Third Generation CD19-CAR T Cells for Relapsed and Refractory Lymphoma and Leukemia Report from the Swedish Phase I/IIa Trial

Chimeric antigen receptor (CAR) T cells have shown promising results in patients with B cell malignancy. In preclinical studies we showed that CD19-targeting third generation (3G) CAR T cells containing signaling domains from both CD28 and 4-1BB as co-stimulatory molecules have greater activation and proliferation in response to antigens than 2G CARs containing CD28 only. Herein we report results from a phase I/IIa study (NCT:02132624) using these 3G CAR T cells. Patients with relapsed or refractory CD19+ B-cell malignancy were eligible, provided there was no curative treatment available. Of the first eleven patients reported, nine had lymphoma and two had acute lymphoblastic leukemia (ALL). Autologous CAR T cells were manufactured using a gamma retrovirus encoding the CAR and expanded by αCD3/αCD28/IL2. During CAR T cell production, all lymphoma patients received treatment to control tumor burden (-90 to -3 days before T cell infusion). Their treatment depended on the type of lymphoma and previous treatments. In addition, prior to T cell infusion (day -2 to -1) patients #6-11 received cyclophosphamide (500mg/m²) and fludarabine (25mg/m²) as conditioning to decrease immunosuppressive cells.

The patients received one infusion of CAR T cells (2x10⁷ cells/m² patients 1 and 2; 1x10⁸ patients 4, 5, 7, 8, 9; and 2x10⁸ patients 6, 10, 11, 12). Patient #1 (DLBCL) had a mild cytokine release syndrome (CRS) after four weeks (never requiring treatment), followed by a complete response of his lymphoma. A relapse and a second CRS occurred after six weeks and he was treated with prednisone with good symptomatic effect and reduction of tumor size. The patient progressed after three months. Patients #2, 4, 5 (CLL, MCL, MCL) all progressed after 2, 1, and 3 months, respectively. Patient #6 (DLBCL) responded to treatment (CR) prior to T cell infusion and remained in complete remission for 6 months post T cell infusion. Patients #7 (CLL) and #9 (DLBCL) also responded to treatment prior to T cell infusion and remains in complete remission +4 and +5  months,respectively. The CLL patient has a tumor negative bone marrow. Patient #8 (FL-DLBCL) had a mild CRS but progressed after 1 month but. Patient #10 (ALL) experienced transient CNS toxicity followed by a complete response. However, at 3 months the patient relapsed with a CD19 negative ALL, accompanied by increased levels of immunosuppressive cells such as T regulatory cells and myeloid derived suppressor cells. Patient #11 (ALL) is in complete remission after a CRS (+3 month) and patient #12 (FL/Burkitt) had a major CRS requiring intensive care and a stable disease for one month before progression. The CAR transgene could be detected in blood at the time of clinical symptoms of response and most patients that progressed lost CAR signal.

In summary, 6 of 11 patients (3 DLBCL, 1 CLL and 2 ALL) treated with increasing doses of 3^rd generation CAR T cells in Sweden had CR or CCR. CRS occurred in 4/11 but was mild in all but one and CNS-toxicity occurred in 2/11 patients of which one required hospitalisation. Correlations between the levels of T regulatory cells and myeloid derived suppressor cells in blood and patient response are currently under investigation.