FL tumor cells is necessary to develop novel therapeutic strategies. We found that IL-4 and CD40L are expressed by intratumoral TFH and induce production of CCL17 and CCL22 by FL tumor cells. IL-4 alone induces only CCL17 but enhances stimulation by CD40L of both CCL17 and CCL22. Consistent with our in vitro results, mRNA transcripts of IL-4 correlated with CCL17, but not CCL22, in gene expression profiling studies of FL biopsies, whereas CD40L correlated with both CCL17 and CCL22. Tumor supernatants induced preferential migration of Tregs and IL-4–producing T cells rather than IFN-γ–producing T cells, and Abs to CCR4 significantly abrogated the migration of Tregs. Our results suggest that through two distinct mechanisms, intratumoral TFH induce production of CCL17 and CCL22 by FL tumor cells and facilitate active recruitment of Tregs and IL-4–producing T cells, which, in turn, may stimulate more chemokine production in a feed-forward cycle. Thus, TFH appear to play a major role in generating an immunosuppressive tumor microenvironment that promotes immune escape and tumor survival and growth. Our results provide novel insights into the cross talk among TFH, tumor cells, and Tregs in FL, and offer potential targets for development of therapeutic strategies to overcome immune evasion.

Despite the potent ability of dendritic cells (DCs) to stimulate lymphocyte responses and host immunity, granulocyte-macrophage colony-stimulating factor-derived DCs (GM-DCs) used as antitumor vaccines have demonstrated relatively modest success in cancer immunotherapy. We found that injecting GM-DCs into melanoma tumors in mice, or culturing GM-DCs with melanoma-secreted cytokines or melanoma-conditioned medium, rapidly suppressed DC-intrinsic expression of the gene encoding inhibitor of differentiation 2 (ID2), a transcriptional regulator. Melanoma-associated cytokines repressed Id2 transcription in murine DCs through the activation of signal transducer and activator of transcription 3 (STAT3). Enforced expression of ID2 in GM-DCs (ID2-GM-DCs) suppressed their production of the proinflammatory cytokine tumor necrosis factor-α (TNF-α). Vaccination with ID2-GM-DCs slowed the progression of melanoma tumors and enhanced animal survival, which was associated with an increased abundance of tumor-infiltrating interferon-γ-positive CD4(+) effector and CD8(+) cytotoxic T cells and a decreased number of tumor-infiltrating regulatory CD4(+) T cells. The efficacy of the ID2-GM-DC vaccine was improved by combinatorial treatment with a blocking antibody to programmed cell death protein-1 (PD-1), a current immunotherapy that overcomes suppressive immune checkpoint signaling. Collectively, our data reveal a previously unrecognized STAT3-mediated immunosuppressive mechanism in DCs and indicate that DC-intrinsic ID2 promotes tumor immunity by modulating tumor-associated CD4(+) T cell responses. Thus, inhibiting STAT3 or overexpressing ID2 selectively in DCs may improve the efficiency of DC vaccines in cancer therapy.

T-cell leukemia/lymphoma Antigen1 (TCL1) is a B-cell oncoprotein that is overexpressed in multiple forms of B-cell lymphoma. In our previous study, we identified a HLA*A0201-restricted T cell epitope from TCL1 that stimulated CD8+ T cells to specifically lyse lymphoma cells. In this study, we have cloned the TCL170-79 peptide-specific T-cell receptor (TCR) gene that after lentivirus transduction into donor T cells can redirect the specificity of T cells to lyse T2 cells pulsed with TCL170-79 but not control peptide. The TCR-transduced CD8+ T cells efficiently lysed HLA-0201+, TCL1-expressing human lymphoma cell lines and primary lymphoma cells, but not normal B cells. Adoptive transfer of TCR-transduced T cells into a mantle cell lymphoma xenograft mouse model inhibited the tumor growth and significantly extended the survival of mice. In addition, we found that TCL1 is expressed in multiple solid tumors. The TCR-transduced T cells lysed colon and liver tumor cells but not normal human cells in vitro as well as in a mouse xenograft model. Collectively, our data demonstrate that TCL1-specific TCR-based immunotherapy is highly effective against human B-cell lymphomas and non-hematological tumors. Citation Format: Jinsheng Weng, Kelsey E. Moriarty, Yong Pan, Flavio Egidio Baio, Hua Wang, Hiroki Torikai, Sourindra N. Maiti, Fuliang Chu, Xiaoyun Cheng, Swathi Karri, Deepshika Medapalli, Laurence J. N. Cooper, Sattva S. Neelapu. A TCL1-specific T-cell receptor redirects T cells against B-cell lymphomas and non-hematological tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2566.

Three-dimensional structures of β2-microglobulin (β2m) from chicken and various mammals have been described previously, but aside from genomic sequences, very little is known about the three-dimensional structures of β2m in species other than warm-blooded vertebrates. Here, we present the first three-dimensional structure of β2m from bony fish grass carp (Ctid-β2m), resolved at 2.1 Å. The key structural differences between this new structure and previously published structures are two new hydrogen bonds at positions Ile37 and Glu38 in strand C and Lys66 in strand E, and a hydrophobic pocket around the center of the protein found in Ctid-β2m. Importantly, Ctid-β2m has a short D strand and a long loop between stands C and D, rather than the flexible region found in other β2m structures that serves as a putative binding region for the major histocompatibility complex heavy chain. Comparing the Ctid-β2m structure with those of bovine and human β2ms, the Cα root mean square deviation of the latter are 1.3 Å and 1.8 Å, respectively. Compared with the constant domains of Lamprey T cell receptor-like receptor (Lamp-TCRLC) and Amphioxus V and C domain-bearing protein (Amphi-VCPC), Ctid-β2m exhibits very different topology. The three-dimensional structures of domains predicted from Amphi-VCPC/Lamp-TCRLC are distinctly lacking in strand A of β2ms. There are 18 amino acids at the N terminus of Amphi-VCPC that may have evolved into strand A of β2ms. A mutation in the BC loops of Amphi-VCPC may have led to the novel topology found in β2m. Based on these results, Ctid-β2m may well reflect evolutionary characteristics of ancestral C set molecules.

The leukocyte Ig-like receptor (LILR/ILT/LIR) family comprises 13 members that are either activating or inhibitory receptors, regulating a broad range of cells in the immune responses. LILRB1 (ILT2), LILRB2 (ILT4) and LILRA1 (LIR6) can recognize MHC (major histocompatibility complex) class I or class I-like molecules, and LILRB1/HLA-A2, LILRB1/UL18 and LILRB2/HLA-G complex (extracellular domains D1D2) structures have been solved recently. The details of binding to MHC have been described. Despite high levels of sequence similarity among LILRA1, LILRA2 (ILT1), LILRA3 (ILT6) and LILRB1/B2, all earlier experiments showed that LILRA2 does not bind to MHC, but the reason is unknown. Here, we report the LILRA2 extracellular D1D2 domain crystal structure at 2.6 A resolution, which reveals structural shifts of the corresponding MHC-binding amino acid residues in comparison with LILR B1/B2, explaining its non-binding to MHC molecules. We identify some key residues with great influence on the local structure, which exist only in the MHC-binding receptors. Moreover, we show that LILRA2 forms a domain-swapped dimer. Further work with these key swapping residues yields a monomeric form, confirming that the domain-swapping is primarily amino acid sequence-specific. The structure described here supports the dimer conformation in solution observed earlier, and implies a stress-induced regulation by dimerization, consistent with its function as a heat shock promoter.

