Abstract 6708: Neoadjuvant pembrolizumab with therapeutic DNA vaccine reshape intratumoral immunity in a phase 2 trial of HPV-positive HNSCC

Abstract Therapeutic cancer vaccines are a promising strategy for inducing antigen-specific T-cell immunity, but their efficacy in solid tumors remains limited by inadequate magnitude, persistence, and functional quality of vaccine-elicited responses. These challenges have intensified efforts to identify adjuvants that can strengthen durable antitumor immunity. Interleukin-7 (IL-7), a cytokine essential for T-cell survival and memory formation, provides a mechanistically grounded strategy for enhancing vaccine responses. To evaluate this in a defined viral antigen setting, HPV-associated head and neck squamous cell carcinoma offers an ideal tumor model for dissecting vaccine immunity and adjuvant mechanisms. We first tested long-acting IL-7 in an HPV16 E6/E7-expressing TC-1 model. IL-7 improved the efficacy of HPV DNA vaccination with PD-1 blockade, producing superior tumor control and enhancing stem-like and memory-associated transcriptional programs within intratumoral CD8+ T cells—features consistent with strengthened long-term responsiveness. Guided by these results, we conducted a phase 2 neoadjuvant trial combining pembrolizumab, HPV DNA vaccine (GX-188E), and long-acting IL-7 (GX-I7) in patients with resectable HPV-positive HNSCC. Major pathologic responses occurred in 63.6% of patients, including 36.4% complete responses. Paired single-cell RNA/TCR sequencing and spatial AI analysis revealed coordinated reshaping of the intratumoral immune landscape. A GZMK+ effector-memory CD8+ population expanded prominently, displaying early memory priming, lymph node-to-tumor recirculation potential, and enrichment of tumor-reactive programs. Increased tertiary lymphoid structures correlated with reduced exhaustion among tumor-reactive CD8+ T cells and appeared to facilitate entry and renewal of GZMK+ CD8+ T cells within tumors. Higher GZMK+ CD8+ abundance corresponded with greater TCR diversity among tumor-reactive clones, indicating sustained replenishment of antitumor specificities. To reconfirm upstream regulatory pathways, foundation-model-based in silico perturbations showed that knockout of IL7R or STAT5 markedly diminished GZMK-directed differentiation, supporting an IL-7-dependent mechanism underlying this effector-memory programming. Analyses of independent HPV-positive HNSCC cohorts aligned with these observations, showing that tumors enriched for GZMK-programmed CD8+ states exhibit stronger antitumor immunity and improved long-term outcomes. Taken together, these comprehensive preclinical, clinical, and exploratory analyses reveal that IL-7 amplifies a GZMK+ effector-memory CD8+ T-cell program driving sustained recirculation, diversification, and renewal of tumor-reactive CD8+ T cells, highlighting a mechanistic axis with potential to enhance the durability of cancer vaccine responses. Citation Format: Hye Ryun Kim, June-Young Koh, Chang Gon Kim, Min Hee Hong, Hyun Jun Hong, Dahee Kim, Nam Suk Sim, Sun Och Yoon, Gamin Kim, Wonrak Son, Yeju Kim, Chang Geol Lee, Kyung Hwan Kim, Jeong Seok Lee, Chan-Young Ock, Yoon Woo Koh. Neoadjuvant pembrolizumab with therapeutic DNA vaccine reshape intratumoral immunity in a phase 2 trial of HPV-positive HNSCC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6708.