Prolium Bioscience, a New York-based clinical-stage biotechnology company focused on developing therapies for severe autoimmune diseases, has launched with USD 50 million in Series A financing. The company’s sole asset is PRO-203, a bispecific CD20xCD3 T-cell engager that the company is advancing into multiple autoimmune indications, beginning with systemic sclerosis.
The round was led exclusively by RTW Investments, a New York-based life sciences investment firm that also served as founding investor. No other participants in the financing were disclosed. Prolium said proceeds will fund clinical development of PRO-203 in systemic sclerosis and additional autoimmune diseases driven by aberrant B-cell activity.
PRO-203 works by simultaneously binding CD20 on B cells and CD3 on T cells, forming an immunological synapse that redirects T cells to eliminate B cells via T-cell dependent cellular cytotoxicity. The approach is designed to achieve deeper B-cell depletion in tissues than conventional anti-CD20 monoclonal antibodies such as rituximab, which rely on antibody-dependent and complement-dependent cytotoxicity. Prolium has positioned the molecule as an off-the-shelf alternative to CAR-T cell therapy for autoimmune disease, avoiding the need for patient-specific manufacturing and lymphodepleting chemotherapy.
The company said it has begun dosing healthy volunteers in a single ascending dose study and expects to initiate a multinational Phase I/II trial in systemic sclerosis in Q2 2026. Separately, five patients with treatment-refractory systemic lupus erythematosus, all of whom also had lupus nephritis, have been treated with PRO-203 in an investigator-initiated study, with results to be reported at a future medical conference. Prolium said it plans to initiate additional clinical studies in other autoimmune diseases later this year.
Prolium in-licensed global rights to PRO-203 for all non-oncology indications and ex-Asia oncology rights from China-based firms KeyMed Biosciences and InnoCare Pharma. The molecule was previously studied in a Phase I/II trial in relapsed/refractory non-Hodgkin lymphoma in China, where it produced a complete response rate of 59% and an overall response rate of 82% at therapeutic doses. Terms of the licensing agreement were not disclosed. Scott Requadt serves as CEO of Prolium. The Series A represents the company’s first disclosed financing round, and no additional partnerships or collaborations beyond the KeyMed/InnoCare license have been announced.