Genomic Characteristics and Single-Cell Profiles After Immunotherapy in Fumarate Hydratase-Deficient Renal Cell Carcinoma

Abstract Purpose: Fumarate hydratase–deficient renal cell carcinoma (FHRCC) is highly malignant, but the urgent need for effective treatment remains unmet. We aimed to analyze the genomic characteristics and microenvironment of FHRCC and the cause of heterogeneous response to immune checkpoint inhibitor (ICI)-based treatment at single-cell level. Experimental Design: Whole-exome sequencing and IHC staining analyses were performed in 30 advanced FHRCC patients. Single-cell RNA sequencing following ICI-based treatment was conducted in 4 patients. The clinical characteristics, therapeutic effect, and follow-up data were analyzed. Results: The median tumor mutation burden was only 0.14 mutations per megabase. IHC staining showed an immune-active tumor microenvironment characterized by extensive CD8+ T-cell infiltration. ATM expression was inversely correlated with percentage of tumor-infiltrating CD8+ T cells. Trajectory analysis indicated gradually upregulated exhausted markers and an increased apoptotic trend of CD8+ T cells despite continuous exposure to ICI-based treatment. ICI-based treatment was associated with improved overall response rate (17.6% vs. 0%, P = 0.046) and disease control rate (DCR; 64.7% vs. 12.5%, P = 0.004) compared with tyrosine kinase inhibitor. Among patients with germline mutation, the ORR (16.7% vs. 0%, P = 0.086) and the DCR (66.7% vs. 14.3%, P = 0.011) were higher after ICI-based treatment. Conclusions: Immune infiltration is frequent in FHRCC. ICI-based treatment is a promising regimen, and treatment response depends on the functional status of tumor-infiltrating lymphocytes. ICI-based treatment cannot reverse the exhaustion of CD8+ T cells in patients with progressive disease, highlighting the need for additional therapeutic strategies.