Inclusion Criteria:  1. Relapsed or refractory CD19 Positive Acute Lymphoblastic Leukemia. All subjects must be younger than 26 years old at the time of obtaining informed consent  a. 2nd or greater BM[bone marrow] relapse OR b. Any BM relapse after allogeneic SCT[stem cell transplant] and must be ≥ 6 months from SCT at the time of SNUH_CD19_CAR-T infusion OR c .Refractory as defined by not achieving a CR after 2 cycles of a standard chemotherapy regimen or chemorefractory as defined by not achieving a CR after 1 cycle of standard chemotherapy for relapsed leukemia OR d. Ineligible for allogeneic SCT because of:  Severe comorbid disease Other contraindications to allogeneic SCT conditioning regimen  Lack of suitable donor  2. Documentation of CD19 tumor expression in bone marrow or peripheral blood by flow cytometry.  3. Karnofsky (age ≥ 16 years) or Lansky (age < 16 years) performance status ≥ 50 at screening  Exclusion Criteria:  Evidence of uncontrolled hepatitis B virus (HBV) or hepatitis C virus (HCV) based on assessment done by treating physicians. Known human immunodeficiency virus (HIV) infection. Presence of clinically active uncontrolled infection based on assessment done by treating physicians. Infections are considered controlled if appropriate therapy has been instituted and, at the time of screening, no signs of progression are present. Persisting fever without other signs or symptoms will not be interpreted as progressing infection. Pregnant or nursing (lactating) women.