Abstract Cancer treatment has been transformed by immunotherapies that enhance anti-tumor T-cell responses. Here we demonstrate that highly selective inhibition of the intracellular immune checkpoint HPK1 improves the efficacy of anti-PD-1/PD-L1 blockade. Single-cell profiling of ex vivo antigen-stimulated T cells reveals that HPK1 inhibition expands tumor-specific clones that substantially overlap with those responsive to PD-1 blockade. HPK1 inhibition induces progenitor exhausted CD8+ T cells (TPEX cells) to differentiate and acquire phenotypic and functional features of intermediate exhausted CD8+ T cells (TIEX cells). In a mouse tumor model, HPK1 inhibition enhances TPEX cell expansion in tumor-draining lymph nodes and migration to tumors during PD-1 blockade. Moreover, HPK1 inhibition promotes lymph node TPEX cells’ differentiation into tumor TIEX cells during PD-1 blockade, highlighting an underappreciated immunotherapy mechanism. Our findings reveal that HPK1 inhibition induces progenitor-to-intermediate differentiation of exhausted CD8+ T cells, enhancing the efficacy of anti-PD-1/PD-L1 blockade. Citation Format: Yong Joon Lee, Seung Hyuck Jeon, Seungmook Lim, Minwoo Jeon, Heejin Nam, A Yeong Park, Boeun Gu, Jee Ye Kim, Seung Il Kim, Jeon Yeob Jang, Chul-Ho Kim, Shin Hwang, Gi-Won Song, Jae-Ho Cheong, Byung Soh Min, Su-Hyung Park, Seong Il Seo, Jinhwa Lee, Minyong Kang, Jae Eun Kim, Eui-Cheol Shin. Progenitor-to-intermediate differentiation of exhausted CD8+T cells is enhanced by HPK1 inhibition during anti-PD-1 therapy abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86 (8Suppl): Abstract nr LB149.
Lee et al. (Fri,) studied this question.