Disruption of CD91 association with AXL and Fgr abrogates HSP-mediated signaling and cancer immunosurveillance.

CD91 serves as a receptor that causes the activation of antigen-presenting cells in response to cancer cells by binding HSPs. In this context, the HSP-CD91 axis is responsible for the rejection of emerging and nascent cancers. The role of CD91 in the cross-presentation of HSP-chaperoned peptides is well established, but its contribution to cell signaling and costimulation is less clear. We investigated CD91-mediated signaling with respect to cancer immunosurveillance by examining two key adaptor proteins, Fgr and AXL. To investigate the interactions between the β chain of CD91 and Fgr and AXL, AlphaFold was used to predict protein‒protein binding areas. Signaling was further investigated by examining NF-κB phosphorylation and cytokine production in iBMDMs with CRISPR-induced tyrosine mutations. Mice conditionally lacking Fgr and AXL in dendritic cells were assessed for their ability to control tumors in inducible and transplantable models of cancer. In silico or CRISPR-mediated disruption of key tyrosines within CD91 abrogates Fgr binding, NF-κB activation, and cytokine release. Using a DC-specific Fgr knockout mouse model, we revealed that loss of Fgr severely impaired tumor immunosurveillance, whereas AXL knockout resulted in a milder phenotype, suggesting a greater downstream role. Loss of Fgr also prevents the development of adaptive immunity to tumors following HSP immunization, but it has no impact on transplantable tumor growth. These findings elucidate key components of the CD91 signaling mechanism, advancing our understanding of how dying tumor cells initiate adaptive immune responses and providing a therapeutic target to enhance this pathway.