This study is a Phase 1/2, open-label clinical trial to test an experimental treatment called QEL-005 in adults with two autoimmune conditions: diffuse cutaneous systemic sclerosis (dcSSc) and difficult-to-treat rheumatoid arthritis (D2TRA). The main goals are to find out whether QEL-005 is safe, how well people tolerate it, and whether it may help reduce disease activity or improve symptoms.

QEL-005 is made from a participant's own white blood cells (autologous cells). These cells are collected and then changed in a laboratory using genetic methods to create specialized immune cells called CAR-T regulatory cells that target a protein on B cells called CD19. These modified cells are then given back to the participant by intravenous (IV) infusion.

To take part, eligible participants will first have a procedure called leukapheresis, where some of their white blood cells are removed from the blood. The study team will use these cells to manufacture QEL005. After QEL005 is ready, participants will receive an IV infusion of their modified cells, stay in hospital overnight for monitoring, and will then be followed closely in the clinic.

Throughout the trial, participants will have regular safety checks, which may include blood tests, imaging scans, questionnaires about symptoms and daily functioning, and biopsies taken from involved tissues, to help understand how QEL005 is working in the body. Detailed follow up will be for 1 year after QEL-005 infusion, and there is long-term follow up for a total of 15 years, which is standard for cell therapies. The information from this Phase 1/2 study will help determine an appropriate dose and dosing schedule of QEL005 for future studies.

This is a single-arm, open label, multicentre, Phase 1/2, first in human study of QEL005 in adult participants with diffuse cutaneous systemic sclerosis (dcSSc) or difficult to treat rheumatoid arthritis (D2TRA). QEL005 is an autologous chimeric antigen receptor regulatory T-cell (CAR-Treg) therapy directed against the CD19 marker found on B cells.

The primary objective of this study is to evaluate the safety and tolerability of single IV infusions of QEL005 across different dose levels in participants with dcSSc or D2TRA. Secondary and exploratory objectives include assessment of preliminary clinical efficacy (for example, changes in disease activity scores, skin involvement, or joint symptoms, as appropriate for each disease) and evaluation of biological activity (including effects on B cell populations, immune biomarkers, and other laboratory measures).

The study uses a dose escalation phase then a dose expansion phase. In the dose escalation phase, sequential cohorts of participants receive increasing doses of QEL005 under close safety monitoring. Safety assessments include recording of adverse events, vital signs and laboratory abnormalities.

QEL005 is manufactured from autologous leukapheresis material obtained at baseline. Participants undergo leukapheresis for collection of peripheral blood mononuclear cells, which are then genetically modified ex vivo to express a CD19directed CAR-T regulatory cell.

Over the course of the trial, participants will attend scheduled visits for clinical evaluations, laboratory tests, imaging studies, and patient reported outcome questionnaires, as well as tissue biopsies, to characterize the safety profile and to explore pharmacodynamic and immunologic effects of QEL005. There are detailed assessments over the first year following QEL-005 infusion, and then additional long-term follow up for 15 years, standard for cell therapy trials. Data from this Phase 1/2 trial will inform the recommended dose, regimen, and patient population for subsequent studies of QEL005 in autoimmune diseases.

Inclusion Criteria:

• Participants must be at least 18 years of age at the time of signing the informed consent.
• Up to date vaccination status and no planned vaccinations for post 3 months infusion
• Adequate haematological, liver and renal function
• Willing to undergo annual influenza vaccination
• Willing to enter a 15-year follow-up
• Eastern Cooperative Oncology Group (ECOG) performance status grade < 3
• Able and willing to use a highly effective method of contraception
• Stable dose of steroid prior to screening

Specific inclusion criteria for participants with difficult to treat rheumatoid Arthritis (D2TRA) only:

• Diagnosis of Rheumatoid Arthritis (RA) per 2010 ACR-EULAR criteria
• Diagnosis of D2TRA per 2021 EULAR criteria
• Evidence of clinically active disease a defined by validated clinical or laboratory results consistent with standard definitions of active RA
• Evidence of inflammation in target joints used for the DAS28 CRP assessment

Specific inclusion criteria for participants with diffuse cutaneous systemic sclerosis (dcSSc) only:

• Diagnosis of dcSSc as per the 2013 ACR-EULAR criteria
• Serologically positive for antinuclear antibodies
• Failure to respond sufficiently to immunomodulatory disease modifying anti-rheumatic drugs (DMARDs).
• Skin involvement with a total modified Rodnan Skin Score of at least 15
• Evidence of lung fibrosis based on imaging or pulmonary function testing
• Evidence of active disease based on a validated SSc activity assessment

Exclusion Criteria:

• Presence of a significant medical condition(s), or clinically significant laboratory abnormality
• History or concern of autoimmune diseases other than those under study
• Active infection, or recurrent chronic infection requiring intervention
• Immunodeficiency or receiving immunoglobulin replacement therapy
• Past or current infection with hepatitis B or C, tuberculosis, syphilis, or HIV
• Clinically significant cardiac dysfunction or severe pulmonary impairment
• Use of investigational agents within a pre-defined period prior to study screening
• Received a previous cell therapy
• Received certain B cell related experimental therapies in a clinical trial with the past year
• Any solid organ, bone marrow or stem cell transplant
• History of malignancy in the past 5 years
• Receiving prohibited medication that cannot be stopped at screening