Monoclonal antibody DLC‐48: An effective reagent for use in the depletion of malignant lymphoma from human bone marrow

A combination of large‐cell lymphoma cell lines was used as immunogen in the production of DLC‐48, a mouse monoclonal antibody (MAb) to a B‐cell‐associated antigen. This reagent identifies a protein found on a majority of peripheral blood B‐cells, B‐cell derived tumor cell lines, and lymphoma biopsy specimens. In reactive lymph‐node sections, DLC‐48 stains both germinal center and mantle zone B‐lymphocytes when the immunoperoxidase technique is used. DLC‐48 is an IgM, and is highly cytotoxic in the presence of human serum complement. The conditions for complement‐mediated cytotoxicity were first optimized by utilizing the chromium‐release assay with 2 large‐cell lymphoma cell lines, and were then applied to the treatment of the cell lines prior to cloning in agar. A single treatment with antibody and human serum eliminated 4 orders of magnitude of target cells. The cytolytic activity of this antibody was not inhibited by the presence of a 20‐fold excess of normal human bone marrow. Treatment with antibody and autologous serum did not affect the growth of human hematopoietic progenitor cells (CFU‐GEMM and CFU‐GM). These results suggest that DLC‐48, either alone or in combination with other MAb reagents, should be effective in eliminating malignant cells of B‐lineage from human bone marrow for purposes of autologous bone‐marrow transplantation.