Immunoglobulin-like transcript 1 (ILT1/LIR-7/LILRA2/CD85h) is one of the activating receptors in the ILT family whose members have been reported to regulate a broad range of cells involved in the immune response. Although inhibitory ILT receptors have been extensively studied, however, functions and structures of ILT activating receptors have yet to be elucidated. Obtaining of sufficient amount of recombinant proteins is a requisite for the functional and structural studies of a given protein. As a technical bottleneck of the study, extracellular domains of the ILT1 form aggregation during recombinant production in the past efforts. Here, we report the large-scale stable production of ILT1 D1D2 domains through engineering of site-directed mutagenesis (R142C) that introduces a cysteine at amino acid position 142 to form a disulfide bond with the spare cys132 without topological influences of the native protein based on the known structures of the homologous ILT 2/4/11. The recombinant ILT1 D1D2 domains behave as an equilibrium of both stable dimer and monomer in solution and yield ideal crystals for structural determination. The availability of quantities of soluble ILT1 D1D2 domains provides useful reagent for further studies of its detailed structure and functions.

The infection of rhesus macaques (Macaca mulatta) by the SIV is the best animal model for studying HIV infection and for AIDS vaccine development. A prevalent MHC class I allele, Mamu-A*01, is known to correlate with containment of SIV, which has been extensively explored in studies of CTL-based vaccination concepts. We determined the crystal structures of Mamu-A*01 complexed with two immunodominant SIV epitopes: the nonamer CM9 of group-specific Ag (Gag, 181–189; CTPYDINQM) and the octamer TL8 of transcription activator (Tat, 28–35; TTPESANL). The overall structures of the two Mamu-A*01 complexes are similar to other MHC class I molecules. Both structures confirm the presence of an absolutely conserved proline anchor residue in the P3 position of the Ag, bound to a D pocket of the Mamu-A*01 H chain with optimal surface complementarity. Like other MHC/peptide complex structures, the P2 and C-terminal residues of the epitopes are also important for anchoring to the MHC molecule, whereas the middle residues form an arch and their side chains are directed into solvent. These two structures reveal details of how Mamu-A*01 interacts with two well-studied epitopes at the atomic level. We discuss the structural basis of CTL escape, based on molecular models made possible by these two structures. The results we present in this study are most relevant for the rational design of Mamu-A*01-restricted CTL epitopes with improved binding, as a step toward development of AIDS vaccines.

In order to further the present knowledge of the emerging severe acute respiratory syndrome-associated coronavirus (SARS-CoV), 486 different specimens from 54 patients with a clinical diagnosis of SARS were investigated for the presence of viral RNA, and 314 plasma specimens of 73 patients were examined for IgM and IgG antibodies specific against SARS-CoV using an indirect ELISA. Viral RNA was detectable in 28 of the 54 patients tested. Cumulative data showed that 67 of the 73 SARS patients demonstrated seroconversion by week 5 of illness. In contrast, only 1 of 278 healthy subjects enrolled in the study was found to be positive for the IgG antibody. Coexistence of viral RNA in plasma and specific antibodies was simultaneously observed over three consecutive weeks in two critical cases. In three convalescent patients in particular, cultivable SARS-CoV was detected in stool or urine specimens for longer than 4 weeks (29-36 days). These findings suggest that SARS-CoV may remain viable in the excretions of convalescent patients.

To characterize genetic variation of severe acute respiratory syndrome–associated coronavirus (SARS-CoV) transmitted in the Beijing area during the epidemic outbreak of 2003, we sequenced 29 full-length S genes of SARS-CoV from 20 hospitalized SARS patients on our unit, the Beijing 302 Hospital. Viral RNA templates for the S-gene amplification were directly extracted from raw clinical samples, including plasma, throat swab, sputum, and stool, during the course of the epidemic in the Beijing area. We used a TA-cloning assay with direct analysis of nested reverse transcription–polymerase chain reaction products in sequence. One hundred thirteen sequence variations with nine recurrent variant sites were identified in analyzed S-gene sequences compared with the BJ01 strain of SARS-CoV. Among them, eight variant sites were, we think, the first documented. Our findings demonstrate the coexistence of S-gene sequences with and without substitutions (referred to BJ01) in samples analyzed from some patients.

7519 Background: Follicular lymphoma (FL) tumors are infiltrated with antitumor T cells, however, their function is impaired by immune checkpoints such as PD-1/PD-ligand pathway. Blocking PD-1 enhances the function of antitumor T cells in FL. In addition, blocking PD-1 on NK cells has been shown to enhance the ADCC effect of NK cells. We reasoned that the combination of pembrolizumab (P), an anti-PD-1 antibody (ab), and rituximab (R), an anti-CD20 ab that induces ADCC, is likely to be synergistic through activation of both the innate and adaptive immune systems and result in enhanced clinical activity in FL. Methods: We evaluated P and R in an open-label, non-randomized, single institution, phase II trial (N=30). Key inclusion criteria included adult (age ≥ 18 years), FL grade 1-3a, ECOG 0-1, in relapse after ≥1 prior therapy (tx) and R sensitive disease, defined as a complete (CR) or partial response lasting at least 6 months (mos) after most recent R-containing therapy. Pts received R (375 mg/m2 IV) on days 1, 8, 15, and 22 of cycle 1 and P (200mg IV) q 3 weeks for up to 16 cycles starting on day 2 of cycle 1. Primary endpoint was overall response rate (ORR). Results: 27 pts have initiated therapy, median age 65 (range 42-79), 52% male, 76% had intermediate or high risk FLIPI, 56% met GELF criteria. Median prior tx =1 (range 1-4). Adverse events (AE) regardless of causality were mild, most grade 1-2. Grade 3 AE’s included nausea (N=2), infusion reaction (N=2), aseptic meningitis (N=1), pneumonia (N=1). Immune-related AEs included grade 2 diarrhea (N=2), grade 2 pneumonitis (N=1), grade 2 skin rash (N=1). At the pre-planned interim analysis (N=15), ORR was 80%, CR rate was 60%. With a median follow up of 7 mos (range 0.5-17), median DOR, PFS, and OS has not been reached. PD-L1 expression was tested in 8 baseline tumor samples using PD-L1 22C3 IHC pharmDx and was detected in histiocytes in all 8 tumors, present in only 1-8% of tumor cells in 5 tumors. Additional biomarker analyses are ongoing. Conclusions: The combination of P and R is well tolerated in relapsed FL and is associated with high overall and CR rate. These interim results warrant further investigation of this combination in FL. Clinical trial information: NCT02446457.

