Generation, immunologic characterization and antitumor effects of human monoclonal antibodies for carcinoembryonic antigen

We generated fully human mAbs (HmAbs) to carcinoembryonic antigen (CEA) using the KM mouse, which carries a human chromosome 14 fragment containing the entire Ig H chain loci and human κ L chain segments in the mouse genome. Forty‐six hybridoma clones producing HmAbs to CEA were thus obtained by fusing the P3‐U1 mouse myeloma cells with splenocytes of the KM mice immunized with CEA. Among them, 22 clones produced HmAbs that reacted with CEA but not with 3 other CEA‐related cell adhesion molecule (CEACAM) family members, CEACAM1, CEACAM6 and CEACAM8. In 12 HmAbs examined, 8 were IgG4, 2 were IgG3, 1 was IgG2, and the other was IgG1. The affinity constants for CEA of these HmAbs were comparable to those of the previously prepared mouse anti‐CEA mAbs (MmAbs). BIAcore analyses revealed that 1 and 2 of the 22 HmAbs react with 2 epitopes defined by MmAbs on the domain N and the domain A1 or B1 of CEA, respectively. In the presence of human complement in vitro, 2 HmAbs tested showed substantial cytotoxicity, namely, 50–65%, against CEA‐expressing tumor cells. With human lymphokine‐activated killer cells in vitro, 3 HmAbs tested exhibited 40–65% Ab‐dependent cell‐mediated cytotoxicity against the tumor cells. Moreover, one of the HmAbs induced a significant inhibition of tumor growth when administered to mice xenografted with the CEA‐expressing cells. Considering their lack of immunogenicity to humans, these CEA‐specific HmAbs may be useful for immunotherapeutic approaches as well as for immunodiagnosis. © 2003 Wiley‐Liss, Inc.