Previous studies have suggested that the gut microbiome influences the response to checkpoint inhibitors (CPIs) in patients with cancer. CBM588 is a bifidogenic live bacterial product that we postulated could augment CPI response through modulation of the gut microbiome. In this open-label, single-center study (NCT03829111), 30 treatment-naive patients with metastatic renal cell carcinoma with clear cell and/or sarcomatoid histology and intermediate- or poor-risk disease were randomized 2:1 to receive nivolumab and ipilimumab with or without daily oral CBM588, respectively. Stool metagenomic sequencing was performed at multiple timepoints. The primary endpoint to compare the relative abundance of Bifidobacterium spp. at baseline and at 12 weeks was not met, and no significant differences in Bifidobacterium spp. or Shannon index associated with the addition of CBM588 to nivolumab–ipilimumab were detected. Secondary endpoints included response rate, progression-free survival (PFS) and toxicity. PFS was significantly longer in patients receiving nivolumab–ipilimumab with CBM588 than without (12.7 months versus 2.5 months, hazard ratio 0.15, 95% confidence interval 0.05–0.47, P = 0.001). Although not statistically significant, the response rate was also higher in patients receiving CBM588 (58% versus 20%, P = 0.06). No significant difference in toxicity was observed between the study arms. The data suggest that CBM588 appears to enhance the clinical outcome in patients with metastatic renal cell carcinoma treated with nivolumab–ipilimumab. Larger studies are warranted to confirm this clinical observation and elucidate the mechanism of action and the effects on microbiome and immune compartments.

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The treatment landscape for metastatic renal cell carcinoma (mRCC) and urothelial carcinoma (mUC) has evolved rapidly in recent years with the approval of several checkpoint inhibitors. Despite these advances, survival rates for metastatic disease remain poor, and additional strategies will be needed to improve the efficacy of checkpoint inhibitors. Combining anti-VEGF/VEGFR agents with checkpoint inhibitors has emerged as a potential strategy to advance the immunotherapy paradigm, because VEGF inhibitors have immunomodulatory potential. Cabozantinib is a tyrosine kinase inhibitor (TKI) whose targets include MET, AXL, and VEGFR2. Cabozantinib has a unique immunomodulatory profile and has demonstrated clinical efficacy as a monotherapy in mRCC and mUC, making it a potentially suitable partner for checkpoint inhibitor therapy. In this review, we summarize the current status of immunotherapy for mRCC and mUC and discuss the development of immunotherapy-TKI combinations, with a focus on cabozantinib. We discuss the rationale for such combinations based on our growing understanding of the tumor microenvironment, and we review in detail the preclinical and clinical studies supporting their use.

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Background Cluster of differentiation 70 (CD70) is frequently expressed in renal cell carcinoma (RCC) and has immunomodulatory properties. An antibody‐drug conjugate targeting CD70, SGN‐CD70A, was developed to treat patients with CD70‐positive RCC. Methods The objective of this phase 1, open‐label, dose‐escalation, multicenter study was to evaluate the safety and tolerability of SGN‐CD70A and establish its maximum tolerated dose in patients with CD70‐positive, metastatic RCC (mRCC). All subtypes of RCC were permitted, and no limit was set on the number of prior therapies. Safety assessments consisted of monitoring and recording all adverse events (AEs) and dose‐limiting toxicities (DLTs). Treatment response was assessed by radiographic tumor evaluation according to the Response Evaluation Criteria for Solid Tumors, version 1.1. A model‐based, modified continual‐reassessment method was used to estimate the probabilities of DLT and response. Results The maximum tolerated dose was determined to be 30 μg/kg, with thrombocytopenia as the DLT. The most common AEs were fatigue (67%), anemia (61%), and thrombocytopenia (56%). Of 18 enrolled patients, 1 achieved a partial response and 13 achieved stable disease, for a clinical benefit rate of 78%. Limitations of the study included the heavily pretreated nature of patients, receipt of a median of 4 prior lines of therapy (range, 1‐8 prior lines of therapy), and diminishing response potential. Conclusions The modest antitumor activity of SGN‐CD70A does not support its development in mRCC. However, given the high disease control rate in a heavily pretreated population and the modest toxicity profile, CD70 remains of interest because of its immunomodulatory properties.