Pfizer has terminated a Phase II study of its CD47 immune checkpoint inhibitor, maplirpacept, due to low recruitment.
In an update on ClinicalTrials.gov, the company stated the study (NCT05626322) was terminated due to “the inability to recruit the planned number of subjects”, adding it was not due to any safety or efficacy concerns.
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The listing states only six patients were enrolled, much lower than the 70 the company had initially hoped to enrol when the study was first recorded on the registry in 2022.
The study had hoped to evaluate the efficacy and safety of a combination therapy of maplirpacept with Monjuvi (tafasitamab) and Revlimid (lenalidomide) in patients with relapsed or refractory diffuse large B-cell lymphoma (DLBCL).
Pfizer acquired maplirpacept during a $2.3bn buyout of Trillium Therapeutics in 2021.
A Pfizer spokesperson told the Clinical Trials Arena: “This Phase Ib/II open-label study has been terminated due to the inability to recruit the planned number of subjects. The decision was not based on any safety and/or efficacy concerns or any requests from regulatory authorities. Pfizer is continuing to investigate maplirpacept in other trials involving haematologic malignancies.”
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By GlobalDataThis is the second study that Pfizer has terminated, with a Phase I trial of the CD47 in peripheral T cell lymphoma (PTCL) being terminated in August 2024.
The therapy is still being evaluated in a Phase II investigator-led study (NCT05507541) in combination with Keytruda (pembrolizumab) in patients with relapsed or refractory DLBCL. Other than this, there are no other active studies of the drug in any indication.
If approved, GlobalData analysts predict global sales of the drug to reach $120m in 2031.
GlobalData is the parent company of Clinical Trials Arena.
Ongoing difficulties in CD47 field
Pfizer is not the only company to have struggled with the CD47 pathway, with Gilead Sciences also ending all Phase III clinical trials of magrolimab in blood cancers, stating that an “increased risk of death” had been detected. Gilead acquired magrolimab through a $4.9bn acquisition of its original developer Forty Seven in 2021.
AbbVie has also cut ties with its CD47 partner I-Mab, stopping all development of lemzoparlimab, which was being investigated in myelodysplastic syndromes.
In April 2025, ALX Oncology’s CD47-blocker evorpacept, in combination with MSD’s blockbuster Keytruda (pembrolizumab), failed to show benefit in two Phase II trials.
Editor’s note: This article has been updated to include a comment from a Pfizer spokesperson.
