Melanoma is responsible for 80% of skin cancer-related deaths. Approximately 50% of melanoma patients carry the BRAFV600E mutation, which promotes tumor growth. While the use of BRAF inhibitors (BRAFi) has improved outcomes, acquired resistance is a persistent clinical challenge and the impact of BRAFi resistance on the immune tumor microenvironment (iTME) is incompletely understood. We have shown that the addition of the synthetic triterpenoid CDDO-Me to the BRAFi PLX4720 arrested resistance and significantly reduced tumor burden, while CDDO-Me as a single agent or in combination with BRAFi prior to resistance was ineffective. Thus, we hypothesize that this disparity in treatment efficacy may be attributable to temporally regulated BRAFi treatment-induced changes to the iTME.
Drug-induced changes in the iTME pre and post-resistance were characterized in tumors of engrafted transgenic BRAF/Pten mice using scRNA-seq, flow cytometry, and ELISA. T cell proliferation assays were used to assess functional changes in tumor-conditioned myeloid cells.
BRAFi treatment attenuated immunosuppressive myeloid activation pre-resistance, while BRAFi resistance was associated with enhanced tumor-associated macrophage (TAM) recruitment and immunosuppressive myeloid subset activation. However, the addition of CDDO-Me to BRAFi at resistance reversed these outcomes and rescued the ability of TAMs to induce T cell proliferation.
The iTME changes with tumor progression and responds dynamically to BRAFi treatment and resistance. This work establishes for the first time that BRAFi promotes myeloid-mediated induction of T cell activation, which is lost at resistance but can be rescued with the addition of CDDO-Me. Because BRAFi resistance and iTME immunosuppression is reversed by CDDO-Me treatment, these results provide the foundation for its potential use in combination therapies for melanoma.
Dartmouth Health Cancer Center Developmental Funding (Prouty Pilot Grant)
Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)
Chen-Yu Wang, G. Torres, Helen C. Jarnagin et al.· Journal of Immunology· 0 citations
T cell exhaustion limits the durability of adoptive cell therapy (ACT) in solid tumors. Because PI3Kδ signaling governs T cell differentiation, we hypothesized that transient, high-dose PI3Kδ inhibition would endow T cells with durable stemness and metabolic fitness to resist terminal exhaustion and alter the immune composition of the tumor microenvironment (TME).
Mouse and human T cells were treated in vitro with the PI3Kδ inhibitor CAL-101 (30 uM) prior to chronic antigen stimulation and ACT into B16 melanoma. Metabolic fitness was assessed by mitochondrial dependence and spare respiratory capacity. Single-cell RNA sequencing and spatial transcriptomics profiled T cell states, spatial localization, and TME remodeling post ACT. Pathway analyses interrogated oxidative phosphorylation (OXPHOS), glycolysis, proliferation, inflammatory signaling, and myeloid composition.
CAL-101—treated T cells acquired enhanced stemness and metabolic fitness, with increased mitochondrial dependence and spare respiratory capacity while maintaining normal basal metabolism. Under chronic stimulation, including in human T cells, they resisted terminal exhaustion and preserved stem-like properties. In tumors, treated cells preferentially differentiated into progenitor exhausted T cells (Tpex), displayed superior infiltration, and upregulated the Cxcl10/Cxcr3 axis. Tumors harboring CAL-101—treated T cells showed reduced glycolysis, OXPHOS, and proliferation alongside increased pro-inflammatory signaling and fewer immunosuppressive tumor-associated macrophages. Single-cell analysis revealed CAL-101 treated T cells concurrently increased OXPHOS, proliferation, and immune signaling pathways.
Brief PI3Kδ inhibition programs T cells with stemness and metabolic fitness that favor Tpex differentiation, resist terminal exhaustion, and remodel the TME toward an inflammatory state, supporting a practical strategy to improve ACT efficacy in solid tumors.
NIH RO1 grant: CA257954, Dartmouth TQCR Training Grant: T32CA260626
Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)
Alexandrea Turnquist, Azka Javaid, F. Kolling et al.· Journal of Immunology· 0 citations