CD4 and neoplasm: The high affinity of peptides 17.1 and 17.1B to Hsp70 allows them to form stable complexes (17.1-Hsp70 and 17.1B-Hsp70) on the surface of Hsp70+ tumor cells and prevent CD4 + CD25 + lymphocytes from interacting with these cells, blocking the cytotoxic activity of these lymphocytes.