Increased frequency of CD4+ PD-1+ HLA-DR+ T cells is associated with disease progression in CLL

NFKBIE mutations are selected by the tumor microenvironment and contribute to immune escape in chronic lymphocytic leukemia

Loss-of-function mutations in NFKBIE, which encodes for the NF-κB inhibitor IκBε, are frequent in chronic lymphocytic leukemia (CLL) and certain other B-cell malignancies and have been associated with accelerated disease progression and inferior responses to chemotherapy. Using in vitro and in vivo murine models and primary patient samples, we now show that NFKBIE-mutated CLL cells are selected by microenvironmental signals that activate the NF-κB pathway and induce alterations within the tumor microenvironment that can allow for immune escape, including expansion of CD8+ T-cells with an exhausted phenotype and increased PD-L1 expression on the malignant B-cells. Consistent with the latter observations, we find increased expression of exhaustion markers on T-cells from patients with NFKBIE-mutated CLL. In addition, we show that NFKBIE-mutated murine CLL cells display selective resistance to ibrutinib and report inferior outcomes to ibrutinib treatment in NFKBIE-mutated CLL patients. These findings suggest that NFKBIE mutations can contribute to CLL progression through multiple mechanisms, including a bidirectional crosstalk with the microenvironment and reduced sensitivity to BTK inhibitor treatment.

Relationships between T-lymphocytes and physical function in adults with chronic lymphocytic leukemia: Results from the HEALTH4CLL pilot study

OBJECTIVE

Examine physical function and T-cell phenotype in patients with chronic lymphocytic leukemia (CLL) before and after a physical activity (PA) intervention.

METHODS

Physical function measures and blood samples were collected from CLL patients (Rai stage 0-4, 50% receiving targeted therapy, N = 24) enrolled in a 16-week intervention of at-home aerobic and/or resistance exercise. Flow cytometry characterized T-cells in cryopreserved peripheral blood cells. Wilcoxon signed-rank test compared physical function and T-cell phenotype at baseline and 16-weeks; Kendall's Tau assessed associations between variables.

RESULTS

Godin leisure-time PA score increased from baseline to 16-weeks (mean difference: 14.61, p < .01) and fatigue decreased (mean difference: 6.71, p < .001). At baseline, lower fatigue correlated with a lower proportion of CD8+ T-cells (τ = 0.32, p = .03) and cardiorespiratory fitness (CRF) inversely correlated with the percentage of PD-1+CD8+ T-cells (τ -0.31, p = .03). At 16-weeks, CRF inversely correlated with the proportion of PD-1+CD4+ T-cells (τ -0.34, p = .02). Reduced fatigue at 16-weeks correlated with an increased CD4:CD8 ratio (τ = 0.36, p = .02) and lower percentage of HLA-DR+PD-1+CD4+ T-cells (τ = -0.37, p = .01).

CONCLUSIONS

This intervention increased leisure-time PA and decreased fatigue in CLL patients. These changes correlated with an increased CD4:CD8 T-cell ratio and reduced proportion of T-cells subsets previously associated with poor outcomes in CLL patients.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02194387.

Prediction of Clinical Outcomes with Explainable Artificial Intelligence in Patients with Chronic Lymphocytic Leukemia

BACKGROUND

The International Prognostic Index (IPI) is applied to predict the outcome of chronic lymphocytic leukemia (CLL) with five prognostic factors, including genetic analysis. We investigated whether multiparameter flow cytometry (MPFC) data of CLL samples could predict the outcome by methods of explainable artificial intelligence (XAI). Further, XAI should explain the results based on distinctive cell populations in MPFC dot plots.

METHODS

We analyzed MPFC data from the peripheral blood of 157 patients with CLL. The ALPODS XAI algorithm was used to identify cell populations that were predictive of inferior outcomes (death, failure of first-line treatment). The diagnostic ability of each XAI population was evaluated with receiver operating characteristic (ROC) curves.

RESULTS

ALPODS defined 17 populations with higher ability than the CLL-IPI to classify clinical outcomes (ROC: area under curve (AUC) 0.95 vs. 0.78). The best single classifier was an XAI population consisting of CD4+ T cells (AUC 0.78; 95% CI 0.70-0.86; p < 0.0001). Patients with low CD4+ T cells had an inferior outcome. The addition of the CD4+ T-cell population enhanced the predictive ability of the CLL-IPI (AUC 0.83; 95% CI 0.77-0.90; p < 0.0001).