Monoclonal antibodies specific for programmed cell death 1 (PDCD1, best known as PD-1) have been shown to mediate antineoplastic effects in follicular lymphoma patients. However, the relative proportion of intratumoral PD-1+ T-cell subsets, in particular follicular helper T cells (which exert pro-tumor functions) and effector T cells (which have anticancer activity), may impact clinical outcome, and should therefore be carefully considered for patient selection in this setting.

Summary Background Endogenous or iatrogenic antitumour immune responses can improve the course of follicular lymphoma, but might be diminished by immune checkpoints in the tumour microenvironment. These checkpoints might include effects of programmed cell death 1 (PD1), a co-inhibitory receptor that impairs T-cell function and is highly expressed on intratumoral T cells. We did this phase 2 trial to investigate the activity of pidilizumab, a humanised anti-PD1 monoclonal antibody, with rituximab in patients with relapsed follicular lymphoma. Methods We did this open-label, non-randomised trial at the University of Texas MD Anderson Cancer Center (Houston, TX, USA). Adult (≥18 years) patients with rituximab-sensitive follicular lymphoma relapsing after one to four previous therapies were eligible. Pidilizumab was administered at 3 mg/kg intravenously every 4 weeks for four infusions, plus eight optional infusions every 4 weeks for patients with stable disease or better. Starting 17 days after the first infusion of pidilizumab, rituximab was given at 375 mg/m 2 intravenously weekly for 4 weeks. The primary endpoint was the proportion of patients who achieved an objective response (complete response plus partial response according to Revised Response Criteria for Malignant Lymphoma). Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00904722. Findings We enrolled 32 patients between Jan 13, 2010, and Jan 20, 2012. Median follow-up was 15·4 months (IQR 10·1–21·0). The combination of pidilizumab and rituximab was well tolerated, with no autoimmune or treatment-related adverse events of grade 3 or 4. The most common adverse events of grade 1 were anaemia (14 patients) and fatigue (13 patients), and the most common adverse event of grade 2 was respiratory infection (five patients). Of the 29 patients evaluable for activity, 19 (66%) achieved an objective response: complete responses were noted in 15 (52%) patients and partial responses in four (14%). Interpretation The combination of pidilizumab plus rituximab is well tolerated and active in patients with relapsed follicular lymphoma. Our results suggest that immune checkpoint blockade is worthy of further study in follicular lymphoma. Funding National Institutes of Health, Leukemia and Lymphoma Society, Cure Tech, and University of Texas MD Anderson Cancer Center.

Nectin-2 belongs to a family of immunoglobulin-like cell adhesion molecules that are characterized by the presence of three immunoglobulin-like domains (V, C2 and C2) in the extracellular region. The V domain plays important roles in cell adhesion, NK cell activation and the entry of some herpesvirus. In this study, the V domain of human nectin-2 was expressed in Escherichia coli in the form of inclusion bodies, which were subsequently denatured and refolded. The soluble protein was crystallized using the hanging-drop vapour-diffusion method. The crystals diffracted to 1.85 A resolution and belonged to space group P2(1), with unit-cell parameters a = 52.3, b = 43.9, c = 56.1 A, beta = 118.2 degrees .

Immunotherapy with therapeutic idiotype vaccines offers promise for treatment of B-cell malignancies. However, identification of novel immunogenic lymphoma-associated antigens that are universally expressed is necessary to overcome the barriers of patient-specific idiotype vaccines. Here, we determined whether T-cell leukemia/lymphoma 1 (TCL1) oncoprotein encoded by the TCL1 gene could be a target for immunotherapy of B-cell malignancies. We show that TCL1 mRNA and protein are selectively expressed in normal B cells but markedly hyperexpressed in multiple human B-cell lymphomas, including follicular lymphoma, chronic lymphocytic leukemia, mantle cell lymphoma, diffuse large B-cell lymphoma, and splenic marginal zone B-cell lymphoma. We demonstrated that TCL1-specific CD8+ T cells can be generated from HLA-A*0201 (HLA-A2)+ normal donors and identified TCL171-78 (LLPIMWQL) as the minimal epitope recognized by these T cells. More importantly, TCL171-78 peptide-specific T cells were present in the peripheral blood and tumor-infiltrating lymphocytes of lymphoma patients, could be expanded in vitro, and lysed autologous tumor cells but not normal B cells in an HLA-A2–restricted manner. Our results suggest that TCL1 is naturally processed and presented on the surface of lymphoma cells for recognition by cytotoxic T cells and can serve as a novel target for development of immunotherapeutic strategies against common B-cell lymphomas.

Streptococcus suis ( S. suis ), a group of heterogeneous species with thirty-five serotypes, is considered a previ - ously-neglected but recently-emerging human pathogen. Lack of full understanding of molecular mechanism by which this group of pathogenic bacteria infects both swine and humans greatly hampered the availability of specific/effective therapeutics against severe S. suis infections. The release of the first genomic sequence of S. suis announced the ar - rival of its “Omics-Era”. This review concentrates on recent highlights of S. suis studies in aspects of Omics. Also, we discussed remaining research gaps and future perspectives.

Foxp3(+) regulatory T (T(reg)) cells suppress different types of immune responses to help maintain homeostasis in the body. How T(reg) cells regulate humoral immunity, including germinal center reactions, is unclear. Here we identify a subset of T(reg) cells expressing CXCR5 and Bcl-6 that localize to the germinal centers in mice and humans. The expression of CXCR5 on T(reg) cells depends on Bcl-6. These CXCR5(+)Bcl-6(+) T(reg) cells are absent in the thymus but can be generated de novo from CXCR5(-)Foxp3(+) natural T(reg) precursors. A lack of CXCR5(+) T(reg) cells leads to greater germinal center reactions including germinal center B cells, affinity maturation of antibodies and the differentiation of plasma cells. These results unveil a Bcl-6-CXCR5 axis in T(reg) cells that drives the development of follicular regulatory T (T(FR)) cells that function to inhibit the germinal center reactions.

