Expression of extracellular Hsp90 is a molecular signature of T cell activation, providing a means to image and target T Cell activation in autoimmune disease

Heat shock protein 90 (Hsp90) maintains cellular proteostasis during stress and has been under investigation as a therapeutic target in cancer for over two decades. We and others have identified an extracellularly expressed form of Hsp90, eHsp90, that previously appeared to be restricted to rapidly proliferating cells exhibiting a metastatic phenotype. Here, we used HS-131, a fluor-tethered eHsp90 inhibitor, to quantify the effect of T cell activation on the expression of eHsp90 in human and mouse T cells. In cell based assays, stimulation of human T cells induced a 20-fold increase in eHsp90 expression at the plasma membrane, suggesting trafficking of eHsp90 is acutely regulated by TCR and inflammatory mediated signaling. Following injection of HS-131 in mouse models of human rheumatoid arthritis and inflammatory bowel disease, we detected localization of the probe at sites of active disease, consistent with immune cell invasion. Moreover, despite rapid hepatobiliary clearance, HS-131 demonstrated efficacy in delaying the onset and progression of disease in the arthritis model. Our results suggest eHsp90 expression at the plasma membrane of T cells is a molecular marker of autoimmune induced activation and potentially a therapeutic target for chronic diseases such as rheumatoid arthritis and inflammatory bowel disease. Perspective T cells mediate many maladaptive disease pathologies such as autoimmune disorders. Many immunosuppressants in clinical use act by preventing the activation of T cells. However, this approach can lead to increased rates of opportunistic infection and malignancy. Here, we show for the first time that eHsp90 is upregulated during T cell activation in response to exogenous ligands. Therefore, pharmacological inhibition of eHsp90 may provide a means to target only activated T cells for immunosuppression. Selective targeting of only activated T cells could be efficacious against autoimmune disease without increasing the incidence of undesirable outcomes. Additionally, the presence of eHsp90 on the surface of activated T cells could be diagnostically useful to track the status and progression of autoimmune disease in patients. ### Competing Interest Statement The authors have declared no competing interest.