Introduction: B7-H3, a B7 family member, is widely expressed in multiple cancers and is associated with poor clinical prognosis. Enoblituzumab (also known as MGA271 or TJ271) is an investigational, Fc-optimized monoclonal antibody that targets B7-H3 and exhibits enhanced antibody-dependent cell-mediated killing of B7-H3 expressing cancer cells. Here we identified the immuno-modulatory function of TJ271 in different cell subsets and pathways as a new mechanism for cancer treatment.

Experiments: The function of B7-H3 and TJ271 in regulating immune response was investigated in human PBMCs stimulated with anti-CD3 antibody with or without plate-coated B7-H3 in the presence or absence of TJ271. Gene expression profiles and immunophenotyping of PBMCs after treatments were evaluated by Nanostring nCounter platform and CyTOF mass cytometry, respectively. IFN-γ production from cell supernatant was measured by ELISA. In vitro tumor killing activity by TJ271 and urelumab, a 4-1BB agonist, was evaluated by co-culture of B7-H3 expressing tumor cells and PBMCs stimulated with anti-CD3. The tumor cell killing activity was evaluated by 7-AAD staining on the Incucyte platform.

Results: Gene expression of cell lineage markers in antigen-presenting cells, including macrophages and neutrophils was induced, while those in natural killer (NK) cells was suppressed by B7-H3 stimulation, respectively. Furthermore, expression of activation markers and co-stimulatory receptors, including IFNγ, ULBP2, GITR, and 4-1BB, was down-regulated while expression of exhaustion markers in CD8+ T cells and NK cells, including PD-L1, PD-L2, and IDO1, and of genes associated with M2-like macrophages were up-regulated by B7-H3. All this B7-H3-induced differential gene expression pattern was reversed by TJ271 treatment. As revealed by CyTOF, TJ271 treatment abolished B7-H3-mediated increase in the frequency of M2-like monocytes (B7-H3+CD68+CD206+CD16lo or B7-H3-CD68+CD163+CD16+) and led to increased frequency of 4-1BB-expressing CD4, CD8, and NK cells. TJ271 exhibited strong tumor killing activity against ES-2, a B7-H3-expressing ovarian cancer cell line in vitro. Consistent with the TJ271-associated increased 4-1BB expression in T and NK cells, activation of 4-1BB by urelumab further enhanced TJ271-mediated tumor killing activity.

Conclusion: Our data confirm the immunosuppressive function of B7H3 and demonstrate the immunoregulatory function of TJ271 as evidenced by the activation of cytolytic T cell and NK cells, reinvigoration of exhausted cells, and suppression of M2-like myeloid cells. These findings provide rationale for combination therapy with blockade of B7-H3 by TJ271 with other immunotherapies to achieve increased clinical efficacy against cancers.

Citation Format: Yanni Zhang, Xuejun Liu, Xinyun Zhu, Zhen Sheng, Yan Liu, Zhengyi Wang, Taylor B. Guo. Inhibition of B7-H3 by enoblituzumab elicits antitumor immune modulation in both innate and adaptive immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4228.