Project 3 Immunotherapeutic Targeting of SLC45A2 for Treatment of Uveal Melanoma

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Project 3: Project Summary/Abstract While novel immunotherapy regimens show promise in treating cutaneous melanoma, effective therapies for advanced uveal melanoma remain a clear unmet need in the field for a disease that is highly treatment refractory and leads to dismal patient survival rates. Adoptive cell therapy (ACT) is a form of immunotherapy with strong potential to improve the outcome for uveal melanoma patients. ACT involves the ex vivo isolation and expansion of antigen-specific, tumor-reactive T cells that are infused into the patient with the aim of mediating disease regression and maintaining a durable response. Our group has demonstrated that longer persistence of adoptively transferred cytotoxic T lymphocytes (CTL) in patients with cutaneous melanoma correlates with improved clinical response, and we have accordingly developed an in vitro process using IL-21 to generate long-lived central memory-type T cells whose in vivo survival extends up to years from the time of infusion. Following our crucial identification of an epitope of the melanoma-associated transporter protein SLC45A2 that is highly expressed in uveal melanoma cells but not in normal melanocytes and capable of eliciting a potent cytotoxic response against uveal melanoma cell lines, we will evaluate this epitope and search for others within the same protein that can mediate adoptively transferred CTL-driven uveal melanoma disease regression. Specifically, we propose a Phase I study in which we will determine the safety and clinical efficacy of ACT targeting SLC45A2 in patients with metastatic uveal melanoma. This study will include a dose- escalation cohort of SLC45A2-specific CTL primed by IL-21 to enrich for central-memory-like CD8 T cells, followed by an expansion cohort of the same CTL at a dose without limiting toxicities in combination with CTLA4 blockade (ipilimumab). We have previously demonstrated the ability of this combination to achieve complete, durable responses with strong T cell persistence and antigen-spreading in refractory metastatic melanoma. To evaluate the study, we will measure in vivo persistence of transferred SLC45A2-specific T cells at weekly intervals and correlate with clinical response, and additionally assess induction of a multivalent T cell response through antigen-spreading. Finally, in an effort to expand the number of melanoma patients eligible for SLC45A2-targeted immunotherapy, we will, 1) identify additional epitopes from this protein that may be presented by other prevalent HLA class allotypes, and 2) search for HLA class II-restricted peptides from SLC45A2 to boost helper T cell-mediated amplification of the anti-tumor immune response. These studies represent a critical new avenue for uveal melanoma treatment using targeted immunotherapy, which holds the potential to improve patient survival for this challenging malignancy.