A novel Raji-Burkitt's lymphoma model for preclinical and mechanistic evaluation of CD52-targeted immunotherapeutic agents.

PURPOSE To date, efforts to study CD52-targeted therapies, such as alemtuzumab, have been limited due to the lack of stable CD52 expressing transformed B-cell lines and animal models. We describe generation and utilization of cell lines that stably express CD52 both in vitro and in vivo. EXPERIMENTAL DESIGN By limiting dilution, we have established several clones of Raji-Burkitt's lymphoma cell line that express surface CD52. Immunophenotype and cytogenetic characterization of these clones was done. In vivo usefulness of the CD52(high) cell line to evaluate the therapeutic efficacy of CD52-directed antibody was investigated using a SCID mouse xenograft model. RESULTS Stable expression of CD52 was confirmed in cells cultured in vitro up to 52 weeks of continuous growth. The functional integrity of the expressed CD52 molecule was shown using alemtuzumab, which induced cytotoxic effects in vitro in the CD52(high) but not the CD52(low) clone. Compared with control antibody, alemtuzumab treatment in CD52(high) inoculated mice resulted in significantly increased median survival. Comparable levels of CD52-targeted direct cytotoxicity, complement-dependent cytotoxicity, and antibody-dependent cytotoxicity and anti-CD52 immunoliposome-mediated delivery of synthetic oligodeoxyribo nucleotides in CD52(high) clone and primary B-chronic lymphocytic leukemia cells implicated potential in vivo application of this model for evaluation of CD52-targeted antibody and immunoliposomes encapsulating therapeutic agents. CONCLUSIONS These results show the in vitro utility of the cloned Raji cell lines that stably express high levels CD52. The disseminated leukemia-lymphoma mouse model described herein using these stable cell lines can serve as an excellent system for in vivo therapeutic and mechanistic evaluation of existing and novel antibodies directed against CD52 molecule.