Spatial expression of fibroblast activation protein-α in clear cell renal cell carcinomas revealed by multiplex immunoprofiling analysis of the tumor microenvironment.

Clear cell renal cell carcinoma (ccRCC) is one of the most challenging neoplasms because of its phenotypic variability and intratumoral heterogeneity. Because of its variability, ccRCC is a good test bench for the application of new technological approaches to unveiling its intricacies. Multiplex immunofluorescence (mIF) is an emerging method that enables the simultaneous and detailed assessment of tumor and stromal cell subpopulations in a single tissue section. This novel approach represents a promising step forward for analyzing the microenvironmental cell composition and distribution across the tumor and understanding its possible interactions with tumor cells. This study provides the first characterization of the spatial distribution of fibroblast activation protein-α (FAP)-expressing cancer-associated fibroblasts (FAP + CAFs) in conjunction with lymphoid (CD4 + , CD8 + , CD4 + FOXP3 + , and CD20 +) and myeloid (CD68 +) cells in tissue sections from ccRCC in their early phases of evolution (n = 88). Both the tumor center and periphery were analyzed with mIF. FAP + CAFs and tumor-infiltrating lymphocytes (TILs) were significantly concentrated at the tumor periphery. Additionally, elevated percentages of FAP + CAFs were correlated with larger tumors and synchronous metastases. Increased levels of CD68 +  and CD4 + FOXP3 +  cells (above the 75th percentile) were linked to worse cancer-specific survival (CSS) in patients with ccRCC. Furthermore, significant correlations emerged among FAP + CAFs, TILs, and CD68 +  cells, and the co-occurrence of elevated FAP + CAFs, T-cytotoxic (CD8 +), T-regulatory (CD4 + FOXP3 +) cells, and macrophages (CD68 +) at the tumor center were independently associated with worse CSS. These findings suggest that FAP + CAFs contribute to the aggressiveness of ccRCC, and their role is potentially mediated by their ability to foster an immunosuppressive environment within the renal tumor microenvironment.