Abstract 517: Tebentafusp induces transient systemic inflammation and modifies the micro-environment to sensitize uveal melanoma tumors to cytotoxic CD8 cells

Abstract

Abstract Background: Tebentafusp is a unique investigational TCR-anti-CD3 bispecific fusion protein that targets melanoma-expressed gp100 antigen and has shown monotherapy activity in advanced metastatic melanoma [1, 2, 3]. In a phase I/II trial (NCT02570308) that enrolled late stage metastatic uveal melanoma patients, we explored the effects of tebentafusp on serum cytokines and on the tumor and its micro-environment. Methods: NCT02570308 was conducted in HLA-A*02:01+ patients with advanced uveal melanoma: This analysis focuses on patients who went through weekly dosing at Cycle 1, Day1 (C1D1, 20mcg) and C1D8 (30mcg), followed by a dose of 68mcg administered weekly at C1D15 onwards. Serum samples and tumor biopsies were taken pre-treatment and at multiple time points post-treatment, and were profiled as follows: a multiplex panel of 11 immune markers (Luminex) in sera from 124 patients; immunohistochemistry (IHC) and genome-wide transcriptional RNAseq analysis of up to 57 paired baseline and on-treatment biopsies at C1D16. Whole slide digital image analysis was used to calculate positive IHC cells per mm2 in the tumor. Results: Tebentafusp caused transient immune activation as evidenced by significant increases in serum levels of IFNγ and IFNγ-inducible chemokines including CXCL9/10/11 reaching maximal changes at 8-24 hours after dosing (fold change FC: 8-10). Induction of the T cell cytokines IL-2 and IL-10 was accompanied by transient increases in the inflammatory cytokines IL-6, TNFα and the chemokine CCL2 (FC: 5-14).After 3 doses of tebentafusp, a significant increase in CD3 positive immune cells in the tumor was seen (p<0.001; FC=3), particularly cytotoxic CD8+ cells, (p=0.002; FC=2). RNAseq analysis revealed significant induction of IFNα (FC=2) and IFNγ (FC=2) signatures. mRNAs known to be induced by IFNγ and implicated in response to anti-PD1/L1 were significantly increased: CXCL9/10/11, GZMB (FC=3-5). Expression of antigen presentation genes including HLA class 1, TAP1, 2 and PSMB8 was significantly induced (FC=2-3). Homeostasis mechanisms characterized by IDO1 and PD-L1 were induced (FC=4 and 2 respectively); however, low baseline FOXP3 expression levels were unchanged. These immune responses were accompanied by significant reductions in expression levels of tumor-specific melanoma markers gp100 and TYRP1 (30-40% reduction) and tumor proliferation genes including MKI67, BIRC5, CDK2 (20-30% reduction). Conclusions: Tebentafusp caused transient increases in inflammatory cytokines and chemokines in serum and modified the micro-environment of metastatic uveal melanoma tumors to sensitize to cytotoxic CD8+ cells.[1] NCT01211262; ASCO 2019 [2] Clinical Cancer Research; 2020.[3] #195; ESMO IO; 2020 Citation Format: Marcus O. Butler, Sarah Stanhope, Revashnee Naidoo, Emma Leach, Sarnjeet Kaur, Laura Collins, Shaad Abdullah, Koustubh Ranade, Alexander N. Shoushtari. Tebentafusp induces transient systemic inflammation and modifies the micro-environment to sensitize uveal melanoma tumors to cytotoxic CD8 cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 517.