CONCLUSIONS

The ALPODS XAI algorithm detected highly predictive cell populations in CLL that may be able to refine conventional prognostic scores such as IPI.

Decreased TCF1 and BCL11B expression predicts poor prognosis for patients with chronic lymphocytic leukemia

T cell immune dysfunction is a prominent characteristic of chronic lymphocytic leukemia (CLL) and the main cause of failure for immunotherapy and multi-drug resistance. There remains a lack of specific biomarkers for evaluating T cell immune status with outcome for CLL patients. T cell factor 1 (TCF1, encoded by the TCF7 gene) can be used as a critical determinant of successful anti-tumor immunotherapy and a prognostic indicator in some solid tumors; however, the effects of TCF1 in CLL remain unclear. Here, we first analyzed the biological processes and functions of TCF1 and co-expressing genes using the GEO and STRING databases with the online tools Venny, Circos, and Database for Annotation, Visualization, and Integrated Discovery (DAVID). Then the expression and prognostic values of TCF1 and its partner gene B cell leukemia/lymphoma 11B (BCL11B) were explored for 505 CLL patients from 6 datasets and validated with 50 CLL patients from Henan cancer hospital (HNCH). TCF1 was downregulated in CLL patients, particularly in CD8+ T cells, which was significantly correlated with poor time-to-first treatment (TTFT) and overall survival (OS) as well as short restricted mean survival time (RMST). Function and pathway enrichment analysis revealed that TCF1 was positively correlated with BCL11B, which is involved in regulating the activation and differentiation of T cells in CLL patients. Intriguingly, BCL11B was highly consistent with TCF1 in its decreased expression and prediction of poor prognosis. More importantly, the combination of TCF1 and BCL11B could more accurately assess prognosis than either alone. Additionally, decreased TCF1 and BCL11B expression serves as an independent risk factor for rapid disease progression, coinciding with high-risk indicators, including unmutated IGHV, TP53 alteration, and advanced disease. Altogether, this study demonstrates that decreased TCF1 and BCL11B expression is significantly correlated with poor prognosis, which may be due to decreased TCF1+CD8+ T cells, impairing the effector CD8+ T cell differentiation regulated by TCF1/BCL11B.

Effects of ibrutinib on T-cell immunity in patients with chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL), a highly heterogeneous B-cell malignancy, is characterized by tumor microenvironment disorder and T-cell immune dysfunction, which play a major role in the proliferation and survival of CLL cells. Ibrutinib is the first irreversible inhibitor of Bruton’s tyrosine kinase (BTK). In addition to targeting B-cell receptor (BCR) signaling to kill tumor cells, increasing evidence has suggested that ibrutinib regulates the tumor microenvironment and T-cell immunity in a direct and indirect manner. For example, ibrutinib not only reverses the tumor microenvironment by blocking cytokine networks and toll-like receptor signaling but also regulates T cells in number, subset distribution, T-cell receptor (TCR) repertoire and immune function by inhibiting interleukin-2 inducible T-cell kinase (ITK) and reducing the expression of inhibitory receptors, and so on. In this review, we summarize the current evidence for the effects of ibrutinib on the tumor microenvironment and cellular immunity of patients with CLL, particularly for the behavior and function of T cells, explore its potential mechanisms, and provide a basis for the clinical benefits of long-term ibrutinib treatment and combined therapy based on T-cell-based immunotherapies.

Underlying Ciliary Body Uveal Melanoma in a Patient with Chronic Lymphocytic Leukemia Presenting for Hyphema

(1) Background: Ciliary body uveal melanoma is a rare subtype of uveal melanoma which comprises 3–5% of melanomas, an immunogenic cancer, and can present multifaceted initial clinical manifestations, masquerading as various ocular pathologies. Chronic lymphocytic leukemia (CLL) presents immunodeficiency and risk for the development of a secondary malignancy, with Bruton’s tyrosine kinase inhibitor treatment having a mutagenic effect and a secondary anti-platelet aggregation effect. We present the case of a 65-year-old patient undergoing treatment for CLL with ibrutinib who presented with recurrent hyphema that masked an underlying, inferiorly situated, ciliary body uveal melanoma; (2) Methods: Retrospective case review; (3) Results: An ophthalmological examination together with imaging via mode B ultrasound and contrast-enhanced magnetic resonance imaging resulted in the clinical and imagistic diagnosis of a ciliary body uveal melanoma. A pathological examination of the enucleated eye confirmed the diagnosis. Postoperative tumoral reoccurrence was not detected for 1½ years, however, CLL immunosuppression worsened with admission for severe COVID-19 disease. (4) Conclusions: CLL patient screening for melanoma should also include detailed ophthalmological examinations, which could also include ultrasound ophthalmological imaging. The avoidance of uveal melanoma metastatic disease is paramount for patient survival. CLL manifests additional profound immunosuppression.

