Xencor's XmAb819: Phase 1 Expansion for Renal Cancer, Pivotal Trial Planned for 2027
ENPP3-Targeting Renal Cancer Candidate
XmAb819 from Xencor, Inc. (XNCR) is a clinical-stage candidate, not yet assigned a commercial name, designed as a 2+1 bispecific T-cell engager targeting both ENPP3 and CD3. It is engineered to bind to ENPP3, which is highly expressed in cancer cells, and CD3, to induce T-cell cytotoxicity. This approach aims to validate a novel mechanism of action in advanced clear cell renal cell carcinoma (ccRCC), where treatment options are limited after immune checkpoint inhibitors and vascular endothelial growth factor tyrosine kinase inhibitors (VEGF-TKIs).
Early Efficacy Observed in Phase 1
NCT05433142 is an ongoing, multi-center, open-label Phase 1 dose-escalation and expansion study evaluating the safety, tolerability, and biological activity, as well as determining the recommended dose, of intravenous and subcutaneous XmAb819 in patients with recurrent or refractory advanced ccRCC. As of September 19, 2025, 69 patients have been treated in 10 intravenous cohorts and 5 subcutaneous cohorts. In a group of 20 patients who were evaluable for efficacy within the target dose range, an objective response rate (ORR) of 25% and a disease control rate (DCR) of 70% were observed, providing a basis to expand development as a single-agent therapy.
Safety and Administration-Related Risks
Treatment-related Grade 3 or higher adverse events included rash (16%), elevated liver enzymes (7%), and cytokine release syndrome (CRS) (4%). One case of Grade 4 elevation in liver enzymes was reported as a dose-limiting toxicity. No treatment-related Grade 5 events or immune effector cell-associated neurotoxicity syndrome (ICANS) were reported. In the initial 18 patients, a priming dose preparation error related to the use of a diluent port and syringe resulted in plasma concentrations that were 3- to 8-fold higher than expected. The company has completed institutional retraining and plans to introduce a lower-concentration formulation in the first half of 2026. Subcutaneous administration offers convenience and is a key factor in managing exposure and CRS, which will influence the final route of administration.
Competitive Landscape and Development Timeline
The current competitive landscape includes first-line combination therapies such as Keytruda (pembrolizumab, PD-1) from Merck & Co. (MRK) and Inlyta (axitinib, VEGFR) from Pfizer (PFE), as well as subsequent therapies such as Welireg (belzutifan, HIF-2α) from Merck. The FDA approved the Keytruda/Inlyta combination for first-line advanced ccRCC on April 19, 2019, and Welireg for advanced ccRCC after PD-1/PD-L1 inhibitors and VEGF-TKIs on December 14, 2023. No AdComm votes were required for these indications. XmAb819 is currently in Phase 1 development and has not yet been approved by the FDA, EMA, or PMDA. Xencor plans to determine the recommended Phase 3 dose in 2026 and initiate a pivotal trial in advanced ccRCC in 2027. The company estimates the global ccRCC market at approximately USD 12 billion by 2030, which represents a significant commercial opportunity if successful. However, the durability of response in the expanded cohort and the reproducibility of safety in a larger study must first be demonstrated.
The ORR of 25% and DCR of 70% observed in the 20 patients in the target dose group represent the first numerical demonstration of clinical activity for the ENPP3×CD3 mechanism in patients with a median of 4 prior lines of therapy. However, given the small sample size, the expanded data in 2026 will be a near-term catalyst for the company's valuation. In the medium to long term, the planned initiation of a pivotal trial in 2027 will be a key inflection point in the company's efforts to establish a presence in the global ccRCC market, which is projected to be approximately USD 12 billion by 2030. The key competitive products are Welireg (belzutifan, HIF-2α) and Keytruda (pembrolizumab, PD-1)-based combination therapies, which are already marketed. XmAb819 must demonstrate that the mechanistic differentiation observed in Phase 1 can be translated into durable responses and a favorable safety profile. From a research perspective, the selectivity for tumors with high ENPP3 expression and the pharmacokinetics of subcutaneous administration will be critical in determining the scalability of the T-cell engager platform for solid tumors. The stability of CRS and hepatotoxicity in the lower-concentration formulation, which was introduced after the initial preparation errors, will be key determinants of regulatory progress and clinical operational reliability.
Source: ClinicalTrials.gov (api_ct)