NIVIPIT Trial Demonstrates Reduced Toxicity with Intratumoral Anti-CTLA4 in Metastatic Melanoma
Key Insights
The NIVIPIT trial showed that intratumoral ipilimumab combined with intravenous nivolumab significantly reduced severe toxicity compared to standard intravenous dual checkpoint blockade, with grade 3-4 treatment-related adverse events occurring in 22.6% versus 57.1% of patients at 6 months.
Intratumoral delivery achieved a 65.7% response rate in injected lesions and 50% in uninjected lesions, demonstrating both local efficacy and systemic immune activation with tenfold lower ipilimumab dosing.
Analysis of fresh tumor biopsies revealed that therapeutic benefit required pre-existing immune-active tumor microenvironments with MHC-I (search)/II expression, CD8 (search)+ T cells, and unexpectedly, higher baseline activated regulatory T cells and M2 macrophages.
The NIVIPIT trial has demonstrated that delivering ipilimumab directly into tumor lesions while maintaining systemic nivolumab can substantially reduce immune-related toxicity without compromising antitumor efficacy in patients with metastatic melanoma (search). This randomized, multicenter phase 1b study met its primary endpoint, showing a marked reduction in severe treatment-related adverse events compared to standard intravenous dual checkpoint blockade.
Significant Toxicity Reduction with Maintained Efficacy
The trial enrolled patients with previously untreated metastatic melanoma (search), randomizing them 2:1 to receive intravenous nivolumab combined with either intratumoral low-dose ipilimumab (0.3 mg/kg) or standard intravenous ipilimumab (3 mg/kg). The intratumoral approach used a tenfold lower ipilimumab dose, aiming to create high local drug exposure within the tumor microenvironment while minimizing systemic circulation.
The primary endpoint was convincingly met, with grade 3-4 treatment-related adverse events at 6 months occurring in 22.6% of patients receiving intratumoral ipilimumab versus 57.1% in the intravenous control arm. Cumulative grade 3-4 toxicity rates were similarly reduced at 32.5% versus 66.6%, respectively. These results compare favorably with the 60% rate reported with standard-dose intravenous ipilimumab plus nivolumab and the 33.9% rate observed in reduced-dose intravenous regimens.
Notably, no local toxicity at injection sites, no grade 3 or higher procedure-related adverse events, or grade 3 or higher gastrointestinal toxicity were observed in the intratumoral arm, supporting the safety and feasibility of this approach.
Local and Systemic Antitumor Activity
Despite the reduced dosing, intratumoral ipilimumab demonstrated robust antitumor activity. The response rate in injected lesions reached 65.7%, substantially exceeding the 50% response rate observed in uninjected lesions. This finding formally demonstrates the added value of anti-CTLA4 beyond anti-PD1 therapy, with patients serving as their own internal controls for dose-dependent efficacy.
High complete response rates were observed both in injected lesions (31%) and in uninjected target lesions (25%), exceeding those typically reported in melanoma trials and supporting a systemic component of intratumoral anti-CTLA4 activity. The response in uninjected lesions suggests an abscopal-like systemic immune effect, likely mediated by local immune priming, remodeling of tumor-draining lymph nodes, and limited systemic diffusion of ipilimumab.
Pharmacokinetic analyses confirmed markedly lower systemic ipilimumab exposure in the intratumoral arm, with peak serum concentrations approximately 20-fold lower despite a tenfold lower administered dose, suggesting partial retention within injected tumors and their draining lymph nodes.
Biomarker Insights and Mechanism of Action
Analysis of fresh tumor biopsies enabled identification of rapid, biologically grounded biomarkers predictive of response to combined checkpoint blockade. Therapeutic benefit was associated with higher baseline expression of MHC-I (search) and MHC-II (search) and with an abundance of adaptive immune effector cells, particularly an ongoing cytotoxic immune response involving MHC-I-restricted CD8 (search)+ T cells, including PD1+ subsets, together with MHC-II-dependent TH1 CD4 (search)+ T cells expressing TBX21 and CXCR3.
The study identified a coordinated B cell response as an integral component of antitumor immunity, with higher baseline expression of TFH and B cell markers in patients achieving durable clinical benefit and a strong correlation between tumor-infiltrating CD8 (search)+ T cells and CD20 (search)+ B cells.
Unexpectedly, tumors from patients who subsequently achieved durable clinical benefit had higher baseline levels of intratumoral regulatory T cells and M2 macrophages. The coexistence of abundant cytotoxic effector cells with immunosuppressive populations supports the requirement for ongoing intratumoral immunoediting for responsiveness to combined anti-PD1 plus anti-CTLA4 therapy.
Regulatory T Cell Depletion Mechanism
The study provided important mechanistic insights into anti-CTLA4 action in human tumors. Using flow cytometry analysis of fresh tumor samples, researchers demonstrated that the number of CD4 (search)+CD25+CD39+ activated regulatory T cells was selectively decreased upon treatment in patients with durable clinical benefit, concomitant with high intratumoral expression of activating FcγR (search) (CD16A, CD16B and CD64). By contrast, non-responding patients lacked FcγR-rich effector cells, did not deplete activated regulatory T cells, and instead exhibited increased CTLA4 membrane expression on this subset upon treatment.
These findings support the conclusion that anti-CTLA4 antibodies can deplete activated tumor-specific regulatory T cells in humans, but only in tumors that contain both activated regulatory T cells and FcγR (search)-positive effector cells, similar to mechanisms observed in mouse models.
Clinical Implications and Future Applications
The NIVIPIT trial offers a clinically relevant strategy to separate the efficacy of CTLA-4 (search) blockade from its systemic toxicity, addressing one of the main barriers to broader use of nivolumab-ipilimumab combinations. The study suggests that intratumoral anti-CTLA4 may be especially valuable in settings where local disease control and immune priming are central, including oligometastatic disease, neoadjuvant immunotherapy, injectable melanoma lesions, and tumors with immune-active but suppressive microenvironments.
Although most injected lesions were superficial, deeper lesions were not excluded by the protocol. As confidence in safety increased, intratumoral ipilimumab was successfully administered to liver and lung metastases without additional safety signals and with preserved local efficacy.
The approach provides a model for future immunotherapy design, emphasizing not only choosing the right drug but delivering it to the right immune compartment. The ability to analyze fresh tumor samples for rapid biomarker assessment represents a significant advancement, enabling techniques such as flow cytometry and multiplex soluble factor quantification for direct evaluation of immune checkpoint expression and target engagement within hours of sampling.