cyCombine allows for robust integration of single-cell cytometry datasets within and across technologies

Combining single-cell cytometry datasets increases the analytical flexibility and the statistical power of data analyses. However, in many cases the full potential of co-analyses is not reached due to technical variance between data from different experimental batches. Here, we present cyCombine, a method to robustly integrate cytometry data from different batches, experiments, or even different experimental techniques, such as CITE-seq, flow cytometry, and mass cytometry. We demonstrate that cyCombine maintains the biological variance and the structure of the data, while minimizing the technical variance between datasets. cyCombine does not require technical replicates across datasets, and computation time scales linearly with the number of cells, allowing for integration of massive datasets. Robust, accurate, and scalable integration of cytometry data enables integration of multiple datasets for primary data analyses and the validation of results using public datasets.

Immune Microenvironment Characteristics of Urachal Carcinoma and Its Implications for Prognosis and Immunotherapy

Urachal carcinoma (UrC) is an exceedingly rare tumor and lacks effective treatment. Herein, we characterized an immune microenvironment characteristic of UrC in detail and identified its implications for prognosis and immunotherapy. In total, 37 resections of UrC were stained for CD20, CD3, CD4, CD8, FOXP3, CD68, HLA-DR, CD163, PD1, and PD-L1, as well as mismatch repair protein including MSH2, MSH6, MLH1, and PMS2 by immunohistochemistry. Intratumoral and peritumoral immune cell densities or the proportion of PD1 and PD-L1 expression alongside MSH2, MSH6, MLH1, and PMS2 status were manually evaluated using the whole slide. UrC patients with the number of tertiary lymphoid structures (TLS) per slide tended to be higher in tumors with dMMR (p = 0.1919), and tumors with higher number of TLS tended to have longer OS (p = 0.0940) and DFS (p = 0.0700). High densities of CD3+ T, CD8+ T, and CD68+ cells were significantly associated with worse OS and DFS (both p<0.05). Increased intratumoral (p = 0.0111) and peritumoral (p = 0.0485) CD8+ T cell densities were significantly associated with PD-L1 expression or increasing proportion of PD-L1 expression on immune cells. Similarly, increased intratumoral (p = 0.0008) and peritumoral (p = 0.063) CD8+ T cell densities were significantly associated with increasing proportion of PD1 expression on immune cells. Tumors with PD-L1 positive expression on immune cells had a significantly increased proportion of PD1 expression (p = 0.0121). High peritumoral CD8+ T cell density (>73.7/mm²) was significantly associated with worse OS (p = 0.0120) and DFS (p = 0.00095). The number of TLS seems to be considered not only as histopathological characteristics in predicting MMR status of UrC, but also as a prognostic or therapeutic biomarker, and we also provide some important suggestions for targeting PD-1/PD-L1 checkpoint in UrC.

T Cell Fitness and Autologous CAR T Cell Therapy in Haematologic Malignancy

A range of emerging therapeutic approaches for the treatment of cancer aim to induce or augment endogenous T cell responses. Chimeric antigen receptor (CAR) T cell therapy (CTT) is one such approach that utilises the patient’s own T cells, engineered ex vivo to target cell surface antigens, to eliminate haematological malignancies. Despite mediating high rates of responses in some clinical trials, this approach can be limited by dysfunctional T cells if they are present at high frequencies either in the starting material from the patient or the CAR T cell product. The fitness of an individual’s T cells, driven by age, chronic infection, disease burden and cancer treatment, is therefore likely to be a crucial limiting factor of CTT. Currently, T cell dysfunction and its impact on CTT is not specifically quantified when patients are considering the therapy. Here, we review our current understanding of T cell fitness for CTT, how fitness may be impacted by age, chronic infection, malignancy, and treatment. Finally, we explore options to specifically tailor clinical decision-making and the CTT protocol for patients with more extensive dysfunction to improve treatment efficacy. A greater understanding of T cell fitness throughout a patient’s treatment course could ultimately be used to identify patients likely to achieve favourable CTT outcomes and improve methods for T cell collection and CTT delivery.

