Inhibition of human B‐cell chronic lymphocytic leukemia by a monoclonal antibody in xenograft models

To establish xenograft models of human B‐cell chronic lymphocytic leukemia (CLL), we inoculated S × 106 D10‐1 cells, a subline of Epstein‐Barr virus (EBV)‐transformed human B‐cell CLL with a marker chromosomal anomaly, into SCID or irradiated nude mice by the intravenous (i.v.) or intraperitoneal (i.p.) route. All i.p. tumor‐inoculated mice developed rapidly progressive, lethal ascites tumor, and 100% of i.v. tumor‐inoculated mice developed disseminated CLL. All mice died of tumor within 8 weeks of tumor inoculation. Tumor‐inoculated SCID mice died earlier with wider tumor dissemination than the tumor‐inoculated nude mice. All the tumor‐inoculated mice had histologically confirmed metastases in lymph nodes, and most of them also had metastases in one or more internal organs. Cytogenetic analysis confirmed the origin of these tumors from the xenografted D10‐1 cells. The D10‐1 cells harvested from the xenografts did not differ from the parent D10‐1 cells as regards (i) reactivity with 2 monoclonal antibodies (MAbs) directed against CLL‐associated cell‐surface antigens; (ii) rate of proliferation in vitro; and (Hi) sensitivity to the 2 chemotherapeutic agents, methotrexate and adriamycin. Administration of 50 μg/mouse of Dal B02, an IgG1 (K) MAb directed against surface‐associated antigens of human B‐cell CLL, significantly prolonged the survival of D10‐1‐inoculated nude and SCID mice. The MAb was more effective in D10‐1‐inoculated nude mice than in SCID mice. In all the D10‐1 xenograft models, the effectiveness of Dal B02 decreased with higher tumor load but increased with the amount of MAb injected. Dal B02 F(ab)'2 fragment failed to demonstrate any anti‐tumor activity in D10‐1‐inoculated nude mice. In vttro assays revealed that Dal B02 had no direct inhibitory effect on D10‐1 cells, but could be cytotoxic towards D10‐1 cells in the presence of splenic cells or peritoneal macrophages from nude and SCID mice, or together with rabbit complement.