Background. Severe acute respiratory syndrome coronavirus (SARS-CoV), which emerged with highly contagious and life-threatening characteristics in 2002, remains a potential risk for future outbreaks. Membrane (M) and envelope (E) proteins are major structural proteins of the SARS-CoV. The M protein has been determined as a protective antigen in humoral responses. However, its potential roles in stimulating cellular immunity remain elusive. Methods. In this study, a panel of peptides derived from M and E proteins were tested by in vitro refolding, T2 cell-binding assays, and responses stimulated by cytotoxic T-lymphocyte (CTL) epitopes in HLA-A2.1/Kb transgenic mice and human peripheral blood mononuclear cells (PBMCs). Results. A nonameric epitope Mn2 and a decameric epitope Md3 derived from the M protein were identified and used for the evaluation of M protein-specific immunity. Responses stimulated by M protein-specific CTL epitopes have been found in the PBMCs of donors who had recovered from SARS infection. Additionally, the transmembrane domain of the M protein may contain a T cell epitope cluster revealed by the immunogenic and structural analysis of a panel of truncated peptides overlapping with Mn2 and Md3. Conclusions. The M protein of SARS-CoV holds dominant cellular immunogenicity. This, together with previous reports of a strong humoral response against the M protein, may help to further explain the immunogenicity of SARS and serves as potential targets for SARS-CoV vaccine design.

Three-dimensional structures of beta(2)-microglobulin (beta2m) from chicken and various mammals have been described previously, but aside from genomic sequences, very little is known about the three-dimensional structures of beta2m in species other than warm-blooded vertebrates. Here, we present the first three-dimensional structure of beta2m from bony fish grass carp (Ctid-beta2m), resolved at 2.1 A. The key structural differences between this new structure and previously published structures are two new hydrogen bonds at positions Ile(37) and Glu(38) in strand C and Lys(66) in strand E, and a hydrophobic pocket around the center of the protein found in Ctid-beta2m. Importantly, Ctid-beta2m has a short D strand and a long loop between stands C and D, rather than the flexible region found in other beta2m structures that serves as a putative binding region for the major histocompatibility complex heavy chain. Comparing the Ctid-beta2m structure with those of bovine and human beta2ms, the Calpha root mean square deviation of the latter are 1.3 A and 1.8 A, respectively. Compared with the constant domains of Lamprey T cell receptor-like receptor (Lamp-TCRLC) and Amphioxus V and C domain-bearing protein (Amphi-VCPC), Ctid-beta2m exhibits very different topology. The three-dimensional structures of domains predicted from Amphi-VCPC/Lamp-TCRLC are distinctly lacking in strand A of beta2ms. There are 18 amino acids at the N terminus of Amphi-VCPC that may have evolved into strand A of beta2ms. A mutation in the BC loops of Amphi-VCPC may have led to the novel topology found in beta2m. Based on these results, Ctid-beta2m may well reflect evolutionary characteristics of ancestral C set molecules.

Background There is increasing evidence to suggest an immunomodulation function both within the intestines and systemically upon consuming probiotic species. We recently isolated a novel LAB, Lactobacillus casei Zhang (LcZhang) from koumiss. LcZhang exhibited favorable probiotic properties, such as acid resistance, bile resistance, gastrointestinal (GI) colonization ability, etc. In order to examine the immunomodulatory qualities of LcZhang, we administered LcZhang to healthy mice with varying doses of either live or heat-killed LcZhang and measured various parameters of the host immune response. Results The study was performed in four separate experiments via oral administration of live and heat-killed LcZhang to BALB/c mice for several consecutive days. We investigated the immunomodulating capacity of LcZhang in vivo by analyzing the profile of cytokines, T cell subpopulations, and immunoglobulin concentrations induced in blood serum and intestinal fluid in BALB/c mice. Only live bacteria elicited a wide range of immune responses, which include the increased production of interferon-γ (IFN-γ), and depression of tumor necrosis factor-α (TNF-α) levels. In addition, interleukin-2 (IL-2) and IL-2 receptor gene transcription increased significantly, but the proportion of T cell subsets appeared to be unaffected. We also observed that LcZhang was capable of inducing gut mucosal responses by enhancing the production of secretory Immunoglobulin A (sIgA) as well influencing the systemic immunity via the cytokines released to the circulating blood. Conclusion The present work shows that the dose-dependent administration of LcZhang is capable of influencing immune responses, implying that it may be a valuable strain for probiotic use in humans.

Streptococcus suis, an important zoonotic pathogen, expresses immunoglobulin G-binding protein, which is thought to be helpful to the organism in eluding the host defence system. Recombinant IgG-binding protein expressed in Escherichia coli has been crystallized using the hanging-drop vapour-diffusion method. The crystals belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 38.98, b = 43.94, c = 78.17 A and one molecule in the asymmetric unit. Diffraction data were collected to 2.60 A resolution.

Beta(2)-microglobulin (beta(2)m) is an essential subunit of MHC I molecules; it stabilizes the structure of MHC I and plays a pivotal role in coreceptor recognition. To date, structures of beta(2)m have been solved for three different mammals: human, mouse and cattle. In order to illuminate the molecular evolutionary origin of beta2m, an understanding of its structure in lower vertebrates becomes important. Here, grass carp (Ctenopharyngodon idellus) beta(2)m (Ctid-beta(2)m) was expressed, purified and crystallized. Diffraction data were collected to a resolution of 2.5 A. The crystal belongs to space group P2(1)2(1)2(1), with unit-cell parameters a = 38.72, b = 40.65, c = 71.12 A. The Matthews coefficient and the solvent content were calculated to be 2.56 A Da(-1) and 52.07%, respectively, for one molecule per asymmetric unit. The structure has been solved by molecular replacement using monomeric human beta(2)m as a model.

The critical role of tumour antigen-specific immune responses to restrain tumour growth in patients with gastric cancer furthers the need to dissect the co-inhibitory pathways involved in tumour infiltrating lymphocyte (TIL) exhaustion/dysfunction. It was previously reported that PD-1 expression was significantly increased on CD4+ and CD8+ T cells from patients with gastric cancer and in gastric cancer tissues, compared to normal donors. In this study, we observed up-regulation of TIM-3 and PD-1 expression on peripheral T cells and up-regulation of CTLA-4, TIGIT, TIM-3 and PD-1 expression on TILs from gastric cancer patients; however TIGIT was down-regulated on CD8+ TILs and TIM-3 up-regulation on CD8+ TILs was not statistically significant. Furthermore, the percentages of PD-1+/TIM-3+ and PD-1+/TIM-3- peripheral T cells was significantly higher in gastric cancer patients than normal donors, and the percentage of PD-1+/TIM-3+ TILs was significantly higher than the percentage of PD-1+/TIM-3+ peripheral T cells in gastric cancer patients. PD-1+/TIM-3+ cells represent the predominant fraction of TILs. PD-1 blockade enhanced cytokine production and the cytotoxicity of TILs and exhibited a synergistic effect with TIM-3 blockade. Collectively, our results suggest that the use of anti-PD-1 blockade in combination with anti-TIM-3 blockade could restore the cytotoxic activity of TILs in patients with gastric cancer. Citation Format: Yunhui Zong, Fuliang Chu, Songbing He, Yu Jing, Sally A Hunsucker, Tina Yang, Ming Zhang, Sisi Ye, Yafen Li, Bin Liu, Jinle Tang, Huimin Meng, Gangli An, Lin Yang. Identification of co-inhibitory receptor expression on T cells from gastric cancer patients. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4094. doi:10.1158/1538-7445.AM2014-4094