O-GlcNAcylation in Chronic Lymphocytic Leukemia and Other Blood Cancers

In the past decade, aberrant O-GlcNAcylation has emerged as a new hallmark of cancer. O-GlcNAcylation is a post-translational modification that results when the amino-sugar β-D-N-acetylglucosamine (GlcNAc) is made in the hexosamine biosynthesis pathway (HBP) and covalently attached to serine and threonine residues in intracellular proteins by the glycosyltransferase O-GlcNAc transferase (OGT). O-GlcNAc moieties reflect the metabolic state of a cell and are removed by O-GlcNAcase (OGA). O-GlcNAcylation affects signaling pathways and protein expression by cross-talk with kinases and proteasomes and changes gene expression by altering protein interactions, localization, and complex formation. The HBP and O-GlcNAcylation are also recognized to mediate survival of cells in harsh conditions. Consequently, O-GlcNAcylation can affect many of the cellular processes that are relevant for cancer and is generally thought to promote tumor growth, disease progression, and immune escape. However, recent studies suggest a more nuanced view with O-GlcNAcylation acting as a tumor promoter or suppressor depending on the stage of disease or the genetic abnormalities, proliferative status, and state of the p53 axis in the cancer cell. Clinically relevant HBP and OGA inhibitors are already available and OGT inhibitors are in development to modulate O-GlcNAcylation as a potentially novel cancer treatment. Here recent studies that implicate O-GlcNAcylation in oncogenic properties of blood cancers are reviewed, focusing on chronic lymphocytic leukemia and effects on signal transduction and stress resistance in the cancer microenvironment. Therapeutic strategies for targeting the HBP and O-GlcNAcylation are also discussed.

Understanding Monoclonal B Cell Lymphocytosis: An Interplay of Genetic and Microenvironmental Factors

The term monoclonal B-cell lymphocytosis (MBL) describes the presence of a clonal B cell population with a count of less than 5 × 10⁹/L and no symptoms or signs of disease. Based on the B cell count, MBL is further classified into 2 distinct subtypes: 'low-count' and 'high-count' MBL. High-count MBL shares a series of biological and clinical features with chronic lymphocytic leukemia (CLL), at least of the indolent type, and evolves to CLL requiring treatment at a rate of 1-2% per year, whereas 'low-count' MBL seems to be distinct, likely representing an immunological rather than a pre-malignant condition. That notwithstanding, both subtypes of MBL can carry 'CLL-specific' genomic aberrations such as cytogenetic abnormalities and gene mutations, yet to a much lesser extent compared to CLL. These findings suggest that such aberrations are mostly relevant for disease progression rather than disease onset, indirectly pointing to microenvironmental drive as a key contributor to the emergence of MBL. Understanding microenvironmental interactions is therefore anticipated to elucidate MBL ontogeny and, most importantly, the relationship between MBL and CLL.

Impact of Immune Parameters and Immune Dysfunctions on the Prognosis of Patients with Chronic Lymphocytic Leukemia

Simple Summary

In chronic lymphocytic leukemia (CLL), immune alterations—affecting both the innate and adaptive immunity—are very common. As a clinical consequence, patients with CLL frequently present with autoimmune phenomena, increased risk of infections and second malignancies. The aim of this review article is to present available data on CLL-associated alterations of immune parameters that correlate with known prognostic markers and with clinical outcome. Also, data on the impact of immune-related clinical manifestations on the prognosis of patients with CLL will be discussed.

Abstract

Chronic lymphocytic leukemia (CLL) is characterized by a wide spectrum of immune alterations, affecting both the innate and adaptive immunity. These immune dysfunctions strongly impact the immune surveillance, facilitate tumor progression and eventually affect the disease course. Quantitative and functional alterations involving conventional T cells, γδ T cells, regulatory T cells, NK and NKT cells, and myeloid cells, together with hypogammaglobulinemia, aberrations in the complement pathways and altered cytokine signature have been reported in patients with CLL. Some of these immune parameters have been shown to associate with other CLL-related characteristics with a known prognostic relevance or to correlate with disease prognosis. Also, in CLL, the complex immune response dysfunctions eventually translate in clinical manifestations, including autoimmune phenomena, increased risk of infections and second malignancies. These clinical issues are overall the most common complications that affect the course and management of CLL, and they also may impact overall disease prognosis.

