Paradoxical Effect of Myosteatosis on the Immune Checkpoint Inhibitor Response in Metastatic Renal Cell Carcinoma

Abstract

Background: Treatment for metastatic renal cell carcinoma (mRCC) has shifted from tyrosine kinase inhibitor (TKI) therapy to immune checkpoint inhibitor (ICI)-based therapy, improving outcomes but with variable individual responses. This study investigated the prognostic implications of pretreatment low skeletal muscle mass (LSMM) and myosteatosis in patients with mRCC undergoing first-line ICI-based therapies, comparing outcomes between PD-1 inhibitor + CTLA-4 inhibitor and PD-1 inhibitor + TKI, incorporating single-cell RNA sequencing.

Methods: A retrospective analysis was performed on 90 patients with mRCC treated with ICI-based therapies between November 2019 and March 2023. Patients were grouped based on whether they received PD-1 inhibitor + CTLA-4 inhibitor or PD-1 inhibitor + TKI combinations. LSMM was defined as skeletal muscle index below 40.8 cm²/m² for men and 34.9 cm²/m² for women. Myosteatosis was defined using skeletal muscle density, with cut-off values < 41 HU for BMI < 25 kg/m² and < 33 HU for BMI ≥ 25 kg/m². Progression-free survival (PFS) and overall survival (OS) were compared using Kaplan-Meier curves and multivariable models. Single-cell RNA sequencing was performed on pretreatment samples to compare the immune microenvironment between patients with and without myosteatosis.

Results: The study cohort (26.7% female; median age: 60.5 years) included 59 patients (65.6%) treated with PD-1 inhibitor + CTLA-4 inhibitor and 31 patients (34.4%) treated with PD-1 inhibitor + TKI. LSMM was present in 18.9% of patients, and myosteatosis in 41.1%, with comparable proportions across groups. During follow-up, 29 patients (32.2%) died: 16 in the PD-1 inhibitor + CTLA-4 inhibitor group and 13 in the PD-1 inhibitor + TKI group. The overall 1-year mortality rate was 22.2%, and PFS rate was 53.3%. Myosteatosis predicted poor OS (HR, 5.389; p = 0.008) and PFS (HR, 2.930; p = 0.022) in the PD-1 inhibitor + TKI group but was protective for PFS (HR, 0.461; p = 0.049) in the PD-1 inhibitor + CTLA-4 inhibitor group. LSMM did not significantly affect outcomes in either group. Single-cell RNA sequencing revealed higher CTLA-4 expression in regulatory T cells and more effector memory CD8⁺ T cells in patients with myosteatosis, whereas patients without myosteatosis had more anti-tumoural non-classical monocytes.

Conclusions: Myosteatosis negatively impacts OS and PFS in patients with mRCC treated with PD-1 inhibitor + TKI therapy but is protective for PFS in those treated with PD-1 inhibitor + CTLA-4 inhibitor therapy. Altered checkpoint expression and immune cell composition associated with myosteatosis may contribute to these differential responses.

Keywords: body composition; immune checkpoint inhibitors; low skeletal muscle mass; metastatic renal cell carcinoma; myosteatosis; single‐cell RNA sequencing.

FIGURE 1

Patient selection process.

FIGURE 2

Automated segmentation of skeletal muscles. (a) Axial postcontrast computed tomography (CT) image at the third lumbar vertebra level in a 70‐year‐old male with a BMI of 28.9 kg/m². (b) Visualization of segmented skeletal muscles highlighted in red overlays. SMI = 49.35 cm²/m² and SMD = 24.21 HU, indicating myosteatosis in the patient. BMI, body mass index; HU, Hounsfield unit; SMI, skeletal muscle index; SMD, skeletal muscle density.

FIGURE 3

Kaplan–Meier curve analysis of overall survival (OS) and progression‐free survival (PFS) based on treatment regimen and muscle‐related parameters (low skeletal muscle mass [LSMM] and myosteatosis). (a) Kaplan–Meier curve analysis of OS and PFS according to treatment regimen and the presence of LSMM. (b) Kaplan–Meier curve analysis of OS and PFS according to treatment regimen and presence of myosteatosis.

FIGURE 4

Single‐cell RNA‐seq analysis and differences in CD8⁺ T cells: Group 1 (without myosteatosis, n = 7) vs. Group 2 (with myosteatosis, n = 5). (a) UMAP plot of 92 288 cells from 12 patients with mRCC, coloured by global cell types. (b) Proportions of global cell subtypes in each sample according to myosteatosis group. (c) UMAP plot of CD8⁺ T cells, coloured by cell subtypes. (d) Proportions of CD8⁺ T‐cell subtypes in each sample according to myosteatosis group. (e) GSEA using the Reactome database for DEGs between Group 1 and Group 2 in CD8⁺ effector memory cells; (above) GSEA results for tissue; (below) GSEA results for PBMCs. DEGs p.adj < 0.05, GSEA p < 0.05. (f) Differential gene expression related to immunotherapy response between two groups in all CD8⁺ effector memory cells. Dots represent the mean expression.

FIGURE 5

Differential expression of immune checkpoint molecules in T cells and monocytes: Group 1 (without myosteatosis, n = 7) vs. Group 2 (with myosteatosis, n = 5). (a) UMAP plot of CD4⁺ T cells, coloured by cell subtypes. (b) Proportions of CD4⁺ T‐cell subtypes in each sample according to myosteatosis group. (c) Higher expression of immune checkpoint molecules in CD4⁺ T, CD8⁺ T, and Tregs of the tumour microenvironment in a group of patients with myosteatosis. A patient with a singular CD4⁺ T‐cell count was excluded from the CD4⁺ T and Treg plot. (d) UMAP plot of myeloid cells, coloured by cell subtypes. (e) Proportions of myeloid cell subtypes in each sample according to myosteatosis group. (f) GSEA using GO biological process for DEGs of non‐classical monocytes. DEGs p.adj < 0.05, GSEA p < 0.01.