Utilization of TREC and KREC quantification for the monitoring of early T- and B-cell neogenesis in adult patients after allogeneic hematopoietic stem cell transplantation

European Society for Immunodeficiencies guidelines for the management of patients with congenital athymia

Congenital athymia is a life-limiting disorder due to rare inborn errors of immunity causing impaired thymus organogenesis or abnormal thymic stromal cell development and function. Athymic infants have a T-lymphocyte-negative, B-lymphocyte-positive, natural killer cell-positive immunophenotype with profound T-lymphocyte deficiency and are susceptible to severe infections and autoimmunity. Patients variably display syndromic features. Expanding access to newborn screening for severe combined immunodeficiency and T lymphocytopenia and broad genetic testing, including next-generation sequencing technologies, increasingly facilitate their timely identification. The recommended first-line treatment is allogeneic thymus transplantation, which is a specialized procedure available in Europe and the United States. Outcomes for athymic patients are best with early diagnosis and thymus transplantation before the development of infectious and inflammatory complications. These guidelines on behalf of the European Society for Immunodeficiencies provide a comprehensive review for clinicians who manage patients with inborn thymic stromal cell defects; they offer clinical practice recommendations focused on the diagnosis, investigation, risk stratification, and management of congenital athymia with the aim of improving patient outcomes.

A high-throughput newborn screening approach for SCID, SMA, and SCD combining multiplex qPCR and tandem mass spectrometry

Early diagnosis of severe combined immunodeficiency (SCID), spinal muscular atrophy (SMA), and sickle cell disease (SCD) improves health outcomes by providing a specific treatment before the onset of symptoms. A high-throughput nucleic acid-based method in newborn screening (NBS) has been shown to be fast and cost-effective in the early detection of these diseases. Screening for SCD has been included in Germany's NBS Program since Fall 2021 and typically requires high-throughput NBS laboratories to adopt analytical platforms that are demanding in terms of instrumentation and personnel. Thus, we developed a combined approach applying a multiplexed quantitative real-time PCR (qPCR) assay for simultaneous SCID, SMA, and 1st-tier SCD screening, followed by a tandem mass spectrometry (MS/MS) assay for 2nd-tier SCD screening. DNA is extracted from a 3.2-mm dried blood spot from which we simultaneously quantify T-cell receptor excision circles for SCID screening, identify the homozygous SMN1 exon 7 deletion for SMA screening, and determine the integrity of the DNA extraction through the quantification of a housekeeping gene. In our two-tier SCD screening strategy, our multiplex qPCR identifies samples carrying the HBB: c.20A>T allele that is coding for sickle cell hemoglobin (HbS). Subsequently, the 2nd tier MS/MS assay is used to distinguish heterozygous HbS/A carriers from samples of patients with homozygous or compound heterozygous SCD. Between July 2021 and March 2022, 96,015 samples were screened by applying the newly implemented assay. The screening revealed two positive SCID cases, while 14 newborns with SMA were detected. Concurrently, the qPCR assay registered HbS in 431 samples which were submitted to 2nd-tier SCD screening, resulting in 17 HbS/S, five HbS/C, and two HbS/β thalassemia patients. The results of our quadruplex qPCR assay demonstrate a cost-effective and fast approach for a combined screening of three diseases that benefit from nucleic-acid based methods in high-throughput NBS laboratories.

A preliminary study of tracking B-cell kinetics in patients with lung transplantation by monitoring kappa-deleting recombination excision circles

Background

This study aims to evaluate humoral immune system response by measuring copy numbers of kappa-deleting recombination excision circles (KREC) gene segment from B lymphocytes in patients with lung transplantation.

Methods

Between September 2015 and November 2016, a total of 11 patients (8 males, 3 females; mean age: 45.4±12.0 years; range, 23 to 59 years) who underwent lung transplantation with different primary indications were included. The copy numbers of KREC gene segment were quantified using real-time polymerase chain reaction method in peripheral blood samples collected pre- and post-transplantation. The samples of the patients were compared with the KREC l evels i n deoxyribonucleic acid extracted from blood samples of healthy children.

Results

There was no significant change in KREC levels between pre- and post-operation (p=0.594 and p=0.657), although the median values indicated that the highest increase in the KREC levels (7x105- 12x105; 85-170) was on Day 7 of transplantation. There was a positive correlation between the KREC levels (mL in blood) and lymphocytes at 24 h after transplantation (p=0.043) and between KREC copies per 106 of blood and age on Day 7.

Conclusion

Our preliminary results suggest that KREC l evels a s an indicator of B lymphocyte production are elevated after lung transplantation. A prognostic algorithm by tracking B cell kinetics after post-transplantation for long-term follow-up can be developed following the confirmation of these preliminary results with more patient samples.

T cell receptor excision circles are potential predictors of survival in adult allogeneic hematopoietic stem cell transplantation recipients with acute myeloid leukemia

Background

Lymphocyte neogenesis from primary lymphoid organs is essential for a successful reconstitution of immunity after allogeneic hematopoietic stem cell transplantation (HSCT). This single-center retrospective study aimed to evaluate T cell receptor excision circles (TREC) and kappa-deleting recombination excision circles (KREC) as surrogate markers for T and B cell recovery, as predictors for transplantation-related outcomes in adult acute myeloid leukemia (AML) patients.

