Prolium Bioscience Launches with $50 Million to Develop Next-Generation T-cell Engager for Severe Autoimmune Diseases
New York — Prolium Bioscience, a clinical-stage biotechnology company pioneering the development of bispecific T-cell engaging antibodies for autoimmune disease, announced today the closing of a $50 million Series A financing. The company also announced that the first patients have been dosed with its lead candidate, PRO-203, a potential best-in-class CD20xCD3 T-cell engager being developed for the treatment of severe autoimmune diseases including systemic sclerosis and systemic lupus erythematosus.
This announcement marks a significant milestone in the application of T-cell engager technology — originally developed for cancer immunotherapy — to the treatment of B-cell-mediated autoimmune diseases. The approach leverages the proven mechanism of CD20 targeting while introducing a novel therapeutic angle that could offer deep, durable remissions without the complexity and cost of Electra Therapeutics' SIRP-targeted approach.
Funding Overview
The Series A financing was led by RTW Investments, a healthcare-focused investment firm that served as the founding investor of Prolium. The $50 million in financing will fund continued clinical development of PRO-203 across multiple autoimmune indications and support the expansion of Prolium's pipeline of next-generation T-cell engaging therapeutics.
RTW Investments has demonstrated a strong commitment to innovative autoimmune therapies, with a track record of backing companies pursuing novel mechanisms in this space. The firm's partner and president, Peter Fong, noted that the investment reflects confidence in both the science behind PRO-203 and Prolium's experienced management team.
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, said Scott Requadt, Chief Executive Officer of Prolium.
The Challenge: Unmet Need in Autoimmune Disease
Autoimmune diseases affect approximately 8% of the global population, with over 100 different conditions recognized. Among the most serious are B-cell-mediated autoimmune diseases, in which the immune system mistakenly attacks the body's own tissues. These include systemic lupus erythematosus, systemic sclerosis, rheumatoid arthritis, and multiple sclerosis.
While significant progress has been made in developing biologic therapies that target components of the immune system, many patients with severe autoimmune disease remain inadequately treated. Current therapies often require chronic administration, may lose effectiveness over time, and can be associated with significant immunosuppression that increases infection risk.
Systemic sclerosis (SSc), also known as scleroderma, represents one of the most challenging autoimmune conditions. Characterized by progressive fibrosis of the skin and internal organs, SSc can lead to devastating complications including kidney failure, pulmonary hypertension, and cardiac involvement. The disease has among the highest mortality rates of any autoimmune condition, with a 10-year survival rate of approximately 50-60% for patients with diffuse cutaneous disease.
Similarly, systemic lupus erythematosus (SLE) affects millions worldwide and can involve virtually any organ system. Lupus nephritis, kidney inflammation caused by SLE, is a particularly serious manifestation that can progress to end-stage renal disease. Current treatments for these conditions remain significantly limited.
The fundamental problem in many of these autoimmune conditions is the presence of pathogenic B-cells — immune cells that produce autoantibodies and drive inflammation. While Rituxan (rituximab), an anti-CD20 antibody, has shown benefit in some autoimmune conditions, its mechanism of action is limited and many patients do not achieve adequate disease control. Similar to how Vivacta's in vivo CAR-T therapy is advancing cell therapy delivery, PRO-203 offers a novel mechanism to target these pathogenic cells.
PRO-203: A Next-Generation T-cell Engager
PRO-203 is a bispecific antibody designed to redirect T-cells to eliminate CD20-expressing B-cells. Unlike conventional anti-CD20 antibodies like rituximab, which work primarily through antibody-dependent cellular cytotoxicity (ADCC) and complement activation, PRO-203 actively engages T-cells through its CD3-binding domain.
The bispecific antibody format enables PRO-203 to bind simultaneously to CD20 on target B-cells and CD3 on T-cells, forming an immunological synapse that redirects T-cell killing to the B-cell target. This mechanism — known as T-cell dependent cellular cytotoxicity (TDCC) — induces more potent and complete B-cell depletion than traditional antibody approaches.
CD20 is an ideal target for autoimmune disease because it is expressed on the surface of most B-cells but not on plasma cells, the antibody-producing cells that are essential for immune function. This selective targeting allows for depletion of pathogenic B-cells while preserving some humoral immunity.
As noted by Scott Requadt, CEO of Prolium, T-cell engagers represent 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 therapy.
Unlike CAR T-cell therapy, which requires custom manufacturing for each patient, T-cell engagers are off-the-shelf biologics that can be manufactured at scale and administered like conventional antibodies. This could dramatically improve patient access and reduce healthcare costs.
Clinical Data: Prior oncology Experience
PRO-203 was previously developed for the treatment of relapsed or refractory non-Hodgkin lymphoma (NHL), with clinical data generated in partnership with Chinese pharmaceutical companies. Although Prolium is now focused on autoimmune indications, the prior oncology experience provides important safety and efficacy insights.
In Phase 1/2 clinical trials conducted in China, PRO-203 demonstrated compelling efficacy in patients with relapsed or refractory NHL. At therapeutic doses, the Overall Response Rate (ORR) was 82%, with an impressive Overall Complete Response (CR) rate of 59%.
These response rates compare favorably with other CD20-targeting agents in development and suggest that the T-cell engaging mechanism may provide enhanced anti-tumor activity compared to conventional anti-CD20 antibodies.
The safety profile of PRO-203 was manageable in the oncology studies, with cytokine release syndrome (CRS) observed in some patients — a known class effect of T-cell engaging therapies. However, CRS was generally mild to moderate and responsive to standard management approaches.
