Abstract 6422: Combined TGFβ/PD-L1 blockade enhances systemic antitumor immunity in head and neck cancer
Authors: Rainey Magdalena , Craveiro Marco , Robbins Yvette , Sievers Cem , Allen Clint T. 
Published: April 2023

Abstract
Head and neck squamous cell carcinoma (HNSCC) unrelated to human papillomavirus (HPV) confers poor prognosis, with half of patients experiencing disease relapse in advanced stages. Response rates to traditional immunotherapies are low and novel approaches such as the bifunctional fusion protein Bintrafusp alfa (BA) that concurrently blocks PD-L1 signaling and neutralizes TGFβ are actively under investigation. Our group showed that when HNSCC patients received neoadjuvant BA therapy, it reversed exhaustion of tumor-infiltrating lymphocytes (TILs) by promoting antigen-mediated signaling. Additionally, we observed that BA promoted recirculation of TILs into peripheral blood possibly through decreased expression of the TGF-β-driven tissue-retention marker CD103. We hypothesize that addition of TGFβ neutralization to PD-L1 blockade can enhance systemic anti-tumor immunity compared to PD-L1 blockade alone. We assessed immune responses to BA in wild-type mice bearing established mouse oral cancer (MOC)-1 tumors that were randomized into the following groups: 1) vehicle; 2) anti-PD-L1 antibody (Avelumab); 3) TGFβ neutralizing construct with a mutated PD-L1 antibody (BA-M); 4) TGFβ neutralizing construct with a functional PD-L1 antibody (BA). Additionally, since our previous data suggests that BA responsiveness depends on CD8 T cell activity, we included two extra groups 5) CD8 depleting antibody alone or 6) in combination with BA. Three days after completing treatment, MOC-1 tumor cells were injected into the contralateral flank and engraftment and progression of secondary challenge tumors was analyzed. Primary tumor progression was significantly inhibited by BA and to a lesser extent avelumab compared to control or BA-M. Engraftment or progression of secondary challenge tumors was significantly inhibited by BA and to a lesser extent avelumab compared to control or BA-M. The growth inhibitory effects of BA were abrogated by CD8 depletion in both the primary and challenge tumors. Flow cytometry analysis of tissue collected on day 7 post-tumor challenge showed that BA-mediated clearance of the tumors was associated with a proportional increase of CD4+ and CD8+ TILs. We also observed that the frequency of CD103 expression among CD4+ TILs was reduced both in the primary and challenge tumors. Although TGFβ neutralization alone fails to induce anti-tumor immunity, the addition of TGFβ neutralization to PD-L1 blockade provides greater control of primary tumor growth and protection from engraftment of a challenge tumor compared to PD-L1 blockade alone. Through adoptive transfer of tumor-specific T cell receptor-engineered T cells, ongoing experiments aim to determine if TGFβ-driven CD103 expression is required for T cell tumor residency and if neutralization of TGFβ in the setting of PD-L1 immune checkpoint blockade allows for recirculation of tumor-specific T cells into the periphery.
Citation Format: Magdalena Rainey, Marco Craveiro, Yvette Robbins, Cem Sievers, Clint T. Allen. Combined TGFβ/PD-L1 blockade enhances systemic antitumor immunity in head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6422.