COMPARISON OF 2 ANTIBODY-BASED METHODS FOR ELIMINATION OF BREAST-CANCER CELLS FROM HUMAN BONE-MARROW

Three monoclonal antibodies reactive with antigens abundantly expresse d on human carcinoma cells were used to develop and compare the effica cy of immunotoxins (ITs) and immunobeads for purging breast cancer cel ls from bone marrow. ITs constructed as conjugates of the monoclonal a ntibodies and Pseudomonas exotoxin A showed high specific cytotoxicity against three breast cancer cell lines, inhibiting protein synthesis by 50% at concentrations of 4 x 10(-13) M to 1 x 10(-10) M. Tested in a reproducible clonogenic assay, two of the ITs used at a concentratio n of 0.1 mug/ml killed >5 log units of MCF7 cells, the maximal sensiti vity for assessing cytotoxic effects, and 1.5 log of T-47D tumor cells . At 1 mug/ml, each of the three ITs eliminated >5 log of both cell li nes. The immunobead procedure removed 2.0-4.1 log of tumor cells with one purging cycle and up to 6.0 log with two cycles. The mixture of th e three ITs or immunobeads was not clearly superior in efficacy, compa red to the use of individual molecules, probably reflecting an overlap in expression of the respective antigens in these cell lines. For bot h methods, the purging efficacy was not reduced when the tumor cells w ere admixed with normal bone marrow cells at a ratio of 1:10. The surv ival of colony-forming units, granulocyte/macrophage, was 49-86% with the immunobeads and 44-75% even at high concentrations (up to 2.5 mug/ ml x 3) of the ITs. The results indicate that each of the two immunolo gical methods can be safely used for effective elimination of tumor ce lls from the graft of breast cancer patients undergoing autologous bon e marrow transplantation.