Importantly, the autoimmune dosing regimen is expected to involve lower doses and less frequent administration than oncology protocols, potentially reducing the incidence and severity of cytokine release events.
Current Clinical Development
Prolium is currently advancing PRO-203 in multiple clinical programs focused on autoimmune disease:
A single ascending dose study is underway in healthy volunteers to characterize the safety and pharmacokinetic profile of PRO-203 in a non-patient population. This study will inform dosing selections for the autoimmune disease studies.
A Phase 1/2 study in systemic sclerosis is expected to initiate in Q2 2026, evaluating PRO-203 in patients with diffuse cutaneous disease. This will be the primary registrational focus for the development program.
An investigator-initiated study in systemic lupus erythematosus with lupus nephritis has already enrolled five patients, with results expected to be presented at a future medical conference. This study provides important early proof-of-concept for the autoimmune application.
The company plans to expand development to additional autoimmune indications, consistent with the broad potential of B-cell depletion through T-cell engagement.
Scientific Rationale
The approach taken by Prolium is grounded in deep understanding of B-cell biology and the immunopathogenesis of autoimmune disease. CD20 is the most well-validated target in B-cell driven autoimmune diseases, having been targeted successfully in conditions including rheumatoid arthritis, membranous nephropathy, and pemphigus vulgaris.
What distinguishes PRO-203 from prior CD20-targeting approaches is the T-cell engaging mechanism. By actively recruiting cytotoxic T-cells to the B-cell target, PRO-203 can achieve more complete and durable B-cell depletion than antibodies that rely solely on endogenous effector mechanisms.
This enhanced mechanism may be particularly important in tissues where B-cells are densely infiltrate and may be protected from antibody-dependent killing. The formation of an immunological synapse ensures directed T-cell attack regardless of the patient's own immune status.
Additionally, T-cell engagers may be able to eliminate B-cells that have downregulated Fc receptor expression or otherwise escaped conventional antibody killing. This could lead to more complete remissions and potentially longer duration of response.
Leadership Team
Prolium was founded in 2025 and is led by an experienced team with deep expertise in antibody development and autoimmune disease. Scott Requadt serves as Chief Executive Officer, bringing extensive industry experience from prior roles in biotechnology company leadership.
The company's scientific advisory board includes leading experts in rheumatology, immunology, and antibody therapeutics. This expertise informs both pipeline development and clinical trial design.
RTW Investments serves as the founding investor and has provided significant operational support, reflecting the firm's thesis that T-cell engaging antibodies represent a major frontier in autoimmune disease treatment.
Competitive Landscape
Multiple companies are pursuing T-cell engaging antibodies for autoimmune disease, representing one of the most active areas of biotechnology development. Key competitors include:
Iverness, a Bristol Myers Squibb Company, is developing CD19xCD3 T-cell engagers for autoimmune disease with clinical trials in lupus and other conditions. The company leverages its experience with the TCE platform in oncology to accelerate autoimmune development.
Acepodia is developing cell therapy approaches using non-viral gene editing to engineer T-cells for autoimmune disease, taking a differentiated cellular therapy approach compared to antibody-based TCEs.
Roche and Genentech continue to advance their TCE pipeline in oncology while exploring autoimmune applications of their platform technologies.
Prolium differentiates through its focus on CD20 as a target, the well-established autoimmune target, combined with the potency of T-cell engagement. The prior oncology data validating PRO-203's mechanism provides confidence in the clinical trajectory.
Market Opportunity
The market for autoimmune disease therapeutics exceeds $100 billion globally and continues to grow as diagnostic capabilities improve and patient identification expands. Within this market, B-cell-directed therapies represent a significant and growing segment.
Systemic sclerosis alone represents a market opportunity exceeding $2 billion annually for disease-modifying therapies. Currently, no approved therapies effectively halt or reverse disease progression, creating massive unmet need.
Lupus nephritis represents an even larger market opportunity, with over 1 million patients in the United States alone affected by SLE. The recent approval of lupus nephritis therapies validates this market and creates precedent for reimbursement of novel agents.
If approved, PRO-203 could capture significant market share based on its mechanism advantage and potential for improved efficacy over existing therapies.
Strategic Outlook
The $50 million Series A provides Prolium with runway to execute on its clinical development strategy and generate key data readouts across multiple indications. The company expects substantial data readouts within the next two years, including:
Healthy volunteer safety data from the single ascending dose study (expected 2026)
Initial efficacy and safety data from the systemic sclerosis Phase 1/2 study (expected 2026-2027)
Potential lupus nephritis data from the investigator-initiated study (expected 2027)
These data will inform regulatory discussions and potential accelerated approval pathways for the most promising indications.
PRO-203 has the potential to change the treatment paradigm in scleroderma and other serious autoimmune diseases. Prolium's team is executing impressively to generate substantial data readouts of PRO-203 in several autoimmune disorders within the next two years, noted Peter Fong of RTW Investments.
Looking Ahead
With the completion of this $50 million financing and initiation of clinical development, Prolium enters a pivotal period. The company must execute on its ambitious clinical development plan while continuing to build its pipeline and organizational capabilities.
If PRO-203 demonstrates the anticipated efficacy and safety profile, it could represent a major advancement for patients with severe autoimmune disease. The company's approach exemplifies the broader trend of applying cancer immunotherapy mechanisms to autoimmune disease — a frontier that promises significant clinical benefit for millions of patients worldwide.
The biotechnology industry will watch closely as Prolium advances this next-generation T-cell engager through clinical development.