1215P - T cell repertoire sequencing reveals dynamics of response to dendritic cell vaccine plus dasatinib for checkpoint blockade resistant metastatic melanoma

Abstract

BackgroundWe recently conducted an open- label, single-center, prospective randomized Phase II clinical trial for HLA-A2+ patients with advanced-stage melanoma (NCT01876212) at the University of Pittsburgh Hillman Cancer Center. Patients received ID injections of Type-1-polarized, autologous DC loaded with a mixture of peptides derived from six tumor-associated vascular antigens (DLK1, EPHA2, HBB, NRP1, RGS5, TEM1) combined +/- daily oral administration of dasatinib (70mg BID) as an immune adjuvant/conditioning agent. Here we report an exploratory analysis of T cell repertoire profiling of longitudinally-sampled peripheral blood leukocytes (PBL) to define potential pharmacodynamic and response biomarkers. MethodsTotal RNA was extracted from pre- and post-treatment PBL from 13 therapy recipients (6 responders, 7 non-Responders) including extended longitudinal samples for four responders. TCRB sequencing was performed via the Oncomine TCRB-LR assay using 25ng total RNA as input. We evaluated T cell clonal expansion and TCR convergence as potential biomarkers of response. ResultsTCR convergence values were elevated in pretreatment PBL of responders compared to non-responders (mean frequency .012 vs .006; p=.01, Wilcoxon), and remained elevated in responders up to 25 weeks post treatment. TCR evenness (normalized Shannon entropy) decreased at week 5 compared to baseline (p=.01, one-sided student’s t-test), indicating increased clonal expansion following treatment. ConclusionsThese data suggest that peripheral blood TCRB convergence may serve as a predictive or prognostic biomarker for response to dendritic cell-based immunotherapy. Our finding of increased T cell clonal expansion at week 5 of treatment supports the notion that TCR sequencing may serve as a tool for the measurement of pharmacodynamic markers of therapeutic agent activity. Ongoing and future studies will further clarify the utility of TCR convergence and clonal expansion as immune repertoire biomarkers. Clinical trial identificationNCT01876212. Legal entity responsible for the studyUniversity of Pittsburgh School of Medicine & Hillman Cancer Center. FundingThermo Fisher Scientific. DisclosureL. Quagliata: Full / Part-time employment: Thermo Fisher Scientific. T. Looney: Full / Part-time employment: Thermo Fisher Scientific. D. Topacio-Hall: Full / Part-time employment: Thermo Fisher Scientific. G. Lowman: Full / Part-time employment: Thermo Fisher Scientific. All other authors have declared no conflicts of interest.