Abstract 2272: Exploratory analysis of T cell repertoire dynamics upon systemic treatment with the oncolytic virus pelareorep in combination with pembrolizumab and chemotherapy in patients with advanced pancreatic adenocarcinoma

Abstract

Abstract Background: Pelareorep is an immuno-oncolytic virus that induces an inflamed tumor phenotype in metastatic adenocarcinoma of the pancreas (MAP). Systemically delivered pelareorep in combination with chemotherapy achieves 1 & 2 year-survival rates of 46% & 24% in MAP pts, respectively. Analysis of tumor tissue from patients (pts) treated with pelareorep, chemotherapy and anti-PD-L1 have shown reovirus RNA and protein replication, T-cell infiltration, and upregulation of PD-L1, highlighting that effective T-cell recognition of tumor antigens may be critical to success for this combination therapy. Thus, we hypothesized that pelareorep in combination with chemo and pembrolizumab in pts with MAP would alter the peripheral T-cell repertoire, creating new T-cell clones via the release of novel neoantigens in addition to expanding existing T-cell clones. Methods: A phase 1b study enrolled 11 MAP pts who progressed after first-line treatment. Pts received pelareorep (4.5e10 TCID 50 IV, D1 & D2), plus pembrolizumab (2mg/kg IV, D8) plus either 1) 5-FU (LV (200 mg/m2 /5-FU 200 mg /m2 IV bolus, 5-FU 1200mg/m2 continuous IV infusion D1) or 2) gemcitabine (1000 mg/m2 IV, D1), or 3) irinotecan (125 mg/m2 IV, D1) q3w, until disease progression/unacceptable toxicity. DNA from peripheral blood mononuclear cells from nine patients at cycle 1 day 1 (C1D1) & C2D1 (approx. 3 weeks later) was analyzed using the immunoSEQ® Assay (Adaptive Biotechnologies, Seattle) sequencing the T-cell receptor beta chain region to interrogate changes in the T-cell repertoire. Results: The median Morisita index between C2D1 and C1D1 was 0.83 with 3 samples below 0.6, indicative of significant peripheral repertoire turnover. The median number of expanded clones equated to 45.7 per 100,000 cumulative templates; normal variation over 4 weeks is ~ 5-10 expanded clones. Strikingly, most (median: 86%) peripheral clonal expansion occurred in clones below the limit of detection at C1D1. Cox regression analysis revealed that high peripheral clonality correlates with progression free survival at C1D1 (p=0.01, HR=0.053). Moreover, high clonality correlates with overall survival at both C1D1 (p=0.013, HR=0.124) and C2D1 (p=0.010, HR=0.079). Conclusions: High levels of peripheral T-cell repertoire turnover occur between C1D1 and C2D1. Repertoire turnover is accompanied by significant clonal expansion, mostly by expansion of new clones (i.e. undetected in C1D1). Higher peripheral clonality is associated with better progression free survival at C1D1, and overall survival at C1D1 and C2D1. This research highlights the potential utility of T-cell clonality as a predictive and prognostic biomarker to pelareorep therapy and warrants further clinical investigation. Citation Format: Grey A. Wilkinson, Devalingam Mahalingam, Sukeshi Patel Arora, Paul A. Fields, Patrick Raber, Karol Cheetham, Matt Coffey. Exploratory analysis of T cell repertoire dynamics upon systemic treatment with the oncolytic virus pelareorep in combination with pembrolizumab and chemotherapy in patients with advanced pancreatic adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2272.