Improving therapy of chronic lymphocytic leukemia with chimeric antigen receptor T cells

Abstract

Adoptive cell immunotherapy for the treatment of chronic lymphocytic leukemia (CLL) has heralded a new era of synthetic biology. The infusion of genetically engineered, autologous chimeric antigen receptor (CAR) T cells directed against CD19 expressed by normal and malignant B cells represents a novel approach to cancer therapy. The results of recent clinical trials of CAR T cells in relapsed and refractory CLL have demonstrated long-term disease-free remissions, underscoring the power of harnessing and redirecting the immune system against cancer. This review will briefly summarize T-cell therapies in development for CLL disease. We discuss the role of T-cell function and phenotype, T-cell culture optimization, CAR design, and approaches to potentiate the survival and anti-tumor effects of infused lymphocytes. Future efforts will focus on improving the efficacy of CAR T cells for the treatment of CLL and incorporating adoptive cell immunotherapy into standard medical management of CLL.

Keywords: CAR; CLL; Immunotherapy; Leukemia; T cell.

Figure 1. Structure of First, Second and Third Generation Chimeric Antigen Receptors (CARs)

CARs are composed of antigen-binding moieties (i.e., scFv consisting of an interconnected variable heavy chain (V_H) and variable light chain (V_L)) fused to a transmembrane (TM) region of a protein such as CD8 that is, in turn, linked to a signal transduction domain. First generation CARs contained only the ζ chain of the T cell receptor (TCR). Second generation CARS incorporate a co-stimulatory endodomain fused to CD3ζ (e.g., CD28 or 4-1BB), and third generation antigen receptors of this type possess a second intracellular signaling module linked in tandem (e.g., both 4-1BB and CD28). Upon binding of the scFv to a cognate antigen, second and third generation CAR T cells receive a primary activation signal, as well as concomitant co-stimulation.

Figure 2. Manufacturing scheme for CTL019 cells

T lymphocytes are initially isolated from the peripheral blood of CLL patients and enriched, as well as activated with anti-human CD3/CD28-coated polystyrene beads. Gene transfer is accomplished by lentiviral transduction and following a ten day expansion period, beads are removed and cells are frozen in an infusible media for adoptive transfer into patients.

Figure 3. Features of T cell pseudoexhaustion and immunosuppression in CLL that could hamper the clinical efficacy of manufactured CAR T cells

T cells isolated from CLL patients exhibit some functional and phenotypic hallmarks of chronic exhaustion, such as high levels of inhibitory molecules (e.g., PD-1, CD244 and CD160), impaired proliferative capacity and cytolytic defects. Soluble immunosuppressive factors elaborated by CLL cells may further contribute to inhibition of T cell function in the setting of adoptive cell therapy.