Abstract B084: Tracking tumor-specific CD4 T cells in pancreatic cancer reveals an essential role for cognate interactions with myeloid cells in remodeling the tumor microenvironment following immunotherapy

Abstract

Our study identified an antigen (Ag)-specific CD4 T cell population in a preclinical orthotopic model of pancreatic ductal adenocarcinoma (PDA) that, upon expansion, elicited robust antitumor control. We developed an affinity-enhanced MHC-II tetramer to follow the endogenous tumor-specific CD4 T cells during pancreatic tumor growth. We show Ag-specific TH1 cells decreased in number over time, with the few remaining cells acquiring features of chronic antigen stimulation within the tumor microenvironment (TME). In contrast, Ag-specific CD4 T cells exhibited a T follicular helper state in tumor draining lymph nodes. Agonistic anti-CD40 transiently reduced antigen-specific TREG cells but led to a dramatic rebound of intratumoral TREG cells at later timepoints which was dependent on PD-1:PD-L1 signaling. Single cell sequencing of CD4 T cells in immunotherapy-responsive and poorly responsive models showed intratumoral CD4 T cell clonal expansion distinguishes responsive tumors. Combination of CD40 agonist with anti-PD-L1 further increased TH1 cell number, destabilized TREG cells, and organized CD4 T cells within tertiary lymphoid structures (TLS) and immune cell triads (CD4:CD8:CD11c). This dramatic TME remodeling in response to immunotherapy required antigen presentation by Ccr2+ myeloid cells during the effector phase and was independent of B cells. Transcriptional analyses of the myeloid compartment revealed αCD40 and αPD-L1 drove an intratumoral Stat1+ myeloid cell population while decreasing regulatory dendritic cells. NicheNet analysis supports CD4 T cell-generated inflammatory cytokines are responsible for driving myeloid cell reprogramming. In a head and neck cancer immunotherapy clinical trial, TH1 potentiation and TREG destabilization were shared features that correlated with clinical responses. Finally, despite Ag-specific TH1 and TREG cells both expressing abundant CD122 (IL-2Rb), addition of IL-15 complex, which improves overall immunotherapy efficacy, selectively expanded Ag-specific TH1 cells but not TREG cells. Together, our findings demonstrate that cooperation between Ag-specific CD4 T cell and myeloid cell result in TME remodeling and immunotherapy response in PDA. Strategies to promote tumor Ag-specific CD4 T cells toward a durable TH1 fate while mitigating Ag-specific TREG cell rebound may improve immunotherapy outcomes.