John C. Riches

T cells from CLL patients exhibit features of T-cell exhaustion but retain capacity for cytokine production

T-cell exhaustion, originally described in chronic viral infections, was recently reported in solid and hematologic cancers. It is not defined whether exhaustion contributes to T-cell dysfunction observed in chronic lymphocytic leukemia (CLL). We investigated the phenotype and function of T cells from CLL patients and age-matched controls. CD8+ and CD4+ T cells from CLL patients had increased expression of exhaustion markers CD244, CD160, and PD1, with expansion of a PD1+BLIMP1HI subset. These molecules were most highly expressed in the expanded population of effector T cells in CLL. CLL CD8+ T cells showed functional defects in proliferation and cytotoxicity, with the cytolytic defect caused by impaired granzyme packaging into vesicles and nonpolarized degranulation. In contrast to virally induced exhaustion, CLL T cells showed increased production of interferon-γ and TNFα and increased expression of TBET, and normal IL2 production. These defects were not restricted to expanded populations of cytomegalovirus (CMV)–specific cells, although CMV seropositivity modulated the distribution of lymphocyte subsets, the functional defects were present irrespective of CMV serostatus. Therefore, although CLL CD8+ T cells exhibit features of T-cell exhaustion, they retain the ability to produce cytokines. These findings also exclude CMV as the sole cause of T-cell defects in CLL.

Understanding the Immunodeficiency in Chronic Lymphocytic Leukemia: Potential Clinical Implications

Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults. Although significant advances have been made in the treatment of CLL in the last decade, it remains incurable. Treatments may be too toxic for some elderly patients, who constitute most of the individuals with this disease, and there remain subgroups of patients for which this therapy has minimal activity. This article summarizes the current understanding of the immune defects in CLL. It also examines the potential clinical implications of these findings.

Trisomy 12 chronic lymphocytic leukemia cells exhibit upregulation of integrin signaling that is modulated by NOTCH1 mutations

The leukocyte adhesion cascade is important in chronic lymphocytic leukemia (CLL), as it controls migration of malignant cells into the pro-survival lymph node microenvironment. Circulating trisomy 12 CLL cells have increased expression of the integrins CD11a and CD49d, as well as CD38, but the tissue expression of these and other molecules, and the functional and clinical sequelae of these changes have not been described. Here, we demonstrate that circulating trisomy 12 CLL cells also have increased expression of the integrins CD11b, CD18, CD29, and ITGB7, and the adhesion molecule CD323. Notably, there was reduced expression of CD11a, CD11b, and CD18 in trisomy 12 cases with NOTCH1 mutations compared with wild type. Trisomy 12 cells also exhibit upregulation of intracellular integrin signaling molecules CALDAG-GEFI, RAP1B, and Ras-related protein ligand, resulting in enhanced very late antigen-4 [VLA-4] directed adhesion and motility. CD38 expression in CLL has prognostic significance, but the increased CD38 expression in trisomy 12 CLL cells must be taken into account in this subgroup, and the threshold of CD38 positivity should be raised to 40% for this marker to retain its prognostic value. In conclusion, trisomy 12 CLL cells exhibit functional upregulation of integrin signaling, with β2-integrin expression being modulated by NOTCH1 mutation status.

Mechanisms of PD-L1/PD-1–mediated CD8 T-cell dysfunction in the context of aging-related immune defects in the Eµ-TCL1 CLL mouse model

T-cell defects, immune suppression, and poor antitumor immune responses are hallmarks of chronic lymphocytic leukemia (CLL), and PD-1/PD-L1 inhibitory signaling has emerged as a major immunosuppressive mechanism. However, the effect of different microenvironments and the confounding influence of aging are poorly understood. The current study uses the Eμ-TCL1 mouse model, which replicates human T-cell defects, as a preclinical platform to longitudinally examine patterns of T-cell dysfunction alongside developing CLL and in different microenvironments, with a focus on PD-1/PD-L1 interactions. The development of CLL was significantly associated with changes in T-cell phenotype across all organs and function. Although partly mirrored in aging wild-type mice, CLL-specific T-cell changes were identified. Murine CLL cells highly expressed PD-L1 and PD-L2 in all organs, with high PD-L1 expression in the spleen. CD3(+)CD8(+) T cells from leukemic and aging healthy mice highly expressed PD-1, identifying aging as a confounder, but adoptive transfer experiments demonstrated CLL-specific PD-1 induction. Direct comparisons of PD-1 expression and function between aging CLL mice and controls identified PD-1(+) T cells in CLL as a heterogeneous population with variable effector function. This is highly relevant for therapeutic targeting of CD8(+) T cells, showing the potential of reprogramming and selective subset expansion to restore antitumor immunity.

T-cell function in chronic lymphocytic leukaemia.

