Light chain variants of an IgG3 anti-GD3 monoclonal antibody and the relationship among avidity, effector functions, tumor targeting, and antitumor activity.

R24 is an IgG3 mouse monoclonal antibody which recognizes the ganglioside GD3. Two variants of R24, in which one (V2-R24) or both (V1-R24) light chains were substituted by MOPC-21 light chains, were isolated and characterized. R24 had a 40-fold higher avidity for GD3 than either variant, suggesting that high avidity binding required the presence of two R24 light chains and, thus, divalency. R24 and both variants mediated antibody-dependent cellular cytotoxicity but antibody-dependent cellular cytotoxicity mediated by variants was weak compared to R24. The presence of at least one R24 light chain was required for complement-dependent cytotoxicity; complement-dependent cytotoxicity was mediated by R24 and weakly by V2-R24 but not by V1-R24. R24, but not V1-R24 or V2-R24, inhibited attachment of melanoma cells to plastic and activated T-lymphocytes, suggesting a threshold of avidity required for these biological effects. In a human melanoma xenograft model in nu/nu mice, radiolabeled R24, variants, and isotype-matched control monoclonal antibodies all appeared to localize in tumors (based on tumor:normal tissue ratios), but specific tumor targeting by R24 was generally 3- to 6-fold higher. R24 prevented melanoma outgrowth in nu/nu mice, while V2-R24 induced partial tumor protection. V1-R24 and the negative control monoclonal antibody did not inhibit tumor outgrowth. Antitumor activity of R24 corresponded to avidity and ability to mediate complement-dependent cytotoxicity in vitro.

Treatment of epidemic Kaposi's sarcoma with a combination of interferon-alpha 2b and etoposide.

A prospective clinical trial of concomitant interferon-alpha 2b and etoposide was conducted in 24 previously untreated patients with epidemic Kaposi's sarcoma. Eight of 21 evaluable patients (38%) achieved either a complete response (1 patient) or a partial response (7 patients). None of the responders had a prior history of opportunistic infection. Hematologic toxicity was severe, and 8 patients developed an opportunistic infection. The combination of interferon-alpha 2b and etoposide has modest activity, but no additive or synergistic activity was evident in the dose and schedule utilized in this study. The exact role for interferon-alpha in epidemic Kaposi's sarcoma, both as a single agent and in combinations, remains to be determined.

Kaposi's sarcoma and AIDS.

Mucocutaneous lesions are often a prominent manifestation of the acquired immune deficiency syndrome (AIDS). Patients with this syndrome are susceptible to a number of opportunistic skin infections as well as an aggressive form of Kaposi's sarcoma. The diagnosis, the clinical setting, and the treatment of these diseases are discussed.