Terminal deoxynucleotidyl transferase (TdT) enzyme in thymus and bone marrow. I. Age-associated decline of TdT in humans and mice

Hindlimb unloading, a physiological model of microgravity, modifies the murine bone marrow IgM repertoire in a similar manner as aging but less strongly

BACKGROUND

The spaceflight environment is an extreme environment that affects the immune system of approximately 50% of astronauts. With planned long-duration missions, such as the deployment of the Lunar Gateway and possible interplanetary missions, it is mandatory to determine how all components of the immune system are affected, which will allow the establishment of countermeasures to preserve astronaut health. However, despite being an important component of the immune system, antibody-mediated humoral immunity has rarely been investigated in the context of the effects of the space environment. It has previously been demonstrated that 30 days aboard the BION-M1 satellite and 21 days of hindlimb unloading (HU), a model classically used to mimic the effects of microgravity, decrease murine B lymphopoiesis. Furthermore, modifications in B lymphopoiesis reported in young mice subjected to 21 days of HU were shown to be similar to those observed in aged mice (18-22 months). Since the primary antibody repertoire composed of IgM is created by V(D) J recombination during B lymphopoiesis, the objective of this study was to assess the degree of similarity between changes in the bone marrow IgM repertoire and in the V(D)J recombination process in 2.5-month-old mice subjected to 21 days of HU and aged (18 months) mice.

RESULTS

We found that in 21 days, HU induced changes in the IgM repertoire that were approximately 3-fold less than those in aged mice, which is a rapid effect. Bone remodeling and epigenetics likely mediate these changes. Indeed, we previously demonstrated a significant decrease in tibial morphometric parameters from day 6 of HU and a progressive reduction in these parameters until day 21 of HU, and it has been shown that age and microgravity induce epigenetic changes.

CONCLUSION

These data reveal novel immune changes that are akin to advanced aging and underline the importance of studying the effects of spaceflight on antibody-mediated humoral immunity.

Newborn and child-like molecular signatures in older adults stem from TCR shifts across human lifespan

CD8+ T cells provide robust antiviral immunity, but how epitope-specific T cells evolve across the human lifespan is unclear. Here we defined CD8+ T cell immunity directed at the prominent influenza epitope HLA-A*02:01-M158-66 (A2/M158) across four age groups at phenotypic, transcriptomic, clonal and functional levels. We identify a linear differentiation trajectory from newborns to children then adults, followed by divergence and a clonal reset in older adults. Gene profiles in older adults closely resemble those of newborns and children, despite being clonally distinct. Only child-derived and adult-derived A2/M158+CD8+ T cells had the potential to differentiate into highly cytotoxic epitope-specific CD8+ T cells, which was linked to highly functional public T cell receptor (TCR)αβ signatures. Suboptimal TCRαβ signatures in older adults led to less proliferation, polyfunctionality, avidity and recognition of peptide mutants, although displayed no signs of exhaustion. These data suggest that priming T cells at different stages of life might greatly affect CD8+ T cell responses toward viral infections.

Two types of human TCR differentially regulate reactivity to self and non-self antigens

Based on analyses of TCR sequences from over 1,000 individuals, we report that the TCR repertoire is composed of two ontogenically and functionally distinct types of TCRs. Their production is regulated by variations in thymic output and terminal deoxynucleotidyl transferase (TDT) activity. Neonatal TCRs derived from TDT-negative progenitors persist throughout life, are highly shared among subjects, and are reported as disease-associated. Thus, 10%–30% of most frequent cord blood TCRs are associated with common pathogens and autoantigens. TDT-dependent TCRs present distinct structural features and are less shared among subjects. TDT-dependent TCRs are produced in maximal numbers during infancy when thymic output and TDT activity reach a summit, are more abundant in subjects with AIRE mutations, and seem to play a dominant role in graft-versus-host disease. Factors decreasing thymic output (age, male sex) negatively impact TCR diversity. Males compensate for their lower repertoire diversity via hyperexpansion of selected TCR clonotypes.

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Over 10⁸ TCR CDR3 sequences from ∼10³ individuals and 7 cohorts were analyzed

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The TCR repertoire is composed of two layers: neonatal and TDT-dependent layer

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∼70% of frequent cord blood TCRs are associated with common pathogens

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Acute graft-vs-host disease correlates with a high proportion of TDT-dependent TCRs

Terminal Deoxynucleotidyl Transferase (TdT) Inhibiti on of Cord Blood Derived B and T Cells Expansion

