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Kaposi sarcoma (KS) can pose diagnostic challenges in biopsy specimens. Multiple histologic variants of cutaneous KS have been described; however, the histomorphologic spectrum of gastrointestinal (GI) KS has not been systematically studied. This large series comprehensively evaluated 46 cases of KS involving the GI tract and identified 7 histomorphologic variants, some that have not been previously described. Five of them are inconspicuous but have unique morphologic patterns, including lymphangioma/lymphangiectatic-like (n=17), mucosal hemorrhage/telangiectatic-like (n=17), mucosal inflammation-like (n=15), granulation tissue-like (n=13), and mucosal prolapse-like (n=4) variants. These variants can be easily misdiagnosed or misinterpreted on routine examination if KS is not considered, and if the immunohistochemical stain for human herpesvirus-8 is not performed. The other 2 morphologic variants present as spindle cell proliferations and are the GI stromal tumor-like (n=8) and inflammatory myofibroblastic tumor-like (n=2). These variants raise a broad differential diagnosis of spindle cell tumors of the GI tract and could pose diagnostic challenges. In summary, GI KS lesions exhibit variable, often unconventional histomorphologic patterns. KS should be included in the differential diagnosis even if features of conventional KS are not seen, particularly in limited biopsies in immunocompromised patients, such as those with human immunodeficiency virus infection. Although the clinical significance of these morphologic variants is yet to be determined, they are nonetheless important from a diagnostic standpoint. Misdiagnosis and delay in appropriate management can be avoided by recognizing the morphologic diversity of GI KS and appropriately utilizing the human herpesvirus-8 immunohistochemical stain.

Supplemental Figure 1. Sequence of pIRS-21097-1105 TCR chains. Supplemental Figure 2. Sequence of pCDC25b38-46 TCR chains. Supplemental Figure 3. Electroporation of IVT RNA encoding murine TCR chains results in functional cell surface expression of phosphopeptide-specific TCR. Supplemental Figure 4. pSer1100-IRS-2 staining of colon melanoma metastasis

T cells are important in tumour immunity but a better understanding is needed of the differentiation of antigen-specific T cells in human cancer1,2. Here we studied CD8 T cells in patients with human papillomavirus (HPV)-positive head and neck cancer and identified several epitopes derived from HPV E2, E5 and E6 proteins that allowed us to analyse virus-specific CD8 T cells using major histocompatibility complex (MHC) class I tetramers. HPV-specific CD8 T cells expressed PD-1 and were detectable in the tumour at levels that ranged from 0.1% to 10% of tumour-infiltrating CD8 T lymphocytes (TILs) for a given epitope. Single-cell RNA-sequencing analyses of tetramer-sorted HPV-specific PD-1+ CD8 TILs revealed three transcriptionally distinct subsets. One subset expressed TCF7 and other genes associated with PD-1+ stem-like CD8 T cells that are critical for maintaining T cell responses in conditions of antigen persistence. The second subset expressed more effector molecules, representing a transitory cell population, and the third subset was characterized by a terminally differentiated gene signature. T cell receptor clonotypes were shared between the three subsets and pseudotime analysis suggested a hypothetical differentiation trajectory from stem-like to transitory to terminally differentiated cells. More notably, HPV-specific PD-1+TCF-1+ stem-like TILs proliferated and differentiated into more effector-like cells after in vitro stimulation with the cognate HPV peptide, whereas the more terminally differentiated cells did not proliferate. The presence of functional HPV-specific PD-1+TCF-1+CD45RO+ stem-like CD8 T cells with proliferative capacity shows that the cellular machinery to respond to PD-1 blockade exists in HPV-positive head and neck cancer, supporting the further investigation of PD-1 targeted therapies in this malignancy. Furthermore, HPV therapeutic vaccination efforts have focused on E6 and E7 proteins; our results suggest that E2 and E5 should also be considered for inclusion as vaccine antigens to elicit tumour-reactive CD8 T cell responses of maximal breadth. An analysis of human papillomavirus (HPV)-specific CD8 T cells in patients with head and neck cancer identifies functional PD-1+TCF-1+CD8 T cells in the tumour with implications for therapeutic vaccination and PD-1 directed immunotherapy.

