This is a single-center, single-arm, open-label phase 1/2 study of CART19 in children and young adults with refractory Systemic lupus erythematosus (SLE), including both patients diagnosed with lupus nephritis (LN) and patients with non-renal Systemic lupus erythematosus (SLE).

Phase 1 will evaluate the safety of CART19 in 6-12 patients with Systemic lupus erythematosus (SLE). There is no planned dose escalation, but a dose de-escalation will be made based on the incidence of Dose Limiting Toxicities. Phase 2 will evaluate the efficacy and further evaluate the safety of CART19 in this population.

Lupus disease activity is associated with increased numbers of activated naïve B cells and polyclonal expansion of antibody secreting cells, indicating a central role for B cells in the pathogenesis of SLE. While traditional anti-CD19 antibody therapies have been utilized with varying success in the treatment of Systemic lupus erythematosus (SLE), CD19 directed cellular therapies have emerged as an attractive therapeutic option that may lead to immunosuppression-free remission in this population given the ability of CD19 directed CAR T cells to more deeply deplete the B cell compartment. Previous clinical experience utilizing CD19 directed CAR T cells in patients diagnosed with Systemic lupus erythematosus (SLE) have exceeded any other Systemic lupus erythematosus (SLE) therapeutic available; although, those clinical trials have treated a limited number of subjects. During this trial the test article will be CART19 cells transduced with a lentiviral vector to express anti-CD19 scFv:41-BB:TCRζ, administered by IV injection.

Inclusion Criteria:

1. Signed informed consent form must be obtained prior to any study procedure. Labs or other procedures obtained during routine clinical care may be used for eligibility if obtained within the protocol required window.

2. Patient age must be 12-29 years, inclusive, at time of enrollment.

3. Meeting ACR/EULAR Classification Criteria for SLE

4. ANA positive > 1:80 and/or double-stranded DNA (dsDNA) positive

5. Active (refractory) disease, defined as follows:

   a. Lupus nephritis subjects must meet both the following criteria: i. ISN/RPS active nephritis Class III/IV +/- V lupus nephritis diagnosed by biopsy within past 12 months.

ii. Persistent and clinically significant: ≥2 measurements with urine protein with either of the following:

1. > 1mg/mg creatinine
2. > 0.5 mg/mg creatinine associated with renal dysfunction or low albumin.
3. > 0.5 mg/mg creatinine in a patient with rising proteinuria after prior complete renal response b. Non-renal SLE subjects must meet either of the following criteria: i. SLEDAI-2K ≥ 8 and clinical SLEDAI-2K ≥ 6 ii. Inability to decrease prednisone ≤7.5mg/day or 0.15mg/kg/day, whichever is lower, due to active disease.

6. Patients must have had at least 3 months of cumulative conventional therapy defined as:

1. Conventional induction immunosuppressive agent(s) (e.g., mycophenolate mofetil, cyclophosphamide), and
2. At least one additional therapy:

i. B-cell directed biologic therapy (e.g., rituximab, belimumab, ofatumumab, obinutuzumab) ii. Calcineurin inhibitor (e.g., tacrolimus, cyclosporine, voclosporin) iii. Other immunosuppressive medication for SLE (e.g., anifrolumab, abatacept, JAK inhibitor) 7. Adequate organ function status

1. Renal: eGFR must be ≥30 and subject cannot be receiving dialysis.
2. Hepatic: Transaminases < 5x upper limit of normal and serum conjugated (Direct) bilirubin <1.5x upper limit of normal unless attributable to SLE. If attributable to autoimmune disease, Child-Pugh score must be class A or class B. Child-Pugh score cannot be class C.
3. Cardiac: Shortening fraction > 28%, left ventricular ejection fraction >45%, and no evidence of severe pulmonary hypertension
4. Pulmonary: Must have a minimum level of pulmonary reserve defined as ≤ Grade 1 dyspnea and \