Detection of identical T-cell clonotype expansions in both the donor and recipient after allogeneic bone marrow transplantation

T-large granular lymphocyte leukemia: current molecular concepts

T-large granular lymphocyte (T-LGL) leukemia is a chronic and often indolent T cell lymphoproliferation characterized by extreme expansion of a semi-autonomous cytotoxic T lymphocyte (CTL) clone. Clinically, T-LGL can be associated with various cytopenias; neutropenia constitutes the most frequent manifestation. LGL clone represents a pathologic counterpart of the cytotoxic effector T cell but an abnormal memory CD8 cell seems to provide the supply of the matured LGL population. Analysis of clonal T cell receptor (TCR) rearrangement and complementarity determining region 3 (CDR3) of the TCR beta-chain is a useful tool to investigate clonal expansions, track the frequency of expanded clones and also clinically useful to monitor the response to therapy. The lessons learned from molecular analysis of clonal repertoire support a clinically-derived conclusion that the LGL clone arises in the context of an initially polyclonal immune response or an autoimmune process. Consequently, specific manifestations of T-LGL may be a result of the recognition spectrum of the transformed clone and the cytokines it produces. Due to the often monoclonal manifestation, T-LGL constitutes a suitable model to investigate polyclonal CTL-mediated processes. Application of new technologies, including TCR repertoire analysis by sequencing, clonotypic quantitative PCR and VB flow cytometry facilitate clinical diagnosis and may allow insights into the regulation of TCR repertoire and consequences resulting from the contraction of clonal diversity.

T-cell receptor repertoire usage in hematologic malignancies

Over the last few years several studies have addressed the possible influence of different immune mechanisms on the evolution of hematologic malignancies. More specifically, a fundamental role of reactive T-cells has now been demonstrated in the pathogenesis of many of these disorders as well as in the typical immunological milieu observed after stem cell transplantation in patients affected by these malignancies. In this context the study of the T-cell receptor (TCR) repertoire performed by different techniques, such as for instance flow cytometry and spectratyping, has undoubtedly provided a fundamental contribution. More recently, these seminal observations have even opened new potential therapeutic avenues based on the employment of adoptive T-cells somehow engineered toward potential neoplastic targets. This review will run through the most relevant studies which have tried to dissect the TCR repertoire usage in patients with different hematologic malignancies, especially focusing on the possible pathogenetic and therapeutic implications.

Pathologic clonal cytotoxic T-cell responses: nonrandom nature of the T-cell–receptor restriction in large granular lymphocyte leukemia

T-cell large granular lymphocyte (T-LGL) leukemia is a clonal lymphoproliferation of cytotoxic T cells (CTLs) associated with cytopenias. T-LGL proliferation seems to be triggered/sustained by antigenic drive; it is likely that hematopoietic progenitors are the targets in this process. The antigen-specific portion of the T-cell receptor (TCR), the variable beta (VB)–chain complementarity-determining region 3 (CDR3), can serve as a molecular signature (clonotype) of a T-cell clone. We hypothesized that clonal CTL proliferation develops not randomly but in the context of an autoimmune response. We identified the clonotypic sequence of T-LGL clones in 60 patients, including 56 with known T-LGL and 4 with unspecified neutropenia. Our method also allowed for the measurement of clonal frequencies; a decrease in or loss of the pathogenic clonotype and restoration of the TCR repertoire was found after hematologic remission. We identified 2 patients with identical immunodominant CDR3 sequence. Moreover, we found similarity between multiple immunodominant clonotypes and codominant as well as a nonexpanded, “supporting” clonotypes. The data suggest a nonrandom clonal selection in T-LGL, possibly driven by a common antigen. In contrast, the physiologic clonal CTL repertoire is highly diverse and we were not able to detect any significant clonal sharing in 26 healthy controls.