Tumours often contain B cells and plasma cells but the antigen specificity of these intratumoral B cells is not well understood1-8. Here we show that human papillomavirus (HPV)-specific B cell responses are detectable in samples from patients with HPV-positive head and neck cancers, with active production of HPV-specific IgG antibodies in situ. HPV-specific antibody secreting cells (ASCs) were present in the tumour microenvironment, with minimal bystander recruitment of influenza-specific cells, suggesting a localized and antigen-specific ASC response. HPV-specific ASC responses correlated with titres of plasma IgG and were directed against the HPV proteins E2, E6 and E7, with the most dominant response against E2. Using intratumoral B cells and plasma cells, we generated several HPV-specific human monoclonal antibodies, which exhibited a high degree of somatic hypermutation, consistent with chronic antigen exposure. Single-cell RNA sequencing analyses detected activated B cells, germinal centre B cells and ASCs within the tumour microenvironment. Compared with the tumour parenchyma, B cells and ASCs were preferentially localized in the tumour stroma, with well-formed clusters of activated B cells indicating ongoing germinal centre reactions. Overall, we show that antigen-specific activated and germinal centre B cells as well as plasma cells can be found in the tumour microenvironment. Our findings provide a better understanding of humoral immune responses in human cancer and suggest that tumour-infiltrating B cells could be harnessed for the development of therapeutic agents.

Better prognostication/stratification of pancreatic neuroendocrine tumors (PanNETs) is needed. In this detailed morpheomic study of 163 resected PanNETs, 11 unusual variants, some of which were not previously recognized, and others scarcely documented in the literature, were identified, and their pathologic characteristics were further analyzed. By behavior and clinicopathologic associations, these variants could be grouped into three prognostically different categories. I. More aggressive (20%). Included in this group were the variants that in average showed higher grade and stage and adverse outcome including oncocytic, plasmacytoid, lipid-rich and previously unrecognized hepatoid variants, which often had a more diffuse/broad-band growth pattern, with some also displaying discohesiveness. They were characterized by abundant cytoplasm and often had prominent nucleoli (as seen in metabolically active cells), thus the provisional name "metabolic cell phenotype." Because of their diversion from classical neuroendocrine cytomorphology, these variants created challenges on original diagnostic workup, particularly hepatoid examples, which revealed Arginase 1/Hep Par-1 expression in 50%. II. Less aggressive (10%). These cases either showed signs of maturation, including nested growth, paraganglioid pattern (which was previously unrecognized), and organoid PanNETs such as "ductulo-insular" growth, or showed symplastic/degenerative changes, and despite their paradoxically disconcerting histology, were more benevolent in behavior. III. Undetermined. There were other variants including mammary tubulolobular-like, pseudoglandular, peliotic, and sclerotic PanNETs, which although diagnostically challenging, their biologic significance could not be determined because of rarity or heterogeneous characteristics. Prognostic associations: Features that were significantly different in the more aggressive group than the less aggressive group were median size (5.0 vs 1.6 cm, p < 0.001), percentage of pT3+T4 cases (72% vs 12%, p < 0.001), Ki67 index (5.3% vs 2.3%, p = 0.001), % G2 and G3 cases (77% vs 27%, p < 0.001), and rate of lymph node and distant metastasis (96% vs 27%, p < 0.001). In stepwise logistic regression model using the 3 established prognosticators of T stage, size, and grade along with morphology, only aggressive-morphology (metabolic cell phenotype) was found to be associated with metastatic behavior with an odds ratio of 5.9 with 95% confidence interval (C.I.) 1.688 to 22.945 and p value 0.007. In conclusion, PanNETs display various morphologic patterns that are not only challenging and important diagnostically but appear to have biologic significance. Tumors with more diffuse growth of cells with nucleoli and abundant cytoplasm and/or discohesion (oncocytic, hepatoid, lipid-rich, plasmacytoid PanNETs), provisionally termed "metabolic cell phenotype," show aggressive characteristics and are an independent determinant of adverse outcome and thus may require closer post-surgical follow-up, whereas variants with more degenerative or mature features (ductuloinsular, pleomorphic, paraganglioma-like) appear to be more benevolent despite their more atypical and worrisome morphology.

