Selective depletion of human myeloma clonogenic stem cells from bone marrow cell preparations by a plasma-cell reactive antibody and complement

The monoclonal antibody MM4 reacts with human myeloma cells from plasma cell dyscrasia (PCD)-derived cell lines and bone marrow (BM) biopsies from PCD patients, but not with normal BM or peripheral blood mononuclear (PBM) cells. We examined cytotoxicity of MM4 and rabbit complement (MM4:C') on mixtures of normal BM mononuclear cells and myeloma cells from three different PCD-derived cell lines, RPMI 8226, GM 1312, or ARH-77. For cell preparations containing 10% myeloma cells, treatment with MM4 (500 micrograms per 10(5) cells, 4 degrees C, 60 min) and two cycles of complement (1:8, 23 degrees C, 2 x 30 min) consistently eliminated 2 logs or more of clonogenic myeloma stem cells, as determined by colony growth assays and limiting dilution analysis (99.4%, 98.9%, and 99.96% reduction of RPMI 8226, GM 1312, and ARH-77 cells, respectively). The majority of normal marrow progenitors were spared (inhibition of CFU-C: 10-13%; BFU-E: 0%). These observations suggest that MM4 may be useful for selective depletion of human myeloma clonogenic stem cells from bone marrow ex vivo.