Major histocompatibility complex-restricted recognition of autologous chronic lymphocytic leukemia by tumor-specific T cells

T Cell Defects and Immunotherapy in Chronic Lymphocytic Leukemia

In the past few years, independent studies have highlighted the relevance of the tumor microenvironment (TME) in cancer, revealing a great variety of TME-related predictive markers, as well as identifying novel therapeutic targets in the TME. Cancer immunotherapy targets different components of the immune system and the TME at large in order to reinforce effector mechanisms or relieve inhibitory and suppressive signaling. Currently, it constitutes a clinically validated treatment for many cancers, including chronic lymphocytic leukemia (CLL), an incurable malignancy of mature B lymphocytes with great dependency on microenvironmental signals. Although immunotherapy represents a promising therapeutic option with encouraging results in CLL, the dysfunctional T cell compartment remains a major obstacle in such approaches. In the scope of this review, we outline the current immunotherapeutic treatment options in CLL in the light of recent immunogenetic and functional evidence of T cell impairment. We also highlight possible approaches for overcoming T cell defects and invigorating potent anti-tumor immune responses that would enhance the efficacy of immunotherapy.

Expression of inhibitory receptor ILT3 on neoplastic B cells is associated with lymphoid tissue involvement in chronic lymphocytic leukemia

T cell responses against leukemia-associated antigens have been reported in chronic lymphocytic leukemia (CLL). However, the relentless accumulation of CLL B cells in some patients indicates that anti-tumor immune responses are inefficient. Inhibitory receptors from the Ig-like transcript (ILT) family, such as ILT3 and ILT4, are crucial to the tolerogenic activity of antigen presenting cells. In this study, we examined the expression of ILT3 on CD5+ B cells obtained from 47 patients with CLL. Using flow cytometry and RT-PCR, we found that B CLL cells from 23 of 47 patients expressed ILT3 protein and mature ILT3 mRNA. ILT3 protein and mRNA were not found in normal B cells obtained from donors without CLL. Expression of ILT4 in normal and B CLL cells showed a pattern similar to ILT3. The frequency of ILT3 positive CLL B cells was higher in patients with lymphoid tissue involvement, suggesting that ILT3 may have prognostic value in CLL. Our findings indicate that expression of ILT3 and ILT4 on CLL B cells represents a phenotypic abnormality that may play a role in tolerization of tumor-specific T cells.

Abnormal T-cell function in B-cell chronic lymphocytic leukaemia

There is increasing evidence of T cell dysfunction in B cell chronic lymphocytic leukaemia (B-CLL) which may contribute to the aetiology and progress of the disease. An absolute CD8+ lymphocytosis correlates with disease progression and low expression of CD4 and CD8 (as found in autoimmune disease) is seen with abnormal expression of other surface molecules. Although the expression of T cell surface activation markers, CD25 and CD152, may be increased on culture in B-CLL serum, response to the common mitogens, PHA and PWM, is reduced. This and the excess of CD8 cells may explain partly the variable cooperation of T cells with B cell production of immunoglobulin in B-CLL. In the context of T cell cross-talk with antigen presenting cells, B-CLL B cells are poor antigen presenters. But the T cells themselves have significant abnormalities of expression of the many antigens and ligands necessary for this process. In particular, they exhibit variable expression of the low affinity and non-specific adhesion molecules LFA-1 and ICAM-1, variable, clonally restricted and skewed expression of the TCR repertoire (implying repeated antigenic stimulation possibly by CLL antigens), reduced CD28 and CD152 expression (implying impairment of ability to start or stop an immune response) and reduced IL2 and CD25 (IL2 R) expression (critical for positive feed-back in maintenance and expansion of the T cell response to antigen presentation). Although the production of IL2 and other cytokines by the T cell in B-CLL may be impaired, production of the anti-apoptotic cytokine IL4 is not and there may be a unique and expanded subset of CD8/CD30 cells capable of releasing IL4. The relationship of this T cell subset to the malignant B cell in vivo is unknown. However, T cells which are CD4+/CD152+/CCR4+ migrate selectively in vitro in response to the chemokine CCL22 (specific for the receptor CCR4) produced by the malignant B cells and are always seen amongst the malignant cells in bone marrow and lymph nodes from B-CLL patients. Other abnormalities of cytokine secretion are described. These findings suggest that the T cell in B-CLL may be unable to start, maintain and complete an immune response to the malignant B cell and other antigens and may be involved directly in sustaining the tumour. However, autologous tumour specific cytotoxicity has been shown in vitro and T cells which recognise tumour-derived heavy chain fragments circulate in vivo. If adoptive immunotherapy of any nature is to succeed in B-CLL, manipulation to optimise these CTL responses is needed to overcome the profound and variable T cell dysfunction in this disease.

