Tumor-Associated Macrophages May Improve Outcomes in Metastatic RCC

To improve the efficacy of PD-1 blockade, investigators have reprogrammed tumor-associated macrophages (TAMs) from a protumorigenic to an antitumorigenic state, as high levels of CD163-positive TAMs are associated with improved outcomes to anti–PD-1 therapy in metastatic clear cell renal cell carcinoma (ccRCC), according to Berkay Şimşek, MD.¹

During a presentation at the 2025 Kidney Cancer Research Summit, Şimşek outlined the goals of assessing the association of CD163-positive TAMs with clinical outcomes to first-line nivolumab (Opdivo) in metastatic ccRCC, and to investigate whether TAMs and exhausted CD8-positive tumor-infiltrating lymphocytes (TILs) are located and interact within a “spatially defined niche.”

The Role of TAMs in RCC

TAMs promote immune suppression in the tumor microenvironment (TME), despite having a reputation for being associated with resistance to immune checkpoint inhibitors in other cancer types, including colorectal cancer and pancreatic ductal adenocarcinoma, along with observed responses in Hodgkin lymphoma, Şimşek, a research fellow in Pathology at the Brigham and Women’s Hospital in Boston, Massachusetts, explained in the presentation. Nevertheless, “the role [of TAMs] as predictors of clinical outcomes still remains somewhat unclear,” he noted.

Furthermore, TAMs promote T-cell exhaustion based on observations from preclinical models.

“Chemokines cause recruitment of monocytes from blood circulation into [the] TME, and those monocytes develop into differentiated macrophages,” Şimşek stated. “Ineffective antigen presentation, immunosuppressive ligand-receptor interactions between TAMs and TILs, coupled with the secretion of immunosuppressive cytokines into the TME, cause exhaustion of cytotoxic T cells and diminish their ability to mount an effective response against the tumor.”

Şimşek noted that the first method to investigate the respective goals was to analyze pretreatment tumor samples from 67 patients who were enrolled in the phase 2 HCRN GU16-260 trial (NCT03117309), which evaluated first-line nivolumab in patients with metastatic ccRCC.

HCRN GU16-260 also examined the association between PD-1 expression on tumor-infiltrating regulatory T cells (Tregs) and resistance to first-line nivolumab in advanced ccRCC.²

Of note, the percentage of PD-1–positive Tregs did not have a statistically significant association with progression-free survival (PFS; HR, 2.62; P =.169) or objective response rate (ORR; OR, 0.72; P =.42).

“To identify TAMs and CD8-positive TILs in various states of exhaustion, we utilized the workflow previously developed in our lab based on multiplex immunofluorescent stain in the tissue," Şimşek said.

"We identified CD163- positive TAMs [and] nonterminal exhausted CD8-positive TILs as the cells defined with coexpression of CD8 and PD-1 but negative for TIM3 and LAG3, and terminally exhausted CD8-positive TILs, with cells defined with coexpression of CD8, PD-1, and either TIM3 or LAG3,” Şimşek continued.

Additionally, in the second method, investigators assessed statistical and bioinformatics analyses to help inform the aims to observe potential associations of density of CD163-positive TAMs with PFS and ORR that were assessed via univariable Cox and logistic regression models, respectively.¹ Another aim included a spatial proximity analysis performed using the “sf” package within the R software.

Density of CD163-Positive TAMs

Based on the efficacy data, focusing on the density of CD163-positive TAMs with firstline nivolumab in patients with metastatic ccRCC, the unadjusted and adjusted for International mRCC Database Consortium risk group (favorable vs poor/intermediate) ORs for ORR were 2.21 (95% CI, 1.33–3.69; P =.002) and 2.58 (95% CI, 1.43–4.64; P =.002), respectively.

Moreover, the respective unadjusted and adjusted PFS ORs were 0.77 (95% CI, 0.61–0.97; P =.029) and 0.78 (95% CI, 0.62–0.98; P =.032).

Additionally, a high density of CD163- positive TAMs was associated with improved ORR and PFS on first-line nivolumab. Specifically, among patients with a high density (n = 34), 65% achieved a response compared with 15% of patients who had low density (n = 5/33; P <.001).

T he median PFS was 16.6 months (95% CI, 5.5-32.9) vs 5.5 months (95% CI, 4.1–10.6) in patients with high and low density, respectively (P =.009).

Spatial Proximity Analysis and the Role of Exhausted CD8-Positive TILs

Regarding the spatial proximity analysis, Şimşek noted that the density of terminally exhausted CD8-positive TILs and the density of nonterminally exhausted CD8-positive TILs were determined within a 30 µm radius area that focused on CD163-positive TAMs—determined as the proximal area—and outside of this area, which was the nonproximal area.

“[We examined the] areas and for both exhausted TIL subsets, we calculated their enrichment levels in the proximal vs nonproximal areas, and compared their enrichment levels with each other,” Şimşek explained.

The densities of TILs in the proximal and nonproximal areas of TAMs were compared, and investigators established that the density of nonterminally exhausted CD8-positive TILs was higher in areas that were proximal to TAMs vs their densities in nonproximal areas to TAMs, he reported.

“Both terminally exhausted TIL subsets were enriched in proximity of the CD163-positive TAMs, but when we compared their enrichment levels, we observed that enrichment levels for terminally exhausted CD8-positive TILs in proximity of the CD163-positive TAMs were significantly higher compared with the enrichment levels of nonterminally exhausted CD8-positive TILs,” Şimşek concluded.

REFERENCES:

1. Şimşek B. CD163+ tumor-associated macrophages and clinical outcomes to first-line nivolumab therapy in patients with metastatic clear cell renal cell carcinoma: insights from the HCRN GU16-260 trial. Presented at: 2025 Kidney Cancer Research Summit; July 17-18, 2025; Boston, MA.

2. Mohanna R, Şimşek B, El Ahmar N, et al. Association between PD-1 expression on tumor-infiltrating regulatory T cells and resistance to first-line nivolumab in advanced clear cell renal cell carcinoma: insights from the HCRN GU16-260 clinical trial. J Clin Oncol. 2025;43(suppl 5):590. doi:10.1200/ JCO.2025.43.5_suppl.590