Rallybio Corporation has outlined its Phase II trial plans after revealing positive preliminary data from a Phase I study investigating RLYB212.

The Phase I study evaluated the safety and pharmacokinetics (PK) of RLYB212 for the prevention of foetal and neonatal alloimmune thrombocytopenia (FNAIT), which is a rare disease with life-altering effects for mothers and babies that is only detectable at birth.

The Phase II dose confirmation trial will investigate the candidate in pregnant women who are at higher risk of FNAIT, with an expected initiation date in H2 2024.

Rallybio expects to submit both the clinical pharmacology model and the Phase II dosing approach to a peer-reviewed journal in 2024.

Candidate well tolerated in Phase I

Eight HPA-1a negative subjects participated in the study with six subjects receiving RLYB212 every two weeks while two received a placebo every two weeks. The study was initiated in the first quarter of 2023 and lasted over 12 weeks.

Preliminary data demonstrated that multiple-dose PK was consistent within and between subjects. The data also supports a once monthly dosing regimen which will be evaluated further in the Phase II cohort.

RLYB212 was observed to be generally well-tolerated with no reports of injection site reactions or serious adverse events.

Programme lead Dr Róisín Armstrong said that the data supports the potential use of the candidate for the prevention of HPA-1a alloimmunisation and FNAIT.

What is RLYB212?

RLYB212 is under development as a prophylactic treatment to prevent FNAIT and post-delivery immunisation. It is a monoclonal HPA-1a antibody, which is administered through a subcutaneous route.

Rallybio acquired RLYB212 and RLYB211, which are also being investigated in FNAIT, from Prophylix AS in 2019. Both product candidates have received orphan drug designations from the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA), and rare paediatric disease designation from the FDA.

RallyBio is also developing other candidates, including RLYB116 in several complement dysregulation diseases.

Clinical Trials Arena has previously reported on the challenges of designing clinical trials for the pregnant population. Experts shared why protection by exclusion leads to a lack of evidence-based research and medicine.