The goal of this clinical trial is to test the safety and potential benefit of a new immune cell therapy called anti-BCMA-CD19 CAR-T cells in adults (18-75 years) with IgG4-related disease (IgG4-RD) that has come back or not improved after standard treatments such as glucocorticoids or rituximab.

The main questions this study aims to answer are:

• What medical problems (side effects) occur after receiving anti-BCMA-CD19 CAR-T cell therapy?
• Does anti-BCMA-CD19 CAR-T cell therapy improve IgG4-RD disease activity scores at 12 weeks and 26 weeks?

Participants will:

• Have their own blood immune cells collected by a procedure called leukapheresis
• Receive short-term chemotherapy to prepare the immune system
• Receive one intravenous infusion of anti-BCMA-CD19 CAR-T cells
• Return for regular clinic visits over 26 weeks for safety checks, blood tests, and imaging
• May be followed for up to one year in total

This is a Phase 2, open-label, single-arm exploratory clinical trial using a 3+3 dose-escalation design to assess the safety, feasibility, and preliminary efficacy of autologous anti-BCMA-CD19 chimeric antigen receptor T (CAR-T) cell therapy in patients with relapsed or refractory IgG4-related disease (IgG4-RD).

Background IgG4-RD is a chronic, immune-mediated fibroinflammatory disorder that can involve multiple organs, including the pancreas, bile ducts, salivary glands, kidneys, lungs, and retroperitoneum. Although standard treatments such as glucocorticoids and anti-CD20 monoclonal antibodies (e.g., rituximab) are effective for most patients, some develop treatment resistance, frequent relapses, or contraindications to conventional immunosuppressive agents. This creates an unmet clinical need for novel therapeutic strategies.

Recent translational studies show that IgG4-RD lesions often contain abundant CD19+ B cells, plasmablasts, and long-lived plasma cells expressing B-cell maturation antigen (BCMA), many of which may be resistant to conventional B-cell depletion. Dual-target CAR-T cells directed against both CD19 and BCMA may achieve more complete depletion of pathogenic B-lineage cells and offer a promising treatment for refractory IgG4-RD.

Methods Eligible participants will undergo leukapheresis for autologous peripheral blood mononuclear cell (PBMC) collection. Cells will be transduced ex vivo with a lentiviral vector encoding a CAR construct targeting CD19 and BCMA, then expanded and prepared for infusion. Lymphodepletion chemotherapy with cyclophosphamide (250 mg/m^2/day, IV) and fludarabine (30 mg/m^2/day, IV) will be given on Days -5 to -3. The doses of fludarabine and cyclophosphamide may be adjusted based on the patient's condition.

CAR-T cells will be infused on Day 0 at one of three sequential dose levels (1×10^6, 2×10^6, or 3×10^6 CAR+ T cells/kg, ±20%). Participants will be followed regularly for safety (adverse events [AEs], serious adverse events [SAEs], cytokine release syndrome [CRS], immune effector cell-associated neurotoxicity syndrome [ICANS]), pharmacokinetics (CAR-T cell expansion and persistence), and immunologic responses.

Endpoints The primary endpoints are safety (incidence of dose-limiting toxicities [DLTs] within 28 days post-infusion) and efficacy (change in IgG4-RD Responder Index [RI] at Week 12 and Week 26). Secondary endpoints include changes in target lesion size, serum IgG4, IgE, and eosinophil counts, as well as histopathologic changes in affected tissue.

Exploratory Analyses Exploratory studies will assess immune cell profiles in blood, bone marrow, and tissue biopsies using flow cytometry, multiplex cytokine assays, and spatial or single-cell transcriptomic techniques.

Inclusion Criteria:

To participate, subjects must meet all of the following criteria:

1. Aged 18 to 75 years, inclusive, regardless of sex.

2. Meet the 2019 ACR/EULAR classification criteria for IgG4-related disease.

3. Involvement of two or more important systems/sites (including but not limited to the pancreas, bile ducts, kidneys and dura mater).

4. Relapsed or refractory IgG4-RD: The disease either remains active after 3 months of glucocorticoid and/or rituximab therapy or relapses within 6 months post-treatment.

5. Important organ function meeting the following conditions:

   • Bone marrow: (i) neutrophil count ≥1×10^9/L (excluding disease-related neutropenia); (ii) hemoglobin ≥60 g/L.
   • Hepatic function: ALT≤3×ULN (elevation caused by disease may be excluded); AST≤3×ULN (elevation caused by disease may be excluded); TBIL≤1.5×ULN (elevation caused by disease may be excluded).
   • Renal function: creatinine clearance (Cockcroft-Gault formula) ≥30 ml/min (excluding acute decline due to disease).
   • Coagulation: international normalized ratio (INR) ≤ 1.5×ULN, prothrombin time (PT) ≤ 1.5×ULN
   • Cardiac function: stable hemodynamics.

6. Women of childbearing potential and male subjects with partners of childbearing potential must use medically accepted contraception or abstain during study treatment and for at least 12 months after the end of treatment. Women of childbearing potential must have a negative serum HCG test within 7 days before enrollment and must not be breastfeeding.

7. Voluntary participation in this clinical study with signed informed consent and willingness to comply with study procedures and follow-up.

8. Patent superficial peripheral veins adequate for intravenous infusion.

Exclusion Criteria:

Subjects will be excluded if any of the following criteria are met:

1. History of severe drug allergy or allergic constitution.
2. Current or suspected uncontrollable or treatment-requiring fungal, bacterial, viral or other infections.
3. Central nervous system disease (excluding disease-related epilepsy, psychosis, organic brain syndrome, cerebrovascular accident, encephalitis or central nervous system vasculitis).
4. Cardiac insufficiency that precludes participation.
5. Congenital immunoglobulin deficiency.
6. Congenital malformation or nutritional disorder causing severe organ impairment.
7. History of malignancy within the past five years.
8. End-stage renal failure.
9. Positive hepatitis B surface antigen and hepatitis B core antibody with HBV-DNA titers above the assay limit of detection; positive hepatitis C antibody with HCV-RNA positivity; positive human immunodeficiency virus antibody; positive syphilis serology.
10. Psychiatric disorders or severe cognitive impairment.
11. Participation in other clinical trials within three months before enrollment.
12. Receipt of any investigational drug within 12 weeks before screening or within five half-lives of the agent (whichever is longer).
13. Pregnant or intending to become pregnant.
14. Any other reason deemed by the investigator to preclude enrollment.

Access to the data underlying this study can be obtained from the corresponding author upon reasonable request and subject to any required ethical approvals.