Abstract 3741: Helper/killer hybrid epitope long peptide (H/K-HELP) cancer vaccine augments Th1-dependent CTL induction at tumor-draining lymph node to eradicate solid tumor: its application to develop an innovative combination cancer immunotherapy(iCCI)

Abstract We have initially demonstrated the pivotal role of IFN-γ-producing tumor-antigen-specific Th1 cells for the complete eradication of established tumor mass by CTL. The accumulated evidence has clearly demonstrated that induction of Th1-dependent full activation of CTL at tumor-draining lymph nodes (TDLN) are crucial for inducing complete rejection of solid tumor by CTL. To induce Th1 immunity efficiently at TDLN in tumor-bearing host, we developed an artificially synthesized helper/killer-hybrid epitope long peptide (H/K-HELP), which conjugated killer and helper epitope peptides of cancer antigen by a glycine-linker. In mouse model, OVA-H/K-HELP was selectively presented in vivo by professional DC in vaccinated TDLN and sustained antigen presentation capability of DC to stimulate both CTL and Th1 cells. Thus, in contrast to short peptide, vaccination of OVA-expressing EG7-bearing mice with OVA-H/K-HELP caused a complete eradication of EG7 tumor mass. To apply these basic findings to clinical treatment of cancer patients, we then developed Survivin-H/K-HELP. Treatment of a patient with a triple-negative breast cancer patient with Survivin-H/K-HELP induced a complete response in a triple-negative breast cancer patient concomitantly with the induction of Th1-dependent cellular and humoral immune responses. In this clinical study, the patients showed Th1-dependent C’-fixing IgG antibody production and exhibited IFN-γ-producing Th1 cellular responses. Finally, we also applied H/K-HELP-pulsing DC-vaccine to develop an innovative combination cancer immunotherapy (iCCI). The iCCI consisting of radiation, low dose of immune check point inhibitors (ICIs:Nibolumab, Ipilimumab) and H/K-HELP-pulsed DC, all of which have been shown to initially modulate antitumor immunity at TDLN. Here, we described a successful outcome of a case of the stage IVA inoperable advanced hypopharyngeal squamous cell cancer patient with lymph node-metastasis. The iCCI treatment of the patient caused a complete disappearance of all cancers and the patient has been cancer free for over 15 months so far. Although the destruction mechanism of cancer is not determined, we image this iCCI might improve patient’s antitumor immune capability in immune microenvironment around tumor (IMAT) including TDLN and TME. Our developed iCCI will become a promising strategy to overcome inoperable advanced cancers in future. Citation Format: Takanori Iwasaki, Yuichiro Yazaki, Takashi Masuko, Takashi Nishimura. Helper/killer hybrid epitope long peptide (H/K-HELP) cancer vaccine augments Th1-dependent CTL induction at tumor-draining lymph node to eradicate solid tumor: its application to develop an innovative combination cancer immunotherapy(iCCI) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3741.