Affibody has reported positive Phase 1 data from its licensee Rallybio Corporation demonstrating complete and sustained inhibition of terminal complement with the investigational C5 inhibitor RLYB116.

Rallybio said the confirmatory pharmacokinetic/pharmacodynamic study evaluated once-weekly, small-volume subcutaneous dosing of RLYB116 in healthy volunteers. The candidate is being developed for complement-mediated diseases, initially targeting immune platelet transfusion refractoriness and refractory antiphospholipid syndrome.

According to the company, a 300 mg once-weekly dose achieved complete and sustained inhibition of terminal complement. Ex vivo haemolytic activity assays showed complete and sustained blockade, which the company said demonstrates clinically effective terminal complement inhibition.

RLYB116 administered at 150 mg and 300 mg once weekly was reported to be well tolerated, with no gastrointestinal side effects observed. The most common adverse events were mild-to-moderate injection site reactions in both cohorts, consistent with other subcutaneously administered biologics. None were severe or led to treatment discontinuation. The company said the findings support recent manufacturing process enhancements aimed at improving the tolerability profile of the molecule.

David Bejker, CEO of Affibody, said: “We are very pleased with the highly encouraging results demonstrating complete and sustained inhibition of terminal complement by RLYB116 using a convenient, small volume, once-weekly subcutaneous dosing.” He added: “These data further illustrate the potential of the Affibody platform to deliver best-in-class therapies.”

The single-blind, multiple ascending dose Phase 1 confirmatory study (NCT06797375) enrolled two cohorts of eight participants each, randomised 3-to-1 to receive RLYB116 or placebo once weekly for four weeks. Cohort 1 received 150 mg and Cohort 2 received 300 mg. Participants were followed for 10 weeks after treatment.

RLYB116 is a long-acting, subcutaneously injected inhibitor of complement factor 5 based on the Affibody protein platform. The molecule was initially discovered by Affibody under a collaboration with Swedish Orphan Biovitrum AB.

Rallybio said it plans to initiate a Phase 2 clinical study of RLYB116 in platelet transfusion refractoriness in the second half of 2026, with potential topline data in 2027.