Rallybio Discontinues Lead Drug for Rare Maternal Disorder, Shifts Focus to C5 Inhibitor

Rallybio, a biotechnology company focused on rare diseases, has announced the discontinuation of its lead candidate RLYB212 for the treatment of fetal and neonatal alloimmune thrombocytopenia (FNAIT), a rare blood disorder in pregnant women. The decision comes after disappointing results from a Phase 2 pharmacokinetic study, prompting the company to redirect its efforts towards other promising candidates in its pipeline.

RLYB212 Falls Short in Phase 2 Trial

RLYB212, a monoclonal antibody targeting the HPA-1a protein, was being developed to prevent FNAIT, a condition where a mother's immune system attacks her baby's platelets. The Phase 2 trial aimed to assess the drug's pharmacokinetics and safety in pregnant women at higher risk of HPA-1a alloimmunization and FNAIT.

However, the study revealed that RLYB212 did not achieve the predicted target concentration levels necessary for efficacy. Specifically, the drug's concentrations fell near or below the assay's lower limit of quantitation, far short of the minimum 3 ng/mL required for efficacy. Rallybio's current hypothesis suggests that HPA-1a antigen expression on the placenta may have impacted the plasma concentrations of RLYB212.

"The values were near or below the assay's lower limit of quantitation," Rallybio stated, explaining that adjusting the dose did not seem feasible given the magnitude of the shortfall.

Strategic Shift to RLYB116 and Preclinical Programs

Following this setback, Rallybio has announced a strategic pivot to focus on RLYB116, a once-weekly low volume C5 inhibitor, and other preclinical programs. RLYB116 is an antibody mimetic fusion protein designed to inhibit C5, with plans to begin an early-stage study in the second quarter of this year.

Steve Uden, M.D., CEO of Rallybio, emphasized the company's expertise in the C5 space, drawing from the leadership team's experience at Alexion Pharmaceuticals. The company aims to position RLYB116 as a drug that patients can self-administer at home, with the goal of achieving complete and sustained complement inhibition with improved tolerability.

Rallybio expects to share results from the first two cohorts of the RLYB116 study in the third and fourth quarters of this year.

Market Impact and Financial Implications

The discontinuation of RLYB212 represents a significant blow to Rallybio's pipeline and market potential. The company had previously estimated the commercial opportunity for RLYB212 in FNAIT to be greater than $1.6 billion. The news has had a substantial impact on Rallybio's stock, with shares plummeting by 50% in pre-market trading to 21 cents from the previous day's closing price of 42 cents.

This development also affects Rallybio's partnership with Johnson & Johnson, which had provided an equity investment of $6.6 million, an upfront payment of $500,000, and additional funding of up to $3.7 million to support a natural history study for RLYB212.