Fierce 15 winner Rallybio establishes proof-of-concept in phase 1/2 study for rare fetal bleeding disorder

2018 Fierce 15 winner Rallybio has established proof-of-concept for an antibody treatment aiming to prevent a rare disease that causes a mother’s immune system to attack her fetus or newborn child’s platelets.

Rallybio is conducting a phase 1/2 study of RLYB211 to prevent fetal and neonatal alloimmune thrombocytopenia (FNAIT), which can cause uncontrollable bleeding in fetuses and newborns.

FNAIT occurs when the mother and fetus have an incompatible immune system. When the mother's and fetus' blood mixes, the mother's platelets develop antibodies that pass into the fetus and launch an attack on its opposing platelets. This can lead to miscarriage, stillbirth or death of the newborn, or patients can experience lifelong neurological disability.

While still in early clinical testing and just a small group of patients reporting, RLYB211 has been found to clear the troublesome platelets in men injected with them. Rallybio said the data shows that the polyclonal anti-HPA-1a antibody they are developing could be a viable approach for FNAIT.

“We are thrilled with the clear signal demonstrated by RLYB211 in this first cohort of participants,” said Rallybio CEO and co-founder Martin Mackay.

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If RLYB211 can clear the mismatched fetal platelets in the mother’s circulation, the immune attack should be prevented, according to one of the lead authors of the study, Dr. Christoph Geisen from the Institute of Transfusion Medicine and Immunohaematology, German Red Cross Blood Transfusion Service. That would in turn prevent FNAIT.

“This would represent a significant step forward for at-risk families, where no approved preventive therapy or treatment presently exist,” Geisen said. The therapy will ultimately be administered to mothers who are at risk to prevent the disorder.

New Haven, Connecticut-based Rallybio is also developing RLYB212, considered the biotech’s lead candidate, for the same condition. The therapy is expected to enter the clinic in the first quarter of 2022.

“These data reinforce our conviction in our approach as we prepare to move RLYB212 into the clinic,” Mackay said.

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The company will present detailed data at the upcoming International Society on Thrombosis and Haemostasis 2021 Virtual Congress beginning July 17.

Rallybio focuses on rare and severe disorders. The company launched in January 2018 and has collected a portfolio of product candidates in hematology, immuno-inflammation and metabolism.