The production of noncanonical mRNA transcripts is associated with cell transformation. Driven by our previous findings on the sensitivity of T cell acute lymphoblastic leukemia (T-ALL) cells to SF3B1 inhibitors, we identified that SF3B1 inhibition blocks T-ALL growth in vivo with no notable associated toxicity. We also revealed protein stabilization of the U2 complex component SF3B1 via deubiquitination. Our studies showed that SF3B1 inhibition perturbs exon skipping, leading to nonsense-mediated decay and diminished levels of DNA damage response–related transcripts, such as the serine/threonine kinase CHEK2, and impaired DNA damage response. We also identified that SF3B1 inhibition leads to a general decrease in R-loop formation. We further demonstrate that clinically used SF3B1 inhibitors synergize with CHEK2 inhibitors and chemotherapeutic drugs to block leukemia growth. Our study provides the proof of principle for posttranslational regulation of splicing components and associated roles and therapeutic implications for the U2 complex in T cell leukemia., Description, The splicing factor SF3B1 is regulated at the protein level and is a therapeutic target in T cell leukemia.

Combination therapy with PD-1 blockade and IL-2 is highly effective during chronic lymphocytic choriomeningitis virus infection(1). Here we examine the underlying basis for this synergy. We show that PD-1 + IL-2 combination therapy, unlike PD-1 monotherapy, dramatically changes the differentiation program of the PD-1(+)TCF-1(+) stem-like CD8(+) T cells and results in the generation of transcriptionally and epigenetically distinct effector CD8(+) T cells that resemble highly functional effector CD8(+) T cells seen after an acute viral infection. The generation of these qualitatively superior CD8(+) T cells that mediate viral control underlies the synergy between PD-1 and IL-2. Our results show that the PD-1(+)TCF-1(+) stem-like CD8(+) T cells, also referred to as precursors of exhausted CD8(+) T cells, are not fate-locked into the exhaustion program and their differentiation trajectory can be changed by IL-2 signals. These virus-specific effector CD8(+) T cells emerging from the stem-like CD8(+) T cells after combination therapy expressed increased levels of the high affinity IL-2 trimeric (CD25, CD122, CD132) receptor. This was not seen after PD-1 blockade alone. Finally, we show that CD25 engagement with IL-2 plays an important role in the observed synergy between IL-2 cytokine and PD-1 blockade. Either blocking CD25 with an antibody or using a mutated version of IL-2 that does not bind CD25 but still binds CD122/CD132 almost completely abrogated the synergistic effects seen after PD-1 + IL-2 combination therapy. There is currently considerable interest in PD-1 + IL-2 combination therapy for patients with cancer(2,3) and our fundamental studies defining the underlying mechanisms of how IL-2 synergizes with PD-1 blockade should inform these human translational studies.

The importance of tumor-associated antigen-specific T cells in the effective control of cancer has been highlighted by recent advances in cancer immunotherapies that target the programmed cell death-1 (PD-1) pathway or that utilize modified T cell receptors. Phosphopeptide-specific T cells are of interest because they recognize a new class of tumor antigens that are derived from proteins relevant for cancer development and growth. These T cell lines or their antigen receptors can be used in combination with other forms of therapy to improve the immune response and survival of cancer patients. We describe here a protocol for the generation of human and transgenic murine phosphopeptide-specific T cells lines as tools for investigating T cell reactivity against melanoma phosphoantigens displayed by HLA-A*0201.

The importance of tumor-associated antigen-specific T cells in the effective control of cancer has been highlighted by recent advances in cancer immunotherapies that target the programmed cell death-1 (PD-1) pathway or that utilize modified T cell receptors. Phosphopeptide-specific T cells are of interest because they recognize a new class of tumor antigens that are derived from proteins relevant for cancer development and growth. These T cell lines or their antigen receptors can be used in combination with other forms of therapy to improve the immune response and survival of cancer patients. We describe here a protocol for the generation of human and transgenic murine phosphopeptide-specific T cells lines as tools for investigating T cell reactivity against melanoma phosphoantigens displayed by HLA-A*0201.

