Preferential expansion of CD8+ CD19-CAR T cells postinfusion and the role of disease burden on outcome in pediatric B-ALL

Abstract

T cells expressing CD19-specific chimeric antigen receptors (CD19-CARs) have potent antileukemia activity in pediatric and adult patients with relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL). However, not all patients achieve a complete response (CR), and a significant percentage relapse after CD19-CAR T-cell therapy due to T-cell intrinsic and/or extrinsic mechanisms. Thus, there is a need to evaluate new CD19-CAR T-cell products in patients to improve efficacy. We developed a Phase 1/2 clinical study to evaluate an institutional autologous CD19-CAR T-cell product in pediatric patients with relapsed/refractory B-ALL. Here we report the outcome of the phase 1 study participants (n=12). Treatment was well tolerated, with low incidence of both cytokine release syndrome (any grade, n=6) and neurotoxicity (any grade, n=3). Nine out of 12 patients (75%) achieved a minimal residual disease-negative CR in the bone marrow. High disease burden (≥40% morphologic blasts) prior to CAR T-cell infusion correlated with increased side effects and lower response rate, but not with CD19-CAR T-cell expansion. Postinfusion, CD8+ CAR T cells had a proliferative advantage over CD4+ CAR T cells, and at peak expansion had an effector memory phenotype with evidence of antigen-driven differentiation. Patients that proceeded to allogeneic hematopoietic cell transplantation had sustained, durable responses. In summary, initial evaluation of our institutional CD19-CAR T-cell product demonstrates safety and efficacy, while highlighting the impact of pre-infusion disease burden on outcomes. This trial was registered at www.clinicaltrials.gov as #NCT03573700.

Common Trajectories of Highly Effective CD19-Specific CAR T Cells Identified by Endogenous T-cell Receptor Lineages

“…To determine features of effective CAR T cell therapies, we undertook a comprehensive gene expression profiling of 16 pediatric patients with relapsed/refractory B-ALL, 15 of whom had received autologous T cells expressing a CD19.4-1BBz CAR (CD19-CAR) (9,10) post lymphodepleting chemotherapy on our investigator-initiated clinical study (NCT03573700; Fig 1A). Patients 0 through 12 have been reported in detail elsewhere (11). Twelve out of the 15 patients who were infused with CAR T cells achieved a complete response (CR), with 11/12 CRs being measurable residual disease negative (MRDneg) at four weeks post CD19-CAR T cell infusion (see Supplementary Clinical Information).…”

“…The clinical grade lentiviral vector encoding the CD19.4-1BBz CAR, and CD19-CAR T cell products were manufactured at the Children's Good Manufacturing Practice facility of St. Jude. The study, lentiviral vector, and the manufacturing of autologous CD19-CAR T cells is described in detail elsewhere (11).…”

“…The first six patients received 1x10 6 CAR-positive T cells/kg, and starting with patient 7, 3x10 6 CAR-positive T cells/kg were infused. The highest dose provided only three-fold more cells than the lowest dose, and there were no major differences observed between dosages (11). Response, at 4 weeks post infusion, was categorized as complete response (CR), either minimal-residual disease (MRD)-negative or MRD-positive, or no response (NR).…”

“…Peripheral blood samples analyzed for this study were collected at weeks 1-4, 8, and months 3 and 6 post infusion; bone marrow aspirates were obtained at week 4 and month 3 post infusion. qPCR assays for the CD19-CAR transgene were performed as previously described (11).…”

Latent human herpesvirus 6 is reactivated in chimeric antigen receptor T cells

“…Using single-cell sequencing, we identify a rare population of HHV-6 ‘super-expressors’ (~1 in 300-10,000 cells) that possess high viral transcriptional activity in chimeric antigen receptor (CAR) T cell culture before spreading to infect other cells in vitro . Through the analysis of single-cell sequencing data from patients receiving cell therapy products that are FDA-approved 2 or used in clinical studies 3,4 , we identify the presence of CAR+, HHV-6 super-expressor T cells in vivo . Together, our study implicates cell therapy products as a source of lytic HHV-6 reported in clinical trials 1,5–7 and has broad implications for the design, production, and monitoring of cell therapies.…”