Ongoing studies involve the design and use of recombinant immunoglobulin (Ig) forms for cancer therapy and diagnosis. Murine monoclonal antibody (MAb) CC49 selectively reacts with the pancarcinoma antigen, tumor associated glycoprotein (TAG)-72. Preclinical studies and clinical trials have demonstrated the diagnostic and potential therapeutic utility of this MAb. To optimize therapeutic efficacy and minimize toxicity and host immune responses, emphasis is now being placed on the design and translational research of novel recombinant Ig forms of CC49. The genes encoding these antibodies have been cloned and mouse-human chimeric and humanized versions of these MAbs have been generated. The humanized MAb CC49 (HuCC49) was used as a prototype to develop genetically altered MAbs. A humanized CH2 domain-deleted CC49 has been constructed and demonstrates significantly faster plasma clearance and better tumor-targeting than the intact CC49. To facilitate ex vivo transfection and in vivo expression of recombinant CC49 for therapeutic use, we developed a single-gene construct encoding a single-chain immunoglobulin-IL-2 fusion protein. In vivo expression of the fusion protein in Balb/c mice was successfully demonstrated using both a transcutaneous gene gun and intramuscular injection. In a separate study, to minimize idiotypic responses of patients to HuCC49, murine CDRs not critical for antigen binding were identified and replaced with human CDRs. Efforts are underway to identify dispensable regions of the essential murine CDRs and to replace them with the homologous regions of human CDRs. Collaborative studies have recently been initiated to generate specific redirected antitumor human T-cell populations. To that end, MHC-unrestricted antigen receptors, containing single-chain antitumor Ig genes and the zeta chain of the CD3 complex of the T cell have been introduced into T lymphocytes by retroviral gene transfer. Yet another initiative recently undertaken for the immunotherapy of human carcinomas is based on genetically conjugating an antigenic peptide of a tumor antigen to the anti-human FcgR1 antibody. These molecules will be used to target antigenic peptides to professional antigen presenting cells for internalization and presentation of the peptide in the context of MHC class 1. Constructs encoding a Fab' fragment of an anti-human FcgR1 antibody and an immunogenic peptide derived from carcinoembryonic antigen have already been made.
