ANALYSIS OF CELLULAR SENTINELS FOR EXTRACELLULAR HEAT SHOCK PROTEIN-PEPTIDE COMPLEXES

Since the discovery of gp96 in the 1980’s as a “tumor rejection antigen,” Heat Shock Proteins (HSPs) have received attention from immunologists for their ability to prime immune responses. Originally known for their important intracellular roles as chaperones to newly synthesized, misfolded, and/or recently degraded proteins, it is now understood that HSPs released into the extracellular environment can also initiate immune responses. Shown both in vitro and in vivo, HSPs act on antigen presenting cells (APC) to 1) deliver antigenic peptides for presentation by both MHC class I and class II molecules and 2) activate APC to increase expression of co-stimulatory molecules. Both of these activities contribute to productive T cell responses, which has led to current trials using HSP-peptide complexes as cancer vaccines. However, the cell populations responsible for monitoring exogenous HSPs and priming resulting immune responses have yet to be fully characterized. This study identifies the cells that incorporate HSPs in vivo, following either vaccination or release by tumors, and analyzes the immune response generated by these cells. A CD11c+CD11b+CD4+ dendritic cell population selectively takes up HSPs, coincident with higher expression of the HSP receptor CD91 on these cells. We also show the dependence on CD91 of HSP-mediated immune responses. Increased knowledge of the process by which HSPs shape immune responses will contribute to the understanding of HSP-mediated immunity as well as assist in optimizing current tumor-vaccine strategies