SummaryThis longitudinal study investigates the change of erythrocyte complement receptor (E-CR1) expression in patients with severe acute respiratory syndrome (SARS). Circulating E-CR1 expression was semiquantified by flow cytometric analyses in 54 SARS patients and in 212 healthy individuals as a control. Since E-CR1 expression is influenced by the genetic polymorphisms in the CR1 gene, a major genetic polymorphism located within intron 27 of the CR1 gene was simultaneously analysed by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). The results showed that the expression level of E-CR1 (referred to as net fluorescence intensity values, NFI) was statistically correlated with the relevant genetic genotypes among the Chinese population including the healthy individuals (NFI: 5·14 ± 0·82, 3·57 ± 0·66 and 2·67 ± 0·32 for HH, HL and LL genotypes, respectively) and SARS patients (NFI: 3·52 ± 0·91 and 2·63 ± 0·70 for HH and HL genotypes, respectively). Interestingly, the expression density of E-CR1 was found to fall significantly during the initiation and progressive phases (weeks 1 and 2 after the disease onset) and gradually returned close to normal through their whole convalescent phase (beginning from weeks 2 or 3 to weeks 7 or 8) in SARS patients irrespective CR1 genotype. In conclusion, our findings, at least, suggest that E-CR1 is likely involved in immune pathogenesis of SARS disease.

Optimal expansion protocol for adoptive T-cell therapy often include interleukin (IL)-15, however, the mechanism by which IL-15 improves the in vivo anti-tumor effect of T cells remains to be elucidated. Using T cells generated from HLA-A2+ normal donors against novel T-cell epitopes derived from the U266 myeloma Ig light chain V-region (idiotype) as a model, we confirmed that T cells cultured with IL-15 provide more potent anti-tumor effects than IL-2-cultured T cells, after adoptive transfer in vivo into immunodeficient hosts. This effect was associated with delayed/reversed senescence in IL-15 expanded idiotype-specific memory CD8 T cells. In vitro experiments revealed IL-15 mediated senescence delay/reversal through JAK3-STAT5 and IL-2 receptor βγ signaling pathway. Specifically, we found DNA damage molecules MDC1, 53BP1, and ATM are the direct targets of IL-15 signaling and STAT5 represses the promoter activity of these genes through the competition with STAT3 to bind to the STATs sites. Thus, our study provides the first evidence for IL-15-inducing the repression of transcription of DNA damage molecules and senescence delay in human memory CD8 T cells.

Monoclonal antibodies specific for programmed cell death 1 (PDCD1, best known as PD-1) have been shown to mediate antineoplastic effects in follicular lymphoma patients. However, the relative proportion of intratumoral PD-1+ T-cell subsets, in particular follicular helper T cells (which exert pro-tumor functions) and effector T cells (which have anticancer activity), may impact clinical outcome, and should therefore be carefully considered for patient selection in this setting.

Abstract 162 Background: The coinhibitory receptor programmed death (PD)-1 is markedly increased on peripheral blood (PB) and intratumoral T cells in follicular lymphoma (FL) and is associated with impaired T-cell function. CT-011 (pidilizumab), a humanized anti PD-1 monoclonal antibody, blocks the PD-1/PD-ligand pathway and enhances the function of antitumor T and NK cells. We conducted a phase II trial to determine the safety and efficacy of CT-011 and rituximab in patients (pts) with relapsed FL and the clinical results are reported separately. Here, we evaluated the effects of CT-011 on immune cells both in the PB and tumor microenvironment. We also determined predictors of clinical outcome based on PB immune cell subsets and molecular features of tumor-infiltrating immune cells at baseline. Methods: CT-011 was given every 4 wks × 4 and rituximab weekly × 4 starting on day 17 after the first infusion of CT-011. Pts with response or stable disease received 8 additional optional infusions of CT-011 every 4 wks. PB and core needle biopsies from involved lymph nodes were collected prior to and on day 14 after the first infusion of CT-011. PB mononuclear cells (PBMC) were analyzed by multiparametric flow cytometry to determine various immune cell subsets. Whole genome gene expression profiling (GEP) was performed on core needle biopsies. Results: Of 29 pts eligible for efficacy analysis, 19 had an objective response for an ORR of 66%. CR was observed in 15 (52%) and PR in 4 (14%). After a median follow up of 14 mo, median PFS was 21.1 mo, and was not reached for the responders. We observed a significant increase in the absolute number of PB immune cells in day 14 samples compared with baseline including total lymphocyte count (p We analyzed GEP of baseline tumor biopsies from 18 pts to find gene signatures that correlated with clinical outcome, as measured by PFS and/or quantitative change in tumor size (%change). We tested a “PD-1hi_Down” signature of 41 genes previously reported by us (Chu et al, Blood, Nov 2011; 118:2648) to be less expressed in CD4+ T cells strongly positive for PD-1, likely to be follicular helper T cells (Tfh, PD-1hi), than in CD4+ T cells with intermediate or low levels of PD-1 surface staining, likely to be exhausted effector T cells (Teffs, PD-1int) or activated effector or naïve T cells (PD-1lo). The PD-1hi_Down gene signature correlated significantly with PFS by univariate Cox regression and was also significant when examined by gene set enrichment analysis based on ranking all genes by correlation with %change. Low expression of this signature, suggesting more Tfh and fewer PD-1+ Teffs within the tumor, predicted shorter PFS duration and less tumor shrinkage. Combined with our in vitro findings that anti-PD-1 Ab enhances the function of Tfh and PD-1+ Teffs but has no effect on PD-1lo T cells in FL, these results suggest that CT-011 therapy enhances the respective pro- and anti-tumor effects of one or both of these cell types. In support of our conclusion that the effect of the PD-1hi_Down signature on outcome depends on CT-011 therapy, we found that this signature did not correlate with overall survival in an external dataset of FL pts treated largely with chemotherapy alone (Dave et al., NEJM 2004; 351: 2109). Conclusions: Administration of CT-011 (pidilizumab) was associated with increase in the numbers of naïve, effector memory, and central memory CD4+ T cells and resulted in activation of T and NK cells in the PB and the tumor microenvironment in FL. A high expression of PD-1hi_Down gene signature, consistent with relatively increased numbers of antitumor Teffs compared with protumor Tfh was predictive of good response and improved PFS suggesting that CT-011 restores function of exhausted Teffs. These results provide insight into the mechanism of action of CT-011 and offer a predictive biomarker for selection of pts for future clinical trials with this class of agents in FL. Disclosures: Rotem-Yehudar: CureTech Ltd: Employment, Research Funding. Neelapu:Cure Tech, Ltd.: Research Funding.

