Rallybio Corporation has begun dosing the first patient in its Phase 2 clinical trial assessing RLYB212 in pregnant individuals at increased risk of fetal and neonatal alloimmune thrombocytopenia (FNAIT). Dosing initiation was announced in a recent press release.
FNAIT occurs when the human platelet antigen (HPA) expressed on the fetus’ platelets is incompatible with that of the mother. This leads the mother’s immune system to produce antibodies that attack the fetus’ platelets in a process known as maternal alloimmunization. In many cases, the condition is caused when the mother produces antibodies against HPA-1a.
Currently, there are no approved treatments for the prevention of FNAIT. Most therapies are aimed at mitigating complications that may arise after maternal alloimmunization has already occurred.
RLYB212 is a monoclonal antibody that binds to fetal platelets in the mother’s bloodstream and removes them from circulation. If effective, the mother would not produce antibodies against the fetal HPA, and FNAIT would not develop.
Read more about FNAIT therapies
In this Phase 2 trial, the investigators aim to evaluate the safety and efficacy of RLYB212, monitor for the emergence of anti HPA-1a antibodies, and analyze neonatal outcomes.
The study, which has multiple sites across Europe, plans to include eight participants in total: The initial patient, a cohort of three women, and another cohort of four women.
Dosing of participants will begin at 16 weeks’ gestation and will continue every four weeks until birth. The drug will be administered via subcutaneous injection. Results from the second trimester of pregnancy are expected to be released during the second quarter of 2025, while outcomes at the time of delivery should be shared during the third quarter of 2025.
All participants must be negative for HPA-1a but are carrying a fetus who is positive for the antigen. They must also not possess anti-HPA-1a antibodies at the time of enrollment. Those with a history of FNAIT caused by anti-HPA-1a antibodies are ineligible for this study.
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