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The aim of adoptive T-cell therapy of cancer is to selectively confer immunity against tumor cells. Autoimmune side effects, however, remain a risk, emphasizing the relevance of a suicide mechanism allowing in vivo elimination of infused T cells. We investigated the use of human CD20 as suicide gene in T-lymphocytes. Potential effects of forced CD20 expression on T-cell function were investigated by comparing CD20- and mock-transduced cytomegalovirus (CMV) specific T cells for cytolysis, cytokine release and proliferation. The use of CD20 as suicide gene was investigated in CMV specific T cells and in T cells genetically modified with an antigen specific T-cell receptor. No effect of CD20 on T-cell function was observed. CD20-transduced T cells with and without co-transferred T-cell receptor were efficiently eliminated by complement dependent cytotoxicity induced by therapeutic anti-CD20 antibody rituximab. The data support the broad value of CD20 as safety switch in adoptive T-cell therapy.

Reduced-intensity conditioning (RIC) has allowed the use of allogeneic stem cell transplantation (alloSCT) for haematological malignancies in elderly patients. A major problem of this type of transplantation is the high incidence of persisting chronic graft-versus-host disease (GvHD), leading to increased morbidity and mortality. The inclusion of alemtuzumab added to the graft ('Campath in the bag') for donor T-cell depletion offers an easy procedure to diminish the incidence of GvHD. Good engraftment is observed in most patients, whereas almost no GvHD is observed after transplantation. Most patients become mixed chimeric after transplantation, requiring donor lymphocyte infusion for conversion to full donor chimerism. Although subsequent acute and chronic GvHD is observed in 50-60% of patients, it is responsive to therapy in many patients, resulting in a low incidence of persisting chronic GvHD. AlloSCT with RIC and alemtuzumab-induced T-cell depletion offers a suitable platform for the investigation of novel cellular immunotherapy.

Adoptive transfer of antigen-specific T cells is an attractive strategy for the treatment of hematologic malignancies. It has been shown that T cells recognizing minor histocompatibility antigens (mHag) selectively expressed on hematopoietic cells mediate antileukemic reactivity after allogeneic stem cell transplantation. However, large numbers of T cells with defined specificity are difficult to attain. An attractive strategy to obtain large numbers of leukemia-reactive T cells is retroviral transfer of mHag-specific T-cell receptors (TCR). TCR transfer into T cells specific for persistent viruses may enable these T cells to proliferate both after encountering with viral antigens as well as mHags, increasing the possibility of in vivo survival. We analyzed whether the dual specificity of the TCR-transferred T cells after repetitive stimulation via either the introduced antileukemic HA-2-TCR or the endogenous cytomegalovirus (CMV) specific CMV-TCR was preserved. We show that after repetitive stimulation, T cells skew to a population predominantly expressing the triggered TCR. However, HA-2-TCR-transferred CMV-specific T cells with high antileukemic HA-2-TCR expression but low CMV-TCR expression were able to persist and proliferate after repetitive stimulation with pp65. Moreover, HA-2-TCR-transferred CMV-specific T cells remained dual specific after repetitive stimulation and TCR expression could be reverted after additional stimulation via the previously nonstimulated TCR, restoring high-avidity interactions. These data imply persistence of TCR-transferred virus-specific T cells with both antileukemic and antivirus reactivity in vivo.

