Gut Microbiota Modulation for Immunotherapy Resensitization in Advanced Renal Cell Carcinoma

The combination of immune checkpoint inhibitors (ICIs) and tyrosine kinase inhibitors (TKIs) has significantly improved clinical outcomes in patients with advanced renal cell carcinoma (RCC). However, 40%-60% of patients still develop primary or acquired resistance. For those with resistant disease, current immune rechallenge strategies have yet to demonstrate clear clinical benefit. Emerging evidence indicates that the gut microbiota plays a critical role in modulating responses to immunotherapy. Microbiota-modulating approaches, including fecal microbiota transplantation (FMT) and live bacterial formulations such as CBM588, have shown preliminary potential to enhance sensitivity to immunotherapy and improve patient outcomes. Nevertheless, whether gut microbiota modulation can resensitize advanced RCC to immunotherapy remains to be investigated.

The REMEDY-RCC trial is an investigator-initiated, prospective, open-label, phase II, parallel two-cohort exploratory study primarily designed to investigate whether gut microbiota modulation can restore sensitivity to immunotherapy in patients with advanced RCC. Given the substantial differences in the tumor immune microenvironment and response to ICIs between clear cell RCC (ccRCC) and non-clear cell RCC (nccRCC), this study employs a parallel two-cohort design to stratify these two patient populations: a primary cohort consisting of patients with metastatic ccRCC, and an exploratory cohort consisting of patients with metastatic nccRCC. The primary and secondary endpoints will be analyzed in the primary cohort, whereas the exploratory cohort will be used solely for exploratory and descriptive analyses. The study plans to enroll approximately 33 adult patients with advanced or metastatic RCC, including 27 with metastatic ccRCC and 6 with metastatic nccRCC. Eligible patients will receive the following sequential interventions: bowel decontamination with amoxicillin-clavulanate potassium followed by polyethylene glycol (PEG) solution, high-dose gut colonization and maintenance supplementation with live Clostridium butyricum powder combined with soluble dietary fiber, and immune rechallenge therapy consisting of a PD-1 immune checkpoint inhibitor (ICI) combined with four cycles of a CTLA-4 ICI, followed by maintenance therapy with the PD-1 ICI alone. Treatment will continue until disease progression, unacceptable toxicity, completion of the planned treatment cycles, or withdrawal of consent.

The REMEDY-RCC trial requires specific follow-up for enrolled patients. Radiological response is assessed longitudinally using computed tomography (CT). Tissue and body fluid samples collected from patients will be used for biomarker and multi-omic analyses.

The primary endpoint of the trial is the objective response rate (ORR) in the primary cohort, as assessed by the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1. Sample size for the primary cohort was determined using Simon's optimal two-stage design, with a one-sided α of 0.10 and power (1-β) of 0.80. The unacceptable response rate (P0) was set at 17.4%, based on the ORR observed in the FRACTION-RCC study for nivolumab plus ipilimumab rechallenge in patients with metastatic ccRCC who had progressed after prior immunotherapy. The target response rate (P1) was established considering that FMT has been shown to increase ORR by approximately 20% in immunotherapy-resistant melanoma. Given that metastatic RCC and melanoma are both considered immunologically responsive tumor types, a comparable therapeutic benefit from gut microbiota remodeling is anticipated. Accordingly, P1 was set at 37.4%. This effect size is clinically meaningful and would be non-inferior to the clinical efficacy of cabozantinib in metastatic RCC that has progressed following immunotherapy.

The primary cohort will initially enroll six patients for safety assessment. If the treatment is deemed safe, further accrual will follow Simon's two-stage design, and enrollment of the exploratory cohort will be considered. After these six patients, an additional six patients will be enrolled, bringing the total to 12, at which point an interim analysis will be performed. If the number of objective responses at the interim analysis is ≤ 2, the trial will be terminated early. If ≥3 objective responses are observed, an additional 12 patients will be enrolled, resulting in a total sample size of 24 patients. Accounting for a potential 10% dropout rate, the study plans to enroll 27 patients in total.

The exploratory cohort is planned to enroll no more than 6 patients (not exceeding 20% of the total enrollment), with a fixed-sample descriptive design. The sample size calculation is not based on statistical hypothesis testing, and all efficacy endpoints will be reported using descriptive statistics. The total planned sample size is 33 patients, comprising 27 patients in the primary cohort and 6 patients in the exploratory cohort.