Comprehensive proteomic profiling of plasma samples associated with response or resistance to immune checkpoint inhibitors (ICI) in patients with renal cell carcinoma (RCC).

562 Background: ICI-based therapies are the cornerstone of treatment for advanced RCC. While many studies have focused on tumor-based biomarkers, circulating factors play an important role in therapeutic response. This study utilized a high dimensional proteomic platform to investigate plasma proteins from RCC patients undergoing ICI-based therapies to identify potential biomarkers associated with treatment outcomes. Methods: A total of 43 plasma samples (n = 40 clear cell; n = 3 non-clear cell) were collected from 33 advanced RCC patients, with 16 paired samples (pre- and post-treatment) from 6 patients and 27 unpaired samples. The cohort included patients treated with ICI monotherapy (n = 22), ICI + ICI (n = 13), ICI + VEGF inhibitors (n = 7), and ICI + CCR2/CCR5 antagonist (n = 1). For this study, we analyzed pre-treatment samples from responders (R) (n = 8; complete or partial responses), and non-responders (NR) (n = 4; progressive disease). We performed plasma proteomic analysis using the SomaScan 11k proteomic platform, and Mann-Whitney U-test comparisons between ICI-naïve samples of R and NR groups. We also performed a paired test between ICI-naïve and ICI-exposed samples in R (n = 3 patients with paired samples). Nominal p-values are reported. Results: All 43 samples passed quality control. In ICI-naïve samples, we observed that ICAM1 and ITIH3 levels were significantly higher in R compared to NR (p = 0.016 for both). Conversely, CILP2 and leptin were significantly elevated in NR (p = 0.016, p = 0.004, respectively). Further analysis for treatment evolution through paired samples showed that PD-1, CXCL9, and HLA-B were significantly elevated in ICI-exposed samples compared to ICI-naïve samples in R (p = 0.021, p = 0.022, p = 0.041, respectively). Conclusions: Our exploratory proteomic analysis identified higher ICAM1 and ITIH3 levels in ICI responders, which may reflect anti-tumor inflammation and the recruitment of immune cells to tumors. Elevated CILP2 and leptin levels were observed in ICI non-responders, highlighting their potential contributions to an immunosuppressive environment through Tregs and the TGF-β pathway. Beyond the potential biomarkers, the post-ICI elevation of CXCL9 and HLA-B in responders suggests that these may be linked to sustained immune activation during treatment, offering a foundation to understand treatment evolution in RCC.