The immunogenic heat shock proteins (HSPs) gp96, hsp70 and calreticulin (CRT) bind to CD91 on antigen-presenting cells (APCs) for cross-presentation of the HSP-chaperoned peptides. This event leads to priming of T-cell responses. Here we show that CD91 serves as a signalling receptor for these HSPs, allowing for the maturation of APCs, secretion of cytokines and priming of T-helper (Th) cells. Specifically, CD91 is phosphorylated in response to HSPs in a unique pattern and phospho-CD91 triggers signalling cascades to activate nuclear factor-kappa B. Each HSP-CD91 interaction on APCs stimulates a unique cytokine profile, which dictates priming of specific Th cell subsets. Thus, in a transforming growth factor-β tumour microenvironment, immunization with CRT, but not gp96 or hsp70, primes Th17-cell responses in a CD91-dependent manner. These results are important for development of T-cell responses in situ in tumour-bearing hosts and for vaccination against cancer and infectious disease.