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