| Budget Amount *help |
¥3,980,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥480,000)
Fiscal Year 2007: ¥2,080,000 (Direct Cost: ¥1,600,000、Indirect Cost: ¥480,000)
Fiscal Year 2006: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
There are numerous tumor-associated antigens currently used for the diagnosis and treatment of cancer. However, no tumor-associated antigen can always be an exact and complete target molecule, because almost all of them are not absolutely tumor-specific. In the present study, we prepared human mAbs against a pan-carcinoma antigen, Ep-CAM, using a genetically engineered mouse (KM mouse^<TM>) that contains the human immunoglobulin genes. Spleen cells from KM mice immunized with recombinant Ep-CAM were fused with the P3-U1 mouse myeloma cells. Of 44 anti-Ep-CAM clones analyzed, two were of IgG4 and the others of IgM clones. The two IgG4 clones were suggested to recognize the same antigenic determinant or two closely located determinants. The two IgG4 and one of the IgM clones tested revealed antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity, respectively, against Ep-CAM-expressing cells in vitro. It is also known that IgG4 hardly binds to the FcγIII receptor, which involves in ADCC by NK cells. In the presence of the IgG4 clone M13-13, however, a slight increase was observed in the cytotoxicity of IL-2-activated PBMC against tumor cells. IgG4 antibodies are able to bind to the FcγI receptor on monocytes and thereby exert ADCC. The ADCC activity observed with M13-13 might be due to activated monocytes. Therefore, we engineered our IgM clone M11-29 to convert it to the IgG1 type using its V-region genes so that it can exhibit both ADCC and CDC to Ep-CAM-expressing tumor cells. The V-region genes obtained were also useful to prepare single chain Fv antibodies to retarget cylotoxic T cells or a retrovector to tumor cells. Taken together, these data suggest that these fully human mAbs produced against Ep-CAM and their V-region genes, which are applicable for preparation of engineered antibody fragments, may be useful for antibody-based therapy of cancer.
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