Abstract 5296: Enhancing the strength and durability of vaccine-induced anti-tumor immunity with CD27 agonism of CD4+ T cells

Abstract Despite encouraging early phase clinical trials, decades of research have yet to yield effective cancer vaccine immunotherapies. To determine potential markers for success, we performed a follow-up study of a HER2-pulsed dendritic cell cancer vaccine Phase I trial performed in advanced HER2+ cancer patients. Surprisingly, we found that all treated patients were alive at over 18 years post-treatment. These patients still possessed significant HER2-specific memory T cell responses, typified by CD27 expression. The expansion of HER2-specific CD27+ memory T cells was also observed in patients from a separate clinical trial, who received a HER2-expressing viral vaccine. To validate these clinical responses, we vaccinated human CD27 transgenic mice with a HER2 viral vector again observing HER2-specific CD27+ memory T cells, suggesting the significance of this axis in eliciting and maintaining effective vaccine-specific memory T cell responses. We hypothesized that CD27 expression was not just a marker of memory T cells, but represented a critical activation pathway during memory formation. To determine the potential impact of CD27 agonism in vaccination, we combined HER2 vaccination with an anti-CD27 agonist antibody (Varlilumab). The combination treatment elicited a robust increase in HER2-specific CD4+ memory T cell responses that was maintained for at least 300 days post-vaccination. Using therapeutic HER2 vaccination in combination with anti-CD27 of HER2+ tumor bearing mice, we show significantly increased anti-tumor efficacy and further enhancement in combination with PD1 inhibition. The anti-tumor response was triggered by anti-CD27 antibody during the vaccine priming phase, which enhanced HER2-specific CD4+ T cells. Critically, we found that HER2 specific CD4+ T cell responses allowed for anti-tumor responses that persisted after CD8+ T cell depletion, indicating a direct role for antigen-specific CD4+ T cells independent of CD8+ T cells. Collectively, our results support a central role for antigen-specific CD27+ CD4+ T cells in cancer vaccination. These data support the addition of CD27 agonism to improve the therapeutic index of cancer vaccines and potentially enhance responses to immune checkpoint blockade in refractory cancers. Citation Format: Bin-Jin Hwang, Erika Crosby, Timothy Trotter, Li-Chung Tsao, Tao Wang, Congxiao Liu, Xiao Yang, Gangjun Lei, Junping Wei, Xingru Ma, Bushanqing Liu, Amy Hobeika, Michael Morse, Tibor Keler, Li-Zhen He, Herbert Kim Lyerly, Zachary Hartman. Enhancing the strength and durability of vaccine-induced anti-tumor immunity with CD27 agonism of CD4+ T cells [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 5296.