{beta}-catenin ({beta}cat) is an important downstream effector in the Wnt signaling pathway and plays an important role in the development and progression of many cancers including melanoma. {beta}cat expression is regulated by GSK-3{beta}-mediated phosphorylation at positions 33, 37 and 41. In normal cells, phosphorylation at these sites triggers proteasomal degradation, which in turn prevents accumulation of free cytoplasmic {beta}cat. In cancer cells, stabilized {beta}-catenin translocates into the nucleus, where it associates with TCF/Lef proteins to activate transcription of genes that promote tumorigenesis and metastasis. It has been suggested that nuclear phospho-{beta}cat (p{beta}cat) staining may be diagnostically useful in differentiating primary from metastatic melanoma. Also, a p{beta}cat peptide (residues 30-39, p33) is naturally presented by melanoma cells as a T-cell target. We evaluated the expression of pS33-{beta}cat in primary and metastatic melanoma tissues by immunohistochemistry. pS33-{beta}cat was detected in primary and metastatic melanomas and was most commonly cytoplasmic and almost never exclusively nuclear. Interestingly, staining with pS33-{beta}cat and pS33/37/T41-{beta}cat antibodies was most intense in mitotic melanoma cells, consistent with prior studies demonstrating changes in the level of {beta}cat during cell division. We observed no significant differences in p{beta}cat staining location or intensity between primary and metastatic melanomas, suggesting that p{beta}cat may have limited diagnostic or prognostic utility in melanoma. However, the high expression in dividing cells suggests promise as an immunotherapeutic target.

The College of American Pathologists (CAP) developed the Biorepository Accreditation Program (BAP) in 2012. This program integrates best practices from the International Society for Biological and Environmental Biorepositories, the National Cancer Institute, the Organisation for Economic Cooperation and Development, the Center for Medicare and Medicaid Services, and the CAP Laboratory Accreditation Program. The goal of this elective program is to provide requirements for standardization in biorepository processes that will result in high-quality specimens that can be used to support research, drug discovery, and personalized medicine. CAP uses a peer inspection model to ensure the inspectors have proper expertise and to promote educational efforts through information sharing. Lead inspectors are comprised of pathologists, PhDs, and managers of biorepositories and they are often supported by CAP staff inspectors. Accreditation is a 3-year continuous cycle of quality with a peer inspection occurring at the start of year 1 and a self-inspection and CAP desk assessment at the start of year 2 and 3. At this time 53 biorepositories are fully CAP BAP accredited and 13 are in the process of obtaining accreditation. There are currently 273 established standards with requirement lists customized based on the scope of activities performed by a biorepository. A total of 90 inspections were completed between May 2012 and December 2016. Sixty-one were initial inspections and 29 were reinspections. A total of 527 deficiencies were identified in the areas of Equipment/Instrumentation (22%), Information Technology (18%), Specimen Handling and QC (15%), Quality Management (16%), Personnel (11%), Safety (10%), Facilities (6%), and Regulatory (2%). Assessment of common deficiencies identifies areas of focus for continuous improvement and educational opportunities. Overall success of the program is high based on the current enrollment of 66 biorepositories, anecdotal participant feedback and increasing national recognition of the BAP in federal documents.

Introduction/Objective The presence of inducible lymphoid structures known as tertiary lymphoid structures in the tumor microenvironment has been shown to correlate with positive clinical outcome. However, the maturation states of lymphoid aggregates in lung adenocarcinoma are not completely understood. Methods/Case Report Seventy tumor samples from 69 patients diagnosed with lung adenocarcinoma (Stages I to III) between 2013 and 2015 were included in the study. The presence and maturation states of the lymphoid structures within the tumors were evaluated by conventional and 26 samples were further analyzed by multiplexed immunohistochemistry of formalin fixed paraffin embedded tissues and then quantified. Mature lymphoid follicles containing germinal centers were identified by the presence of CD21+ and BCL-6+ cells in an organized configuration within tight clusters of T and B cells. Results (if a Case Study enter NA) Samples with fully mature lymphoid structures (germinal centers) had larger tumors and higher disease stage. The number of mature lymphoid structures correlated with the total number of lymphoid aggregates present in the tumor microenvironment. Additionally, tumor samples with ≥10 mature lymphoid structures had more primary follicles. While there was no difference in overall survival, progression free survival was significantly longer in patients who had ≥10 mature lymphoid structures in comparison with patients who had Conclusion In conclusion, a spectrum of lymphoid aggregates in different stages of maturation are present in lung adenocarcinoma. An increase in the number of mature lymphoid structures may be associated with progression free survival in patients with lung adenocarcinoma.

