Insight into normal thymic activity by assessment of peripheral blood samples

Thymic microenvironment's impact on immunosenescence

Age-related thymic involution is characterized by the loss of T cell development and the supporting epithelial network, which are replaced by adipose tissue. We previously showed that aging functionally impairs lymphohematopoietic progenitor cells, including thymic early T cell progenitors (ETPs), contributing to thymic involution. Considering that the thymic microenvironment is essential for thymocyte incubation, we aimed to investigate its role in age-related thymic involution and the mechanisms underlying these changes. The challenge in studying these processes led us to transplant T cell-depleted fetal thymus tissue into the kidney capsule of aged mice. This model allowed us to identify the mechanisms driving age-related changes in the thymic microenvironment and to assess whether these changes could be reversed. Flow cytometry was used to detect naïve T cells (CD62L+CD44-), including CD4 CD8 double-negative, double-positive, and single-positive T cells. Real-time PCR was used to detect and quantify signal-joint T cell receptor excision circles. We rearranged δRec-ΨJα in murine peripheral blood leukocytes to evaluate the thymic output of newly developed naïve T cells in the mice and gene expression in the thymus. Age-related thymic involution decreased naïve T cells and increased memory T cells, while fetal thymus transplantation improved thymic output and T cell production and reversed the impairment of thymopoiesis due to thymic involution in aged mice. Furthermore, the expression of key cytokines was restored and ETPs in the aged mice showed normal thymic T cell development. Our study suggests that degenerative changes in the thymic microenvironment are the primary cause of thymic dysfunction, leading to immunosenescence associated with age-related thymic involution.

Can T-cell and B-cell excision circles predict development of inhibitors in pediatric hemophilia A?

BACKGROUND

Hemophilia A (HA) therapy requires intravenous replacement infusions of factor (F) VIII concentrate. Inhibitors are high-affinity immunoglobulin G that are directed against FVIII and thereby render replacement therapy ineffective. This complication has significant prognostic implications. We aimed to examine the immune system involvement in inhibitor formation specifically T-cell excision circles (TRECs) and B-cell excision circles (KRECs), markers of new T and B cells, respectively, and examine them as surrogate markers for inhibitor formation.

METHODS

Blood samples were collected from 35 children with severe HA. Children were divided into two groups: with FVIII inhibitors and without FVIII inhibitors. TRECs and KRECs were measured in peripheral blood.

RESULTS

A total of 11 patients with inhibitors and 24 without were evaluated. Children with inhibitors had higher levels of TRECs however not statistically significant (p = 0.085). CjKREC levels were higher in the inhibitor patients (p = 0.003). Moreover, the sj/cjKREC ratio was lower in the inhibitor patients (p = 0.015).

CONCLUSIONS

Our findings may add to the notion that inhibitor formation is attributed to humoral immunity due to peripheral B-cell expansion and loss of peripheral tolerance. Improved knowledge regarding the involvement of the immune system in the formation of FVIII inhibitors will enable better therapy tailoring in the era of non-replacement therapies.

IMPACT

The etiology of FVIII inhibitor formation is multifactorial, in which the immune system plays a pivotal role. Our findings may add to the notion that inhibitor formation is attributed to humoral immunity due to peripheral B-cell expansion and production of antibodies against FVIII. Improved knowledge regarding the involvement of the immune system in the development of FVIII inhibitors will enable the identification of patients prone to inhibitor development and better therapy tailoring in the new era of non-replacement therapies.

Immune and TRG repertoire signature of the thymus in Down syndrome patients

BACKGROUND

Patients with Down syndrome (DS) are at increased risk for infections and autoimmune disorders. Although several immunological abnormalities were previously found, differences in T cell receptor repertoire have never been shown. Thus we compared the T cell receptor gamma (TRG) repertoire in DS and non-syndromic pediatric patients by next-generation sequencing, in addition to other immunological markers.

METHODS

Genomic DNA was extracted from thymuses of pediatric patients who underwent heart surgery, where six were with DS and six were non-syndromic patients. Peripheral blood counts, T cell subpopulations, thymus TCR excision circles (TRECs), spectratyping, and next-generation sequencing for TRG were analyzed.

RESULTS

The mean age of the patients was 7 months and the mean lymphocyte count was slightly lower in patients with DS, whereas thymus TREC results were similar to non-syndromic patients (p = 0.197). The TRG repertoire analysis showed that patients with DS had a significantly larger number of unique TRG sequences, together with decreased clonal expansion. Lastly, the V and J gene usages in the thymus were similar in DS and non-syndromic patients.

CONCLUSIONS

Patients with DS showed increased TRG repertoire diversity with decreased clonal expansion compared to non-syndromic patients.

IMPACT

Alterations in T cell receptor gamma repertoire were found in patients with Down syndrome using next-generation sequencing (NGS) technique. Patients showed increased repertoire diversity and decreased clonal expansion compared to controls. These findings add to previous reports on abnormalities of other immune system components in patients with Down syndrome. NGS technique may point out differences not seen by previous methods. Repertoire abnormalities may contribute to those patients' predisposition to infections and autoimmune diseases.

DNA demethylating agent decitabine broadens the peripheral T cell receptor repertoire

Purpose

Decitabine, a promising epi-immunotherapeutic agent has shown clinical responses in solid tumor patients, while the anti-tumor mechanisms were unclear. We aimed to investigate the immunomodulatory effect of decitabine in peripheral T cells.

