Design and use of conditional MHC class I ligands.

Major histocompatibility complex (MHC) class I molecules associate with a variety of peptide ligands during biosynthesis and present these ligands on the cell surface for recognition by cytotoxic T cells. We have designed conditional MHC ligands that form stable complexes with MHC molecules but degrade on command, by exposure to a defined photostimulus. 'Empty MHC molecules' generated in this manner can be loaded with arrays of peptide ligands to determine MHC binding properties and to monitor antigen-specific T-cell responses in a high-throughput manner. We document the value of this approach by identifying cytotoxic T-cell epitopes within the H5N1 influenza A/Vietnam/1194/04 genome.

RNA interference targeting programmed death receptor-1 improves immune functions of tumor-specific T cells.

Adoptive cell transfer (ACT), either using rapidly expanded tumor infiltrating lymphocytes or T-cell receptor transduced peripheral blood lymphocytes, can be considered one of the most promising approaches in cancer immunotherapy. ACT results in the repopulation of the host with high frequencies of tumor-specific T cells; however, optimal function of these cells within the tumor micro-environment is required to reach long-term tumor clearance. We and others have shown that ongoing anti-tumor immune responses can be impaired by the expression of ligands, such as PD-L1 (B7-H1) on tumor cells. Such inhibitory molecules can affect T cells at the effector phase via their receptor PD-1. PD-L1/PD-1 interaction has indeed been shown crucial in inducing T-cell anergy and maintaining peripheral tolerance. In order to maximize anti-tumor responses, antibodies that target the PD-1/PD-L1 axis are currently in phase I/II trials. Alternatively, a more refined approach could be the selective targeting of PD-1 in tumor-specific T cells to obtain long-term resistance against PD-1-mediated inhibition. We addressed whether this goal could be achieved by means of retroviral siRNA delivery. Effective siRNA sequences resulting in the reduction of surface PD-1 expression led to improved murine as well as human T-cell immune functions in response to PD-L1 expressing melanoma cells. These data suggest that blockade of PD-1-mediated T-cell inhibition through siRNA forms a promising approach to achieve long-lasting enhancement of tumor-specific T-cell function in adoptive T-cell therapy protocols.

Immunogenicity, including vitiligo, and feasibility of vaccination with autologous GM-CSF-transduced tumor cells in metastatic melanoma patients.

PURPOSE: To determine the feasibility, toxicity, and immunologic effects of vaccination with autologous tumor cells retrovirally transduced with the GM-CSF gene, we performed a phase I/II vaccination study in stage IV metastatic melanoma patients. PATIENTS AND METHODS: Sixty-four patients were randomly assigned to receive three vaccinations of high-dose or low-dose tumor cells at 3-week intervals. Tumor cell vaccine preparation succeeded for 56 patients (88%), but because of progressive disease, the well-tolerated vaccination was completed in only 28 patients. We analyzed the priming of T cells against melanoma antigens, MART-1, tyrosinase, gp100, MAGE-A1, and MAGE-A3 using human leukocyte antigen/peptide tetramers and functional assays. RESULTS: The high-dose vaccination induced the infiltration of T cells into the tumor tissue. Three of 14 patients receiving the high-dose vaccine showed an increase in MART-1- or gp100-specific T cells in the peripheral blood during vaccination. Six patients experienced disease-free survival for more than 5 years, and two of these patients developed vitiligo at multiple sites after vaccination. MART-1- and gp100-specific T cells were found infiltrating in vitiligo skin. Upon vaccination, the T cells acquired an effector phenotype and produced interferon-gamma on specific antigenic stimulation. CONCLUSION: We conclude that vaccination with GM-CSF-transduced autologous tumor cells has limited toxicity and can enhance T-cell activation against melanocyte differentiation antigens, which can lead to vitiligo. Whether the induction of autoimmune vitiligo may prolong disease-free survival of metastatic melanoma patients who are surgically rendered as having no evidence of disease before vaccination is worthy of further investigation.

Immune-escape markers in relation to clinical outcome of advanced melanoma patients following immunotherapy.

In this study, we investigated a large series of immune (escape) markers, relevant to T-cell function, as potential biomarkers for clinical outcome following immunotherapy. We retrospectively studied the expression of immune (escape) markers in metastatic melanoma tissues of 27 patients before autologous tumor cell vaccination, and 16 patients who were intended to treat but were not vaccinated because of rapid disease progression. Immunohistochemical data of infiltrating (suppressive) cells, such as T cells, regulatory T cells, myeloid-derived suppressor cells, and mast cells, or the expression of T-cell inhibitory factors (PD-1/PD-L1, IDO, and galectins), cytotoxic molecules (granzyme-B), melanocyte differentiation antigens, HLA class-I and tolerogenic cytokines [interleukin (IL)-1, IL-6, IL-10, TNF-α, and TGF-ß] were correlated statistically to clinical outcome and overall survival (OS). Significantly more tumor-infiltrating CD4(+) and CD8(+) T cells (both P < 0.05) were found in nonprogressors to vaccination (n = 9; median OS, 56 months), compared with progressors (n = 18; median OS, 9.5 months). Moreover, granzyme-B expression was elevated in the tumors of nonprogressors, suggesting activated cytotoxic T cells or natural killer cells. T-cell infiltration and granzyme-B expression significantly correlated with overall OS. T-cell inhibitory factors and suppressive cells did not correlate with OS, suggesting minor influence of these immune-escape markers on clinical outcome. The data of progressors were comparable with those from patients with rapid progression (not vaccinated; n = 16; median OS, 3 months). Our study shows that high numbers of intratumoral activated CD4(+) or CD8(+) T cells, before autologous tumor cell vaccination, are associated with favorable clinical outcome. Analyses of these markers in the patients' tumor tissues before immunotherapy may therefore be a valuable tool to select patients for whom the treatment may result in potential clinical benefit.

Selecting highly affine and well-expressed TCRs for gene therapy of melanoma.

A recent phase 1 trial has demonstrated that the generation of tumor-reactive T lymphocytes by transfer of specific T-cell receptor (TCR) genes into autologous lymphocytes is feasible. However, compared with results obtained by infusion of tumor-infiltrating lymphocytes, the response rate observed in this first TCR gene therapy trial is low. One strategy that is likely to enhance the success rate of TCR gene therapy is the use of tumor-reactive TCRs with a higher capacity for tumor cell recognition. We therefore sought to develop standardized procedures for the selection of well-expressed, high-affinity, and safe human TCRs. Here we show that TCR surface expression can be improved by modification of TCR alpha and beta sequences and that such improvement has a marked effect on the in vivo function of TCR gene-modified T cells. From a panel of human, melanoma-reactive TCRs we subsequently selected the TCR with the highest affinity. Furthermore, a generally applicable assay was used to assess the lack of alloreactivity of this TCR against a large series of common human leukocyte antigen alleles. The procedures described in this study should be of general value for the selection of well- and stably expressed, high-affinity, and safe human TCRs for subsequent clinical testing.