Objectives To identify clear cell renal cell carcinoma-related gene mutations potentially associated with aggressive disease, sarcomatoid differentiation or poor prognosis. Methods We carried out genomic analysis of 217 tumor foci from 25 patients with conventional clear cell renal cell carcinoma (14 patients), clear cell renal cell carcinoma with sarcomatoid differentiation (six patients) and non-clear cell renal cell carcinoma (five patients). Each tumor nodule on the tissue block that corresponded to the same focus on the slide was separated from the normal parenchyma and other histologically distinct areas of tumor. The isolated tumor foci were used for subsequent analyses and sequencing. Deoxyribonucleic acid from the formalin-fixed paraffin-embedded tissues was extracted. Multiplex bar-coded polymerase chain reaction amplification was carried out using next-generation sequencing libraries. Results Overall, 67 protein alterations, including amino acid alterations, frame shifts and splice site mutations in seven genes were identified in the cohort of renal cell carcinoma tumors included in this study. Fewer patients with clear cell renal cell carcinoma with sarcomatoid differentiation had clear cell renal cell carcinoma-related mutations in comparison with patients with conventional clear cell renal cell carcinoma. Additionally, the average number of unique clear cell renal cell carcinoma-related protein alterations per patient was significantly lower in clear cell renal cell carcinoma with sarcomatoid differentiation than in conventional clear cell renal cell carcinoma. Mutations in PBRM1 were identified in a higher proportion of patients with high-grade tumors (World Health Organization/International Society of Urological Pathology grade 4) and in the primary tumors of six of 10 (60%) patients with metastatic disease. Conclusions Although there are pitfalls due to intratumoral heterogeneity and sampling bias, mutations in PBRM1 may be associated with metastasis and aggressive disease in clear cell renal cell carcinoma.

β-catenin (βcat) is an important downstream effector in the Wnt signaling pathway and plays important roles in the development and progression of many cancers including melanoma. βcat expression is regulated by GSK-3β-mediated phosphorylation at positions 33, 37 and 41. In normal cells, phosphorylation at these sites triggers proteasomal degradation, which prevents accumulation of free cytoplasmic βcat. In cancer cells, stabilized β-catenin translocates into the nucleus, where it associates with TCF/Lef proteins to activate transcription of genes that promote tumorigenesis and metastasis, including PD-L1. It has been suggested that nuclear phospho-βcat (pβcat) staining may be diagnostically useful in differentiating primary from metastatic melanoma. Also, a pβcat peptide (residues 30–39, with only S33 phosphorylated) is naturally presented by melanoma cells as a T-cell target. We evaluated expression of pS33-βcat in primary and metastatic melanomas by immunohistochemistry and found its expression varied widely but was most commonly cytoplasmic. Nuclear staining was identified in only 18% of metastatic melanomas. Staining with antibodies to pS33-βcat and pS33/37/T41-βcat was most intense in mitotic melanoma cells; however, pS33-βcat intensity was not significantly associated with AJCC stage, tumor location, BRAF mutation status, or immune infiltrates. Yet, PD-L1 and PD-L2 expression by tumor cells were significantly higher in tumors with high pS33-βcat expression. The low rate of nuclear pS33-βcat expression suggests that pS33-βcat may have limited utility for identifying metastatic melanomas. However, high expression in dividing cells and strong associations with PD-L1 and PD-L2 expression may inform future personalized therapies for tumors with high pS33-βcat expression.

Cancer cells display novel phosphopeptides in association with MHC class I and II molecules. In this study, we evaluated two HLA-A2–restricted phosphopeptides derived from the insulin receptor substrate (IRS)-2 and the cell-cycle regulator CDC25b. These proteins are both broadly expressed in multiple malignancies and linked to cancer cell survival. Two phosphopeptides, termed pIRS-21097–1105 and pCDC25b38–46, served as targets of strong and specific CD8 T-cell memory responses in normal human donors. We cloned T-cell receptor (TCR) cDNAs from murine CD8 T-cell lines specific for either pIRS-21097–1105 or pCDC25b38–46. Expression of these TCRs in human CD8 T cells imparted high-avidity phosphopeptide-specific recognition and cytotoxic and cytokine-secreting effector activities. Using these cells, we found that endogenously processed pIRS-21097–1105 was presented on HLA-A2+ melanomas and breast, ovarian, and colorectal carcinomas. Presentation was correlated with the level of the Ser1100-phosphorylated IRS-2 protein in metastatic melanoma tissues. The highest expression of this protein was evident on dividing malignant cells. Presentation of endogenously processed pCDC25b38–46 was narrower, but still evident on HLA-A2+ melanoma, breast carcinoma, and lymphoblastoid cells. Notably, pIRS-21097–1105–specific and pCDC25b38–46–specific TCR-expressing human CD8 T cells markedly slowed tumor outgrowth in vivo. Our results define two new antigens that may be developed as immunotherapeutic agents for a broad range of HLA-A2+ cancers. Cancer Res; 74(23); 6784–95. ©2014 AACR.