Molecular and flow cytometric characterization of the CD4 and CD8 T-cell repertoire in patients with myelodysplastic syndrome

We studied 18 patients with myelodysplastic syndrome (MDS), measuring clonality and T-cell receptor Vbeta (TCRBV) expression of CD4 and CD8 T cells by polymerase chain reaction and by flow cytometric analysis of TCRBV families. The CD4 and CD8 T-cell repertoire in most MDS patients is characterized by an abnormal TCRBV-restricted expansion of T cells in CD4 and CD8 cells, and increased expression of the CD8 effector marker CD57 of multiple TCRBV in CD8 cells. Clonality analysis of CD4 and CD8 cells showed that seven of 10 patients analysed had a major clone in the CD8 cells but not in CD4 cells. Furthermore, in one patient we found that both the CD57- and CD57+ fraction contained the clone (which was absent from the TCRBV-negative fraction). These data suggest that, in MDS, multiple T-cell expansions can be found in both helper and cytotoxic T cells, and that, in the CD8 cells, T cells functionally differentiate in vivo from memory to effector T cells. Together, these data support the hypothesis of the involvement of T cells in the pathogenesis of MDS.

Antigen presenting cells integrate opposing signals from CD4+ and CD8+ regulatory T lymphocytes to arbitrate the outcomes of immune responses

An individual's set of polymorphic HLA class II and I molecules is known to select the T cell repertoire in the thymus and to present processed antigenic peptides (pAg) to mature peripheral CD4+ T helper (Th) and CD8+ T cytotoxic (Th) cells in the periphery. This review highlights new studies which address how antigen presenting cells (APC) integrate the responses of cognate Th and T suppressor (Ts) cells to determine the outcome of immune responses. Together with other findings, these studies emphasize that understanding the mechanism of immune processes requires consideration of HLA molecules in the context of the peptides they bind, the antigen presenting cells (APC) that express them and the T lymphocytes that recognize them. The activities of lymphocyte and APC surface structures are becoming integrated into a physiological understanding of the cellular interactions between regulatory and effector T cells with APC.

Hairy Cell Leukemia-Specific Recognition by Multiple Autologous HLA-DQ or DP-Restricted T-Cell Clones

We studied in patients with hairy cell leukemia (HCL) whether autoreactive T cells could be isolated with specific reactivity to the HCL cells. HCL cells were activated via triggering of CD40 on the cell membrane and used as stimulator cells to generate autologous T-cell clones. Two types of CD4+BV2+ T-cell clones with different CDR3 rearrangements and one type of CD4+BV8S3+ T-cell clone were generated from the spleen or blood. These clones specifically recognized the autologous HCL cells, without reactivity to autologous peripheral blood mononuclear cells (PBMC), phytohemagglutinin blasts, or Epstein-Barr virus–transformed B cells in a primed lymphocyte test. Blocking and panel studies using HCL cells from 11 other patients showed that recognition of the HCL cells by the BV2+ T cells was restricted by HLA-DQA1*03/DQB1*0301, and the BV8S3+ T cells were restricted by DPB1*04. The T-cell clones did not recognize DPB1*04+ or DQ3+ PBMC from healthy donors or DP/DQ matched malignant cells from patients with other hematologic malignancies, except for one patient with acute lymphoblastic leukemia. These HCL-specific T-cell clones may be used for the detection of an HCL-specific tumor antigen.

Hairy Cell Leukemia-Specific Recognition by Multiple Autologous HLA-DQ or DP-Restricted T-Cell Clones

We studied in patients with hairy cell leukemia (HCL) whether autoreactive T cells could be isolated with specific reactivity to the HCL cells. HCL cells were activated via triggering of CD40 on the cell membrane and used as stimulator cells to generate autologous T-cell clones. Two types of CD4+BV2+ T-cell clones with different CDR3 rearrangements and one type of CD4+BV8S3+ T-cell clone were generated from the spleen or blood. These clones specifically recognized the autologous HCL cells, without reactivity to autologous peripheral blood mononuclear cells (PBMC), phytohemagglutinin blasts, or Epstein-Barr virus–transformed B cells in a primed lymphocyte test. Blocking and panel studies using HCL cells from 11 other patients showed that recognition of the HCL cells by the BV2+ T cells was restricted by HLA-DQA1*03/DQB1*0301, and the BV8S3+ T cells were restricted by DPB1*04. The T-cell clones did not recognize DPB1*04+ or DQ3+ PBMC from healthy donors or DP/DQ matched malignant cells from patients with other hematologic malignancies, except for one patient with acute lymphoblastic leukemia. These HCL-specific T-cell clones may be used for the detection of an HCL-specific tumor antigen.