Rallybio announced Tuesday that it is discontinuing its clinical trial investigating the drug RLYB212 intended for the prevention of fetal and neonatal alloimmune thrombocytopenia (FNAIT).
The company stated the drug was discontinued because researchers could not establish an appropriate therapeutic dose, and phase 2 results “significantly deviated from the predicted range.”
RLYB212 is an experimental monoclonal antibody that binds to fetal platelets in the maternal circulation and removes them. Early removal prevents the immunization process that leads to anti-human platelet antigen (HPA) antibody production and FNAIT. The drug is administered subcutaneously once every four weeks.
The suspended clinical trial aimed to determine the dosage needed for the medication to be effective without producing any serious adverse effects. Researchers realized that the required concentration in maternal blood for the drug to work was 6 ng/ml. However, the administered doses did not translate into appropriate blood concentrations. Administering higher doses was not possible due to the risk of adverse effects.
According to researchers, the presence of anti-HPA antibodies in the placenta could be responsible for the low drug concentration in maternal serum.
Currently, there are no available preventive treatments for FNAIT, and most treatment alternatives focus on treating the complications associated with platelet destruction during pregnancy and after birth. These options include intrauterine platelet transfusions, corticosteroid treatment, and intravenous immunoglobulin (IVIG) administration. Close control of platelet counts after birth and early detection of bleeding are mandatory after birth.
“We are disappointed by the PK results of the RLYB212 Phase 2 trial,” said Stephen Uden, M.D., Chief Executive Officer of Rallybio. “Given that the results significantly deviated from the predicted range and the absence of empirical data to further inform dose adjustment, the risk/benefit ratio no longer supports continued dosing.”
