Peripheral blood mononuclear cells express antigens associated with multidrug resistance in a small cell lung cancer cell line.

H69AR is a multidrug resistant small cell lung cancer (SCLC) cell line that does not overexpress P-glycoprotein, the plasma membrane drug efflux pump usually associated with this type of resistance. Monoclonal antibodies (MAbs) were previously raised against H69AR cells, and three of these MAbs, 2.54, 3.50, and 3.186, cross-reacted with peripheral blood mononuclear cells. T cells (CD3+), B cells (CD19+), NK cells (CD16+) and monocytes (CD14+) expressed each of the three antigens, but to differing degrees. Immunoprecipitation and partial proteolytic mapping experiments demonstrated that the antigens detected by MAbs 2.54 and 3.186 are identical in H69AR cells and PBMCs. SCLC cells are known to express many hematopoietic antigens; however, this is the first report of SCLC multidrug resistance-associated antigens being expressed on hematopoietic cells.