Rallybio has reported positive data from a Phase I/II clinical trial, during which antibody candidate RLYB211 demonstrated proof of concept in fetal and neonatal alloimmune thrombocytopenia (FNAIT).

RLYB211 is a polyclonal anti-human platelet antigen (HPA)-1a antibody being developed to prevent FNAIT, a rare disease characterised by uncontrolled bleeding in fetuses and newborns.

Results from the first cohort of the ongoing Phase I/II trial showed that RLYB211 quickly and entirely cleared HPA-1a positive platelets from the circulation of HPA-1a negative subjects.

This indicates that treatment with an anti-HPA-1a antibody could help prevent FNAIT, the company said.

Rallybio co-founder and CEO Martin Mackay said: “These data reinforce our conviction in our approach as we prepare to move RLYB212 into the clinic.

“We will continue to work expeditiously with our partners, including the Fraunhofer Institute for Translational Medicine and Pharmacology and German Red Cross, to advance a potential preventive treatment to benefit the mothers and babies at high risk of this devastating disease.”

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By GlobalData

HPA-1a negative healthy male subjects in the first cohort of the Phase I/II trial received 1000 IU RLYB211 or placebo one hour following administration of HPA-1a positive platelets.

According to the data, RLYB211 noticeably fast-tracked the HPA-1a positive platelets clearance when compared to placebo. The mean half-life was 0.32 hours versus 65.29 hours, respectively.

RLYB211 was also observed to be safe and well-tolerated, without any serious adverse events.

The Phase I/II trial is designed to determine the RLYB211 dose required to rapidly eliminate HPA-1a positive platelets. It is being conducted in Germany.

Apart from RLYB211, the company is developing RLYB212 for FNAIT prevention.

Designed for subcutaneous use, RLYB212 is a human monoclonal anti-HPA-1a antibody that is anticipated to enter the clinic in the first half of next year.

When given to expectant at-risk mothers, both RLYB211 and RLYB212 are intended to rapidly remove fetal HPA-1a positive platelets from circulation and avert maternal alloimmunisation, subsequently avoiding the FNAIT risk in the fetus.