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
News

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

Published
Topics

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 -- 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.

Important Disclosure

This post is for informational purposes only and does not constitute an offer to sell or a solicitation to buy any securities. RTW or its clients are investors in the companies referenced herein. The information presented reflects selected portfolio company announcements based on predetermined categories of corporate events. Past performance is not indicative of future results, and no representation is made that any investment will achieve similar results or be profitable.

Share article
Back to news

Related

AbbVie to Acquire Apogee Therapeutics, Deepening Immunology Portfolio

Boundless Bio and Serapha Bio Announce Merger Agreement and $230 Million Concurrent Private Placement

Windward Bio Announces $165M Crossover Financing to Advance Pipeline of Long-Acting Immunology Therapies With Best-in-Disease Potential

Kailera Therapeutics Announces Pricing of Initial Public Offering

This website is not intended to offer or to promote the offer or sale of the shares (the “Shares”) of RTW Biotech Opportunities Ltd (the “Company”) in the United States or to any “U.S. persons” as defined in Regulation S (“US persons”) under the US Securities Act of 1933, as amended (the “Securities Act”). The materials contained herein are not for release, publication or distribution, directly or indirectly, in whole or in part, to any persons to whom or into or within any jurisdiction where to do so would constitute a violation of applicable law or regulation.

The information contained herein and on the pages that follow does not constitute or form a part of any offer to sell or issue, or the solicitation of any offer to purchase, subscribe for or otherwise acquire, any securities in the United States or in any jurisdiction in which, or to any person to whom, such an offer or solicitation would be unlawful.

The Company has not been and will not be registered under the US Investment Company Act of 1940, as amended (the “Investment Company Act”), and as such holders of the Shares are not and will not be entitled to the benefits of the Investment Company Act. The Shares have not been and will not be registered under the Securities Act, or with any securities regulatory authority of any state or other jurisdiction of the United States, and may not be offered, sold, resold, pledged, delivered, assigned or otherwise transferred, directly or indirectly, into or within the United States or to, or for the account or benefit of, any US Persons, except pursuant to an exemption from, or in a transaction not subject to, the registration requirements of the Securities Act and in compliance with any applicable securities laws of any state or other jurisdiction of the United States and in a manner which would not result in the Company being required to register under the Investment Company Act. There has been and will be no public offer of the Shares in the United States. The offer and sale of the Shares have not been and will not be registered under the applicable securities laws of Australia, Canada, Japan or South Africa. Potential users of the information contained herein and on the pages that follow are requested to inform themselves about and to observe all applicable restrictions.

The information contained herein and on the pages that follow may contain forward-looking statements. Any statement other than a statement of historical fact is a forward-looking statement. Actual results may differ materially from those expressed or implied by any forward-looking statement. The Company does not undertake any obligation to update or revise any forward-looking statements, whether as a result of new information, future events, or otherwise. You should not place undue reliance on any forward-looking statement, which speaks only as of the date of its issuance. The Company may change these terms and conditions from time to time and any such changes will be posted on this website. Your access to this website is governed by the version of these terms and conditions then in force.

By clicking “Agree” below, you represent, warrant, undertake and agree that (1) you have read, understood and agree to be bound by the terms and conditions and other information set out herein, (2) you are permitted under applicable laws and regulations to receive the information contained herein and on the pages that follow, (3) you are either (a) located outside the United States and are not a US Person or (b) an existing shareholder of the Company who is a “qualified purchaser” as defined under the Investment Company Act and (4) you will not further transmit or send any information contained in this website to any other persons in the United States, to US Persons, or to any publications with a general circulation in the United States. If you cannot so represent, warrant, undertake and agree, you must click the button labelled “Decline” or otherwise exit this website.

You must accept preferences cookies and refresh your browser to view this video.

Alternatively, if cookies are being blocked by the browser, or you wish to view the video at its source, you can do so by visiting the link below: