Pfizer Terminates Phase II CD47 Trial in Blood Cancer Due to Recruitment Challenges
核心洞察
Pfizer has terminated a Phase II trial of maplirpacept in diffuse large B-cell lymphoma (搜索) after enrolling only six patients since August 2023 due to recruitment difficulties.
The decision was not based on safety or efficacy concerns, according to the company's statement to federal clinical trials database.
This setback adds to mounting challenges for Pfizer's $2.26 billion Trillium acquisition and the broader CD47 (搜索)-targeting therapeutic space.
Pfizer has terminated a Phase II clinical trial evaluating its investigational CD47 (搜索)-targeting fusion protein maplirpacept in patients with diffuse large B-cell lymphoma (搜索) (DLBCL), citing recruitment challenges that prevented the study from reaching its enrollment goals.
According to an update to the federal clinical trials database, the study was discontinued due to the "inability to recruit the planned number of subjects." The trial, which began in August 2023, had enrolled only six patients before termination. The database update specifically noted that "the decision was not based on any safety and/or efficacy concerns."
A Pfizer spokesperson confirmed to Endpoints News that "recruiting challenges" led to the decision to discontinue the trial, emphasizing that the termination was not related to safety or efficacy issues with the investigational therapy.
CD47 Mechanism and Therapeutic Rationale
Maplirpacept is a recombinant fusion protein designed for intravenous delivery that targets CD47 (搜索), a cell surface ligand that binds to immune cells and prevents phagocytosis. According to Pfizer's website, CD47 is present at low levels in almost all cells of the body but becomes overexpressed in blood cancer (搜索) cells, allowing them to evade immune activity. The protein has been linked to worse clinical outcomes, and blocking CD47 helps boost both innate and adaptive immune responses.
Ongoing Development Programs
Despite this setback, Pfizer continues to advance maplirpacept in other blood cancer (搜索) indications. The company is currently studying the asset in multiple myeloma (搜索) and maintains a Phase I/II trial combining maplirpacept with Roche's Columvi in patients with relapsed or refractory diffuse large B-cell lymphoma (搜索). The clinicaltrials.gov webpage indicates this combination study is actively recruiting, with a primary completion date of September 2026.
Broader Implications for Trillium Acquisition
The terminated trial represents another challenge for Pfizer's $2.26 billion acquisition of Trillium Therapeutics (搜索), completed in August 2021. The acquisition brought maplirpacept and other CD47 (搜索)-targeting assets into Pfizer's pipeline, but the program has faced multiple setbacks over the past year.
According to industry reports, Pfizer has attributed most of its CD47 (搜索) trial terminations to administrative reasons rather than toxicity concerns. This approach may reflect lessons learned from competitor experiences, particularly Gilead's magrolimab program, which was discontinued first in hematologic cancers and subsequently in solid tumors due to increased risk of death.
Challenges in CD47 Development Space
The maplirpacept discontinuation adds to mounting challenges across the CD47 (搜索)-targeting therapeutic space. Earlier this year, ALX Oncology reported that its CD47 blocker evorpacept, in combination with Merck (搜索)'s Keytruda, failed two mid-stage studies in metastatic or unresectable recurrent head and neck cancer (搜索).
Despite these industry-wide setbacks, some companies continue to pursue CD47 (搜索)-targeting approaches. ALX Oncology continues developing evorpacept despite various setbacks, most recently in gastric cancer (搜索), while Pfizer maintains its commitment to the CD47 program through ongoing studies in multiple myeloma (搜索) and combination trials.