The development of J-5, a monoclonal antibody specific for a leukemia-associated antigen (CALLA), has allowed us to study the in vitro response of human tumor cells to specific antibody. Our results demonstrate that J-5 antibody induces antigenic modulation of CALLA+ leukemic cells and cell lines. Antigenic modulation, in this context, is shown to be a specific loss of J-5 antibody and common ALL antigen (CALLA) from the surface membranes of these cells as determined by indirect immunofluorescence assay. This phenomenon is temperature dependent, occurs rapidly in response to addition of J-5 antibody to cell culture media at 37°C, and results in development of resistance to lysis with rabbit complement. In addition, a dose response relationship exists between the amount of J-5 antibody added to culture supernatants and the extent of CALLA modulation. The CALLA-modulated phenotype can be maintained for prolonged periods in vitro by continued addition of J-5 antibody to culture supernatants but re-expression of CALLA occurs rapidly after transfer of modulated cells to antibody free media. Antigenic modulation in response to J-5 antibody represents a specific loss of CALLA without concomitant loss of other cell surface antigens such as Ia or β2 microglobulin. In addition, Ia antigen and β2 microglobulin do not undergo modulation in response to specific monoclonal antibody under these conditions. This suggests that antigenic modulation may be a unique property of specific cell surface proteins and that this may represent a mechanism whereby human leukemic cells can escape antibody-mediated lysis.
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Ritz et al. (1980) studied this question.