Abstract 2718 Gene expression profiling of follicular lymphoma (FL) tumors showed that genes attributable to infiltrating T cells were associated with improved survival (Dave et al., NEJM 2004; 351: 2109). However, the precise nature of the protective T cell subsets is unknown. Recent studies suggest that master transcription factors (TFs) such as T-bet, GATA-3, RORgt, and Bcl6 regulate the differentiation of effector T cells (Teffs) into TH1/TC1, TH2/TC2, TH17/TC17, and follicular helper T cell (TFH) subsets, respectively. These dominant TFs along with other TFs imprint specific cytokine and chemokine receptor expression in both CD4+ and CD8+ T-cell subsets. Based on these studies, identification of TH1/TC1, TH2/TC2, TH17/TC17, and TFH subsets using chemokine receptor expression pattern has been described in normal donors (Duhen et al., Blood 2012; 119: 4430). To determine whether this chemokine receptor expression pattern could be used for identification of Teff subsets in FL tumors, we FACSorted T cells from single cell suspensions of FL tumors and performed real-time PCR for master TFs and subset-specific cytokines. We found that T cell subsets in FL tumors have similar chemokine receptor expression pattern as peripheral blood T cells from normal donors: TH1/TC1 are CXCR3+, TH17/TC17 are CXCR3-CCR6+CCR4+, and TFH are CXCR5hiPD-1hi. A similar profile was also observed in tonsils, widely accepted as suitable controls for FL. Recent studies also suggest that the TFs essential for Teff differentiation are also involved in polarization of Foxp3+ regulatory T cells (Tregs) into specialized subsets that regulate the corresponding Teff subsets. Moreover, these Treg subsets express identical chemokine receptors as their target Teffs. Using Foxp3 and chemokine receptor expression pattern we found two major subsets of Tregs in FL and tonsils: Foxp3+CXCR3+ Tregs that regulate TH1/TC1 and Foxp3+CXCR5hiPD-1hi follicular regulatory T cells (TFR) that regulate TFH. Next, using 10-color, 12-parameter flow cytometry we analyzed single cell suspensions of FL tumors (n=41) and normal tonsils (n=11) and determined the percentages of various Teff and Treg subsets, B cells, NK cells, and macrophages of total live cells. We found that NK cells and macrophages were not significantly different between the two but the percentage of B cells was significantly lower in FL vs tonsils (p Disclosures: No relevant conflicts of interest to declare.

Abstract 793 Background: Follicular lymphoma (FL) is one of the most immune-responsive of all cancers. However, immunosuppressive mechanisms in the tumor microenvironment may impair optimal antitumor immune responses. Expression of programmed death (PD)-1, a coinhibitory receptor, is markedly increased on intratumoral T cells in FL and is associated with impaired T-cell function. CT-011 (pidilizumab), a humanized anti-PD-1 monoclonal antibody, blocks the PD-1/PD-ligand pathway, and can enhance the function of antitumor T cells and NK cells. Rituximab, the monoclonal anti-CD20 antibody, acts in part via activation of NK cell-mediated antibody-dependent cellular cytotoxicity. Therefore, the combination of CT-011 and rituximab may have additive and/or synergistic effects via activation of both innate (NK cells) and adaptive (T cells) arms of the immune system and enhance clinical efficacy without increasing toxicity. We conducted a single arm phase II trial to determine the safety and efficacy of CT-011 and rituximab in patients (pts) with relapsed FL. Methods: Pts with rituximab-sensitive, grade 1–2 FL relapsed after 1–4 prior therapies with measurable disease, adequate organ function, and absolute lymphocyte count of ≥ 0.6×109/L were eligible for enrollment. Pts with HIV, hepatitis B or C, and history of autoimmune diseases or allogeneic stem cell transplantation were excluded. CT-011 was dosed at 3 mg/kg IV every 4 weeks (wks) for 4 infusions and rituximab was dosed at 375 mg/m2 IV weekly for 4 wks starting 2 wks after the first infusion of CT-011. Pts with complete response (CR), partial response (PR), or stable disease (SD) received 8 additional optional infusions of CT-011 every 4 wks (for a total of 12). Pts were evaluated for response by CT scans and/or PET after 2 and 4 infusions of CT-011 and every 3 months (mo) thereafter for up to 2 yrs. Bone marrow biopsy was performed to confirm CR when appropriate. Blood and tumor samples were collected to assess the effect of CT-011 on immune cells and are reported separately. The primary objective was to determine the overall response rate (ORR). The secondary objectives were to determine the safety and toxicity, CR rate, progression-free survival (PFS), effect of CT-011 on T and NK cells, and to evaluate the immunogenicity and pharmacokinetics of CT-011. The combination was estimated to induce an ORR of at least 60% as compared to an ORR of 40% with rituximab retreatment (Davis et al, J Clin Oncol, 2000). A sample size of 30 was estimated to be adequate for this purpose. Results: Of the 30 pts enrolled and treated on the study, one pt was not evaluable for efficacy analysis. Characteristics of the 29 evaluable pts were: median age 61 years (range, 35–79); 57% male; FLIPI low-41%, int-24%, high-35%, FLIPI2 low-24%, int-48%, high-28%; and median prior therapies 1 (range, 1–4). All pts previously received rituximab, median number of prior doses was 6 (range, 2–22), 69% had prior chemotherapy or chemoimmunotherapy, 41% combination biologic therapy, 21% maintenance rituximab, 7% radioimmunotherapy, and 3% single agent rituximab. The median number of CT-011 infusions administered was 10 (range, 1 – 12). The treatment was well tolerated with no therapy-related grade 3/4 toxicities, and no pt discontinued therapy due to toxicity. Of 29 pts eligible for efficacy analysis, 19 pts had an objective response for an ORR of 66%. CR was observed in 15 (52%) and PR in 4 (14%). Altogether, 25 (86%) pts had measurable tumor regression. Median time to response was 88 days. Of note, 17% of pts achieved initial response >3 mo from first treatment. After a median follow up of 14 mo, median PFS was 21.1 mo, and was not reached for the 19 responders or the 25 pts with measurable tumor regression. Clinical response was not significantly associated with FLIPI, FLIPI2, prior chemotherapy, number of prior rituximab doses, or duration of response to prior therapy (p>0.05). However, PFS was significantly associated with both FLIPI (median PFS for low/int versus high, not reached (NR) versus 12.65 mo; p=0.0056) and FLIPI2 (median PFS for low/int versus high, NR versus 13.47 mo; p=0.0344). Conclusions: The combination of CT-011 (pidilizumab) and rituximab was active and well tolerated in pts with relapsed FL. The ORR of 66% and CR rate of 52% compare favorably with the previously reported ORR of 40% and CR rate of 11% with rituximab retreatment in relapsed FL. These data support further evaluation of PD-1 targeted therapy in FL. Disclosures: Fanale: Genetech: Research Funding. Rotem-Yehudar:CureTech Ltd: Employment, Research Funding.

