⁃ Males or female subjects, ≥ 18 years of age at the time of signing informed consent.

⁃ Ability to understand the requirements of the study.

⁃ Willingness to provide written informed consent.

⁃ Willingness to comply with the study protocol procedures.

⁃ Women of childbearing potential and all male participants must agree to use two acceptable methods of contraception together to avoid pregnancy. The following are examples of acceptable methods of contraception including:

• Established use of oral, inserted, injected, or implanted hormonal methods of contraception.

∙ Correctly placed copper containing intrauterine device (IUD).

∙ Male condom or female condom used WITH a spermicide (i.e., foam, gel, film, cream, suppository).

∙ Male sterilization with appropriately confirmed absence of sperm in the post-vasectomy ejaculate.

∙ Bilateral tubal ligation or bilateral salpingectomy.

⁃ Oral steroids will be tapered to \<20 mg/day of prednisone (or equivalent) at least 1 week prior to the first study treatment. The tapering schedule will be at the discretion of the Investigator.

⁃ Subjects must have a predicted diffusing capacity for carbon monoxide (DLCO) of \>60% and a forced expiratory volume 1 (FEV1) \>70% at screening.

⁃ Left ventricular ejection fraction (LVEF) ≥ 45% by Echocardiogram. Rituximab and AB-101 in autoimmune diseases Clinical Study Protocol V. 1.1 Confidential Page 11 of 101 April 16, 2024

⁃ Baseline laboratory values fulfilling the following requirements to demonstrate adequate hematologic, renal, and hepatic function:

• RA PV MPA / GPA SLE Absolute neutrophil count (/mm3)

• 1500

• 1500 Platelets (/mm3)

• 100,000

• 75,000 Hemoglobin (g/dL)

• 9

• 8 Creatinine clearance (mL/min/1.73 m2)

• 60

• 60 Total serum bilirubin (mg/dL) \< 2.5 \< 2.5 \< 2.5 \< 2.5 Liver transaminases (AST/ALT/ALP)

• ≤ 3x ULN

⁃ 3x ULN Additional Disease-specific Inclusion Criteria Rheumatoid Arthritis

‣ 1\. Documented diagnosis of RA, meeting the 2010 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) classification criteria for RA (Kay, 2012).

‣ 2\. Have had prior treatment for a period of at least 12 weeks with a biologic disease-modifying anti-rheumatic drugs (bDMARD e.g., infliximab, rituximab, etanercept, tocilizumab)) and/or a targeted synthetic disease-modifying anti-rheumatic drugs (tsDMARD e.g., baricitinib, tofacitinib)) and were deemed refractory by either:

• In the opinion of the Investigator, there was a lack of benefit to at least two bDMARDs or one bDMARD and one tsDMARDs. Lack of benefit may include inadequate improvement in joint counts, physical function, or disease activity.

• Intolerance to at least two lines of prior therapy, including bDMARDs and/or tsDMARDs.

⁃ 3\. Minimum of 6 swollen joint counts (SJC) and 6 tender joint counts (TJC). Pemphigus Vulgaris

‣ Confirmed diagnosis of pemphigus vulgaris with active lesions.

‣ Positive for anti-desmoglein Dsg1 or Dsg3.

‣ Pemphigus Disease Area Index score of \> 10%.

‣ Subjects will have tried and failed at least 12 weeks of treatment of immunosuppressive or biologic standard-of-care agent (methotrexate, azathioprine, mycophenolate mofetil (MMF) or mycophenolic acid (MPA) and corticosteroids, and/or 12 weeks of therapy with IV Gamma globulin treatments with an exposure of 12 weeks to be considered resistant/refractory and will be included in this study.

∙ Granulomatosis with polyangiitis (GPA) / microscopic polyangiitis (MPA)

⁃ <!-- -->

∙ Clinical diagnosis of granulomatosis with polyangiitis (GPA) or microscopic polyangiitis (MPA).

‣ Presence of cytoplasmic Antineutrophil cytoplasmic antibody (c-ANCA) or proteinase-3 (PR3-ANCA) or myeloperoxidase ANCA (MPO-ANCA)

‣ Have ≥ 1 major item, or ≥ 3 other items, or ≥ 2 renal items on the Birmingham Vasculitis Activity Score Version 3 (BVASv3).

‣ For GPA/MPA, subjects will have tried and failed at least 12 weeks of treatment of immunosuppressive (Cyclophosphamide, mycophenolate mofetil (MMF) or mycophenolic acid (MPA) and corticosteroids), or a biologic standard-of-care agent such as Rituximab will be included in this study.

⁃ Systemic Lupus Erythematous

‣ Diagnosis of SLE according to the 2019 European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) Classification Criteria.

‣ Total systemic lupus erythematosus disease activity index (SLEDAI-2K) ≥ 8 at screening excluding alopecia, mucosal ulcers, and fever.

‣ Positive for anti-double-stranded deoxyribonucleic acid (dsDNA) antibodies.

‣ For SLE, subjects will have tried and failed at least 12 weeks of 2 conventional therapies which, at the discretion of the investigator, includes antimalarials, corticosteroids, immunosuppressive agents, such as mycophenolate mofetil, Methotrexate, Azathioprine, as well as biologic agents such as Belimumab, Anifrolumab, and Rituximab.

⁃ The following criteria for standard-of-care therapies must be met:

‣ <!-- -->

⁃ If receiving antimalarial drugs (e.g., hydroxychloroquine, chloroquine, quinacrine), must have used the medication for ≥ 12 weeks prior to first study treatment and at a stable dose for a minimum of 6 weeks prior to first administration of AB-101.

• If receiving immunomodulatory drugs (mycophenolate mofetil \[MMF\]/mycophenolic acid ≤ 2 g/day, azathioprine/6 mercaptopurine (AZA/6 MP) ≤ 2 mg/kg/day, leflunomide ≤ 40 mg/day, methotrexate (MTX) ≤ 25 mg/wk with concomitant folic acid \[recommend ≥ 5 mg/wk\]), calcineurin inhibitor, and/or cyclosporin A, receiving a stable dose for at least 12 weeks prior to the first administration of AB-101.

⁃ Oral corticosteroid (OCS) \<20 mg/day prednisone or equivalent started at least 12 weeks prior to first study treatment and at a stable dose for at least 4 weeks prior to first administration of study treatment. It must be planned that the background standard-of-care treatment remains at a stable dose throughout the Screening Period.