Regeneron’s CD20xCD3 bispecific antibody has achieved an 80% complete response rate in a small trial of patients with relapsed or refractory follicular lymphoma. The strong early signs of efficacy led Regeneron to target a 2019 start date for a potentially registrational phase 2 study.

REGN1979 is designed to bind to T cell surface antigen CD3 and tumor-associated antigen CD20. By cross-linking the immune and cancer cells, Regeneron thinks REGN1979 may trigger specific, local T cell activation and thereby drive potent cytotoxic attacks against tumor B cells.

Regeneron had reported early signs of antitumor activity two years ago at a meeting of the American Society of Hematology. And it arrived at this year’s event armed with its strongest evidence yet.

All 10 follicular lymphoma patients who received 5mg or more of REGN1979 responded to the drug. Eight of the patients experienced complete responses. The responses of nine of the patients were maintained during treatment. To round out the upbeat update, Regeneron reported that the broader phase 1 trial saw no clinically significant neurotoxicities.

High response rates are relatively common in follicular lymphomas—a Keytruda-rituximab cocktail triggered complete responses in 50% of patients last year—but Regeneron’s results still stand out, particularly as the patients were relapsed or refractory. Buoyed by the data, Regeneron plans to start a phase 2 trial that could support approval in the indication next year.

The planned relapsed or refractory follicular lymphoma trial is part of Regeneron’s multi-front clinical development strategy for REGN1979. Regeneron has aspirations to develop REGN1979 as a first-line treatment for follicular lymphoma, is investigating the effect of the bispecific on diffuse large B-cell lymphoma (DLBCL) and exploring its use in combination with checkpoint inhibitor Libtayo.

Data from the DLBCL side of the program were presented alongside the follicular lymphoma readout. Among the 10 heavily pretreated relapsed or refractory DLBCL patients who received 18mg to 40mg doses of REGN1979, two subjects had complete responses and a further four people experienced partial responses. 

REGN1979 is advancing in parallel to a rival CD20xCD3 bispecific that is in development at Roche. The rival bispecific, mosunetuzumab, emerged from an early clinical test looking less effective than REGN1979 in follicular lymphoma but competitive in DLBCL. Mosunetuzumab was associated with a lower rate of cytokine storm, too. 

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