Nature Communications | Antitumor Activity of High-Dose Anti-CTLA-4 Combined with Paclitaxel in Refractory Metastatic Urothelial Carcinoma

This study provides a novel chemo-immunotherapy strategy for patients with metastatic urothelial carcinoma (mUC) who have developed resistance to anti-PD-(L)1 therapy, suggesting that high-dose anti-CTLA-4 may reactivate T-cell responses in an otherwise immunosuppressed microenvironment, offering critical guidance for the design of future clinical trials.

 

Literature Overview

This article, titled “Tremelimumab with or without durvalumab in combination with paclitaxel in metastatic urothelial cancer: phase I/II ICRA trial” and published in Nature Communications, systematically investigates the efficacy and safety of combining paclitaxel with high-dose tremelimumab (anti-CTLA-4) in patients with metastatic urothelial carcinoma (mUC) who have progressed after platinum-based and anti-PD-(L)1 therapies. The study employs a multicenter, open-label phase Ib-II design, evaluating objective response rates across different combination regimens and integrating transcriptomic analysis and mouse models to elucidate underlying mechanisms. Results show that paclitaxel combined with high-dose anti-CTLA-4 achieves an objective response rate of 26%, significantly higher than monotherapy, with manageable safety. This study provides clinical evidence that immune reactivation remains possible even after immune checkpoint inhibitor resistance.

Background Knowledge

Metastatic urothelial carcinoma (mUC) lacks effective treatment options after failure of platinum-based chemotherapy and anti-PD-(L)1 therapy, representing a significant unmet clinical need. Although anti-PD-(L)1 agents are established in the second-line setting, most patients eventually progress, entering a state of anti-PD-(L)1 resistance. Whether further benefit can be derived from other immunotherapies, particularly anti-CTLA-4, remains unclear. CTLA-4 regulates early T-cell activation and acts non-redundantly with the PD-1 pathway, theoretically enhancing T-cell priming. However, previous anti-CTLA-4 monotherapy in mUC showed limited activity, possibly due to suboptimal dosing. The HIMALAYA trial demonstrated improved survival with high-dose tremelimumab in liver cancer, highlighting dose-dependent immune activation as a key factor. Yet, data on the feasibility and efficacy of high-dose anti-CTLA-4 combined with chemotherapy in mUC are lacking. Furthermore, the tumor microenvironment (TME) may become highly immunosuppressive after multiple lines of therapy, limiting responsiveness to immunotherapy. Therefore, this study aims to determine whether high-dose anti-CTLA-4 combined with paclitaxel can restore antitumor immunity in anti-PD-(L)1-resistant mUC, while using transcriptomic analysis to uncover the mechanism and identify potential biomarkers for future studies.

 

 

Research Methods and Experiments

The study employed a three-stage design: a safety lead-in phase, a randomized phase II main trial, and an expansion phase. A total of 53 patients were enrolled and assigned to three arms: Arm A (paclitaxel + high-dose tremelimumab 750mg), Arm B (paclitaxel + tremelimumab 300mg + durvalumab), and Arm C (tremelimumab monotherapy). The primary endpoint was objective response rate (ORR), assessed by RECIST 1.1 criteria. Overall survival (OS) and progression-free survival (PFS) were evaluated using the Kaplan-Meier method, and baseline and on-treatment tumor tissues were collected for RNA sequencing and immunohistochemical analysis. Additionally, the study utilized the G69 mouse bladder cancer model to verify whether paclitaxel induces immunogenic cell death (ICD) and assessed the synergistic antitumor effects of combining it with anti-CTLA-4. These experimental systems collectively support the mechanistic interpretation of the clinical findings.

Key Conclusions and Perspectives

• Paclitaxel combined with high-dose tremelimumab (Arm A) achieved an ORR of 26% (88% CI [14, 36%]), significantly higher than anti-CTLA-4 monotherapy (8%), indicating clinical activity of anti-CTLA-4 combined with chemotherapy in refractory mUC and suggesting that future studies should prioritize high-dose regimens.
• The ORR of the combination therapy was independent of PD-L1 expression status or metastatic site, suggesting broad applicability across patient populations and providing a rationale for pan-population enrollment in future clinical trials.
• Transcriptomic analysis revealed that patients with high baseline expression of CD8+ T-cell effector and IFN-γ signaling were more likely to achieve durable responses, and these inflammatory signals were further upregulated post-treatment, indicating that the inflammatory state of the tumor microenvironment is a potential predictive biomarker and should be included in future biomarker validation studies.
• Mouse models confirmed that paclitaxel induces immunogenic cell death and synergizes with anti-CTLA-4 to produce antitumor effects, providing mechanistic support for the observed clinical efficacy and suggesting that paclitaxel has immunomodulatory functions beyond its cytotoxic effects.
• Although the triplet regimen (Arm B) had higher toxicity (75% Grade 3–4 AE), the doublet regimen (Arm A) showed manageable safety (45% Grade 3–4 AE), supporting its use as a viable treatment strategy, particularly in patients with good performance status.

Research Significance and Prospects

This study challenges the traditional notion that “immune resistance after anti-PD-(L)1 failure implies no further benefit from immunotherapy” by demonstrating that antitumor immunity can be reactivated via high-dose anti-CTLA-4 even after immunotherapy failure, laying the foundation for developing later-line immunotherapeutic strategies. This finding has important implications for drug development: future efforts should explore high-dose or novel CTLA-4 formulations combined with other immunomodulators (e.g., antibody–drug conjugates) to enhance efficacy while reducing toxicity. Meanwhile, IFN-γ and CD8+ T-cell-related gene signatures can serve as candidate biomarkers to guide patient stratification and advance precision immunotherapy. Furthermore, this study supports conducting larger phase III trials in mUC to validate the survival benefit of this dual-combination regimen, which could potentially reshape the later-line treatment landscape.

 

 

Conclusion

This study represents a significant breakthrough in the later-line treatment of metastatic urothelial carcinoma. In the challenging context of anti-PD-(L)1 resistance, the combination of paclitaxel and high-dose anti-CTLA-4 achieved a 26% objective response rate, markedly superior to monotherapy, and mechanistic analyses indicate that it restores T-cell function by enhancing inflammatory features within the tumor microenvironment. This finding not only expands the window for immunotherapy application but also suggests that the immune system retains plasticity even after PD-1 pathway inhibition. From bench to bedside, this study provides proof-of-concept for constructing more effective immunotherapy combinations, particularly emphasizing the importance of CTLA-4 dosing and synergy with chemotherapy. In the future, with biomarker-guided patient selection, such regimens may become standard options for refractory mUC, reshaping current care pathways and offering renewed hope for patient survival. Moreover, these findings offer valuable insights for treating other immunologically “cold” tumors, advancing the field toward more precise and durable immune interventions.

 

Sarah M H Einerhand, Hamza Ali, Stephen Q Wong, Britt B M Suelmann, and Michiel S van der Heijden. Tremelimumab with or without durvalumab in combination with paclitaxel in metastatic urothelial cancer: phase I/II ICRA trial. Nature Communications.