Background: Donor lymphocyte infusion is an effective form of adoptive immunotherapy for hematologic malignancies after allogeneic stem cell transplantation. Graft-versus-host disease, however, often develops due to recognition of ubiquitously-expressed minor histocompatibility antigens. Transfer of T-cell receptors recognizing hematopoiesis-restricted minor histocompatibility antigens to virus-specific T cells may be a powerful anti-tumor therapy with a low risk of graft-versus-host disease. The purpose of this study was to develop an optimal T-cell receptors-encoding multi-cistronic retroviral vector and an efficient method for generating T-cell receptors-engineered virus-specific T cells., Design and Methods: Retroviral vectors encoding the T-cell receptors for the hematopoiesis-restricted minor histocompatibility antigen HA-2 with and without selection markers were compared for T-cell receptors surface expression and HA-2-specific lysis. In addition, two different methods, i.e. peptide stimulation of CD8(+) cells and Pro5 MHC pentamer-based isolation of antigen-specific T cells, were investigated for their efficiency to generate T-cell receptors-transduced virus-specific T cells., Results: Bi-cistronic vectors without selection markers most efficiently mediated T-cell receptors surface expression and HA-2-specific lysis. Furthermore, both methods were useful for generating gene-modified cells, but the purity of virus-specific T cells was higher after pentamer isolation. Finally, the capacity of gene-modified cells to express the transgenic T-cell receptors at the cell surface markedly differed between virus-specific T cells and was correlated with lysis of relevant target cells., Conclusions: Our data support T-cell receptors gene transfer to pentamer-isolated virus-specific T cells using bi-cistronic retroviral vectors and illustrate the relevance of selection of gene-modified T cells with appropriate transgenic T-cell receptors surface expression for clinical gene therapy.

Background and Objectives: Cytotoxic T lymphocytes (CTL) may use two effector mechanisms to kill their target cells: perforin (PFN) and granzyme B (GrB)-dependent granule-mediated cell death and death receptor-mediated cell death. Controversy exists whether, in addition to PFN/GrB-mediated apoptosis, death receptor-induced apoptosis contributes to the elimination of human tumor cells by CTL., Design and Methods: Since the two CTL-mediated effector mechanisms differ in time required to eliminate target cells, lysis of target cells was analyzed using CTL clones with slow and rapid kinetics of killing derived from a patient with chronic myeloid leukemia. To determine the involvement of the death receptor pathway, a retroviral construct encoding the antiapoptotic gene FLICE inhibitory protein (FLIP) was introduced into these target cells., Results: A CTL clone capable of killing 50% of the target cells within 2 hours of incubation primarily acted by release of PFN and GrB. In contrast, two CTL clones showing slower target cell killing kinetics partially used the death receptor pathway (approximately 30% inhibition by FLIP)., Interpretation and Conclusions: We demonstrated that the death receptor pathway contributes to T-cell-mediated cell death if not all target cells are destroyed by release of PFN and GrB.

Minor histocompatibility antigens (mHags) play an important role in both graft-versus-tumor effects and graft-versus-host disease (GVHD) after allogeneic stem cell transplantation. We applied biochemical techniques and mass spectrometry to identify the peptide recognized by a dominant tumor-reactive donor T-cell reactivity isolated from a patient with relapsed multiple myeloma who underwent transplantation and entered complete remission after donor lymphocyte infusion. A frequently occurring single nucleotide polymorphism in the human ATP-dependent interferon-responsive (ADIR) gene was found to encode the epitope we designated LB-ADIR-1F. Although gene expression could be found in cells from hematopoietic as well as nonhematopoietic tissues, the patient suffered from only mild acute GVHD despite high percentages of circulating LB-ADIR-1F-specific T cells. Differential recognition of nonhematopoietic cell types and resting hematopoietic cells as compared with activated B cells, T cells, and tumor cells was demonstrated, illustrating variable LB-ADIR-1F expression depending on the cellular activation state. In conclusion, the novel mHag LB-ADIR-1F may be a suitable target for cellular immunotherapy when applied under controlled circumstances.