Hexon modification of adenovirus type 5 (Ad5) vectors with the hypervariable regions (HVRs) of Ad48 has been shown to allow Ad5HVR48 vectors to circumvent the majority of the preexisting Ad5-neutralizing antibodies. However, it remains unclear whether modifying hexon HVRs impacts innate or adaptive immune responses elicited by this vector. In this study, we investigated the influence of the HVR substitution of Ad5 on innate and adaptive immune responses following vaccination. Ad5HVR48 displayed an intermediate level of innate immune cytokines and chemokines relative to those of Ad5 and Ad48, consistent with its chimeric nature. Hepatotoxicity was observed after Ad5 immunization but not after Ad5HVR48 or Ad48 immunization. However, the CD8 + T-cell responses elicited by Ad5HVR48 vectors displayed a partially exhausted phenotype, as evidenced by the sustained expression of programmed death 1 (PD-1), decreased effector-to-central memory conversion, and reduced memory recall responses, similar to those elicited by Ad5 vectors and in contrast to those induced by Ad48 vectors. Taken together, these results indicate that although Ad5HVR48 largely bypasses preexisting Ad5 neutralizing antibodies and shows reduced hepatotoxicity compared to that of Ad5, it induces adaptive immune phenotypes that are functionally exhausted similar to those elicited by Ad5.

Prime-boost immunization regimens have proven efficacious at generating robust immune responses. However, whether the level of replication of the boosting antigen impacts the magnitude and protective efficacy of vaccine-elicited immune responses remains unclear. To evaluate this, we primed mice with replication-defective adenovirus vectors expressing the lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP), followed by boosting with either LCMV Armstrong, which is rapidly controlled, or LCMV CL-13, which leads to a more prolonged exposure to the boosting antigen. Although priming of naive mice with LCMV CL-13 normally results in T cell exhaustion and establishment of chronic infection, boosting with CL-13 resulted in potent recall CD8 T cell responses that were greater than those following boosting with LCMV Armstrong. Furthermore, following the CL-13 boost, a greater number of anamnestic CD8 T cells localized to the lymph nodes, exhibited granzyme B expression, and conferred improved protection against Listeria and vaccinia virus challenges compared with the Armstrong boost. Overall, our findings suggest that the replicative capacity of the boosting antigen influences the protective efficacy afforded by prime-boost vaccine regimens. These findings are relevant for optimizing vaccine candidates and suggest a benefit of robustly replicating vaccine vectors. IMPORTANCE The development of optimal prime-boost vaccine regimens is a high priority for the vaccine development field. In this study, we compared two boosting antigens with different replicative capacities. Boosting with a more highly replicative vector resulted in augmented immune responses and improved protective efficacy.

