Abstract 4210: Stromal remodeling danger signals regulate “second-touch” antigenic encounters and promote CD8+ T cell effector differentiation in the TME
Authors: Papadas Athanasios , Hong Duncan , Cicala Alexander , Gibbons Alicia , Lagal Daniel J. , Huang Yun , Dou Yaling , Asimakopoulos Fotis 
Published: March 2024

Abstract
Tumor immune infiltration (“hot” tumor microenvironment, TME) constitutes a powerful predictor of outcomes and immunotherapy efficacy, however underlying mechanisms remain elusive. Recent evidence shows that TME-repriming of incoming CD8+ T cells is required for full effector functionality. Reminiscent of the “second-touch” hypothesis proposed by Klaus Ley for CD4+ differentiation, tumor-draining lymph node (TDLN) priming (“first-touch”) generates antigen-specific stem-like TCF1+CD8+ T cells. These stem-like CD8+ T cells then migrate to the tumor periphery where “second-touch” antigenic encounters with non-migratory CCR7neg dendritic cells (DC) (importantly, the cross-presenting cDC1 subset) leads to effector CD8+ T cell differentiation and tumor entry. These second-touch encounters occur within specialized stromal niches that are rich in antigen-presenting cells (APC). We have hypothesized that productive APC:CD8+ interactions require stroma-derived signals that emulate provisional matrix remodeling in embryonic development and/or adult wound healing. Thus, stroma remodeling by the expanding tumor translates into a conserved “danger signal” that licenses APC to activate CD8+ T cell responses. We have focused on a prototypical pathway of provisional matrix remodeling, the regulated proteolysis of the matrix proteoglycan versican (VCAN) to generate a bioactive fragment endowed with immunostimulatory activities, versikine. Stromal VCAN proteolysis at the site releasing versikine is associated with T-cell infiltration across human solid and liquid tumors. To investigate the mechanisms by which versikine regulates first- and second-touch antigenic encounters, we dissected the immune microenvironment of versikine-replete tumors of immunocompetent models at single-cell resolution. Non-migratory Ccr7neg cDC1 in versikine-replete tumors overexpress MHC-I and MHC-II antigen presentation machinery (Tap1, Ciita), maturation (Irf7, ISGs, Tlr3) and co-stimulation markers (Cd86, 4-1BBL), while Ccr7pos DC (mregDC) markedly overexpress Cd40 compared to control mregDC. In parallel, Cd4+ Tfh-like cells (overexpressing Cd40lg, Icos and Maf) accumulate in versikine-replete tumors, mirroring the accumulation of CD4+ T-cells in the stroma of human tumors displaying intense VCAN proteolysis. Consequently, versikine-replete tumors demonstrate expansion of late effector CD8+ T cells (Gzmb+Prf1+). Versikine reverses anti-PD-1 refractoriness in the “cold” model, Lewis Lung Carcinoma (LLC). In “warm” tumor models, versikine with anti-PD-L1 suffices to eradicate tumors and establish immune memory with resistance to tumor rechallenge. Our presentation will focus on the mechanistic dissection of stromal signals regulating antigen presentation across models as well as approaches for translation into novel vaccine platforms.
Citation Format: Athanasios Papadas, Duncan Hong, Alexander Cicala, Alicia Gibbons, Daniel J. Lagal, Yun Huang, Yaling Dou, Fotis Asimakopoulos. Stromal remodeling danger signals regulate “second-touch” antigenic encounters and promote CD8+ T cell effector differentiation in the TME [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4210.