Abstract 4571: Advantage of dendritic cells for the therapeutic cancer vaccine
Authors: Nagaoka Koji , Hosoi Akihiro , Iino Tamaki , Matsushita Hirokazu , Kakimi Kazuhiro 
Published: July 2017

Background: To develop effective cancer vaccine, we examined CTLs induced by peptide vaccination (CTLpep) and DC vaccination (CTLDC) in terms of their antitumor effects.

Methods: For preparation of peptide vaccine, 50 µg hgp100 peptide (KVPRNQDWL) and 20 µg CpG were emulsified with 50 µl CFA or IFA. Bone marrow-derived DCs were matured with LPS and pulsed with hgp100 peptide at 1 µg/ml and used as DC vaccine. To induce CTLpep and CTLDC, C57BL/6 mice were first injected with 1 x 107 naive spleen cells from Pmel-1 TCR transgenic mice to increase hgp100-specific CTL precursors. Then mice were vaccinated twice with 2 weeks interval. The induction of CTLs were evaluated 2 weeks after the second vaccination. To evaluate their antitumor activity, 1 x 106 B16F10 were inoculated into vaccinated mice (prophylactic model). For therapeutic model, 1 x 106 B16F10 were inoculated into mice on day 0. Five days later 1 x 107 Pmel-1 splenocytes were transferred. Then, mice were vaccinated on days 5 and 12, followed by the measurement of tumor growth.

Results: DC vaccine induced 5-times more CTLs than peptide vaccine. The numbers of CTLpep and CTLDC obtained in the spleen were 2.4±0.2x105 and 1.2±0.4x106, respectively. CTLpep expressed PD-1 and Tim-3 at higher level than CTLDC. Most of CTLpep showed effector memory phenotype (CD44hiCD62L-), while CTLDC contained a considerable fraction of central memory cells (CD44hiCD62L+). Although both CTLpep and CTLDC produce IFN-γ and TNF-α at similar level, more CD107a were detected on CTLDC than CTLpep upon re-stimulation. CTLDC displayed better proliferation potential than CTLpep. These phenotypic differences were confirmed by the comprehensive gene expression analysis. Transcriptome analysis revealed that considerable portion of CTLpep and CTLDC were comparable and different from that of naïve CTLs. However, several genes were expressed differentially. CTLpep expressed higher amount of inhibitory receptors, such as Pdcd1, Lag3, Ctla4 and Tigit than CTLDC. CTLDC expressed Fbp1, which inhibits glycolysis, and Cpt1a, which is the rate-limiting enzyme of mitochondrial fatty acid oxidation, suggesting that their metabolic statuses were shifted from glycolysis to fatty acid oxidation. DC vaccine completely inhibited the tumor growth in prophylactic vaccine setting, while peptide vaccine delayed tumor growth compared to control mice. In therapeutic protocol, peptide vaccine showed no antitumor effect, while DC vaccine significantly suppressed tumor growth. The numbers of intratumoral CTLpep and CTLDC on day 19 were 5.2±2.8 x 104/g and 5.0±1.4 x 105/g, respectively. Intratumoral CTLDC expressed lower levels of PD-1, Tim-3 and LAG-3 and more Ki67 than CTLpep. Furthermore, Intratumoral CTLDC produce more IFN-γ and TNF-α than CTLpep.

Conclusion: DC vaccine induced intratumoral CTLs with multi-functionality and high proliferation potential. Therefore, DC vaccine is our choice for the therapeutic cancer vaccine.

Citation Format: Koji Nagaoka, Akihiro Hosoi, Tamaki Iino, Hirokazu Matsushita, Kazuhiro Kakimi. Advantage of dendritic cells for the therapeutic cancer vaccine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4571. doi:10.1158/1538-7445.AM2017-4571