A macrophage-activating immune checkpoint inhibitor, combined with rituximab therapy, was safe and produced durable complete responses in patients with relapsed or refractory non-Hodgkin lymphoma, according to results of a phase 1b study.
Mainly low-grade toxic effects were seen on treatment with Hu5F9-G4 (5F9) and rituximab, which induced responses in more than half of patients, of which more than one-third were complete responses, the study investigators reported.
Most of the responses were ongoing at the time of data cutoff, suggesting durable responses with the combination of rituximab and 5F9 – a humanized monoclonal antibody that blocks CD47, an antiphagocytic or “do not eat me” signal overexpressed by most cancers,, of Stanford (Calif.) University, and her coauthors wrote.
“The macrophage-mediated activity of 5F9 plus rituximab may serve as an effective new immunotherapy for stimulating the innate immune system,” Dr. Advani and her colleagues reported in the.
The study included 22 patients, including 15 with diffuse large B-cell lymphoma (DLBCL) and 7 with follicular lymphoma, who had received a median of four prior therapies. Almost all of the non-Hodgkin lymphomas (21, or 95%) were refractory to rituximab.
All patients received intravenous 5F9 starting with a priming dose of 1 mg/kg followed by weekly maintenance doses of 10-30 mg/kg in three dose-escalation cohorts, given until disease progression or lack of clinical benefit. Intravenous rituximab at 375 mg/m2 weekly was started on the second week of the first cycle, and then monthly for cycles 2 through 6.
“Substantial antitumor activity” was seen with this chemotherapy-free regimen in a group of heavily pretreated, largely rituximab-refractory patients, Dr. Advani and her coauthors wrote in their report.
The objective response rate was 50%, including a 36% complete response rate in the intent-to-treat analysis. For DLBCL, the rates of objective and complete responses were 40% and 33%, while for follicular lymphoma, they were 71% and 43%.
The median duration of response was not reached in either disease cohort with a median follow-up of 6.2 months for DLBCL and 8.1 months for follicular lymphoma. Of the 11 patients who responded, 10 (91%) were still in response at the time of data cutoff. “Longer follow-up is needed,” the investigators wrote.
Most adverse events were seen within the first few weeks of treatment and mainly included anemia and infusion-related reactions. The anemia was an expected, on-target effect of 5F9 because of selective clearance of older red cells, which was predictable, transient, and mitigated by the maintenance dosing strategy employed in this phase 1b trial.
“As red cells age, they lose CD47 expression and gain expression of prophagocytic signals, leading to homeostatic clearance,” they wrote.
The activity of 5F9 and rituximab is “synergistic” based on the results of previous, preclinical investigations in models of lymphoma, Dr. Advani and her coauthors added.
A phase 2 trial of 5F9 plus rituximab in relapsed or refractory B-cell non-Hodgkin lymphoma is ongoing, according to their report.
The study was supported by Forty Seven and the Leukemia & Lymphoma Society. Dr. Advani reported disclosures related to Forty Seven, Bristol-Myers Squibb, Pharmacyclics, Seattle Genetics, and Roche/Genentech, among others.