<img src="https://ml.globenewswire.com/Resource/Download/7b673cfc-5886-4dff-88b8-8aee0df02b23?size=2" nborder="0" align="left" hspace="5" vspace="5" title="Picture1.png" alt="Prolium Bioscience, Inc."/>Phase 1/2 SSc study is expected to enroll patients at over 20 participating clinical sites in at least five countries Recently completed Phase 1 Single Ascending Dose study of PRO-203 in healthy volunteers Investigator-sponsored study of lupus nephritis patients has completed 26-week follow-up of all participants NEW YORK, June 22, 2026 (GLOBE NEWSWIRE) -- Prolium Bioscience, Inc. (Prolium), a clinical stage biotechnology company, today announced that the first patient has been dosed in a multinational, open-label, Phase 1/2 study of PRO-203, a potential best-in-class CD20xCD3 T-cell engager, in systemic sclerosis (SSc). Initiation of this study followed the completion of a Phase 1 Single Ascending Dose (SAD) study of PRO-203 in 20 healthy volunteers, in which Prolium was able to assess the pharmacokinetics and pharmacodynamics of PRO-203 to help inform its selection of an appropriate priming dose regimen of PRO-203 for the Phase 1/2 SSc study. Prolium also announced today the completion of the last patient, last visit in a 26-week investigator-initiated study of PRO-203 in treatment-refractory lupus nephritis (LN) patients. Data from both the LN study and the SAD study will be shared at an upcoming medical meeting. PRO-203 is a CD20xCD3 T-cell engager being developed for severe autoimmune diseases driven predominantly by aberrant B-cells. It works by binding both CD20+ B-cells and CD3 on T-cells, forming an immunological synapse bringing effector T-cells to the vicinity of target cells, thereby redirecting T-cells to eradicate B-cells via T-cell dependent cellular cytotoxicity (TDCC). It is administered subcutaneously. “Dosing the first patient with PRO-203 in systemic sclerosis marks an important milestone for Prolium as we advance our lead program in a disease with profound unmet medical need,” said Scott Requadt, Chief Executive Officer of Prolium. “T-cell engagers represent the next frontier in autoimmune disease, offering the potential for deep, durable B-cell depletion without the complexity or preconditioning of CAR-T therapies. Based on promising data we’ve seen to date, we believe PRO-203 has the potential to achieve sustained remissions in patients with serious autoimmune diseases. We plan to initiate additional studies of PRO-203 in multiple other autoimmune diseases in the near future.” “We’re delighted to have advanced PRO-203 so quickly through what we believe may have been one of the first times a T-cell engager was studied in a SAD study in healthy volunteers,” said Salim Mujais, MD, Chief Medical Officer of Prolium. “Having now established the basis for a priming dose regimen for PRO-203, we look forward to exploring its safety and efficacy in SSc as well as other severe autoimmune diseases.” The Phase 1/2 study (<a href="https://www.globenewswire.com/Tracker?data=lSCfLrQAy68UhUVJ9GwuaKY7yJPEBKskHuo_WvfYuCrcap3UArCu1HZDTmnYK1iHh6N3b3dfF9crcdJ7n6WrbbW2d7_7DNyA046G82xOa1NUmoefCllmjp55OWaeYaoRTrFT3VTX7-bdf2j3_qbdi7n-Lclve5I_PlXiZrF18r4PX6RqVBTDUuW1_kjHLi6tOi4pHSsZmxva-KQXOB_RiQ==" rel="nofollow" target="_blank" title="NCT07641634">NCT07641634</a>) is a two-part study of PRO-203, administered subcutaneously. Part 1, which consisted of a single ascending dose study in healthy adult volunteers, enrolled 20 participants at a single site in Australia and is now complete. Part 2 will enroll up to 24 patients with systemic sclerosis (SSc) across multiple dose cohorts to assess safety and preliminary efficacy. Participants within each cohort will receive a single cycle of PRO-203 and will be followed for a minimum of 13 weeks. Participants will then have the option to continue into a long-term extension (LTE), where they will continue to be evaluated for safety and efficacy outcomes. During the LTE, eligible participants may receive retreatment if they meet retreatment criteria. Total study duration per participant is up to 53 weeks. The trial will be conducted at more than 20 clinical sites spanning at least five different countries. The investigator-sponsored study of PRO-203 (<a href="https://www.globenewswire.com/Tracker?data=lSCfLrQAy68UhUVJ9GwuaD5zDyxcbKhnQtL8CbUh59IUHr0Ap2gF0zA6UYL_zp2j9xFkXpfbdFHiR9VoR6s_JxfM634vAz7jnXQXiI5_8L0EhdDtYoU1t-EMglNzDHUq" rel="nofollow" target="_blank" title="NCT07104344">NCT07104344</a>) enrolled five systemic lupus erythematosus (SLE) patients, all of whom had treatment-refractory lupus nephritis, at a single site in China. Patients were split across two dose cohorts, and each cohort received a single cycle of PRO-203. All patients were assessed both for safety and clinical outcome measures at various time points, and all have now been followed for at least 26 weeks.   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 <a href="https://www.globenewswire.com/Tracker?data=AaGHB3M749gLwWj6v6YdGCW2oc8XfEAJsnZKtmOHqu8DSNZxAdN6txbkBNMN-Hth16HvoX1I8XCvJdY6yqcvyuvgLILDyPv6ovYoBvF9CiI=" rel="nofollow" target="_blank" title="www.proliumbio.com">www.proliumbio.com</a> or follow us on <a href="https://www.globenewswire.com/Tracker?data=68WZJ-YmuKM48UBV8fML4LLLDQN9Cmk-swSuX7u1b9Ofb_MT_9FwFgze_F8kBuebaQ1ggxHMnVCkbpPqaBuoTp9pG8UFKT4iKskIHjdF5KA=" rel="nofollow" target="_blank" title="LinkedIn">LinkedIn</a>. Investor &amp; Media Contact: Chris Brinzey ICR Healthcare <a href="https://www.globenewswire.com/Tracker?data=73e063G5p0M42bJNe-8XJ2JE5VTbMB4Ns4Gn3r1bioBkKi60vvmeh6CBLW1D2ybRmXwRXsrQxwdBBe_Z_WUiy7mtfyN3Nj1_XrhhEM81tI8gNSfnvzxeOdl9mBF92m6uTedDI0eqv7j7mjid_dCn0g==" rel="nofollow" target="_blank" title="Chris.Brinzey@icrhealthcare.com">Chris.Brinzey@icrhealthcare.com</a> <img alt="" src='https://ml.globenewswire.com/media/MTAwZmU2ZmItYjFlNS00NjVmLTk2OGEtOTBhNzA2MjgwZWE3LTEzMjEyNDMtMjAyNi0wNi0yMi1lbg==/tiny/Prolium-Bioscience-Inc-.png' referrerpolicy='no-referrer-when-downgrade' />

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Prolium Bioscience Announces First Patient Dosed in its Multinational, Phase 1/2 Study of PRO-203 in Systemic Sclerosis, and Last Patient, Last Visit in an Investigator-Led Study of PRO-203 in Refractory Lupus Nephritis

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