Positive results from the phase 1 clinical trial of RLYB212, an experimental antibody intended for maternal alloimmunization and fetal and neonatal alloimmune thrombocytopenia (FNAIT) prevention, have been recently announced in a press release.
RLYB212 is an artificial antibody that binds to HPA-1a-positive platelets, clearing them from the maternal bloodstream before the alloimmunization process occurs. The antibody was recently tested in a phase 1 proof-of-concept study, one of the earliest stages in drug development that offers preliminary evidence of the drug’s efficacy to allow it to be tested in phase 2 trials.
Results from the phase 1 study showed that RLYB212 could remove 100% of transfused HPA-1a platelets in HPA-1a negative volunteers; no adverse effects were reported during the study.
“These data were instrumental in our selection of the initial dose for the upcoming Phase 2 trial of RLYB212, which is on track for initiation in the fourth quarter of 2024,” said Stephen Uden, M.D., Chief Executive Officer of Rallybio.
The role of anti-HPA1 antibodies in FNAIT
FNAIT is an immunologically mediated disease in which antibodies produced by the mother can cross the placenta and destroy fetal platelets, which can result in uncontrollable bleeding during pregnancy and the neonatal period. These antibodies target the human platelet antigen 1 (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,” the authors wrote. “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.”
The production of anti-HPA1 antibodies is known as alloimmunization. HPA1 alloimmunization occurs in pregnancies where the mother is HPA-1a negative and the fetus HPA-1a positive. In this context, the maternal immune system will identify HPA-1 as a foreign and produce antibodies against it.
If approved, RLYB212 will be the first drug of its kind to prevent maternal alloimmunization and FNAIT.
