Reversing Type 1 Diabetes After it is Established

Inclusion Criteria: * Must be \> 12 years \< 45 * Must have a diagnosis of T1D of greater than 4 months duration, with an upper limit of 2 years, Now only recruiting for those diagnosed greater than 1 year but less than 2 years. * Must have at least one diabetes-related autoantibody present (e.g., islet cell autoantigen (ICA), GAD, ZnT8, or islet antigen 2 (IA2) autoantibodies) * Must have stimulated C-peptide levels ≥ 0.1 pmol/ml (0.3ng/mL) when measured during a mixed meal tolerance test (MMTT), conducted at least 4 months from diagnosis of diabetes, and within 8 weeks of randomization * Must be EBV PCR negative within two weeks of randomization if EBV seronegative at screening * Be at least 6 weeks from last live immunization * Be willing to forgo live vaccines for 3 months following last dose of study drug * Be willing to comply with intensive diabetes management * Normal screening values for complete blood count (CBC), renal function and electrolytes (CMP). Exclusion Criteria: * Be immunodeficient or have clinically significant chronic lymphopenia: (Leukopenia (\< 3,000 leukocytes /μL), neutropenia (\<1,500 neutrophils/μL), lymphopenia (\<800 lymphocytes/μL), or thrombocytopenia (\<125,000 platelets/μL). * Have a chronic infection at time of randomization * Have a positive PPD * Be currently pregnant or lactating, or anticipate getting pregnant within the next two years * Require use of other immunosuppressive agents * Have serologic evidence of current or past HIV, Tuberculosis, Hepatitis B or Hepatitis C infection * Have any complicating medical issues or abnormal clinical laboratory results that interfere with study conduct, or cause increased risk to include pre-existing cardiac disease, chronic obstructive pulmonary disease (COPD), sickle cell disease, neurological, or blood count abnormalities (e.g., lymphopenia, leukopenia, or thrombocytopenia) * Have a history of malignancies * Evidence of liver dysfunction with angiotensin sensitivity test (AST) or ALT greater than 3 times the upper limits of normal * Evidence of renal dysfunction with creatinine greater than 1.5 times the upper limit of normal * Vaccination with a live virus within the last 6 weeks * Current use of non-insulin pharmaceuticals that affect glycemic control * Active participation in another T1D treatment study in the previous 30 days * Known allergy to G-CSF or ATG * Prior treatment with ATG or known allergy to rabbit derived products * Any condition that in the investigator's opinion, may adversely affect study participation or may compromise the study results