Poster #45: Colette Trouillot MS

Foxd3 expression modulates the tumor immune microenvironment in cutaneous melanoma

Colette Trouillot, M.S. 1, 2, Dan A. Erkes, PhD 1, 3, Diana Melissaratos1, Scott D. Varney, PhD 1, William D. Madden 1, Timothy J. Purwin, PhD 1 and Andrew E. Aplin, PhD 1, 3 1 Department of Pharmacology, Physiology and Cancer Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA. 2School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA, 19104, USA. 3Sidney Kimmel Comprehensive Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USA.

Advances in immune checkpoint (IC) and mitogen activate protein kinase (MAPK) pathway inhibitor therapies have improved progression free survival and overall survival for cutaneous melanoma patients in part due to changes in tumor immune microenvironment (TIME). Roughly 50% of melanomas have activating mutations in v-Raf murine sarcoma viral oncogene homolog B (BRAF). MAPK inhibitor (MAPKi) treatment is approved for treating these BRAF-mutant melanomas while IC inhibitors (ICi) are approved for all cutaneous melanomas. The neural crest transcription factor Forkhead box D3 (FOXD3), known for its role in early embryoblast formation, is increased during MAPKi treatment. FOXD3 downregulates the immune checkpoint protein V-domain Ig suppressor of T cell activation (VISTA); however, additional downstream impact on the TIME is not fully clarified. We used RNA-sequencing (RNA-seq) data from inducibly expressed FOXD3 melanoma cell lines to identify activated and repressed gene signatures for FOXD3. Enrichment analysis confirmed the repressed gene signature in bulk and single cell RNA-seq data. Gene signature scoring of additional publicly available RNA-seq data confirmed FOXD3 expression increases with MAPKi treatment in cell lines and patient data. We analyzed the downregulated signature of malignant tumors against proportions of immune cell types using RNA-seq gene-set activity scoring analyses and found CD8+ T-cell, myeloid derived suppressor cell (MDSC), and dendritic cell (DC) scores were correlated with FOXD3 repressed gene signature score. In vivo mouse experiments confirmed that higher levels of FOXD3 are associated with decreased levels of MDSCs, DCs, and CD8+ T-cells. These findings suggest FOXD3 shapes the TIME by creating an immune-desert phenotype, with almost no immune cells.