Progenitor-to-intermediate differentiation of exhausted CD8+T cells is enhanced by HPK1 inhibition during anti-PD-1 therapy

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 (T PEX cells) to differentiate and acquire phenotypic and functional features of intermediate exhausted CD8 + T cells (T IEX cells). In a mouse tumor model, HPK1 inhibition enhances T PEX cell expansion in tumor-draining lymph nodes and migration to tumors during PD-1 blockade. Moreover, HPK1 inhibition promotes lymph node T PEX cells' differentiation into tumor T IEX 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.