Nonmutated Self-Antigen-Derived Cancer Vaccine Peptides Elicit an IgE-Independent but Mast Cell-Dependent Immediate-Type Skin Reaction without Systemic Anaphylaxis

Abstract

We previously reported an unexpected phenomenon, i.e., several cancer vaccine peptides, including a cyclophilin B-derived peptide (CypB-84), elicited an immediate-type skin reaction in prevaccination skin tests. These peptides were prohibited in the subsequent vaccinations because of a possible induction of systemic anaphylaxis. In this study, we investigated mechanisms involved in the peptide-elicited inflammatory reactions in BALB/c mice whose MHC class I molecule (Kd) shared similar binding motifs with the human HLA-A24 molecule. Among 11 peptides tested, all of which had been scheduled for use in clinical trials with HLA-A24+ cancer patients, three peptides (CypB-84, ART1-170, and ART4-13) elicited immediate footpad reactions in BALB/c mice similar to the skin reactions in humans. The footpad reaction was also observed in C57BL/6, athymic nu/nu, and CB17-SCID mice, but not in mast cell-deficient WBB6F1w/wv mice, indicating the reaction was not mediated by specific immunity, but was mast cell-dependent. Furthermore, the reactions were not correlated to in vivo antitumor effects of the peptides. An anaphylaxis was not elicited when the peptides were systemically injected due to a very rapid clearance of the peptides from the plasma by in vivo degradation. These results suggest that certain peptides of cancer vaccine candidates exhibit an IgE-independent but mast cell-dependent inflammatory response with no elicitation of systemic anaphylaxis, and may provide new insights for further development of peptide-based vaccinations for cancer patients.