Abstract PO030: A Novel T-cell Population Expressing the Ectoenzymes CD38 and CD39 is Associated with Melanoma Patient Non-Response to Immunotherapy

Abstract

Abstract Cancer immunotherapy has emerged as one of the most potent therapeutic tools in treating melanoma and a variety of other malignancies. Immunotherapy includes inhibition of the modulators of T cell antitumor function, the immune checkpoints, by using antibodies against them. In advanced melanoma patients, immune checkpoint inhibitors ipilimumab (IPI) and nivolumab (NIVO) have had unprecedented efficacy. Although many patients respond well to this therapy, many patients remain unresponsive. The mechanism underlying treatment failures remains poorly understood. Using a novel high-dimensional flow cytometry analysis methodology, CytoBrute, we found that in the cohort of advanced melanoma patients receiving sequential NIVO-IPI, high baseline levels of a novel immunophenotype, CD4+CD38+CD39+CD127-GARP- T-cells (median frequency 0.3%), was associated with poor outcomes (disease progression p=0.008, and decreased overall survival p<0.0001 HR = 6.8). Both CD38 and CD39 are ectoenzymes with CD38 hydrolyzing NAD+ to cyclic-ADP ribose and CD39 converting extracellular ATP to immunosuppressive adenosine nucleosides. Both of these proteins are being evaluated as targets to increase the efficacy of immunotherapies. The association of this novel phenotype, which we have termed T-cells expressing ectoenzymes (Tee), was validated in two independent cohorts of melanoma patients treated with NIVO monotherapy, with progressors showing a higher frequency of this immunophenotype at baseline (p=0.047). In IPI+NIVO adjuvant treated melanoma patients, an increase in this population of cells was observed during treatment in relapsing patients, leading to a higher frequency of these cells in relapsing patients relative to patients with no evidence of disease (p=002). Preliminary data obtained from single cell RNA sequencing from the ectoenzyme expressing peripheral blood T cell population, demonstrated predominant expression of IL-32 and CD99 (a membrane glycoprotein associated with lymphocyte diapedesis) in this population, along with several additional clusters distinguished by expression of specific TcR V beta genes. Collectively, we have identified a novel population of ectoenzyme expressing T-cells (CD3+CD4+CD38+CD39+CD127-GARP-) associated with poor melanoma patient outcomes in response to checkpoint immunotherapy. Further investigation of the mechanisms by which this novel T-cell phenotype is associated with poor patient outcomes is under way. Citation Format: Ankita Mitra, David M. Woods, Anjali Rao, Andressa S. Laino, Aidan Winters, Itai Yanai, Pratip K. Chattopadhyay, Jeffrey S. Weber. A Novel T-cell Population Expressing the Ectoenzymes CD38 and CD39 is Associated with Melanoma Patient Non-Response to Immunotherapy [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO030.