RLYB212, C(FNAIT), according to findings from a phase 1b study conducted in Germany and recently published in the journal Thrombosis and Haemostasis.
What is FNAIT?
Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare but serious condition that affects 0.1% of pregnancies in which a pregnant mother’s immune system produces antibodies against the platelets of her fetus. This occurs when a fetus inherits platelet antigens from the father that are not compatible with the mother, typically involving a protein called human platelet antigen (HPA). The mother’s immune system recognizes the fetal platelets as foreign, attacking and destroying them, leading to low platelet levels (thrombocytopenia) in the fetus or newborn.
Recognizing that no treatments are currently available for the prevention of FNAIT, the researchers sought to evaluate the ability of subcutaneously (beneath the skin) administered RLYB212, a monoclonal anti-HPA-1a antibody, to eradicate HPA-1a–positive platelets.
All study participants were randomized to treatment with a single subcutaneous (SC) dose of RLYB212 or placebo on day one. The treatment was followed by a transfusion of 10 x 10 HPA-1a-positive platelets on day eight of the study.
Learn more about FNAIT therapies
The primary objective of the study was to establish whether RLYB212 could significantly speed up the elimination of HPA-1a-positive platelets that were transfused to HPA-1a-negative participants. The primary endpoint was the terminal elimination half-life, or the time it takes for an active substance in a body to be reduced by half, of the platelets that were transfused.
A total of 11 participants were randomized to one of three treatments: four participants received 0.09 mg of SC RLYB212; five participants received 0.29 mg of SC RLYB212; and two participants received SC placebo.
Results of the study showed that treatment with RLYB212 was associated with “rapid elimination of HPA-1a-positive platelets in a concentration-dependent manner.” Researchers noted a result of greater than or equal to a 90% reduction in the platelet elimination half-life compared with placebo.
After HPA-1a platelets were transfused, a rapid decline in the concentration of RLYB212 was seen over a period of between two and 24 hours, which matched the time needed for RLYB212 to bind to approximately 10% of HPA-1a on cell surfaces. The agent was well tolerated, and there were no reports of any treatment-related adverse events.
“The data from this study are consistent with preclinical efficacy data and support the potential use of RLYB212 as a prophylactic treatment for FNAIT that prevents maternal HPA-1a alloimmunization during at-risk pregnancies,” the authors concluded.
