Prolium Bioscience Launches with $50 Million and Announces First Patients Dosed with PRO-203, a Potential Best-in-Class CD20xCD3 T-Cell Engager, for Severe Autoimmune Disease
Initial $50M Series A investment from founding investor RTW Investments
Proceeds will fund clinical development of PRO-203 in systemic sclerosis (SSc) and multiple additional severe autoimmune diseases
NEW YORK, March 03, 2026 (GLOBE NEWSWIRE) -- Prolium Bioscience, Inc. (Prolium), a clinical stage biotechnology company, today announced its launch with a $50 million Series A Financing to develop PRO-203, a potential best-in-class CD20xCD3 T-cell engager, for severe autoimmune disease. The financing was led by its founding investor, RTW Investments (RTW).
Prolium announced that it has begun dosing healthy volunteers in an ongoing single ascending dose study of PRO-203 and expects to initiate a multinational Phase 1/2 study of PRO-203 in systemic sclerosis (SSc) in Q2 2026. Additionally, five patients with treatment-refractory, advanced systemic lupus erythematosus (SLE), all of whom also have lupus nephritis (LN), have been treated with PRO-203 in an investigator-initiated study. Results will be reported at a future medical conference. Prolium plans to initiate further clinical studies this year in additional severe autoimmune diseases that are driven predominantly by aberrant B-cells.
“T-cell engagers are the next frontier in treating autoimmune disease, with the potential to achieve deep B-cell depletion in tissues, like CAR-T, without many of the challenges of CAR-T,” said Scott Requadt, CEO of Prolium. “CD20 is the most well-validated target in B-cell driven autoimmune diseases. Based on promising initial safety and efficacy data, we are excited about the potential of PRO-203 to achieve deep, durable remissions in patients with autoimmune disease and to be an important new therapy for scleroderma and other serious autoimmune diseases.”
“PRO-203 has the potential to change the treatment paradigm in scleroderma and other serious autoimmune diseases,” said Peter Fong, Partner and President, RTW. “Prolium’s team is executing impressively to generate substantial data readouts of PRO-203 in several autoimmune disorders within the next two years.”
Prolium was founded in 2025 by RTW, which invested $50 million in the company. PRO-203 works by binding both CD20+ B-cells and CD3 on T-cells, forming an immunological synapse around the target cells and recruiting effector T cells to the vicinity of target cells, thereby redirecting T-cells to eradicate B-cells via T-cell dependent cellular cytotoxicity (TDCC). The company in-licensed global rights in all non-oncology indications and ex-Asia rights for oncology indications to PRO-203 from KeyMed Biosciences and InnoCare Pharma. PRO-203 has previously been studied in a Phase 1/2 trial in relapsed/refractory Non-Hodgkin Lymphoma (NHL) patients in China, resulting in an overall complete response (CR) rate of 59% and an overall response rate (ORR) of 82% in patients dosed at therapeutic levels.
About Prolium
Prolium Bioscience is a clinical stage company developing PRO-203, a potential best-in-class, bispecific CD20xCD3 antibody for systemic sclerosis and other severe autoimmune diseases. Founded and backed by RTW Investments, Prolium has assembled a team with deep experience in the development of therapeutics in autoimmune disease. For more information about Prolium, please visit www.proliumbio.com.
About RTW Investments, LP
RTW Investments, LP is a New York-based, global, full life-cycle investment firm that focuses on identifying transformational and disruptive innovations across the biopharmaceutical and medical technologies sectors. As a leading partner of industry and academia, RTW combines deep scientific expertise with a solution-oriented investment approach to advance emerging therapies by building and supporting the companies developing them. For further information about RTW, please visit www.rtwfunds.com
Investor & Media Contact:
Chris Brinzey
ICR Healthcare
Chris.Brinzey@icrhealthcare.com
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