In vitro tumoricidal activity of immunoadsorbed leukemic serum

We studied the ability of untreated or immunoadsorbed acute myelogenous leukemia (AML) sera to kill AML blasts. Culture of blasts with sera adsorbed to protein A-bearing Staphylococcus aureus Cowan I (SAC), resulted in a marked loss of blast viability (42.7% of control). Immunoadsorption against non-protein A-bearing Wood 46 strain of S. aureus did not induce serum cytotoxic activity (94.8% viable cells). Sera adsorbed to Sepharose-bound protein A also killed blasts in vitro (64.3% viable cells). The addition of untreated sera to SAC-treated cultures partly abrogated the effect, suggesting a blocking substance in untreated serum. Cytotoxicity was not complement-dependent nor did it appear to be cell mediated. It was, however, eliminated by trypsin treatment of SAC-treated sera. These studies suggest that SAC-treated AML serum contains a protein that is cytotoxic to AML blasts, and that this protein is partly inactivated by untreated AML serum, possibly through interaction with immunoglobulins. The mechanism described here may be one of several mechanisms leading to tumor necrosis in tumor-bearing hosts treated with SAC-immunoadsorbed plasma.