Abstract A041: Preclinical development of a preventive vaccine against ovarian cancer
Authors: Scholler Nathalie , Stein Paul , Sharma Khushboo , Repellin Claire , Kamat Kalika , Harrison Travis , Shoemarker Robert H. , Sei Shizuko , Sambucetti Lidia 
Published: November 2016

Survival of cancer patients with high-grade serous carcinoma of the ovary (HGSCs) remains less than 30% five years after diagnosis, despite initial chemosensitivity of most HGSCs. We hypothesized that a tumor antigen-targeted vaccine capable of eliciting a robust cell-mediated immune response may help prevent ovarian cancer. Mesothelin (meso) is overexpressed by ovarian, lung and pancreatic cancers and is 57% conserved at the protein level between mouse and human. To elicit cell-mediated immune responses directed against mesothelin, we combined a human mesothelin recombinant protein with various adjuvants including: aluminum hydroxide gel (alum, for Th2 immune response); TLR4 ligand (synthetic lipid MPL, for Th1 response); squalene-oil-in-water (AddaVaxTM, for both Th1 and Th2 responses); and STING (stimulator of interferon genes) ligand (CDN) that activates innate immunity and triggers type 1 IFN response and NF-κB-dependent cytokine secretion. We detected robust anti-meso antibody (Ab) responses after 1 prime and 2 boosts with meso/alum/MPL or meso/CDN/AddaVax. The highest and most stable Ab titers were obtained with CDN/AddaVax-based adjuvants.

Four groups of female C57BL/6 mice were immunized with alum/MPL or CDN/AddaVax with or without meso (n = 12 per group). Six weeks after the prime immunization, cells from a luciferase-transduced syngeneic mouse ovarian cancer cell line, ID8 (Luc-ID8) were injected orthotopically in the left ovary of the mice. In vivo bioluminescent imaging (BLI) suggested a 92% take rate of tumors 3 weeks after ID8-Luc injections in mice immunized with meso/alum/MPL or adjuvants only. However, in the group immunized with meso/CDN/Addavax only 30% of the mice showed a detectable signal 3 weeks after ID8-Luc implantation. After 10 weeks the average BLI signal was still significantly lower than in all the other groups. Furthermore, the majority of mice immunized with alum/MPL +/- meso developed ascites by 12 weeks; no significant difference of peritoneal leukocyte numbers or phenotype was observed between the groups immunized with alum/MPL vs. meso/alum/MPL. In contrast, 7 out 11 mice immunized with meso/CDN/Addavax did not develop ascites through 14 weeks post tumor challenge; most of the tumors were unilateral, smaller, with more T and B cells present in the peritoneal lavages compared to the other groups. Immunizations with CDN/AddaVax or meso/CDN/AddaVax strongly increased the frequency of CD62L-CD44+ effector memory T cells, stimulated innate immunity with M1 polarization, profoundly decreased MDSC levels in peritoneal lavages, and correlated with a less aggressive tumor phenotype (EpCAM+ PD-L1-). H&E staining of the harvested tumors and fallopian tubes showed that tumors in animals immunized with meso/CDN/AddaVax were confined to the left ovary and/or fad pad for the majority of the animals as compared to metastatic disease for most animals of the other groups. In addition, tumor-infiltrating lymphocytes (TILs) were visible by H&E in animals immunized with meso/CDN/AddaVax. Further characterization is ongoing. These results support the hypothesis that a vaccine regimen combining mesothelin with CDN and Addavax can protect against aggressive forms of ovarian cancer. A similar vaccination study is in progress implementing a new model of inducible ovarian cancer in mice carrying floxed alleles of Dicer and PTEN. Prevention of ovarian cancer may be possible by vaccination against mesothelin tumor antigen in combination with adjuvants that stimulate type I IFN response.

Citation Format: Nathalie Scholler, Paul Stein, Khushboo Sharma, Claire Repellin, Kalika Kamat, Travis Harrison, Robert H. Shoemarker, Shizuko Sei, Lidia Sambucetti. Preclinical development of a preventive vaccine against ovarian cancer [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A041.