Purpose: The poor immunogenicity of most leukemias and the lack of specificity of the donor T cells limit the in vivo effectiveness of conventional donor lymphocyte infusions in many patients suffering from persistent or recurrent leukemia after allogeneic stem cell transplantation. These limitations may be overcome by the adoptive transfer of in vitro generated leukemia-reactive T cells. Although the potential clinical efficacy of this approach has been shown previously, lack of reproducibility of the procedure and the inability to show persistence and survival of the transferred T cells hampered further clinical application. The purpose of this study was to develop a new, broadly applicable strategy for the efficient generation and isolation of leukemia-reactive T cells with a better probability to survive and expand in vivo., Experimental Design: Myeloid and B-cell leukemias were modified into professional immunogenic antigen-presenting cells, and used to stimulate HLA-matched donor T cells. After two stimulations, responding donor T cells were isolated based on their secretion of IFN-gamma and tested for their capacity to recognize and kill the primary leukemia., Results: Using one universal stimulation and isolation protocol for various forms of leukemia, T-cell populations containing high frequencies of leukemia-reactive T cells could reproducibly be generated and early isolated under mild stimulatory conditions. Isolated T cells still had high proliferative potential and their reactivity seemed to be restricted to cells of the patient's hematopoiesis., Conclusion: We here show a new robust procedure for the generation and isolation of leukemia-reactive T cells for adoptive transfer.

Retroviral transfer of T-cell receptors (TCR) to peripheral blood-derived T cells generates large numbers of T cells with the same antigen specificity, potentially useful for adoptive immunotherapy. One drawback of this procedure is the formation of mixed TCR dimers with unknown specificities due to pairing of endogenous and introduced TCR chains. We investigated whether gammadelta T cells can be an alternative effector population for TCR gene transfer because the gammadeltaTCR is not able to form dimers with the alphabetaTCR. Peripheral blood-derived gammadelta T cells were transduced with human leukocyte antigen (HLA) class I- or HLA class II-restricted minor histocompatibility antigen (mHag) or virus-specific TCRs. Because most gammadelta T cells do not express CD4 and CD8, we subsequently transferred these coreceptors. The TCR-transduced gammadelta T cells exerted high levels of antigen-specific cytotoxicity and produced IFN-gamma and IL-4, particularly in the presence of the relevant coreceptor. gammadelta T cells transferred with a TCR specific for the hematopoiesis-specific mHag HA-2 in combination with CD8 displayed high antileukemic reactivity against HA-2-expressing leukemic cells. These data show that transfer of alphabetaTCRs to gammadelta T cells generated potent effector cells for immunotherapy of leukemia, without the expression of potentially hazardous mixed TCR dimers.

Objective: Donor lymphocyte infusion (DLI) after allogeneic stem cell transplantation is largely unsuccessful in the treatment of acute lymphoblastic leukemia (ALL). To allow identification of the causes of this failure, we established an animal model of DLI in human ALL., Methods: NOD/scid mice were inoculated with primary human ALL cells. Cells from five different patients were studied. After engraftment, DLI was performed by infusion of human leukocyte antigen (HLA)-identical donor T cells or HLA-disparate donor T cells., Results: DLI resulted in expansion of activated, leukemia-reactive T cells in all donor-patient combinations. After 40 days of expansion, T cells abruptly declined in numbers and displayed loss of cytotoxicity. At this moment, remissions were observed in three of five donor-patient combinations. In animals engrafted with the two unresponsive ALL, remissions could be achieved when HLA-disparate DLI was given., Conclusion: Our results indicate that the inefficacy of DLI in ALL may be due to the limitation of the proliferative capacity of ALL-reactive T cells and that the antileukemic efficacy during the limited time span of proliferation depends on the antigenic disparity between the donor and the patient. The model can be used to study whether alternative strategies may result in more sustained antileukemic responses after DLI in ALL.

