Abstract 4369: B7-H3 vaccine induces robust humoral and cellular immunity and inhibits tumor growth in mice

Abstract Background: B7-H3 (CD276) is an immune checkpoint molecule frequently overexpressed in a wide range of cancers, where it plays critical roles in immune evasion, tumor progression, and metastasis, underscoring its potential as a promising target for cancer immunotherapy. Here, we developed a novel protein vaccine to induce humoral and cellular immunity against B7-H3 and evaluated its anti-tumor efficacy in syngeneic mouse colon cancer models. Methods: A recombinant vaccine protein was generated, consisting of tandem repeats of the FG loop fragment of human B7-H3 - a structural motif linking the F and G β-strands of B7 family proteins that is critical for ligand-receptor interactions (though no ligand has yet been identified for B7-H3) - combined with an N-terminal cell-penetrating peptide to enhance immunogenicity. Immunogenicity of this B7-H3 vaccine, adjuvanted with CpG ODN 1826, was studied in BALB/c and C57BL/6 mice vaccinated subcutaneously weekly for 6 weeks. Controls were mice administered adjuvant only. Serum samples was collected at multiple time points to determine anti-B7-H3 antibody titer by ELISA. Splenocytes were harvested to assess cellular immunity using IFNγ ELISPOT assay. Anti-tumor efficacy of vaccine was evaluated in both prophylactic and therapeutic studies using B7-H3-humanized mouse colon cancer cell lines, CT26-hB7-H3 and MC38-hB7-H3, in BABL/c and C57BL/6 mice, respectively. Tumor growth was recorded. Tumor-infiltrating lymphocytes (TILs) were characterized by flow cytometry. Results: The B7-H3 vaccine induced robust humoral and cellular immunity against human B7-H3 in both BALB/c and C57BL/6 mice. In prophylactic studies, the vaccine demonstrated significant anti-tumor activity: 1) in the CT26-hB7-H3 model, tumor growth inhibition (TGI) in vaccinated mice was 99.8%, compared to controls and 90% of vaccinated mice were tumor-free at the endpoint; 2) in the MC38-hB7-H3 model, TGI was 72.4%. Using tumors collected from the MC38-hB7-H3 study, TIL characterization using flow cytometry revealed 1.2-fold and 4.3-fold increases of activated CD4+IFNγ+ and CD8α+IFNγ+ T-cells, respectively. In therapeutic studies, TGI in CT26-hB7-H3 tumor-bearing mice was 91.2%, with 7/12 of mice becoming tumor-free at the end point, and TGI in MC38-hB7-H3 tumor-bearing mice was 85%. In MC38-hB7-H3 tumors, TIL analysis showed a 2.8-fold increase in CD8α+IFNγ+ T cells. Conclusions: Our study demonstrates that the B7-H3 vaccine induces robust humoral and cellular immunity, effectively suppressing the growth of B7-H3-positive tumors in mice. These findings highlight its potential for clinical translation as a therapeutic strategy for B7-H3-overexpressing cancers in humans. Citation Format: Kenneth Nansheng Lin, Melvin Toh, HONG WANG. B7-H3 vaccine induces robust humoral and cellular immunity and inhibits tumor growth in mice abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4369.