Introduction: Loss of immune surveillance is required for cancer cell growth and metastasis; tumors co-opt suppressive mechanisms to evade detection by the immune system. The immune system is equipped with multiple feedback mechanisms to limit inflammation to prevent autoimmunity; tumors activate these pathways to escape immunity. HPK1 (hematopoietic progenitor kinase 1) is a negative regulator of T-cell activation; the kinase activity limits T-cell signaling and tumoricidal cytokine production. Recent literature has shown that inactivation of the kinase function of HPK1 prevents tumor progression in murine tumor models (1).

Experimental Procedures: We used lentiviral delivered shRNAs and CRISPR/Cas9 technology to delete HPK1 in Jurkat cells and primary human T cells, respectively. Jurkat T cells (wt/KO) were activated with anti-CD3 antibody and cell lysates were assessed by Western blot to examine signaling events downstream of the T-cell receptor (TCR). Primary human T cells or CRISPR/Cas9 KO T cells were activated in vitro using anti-CD3/anti-CD28 antibodies in the presence or absence of prostaglandin E2 (PGE2). Cytokines were quantified by ELISA.

Results: We present novel findings demonstrating that the role of HPK1 is conserved in human Jurkat cells as well as in primary human T cells. Loss of HPK1 enhanced T-cell receptor signaling in Jurkat cells. In CRISPR/Cas9 KO HPK1 primary human T cells, TCR activation resulted in enhanced cytokine secretion and proliferation concomitant to a decrease in pSLP76, the target molecule phosphorylated by HPK1. In addition, HPK1 KO cells were rescued from PGE2-mediated suppression. A screening and assessment of HPK-1 inhibitor compounds that enhance T-cell function is ongoing.

Conclusions: In summary, HPK1 function is conserved in human T cells and inhibitors of HPK1 could enhance antitumor immunity through increased T-cell function, overcoming suppressive signals in the tumor microenvironment and broadening the response to check point inhibitors for cancer immunotherapy.


1. Hernandez S, Qing J et al. The kinase activity of hematopoietic progenitor kinase 1 is essential for the regulation of T cell function. Cell Rep 2018;25:80-94.

Citation Format: Neil Grimster, Lisa Drew, Stephen Fawell, Deanna A Mele, Gayathri Bommakanti, Minhui Shen, Kevin Xu, Kun Song, Rob Ziegler, Jason Kettle, Adelphe Mfuh, Jason Sheilds. Releasing the brake on T-cell activation through inhibition of HPK1 [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A56.