Driving Out Chronic Lymphocytic Leukemia With CAR T Cells

Advancing CAR T-cell therapy for chronic lymphocytic leukemia: exploring resistance mechanisms and the innovative strategies to overcome them

Chimeric antigen receptor (CAR) T-cell therapy has ushered in substantial advancements in the management of various B-cell malignancies. However, its integration into chronic lymphocytic leukemia (CLL) treatment has been challenging, attributed largely to the development of very effective chemo-free alternatives. Additionally, CAR T-cell responses in CLL have not been as high as in other B-cell lymphomas or leukemias. However, a critical void exists in therapeutic options for patients with high-risk diseases who are resistant to the current CLL therapies, underscoring the urgency for adoptive immunotherapies in these patients. The diminished CAR T-cell efficacy within CLL can be traced to factors such as compromised T-cell fitness due to persistent antigenic stimulation inherent to CLL. Resistance mechanisms encompass tumor-related factors like antigen escape, CAR T-cell-intrinsic factors like T-cell exhaustion, and a suppressive tumor microenvironment (TME). New strategies to combat CAR T-cell resistance include the concurrent administration of therapies that augment CAR T-cell endurance and function, as well as the engineering of novel CAR T-cells targeting different antigens. Moreover, the concept of "armored" CAR T-cells, armed with transgenic modulators to modify both CAR T-cell function and the tumor milieu, is gaining traction. Beyond this, the development of readily available, allogeneic CAR T-cells and natural killer (NK) cells presents a promising countermeasure to innate T-cell defects in CLL patients. In this review, we explore the role of CAR T-cell therapy in CLL, the intricate tapestry of resistance mechanisms, and the pioneering methods studied to overcome resistance.

Chimeric Antigen Receptor T-cell Therapy for Chronic Lymphocytic Leukemia: What is the supporting evidence so far?

While acknowledging that newer therapies have improved survival rates in chronic lymphocytic leukemia (CLL), patients with high-risk disease features are at an increased risk of treatment failure. Allogeneic hematopoietic cell transplantation (allo-HCT) was traditionally offered as front-line consolidation in high-risk CLL; however, with the emergence of targeted therapies like Bruton tyrosine kinase (BTK) and B-cell lymphoma 2 (BCL-2) inhibitors, the role of allo-HCT has been relegated to later stages of the disease. Patients with relapsed/refractory (R/R) CLL who have failed both BTK and BCL-2 inhibitors represent a therapeutic challenge owing to a poor prognosis. Chimeric antigen receptor T-cell (CAR T) therapies targeting CD19 have improved response rates and overall survival in various types of R/R B-cell non-Hodgkin lymphomas. For CLL, no approved CAR T-cell therapies are yet available. Emerging data appear to show a therapeutic benefit of CAR T-cell therapy in patients with R/R CLL, even after failing an allo-HCT.

Broadening the horizon: potential applications of CAR-T cells beyond current indications

Engineering immune cells to treat hematological malignancies has been a major focus of research since the first resounding successes of CAR-T-cell therapies in B-ALL. Several diseases can now be treated in highly therapy-refractory or relapsed conditions. Currently, a number of CD19- or BCMA-specific CAR-T-cell therapies are approved for acute lymphoblastic leukemia (ALL), diffuse large B-cell lymphoma (DLBCL), mantle cell lymphoma (MCL), multiple myeloma (MM), and follicular lymphoma (FL). The implementation of these therapies has significantly improved patient outcome and survival even in cases with previously very poor prognosis. In this comprehensive review, we present the current state of research, recent innovations, and the applications of CAR-T-cell therapy in a selected group of hematologic malignancies. We focus on B- and T-cell malignancies, including the entities of cutaneous and peripheral T-cell lymphoma (T-ALL, PTCL, CTCL), acute myeloid leukemia (AML), chronic myeloid leukemia (CML), chronic lymphocytic leukemia (CLL), classical Hodgkin-Lymphoma (HL), Burkitt-Lymphoma (BL), hairy cell leukemia (HCL), and Waldenström's macroglobulinemia (WM). While these diseases are highly heterogenous, we highlight several similarly used approaches (combination with established therapeutics, target depletion on healthy cells), targets used in multiple diseases (CD30, CD38, TRBC1/2), and unique features that require individualized approaches. Furthermore, we focus on current limitations of CAR-T-cell therapy in individual diseases and entities such as immunocompromising tumor microenvironment (TME), risk of on-target-off-tumor effects, and differences in the occurrence of adverse events. Finally, we present an outlook into novel innovations in CAR-T-cell engineering like the use of artificial intelligence and the future role of CAR-T cells in therapy regimens in everyday clinical practice.

The role of allogeneic hematopoietic cell transplantation for chronic lymphocytic leukemia: A review

Although the use of allogeneic hematopoietic cell transplantation (HCT) for chronic lymphocytic leukemia (CLL) has declined with the development of novel targeted agents, it continues to play an important role for eligible patients with high-risk or heavily pretreated CLL who lack other treatment options. CLL is susceptible to a potent graft-versus-leukemia (GVL) effect which produces long-lasting remissions in 30-50% of transplanted patients. While allogeneic HCT is associated with significant risks of graft-versus-host disease (GVHD), infection, and non-relapse mortality (NRM), improvements in patient and donor selection, reduced intensity conditioning (RIC), GVHD prophylaxis, and supportive care have rendered this an increasingly safe and effective procedure in the current era. In this review, we discuss recent advances in allogeneic HCT for CLL, with a focus on the optimal evidence-based strategies to maximize benefit and minimize toxicity of this potentially curative cellular therapy.

Interleukin (IL)-9 Supports the Tumor-Promoting Environment of Chronic Lymphocytic Leukemia

Simple Summary

Interleukin 9 (IL-9), a soluble factor secreted by immune cells, has been found in several tumor niches where, depending on the specific tumor type, it either promotes or counteracts tumor development. Recently, IL-9 has been implicated in the development of chronic lymphocytic leukemia, although the underlying molecular mechanism remains unknown. Here, we summarize the current knowledge concerning the roles of IL-9 in disease, with a focus on its implication in the pathogenesis of chronic lymphocytic leukemia.

Abstract

Interleukin (IL)-9 is a soluble factor secreted by immune cells into the microenvironment. Originally identified as a mediator of allergic responses, IL-9 has been detected in recent years in several tumor niches. In solid tumors, it mainly promotes anti-tumor immune responses, while in hematologic malignancies, it sustains the growth and survival of neoplastic cells. IL-9 has been recently implicated in the pathogenesis of chronic lymphocytic leukemia; however, the molecular mechanisms underlying its contribution to this complex neoplasia are still unclear. Here, we summarize the current knowledge of IL-9 in the tumor microenvironment, with a focus on its role in the pathogenesis of chronic lymphocytic leukemia.