• Age \<21 years old

• Relapsed/refractory CD19- and/or CD22-positive acute leukemia defined as:

• \*CD19 and/or CD22-positivity confirmed within 2 months and after receipt of any CD19 or CD22-directed therapy

⁃ Second or greater relapse

⁃ Any relapse after allogeneic HCT

⁃ Refractory disease (primary or in relapse) despite therapy designed to induce remission

• Estimated life expectancy of \> 12 weeks

• Karnofsky or Lansky (age-dependent) performance score ≥50 (Appendix A)

• For females of childbearing age:

‣ Not lactating with intent to breastfeed

⁃ Not pregnant with negative serum or urine pregnancy test within 7 days prior to enrollment

• Age \< 21 years old

• Detectable CD19- and/or CD22-positive leukemic disease in the bone marrow

• Estimated life expectancy of \> 8 weeks

• Karnofsky or Lansky (age-dependent) performance score \> 50 (Appendix A)

• Adequate cardiac function defined as left ventricular ejection fraction \>40%, or shortening fraction \> 25%

• EKG without evidence of clinically significant arrhythmia

• Adequate renal function defined as creatinine clearance or radioisotope GFR \>50 mL/min/1.73m2 (GFR \>40 mL/min/1.73m2 if \<2 years of age)

• Adequate pulmonary function defined as forced vital capacity (FVC) \>50% of predicted value; or pulse oximetry \>92% on room air

• Total bilirubin \< 3 times the upper limit of normal for age, except in subjects with Gilbert's syndrome

• Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \< 5 times the upper limit of normal for age

• Has recovered from all NCI CTAE grade III-IV, non-hematologic acute toxicities from prior therapy

• Prior to planned CAR T cell infusion, patients with a history of prior allogeneicHCT must be at least 3 months from HCT, have no evidence of acute GVHD, and have not received a donor lymphocyte infusion (DLI) within the 28 daysprior to planned infusion

• For females of childbearing age:

‣ Not lactating with intent to breastfeed

⁃ Not pregnant with negative serum or urine pregnancy test within 7 days prior to enrollment

⁃ If sexually active, agreement to use birth control until 3 months after T cell infusion. Male partners should use a condom.