Purpose: In patients treated with allogeneic stem cell transplantation for advanced mantle cell lymphoma (MCL), complete sustained remissions have been observed illustrating susceptibility of MCL cells to a graft-versus-lymphoma effect. To potentiate this graft-versus-lymphoma effect, adoptive transfer of in vitro selected MCL-specific CTL can be an attractive approach. The lack of expression of costimulatory molecules on MCL cells hampers the generation of MCL-reactive T-cell responses. The purpose of this study was to modify MCL cells into antigen-presenting cells (APC) and to use these MCL-APCs to induce allogeneic MCL-reactive T-cell responses., Experimental Design: Interleukin (IL)-4, IL-10, CpG, and CD40 activation were tested for their capacity to up-regulate costimulatory molecules on MCL cells. Primary MCL cells or the modified MCL-APCs were then used to evaluate the induction of MCL-reactive T-cell responses in HLA-matched donors., Results: Ligation of CD40 on MCL cells was essential to up-regulate costimulatory molecules and to induce production of high amounts of IL-12. In contrast to primary MCL cells, MCL-APC cells as stimulators were capable of inducing CD8+ CTL lines from HLA class I-matched donors. High numbers of CTL clones could be generated capable of efficiently killing the primary MCL cells and MCL-APC but not donor-specific targets., Conclusion: These results show the feasibility to generate primary allogeneic T-cell responses against MCL-APC, and may provide new immunotherapeutic tools to further exploit the graft-versus-lymphoma effect following allogeneic stem cell transplantation in patients with MCL.

T cells directed against minor histocompatibility antigens (mHags) might be responsible for eradication of hematological malignancies after allogeneic stem cell transplantation. We investigated whether transfer of T cell receptors (TCRs) directed against mHags, exclusively expressed on hematopoietic cells, could redirect virus-specific T cells toward antileukemic reactivity, without the loss of their original specificity. Generation of T cells with dual specificity may lead to survival of these TCR-transferred T cells for prolonged periods of time in vivo due to transactivation of the endogenous TCR of the tumor-reactive T cells by the latent presence of viral antigens. Furthermore, TCR transfer into restricted T cell populations, which are nonself reactive, will minimize the risk of autoimmunity. We demonstrate that cytomegalovirus (CMV)-specific T cells can be efficiently reprogrammed into leukemia-reactive T cells by transfer of TCRs directed against the mHag HA-2. HA-2-TCR-transferred CMV-specific T cells derived from human histocompatibility leukocyte antigen (HLA)-A2+ or HLA-A2- individuals exerted potent antileukemic as well as CMV reactivity, without signs of anti-HLA-A2 alloreactivity. The dual specificity of these mHag-specific, TCR-redirected virus-specific T cells opens new possibilities for the treatment of hematological malignancies of HLA-A2+ HA-2-expressing patients transplanted with HLA-A2-matched or -mismatched donors.

Objective: Allogeneic stem cell transplantation (alloSCT) following reduced-intensity conditioning offers a relatively nontoxic regimen while preserving rapid and sustained engraftment. Acute and chronic graft-vs-host disease (GVHD) is, however, a significant cause of severe morbidity. To reduce the incidence of GVHD, we treated a group of high-risk patients with a reduced-intensity conditioning regimen followed by in vitro T-cell-depleted alloSCT using Campath 1-H incubation., Patients and Methods: Eighteen patients were treated with fludarabine (6 x 30 mg/m(2)), busulphan (2 x 3.2 mg/kg), and ATG (4 x 10 mg/kg) followed by the infusion of high-dose T-cell-depleted peripheral stem cells from sibling donors. No posttransplant GVHD prophylaxis was administered. At 6 months after alloSCT, low-dose donor lymphocyte infusion (DLI) was administered., Results: All patients had sustained engraftment of donor cells with a median of 95% donor cells at 3 months after alloSCT. Minimal acute and no chronic GVHD was observed after alloSCT. A high incidence of cytomegalovirus (CMV) reactivation but no CMV disease was observed. Eleven patients received DLI at a median of 6.5 months after alloSCT. Acute GVHD grade II-III developed in 6 patients. All patients showed improvement of donor chimerism after DLI. With a median follow-up of 211 days, 11 patients are alive. Particular in patients with chronic lymphocytic leukemia and acute myeloid leukemia, a significant graft-vs-tumor effect was observed., Conclusions: In vitro T-cell-depleted alloSCT following reduced-intensity conditioning leads to durable donor engraftment without GVHD. The high levels of donor chimerism allow the subsequent use of cellular immunotherapy to treat residual disease.