Vitamin D3 Treatment in Pediatric Systemic Lupus Erythematosus

Inclusion Criteria: * Written informed consent signed by the subject or parent/guardian as appropriate; child assent as appropriate; * Before the age of 19, met at least 4 of the 11 modified American College of Rheumatology (ACR) 1982 Revised Criteria for the Classification of Systemic Lupus Erythematosus as updated in 1997; * Date of SLE diagnosis (as described in Inclusion Criterion 2) at least 24 weeks prior to randomization; * Serum 25-hydroxyvitamin D \[25(OH)D\] \< 20 ng/mL at Screening; * SELENA SLEDAI score \> 0 and \< 8 at Screening and at Baseline; * If taking prednisone (or equivalent corticosteroid), the dose must be ≤ 15 mg/day or ≤0.5 mg/kg/day, whichever is lower, and stable for at least four weeks prior to randomization. Note, if subjects are taking steroids every other day, divide their dose by 2 to evaluate eligibility; * Stable immunosuppressive dose for at least 12 weeks prior to randomization; --Immunosuppressive medications allowed include mycophenolate (MMF), azathioprine, methotrexate, antimalarial medications (e.g., hydroxychloroquine), cyclosporine A (CsA), tacrolimus, intravenous immune globulin (IVIG), and abatacept. * Body weight \> 25 kg; * Able to swallow pills; * Males and females with reproductive potential must agree to practice effective measures of birth control. Exclusion Criteria: * Any condition or treatment that, in the opinion of the investigator, places the subject at an unacceptable risk as a participant in the trial; * Current pharmacologic vitamin D2 or D3 intake \> 800 IU daily or use of calcitriol at any dose over the past four weeks prior to randomization; * Cyclophosphamide or IV glucocorticoid exposure within 12 weeks prior to randomization; * Any BILAG A or B manifestation with the exception of a BILAG B mucocutaneous manifestation at screening, and excluding the renal BILAG criteria (see rituximab or belimumab criterion, below); * Significant renal insufficiency defined as: * Estimated GFR \< 60 mL/min/1.73m\^2 or estimated GFR \< 90 mL/min/1.73m\^2 with a reduction of the GFR by \> 15% from the last measurement; * Urine dipstick value of 2+ or higher for protein, unless this is a stable value from the last measurement or, urine protein-creatinine ratio ≥ 50 mg/mmol unless the value represents an improvement of ≥ 25% from the last measurement. * Rituximab or belimumab exposure use within 24 weeks prior to randomization; * The following laboratory parameters at the Screening visit: * Platelets \< 50,000; WBC \< 2,500; ANC \< 1,000; * Hemoglobin \< 9 mg/dL; * ALT, AST, bilirubin \> 2x upper limit of normal (ULN); * Hypercalcemia (calcium \> ULN); * Hypercalciuria (urinary calcium/creatinine ratio \> 0.2). * Primary hyperparathyroidism (known); * History of nephrolithiasis (known); * Diabetes mellitus requiring insulin therapy; * Medications that interfere with vitamin D absorption; * History of vertebral compression fractures (known); * Pregnancy (girls ≥ 11 years of age must have a negative urine/serum pregnancy test); * A history of non-adherence/non-compliance; * Other investigational drug and/or treatment during the four weeks or seven half-lives of the other investigational drug prior to the start of study product dosing (Day 0), whichever is the greater length of time to enrollment; * Current diagnosis of cancer or chronic infection such as Hepatitis B, Hepatitis C, or tuberculosis; * Treatment with digoxin; * Flu (influenza) vaccination within one week prior to randomization.