CLL-Derived Extracellular Vesicles Impair T-Cell Activation and Foster T-Cell Exhaustion via Multiple Immunological Checkpoints

Abstract

Background: Chronic lymphocytic leukemia (CLL) is characterized by the clonal expansion of malignant B-cells and multiple immune defects. This leads, among others, to severe infectious complications and inefficient immune surveillance. T-cell deficiencies in CLL include enhanced immune(-metabolic) exhaustion, impaired activation and cytokine production, and immunological synapse malformation. Several studies have meanwhile reported CLL-cell–T-cell interactions that culminate in T-cell dysfunction. However, the complex entirety of their interplay is incompletely understood. Here, we focused on the impact of CLL cell-derived vesicles (EVs), which are known to exert immunoregulatory effects, on T-cell function. Methods: We characterized EVs secreted by CLL-cells and determined their influence on T-cells in terms of survival, activation, (metabolic) fitness, and function. Results: We found that CLL-EVs hamper T-cell viability, proliferation, activation, and metabolism while fostering their exhaustion and formation of regulatory T-cell subsets. A detailed analysis of the CLL-EV cargo revealed an abundance of immunological checkpoints (ICs) that could explain the detected T-cell dysregulations. Conclusions: The identification of a variety of ICs loaded on CLL-EVs may account for T-cell defects in CLL patients and could represent a barrier for immunotherapies such as IC blockade or adoptive T-cell transfer. Our findings could pave way for improving antitumor immunity by simultaneously targeting EV formation or multiple ICs.

Extracellular Vesicles Expressing CD19 Antigen Improve Expansion and Efficacy of CD19-Targeted CAR-T Cells

“…42 It is worth noting that TEVs may induce exhaustion of CAR-T cells, impair their proliferation and anti-tumor activity. 19,[43][44][45] Specifically, the immunological checkpoints (IC) including PD-L1 found in TEVs could be responsible for the negative effect of TEVs in CAR-T cells. 19,45 Therefore, in our study, we adopted EVs derived from HEK293T cells to deliver target antigen.…”

“…19,[43][44][45] Specifically, the immunological checkpoints (IC) including PD-L1 found in TEVs could be responsible for the negative effect of TEVs in CAR-T cells. 19,45 Therefore, in our study, we adopted EVs derived from HEK293T cells to deliver target antigen. The HEK293T cell line is derived from human embryonic kidney cells and is frequently used in various experiments and studies associated with EVs.…”

Extracellular Vesicles in Chronic Lymphocytic Leukemia: Tumor Microenvironment Messengers as a Basis for New Targeted Therapies?

“…EVs purified from CLL cells can also impede antitumor immune surveillance by blocking the proliferation, activation, and metabolism of T lymphocytes and promoting T cell exhaustion and the formation of regulatory T cells [ 59 ]. Böttcher et al suggested that these processes are regulated by the detection of immunological checkpoints (ICs) on CLL EVs, although a causal relationship with T cell dysregulation was not demonstrated.…”

“…Two recent studies of anti-CD19 chimeric antigen receptor (CAR)-T cell therapy showed that CLL EVs can disrupt the immune synapse and contribute to the CAR-T-cell’s exhaustion, metabolic quiescence [ 59 ], or even lysis [ 86 ]. These findings might explain the CAR-T-cell treatment failure observed in the clinic.…”

Small extracellular vesicles: multi-faceted tools for leukemia immune evasion in vivo

“… 4 Finally, it was recently shown that CLL-derived sEVs alter CD4 + and CD8 + T-cell leading to an expansion of regulatory T-cell subsets and exhaustion, respectively. 5 …”