Daclizumab

Pfizer’s Phase I program for PF-08046032, an anti-CD25 antibody-drug conjugate designed to deplete immunosuppressive regulatory T cells within the tumor microenvironment, has been terminated after enrolling only six participants, marking one of the earliest discontinuations in the company’s recent oncology pipeline. The NCT06870487 trial terminated before completing dose escalation, the termination reflecting a strategic business decision rather than safety or efficacy concerns, as per the clinicaltrial.gov listing. The open-label Phase I study enrolled adults with advanced or metastatic malignancies across two broad disease categories: lymphomas, including classical Hodgkin lymphoma, peripheral T-cell lymphoma, and diffuse large B-cell lymphoma, and solid tumors, including non-small cell lung cancer, head and neck squamous cell carcinoma, and melanoma. Patients were required to have an ECOG performance status of 0 or 1, measurable disease per RECIST 1.1 or Lugano criteria, and the ability to provide tumor tissue for correlative analyses. Primary endpoints focused on safety characterization. Pfizer has been executing a substantial cost-reduction program since 2024, eliminating multiple early-stage assets as part of a broader effort to redirect capital toward later-stage and revenue-generating oncology programs, including assets acquired through the Seagen transaction. An unvalidated Phase I asset with no efficacy signal and an uncertain differentiation profile would be a plausible candidate for deprioritization under that framework. The clinical trial termination in 2026 leaves the anti-CD25 ADC concept without a clinical proof of concept from this program. Pfizer has not indicated whether the asset will be restarted, out-licensed, or permanently discontinued. The scientific rationale for targeting CD25 on intratumoral Tregs is well established in the preclinical literature. Tregs suppress anti-tumor immune responses through multiple mechanisms, including CTLA-4-mediated co-stimulation blockade, IL-10 and TGF-beta secretion, and IL-2 consumption. Their depletion in the tumor microenvironment has been shown to enhance anti-tumor immunity in animal models, and the combination with PD-1 blockade was designed to provide complementary immune activation. The clinical translation of this concept has proven difficult. Basiliximab and daclizumab, earlier anti-CD25 antibodies developed for transplant indications, demonstrated the on-target pharmacology of CD25 blockade but were not developed as ADCs. More recent ADC-based approaches have sought to use payload delivery to achieve tumor-selective cytotoxicity without systemic immunosuppression, but the therapeutic window remains narrow given the expression of CD25 on activated T cells in the periphery. Several programs targeting Tregs through different mechanisms remain in early clinical development across the industry, including approaches targeting FOXP3, CCR8, and TNFR2. This article was generated with AI assistance and reviewed and edited by the AllSci editorial team Explore more at AllSci News: https://allsci.com/news/ Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Privacy Terms About Us Copyright © 2026. AllSci Corp. All rights reserved.