Regeneron to reconsider CD28 bispecific studies

Aug. 3, 2023

Regeneron Pharmaceuticals is taking a step back from one of its CD28 bispecific drug studies following the deaths of two patients. 

According to the company’s most recent financial reports, the Regeneron has ongoing phase 1 trials for multiple CD28 costimulatory bispecific antibodies in various tumor settings. The trials combine these bispecific antibodies with the company's immunotherapy, Libtayo, a PD-1 inhibitor.

In its ongoing study for REGN5678, a costimulatory bispecific antibody targeting PSMA and CD28 in advanced prostate cancer, the company has observed positive antitumor activity when used in combination with Libtayo, as well as when used alone as a monotherapy. 

However, there have been two immune-mediated Grade 5 adverse events — resulting in death — in the Libtayo combination cohort, one of which occurred last month. As a precaution, the company has stopped enrolling patients receiving the combination of REGN5678 and full-dose Libtayo.

Instead, Regeneron says it plans to investigate REGN5678 combinations with lower doses of Libtayo as well as enroll patients in a REGN5678 monotherapy cohort and explore its use in combination with other immunotherapy methods.