Immunotherapy in prostate cancer

Immunotherapy for the treatment of malignant neoplasms has made significant progress over the last 20 years. Multiple molecular targets and clinical agents have been developed recently, particularly in the field of metastatic adenocarcinoma of the prostate. Sipuleucel-T is currently the only FDA approved immunotherapy for prostate cancer. PSA-TRICOM (Prostvac) currently has a phase III randomized trial underway after a phase II trial showed an improvement in overall survival. Interestingly, both these agents showed improvement in overall survival with no measurable change in disease state, leading to significant controversy as the utility of these agents in prostate cancer. Ipilimumab revealed a benefit for a sub-cohort of men in a post-docetaxel group and is currently undergoing investigation in a pre-docetaxel group. There are a number of other targets such as PD-1 which have shown effectiveness in other neoplasms that will likely be investigated in the future for use in prostate cancer.

Intrinsic function of B7-H1 is linked with p38 MAPK pathway in activated CD8 T cells for T cell survival. (IRM14P.443)

B7-H1 (also named PD-L1) is up-regulated on activated CD8 T cells at the late stage of antigen stimulation, and is required for T cell survival during contraction phase. Since more anti-B7-H1 (PD-L1) antibody has been used in clinical trials of treatment of human cancers, it is necessary to know whether antibody ligation of B7-H1 expressed by T cells would affect T cell function and survival. After screening several anti-B7-H1 antibodies, we found that some antibody triggered the activation of p38 MAPK in activated CD8 T cells. In addition, the levels of activated p38 MAPK increased in T cells isolated from B7-H1 knockout mice compared to wild type mice. Inhibition of DNA-PKcs activation increased the activation of p38 MAPK in wild type T cells but not in B7-H1 KO T cells, suggesting B7-H1 may negatively regulate p38 MAPK through DNA-PKcs pathway. To that end, we identified an association of B7-H1 with DNA-PKcs in activated human T cells but not in resting T cells. Since p38 MAPK inhibition rescued activated CD8 T cells from apoptosis, the pro-survival function of T cell intrinsic B7-H1 may be mediated by suppression of p38 MAPK. However, ligation of B7-H1 by agonist antibody may disrupt B7-H1’s pro-survival function by increasing p38 MAPK activation. Our results identified a link of B7-H1 with p38 MAPK pathway and may help to define agonist function of anti-B7-H1 antibody prior to clinical application.

Endogenous tumor-reactive CD8+ T cells are differentiated effector cells with high expression of CD11a and PD-1 but are unable to control tumor growth (P2089)

We utilized CD11a, an integrin up-regulated on effector and memory CD8+ T cells, as a biomarker to identify, measure, and monitor endogenous tumor-reactive cytotoxic lymphocytes (CTLs) in two mouse tumor models and in melanoma patients. CD11ahigh CD8+ T cells were detected in primary and metastatic tumor sites after tumor cell injection, as well as in spontaneous murine breast cancer tissues. In the peripheral blood of melanoma patients, tumor antigen-specific T cells were detected within the population of CD11ahigh CD8+ T cells that express high levels of PD-1. Infusion of lethally irradiated tumor cells failed to stimulate the expansion of CD11ahigh CD8+ T cells, suggesting that the access of tumor cells to target tissues is required to induce CD11ahigh CD8+ T cell responses. Phenotypic analysis revealed that the CD11ahigh CD8+ T cells detected in our studies were proliferating (Ki67+) activated T cells (CD62L-, CD69+). Although CD11ahigh CD8+ T cells were differentiated effector cells with CTL effector functions, they were typically unable to control tumor growth in our mouse models, possibly due to high expression of PD-1. Our results demonstrate that CD11a can be used as a biomarker to identify and track endogenous tumor-reactive CTLs.

Identification of T cell epitopes on human proteolipid protein and induction of experimental autoimmune encephalomyelitis in HLA class II-transgenic mice

Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the CNS that is associated with HLA class II molecules HLA-DR2, -DR3 and -DR4. Previously, it has been difficult to analyze the role of individual HLA molecules in disease pathogenesis due to heterogeneity of MHC genes, linkage disequilibrium, influence of non-MHC genes and contribution of environment. To overcome some of these problems, we have generated HLA-transgenic (tg) mice to investigate function and interaction of these molecules in disease pathogenesis. To investigate the role of individual HLA class II genes in immune responses to human proteolipid protein (PLP), a candidate autoantigen in MS, mice expressing HLA genes DR2, DR3, DR4 (DRB1*0401 and DRB1*0402), DQ6 and DQ8, lacking endogenous class II molecules were immunized with overlapping peptides of PLP. In all tg mice, the majority of the dominant T cell epitopes were clustered mainly to three region; amino acids 31-70, 91-120 and 178-228, of the PLP molecules. We also identified an encephalitogenic epitope PLP(91-110) that induced clinical EAE in HLA-DR3 tg mice. These tg mice had inflammatory infiltrates classically associated with EAE and showed a Th1 cytokine profile. This humanized mouse model of MS will be valuable in deciphering the role of HLA molecules and autoantigens in MS.

Expression and function of HLA-DQ8 (DQA1*0301/DQB1*0302) genes in transgenic mice

Transgenic mice expressing HLA-DQA1*0301 and HLA-DQB1*0302 genes (DQ8) were produced. The transgenes were then transferred into mouse (Ab degrees) class II negative mice: the only class II molecules expressed in these animals were therefore coded by the HLA-DQ8 genes. Good expression of HLA-DQ molecules was found. Both CD4+ T cells and DQ8-specific T-cell receptor V beta expressing cells were positively selected in these mice. The HLA-DQ8 molecules expressed in these animals can present various foreign and self antigens and induce T-cell proliferation in vitro. These mice will be invaluable in future studies of the structure and function of HLA-DQ8 genes.

Radiation sensitivity of T-lymphocytes from immunodeficient "wasted" mice

Mice with the autosomal recessive gene "wasted" (wst/wst) exhibit neurologic disorders, reduced mucosal immune responses, and abnormal DNA repair mechanisms. The wst/wst mouse has been proposed as a murine model for the human disorder ataxia telangiectasia. Experiments were designed to examine the sensitivity of T-cells from wasted mice to ionizing radiation. Results demonstrated that T-cell clones derived from wasted mice are more sensitive to the killing effects of gamma-rays than similar T-cell clones from control mice. Bulk thymocyte and splenic cell cultures demonstrated similar radiation sensitivity. Both thymic and splenic lymphocytes from wasted mice also expressed low proliferative responses to mitogenic stimulation with concanavalin A (Con A) that could not be attributed to an absence or reduction in T-cell number. However, following activation with Con A, cell cultures exhibited a marked decrease in the percentage of Thyl + cells in wasted mice, in contrast to cultures from control mice in which significant increases in Thyl + cells were observed. Furthermore, when cells were treated with gamma-rays in combination with Con A, Thyl + cells were decreased in control spleen and thymus, but were elevated in similarly treated wasted cultures. These changes were accompanied by an increase in cell volume in T-cells from wasted but not from control mice. These results describe the sensitivity of T-cells from wasted mice to ionizing radiation; in addition, they suggest that the wst/wst abnormality may be associated with cell cycle aberrancies.