Purpose: Terminal deoxynucleotidyl transferase(TdT) is a DNA polymerase that is present in immature pre-B and pre-T cells. TdT inserts N-nucleotides to the V (D) J gene segment during rearrangements of genes, therefore, it plays a vital role in the development and variation of the immune system in vertebrates. Here we evaluated the relationship between cytokines like interleukin-2 (IL-2), interleukin-7 (IL-7), and interleukin-15 (IL-15) and TdT expression in cord blood mononuclear cells and also effect of inhibition in the expansion of B and T cells derived from cord blood. Methodes: The cord blood mononuclear cells were cultured with different combination of cytokines for 21days, which they were harvested in definite days (7, 14 and 21) and evaluated by flow cytometry. Results: Our data indicated that TdT expression increased in cord blood mononuclear cells using immune cell key cytokines without being dependent on the type of cytokines. TdT inhibition reduced both the expansion of B and T cells derived from cord blood and also declined the apoptosis and proliferation. Considered together, TdT played an important role in the control of the expansion of B and T cells derived from cord blood. Conclusion: considered together, it was observed that TdT expression was increased by cytokines and TdT inhibition not only reduced B and Tcells derived from cord blood, but it also affected the rate of apoptosis and proliferation.

Measurement of terminal deoxynucleotidyl transferase mRNA in clinical samples: a new parameter in analysis of leukemia cells

A 1750 base pair cDNA to human terminal deoxynucleotidyl transferase (TdT) has been cloned. This cDNA detects a dominant 2200 base pair messenger RNA species in normal and leukemic cells synthesizing the enzyme. A quantitative dot blot assay was utilized to survey a number of clinical samples from patients with TdT positive and negative leukemias as well as cells from normal volunteers. A linear relationship was detected between the amount of TdT mRNA and the amount of enzyme activity in bone marrow cells. The assay is sensitive enough to detect normal TdT levels in bone marrow, and distinguish these levels from the lack of such mRNA in peripheral blood and bone marrow of patients with myeloid leukemia. Elevated levels of mRNA were found in two cases of patients in clinical remission. The prognostic significance of these observations must await further study.

Studies on terminal deoxynucleotidyl transferase and adenosine deaminase in myasthenic thymus

Thymic function in myasthenic patients was examined using two biochemical markers which specifically define a population of cortisone-sensitive cortical thymocytes. The enzymatic activities of terminal deoxynucleotidyl transferase (TdT) and adenosine deaminase (ADA) were determined in 13 samples. High contents of both enzymes were found in young patients. The enzymatic activities were easily detectable also in the oldest patients, despite the morphological involution and the decrease in TdT which are known to occur with age in the normal thymus. TdT and ADA-containing cells were almost completely depleted in all the 3 treated patients by the corticosteroid treatment which provides a non-surgical alternative to the elimination of this lymphoid population by thymectomy. The persistence of TdT and ADA activity in old age, and their inhibition by the corticosteroid treatment.

Immunohistological demonstration of terminal transferase (TdT) in the age-involuted human thymus

By using a sensitive immunoperoxidase technique, serological determinants of terminal deoxynucleotidyl transferase (TdT, E. C. 2.7.7.31) were found in cortical lymphocytes of thymus biopsies of adult and aged persons (21-70 years) of both sexes. In contrast to biochemical determinations, specific immunohistological studies showed that TdT is continuously present in very large numbers of cortical thymic lymphocytes during human life, despite subtotal physiological involution of the thymus.

Persistent cytomegalovirus infection: association with profound immunodeficiency and treatment with interferon

Cytomegalovirus (CMV) was repeatedly isolated from urine and saliva of a 20-month-old male child with recurrent episodes of pneumonia, high fever, rash, lymphadenopathy, oral ulceration, and neutropenia. Immunologic evaluation revealed decreased serum IgG and IgA, increased IgM, depressed T- and B-lymphocyte functions, and decreased natural killer (NK) activity for herpes simplex-type I virus-infected targets. NK activity was augmented following exposure of the patient's lymphocytes to interferon (IF) in vitro. The child was treated with interferon (four courses, dosage varying from 2 million U/day to 1 million U three times/week for periods of 10, 28, 80, and 67 days, respectively, interspersed over 9 months) and hyperimmune plasma infusions every 3 weeks. Toward the end of interferon therapy oral Levamisole was started and a feeding gastrostomy was inserted to provide nutritional support. Clinical recovery was associated with reversal of immunologic abnormalities except for the hypogammaglobulinemia. Aggressive antiviral therapy (e.g., with IF) followed by immunostimulation (e.g., with Levamisole) may prove effective in controlling certain viral infections in immunodeficiency disorders.

Terminal deoxynucleotidyl transferase (TdT) in RadLV-induced C57BL thymomas

Newborn C57BL mice exposed to RadLV at birth were followed and periodically sampled for thymus and bone marrow TdT activity. Tumors detected at or before 100 days had mostly low TdT levels. Large thymic lymphocytic tumors detected after 100 days had elevated total TdT content per gland. Serial samples showed a changing TdT pattern with time. The mid period shifted from low levels to normal-to-high levels for both TdT content and total TdT per gland. No unusual bone marrow TdT activity change preceded the appearance of thymomas. TdT marks a unique precursor cell highly sensitive to RadLV associated with lymphomagenesis. RadLV induced both TdT+ and TdT- thymic lymphomas and both types were found to occur after lymphoma initiation by injection of RadLV into newborns.