Abstract
In immunotherapy by cancer antigen-derived peptide vaccine, vaccination of cytotoxic T lymphocyte (CTL) peptide alone is common, while it remains unclear whether the addition of helper peptide vaccine to the CTL peptide vaccine is of great advantage for the enhancement of tumor immunity. In the present study, combination vaccine of Wilms’ tumor gene 1(WT1) protein-derived CTL and helper peptides induced the strong infiltration of WT1-specific CD8+ T cells into mouse tumor at frequencies of 8.8%, resulting in the formation of multiple microscopic necrotic lesions in the tumor, whereas the frequencies of WT1-specific CD8+ T cell infiltration into the tumor in the vaccination of the CTL peptide alone were only 0.32%. The majority of the infiltrated WT1-specific CD8+ T cells was effector phenotype T cells, but importantly, WT1-specific CD8+CD44+CD62L+CD103+ resident memory T cells, which could differentiate into a lot of effector phenotype T cells, existed in the tumor of mice vaccinated with the both WT1 peptides. Furthermore, T-cell receptor repertoire analysis showed the oligoclonality of these tumor infiltrating WT1 tetramer+ CD8+ T cells, and 3 clones occupied about half of them. These results indicated that WT1-specific CD4+ T cells played an essential role not only in the priming and activation of WT1-specific CD8+ T cells, but also in trafficking and infiltration of the CD8+ T cells into tumors. These results should provide us with the concept that in the clinical setting, combination vaccine of WT1-specific CTL and helper peptides would be more advantageous than the CTL peptide vaccine alone.
Highlights
In the past two decades, immunotherapy became one of the established treatments against cancer as well as operation, radiotherapy and chemotherapy
Hematoxylin and eosin (HE) staining of the resected tumors revealed that substantial numbers of microscopic necrotic lesions (100 ~ 300 μm) in the tumors were characteristically observed in the mice treated with the combination vaccine, but not detected in the mice vaccinated with Wilms Tumor 1 (WT1) cytotoxic T lymphocyte (CTL) peptide alone (Figure 1B)
CD4+, CD8+ T cells and CD11c+ dendritic cells (DCs) infiltrated into the tumors of both of the mice treated with the CTL peptide vaccine alone or the combination vaccine, the microscopic necrotic lesions had more CD8+ T cell infiltration (Figure 1D)
Summary
In the past two decades, immunotherapy became one of the established treatments against cancer as well as operation, radiotherapy and chemotherapy. The immunological analysis of tumors treated with the immunotherapies revealed the three basic immune profiles of tumors; the immune-inflamed, the immuneexcluded, and the immune-desert phenotypes [3, 4] From these observation of immune phenotypes, totally 7 steps of the cancer-immunity cycle, composed of cancer antigen release, cancer antigen presentation, priming and activation of T cells, trafficking of T cells to tumors, infiltration of T cells into tumor, recognition of cancer cells by T cells, and killing of cancer cells, were proposed to be necessary for the success in tumor immunotherapies [4]. Cancer tumor antigen-derived cytotoxic T lymphocyte (CTL) epitope-based vaccines target the specific steps of priming and activation of antigen-specific CD8+ CTLs, and combination with other therapies that target other steps is desired for the durable response. Helper peptide vaccines could be good candidates for combination with the CTL epitope-based vaccines, because the helper peptide vaccines are expected to help the step of priming and activation of cancer antigen-specific CTLs and to stimulate the steps of trafficking and infiltration of the CTLs into tumors [5, 6]
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