Multiplex immunofluorescent detection of T-cell and myeloid subsets reveals histologic subtype differences in the immunosuppressive landscape of human basal cell carcinoma (BCC)

Summary: Abstract Body: BCC is the most diagnosed skin cancer worldwide. Most skin cancers, including BCC, are known to have an immunosuppressive tumor microenvironment, yet little is known about how immune environments differ by BCC histologic subtype. Since histologic subtype correlates with disease aggressiveness, an understanding of immune microenvironmental differences across subtypes may guide treatment decisions. Utilizing the Vectra Polaris multiplex immunofluorescence system from Akoya Biosciences, we designed two staining panels, targeting either T-cells (CD3, CD4, CD8, FOXP3, PD1) or myeloid cells (neutrophil elastase, CD68, CD163, HLADR, CD1c). PanCK and DAPI were included to stain tumor nests and live cells respectively. A series of formalin-fixed paraffin-embedded (FFPE) BCC tumor specimens (n = 30) were analyzed with both the T-cell and myeloid panels. Most immune cells appeared to reside in the peritumoral margin, so we used a boundary zone of 150 µm around tumor nests to determine immuno-phenotypes. A CD8/T-reg ratio and a M1/M2 macrophage ratio of < 0.5 was observed across all BCC specimens, confirming an overall immunosuppressive phenotype. When assessing different histologic subtypes, we found that infiltrative BCC subtypes had a significantly lower proportion of CD8 T cells (p = .038) and greater proportions of T-regs (p = .039), as well as significantly lower CD8/T-reg (p = .048) and M1/M2 (p = .034) ratios compared to non-infiltrative subtypes. This indicates that infiltrative BCC subtypes are associated with a more immunosuppressed microenvironment, potentially accounting for their more aggressive nature. Overall, we demonstrate a method to determine T cell and myeloid profiles in fixed (FFPE) tissue of human BCC, to identify immune profile differences. Future studies using this technique will help determine how various treatments can reverse the immunosuppressive nature of BCC, to improve long-term clearance. Alan Shen¹, Lauren Heusinkveld¹, Ajay Zalavadia¹, Andrelie Branicki¹, Sanjay Anand¹, Edward Maytin¹ 1. Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States. UV Biology/Injury and Non-melanoma Cancers