ATG-GCSF in New Onset Type 1 Diabetes

Inclusion Criteria: * Must be \> 12 years \< 46 * Must have a diagnosis of T1D for less than 100 days at randomization * Willing to provide Informed Consent or have a parent or legal guardian provide informed consent if the subject is \<18 years of age * Positive for at least one islet cell autoantibody; glutamic acid decarboxylase 65 (GAD65A), Insulin micro IAA (mIAA), if obtained within 10 days of the onset of insulin therapy, islet antigen 2 (IA-2A), Islet Cell Antigen (ICA), or zinc transporter 8 (ZnT8A) * Must have stimulated C-peptide levels = 0.2 pmol/ml measured during a mixed meal tolerance test (MMTT) conducted at least 21 days from diagnosis of diabetes and within one month (37 days) of randomization * Must be Epstein-Barr virus (EBV PCR) negative within two weeks of randomization if EBV seronegative at screening * Be at least 6 weeks from last live immunization * Participants are required to receive killed influenza vaccination at least 2 weeks prior to randomization when vaccine for the current or upcoming flu season is available * Be willing to forgo vaccines during the treatment period and for 3 months following last dose of study drug * Be willing to comply with intensive diabetes management 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 (\<100,000 platelets/µL). * Have active signs or symptoms of acute infection at the time of randomization * Have evidence of prior or current tuberculosis infection as assessed by purified protein derivative (PPD), interferon gamma release assay (IGRA) or by history * Be currently pregnant or lactating, or anticipate getting pregnant within the two year study period * Require use of other immunosuppressive agents including chronic use of systemic steroids * Have evidence of current or past human immunodeficiency virus (HIV), Hepatitis B or Hepatitis C infection * Have any complicating medical issues or abnormal clinical laboratory results that may 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 * Have a history of malignancies other than skin * Evidence of liver dysfunction with aspartate aminotransferase (AST) or alanine transaminase (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 or ongoing use of non-insulin pharmaceuticals that affect glycemic control within prior 7 days of screening * Active participation in another T1D treatment study in the previous 30 days * Prior treatment with abatacept or anti-cd3 * Known allergy to GCSF 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