Rallybio reported data from the Phase 1b proof-of-concept study of RLYB212, a novel monoclonal anti-HPA-1a antibody in development for the prevention of fetal and neonatal alloimmune thrombocytopenia. The data showed that subcutaneous RLYB212 administration produced a dose-dependent, rapid and complete elimination of transfused HPA-1a positive platelets in HPA-1a negative subjects, with both doses meeting the prespecified proof-of-concept criteria of greater than or equal to 90% reduction in mean platelet elimination half-life. Mean platelet elimination half-life was 5.8 hours and 1.5 hours for RLYB212 compared to 71.7 hours for placebo. Consistent with previously reported data, RLYB212 was observed to be well-tolerated with no reports of serious or severe adverse events. Rallybio remains on track to complete the following RLYB212 milestones in the fourth quarter of 2023: Comprehensive toxicology program, including maternal-fetal toxicology; Multiple dose cohort of Phase 1 safety and PK study; Phase 2 Dose Confirmation Study. The Company plans to initiate a Phase 2 dose confirmation study in the second half of 2024, designed to confirm the RLYB212 dose regimen in pregnant women at higher risk of FNAIT prior to initiation of a larger Phase 3 registrational study. This study will employ a sentinel, sequenced cohort design to allow for any required adjustments to the dose regimen, prior to advancing the confirmed dose regimen into the registrational study.
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