Flow Cytometry-Assessed PD1/PDL1 Status in Tumor-Infiltrating Lymphocytes: A Link With the Prognosis of Diffuse Large B-Cell Lymphoma

The PD1/PDL1 status of tumor-infiltrating lymphocytes (TILs) in diffuse large B-cell lymphoma (DLBCL) reflects immune function. However, the previously reported methods for evaluating this status are complex and may not be widely used in clinical practice. In addition, these studies did not introduce healthy controls to designate the cut-off when evaluating the prognostic value of the status. In this study, we retrospectively evaluated the PD1/PDL1 status in TILs of 24 DLBCL tissue samples and normal immune cells in 61 demographically matched healthy controls (tissue samples from patients with reactive hyperplasia [RH]) by flow cytometry. We investigated the prognostic value of the PD1/PDL1 status in TILs by precisely determining the cut-off value and assessing the reliability of flow cytometry. The mean fluorescence intensity (MFI) of PD1 in TIL-T-cells (TIL-Ts; median, 110) and CD8+TIL-Ts (median, 64) was significantly higher than that of CD3+T-cells (median, 64) and CD8+ T-cells (median, 34) in RH. The cut-off values of PD1/PDL1 status for analyzing prognostic values were defined considering the PD1/PDL1 status of samples from both patients with DLBCL and healthy controls. High MFI of PD1 in TIL-Ts (MFI >108, P = 0.022), high proportion of PD1+CD4+TIL-Ts (>1.1% of CD4+TIL-Ts, P = 0.049), high proportion of PD1+CD8+TIL-Ts (>2% of CD8+TIL-Ts, P = 0.025), and high MFI of PDL1 in TIL-Ts (MFI >83, P = 0.023) were risk factors for inferior prognosis of DLBCL. Our results indicate that flow cytometry is a reliable and convenient method for evaluating the immune-checkpoint status of TILs, which probably holds major implications in clinical practice.

Understanding the Immune-Stroma Microenvironment in B Cell Malignancies for Effective Immunotherapy

Cancers, including lymphomas, develop in complex tissue environments where malignant cells actively promote the creation of a pro-tumoral niche that suppresses effective anti-tumor effector T cell responses. Research is revealing that the tumor microenvironment (TME) differs between different types of lymphoma, covering inflamed environments, as exemplified by Hodgkin lymphoma, to non-inflamed TMEs as seen in chronic lymphocytic leukemia (CLL) or diffuse-large B-cell lymphoma (DLBCL). In this review we consider how T cells and interferon-driven inflammatory signaling contribute to the regulation of anti-tumor immune responses, as well as sensitivity to anti-PD-1 immune checkpoint blockade immunotherapy. We discuss tumor intrinsic and extrinsic mechanisms critical to anti-tumor immune responses, as well as sensitivity to immunotherapies, before adding an additional layer of complexity within the TME: the immunoregulatory role of non-hematopoietic stromal cells that co-evolve with tumors. Studying the intricate interactions between the immune-stroma lymphoma TME should help to design next-generation immunotherapies and combination treatment strategies to overcome complex TME-driven immune suppression.

T Cells in Chronic Lymphocytic Leukemia: A Two-Edged Sword

Chronic lymphocytic leukemia (CLL) is a malignancy of mature, antigen-experienced B lymphocytes. Despite great progress recently achieved in the management of CLL, the disease remains incurable, underscoring the need for further investigation into the underlying pathophysiology. Microenvironmental crosstalk has an established role in CLL pathogenesis and progression. Indeed, the malignant CLL cells are strongly dependent on interactions with other immune and non-immune cell populations that shape a highly orchestrated network, the tumor microenvironment (TME). The composition of the TME, as well as the bidirectional interactions between the malignant clone and the microenvironmental elements have been linked to disease heterogeneity. Mounting evidence implicates T cells present in the TME in the natural history of the CLL as well as in the establishment of certain CLL hallmarks e.g. tumor evasion and immune suppression. CLL is characterized by restrictions in the T cell receptor gene repertoire, T cell oligoclonal expansions, as well as shared T cell receptor clonotypes amongst patients, strongly alluding to selection by restricted antigenic elements of as yet undisclosed identity. Further, the T cells in CLL exhibit a distinctive phenotype with features of “exhaustion” likely as a result of chronic antigenic stimulation. This might be relevant to the fact that, despite increased numbers of oligoclonal T cells in the periphery, these cells are incapable of mounting effective anti-tumor immune responses, a feature perhaps also linked with the elevated numbers of T regulatory subpopulations. Alterations of T cell gene expression profile are associated with defects in both the cytoskeleton and immune synapse formation, and are generally induced by direct contact with the malignant clone. That said, these abnormalities appear to be reversible, which is why therapies targeting the T cell compartment represent a reasonable therapeutic option in CLL. Indeed, novel strategies, including CAR T cell immunotherapy, immune checkpoint blockade and immunomodulation, have come to the spotlight in an attempt to restore the functionality of T cells and enhance targeted cytotoxic activity against the malignant clone.

