Rallybio Ends RLYB212 Program Following Phase II Trial Failure in FNAIT

Rallybio has announced the termination of its RLYB212 development program for fetal and neonatal alloimmune thrombocytopenia (FNAIT) after failing to meet key benchmarks in a Phase II trial. FNAIT is a rare condition in which maternal antibodies attack fetal platelets, posing serious bleeding risks.

In the single-arm trial (NCT06435845), RLYB212—an anti-HPA-1a monoclonal antibody—did not demonstrate minimum efficacy or reach predicted pharmacokinetic (PK) targets. Second-trimester data showed the drug failed to achieve the required plasma concentration threshold of 3ng/mL, with predicted levels between 6–10ng/mL also unmet. Rallybio attributes this to possible HPA-1a antigen expression on the placenta affecting drug levels. Dose adjustments were found to be unviable.

As a result, the trial has been halted, enrollment and screening discontinued, and Rallybio’s stock plummeted 41% following the announcement. The company will now prioritize another pipeline candidate targeting complement-driven diseases, while safety follow-up continues per protocol.

21-04-2025