According to the immune-surveillance hypothesis, cancer cells evolve strategies to evade or suppress the immune system as part of the development of this disease. The malignant B-cells of chronic lymphocytic leukaemia are prime examples of this premise, having been shown to generate a variety of ways of suppressing T-cell anti-tumour immune responses and these are summarized here. These mechanisms range from impairment of antigen presentation by the tumour cells themselves, to suppression of the immune microenvironment by contact dependent pathways and alterations in the cytokine milieu. By understanding these defects, novel targeted therapies can be developed with the aim of restoring T-cell function. Indeed, some of the recent advances in the treatment of chronic lymphocytic leukaemia have been demonstrated to have profound immunomodulatory effects, repairing these defects in T-cell function.

Chronic Lymphocytic Leukemia: An Update on Biology and Treatment

Combination chemoimmunotherapy with fludarabine, cyclophosphamide, and rituximab (FCR) has emerged as the current standard of care in the treatment of chronic lymphocytic leukemia (CLL). Despite very high response rates, this treatment is too toxic for many patients, and it remains unclear as how to manage patients who do not respond to these agents or who relapse early after treatment. An increase in our understanding of the biology of CLL has led to the development of a wide range of therapies aimed at specific defects in this disease. B-cell receptor signaling is aberrantly increased in CLL, and so many of these drugs target key steps in these pathways. Antitumor immunity is also impaired, and a number of strategies are being developed to repair this acquired immune dysfunction. This review highlights some of the emerging agents and describes the biological rationale for their use in CLL.

Immunomodulation and Immune Reconstitution in Chronic Lymphocytic Leukemia

Over the past decade, there have been significant advances in our understanding of the pathogenesis of chronic lymphocytic leukemia (CLL), which has been accompanied by an explosion in treatment options. Although the combination of fludarabine, cyclophosphamide, and rituximab is the current frontline treatment of choice for fit patients, targeted therapies such ibrutinib, idelalisib, and ABT-199 are showing great promise in clinical trials. However, none of these drugs seems curative, and allogeneic hematopoietic stem cell transplantation remains the only strategy that produces durable clinical remissions in otherwise poor-risk disease. Immune reconstitution remains an enticing prospect in CLL, as malignant B cells should be particularly susceptible to a T cell-mediated attack. It has recently been demonstrated that the T-cell defect in CLL can be effectively overcome by both lenalidomide treatment and by adoptive transfer of chimeric antigen receptor T cells. A variety of other immunotherapies are in development, including CLL vaccines, CD40 ligand therapies, and monoclonal antibody immune checkpoint blockade. This review explores the nature of the immune defect in CLL and summarizes the recent developments in the immunotherapeutic field.

Immune reconstitution in chronic lymphocytic leukemia.

Chronic lymphocytic leukemia (CLL) is associated with a profound immune defect, which results in increased susceptibility to recurrent infections as well as a failure to mount effective antitumor immune responses. Current chemotherapy-based regimens are not curative and often worsen this immune suppression, so their usefulness is limited, particularly in the frail and elderly. This article reviews the immune defect in CLL and discusses strategies aimed at repairing or circumventing this defect. In particular, it focuses on recent developments in the areas of CD40 ligand (CD40L/CD154) gene therapy, immunomodulatory agents such as lenalidomide, and adoptive transfer of T cells bearing chimeric antigen receptors.

Immune dysfunction in chronic lymphocytic leukemia: the role for immunotherapy

A key feature of the clinical course of chronic lymphocytic leukemia (CLL) is that it induces a state of immunosuppression, causing increased susceptibility to infections and failure of anti-tumor immune responses. Cytotoxic chemotherapy still forms the mainstay of most current treatment regimens, but is not curative, and its lack of specificity means that it also targets normal immune cells, exacerbating this immunosuppression. This can result in effective treatments being limited by infectious complications, particularly in the elderly who comprise the majority of patients with this disease. Immunotherapy potentially offers a way out of this dilemma, due to its improved specificity and ability to enhance immune responses to both the tumor and infectious agents. There has been a dramatic increase in the range of available immunotherapeutic options over the past decade, and many are now in the process of making the transition to the clinic. This review will discuss both the immune defect in CLL, and emerging immunotherapies, including CD40 ligand gene therapy, lenalidomide, CLL vaccines, CXCR4 antagonists, and adoptive cellular immunotherapies such as chimeric antigen receptor modified T-cells.

Immunotherapeutic strategies including transplantation: eradication of disease.

Although there have been recent advances with targeted therapies in chronic lymphocytic leukemia (CLL), chemoimmunotherapy remains the treatment of choice; however, this approach is not curative. A key feature of CLL is that it induces a state of immunosuppression, causing increased susceptibility to infections and failure of an antitumor immune response, often worsened by the immunosuppressive effect of treatment. Because of its improved specificity, immunotherapy potentially offers a way out of this dilemma. Allogeneic stem cell transplantation remains the only curative option, but is hampered by the toxicity of GVHD. After many years of promise but little reward, many other immunotherapeutic approaches are now in transition to the clinical setting. Clinical trials including CLL vaccines, CXCR4 antagonists, and adoptive cellular immunotherapies such as chimeric antigen receptor-modified T cells, CD40 ligand gene therapy, and the immunomodulatory drug lenalidomide are ongoing. Results to date suggest that immunotherapeutic approaches for the treatment of CLL might finally be fulfilling their promise.