A 14-mer Hsp70 peptide stimulates natural killer (NK) cell activity

Compared with normal cells, tumor cell lines exhibit an unusual plasma memb rane localization of heat shock protein 70 (Hsp70). This tumor-selective Hs p70 membrane expression has been found to correlate with an increased sensi tivity to lysis mediated by human natural killer (NK) cells that transientl y adhere to plastic following cytokine stimulation. A human Hsp70-specific monoclonal antibody (mAb) detects membrane-bound Hsp70 on viable tumor cell s and blocks the immune response of NK cells against Hsp70-expressing tumor cells. By peptide scanning (pep-scan) analysis, the epitope of this mAb wa s mapped as the C-terminal-localized 8-mer NLLGRFEL (NLL, amino acids [aa] 454-461). Most interestingly, similar to full-length Hsp70 protein, the N-t erminal-extended 14-mer peptide TKDNNLLGRFELSG (TKD, aa 450-463) was able t o stimulate the cytolytic and proliferative activity of NK cells at concent rations equivalent to full-length Hsp70 protein. Blocking studies revealed that an excess of the 14-mer peptide TKDNNLLGRFELSG inhibits the cytolytic activity of NK cells similar to that of Hsp70 protein. In comparison, other TKD-related peptides, including the 8-mer antibody epitope NLLGRFEL (aa 45 4-461), the 12-mer TKDNNLLGRFEL (aa 450-461), the 13-mer C-terminal-extende d peptide NLLGRFELSGIPP (aa 454-466), the 14-mer TKD-equivalent sequences o f Hsp70hom TKDNNLLGRFELTG (aa 450-463), Hsc70 TKDNNLLGKFELTG (aa 450-463), and DnaK AADNKSLGQFNLDG (aa 447-460) failed to activate NK activity.