Third-Generation CAR T Cells Targeting CD19 Are Associated with an Excellent Safety Profile and Might Improve Persistence of CAR T Cells in Treated Patients

Introduction

T cells transduced with a chimeric antigen receptor (CAR) have demonstrated significant clinical efficacy in patients with lymphoid malignancies including relapsed or refractory (r/r) B-lineage acute lymphoblastic leukemia (ALL) or r/r B-cell non-Hodgkin's lymphoma (NHL). Second-generation CAR T cells comprising 4-1BB or CD28 as costimulatory domains have become commercially available for the treatment of patients with CD19+ lymphoid malignancies. However, achievement of durable clinical responses remains a challenge in CAR T cell therapy. Consequently, third-generation CARs incorporating both elements might display short-term efficacy with potent and rapid tumor elimination (CD28) as well as long-term persistence (4-1BB). So far, only two clinical trials employing third-generation CAR T cells have been reported. Both enrolled 31 patients in summary and demonstrated favorable results for third-generation CAR T cells. Here, we report on first results of our investigator-initiated trial (IIT) on third-generation CD19-directed CAR T cells: The Heidelberg CAR trial 1 (HD-CAR-1; NCT03676504; EudraCT 2016-004808-60) is a phase I/II trial initiated in September 2018 with in-house leukapheresis and CAR T cell manufacturing in full compliance with European Good Manufacturing Practice (GMP) guidelines at the University Hospital Heidelberg.

Methods

Adult and pediatric patients with r/r ALL and patients with r/r chronic lymphocytic leukemia (CLL) or NHL including diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL) or mantle cell lymphoma (MCL) are treated with autologous T lymphocytes transduced with a CD19 targeting third-generation CAR retroviral vector (RV-SFG.CD19.CD28.4-1BBzeta). The main purpose of HD-CAR-1 is to evaluate safety and feasibility of escalating third-generation CAR T cell doses (1-20×10⁶ transduced cells/m²) after lymphodepletion with fludarabine (30 mg/m²/d on days -4 to -2) cyclophosphamide (500 mg/m²/d on days -4 to -2). Patients are monitored for cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity syndrome (ICANS) and/or other toxicities. In vivo function, survival and anti-tumor efficacy of CAR T cells are assessed.

Results

To date, 10 patients (3 adult ALL, 2 CLL, 2 MCL, 2 DLBCL, 1 transformed FL) have been enrolled and subjected to leukapheresis. Transduction efficiency of T lymphocytes ranged between 33%-66% and high numbers of transduced CAR T cells were harvested (70-123x10⁶ CAR T cells). No production failure occurred. CAR T cell products were sterile and free from mycoplasma and endotoxins. The copy number per CAR T cell did not exceed 7. Eight patients (2 adult ALL, 2 CLL, 1 MCL, 2 DLBCL, 1 transformed FL) have received the CAR T cell product (6 patients: 10⁶ transduced cells/m²; 2 patients 5×10⁶ transduced cells/m²). No signs of CRS or ICANS > grade 2 have been observed. Only one patient required tocilizumab. No neurological side-effects occurred, even not in patients with involvement of the central nervous system (CNS). In quantitative real-time PCR, CAR T cells were detectable in the peripheral blood (PB) in 3 of 4 analyzed patients or the cerebrospinal fluid (CSF) of an ALL patient with CNS involvement. The CAR T cell frequency reached up to 200,000 copies/µg DNA, in some patients beyond end-of-study at day 90 after CAR T cell administration. Clinical responses to treatment were observed in 6/8 (75%) treated patients so far (2/8 patients have received CAR T cells recently and are not yet evaluable for response).

Conclusion

Leukapheresis and CAR T cell manufacturing were effective for all patients enrolled in the HD-CAR trial to date. Patients responded clinically to treatment despite low numbers of administered CAR T cells. CAR T cells displayed an excellent safety profile and were detectable for more than 3 months following administration. Furthermore, CAR T cells migrated into different compartments including the CSF in case of CNS involvement. For HD-CAR-1 leukapheresis, CAR T cell manufacturing, CAR T cell administration, patient monitoring and follow-up are performed in-house, providing autarky from transport or production sites outside the University Hospital Heidelberg. Altogether, HD-CAR-1 accounts to clinical evaluation of third-generation CAR T cells that might contribute to long-term CAR T cell persistence, hence improving efficient and durable responses in treated patients.