HSP90 inhibition drives GRP78 relocalization to potentiate CAR-based immunotherapy during tumor evolution

Tumor evolution under therapeutic pressure promotes drug resistance through adaptive proteostasis buffering. HSP90 is a key molecular chaperone that stabilizes mutated proteins and supports tumor adaptation. Whether disrupting this stress-buffering system can improve immunotherapy remains unclear. Using evolving tumor models of multikinase inhibitor-resistant (MKIR) hepatocellular carcinoma (HCC) and patient samples, we demonstrate that low-dose HSP90 inhibition precisely induces relocalization of GRP78 from the endoplasmic reticulum to the tumor cell surface via DnaJ heat shock protein family (Hsp40) member C1 (DNAJC1)-dependent trafficking. This stress-induced tumor antigen (SITA) converts GRP78 into a therapeutically targetable surface antigen and enhances susceptibility to GRP78-directed CAR-NK cells. In xenograft and syngeneic tumor models, proteostasis perturbation of the HSP90-GRP78 axis enhances CAR-NK and CAR-T activity and promotes NK cell and macrophage infiltration within GRP78-high tumor niches. Collectively, these findings uncover a previously unrecognized concept of a SITA, whereby adaptive proteostasis buffering in evolving tumors can be rewired to enable precise CAR-directed immunotherapy against solid tumors.