Abstract Triple negative breast cancer (TNBC) is an aggressive form of breast cancer (BC) characterized by early relapse and poor prognosis. The TNBC mortality burden is unequally distributed among populations of different genetic ancestry, with populations of African descent displaying higher incidence of TNBC with high mortality rates. The tumor microenvironment (TME) plays a key role in TNBC development. Interactions between different TME components, such as T cells, can modulate TNBC progression and resistance to therapies. Additionally, the TME can contribute to the disparities in outcomes observed between TNBC patients of EA versus African ancestry. However, the immunomodulatory mechanisms that mediate immune evasion in TNBC in women of African descent remain understudied. To investigate these mechanisms, we developed organoids from TNBC patients of African American and Ghanian ancestry. TNBC tumors from EA, AA and GH patients were implanted into immunosuppressed mice and PDX-derived organoids (PDXos) were established from these tissues. The expression of epithelial, mesenchymal, stromal and immune markers in PDXos and matching PDXs and primary tissues was assessed using multiplex IF and qRT-PCR. T cells were isolated from healthy control PBMCs and activated as per previously published protocols. 5 different TNBC organoids, including 1 EA, 2 AA and 2 GH PDxOs, were co-cultured with T cells, following which the responsiveness of organoids to T cells was assessed using flow cytometric analysis. Finally, immune-resistant organoids were co-cultured with T cells then sorted for downstream analysis. We have successfully established 8 TNBC organoids (PDxOs) from patients of different genetic ancestries, including 1 EA TNBCs, 3 GH TNBCs and 5 AA TNBCs. Multiplex IF and qRT-PCR analysis revealed that the obtained PDXos retained the epithelial (EpCAM) and mesenchymal (vimentin) signatures of their tissues of origin. Co-culture with T cells revealed that the organoids displayed differing patterns of immune responsiveness and exerted distinct effects on T cell exhaustion and activation. Flow cytometric analysis showed that epithelial TNBC organoids were more responsive to T cells whereas mesenchymal-like organoids were more immune resistant. qRT-PCR analysis of organoids grown in co-culture with T cells revealed that they had increased vimentin expression, suggesting a role for EMT in immune evasion in these organoids. These findings reveal that PDXos recapitulate the epithelial and mesenchymal patterns of their tissues of origin and represent a valuable platform for investigating ancestry-specific pathways of immune responsiveness and resistance in TNBC patients of African ancestry. Citation Format: Batoul Farran, Moses Kamita, Shuk Mei Wong, Sylvester Antwi, Valerie Ofori Aboah, Harriet Larrious-Lartey, Jessica Jessica Bensenhaver, Ali Haythem, Walker Eleonor, Foster Amponsah, Josephine Nsafu., Rose Dampson, Patrick Kafui Akapko, Evelyn Jiage. Investigating the influence of genetic background on TNBC-T cell interactions in TNBC organoids and co-cultures 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 2094.
Farran et al. (Fri,) studied this question.