Hyperthermia-induced changes in antigen expression on human FME melanoma cells

Quantitative changes in the expression of three melanoma-associated antigens on human FME cells were studied by means of flow cytometry as a function of time after exposure to hyperthermia (42 degrees C for 1, 2, and 3 h; 43.5 degrees C for 1 and 2 h; 45 degrees C for 20 min). The expression of the three different surface antigens p250, p210, and p97a recognized by the monoclonal antibodies 9.2.27, 5.1, and 4.1, respectively, underwent qualitatively similar changes after hyperthermia. The antigen expression was reduced immediately after end of the treatment and decreased further to reach a minimum 1 day after treatment. Then the antigen expression gradually increased and reached a maximum above the level for unheated cells before it returned to this level about 1 wk after hyperthermia. The magnitude of these effects increased with increasing temperature and with increasing heating time at a given temperature. Quantitatively there were individual variations for the three different antigens. A positive correlation was found between the surviving fraction of the cells and the minimum level of antigen expression, indicating that different heat treatments which inactivated the same number of cells induced the same reduction in antigen expression. The demonstrated therapy-induced changes in antigen expression may be of importance for the use of monoclonal antibodies in diagnostic imaging of tumor tissue after hyperthermia or as therapeutic agents in combination treatments involving hyperthermia.