Effect of alemtuzumab on neoplastic B cells.
OBJECTIVE
The therapeutic antibody alemtuzumab is directed against the CD52 molecule and is used for the treatment of B-cell lymphocytic leukemia (B-CLL). We investigated the mechanism of action of this antibody in vitro against different neoplastic B cells and compared it to the anti-CD20 antibody rituximab.


METHODS
Complement-mediated cytotoxicity assays were performed on freshly isolated neoplastic cells using human serum as the source of complement. Antibody-dependent cellular cytotoxicity (ADCC) was evaluated by chromium release assays, using peripheral blood mononuclear cells as effector cells, before and after 2 days of culture with interleukin-2 (IL-2).


RESULTS
Alemtuzumab lysed cells from the 23 B-CLL samples through complement activation (mean 80%) much more efficiently than rituximab did (mean 16%), presumably because of the higher expression of CD52 than of CD20. All other leukemic B cells, including 1 prolymphocytic leukemia, 2 hairy cell leukemias and 6 B-non Hodgkin's lymphomas were effective targets for both antibodies, with 88% and 85% mean lysis, respectively. Both CD52 and CD20 were highly expressed in these cells. In contrast, most neoplastic B cell samples were poorly lysed through ADCC using freshly isolated peripheral blood mononuclear cells as effectors with either monoclonal antibody and regardless of target antigen levels. ADCC was, however, significantly increased in all cases by culturing the effector cells with IL-2 for 2 days.


CONCLUSIONS
Complement-mediated lysis is likely to be an important mechanism of action of alemtuzumab in B-CLL and combination with IL-2 may increase this antibody's efficacy through ADCC. Mature neoplastic B cells other than B-CLL express high levels of CD52 and are good targets for alemtuzumab-mediated cytotoxicity.
Golay
Josée
J
Laboratory of Cellular and Gene Therapy G. Lanzani, Division of Hematology, Ospedali Riuniti di Bergamo, Bergamo, Italy. jgolay@ospedaliriuniti.bergamo.it
Manganini
Massimiliano
M
Rambaldi
Alessandro
A
Introna
Martino
M
D000368:Aged; D000369:Aged, 80 and over; D000074323:Alemtuzumab; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D058846:Antibodies, Monoclonal, Murine-Derived; D000912:Antibodies, Neoplasm / Q000494:pharmacology*; D000920:Antibody-Dependent Cell Cytotoxicity / Q000187:drug effects; D015703:Antigens, CD / Q000276:immunology; D000951:Antigens, Neoplasm / Q000276:immunology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001402:B-Lymphocytes / Q000187:drug effects*; D000074301:CD52 Antigen; D045744:Cell Line, Tumor / Q000187:drug effects; D003167:Complement Activation / Q000187:drug effects; D003602:Cytotoxicity, Immunologic / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D005260:Female; D006023:Glycoproteins / Q000276:immunology; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology; D007943:Leukemia, Hairy Cell / Q000473:pathology; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000473:pathology*; D015463:Leukemia, Prolymphocytic / Q000473:pathology; D016393:Lymphoma, B-Cell / Q000473:pathology*; D008228:Lymphoma, Non-Hodgkin / Q000473:pathology; D008297:Male; D008875:Middle Aged; D000069283:Rituximab
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D058846:Antibodies, Monoclonal, Murine-Derived; D000912:Antibodies, Neoplasm; D015703:Antigens, CD; D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D000074301:CD52 Antigen; C000613862:CD52 protein, human; D006023:Glycoproteins; D007376:Interleukin-2; D000074323:Alemtuzumab; D000069283:Rituximab