The biological basis for immunotherapy in patients with chronic myelogenous leukemia

Identification of TCR Vβ11-2-Dβ1-Jβ1-1 T cell clone specific for WT1 peptides using high-throughput TCRβ gene sequencing

We previously identified a TCR Vβ21 T cell clone which was specific to CML patients, and demonstrated that TCR Vα13/β21 gene-modified CD3⁺ T cells had specific cytotoxicity for HLA-A11⁺ K562 cells. However, it remains unclear which antigen is specifically recognized by the TCR Vβ21 T cell clone. In this study, CD3⁺ T cells from healthy donor peripheral blood were stimulated with the WT1 peptide or mixed BCR-ABL peptides in the presence or absence of IL-2 and IL-7. The distribution of the TCR Vβ repertoire was analyzed after different stimulations. We found that the mixed BCR-ABL peptides induced clonally expanded Vβ7–9-Dβ2-Jβ2–7 T cells while the Wilms Tumor 1 peptide induced clonally expanded Vβ11–2-Dβ1-Jβ1–1 T cells by high-throughput TCRβ sequencing and GeneScan. Interestingly, the sequence and CDR3 motif of Vβ11–2 T cell clone are similar to the TCR Vβ21 (a different TCR V region naming system) T cell clone that we previously found in CML patients. Thus, our findings suggest that the TCR Vβ21 T cell clone found in CML patients might be a T cell clone that specifically recognizes WT1.

Generation of V α13/β21+T cell specific target CML cells by TCR gene transfer

Adoptive immunotherapy with antigen-specific T cells can be effective for treating melanoma and chronic myeloid leukemia (CML). However, to obtain sufficient antigen-specific T cells for treatment, the T cells have to be cultured for several weeks in vitro, but in vitro T cell expansion is difficult to control. Alternatively, the transfer of T cell receptors (TCRs) with defined antigen specificity into recipient T cells may be a simple solution for generating antigen-specific T cells. The objective of this study was to identify CML-associated, antigen-specific TCR genes and generate CML-associated, antigen-specific T cells with T cell receptor (TCR) gene transfer. Our previous study has screened an oligoclonal Vβ21 with a different oligoclonal Vα partner in peripheral blood mononuclear cells (PBMCs) derived from patients with CML. In this study, oligoclonally expanded TCR α genes, which pair with TCR Vβ21, were cloned into the pIRES eukaryotic expression vector (TCR Vα-IRES-Vβ21). Next, two recombinant plasmids, TCR Vα13-IRES-Vβ21 and TCR Vα18-IRES-Vβ21, were successfully transferred into T cells, and the TCR gene-modified T cells acquired CML-specific cytotoxicity with the best cytotoxic effects for HLA-A11⁺ K562 cells observed for the TCR Vα13/Vβ21 gene redirected T cells. In summary, our data confirmed TCRVα13/Vβ21 as a CML-associated, antigen-specific TCR. This study provided new evidence that genetically engineered antigen-specific TCR may become a druggable approach for gene therapy of CML.

Immunology of chronic myeloid leukemia: current concepts and future goals

Although chronic myeloid leukemia is a rare malignancy, it has developed into a model system for the study of a variety of aspects of cancer biology and immunology. The introduction of tyrosine kinase inhibitors has resulted in a significant prolongation of the survival rates of chronic myeloid leukemia patients but has not resulted in a cure. There is a growing conviction that this aim can be achieved through immunotherapy. For this concept to be successful, a considerable increase in the present understanding of chronic myeloid leukemia immunology is required. The authors attempt to review and evaluate the current findings that demonstrate a number of immunological aberrations in patients prior to the start of any therapy and their normalization after achieving remission. They also discuss the recent clinical trials with experimental therapeutic vaccines and then present their own strategy on how to address the problem.

Immunology and immunotherapy of chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a clonal bone marrow stem cell neoplasia known to be responsive to immunotherapy. Despite the success of tyrosine kinase inhibitors (TKIs) targeting the BCR-ABL1 oncokinase, patients are not considered to be cured with the current therapy modalities. However, there have been recent advancements in understanding the immunobiology of the disease (such as tumor specific antigens and immunostimulatory agents), and this may lead to the development of novel, curative treatment strategies. Already there are promising results showing that a small proportion of CML patients are able to discontinue the therapy although they have a minimal amount of residual leukemia cells left. This implies that the immune system is able to restrain the tumor cell expansion. In this review, we aim to give a brief update of the novel aspects of the immune system in CML patients and of the developing strategies for controlling CML by the means of immunotherapy.

