GENERATION, CHARACTERIZATION, AND IN-VIVO STUDIES OF HUMANIZED ANTICARCINOMA ANTIBODY CC49

Monoclonal antibody (MAb) CC49 reacts with tumor-associated glycoprote in (TAG)-72, a human pancarcinoma antigen, In clinical trials, radiola beled CC49 has shown excellent turner localization; however, many of t he patients receiving MAb CC49 develop a human antimouse antibody resp onse, In an attempt to prevent this antiimmunoglobulin response, we ha ve developed a humanized CC49 (HuCC49) by grafting the MAb CC49 hyperv ariable regions onto the variable light (V-L) and variable heavy (V,) frameworks of the human MAbs LEN and 21/28' CL, respectively, while re taining those murine framework residues that may be required for the i ntegrity of the antigen combining-site structure, The HuCC49 MAb was c ompared with native murine CC49 (nCC49) and chimeric CC49 (cCC49), usi ng a variety of assays, SDS-PAGE analysis under nonreducing conditions showed that the HuCC49 MAb has virtually identical mobility to that o f cCC49, Under reducing conditions, the HuCC49 yielded two bands of ap proximate to 25-28 and approximate to 50-55 kDa, characteristic of hea vy and light immunoglobulin chains, In competition radioimmunoassays, HuCC49 completely inhibited the binding of I-125-labeled nCC49 to TAG- 72, although 23- to 30-fold more HuCC49 was required to achieve a leve l of competition similar to those of cCC49 and nCC49, The relative aff inity of HuCC49 was 2- to 3-fold less than those of the cCC49 and nCC4 9 MAbs, respectively, The plasma clearance in mice of HuCC49 was virtu ally identical to that of cCC49, Biodistribution studies demonstrated equivalent tumor-targeting of HuCC49 and cCC49 to human colon carcinom a xenografts, These studies thus suggest that HuCC49 and genetically m odified molecules, such as sFv and domain-deleted immunoglobulins deve loped by using the HuCC49 variable region as a cassette, may be potent ially useful in both diagnostic and therapeutic clinical trials in pat ients with TAG-72-positive tumors.