Roles of heat shock proteins in tumor immune microenvironment

Heat shock proteins (HSPs) are the most abundant molecular chaperones in cells, categorized based on function and molecular weight into HSP families, namely, HSP40, HSP70, HSP90, HSP110, and HSPB (heat shock protein B), et al. HSPs are involved in protein homeostasis by assisting in the correct folding of proteins or incorrectly folded proteins, refolding partially denatured proteins, and degrading damaged proteins. High levels of HSPs have been shown to participate in oncogenesis, progression, and chemotherapy resistance in many cancers. Recently a new range of functions besides chaperons, mostly in modulation of immune responses, have been shown for these extracellular HSPs. Here, we review the interactions between the HSPs and different immune cells, such as T lymphocytes, B cells, dendritic cells, macrophages, NK cells, and myeloid suppressor cells in the tumor microenvironment, as well as tumor vasculature and angiogenesis in tumor formation. The underlying mechanisms of HSPs’ regulation on immune response in tumor microenvironments are also discussed. The understanding of new functions of HSPs in tumor microenvironment may provide critical insights for the development of effective immunotherapies.