Abstract 3696 Background: The stromal microenvironment is thought to play a critical role in supporting the survival and growth of follicular lymphoma (FL) tumor cells. However, the key stromal factors involved are not well characterized. We hypothesized that FL tumor cells hijack the survival and growth mechanisms that are usually used by normal B cells in the lymph node microenvironment. For example, follicular dendritic cells (FDC) residing in germinal centers of lymph nodes play a vital role in supporting normal B cell survival and proliferation through adhesion molecules and by secreting chemokines and cytokines. In normal lymph nodes, lymphotoxin-alpha (LTA, TNFSF1) secreted by B cells activates FDC through LTbR and induces secretion of BAFF (TNFSF13B) and CXCL13. CXCL13 recruits follicular helper T cells (Tfh) into the B cell zone and CD40L (expressed by Tfh) together with BAFF prevents apoptosis and promotes proliferation of B cells. Here, we determined whether a similar cross-talk exists between FL tumor B cells, FDC, and Tfh. Methods: FL tumor samples were processed into single-cell suspension and cryopreserved in aliquots for later use. Primary tumor B cells were isolated by magnetic cell separation from single-cell suspensions of FL. The FDC-like cell line HK derived from human tonsil was used in place of primary FDC. Levels of BAFF, CXCL13, and LTA in culture supernatants were determined by ELISA. Apoptosis of tumor cells was determined by Annexin V assay and proliferation by tritiated thymidine incorporation assay. Activation of NFkB was determined by the TransAM NFkB p52 ELISA kit. Results: We developed a co-culture model to mimic the FL tumor microenvironment to study the interactions between tumor cells, FDC and Tfh. We observed that FL tumor cells spontaneously produced low levels of LTA but its production was significantly enhanced when tumor cells were cultured with either recombinant BAFF or CD40L. Dose response curves from FL tumor cells treated with both BAFF and CD40L recombinant proteins showed synergistic increase in LTA secretion. Recombinant BAFF and CD40L also synergistically enhanced the survival and proliferation of FL tumor cells. HK cells spontaneously produced low levels of BAFF and CXCL13 but their production was significantly enhanced by recombinant LTA in a dose-dependent manner. Consistent with the above studies, co-culturing FL tumor cells with HK cells significantly enhanced LTA secretion, possibly due to the effects of BAFF secreted by HK cells. In addition, in this co-culture, we also observed enhanced production of BAFF and CXCL13 possibly due to the effects of LTA secreted by the tumor cells. The production of BAFF and CXCL13 in this co-culture could be inhibited by an LTA neutralizing antibody in a dose-dependent manner suggesting the role of LTA in this mechanism. Co-culturing FL tumor cells with HK cells also significantly enhanced the survival and proliferation of FL tumor cells greater than two-fold compared with FL tumor cells alone. This effect also could be inhibited by LTA neutralizing antibody but not isotype control antibody. The survival benefit for tumor cells was further enhanced upon co-culture with autologous Tfh cells FACSorted from the same tumor sample. We also studied the downstream NFkB signaling mediated by BAFF on tumor B cells and by LTA on HK cells in the co-culture. We found that both tumor B cells and HK cells had significantly higher NFkB activity upon co-culture compared to cells alone. Conclusions: Our results suggest a model where LTA secreted by tumor B cells forms the afferent axis and induces production of BAFF and CXCL13 by FDC. CXCL13 preferentially recruits CXCR5-expressing Tfh into the tumor microenvironment and CD40L expressed by Tfh and BAFF secreted by FDC form the efferent axis and promote further production of LTA by tumor cells. In addition, CD40L and BAFF synergistically enhance the survival and proliferation of FL tumor cells via activation of NFkB. Our results suggest that because of their redundant functions, blocking BAFF-BAFF-R pathway alone or CD40-CD40L pathway alone with monoclonal antibodies as is being done in ongoing clinical trials may not be optimal. In contrast, blocking both pathways simultaneously is likely to significantly enhance the clinical responses. Our results also suggest that neutralizing LTA or blocking its receptor may be another novel therapeutic strategy for management of FL. Disclosures: No relevant conflicts of interest to declare.

Abstract 2648 Background: Programmed death (PD)-1, a coinhibitory receptor expressed by effector T cells (Teffs) is highly expressed on intratumoral T cells (mean 61%, range 34–86% for CD4+ T cells and mean 44%, range 31–69% for CD8+ T cells) in follicular lymphoma (FL), a finding associated with impaired ability to recognize autologous tumor (Nattamai et al, ASH 2007). Hence, PD-1 expression would be expected to confer an unfavorable prognosis in FL. However, correlation of PD-1 with clinical outcome in FL has been inconsistent with two studies showing favorable (Carreras et al, J Clin Oncol 2009; Wahlin et al, Clin Cancer Res 2010) and one study showing unfavorable (Richendollar et al, Hum Pathol 2011) outcome. While differences in method of analysis and type of treatment may explain the disparate results, a more complex model may be necessary to understand the prognostic impact of PD-1 in FL as PD-1 is expressed not only on antitumor Teffs but also on protumor follicular helper T cells (Tfh) and regulatory T cells (Tregs). Methods: To determine the nature of PD-1+ T cells in FL we performed comprehensive genomic and immunologic studies. By flow cytometry, we observed that the intratumoral CD4+ T cells in FL may be categorized into 3 subsets based on PD-1 expression - PD-1 high (PD-1hi), intermediate (PD-1int), and low (PD-1lo). The intratumoral CD8+ T cells consisted of PD-1int and PD-1lo subsets. The 3 CD4+ T cell subsets were FACSorted from FL tumors (n=3) and whole genome gene expression profiling (GEP) was performed. T cell subsets sorted similarly from tonsils served as controls for reactive follicular hyperplasia (FH) (n=3). Differentially expressed genes in GEP studies were confirmed at the mRNA level by real-time PCR (n=5) and at the protein level by flow cytometry when antibodies were available (n=5–10). Results: Our results suggested that CD4+PD-1hi T cells are Tfh cells (CXCR5hiBcl6hi ICOShiCD40LhiSAPhiPRDM1loIL-4hiIL-21hi); the CD4+PD-1int T cells consisted of a mixture of activated Teffs (CD45RO+CD45RA−) including Th1 (Tbet+IFNg+), Th2 (IL-10+), and Th17 cells (RORc+IL-17+), and Tregs (Foxp3+CD25hiCD127lo); and the CD4+PD-1lo T cells consisted of a mixture of activated Teffs (CD45RO+CD45RA− but IFNg−IL-4−IL-10−IL-17−), Tregs, and naïve T cells (CD45RO−CD45RA+CCR7+). Although these subsets were present in both FL and FH, there were important differences. IL-4 expression was significantly higher in Tfh in FL vs. FH and may play a role in the pathogenesis of FL. IL-17 expression was low and expression of coinhibitory molecules BTLA and CD200 was high in CD4+PD-1int T cells in FL vs. FH. BTLA and CD200 were also increased in CD8+PD-1int T cells in FL vs. FH. However, other coinhibitory molecules (LAG-3, Tim-3, CD160, CTLA-4, CD244, KLRG1) were not significantly different between FL and FH. CD4+PD-1int T cells also had higher expression of BATF, a transcription factor associated with T cell exhaustion in FL vs. FH. Together, these results suggest that the CD4+PD-1int T cells in FL may be in a state of T cell exhaustion whereas the CD4+PD-1int T cells in FH may represent recently activated Teffs. Consistent with this, blocking PD-1 with anti-PD-1 blocking antibody significantly enhanced proliferation and the production of Th1 (IFNg, TNFa) but not Th2 (IL-4, IL-5, IL-10, IL-13) cytokines by intratumoral CD4+ and CD8+ T cells in response to stimulation with autologous FL tumor cells (n=3). As expected, Tregs were increased in number in FL vs. FH and were present in the PD-1int and PD-1lo T cell subsets. We found 74% (range 40–97%) of FL Tregs expressed PD-1. Among the CD4+PD-1lo and CD8+PD-1lo T cells, there were more activated Teffs and fewer naïve T cells in FL vs. FH. Conclusions: Our results suggest that the PD-1+ T cells in FL are comprised of a mixture of antitumor Teffs and protumor Tfh and Tregs. The prognostic impact of PD-1+ T cells in FL may dependent on the relative frequency of these subsets as ligation of PD-1 may produce favorable (inhibition of protumor Tfh and Tregs) or unfavorable (inhibition of antitumor Teffs) outcomes by inhibiting or promoting tumor growth, respectively. Conversely, our results imply that agents that block PD-1/PD-ligand pathway may have the opposite effect on these T cell subsets and enumeration of the intratumoral PD-1+ T cell subsets may serve as biomarker to predict response to these agents in FL and possibly other B-cell malignancies. Disclosures: Dong: GSK: Consultancy; Genentech: Honoraria; Tempero: Consultancy; Ono: Consultancy; AnaptysBio: Consultancy. Neelapu:Cure Tech Ltd: Research Funding.

