Patients with relapsed or refractory CD 19+ leukemia who have achieved remission after CD19 CAR-T cell treatment sometimes relapse because the CD 19 CAR-T cells decrease in number over time. Study PLAT-03 will test whether administering T cell antigen presenting cells (T-APCs) at intervals following treatment with CAR-T cells improves CD 19 CAR-T cell persistence and reduces the incidence of leukemia relapse.

This pilot study seeks to examine the feasibility and safety of administering T cell antigen presenting cells (T-APCs) designed to reactivate and numerically expand CD19-specific CAR T cells. The underlying hypothesis to be examined is that after remission is achieved with CAR T cell treatment, the duration, magnitude, and activation state of persisting memory CAR T cells impact on the potential for durable leukemia eradication. This is of particular relevance in two groups of patients we have identified: those who are predicted to lose persistence of their CAR T cells before Day 63, and those who have definitively lost persistence of CAR T cells prior to 6 months. By providing these patients with episodic exposure to T-APCs capable of activating CD19-specific CAR T cells for proliferation and redistribution to tissue beds where tumor cells of ALL seed, ideally over several months following remission induction, it is posited that the incidence of disease relapse will be diminished.

Inclusion Criteria:

• Diagnosis of recurrent or refractory CD19+ leukemia
• Adequate performance status
• Able to tolerate apheresis, including placement of temporary apheresis line if required
• Adequate renal, liver, cardiac, and respiratory function
• Adequate absolute lymphocyte count
• HIV negative; Hepatitis B and C negative within 3 months prior to enrollment.

Exclusion Criteria:

• Evidence of active clinically significant CNS dysfunction
• Evidence of active malignancy other than CD19+ malignancy
• Evidence of active GVHD, or on immunosuppressive GVHD therapy within 4 weeks prior to enrollment