Rallybio Corporation announced the presentation of results from a fetal and neonatal alloimmune thrombocytopenia (FNAIT) systematic literature review and meta-analysis at the Academy of Managed Care Pharmacy (AMCP) 2024 Annual Meeting, which is taking place in New Orleans, LA. The results of this research found that, in a pooled analysis of 198,062 pregnant women, 2.2% were HPA-1a negative and 32.3% of these women were also HPA-1a negative, 32.3% of these Women were also HPA-1 a negative and therefore at 25-fold higher risk for alloimmunization. These rates are consistent with Rallybio's current estimate of annual at-risk pregnancies and translate to tens of thousands of fetuses and newborns at risk each year for the potentially devastating consequences of FNAIT.

Rallybio is developing RLYB212, a novel human monoclonal anti-HPA-1a antibody designed to prevent alloimmunization in pregnant women, thereby eliminating the risk of FNAIT and its potentially devastating consequences in their fetuses and newborns. Rallybio is on track to initiate a Phase 2 dose confirmation study for RLYB212 in pregnant women in the second half of 2024. The company is also conducting an ongoing FNAIT natural history study that will provide a contemporary dataset for HPA-1a alloimmunization frequency in a racially and ethnically diverse population, which is intended to support a future Phase 3 registration study for RLYB212.

RLYB212 is the only investigational therapy currently reported to be in clinical development to address the needs of pregnant women at higher risk of FNAIT who have not alloimmunized. Fetal and Neonatal Alloimmune Thrombocytopenia (FNAIT) is a potentially life-threatening rare disease that can cause uncontrolled bleeding in fetuses and newborns. FNAIT can arise during pregnancy due to an immune incompatibility between an expectant mother and her fetus in a specific platelet antigen called human platelet antigen 1, or HPA-1. There are two predominant forms of HPA-1, known as HPA-1a and HPA-1b, which are expressed on the surface of platelets.

Individuals who are homozygous for HPA-1b, meaning that they have two copies of the HPA-1b allele and no copies of the HPA-1a allele, are also known as HPA-1a negative. Upon exposure to the HPA-1a antigen, these individuals can develop antibodies to that antigen in a process known as alloimmunization. In HPA-1a-negative expectant mothers bearing a HPA-1a-positive fetus, alloimmunization can occur upon mixing of fetal blood with maternal blood.

When alloimmunization occurs in an expectant mother, the anti-HPA-1a antibodies that develop in the mother can cross the placenta and destroy platelets in the fetus. The destruction of platelets in the fetus can result in severely low platelet counts, or thrombocytopenia, and potentially lead to devastating consequences including miscarriage, stillbirth, death of the newborn, or severe lifelong neurological disability in those babies who survive. There is currently no approved therapy for the prevention or prenatal treatment of FNAIT.