TPS305 Background: Follicular lymphoma (FL) is one of the most immune-responsive of all cancers. However, immunosuppressive mechanisms in the tumor microenvironment may impair the efficacy of antitumor immune responses. We have recently identified the programmed death (PD)- 1/PD-ligand pathway as an important immunosuppressive mechanism in the FL tumor microenvironment. Expression of the coinhibitory PD-1 receptor was markedly increased on intratumoral T cells and associated with decreased reactivity to autologous FL tumor cells. Blocking PD-1/PD-ligand pathway with CT-011 enhanced the proliferation of antitumor T cells and augmented the expression of activating receptors on human NK cells. Administration of CT-011 delayed tumor growth and improved survival of mice in lymphoma xenograft models and combination with rituximab further improved survival compared with rituximab alone (Chu et al, Blood, Nov 2009; 114: 724.). In a phase I clinical trial, CT-011 was safe, induced sustained elevations of CD4+ T ce...

Abstract 724 Background: Programmed death (PD)–1 is an inhibitory receptor that impairs the function of activated T-cells and natural killer (NK) cells when engaged by its ligands PD-L1 or PD-L2. We have previously demonstrated that PD-1 is markedly up-regulated in intratumoral and peripheral blood CD4+ and CD8+ T cells in patients with follicular lymphoma (FL), a finding associated with impaired T-cell function, suggesting that PD-1 blockade may improve FL immune control. CT-011, a humanized anti PD-1 monoclonal antibody, was previously studied in a phase I clinical trial in patients with advanced hematological malignancies. CT-011 was well tolerated and induced sustained elevations of CD4+ T cells in the peripheral blood. More importantly, apparent clinical benefit was observed in six patients, including one patient with FL who had large tumor masses that achieved a durable complete remission lasting >14 months. Here, we studied the in vitro and in vivo effects of CT-011 on T-cell and/or NK-cell immune responses against human B-cell lymphoma and the hypothesis that CT-011 may improve tumor control when combined with rituximab, a chimeric anti-CD20 monoclonal antibody for the treatment of human FL. Materials and Methods: To determine the effects of CT-011 on antitumor T cells, intratumoral T cells were isolated from primary FL tumor samples, and cultured with or without autologous tumor cells in the presence or absence of CT-011 or isotype control antibody (50 μg/ml each) for 5 days, and tested for proliferation by 3H thymidine incorporation assay. To determine the effects of CT-011 on NK cells, peripheral blood mononuclear cells (PBMCs) derived from normal donors or patients with FL were cultured in the presence or absence of CT-011 (50 μg/ml) with or without IL-2 for 96 hours and analyzed for expression of various activating receptors including CD16, CD32, CD64, Fas ligand, NKG2D, NKp30, NKp44, and NKp46. The in vivo effects of CT-011 were tested in two B-cell lymphoma xenograft models. Ramos and RL lymphoma tumor cells were injected subcutaneously into nude and SCID mice, respectively, and CT-011 (10 μg/mouse) was injected weekly with or without rituximab starting approximately 7–10 days after tumor inoculation. Results: We observed that CT-011 significantly increased the proliferation of intratumoral T cells in response to autologous tumor cells compared with isotype control antibody. Treatment with CT-011 enhanced the expression of Fas ligand, CD32, CD64, and NKp30 on human NK cells in the presence of IL-2 as compared with PBMCs treated with IL-2 alone or media control. In the RL lymphoma xenograft model in SCID mice, treatment with CT-011 significantly delayed tumor growth (P≤0.05) and improved survival (P≤0.01) compared with control mice injected with saline. In a Ramos lymphoma xenograft model in nude mice, treatment with CT-011 and rituximab eradicated established tumors in a significant proportion of mice (P≤0.05) and markedly improved survival compared with rituximab alone or saline. Conclusions: Taken together, these studies suggest that blockade of PD-1 with CT-011 enhances the function of anti-tumor T-cells and augments the expression of activating receptors on NK cells. Treatment with CT-011 led to improved tumor control against human B-cell lymphoma in xenograft models and the combined use of CT-011 and rituximab was more effective that rituximab alone. These results provide the rationale to test the combination of CT-011 with rituximab in patients with B-cell lymphoma, given that the combination is likely to be complementary and may even be synergistic, leading to enhanced clinical efficacy without increasing toxicity. The development of such approaches that activate both the innate (NK-cells) and adaptive (T-cells) immune systems is likely to minimize the emergence of immune escape variants and improve clinical outcome in patients with lymphoma. A clinical trial evaluating CT-011 in combination with rituximab is planned in patients with relapsed FL. Disclosures: Rodionov: Cure Tech Ltd.: Employment. Rotem-Yehudar:Cure Tech Ltd.: Employment.