Rallybio Publishes RLYB212 Phase 1 Proof-of-Concept Study in Thrombosis and Haemostasis

Rallybio Corporation (Nasdaq: RLYB), a clinical-stage biotechnology company dedicated to developing transformative therapies for rare diseases, has announced the publication of data from its Phase 1 proof-of-concept study of RLYB212 in the journal Thrombosis and Haemostasis. RLYB212 is a novel monoclonal antibody targeting HPA-1a, intended for the prevention of maternal alloimmunization and fetal and neonatal alloimmune thrombocytopenia (FNAIT). Initial results were previously shared at the 31st Congress of the International Society on Thrombosis and Haemostasis (ISTH) in 2023.

Stephen Uden, M.D., CEO of Rallybio, highlighted the importance of these data in selecting the initial dose for the forthcoming Phase 2 trial of RLYB212, scheduled to commence in the fourth quarter of 2024. The primary objective is to advance RLYB212 to address a significant unmet need in maternal fetal health.

The Phase 1 study demonstrated that subcutaneous administration of RLYB212 led to a dose-dependent, rapid, and complete elimination of transfused HPA-1a positive platelets in HPA-1a negative subjects. Both dosages (0.09 mg and 0.29 mg) achieved the prespecified proof-of-concept criteria of at least a 90% reduction in the mean platelet elimination half-life compared to placebo. This data, along with substantial preclinical data, has been instrumental in establishing therapeutic exposure targets, which Rallybio believes will prevent maternal alloimmunization to fetal antigens, a prerequisite for FNAIT.

The study utilized a bolus challenge of HPA-1a positive platelets as a surrogate for a significant fetal-maternal hemorrhage. The resulting platelet elimination profiles post-subcutaneous administration of RLYB212 were similar to those observed with RhD-positive erythrocytes following intramuscular anti-RhD agents, known to effectively prevent RhD alloimmunization in pregnancy. Consistent with prior findings, RLYB212 was generally well-tolerated with no severe adverse events reported.

Rallybio plans to initiate a Phase 2 trial in pregnant women at risk for HPA-1a alloimmunization and FNAIT in the fourth quarter of 2024. The company is also continuing to screen pregnant women in its ongoing FNAIT natural history study, aiming to gather a contemporary dataset on HPA-1a alloimmunization frequency across a diverse population. This data may serve as a control arm for a future Phase 3 trial.

Fetal and Neonatal Alloimmune Thrombocytopenia (FNAIT) is a rare and potentially life-threatening condition that can cause severe bleeding in fetuses and newborns. It occurs when there is an immune incompatibility between a mother and her fetus over a specific platelet antigen, HPA-1. Individuals homozygous for HPA-1b (HPA-1a negative) can develop antibodies against HPA-1a upon exposure, leading to alloimmunization. In HPA-1a negative mothers carrying an HPA-1a positive fetus, mixing of fetal and maternal blood can trigger the mother’s immune system to produce anti-HPA-1a antibodies, which can cross the placenta and destroy fetal platelets. This can result in severe thrombocytopenia, miscarriage, stillbirth, neonatal death, or severe lifelong neurological impairment. Currently, there is no approved therapy for preventing or treating FNAIT during pregnancy.

Rallybio is a biotechnology firm focused on developing and commercializing therapies for severe and rare diseases. Based in New Haven, Connecticut, the company has a diverse pipeline targeting maternal fetal health, complement dysregulation, hematology, and metabolic disorders. Rallybio’s clinical programs include RLYB212 for preventing FNAIT and RLYB116, a complement component 5 (C5) inhibitor with potential applications in multiple complement dysregulation diseases.

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