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US-based biotech Rallybio is ending its RLYB212 programme for the prevention of fetal and neonatal alloimmune thrombocytopenia (FNAIT) following disappointing results from a Phase II trial.
FNAIT is a rare, pregnancy-related condition where a mother's immune system attacks the baby's platelets, leading to a low platelet count (thrombocytopenia) and potentially life-threatening bleeding complications.
The biotech’s lead asset RLYB212 failed to show minimum efficacy signals and pharmacokinetic (PK) data or achieve predicted target concentrations in a Phase II trial (NCT06435845). As a result, the RLYB212 programme is being discontinued.
On the news, the company’s Nasdaq-listed stock dipped by 41% from $0.425 at close on 7 April to a close of $0.25 on 8 April. Globally, the stock markets have been dropping over the past week following the announcement of US tariffs from President Donald Trump.
Rallybio CEO Dr Stephen Uden said: “We are disappointed by the PK results of the RLYB212 Phase II trial. Given that the results significantly deviated from the predicted range and the absence of empiric data to further inform dose adjustment, the risk/benefit no longer supports continued dosing, and we will discontinue RLYB212 development.”
The single-arm Phase II trial was designed to assess the PK and safety of RLYB212, a subcutaneous, human monoclonal anti-HPA-1a antibody, in pregnant women at higher risk for HPA-1a alloimmunisation and FNAIT. Secondary endpoints included the assessment of pregnancy and neonatal/infant outcomes and the occurrence of emergent HPA-1a alloimmunisation.
Second-trimester PK results from patients demonstrated an inability for RLYB212 to achieve predicted target concentrations of 6ng/mL to 10ng/mL, as well as the minimum target concentration required for efficacy of 3ng/mL. The study also determined that dose adjustment is not feasible. Rallybio hypothesises that HPA-1a antigen expression on the placenta may be impacting plasma concentrations of RLYB212.
No further enrolment in the trial is planned and all screening of participants has been stopped. Safety follow-up of patients will continue, as specified in the clinical trial protocol.
Other pipeline products
Rallybio has one other therapy, RLYB-116, a once-weekly low-volume C5 inhibitor for the treatment of complement-driven diseases including myasthenia gravis (MG), in the clinic that it will now prioritise.
RLYB-116 is in a Phase I trial (ACTRN12621001571864), evaluating the therapy in health volunteers. In September 2023, preliminary data from the trial was announced, showing RLYB-116’s early promise.