Antitumor Effect of New

Background: While the benefit of passive immunotherapy is commonly accepted, active immunization may have advantages for the patient’s quality of life. We identified a new epitope of Mab CH401 against Her-2/neu extracellular domain (N: 167-175), and evaluated the effect of active immunization of the 20mer peptide containing the epitope (CH401 peptide). Materials and Methods: Epitopemapping was performed using ELISA with Her-2/neu-related multiple antigen peptides (MAP). BALB/c mice were transplanted with Her-2/neu-expressing lymphoma cell line and immunized with the peptides. For monitoring the condition, ELISA and flow cytometry was performed. Results: CH401 peptide induced Her-2/neu-specific IgG antibody. Tumor growth in immunized mice was suppressed and tumorinfiltrating lymphocytes comprised more CD8+ T-cells, which secreted larger amounts of interleukin-2 after the peptide restimulation. Conclusion: The new Her-2/neu peptide contained epitopes for CD4+ and CD8+ T-cells, which contributes to the suppressive effect on Her-2/neu-expressing tumor cell growth. Molecular targeting reagents have been extensively developed for cancer therapy. Among them, antibodies against tumor-associated antigen (TAA) are considered to be powerful tools through their multiple functions, such as antibody-dependent cell cytotoxicity and blocking of signals for cell proliferation (1-3). The antitumor effect of anti-TAA antibody has been investigated in two ways: via passive immunization with monoclonal antibody (Mab) and active immunization with TAA vaccination (4, 5). However, the processes including the clinical application of Mab therapy require huge amounts of antibodies, and consequently may impose considerable physiological, psychological and financial burdens upon the patients. As for the strategy for overcoming the disadvantage of passive immunization with Mab, active immunization with tumor-specific antigen may avoid adverse effects induced by transfusing large amounts of antibodies repeatedly. However, most of the trials with immunization of whole TAA molecules have not been successful (4), partially because the antibodies sometimes function positively for cancer growth (6-9). Thus, peptides composed of limited amino acid sequences, which do not produce tumor-promotory antibodies, may be useful for effective antitumor antibody production. In past studies, however, the B-cell epitope was tentatively estimated simply from the biochemical/structural nature of the antigen, which is still problematic because epitopes may include the region agonistic to tumor growth (10, 11). Otherwise, B-cell epitopes or mimotopes were artificially found by screening with phage display (12-14). Thus, identifying an epitope of TAA-specific monoclonal antibody, which is already characterized to induce an antitumor effect, and designing a peptide that includes the epitope sequence might be an effective protocol for the peptide design of anti-TAA vaccination. In contrast, T-cell epitope, particularly of CD8+ cytotoxic Tcells (CTL), has been well investigated since the characterization/identification of TAA (15). The techniques for purifying peptide presented on major histocompatibility complex (MHC) class I and II molecules have identified numerous anchoring peptides and categorized (15, 16). 3361 Correspondence to: Yoshie Kametani, Ph.D., Department of Immunology, Tokai University School of Medicine, 143, Shimokasuya, Isehara-shi, Kanagawa, 259-1193, Japan. Tel: +81 463931121 ext. 2589, Fax:+81 463942976, e-mail: y-kametn@is.icc.u-tokai.ac.jp