Molecular Analysis of TCR Clonotypes in LGL: A Clonal Model for Polyclonal Responses

Large granular lymphocytic (LGL) leukemia is a clonal lymphoproliferative disorder of CTL associated with cytopenias resulting from an immune and cytokine attack on hemopoietic progenitor cells. Extreme clonality of CTL expansions seen in LGL leukemia makes it an ideal model to study the role of the T cell repertoire in other less-polarized immune-mediated disorders. Complementarity-determining region 3 (CDR3) of the TCR is a unique Ag-specific region that can serve as a molecular marker, or clonotype, of the disease-specific T cells. We studied the variable portion of the beta-chain spectrum in a cohort of LGL leukemia patients. The CDR3 sequences were determined for the immunodominant clones and used to design clonotype-specific primers. By direct and semi-nested amplification, clonotype amplicons were found to be shared by multiple patients and controls. Analysis of the generated sequences demonstrated that the original clonotypes are rarely encountered in normal control samples; however, high levels of homology were found in both controls and patients. Clonotypes derived from individual LGL patients can be used as tumor markers for the malignant clone. More generally, clonotypic analysis and comparison of the variable portion of the beta-chain CDR3-specific sequences from a large number of patients may lead to better subclassification of not only LGL but also other immune-mediated disorders.

Effect of chemotherapy and stem cell transplantation on T lymphocyte clones in familial haemophagocytic lymphohistiocytosis

Familial haemophagocytic lymphohistiocytosis (FHL) is a rare disorder in infancy, curative only by an allogeneic stem cell transplantation (SCT). We recently confirmed the clonal evidence of T cells in FHL. To confirm the effect of chemotherapy and SCT in FHL, the change of T-cell clones was analysed in two patients using inverse reverse transcription-polymerase chain reaction (RT-PCR) of the T-cell receptor variable region (TCR V) gene, followed by PCR for the junctional region (Jbeta-PCR), a single-strand conformation polymorphism (SSCP) and sequencing analysis at diagnosis, after chemotherapy and after SCT. A high frequency (> 15%) of alphabeta T-cell clones and a predominant bias (Jbeta1:Jbeta2, 85:15) for the Jbeta1 subgroup were observed in the two patients at diagnosis. In one patient, however, an inverted predominant bias (Jbeta1:Jbeta2, 9:91) for the Jbeta2 subgroup and oligoclonal expansion were observed at relapse after chemotherapy. In the other patient, correction of both restricted Jbeta cluster usage and variation of TCR were observed after chemotherapy and SCT. Using sequence analysis, the clonal T cells detected at diagnosis were found to be substituted at low frequency (< 0.75%) by several new clones after chemotherapy and SCT. These results indicate that any genetic defect could influence the regulation of the T-cell network, and normalization of both the variation in each Vbeta repertoire and the Jbeta1/Jbeta2 ratio is needed to achieve remission, and might support the rationale that the only acceptable curative therapy of FHL is allogeneic SCT.

Role of interferon-alpha and clonally expanded T cells in the immunotherapy of chronic myelogenous leukemia

Twenty five percent of patients in the chronic phase of chronic myelogenous leukemia (CML) are treated with interferon-alpha (IFN-alpha) to induce a cytogenic remission. In addition to its direct effects on leukemic cells, IFN-alpha has been shown to induce immunologic alterations, including upregulation of the expression of major histocompatibility (MHC) antigens in antigen-presenting cells (APCs), as well as augmentation of the activity of the lymphocytes against tumor cells. However, there has been little direct evidence supporting a causal interaction between cellular immunoreactivity and clinical responsiveness to IFN-alpha. We have shown that one approach to elucidate the immunological mechanisms by which IFN-alpha exerts its anti-CML activity is by analyzing therapy-induced modulation in T-cell receptor (TCR) Vbeta chain usage, using the reverse transcription-polymerase chain reaction (RT-PCR) followed by single-strand conformation (SSCP) analysis. This method is particularly attractive, since it provides an index of antigen-specific T cell expansion, but does not require the extraction and purification of the antigens involved in the T-cell response. T cell clones that express the Vbeta 10, 12, and 14 families predominate in the peripheral blood (PB) of CML patients. The enhanced expression of the Vbeta 9 and 20 families has been detected in IFN-alpha responsive patients but not patients who are poorly responsive to this agent. This suggests that expansion of T cells expressing these TCR Vbeta gene families may serve as a prognostic factors of the clinical responsiveness of CML patients to IFN-alpha. In addition, since T cell clones that express certain Vbeta families may react with a discrete set of antigenic peptides presented on the surface of malignant cells, a better understanding of the immunobiology of T cells in CML may allow for the design of increasing efficacious immune therapy for this disease.