Fab fragments from the monoclonal antibody ML30 bind to treated human myeloid leukemia cells

Traditionally, heat-shock proteins were believed to be located intracellularly; however, recent studies have demonstrated that under certain circumstances these proteins can be located at the cell surface. Murine ascites developed from the anti-mycobacterial hsp65 hybridoma ML30 have been shown to contain an antibody that binds to the surface of a range of stimulated myelomonocytic cell lines; however, as the purified ML30 monoclonal antibody produced in vitro did not bind to these cell lines, the results were not considered conclusive evidence of cell-surface expression of the hsp60 homologue of the mycobacterial hsp 65 on human cells. In an effort to clarify this situation, we have confirmed that the ascites derived from the ML30 hybridoma bound to the surface of human myeloid leukemia cell lines and myeloid blast cells purified from freshly diagnosed leukemic patients, but that the in vitro-derived ML30 antibody did not. In addition, we have isolated Fab fragments from the ascites derived from the ML30 hybridoma and demonstrated that these fragments bound to the surface of human myeloid leukemia cells after their treatment with the glutamine analog 6-diazo-5-oxo-L-norleucine (DON) for various times up to four days. Evidence has been presented in the literature that the ML30 monoclonal antibody recognizes a molecule corresponding to the human hsp60 homologue of the mycobacterial hsp65; therefore our results from the binding of Fab fragment preparations from ascites imply that when human myeloid leukemic cells are treated with DON, they express a human hsp60 homologue on their surface.