Prostate cancer is the most common cancer among men in the United States and the second most common malignant cause of male deaths in the United States. There is currently no effective therapy for late-stage disease, whereas surgery or radiation therapy is the only choice for early-stage disease. Immunotherapy affords a promising approach to the treatment of various types of cancer, including prostate cancer (1 -5). Although peptide-or dendritic cell -based vaccines can induce antigenspecific immune responses, objective clinical responses remain infrequent and transient (3,6). A possible explanation is that tumor cells may create an immunosuppressive environment in cancer patients. Thus, a better understanding of the interaction between tumor-infiltrating immune cells and cancer cells is critical to efforts to devise strategies that would enhance the therapeutic efficacy of immunologic interventions.Recent studies indicate that preexisting CD4 + regulatory T (Treg) cells at tumor sites may pose major obstacles to effective cancer immunotherapy, as these cells have a potent ability to suppress host immune responses (7 -9). Indeed, increased proportions of CD4 + CD25 + Treg cells in the total CD4 + T-cell populations have been documented in patients with different types of cancers, including lung, breast, and ovarian tumors (10 -12). Our recent findings further show the presence of antigen-specific CD4 + Treg cells at tumor sites, where they induce antigen-specific and local immune tolerance (7,8). The removal or elimination of Treg cell populations with anti-CD25 monoclonal antibody (mAb) treatment results in effective rejection of transplanted tumors in animal models (13), further suggesting a functional role for these Treg cells in tumor progression and immunosuppression.Because Treg cell -mediated immunosuppression exists at tumor sites, a new strategy for depletion of Treg cells or reversal of the suppressive function of Treg cells will be important in efforts to induce antigen-specific effector T cells. Thus, we recently showed that Toll-like receptor 8 (TLR8) ligands can specifically reverse the suppressive function of both antigen-specific and

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Wilms' tumor 1 (WT1) is constantly expressed in leukemic cells of acute leukemia and myelodysplastic syndrome (MDS). A T-cell receptor (TCR) that specifically reacts with WT1 peptide in the context of HLA-A*24:02 has been identified. We conducted a first-in-human trial of TCR-gene transduced T-cell (TCR-T-cell) transfer in patients with refractory acute myeloblastic leukemia (AML) and high-risk MDS to investigate the safety and cell kinetics of the T cells. The WT1-specific TCR-gene was transduced to T cells using a retroviral vector encoding small interfering RNAs for endogenous TCR genes. The T cells were transferred twice with a 4-week interval in a dose-escalating design. After the second transfer, sequential WT1 peptide vaccines were given. Eight patients, divided into 2 dose cohorts, received cell transfer. No adverse events of normal tissue were seen. The TCR-T cells were detected in peripheral blood for 8 weeks at levels proportional to the dose administered, and in 5 patients, they persisted throughout the study period. The persisting cells maintained ex vivo peptide-specific immune reactivity. Two patients showed transient decreases in blast counts in bone marrow, which was associated with recovery of hematopoiesis. Four of 5 patients who had persistent T cells at the end of the study survived more than 12 months. These results suggest WT1-specific TCR-T cells manipulated by ex vivo culture of polyclonal peripheral lymphocytes survived in vivo and retained the capacity to mount an immune reaction to WT1. This trial was registered at www.umin.ac.jp as #UMIN000011519.

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T cells play an important role in cancer immunosurveillance and tumor destruction. However, tumor cells alter immune responses by modulating immune cells through antigen stimulation and immunoregulatory cytokines. A better understanding of the interplay between tumor cells and T cells might provide new strategies to enhance anti-tumor immunity. Through an antigen-screening approach using colorectal tumor-reactive T cells, we identified a HLA-DR11-restricted T-cell epitope encoded by KIAA0040 as well as MHC-unrestricted human galectin-3 (Gal-3) expressed by tumor cells. Although the biological function of KIAA0040 remains to be determined, we found that galectin-3 functioned as an immune regulator for direct T cell activation and function. T cell activation induced by galectin-3 resulted in T cell apoptosis. We showed that a high level of expression of galectin-3 promoted tumor growth in vitro and in vivo. Using a mouse tumor model, we demonstrated that delivery of high doses of galectin-3 inhibited tumor-reactive T cells and promoted tumor growth in mice receiving tumor-reactive CD8+ T cells. These findings suggest that galectin-3 may function as an immune regulator to inhibit T cell immune responses and promote tumor growth, thus providing a new mechanism for tumor immune tolerance.

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CD4+Foxp3+ regulatory T (Treg) cells were shown to control all aspects of immune responses. How these Treg cells develop is not fully defined, especially in neonates during development of the immune system. We studied the induction of Treg cells from neonatal T cells with various TCR stimulatory conditions, because TCR stimulation is required for Treg cell generation. Independent of the types of TCR stimulus and without the addition of exogenous TGF-β, up to 70% of neonatal CD4+Foxp3− T cells became CD4+Foxp3+ Treg cells, whereas generally <10% of adult CD4+Foxp3− T cells became CD4+Foxp3+ Treg cells under the same conditions. These neonatal Treg cells exert suppressive function and display relatively stable Foxp3 expression. Importantly, this ability of Treg cell generation gradually diminishes within 2 wk of birth. Consistent with in vitro findings, the in vivo i.p. injection of anti-CD3 mAb to stimulate T cells also resulted in a >3-fold increase in Treg cells in neonates but not in adults. Furthermore, neonatal or adult Foxp3− T cells were adoptively transferred into Rag1−/− mice. Twelve days later, the frequency of CD4+Foxp3+ T cells converted from neonatal cells was 6-fold higher than that converted from adult cells. Taken together, neonatal CD4+ T cells have an intrinsic “default” mechanism to become Treg cells in response to TCR stimulations. This finding provides intriguing implications about neonatal immunity, Treg cell generation, and tolerance establishment early in life.

Purpose: Preparative lymphodepletion, the temporal ablation of the immune system, has been reported to promote persistence of transferred cells along with increased rates of tumor regression in patients treated with adoptive T-cell therapy. However, it remains unclear whether lymphodepletion is indispensable for immunotherapy with T-cell receptor (TCR) gene-engineered T cells.Experimental Design: We conducted a first-in-man clinical trial of TCR gene-transduced T-cell transfer in patients with recurrent MAGE-A4-expressing esophageal cancer. The patients were given sequential MAGE-A4 peptide vaccinations. The regimen included neither lymphocyte-depleting conditioning nor administration of IL2. Ten patients, divided into 3 dose cohorts, received T-cell transfer.Results: TCR-transduced cells were detected in the peripheral blood for 1 month at levels proportional to the dose administered, and in 5 patients they persisted for more than 5 months. The persisting cells maintained ex vivo antigen-specific tumor reactivity. Despite the long persistence of the transferred T cells, 7 patients exhibited tumor progression within 2 months after the treatment. Three patients who had minimal tumor lesions at baseline survived for more than 27 months.Conclusions: These results suggest that TCR-engineered T cells created by relatively short-duration in vitro culture of polyclonal lymphocytes in peripheral blood retained the capacity to survive in a host. The discordance between T-cell survival and tumor regression suggests that multiple mechanisms underlie the benefits of preparative lymphodepletion in adoptive T-cell therapy.