I. L. M. Wolvers-Tettero

Development of a diverse human T-cell repertoire despite stringent restriction of hematopoietic clonality in the thymus

Significance The number of hematopoietic stem cell clones contributing to T-cell development is restricted at entry of and during further development inside the thymus. However, despite this severe restriction, a fully diverse T-cell receptor repertoire can be generated, indicating that hematological and immunological clonality are independently regulated. The fate and numbers of hematopoietic stem cells (HSC) and their progeny that seed the thymus constitute a fundamental question with important clinical implications. HSC transplantation is often complicated by limited T-cell reconstitution, especially when HSC from umbilical cord blood are used. Attempts to improve immune reconstitution have until now been unsuccessful, underscoring the need for better insight into thymic reconstitution. Here we made use of the NOD-SCID-IL-2Rγ−/− xenograft model and lentiviral cellular barcoding of human HSCs to study T-cell development in the thymus at a clonal level. Barcoded HSCs showed robust (>80% human chimerism) and reproducible myeloid and lymphoid engraftment, with T cells arising 12 wk after transplantation. A very limited number of HSC clones (<10) repopulated the xenografted thymus, with further restriction of the number of clones during subsequent development. Nevertheless, T-cell receptor rearrangements were polyclonal and showed a diverse repertoire, demonstrating that a multitude of T-lymphocyte clones can develop from a single HSC clone. Our data imply that intrathymic clonal fitness is important during T-cell development. As a consequence, immune incompetence after HSC transplantation is not related to the transplantation of limited numbers of HSC but to intrathymic events.

Oligoclonal T Cell Proliferative Disorder in Combined Immunodeficiency

ABSTRACT: Oligoclonal lymphoid proliferations may occur in immunocompromised patients and in the elderly. So far these proliferations have been shown to be of B cell origin. We describe a patient with a combined immunodeficiency, characterized by profound hypogammaglobuline-mia and the initial absence of T lymphocytes in the peripheral blood (PB). From the age of 4 yr CD3+ T cells appeared in PB in rising numbers. These cells mainly expressed the CD4−/CD8+ phenotype (CD4/CD8 ratio: 0.1). Despite the emergence of T lymphocytes no proliferation of PB mononuclear cells could be induced with phytohemagglutinin, concanavalin A, or pokeweed mitogen. Between the ages of 4 and 6 yr the patient gradually developed hepatosplenomegaly and an interstitial pulmonary infiltrate of unknown origin, necessitating biopsies of both liver and lung. Infiltrates consisting of CD8+ T lymphocytes were found in the liver as well as the lung. CD8+ T cells were also abundant in the bronchoalveolar lavage fluid. Southern blot analysis of mononuclear cells from PB and of a lung biopsy specimen was performed to investigate if a clonal T cell population was involved. Analysis of the T cell receptor β genes revealed that at least three expanded T cell clones were present in PB, one of which had invaded the lung. Thus far, i.e. 2 yr after the initial detection of clonal T cell receptor β gene rearrangements, there have been no clinical or histologic signs of malignant behavior. We conclude that this combined immunodeficiency patient has a benign oligoclonal T cell lymphoproliferative disorder. Similar proliferations might well occur in other immunodeficiency states, whether primary or acquired.

Lack of common TCRA and TCRB clonotypes in CD8+/ TCRαβ+ T-cell large granular lymphocyte leukemia: A review on the role of antigenic selection in the immunopathogenesis of CD8+ T-LGL

Clonal CD8+/T-cell receptor (TCR)αβ+ T-cell large granular lymphocyte (T-LGL) proliferations constitute the most common subtype of T-LGL leukemia. Although the etiology of T-LGL leukemia is largely unknown, it has been hypothesized that chronic antigenic stimulation contributes to the pathogenesis of this disorder. In the present study, we explored the association between expanded TCR-Vβ and TCR-Vα clonotypes in a cohort of 26 CD8+/TCRαβ+ T-LGL leukemia patients, in conjunction with the HLA-ABC genotype, to find indications for common antigenic stimuli. In addition, we applied purpose-built sophisticated computational tools for an in-depth evaluation of clustering of TCRβ (TCRB) complementarity determining region 3 (CDR3) amino-acid LGL clonotypes. We observed a lack of clear TCRA and TCRB CDR3 homology in CD8+/TCRαβ+ T-LGL, with only low level similarity between small numbers of cases. This is in strong contrast to the homology that is seen in CD4+/TCRαβ+ T-LGL and TCRγδ+ T-LGL and thus underlines the idea that the LGL types have different etiopathogenesis. The heterogeneity of clonal CD8+/TCRαβ+ T-LGL proliferations might in fact suggest that multiple pathogens or autoantigens are involved.

Clonal T- and natural killer-cell large granular lymphocyte proliferations in a single patient established by array-based comparative genomic hybridization analysis.

Clonal T- and natural killer-cell large granular lymphocyte proliferations in a single patient established by array-based comparative genomic hybridization analysis

Next-Generation Sequencing Analysis of the Human TCRγδ+ T-Cell Repertoire Reveals Shifts in Vγ- and Vδ-Usage in Memory Populations upon Aging

Immunological aging remodels the immune system at several levels. This has been documented in particular for the T-cell receptor (TCR)αβ+ T-cell compartment, showing reduced naive T-cell outputs and an accumulation of terminally differentiated clonally expanding effector T-cells, leading to increased proneness to autoimmunity and cancer development at older age. Even though TCRαβ+ and TCRγδ+ T-cells follow similar paths of development involving V(D)J-recombination of TCR genes in the thymus, TCRγδ+ T-cells tend to be more subjected to peripheral rather than central selection. However, the impact of aging in shaping of the peripheral TRG/TRD repertoire remains largely elusive. Next-generation sequencing analysis methods were optimized based on a spike-in method using plasmid vector DNA-samples for accurate TRG/TRD receptor diversity quantification, resulting in optimally defined primer concentrations, annealing temperatures and cycle numbers. Next, TRG/TRD repertoire diversity was evaluated during TCRγδ+ T-cell ontogeny, showing a broad, diverse repertoire in thymic and cord blood samples with Gaussian CDR3-length distributions, in contrast to the more skewed repertoire in mature circulating TCRγδ+ T-cells in adult peripheral blood. During aging the naive repertoire maintained its diversity with Gaussian CDR3-length distributions, while in the central and effector memory populations a clear shift from young (Vγ9/Vδ2 dominance) to elderly (Vγ2/Vδ1 dominance) was observed. Together with less clear Gaussian CDR3-length distributions, this would be highly suggestive of differentially heavily selected repertoires. Despite the apparent age-related shift from Vγ9/Vδ2 to Vγ2/Vδ1, no clear aging effect was observed on the Vδ2 invariant T nucleotide and canonical Vγ9–Jγ1.2 selection determinants. A more detailed look into the healthy TRG/TRD repertoire revealed known cytomegalovirus-specific TRG/TRD clonotypes in a few donors, albeit without a significant aging-effect, while Mycobacterium tuberculosis-specific clonotypes were absent. Notably, in effector subsets of elderly individuals, we could identify reported TRG and TRD receptor chains from TCRγδ+ T-cell large granular lymphocyte leukemia proliferations, which typically present in the elderly population. Collectively, our results point to relatively subtle age-related changes in the human TRG/TRD repertoire, with a clear shift in Vγ/Vδ usage in memory cells upon aging.