Abstract B042: Loss of PTEN in Triple-Negative Breast Cancer increases expression of PD-L1 in an NF-kB dependent manner

Abstract The immune checkpoint co-inhibitory ligand PD-L1 is expressed in approximately 76% of Triple Negative Breast cancer (TNBC) cases, yet the molecular mechanisms promoting PD-L1 expression are unknown. Recent evidence suggests the loss of the tumor suppressor PTEN, inhibitor of the PI3K/Akt pathway, upregulates PD-L1 expression. Activation of both the PI3K/Akt and NF-κB pathways are common in TNBC, and there is substantial crosstalk between the PI3K/Akt pathway and the NF-κB signaling pathway. We hypothesize that dysregulation of the PI3K/Akt/NF-κB axis may also contribute to immune evasion, for example, by upregulating co-inhibitory ligands. To investigate whether the PI3K/Akt pathway regulates PD-L1 expression in an NF-κB dependent manner, TNBC cell lines with deleted PTEN expression (MDA-MB-436, BT549) and a PTEN knockout in breast epithelial cell line MCF10A were engineered to express PTEN on a tetracycline-inducible system, these cell lines were leveraged to observe localization of NF-κB in the presence and absence of PTEN using confocal microscopy. In the absence of PTEN, increased localization of NF-κB to the nucleus was observed. Further investigation was performed via western blot, flow cytometry, and immunofluorescence following treatment with IKK Inhibitor VII (IKK-16), a selective IKK inhibitor that prevents degradation of IκB kinase, to disrupt interactions between the IKK/NF-κB pathway and the PI3K/Akt axis. The IKK Inhibitor VII treatment allowed for the assessment of the effect on nuclear localization of NF-κB and subsequent expression of PD-L1. Despite increased PI3K and Akt activation as a result of the loss of PTEN, inhibition of IκB kinase and subsequently NF-κB resulted in a decrease in PD-L1 expression. Anti–PD-L1 immunotherapy has shown limited success in clinical trials with overall response rates to ICB alone in TNBC remaining low. This data may support the use of neoadjuvant chemotherapy targeting the PI3K/Akt pathway not only to directly inhibit tumor growth but also for its immunomodulatory effects. Citation Format: Destiny Omili, Stuart Martin, Michele Vitolo. Loss of PTEN in Triple-Negative Breast Cancer increases expression of PD-L1 in an NF-kB dependent manner [abstract]. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr B042.