Heat Shock Protein 72 on Tumor Cells: A Recognition Structure for Natural Killer Cells

Evidence is accumulating that members of the heat shock protein 70 (HSP70) family are found on the cell surface of certain tumor cells where they elicit a strong antitumor immune response. We demonstrated that HSP72, the major heat-inducible form of the HSP70 group, is located on the cell surface of <60% of the human colon carcinoma cells CX2 with two different mAbs by indirect immunofluorescence, by electron microscopy, and by selective cell surface biotinylation. In an effort to analyze the role of HSP72 cell surface expression as a tumor-specific recognition structure within an "autologous" tumor system, the CX2 cells were separated into a stably HSP72 high expressing (CX+: >90%) and a stably HSP72 low expressing (CX-: <20%) subline. The expression "autologous" was written in parentheses to indicate that the colon carcinoma sublines CX+ and CX-derived from the original CX2 tumor cell line differ with respect to the cell surface expression pattern of HSP72, whereas they exhibit an identical cell surface expression pattern of MHC and cellular adhesion molecules (e.g., intercellular cellular adhesion molecule, neural cellular adhesion molecule, vascular cellular adhesion molecule). Within this "autologous" tumor cell system, we demonstrate that the sensitivity to lysis mediated by adherent non-MHC-restricted effector cells correlates (p < 0.05) with the amount of HSP72 that is expressed on the cell surface. Blocking studies using an HSP72-specific mAb revealed that HSP72 might act in an MHC-unrestricted manner as a tumor-specific recognition structure for a distinct NK cell population.