Biological therapy and the immune system in patients with chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder of hematopoietic stem cells that has been recognized as a disease responsive to immunotherapy. Despite the huge success of the tyrosine kinase inhibitors (TKIs), CML remains for the most part incurable, probably due to treatment resistance of leukemic stem cells, which are responsible for rapid disease relapse after discontinuation of therapy. Only allogeneic stem cell transplantation enables disease eradication. In addition to the Bcr-Abl1 oncoprotein, TKIs also inhibit off-target kinases (e.g. c-kit, Src, Tec), some of them having physiological functions in immune responses. In vitro studies have implied immunomodulatory effects of TKIs and interferon-alpha (IFN-α), but comprehensive information from in vivo analyses is missing. This review summarizes the recent advances in the field of immunology of CML, including basic information about leukemia-associated antigens and peptide vaccines, that could lead to the incorporation of TKIs and IFN-α in future therapeutic, potentially curative, interventions for CML.

Antigens in chronic myeloid leukemia: implications for vaccine development

Treatment with imatinib mesylate and other tyrosine kinase inhibitors (TKI) revolutionized the therapy of chronic myeloid leukemia (CML). However, it alone does not cure this disease. Moreover, some patients develop resistance or adverse effects to this therapy. As successful treatment of a portion of CML patients by hematopoietic stem cell transplantation (HSCT) suggests the importance of immune mechanisms in the elimination of leukemic cells, including leukemia stem cells, TKI administration or HSCT might be combined with vaccination to cure CML patients. However, antigens implicated in the immune responses have not yet been sufficiently identified. Therefore, in this report, we compiled and characterized a list of 165 antigens associated with CML (CML-Ag165) and analyzed the expression of the corresponding genes in CML phases, subpopulations of leukemic cells, and CML-derived cell lines using available datasets from microarray transcriptional-profiling studies. From the CML-Ag165 list, we selected antigens most suitable for vaccine development and evaluated their appropriate characteristics.

A molecular and functional analysis of large granular lymphocyte expansions in patients with chronic myelogenous leukemia treated with tyrosine kinase inhibitors

Tyrosine kinase inhibitor (TKI) therapy has become the standard treatment for chronic myelogenous leukemia (CML). Off-target kinase inhibition has been implicated in the appearance of unique adverse effects, such as colitis and pleural effusions. In addition, some patients present oligoclonal expansions of large granular lymphocytes (LGLs). We sought to further investigate this phenomenon in 64 patients treated with five different TKIs. Clonal expansions of cytotoxic T lymphocytes (CTLs) were identified in all TKI-treated patient groups, but only in dasatinib-treated patients were these expansions characterized as LGLs. Survival factors known to be important in LGL leukemia (interleukin-15 [IL-15] transpresentation, plasma platelet-derived growth factor [PDGF]-BB levels, nuclear factor-κB [NF-κB] and T-bet activation) were found to be associated with TKI-induced LGL expansions. Interestingly, patients with LGL expansions had increased cytotoxicity against non-transformed endothelial cells, which may play a role in observed autoimmune-like side effects. Our results indicate that patients with CML treated with TKIs can develop T cell expansions, which can in certain cases be related to some adverse effects.

A systems model for immune cell interactions unravels the mechanism of inflammation in human skin

Inflammation is characterized by altered cytokine levels produced by cell populations in a highly interdependent manner. To elucidate the mechanism of an inflammatory reaction, we have developed a mathematical model for immune cell interactions via the specific, dose-dependent cytokine production rates of cell populations. The model describes the criteria required for normal and pathological immune system responses and suggests that alterations in the cytokine production rates can lead to various stable levels which manifest themselves in different disease phenotypes. The model predicts that pairs of interacting immune cell populations can maintain homeostatic and elevated extracellular cytokine concentration levels, enabling them to operate as an immune system switch. The concept described here is developed in the context of psoriasis, an immune-mediated disease, but it can also offer mechanistic insights into other inflammatory pathologies as it explains how interactions between immune cell populations can lead to disease phenotypes.

A functional immune system requires complex interactions among diverse cell types, mediated by a variety of cytokines. These interactions include phenomena such as positive and negative feedback loops that can be experimentally characterized by dose-dependent cytokine production measurements. However, any experimental approach is not only limited with regard to the number of cell-cell interactions that can be studied at a given time, but also does not have the capacity to assess or predict the overall immune response which is the result of complex interdependent immune cell interactions. Therefore, experimental data need to be viewed from a theoretical perspective allowing the quantitative modeling of immune cell interactions. Here, we propose a strategy for a quantitative description of multiple interactions between immune cell populations based on their cytokine production profiles. The model predicts that the modified feedback loop interactions can result in the appearance of alternative steady-states causing the switch-like immune system effect that is experimentally observed in pathologic phenotypes. Overall, the quantitative description of immune cell interactions via cytokine signaling reported here offers new insights into understanding and predicting normal and pathological immune system responses.