Pfizer insists that the discontinuation of the Phase II study was due to recruitment difficulties and was not linked to maplirpacept’s safety or efficacy.
Pfizer has terminated a Phase II trial that was evaluating its investigational fusion protein maplirpacept in diffuse large B-cell lymphoma after running into recruitment challenges.
According to an update to a federal clinical trials database, the study was dropped because of the “inability to recruit the planned number of subjects.” Only six had been enrolled into the trial since it began in August 2023. “The decision was not based on any safety and/or efficacy concerns,” the update noted.
In a statement to Endpoints News, a spokesperson for Pfizer confirmed that “recruiting challenges” led to the call to discontinue the trial.
Designed to be delivered intravenously, maplirpacept is a recombinant fusion protein that targets CD47, a cell surface ligand that binds to immune cells and prevents phagocytosis. CD47 is present at low levels in almost all cells of the body, but is overexpressed in blood cancer cells, in turn allowing them to evade immune activity. CD47 has been linked to worse clinical outcomes and blocking this protein helps boost both the innate and adaptive immune responses, according to Pfizer’s website.
Pfizer gained ownership of maplirpacept with the $2.26 billion acquisition of Trillium Therapeutics in August 2021. In the statement to Endpoints, the company spokesperson said that Pfizer continues to study maplirpacept in other blood cancers, including multiple myeloma.
The pharma also has a Phase I/II trial of the asset, combined with Roche’s Columvi, in patients with relapsed or refractory diffuse large B-cell lymphoma. The clinicaltrials.gov webpage for this study indicates that it is currently recruiting, with a primary completion date of September 2026.
The discontinuation of maplirpacept’s mid-stage study represents yet another setback for the embattled CD47 space. Earlier this year, ALX Oncology reported that its CD47 blocker evorpacept, in combination with Merck’s Keytruda, failed two mid-stage studies in metastatic or unresectable recurrent head and neck cancer.
Arguably the most high-profile CD47 failure, however, is Gilead’s magrolimab, which was finally completely discontinued last year after a troubled run. In early 2022, the FDA slapped partial clinical holds on several studies of magrolimab after detecting an imbalance of serious toxicities in treated patients. Then, in July 2023, the pharma terminated a late-stage study for the drug in myelodysplastic syndromes, citing futility.