Identification of the antigens (Ags) recognized by CD8+ T cells specific for melanoma and other types of cancer cells has been motivated by the expectation that they will serve as the basis for a therapeutic vaccine or will be useful for the stimulation of more effective CD8+ CTL for adoptive immunotherapy. Few of the currently identified Ags are derived from source proteins directly associated with transformation or metastasis, and many are self-Ags which may be subject to tolerance mechanisms. We have defined a new array of phosphorylated peptides presented by HLA-A1, -A2, -A3, -B7, -B44 and HLA-B27 that are presented on melanomas from multiple patients at >1 copy per cell and derived from source proteins associated with tumorigenesis and metastasis. We evaluated the immunogenicity of several of the HLA-A2-restricted phosphopeptide Ags in an HLA-transgenic murine model system and in vitro human T cell cultures, evaluated the presence of the phosphorylated source protein or display of the phosphorylated epitope on cancers of different histological types, and investigated the ability of phosphopeptide-specific CD8+ T cells to prevent outgrowth of cancer cells in a xenogenic model. Evaluation of metastatic melanoma tissue microarrays and cancer cell lysates demonstrated that the phosphorylated source proteins for β-catenin (Ser33-phosphorylated), Breast cancer anti-estrogen resistance −3 (BCAR3; Thr130-phosphorylated), and Insulin receptor substrate-2 (IRS2; Ser1100-phosphorylated) were broadly expressed in melanomas and other cancers but not normal tissues. In addition, these epitopes can be utilized to elicit phosphopeptide-specific T cells in both murine HLA-A2 transgenic mice in vivo and human in vitro culture. The phospho-β-catenin, phospho-IRS2 and phospho-BCAR3-specific-T cells that were generated differentiate between the phosphorylated and non-modified forms of their respective peptides and recognize the endogenously processed and presented phosphopeptide on the surface of cancer cells. Finally, adoptive transfer of these phosphopeptide-specific T cells slowed outgrowth of melanoma tumors implanted in immunodeficient NOD.SCID.IL2Rα-/- mice. Thus, we have defined a new set of post-translationally modified epitopes derived from source proteins associated with tumorigenesis and metastasis that are immunogenic and capable of slowing tumor outgrowth in a xenograft model. Based on these results, we are currently planning a clinical trial utilizing these HLA-A2-restricted phosphopeptides in melanoma patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1584. doi:1538-7445.AM2012-1584

Dysregulated phosphorylation in cancer cells can lead to the generation of novel tumor antigens modified by phosphorylation, which can be targeted for immunotherapy. Using immobilized metal affinity chromatography and mass spectrometry, we have previously identified phosphorylated peptides presented by MHC molecules on cancer cells. Several of the phosphopeptides are presented by melanoma but not by cultured melanocytes. A significant number of the source proteins for these phosphopeptides are involved in cellular processes known to promote tumor growth and metastasis. These antigens are particularly appealing as immunotherapeutic targets because mutations in or downregulation of the source proteins as a means of immune escape may compromise malignancy. We have also shown that the presence of the phosphate creates new antigenic targets for T cell recognition by creating direct interactions with the T cell receptor leading to specific T cell recognition of the phosphate and peptide sequence. Additionally, the presence of the phosphate can improve HLA-A2 binding affinities of some of the phosphopeptides with suboptimal anchor residues. A phosphopeptide derived from β-catenin was of particular interest as an immunotherapeutic target because its source protein has been shown to cooperate with activated N-Ras in immortalizing melanocytes. β-catenin/LEF signaling can also induce cell growth, motility, and transendothelial migration in melanoma cells. Additionally, nuclear expression of phosphorylated β-catenin has been shown to be associated with poor outcomes in melanoma patients. When pulsed onto bone marrow-derived dendritic cells and used to immunize HLA-A2 transgenic mice, we found that βcatpS3330–39 was only weakly immunogenic. We modified βcatpS3330–39 by replacing a suboptimal Ala at the P10 anchor position with a Val (βcatpS33(V)30–39). This modification enhanced the HLA-A2 binding affinity by 10 fold and substantially enhanced immunogenicity. Intravenous immunization of HLA-A2 transgenic mice with βcatpS33(V)30–39 generated high avidity CD8+ T cells that were highly crossreactive to the natural βcatpS3330–39 phosphopeptide. These high avidity βcatpS33-specific T cells also recognized endogenously processed βcatpS3330–39 on several melanoma cells. However the magnitude of the response to βcatpS33(V)30–39 was considerably less than the response induced using another antigen with a comparable HLA-A2 binding affinity. A 10-fold increase in antigen dose resulted in a sizeable increase in the magnitude of the response and a modest decrease in the average avidity for βcatpS3330–39. The level of crossreactivity on βcatpS3330–39 was not adversely impacted by increasing antigen dose. Our results demonstrate that βcatpS33(V)30–39 is more efficient than βcatpS3330–39 at inducing a βcatpS3330–39–specific immune response. The use of βcatpS33(V)30–39 for peptide vaccination is therefore most likely to be more advantageous for the efficient control of tumors. Citation Information: Clin Cancer Res 2010;16(7 Suppl):B14