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.

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of clonal B cells. Although targeted therapies have improved outcomes, resistance remains a challenge, particularly in high-risk patients with TP53 mutations or unmutated immunoglobulin heavy-chain variable region (IGHV) genes (U-CLL). Ferroptosis, a regulated, iron-dependent form of cell death, may represent an exploitable vulnerability in CLL; however, its mechanisms and clinical relevance remain poorly understood. Here, we identified IGHV status and microenvironmental cues as determinants of ferroptosis sensitivity. Using CLL cell lines, patient samples, and in vivo models, we show that CLL cells exhibit elevated basal levels of lipid peroxides and labile iron, predisposing them to ferroptosis. However, stromal interactions enhance cystine import and glutathione synthesis, thereby mitigating susceptibility to ferroptosis. Mechanistically, BTK inhibition sensitizes CLL cells to ferroptosis by increasing the transferrin receptor (TFRC, CD71) and increasing the intracellular Fe²⁺ level. High TFRC expression was associated with improved survival in two independent CLL patient cohorts, supporting its therapeutic and prognostic relevance. Combining ibrutinib with the GPX4 inhibitor RSL3 enhances ferroptosis and improves antileukemic efficacy in vivo. CLL cells with mutated IGHV genes (M-CLL) display greater TFRC expression and ferroptosis sensitivity than U-CLL cells do. This resistance can be overcome by ibrutinib-mediated TFRC induction or via metabolic targeting of fatty acid metabolism. Notably, ACSL1 is selectively upregulated in U-CLL cells and represents a targetable metabolic enhancer of ferroptosis sensitivity, as shown in vivo. Our findings reveal that TFRC and ACSL1 are functionally distinct yet targetable nodes that govern ferroptosis vulnerability in CLL patients and may guide novel therapeutic strategies for high-risk patients.

Nowadays, T-cell-based approaches play an increasing role in cancer treatment. In particular, the use of (genetically engineered) T-cells has heralded a novel era for various diseases with previously poor outcomes. Concurrently, the relationship between the functional behavior of immune cells and their metabolic state, known as immunometabolism, has been found to be an important determinant for the success of immunotherapy. In this context, immune cell metabolism is not only controlled by the expression of transcription factors, enzymes and transport proteins but also by nutrient availability and the presence of intermediate metabolites. The lack of as well as an oversupply of nutrients can be detrimental and lead to cellular dysfunction and damage, potentially resulting in reduced metabolic fitness and/or cell death. This review focusses on the detrimental effects of excessive exposure of T cells to fatty acids, known as lipotoxicity, in the context of an altered lipid tumor microenvironment. Furthermore, implications of T cell-related lipotoxicity for immunotherapy will be discussed, as well as potential therapeutic approaches.

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Objectives: Allogeneic stem cell transplantation (allo‐SCT) is the only curative treatment option for several haematologic malignancies. Its therapeutic principle is based on the donor T cells' ability to eliminate any residual malignant cells. Despite its success, challenges such as graft‐versus‐host disease (GvHD) and disease relapse persist. Recent studies emphasise the role of the metabolic environment in shaping T‐cell responses. This study investigates the impact of serum metabolites on T‐cell responses following allo‐SCT. Methods: Metabolite levels in serum samples from 55 allo‐SCT patients transplanted between November 2015 and October 2018 were analysed by nuclear magnetic resonance (NMR) spectroscopy for six time points after transplantation. These metabolite profiles were correlated with clinical data and T‐cell characteristics obtained by flow cytometry‐based immunomonitoring. High‐density lipoprotein (HDL) emerged as a key factor of interest. To explore the potential relationship between T‐cell‐related differences and HDL levels, healthy donor T‐cell cultures supplemented with HDL were performed. Results: Elevated HDL levels were associated with acute GvHD (aGvHD) and relapse. Patients with high HDL serum levels exhibited a delayed normalisation of T‐cell frequencies and increased effector‐memory CD8 ⁺ T‐cell frequencies. In vitro experiments revealed reduced proliferation and expression of activation/effector molecules after exposure to HDL. Effects of HDL on memory T‐cell subset formation resembled the in situ findings in patients. Conclusions: AGvHD was linked to elevated HDL levels, potentially affecting T‐cell‐mediated graft‐versus‐leukaemia (GvL) activity and promoting relapse. HDL could therefore be a potential biomarker for the success of allo‐SCT and a lever for improving patients' outcomes.