Abstract IA017: Spontaneous humoral responses in endometrial cancer provide a rationale for novel tumor-penetrating therapeutic antibodies

Abstract The role of humoral responses in endometrial cancer remains insufficiently investigated. Using a cohort of 107 patients with different histological subtypes of endometrial carcinoma, we found that concomitant accumulation of T, B, and plasma cells at tumor beds predicted better survival. However, only B cell markers corresponded with prolonged survival specifically in high-grade endometrioid type and serous tumors. Immune protection was associated with class-switched IgA and, to a lesser extent, IgG. Expression of polymeric immunoglobulin receptor (PIGR) by tumor cells allow dimeric IgA transcytosis. Taking advantage of tumor cell penetration, we demonstrated that mutation-specific dIgA, but not IgG, neutralized KRASG12D inside carcinoma cells and expelled this oncodriver (but not wild-type KRAS) outside tumor cells, abrogating tumor cell proliferation in an antigen-specific manner. Accordingly, KRASG12D-specific dIgA1, but not the same antibody on an IgG backbone, abrogated KRASG12D carcinoma growth in vivo, more effectively than small molecule KRASG12D inhibitors, including in syngeneic tumor-bearing immunocompetent mice. Because 6% of endometrial cancers exhibit KRAS mutations, our results provide a rationale for developing PIGR-targeting tumor cell-penetrating antibodies to effectively target intracellular oncogenes, which could be applicable to many aggressive and frequent human cancers. Citation Format: Jose R. Conejo-Garcia. Spontaneous humoral responses in endometrial cancer provide a rationale for novel tumor-penetrating therapeutic antibodies abstract. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30 (5Suppl): Abstract nr IA017.