No abstract

Peptide-based vaccination has a great potential for the prevention and treatment of various diseases. There is, however, no appropriate monitoring system to measure immune responses to vaccinated peptides, which hampers the development of therapeutically effective vaccine regimens to various diseases. In this study a new multiplexed flow cytometric assay using the Luminex system to monitor humoral immune responses to vaccinated peptides is described. Although the sensitivity is mostly equal to that of the traditional enzyme-linked immunosorbent assay (ELISA), the new assay has several advantages over ELISA in that it minimizes the amount of sera needed, running costs and working periods, and thus will be a novel tool for monitoring immune responses to vaccinated peptides.

Recent clinical trials of peptide vaccine for cancer patients have rarely resulted in tumor regression. One of the reasons for this failure could be an insufficient induction of anti-tumor responses in these regimens, in which peptide-specific memory cytotoxic T lymphocytes (CTLs) were not measured prior to vaccination. We investigated in this study whether pre-vaccination measurement of peptide-specific CTLs can provide any advantages in lung cancer patients receiving peptide vaccination with regard to safety and immunological responses. Ten patients with advanced lung cancer received vaccination with peptides under a regimen of CTL precursor-oriented vaccination, in which pre-vaccination peripheral blood mononuclear cells (PBMCs) were at first screened for reactivity in vitro to each of 14 peptides, followed by in vivo administration of only the reactive peptides. Profiles of the vaccinated peptides varied markedly among the 10 patients. This regimen was generally well-tolerated, although local skin reactions, diarrhea, and colitis were observed in 8, 2, and 1 patient, respectively. Increased CTL responses against the immunized peptides and tumor cells were observed in the post-vaccination PBMCs from 4 of 8 and 3 of 10 patients tested, respectively. Peptidespecific IgG became detectable in post-vaccination sera in 4 of 10 patients tested, and these 4 patients had a long progression-free survival. Furthermore, the median survival time of 9 patients with non-small cell lung cancer was 668.0 ± ± ± ±164.2 days. These results encourage further development of CTL precursor-oriented peptide vaccination for lung cancer patients. (Cancer Sci 2003; 94: 548-556) dentification of a large number of antigenic epitopes 1-9) recognized by cytotoxic T lymphocytes (CTLs) reacting to tumor cells has opened the door to clinical trials of peptide-based immunotherapy for cancer patients. [10][11][12][13][14][15][16] Many clinical trials of peptide-based immunotherapy for malignant melanoma and other epithelial tumors have been conducted in the past decade, but major clinical responses were rarely obtained in these clinical studies, including our trial of a cyclophilin B (CypB) peptide vaccination for advanced lung cancer patients 17) and a SART3 peptide vaccination for advanced colorectal cancer patients.18) One reason for this failure to obtain tumor regression could be an insufficient induction of anti-tumor responses in these vaccine regimens, in which peptide-specific memory T cells were not measured in pre-vaccination peripheral blood mononuclear cells (PBMCs). We have speculated that vaccination based on information from pre-vaccination measurement of peptide-specific CTLs in the circulation might induce potent anti-tumor immune responses in cancer patients. This hypothesis is based on the assumption that initiation of immune-boosting of CTLs through peptide vaccination could be more effective than immune-priming of naive T cells with regard to induction of prompt and strong immunity to both the peptide and tumor cells. We ha...