The goal of this clinical trial is to learn about how an umbilical cord lining-derived stem cell (ULSC) product performs when treating Dermatomyositis/Polymyositis (DM/PM), also known as idiopathic inflammatory myopathy (IIM) in adults. It will assess safety and efficacy in relieving symptoms of DM/PM with ULSC administered in three intravenous (IV) doses of 150 million cells per dose.
The main questions that this study plans to answer are:
* Is ULSC as safe as placebo (a look-alike saline without cells) in repeated IV infusion? * Does ULSC improve symptoms of DM/PM after three doses? Researchers will compare ULSC to placebo and evaluate changes from baseline (before first dose) to after each dose and after all three doses are completed per treatment study period. * For participants undergoing steroid (e.g., prednisone) therapy for DM/PM, does ULSC allow their steroid dose to be reduced? Does ULSC reduce need for rescue therapy?
Participants will have been diagnosed with either DM or PM:
* Diagnosed according to the EULAR/ACR 2017 Classification Criteria for idiopathic inflammatory myositis (IIM), which includes DM and PM. * Positive for myositis-associated antibody or undergone evaluation to exclude mimics.
Participants in this study will:
* Participate for total of 25 months with 15 in-person clinic visits and 8 virtual visits on phone or video call. * Receive both ULSC and placebo for a total of 6 IV infusions (260 mL) 3 months apart. * Receive 3 doses of ULSC and 3 doses placebo in either of two sequences, as assigned: ULSC first and placebo second, or placebo first and ULSC second. * If undergoing steroid therapy, will have steroid dose taper prescribing lower doses starting two weeks after the second infusion. * Return for follow-up visits after each dose and up to 12 months after final dose. * Have follow-ups including self-reported questionnaires, physical exam, muscle strength and endurance tests, blood tests, pulmonary function tests, and other assessments.
Participants will be ≥18 years old.
Diagnosis of idiopathic inflammatory myositis (IIM) based on 2017 EULAR/ACR Classification Criteria for adult IIM, corresponding to a score of ≥ 5.5 (≥ 6.7 with muscle biopsy).
Elevated Creatine Kinase (CK) or Aldolase (more than 1.5 x the upper limit of normal) at screening, OR
MRI positive for active, muscle inflammation within 12 weeks prior to screening, OR
Adequate pulmonary function, defined as saturated oxygen (SpO2 ≥ 94%) on room air.
Left ventricular ejection fraction (LVEF) ≥ 30% as assessed by echocardiogram (ECHO) or multigated acquisition (MUGA) scan performed within 8 weeks prior to Screening.
Participants must have the ability to comply with the requirements of the study.
All participants of reproductive age/capacity will be required to use adequate contraception, defined as at least one form of a highly effective contraceptive (i.e., condoms, hormonal birth control, IUD), with any partners during the study period and for at least three months beyond the study period, for safety.