Experimental design

We applied next-generation sequencing to investigate the complementarity-determining region 3 (CDR3) of the TCRβ gene, the diversity of which acts as the prerequisite for the host immune system to recognize the universal foreign antigens. We collected the peripheral blood mononuclear cells (PBMCs) from 4 patients, at baseline and after 2 cycles of low-dose decitabine therapy.

Results

An increase of the unique productive sequences of the CDR3 of TCRβ was observed in all of the 4 patients after decitabine treatment, which was characterized by a lower abundance of expanded clones and increased TCR diversity compared with before decitabine treatment. Further analysis showed a tendency for CD4 T cells with an increased CD4/CD8 ratio in response to decitabine therapy. In addition, the genome-wide expression alterations confirmed the effects of decitabine on immune reconstitution, and the increase of TCR excision circles (TRECs) was validated.

Conclusions

The low-dose DNMT inhibitor decitabine broadens the peripheral T cell repertoire, providing a novel role for the epigenetic modifying agent in anti-tumor immune enhancement.

Quantification of specific T and B cells immunological markers in children with chronic and transient ITP

BACKGROUND

Immune thrombocytopenic purpura (ITP) is characterized by a transient (nonchronic) or permanent (chronic) decline in the number of platelets. Predicting the course of ITP, at the time of diagnosis, is of importance. Here we studied at diagnosis, clinical and immunological parameters in order to distinguish between different courses. The latter included the measure of new B and T cells using quantification of kappa-deleting recombination excision circles (KRECs) and T-cell receptor excision circles (TRECs), respectively.

METHODS

Blood samples were collected from 44 children with a clinical diagnosis of ITP. Real-time PCR was performed in order to quantify the number of copies of TREC and KREC followed by collection of clinical data from medical files. The children were retrospectively divided into two groups: chronic and nonchronic.

RESULTS

Twenty-four patients (54%) were classified as nonchronic ITP and 20 patients (46%) were classified as chronic ITP. We confirmed some clinical parameters (e.g., gender, age) but not others (e.g., preceding infection, level of thrombocytopenia) that distinguish patients with chronic and nonchronic course. While KREC quantification was similar in patients regardless the outcome of their disease, it was significantly higher than the level of controls (P < 0.05). TREC quantification was not different between patients and controls.

CONCLUSIONS

KREC but not TREC levels are different in patients comparing to controls, pointing to an overreaction of B-cell development as a role in the pathogenesis of ITP. These results may shed more lights on the immune mechanism of ITP.

Thymus activity measured by T-cell receptor excision circles in patients with different severities of respiratory syncytial virus infection

Background

Respiratory syncytial virus (RSV) infection is an important cause of hospitalization in previously healthy infants. Immunological mechanisms predisposing infants to severe disease are poorly understood. Early biomarkers for disease severity may assist clinical decisions. We investigated T-cell receptor excision circles (TREC), episomal DNA made during thymic T-cell receptor rearrangement, and a marker for thymus activity, both during disease and in neonatal screening cards as a risk factor for RSV disease severity.

Methods

One hundred thirteen patients hospitalized with RSV infection <12 months of age, grouped by disease severity, were available for this investigation, in which we conducted both a prospective and a case-control study. The prospective study included 47 RSV positive infants (mild n = 13, moderate n = 10, severe n = 24). TREC counts were determined by PCR of DNA extracted from EDTA-blood collected on hospitalization, and corrected for lymphocytes using ANCOVA. The case-control study included 85 newborns who later in infancy became RSV positive (mild n = 32, moderate n = 24, severe n = 29) and 47 newborns who never developed RSV disease as healthy controls included from health centres in the same catchment area. TRECs were measured using DNA extracted from dry blood spots from stored neonatal screening cards, followed by PCR. Student’s T-test compared patients with controls, ANOVA compared disease severity groups.

Results

During RSV infection patients in the severe disease group had significantly lower (p = 0.017) TREC/200 μL blood compared to the other two disease groups, after correction for lymphocyte count. Newborn TREC levels, were significantly higher in RSV patients compared to controls (p < 0.0001). No significant differences in TREC copies at birth were found between disease severities.

Conclusion

During acute RSV infection a lower number of TREC is found in the severe disease group. TREC has potential as an immunological marker for severe RSV infection. Higher neonatal TREC counts indicate that infants later presenting with severe RSV do not have reduced thymic activity at birth and probably no congenital T-cell defect.

Regulatory T-Cell Development in the Human Thymus

The thymus generates a lineage-committed subset of regulatory T-cells (Tregs), best identified by the expression of the transcription factor FOXP3. The development of thymus-derived Tregs is known to require high-avidity interaction with MHC-self peptides leading to the generation of self-reactive Tregs fundamental for the maintenance of self-tolerance. Notwithstanding their crucial role in the control of immune responses, human thymic Treg differentiation remains poorly understood. In this mini-review, we will focus on the developmental stages at which Treg lineage commitment occurs, and their spatial localization in the human thymus, reviewing the molecular requirements, including T-cell receptor and cytokine signaling, as well as the cellular interactions involved. An overview of the impact of described thymic defects on the Treg compartment will be provided, illustrating the importance of these in vivo models to investigate human Treg development.