Immune Dysfunctions and Immune-Based Therapeutic Interventions in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy characterized by a wide range of tumor-induced alterations, which affect both the innate and adaptive arms of the immune response, and accumulate during disease progression. In recent years, the development of targeted therapies, such as the B-cell receptor signaling inhibitors and the Bcl-2 protein inhibitor venetoclax, has dramatically changed the treatment landscape of CLL. Despite their remarkable anti-tumor activity, targeted agents have some limitations, which include the development of drug resistance mechanisms and the inferior efficacy observed in high-risk patients. Therefore, additional treatments are necessary to obtain deeper responses and overcome drug resistance. Allogeneic hematopoietic stem cell transplantation (HSCT), which exploits immune-mediated graft-versus-leukemia effect to eradicate tumor cells, currently represents the only potentially curative therapeutic option for CLL patients. However, due to its potential toxicities, HSCT can be offered only to a restricted number of younger and fit patients. The growing understanding of the complex interplay between tumor cells and the immune system, which is responsible for immune escape mechanisms and tumor progression, has paved the way for the development of novel immune-based strategies. Despite promising preclinical observations, results from pilot clinical studies exploring the safety and efficacy of novel immune-based therapies have been sometimes suboptimal in terms of long-term tumor control. Therefore, further advances to improve their efficacy are needed. In this context, possible approaches include an earlier timing of immunotherapy within the treatment sequencing, as well as the possibility to improve the efficacy of immunotherapeutic agents by administering them in combination with other anti-tumor drugs. In this review, we will provide a comprehensive overview of main immune defects affecting patients with CLL, also describing the complex networks leading to immune evasion and tumor progression. From the therapeutic standpoint, we will go through the evolution of immune-based therapeutic approaches over time, including i) agents with broad immunomodulatory effects, such as immunomodulatory drugs, ii) currently approved and next-generation monoclonal antibodies, and iii) immunotherapeutic strategies aiming at activating or administering immune effector cells specifically targeting leukemic cells (e.g. bi-or tri-specific antibodies, tumor vaccines, chimeric antigen receptor T cells, and checkpoint inhibitors).

T-cells in chronic lymphocytic leukemia: Guardians or drivers of disease?

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy, which is associated with profound alterations and defects in the immune system and a prevalent dependency on the microenvironmental niche. An abnormal T-cell compartment in the blood of CLL patients was already reported 40 years ago. Since then, our knowledge of T-cell characteristics in CLL has grown steadily, but the question of whether T-cells act as pro-tumoral bystander cells or possess anti-tumoral activity is still under debate. Increased numbers of CD4+ T-helper cell subsets are present in the blood of CLL patients, and T-helper cell cytokines have been shown to stimulate CLL cell survival and proliferation in vitro. In line with this, survival and growth of CLL cells in murine xenograft models have been shown to rely on activated CD4+ T-cells. This led to the hypothesis that T-cells are tumor-supportive in CLL. In recent years, evidence for an enrichment of antigen-experienced CD8+ T-cells in CLL has accumulated, and these cells have been shown to control leukemia in a CLL mouse model. Based on this, it was suggested that CD8+ T-cells recognize CLL-specific antigens and exert an anti-leukemia function. As described for other cancer entities, T-cells in CLL express multiple inhibitory receptors, such as PD-1, and lose their functional capacity, leading to an exhaustion phenotype which has been shown to be more severe in T-cells from secondary lymphoid organs compared with peripheral blood. This exhausted phenotype has been suggested to be causative for the poor response of CLL patients to CAR T-cell therapies. In addition, T-cells have been shown to be affected by drugs that are used to treat CLL, which likely impacts therapy response. This review provides an overview of the current knowledge about alterations of T-cells in CLL, including their distribution, function, and exhaustion state in blood and lymphoid organs, and touches also on the topic of how CLL drugs impact on the T-cell compartment and recent results of T-cell-based immunotherapy. We will discuss potential pathological roles of T-cell subsets in CLL and address the question of whether they foster progression or control of disease.