Methods

Ninety adult patients diagnosed with AML and treated with HSCT between 2010 and 2015 were included in the study. TREC and KREC levels were measured by quantitative PCR at 1, 3, 6, and 12 months after transplantation.

Results

Overall, excision circle levels increased between 3 and 6 months post-HSCT for TREC (p = 0.005) and 1 and 3 months for KREC (p = 0.0007). In a landmark survival analysis at 12 months post-HSCT, TREC levels were associated with superior overall survival (HR: 0.52, 95% CI: 0.34 - 0.81, p = 0.004). The incidence of viral infections within the first 100 days after transplantation was associated with lower TREC levels at 6 months (p = 0.0002). CMV reactivation was likewise associated with lower TREC levels at 6 months (p = 0.02) post-HSCT. KREC levels were not associated with clinical outcomes in statistical analyzes.

Conclusions

Results from the present study indicate that TREC measurement could be considered as part of the post-HSCT monitoring to identify AML patients with inferior survival after transplantation. Further prospective studies are warranted to validate these findings.

A Novel Homozygous TTC7A Missense Mutation Results in Familial Multiple Intestinal Atresia and Combined Immunodeficiency

Rare autosomal-recessive variants in tetratricopeptide repeat domain 7A (TTC7A) gene have been shown to cause intestinal and immune disorders of variable severity. Missense mutations in TTC7A gene, usually retaining most of the functional motifs, is associated with relative milder clinical presentations. In this study, we reported a patient who was suffering from severe multiple intestinal atresia (MIA) with combined immunodeficiency (CID) that led to the pyloric diaphragm, ileum atresia, colon stenosis, and multiple episodes of sepsis. In spite of several surgeries and supportive treatment, the patient died of severe sepsis and multiple organ failure at age of 3 months. The whole exome sequencing (WES) of peripheral blood samples identified a novel homozygous TTC7A missense mutation (c. 206T>C, p. L69P), inherited from his parents with consanguineous marriage. In silico analysis revealed that a hydrogen bond present between Gly65 and Leu69 in the wild-type TTC7A was disrupted by the Leu69Pro mutation. Moreover, this homozygous missense mutation led to a reduced TTC7A expression in lymphocytes and intestinal tissues, accompanied by impeded lymphocyte development. Further studies demonstrated that the PI4K-FAM126A-EFR3A pathway was impaired in colon tissues. Our data strongly support the linkage of severe MIA-CID with the missense mutation in TTC7A gene. More knowledge of the TTC7A protein functions will have important therapeutic implications for patients with MIA-CID.

Implementation of TREC/KREC detection protocol for newborn SCID screening in Bulgaria: a pilot study

Neonatal screening for inborn errors of immunity (IEI), based on quantification of T-cell-receptor- excision circles (TRECs) and kappa-deleting recombination-excision circles (KRECs) from dried blood spots (DBS), allows early diagnosis and improved outcomes for the affected children. Determination of TREC/KREC levels from prospectively collected newborns' Guthrie cards and from DBS samples of patients with confirmed IEI was done using a commercial kit. Retrospective assessment of flow cytometry evaluation of TREC/KREC correspondence with lymphocyte subpopulations and evaluation of the correlations between TREC and KREC with immune cells, based on the data from patients with suspected or confirmed immune disorders, were conducted. 2,228 Guthrie cards were tested, 1276 for TREC only and 952 for both TREC and KREC. Eight newborns (0.36%) were TREC positive and 10 (1.05%) had KREC below the cut-off. The re-testing rate was 1.88%. Retrospective analysis demonstrated that the TREC/KREC assay identifies 100% of severe combined immune deficiencies (SCID) cases when DBS were collected at birth. Correlation analysis showed moderate significant correlations between TREC and the absolute numbers of CD4 cells (r = 0.634, p < 0.01) and total T cells (r = 0.536, p < 0.01). The ability of KREC levels to predict abnormal absolute (AUC of 0.772) and relative (AUC 0.731) levels of B cells was demonstrated.

TREC/KREC Levels in Young COVID-19 Patients

COVID-19 patients with acute respiratory distress syndrome (ARDS) have an immune imbalance when systemic inflammation and dysfunction of circulating T and B cells lead to a more severe disease. Using TREC/KREC analysis, we studied the level of mature naive T and B cells in peripheral blood of COVID-19 patients and its relationship with clinical and laboratory data. TREC/KREC analysis was performed by multiplex real-time quantitative PCR on a sample of 36 patients aged 45 years or younger. The reduced TREC/KREC level was observed in ARDS patients compared with non-ARDS patients, and similar results were found for the deceased patients. During days 6 to 20 of hospitalization, a higher neutrophil-to-lymphocyte ratio (NLR) was detected in ARDS patients compared with non-ARDS patients. TREC/KREC negatively correlated with NLR; the highest correlation was recorded for TREC per 100,000 cells with the coefficient of determination R² = 0.527. Thus, TREC/KREC analysis is a potential prognostic marker for assessing the severity and outcome in COVID-19.

Clinical and immunologic impact of short-course enzalutamide alone and with immunotherapy in non-metastatic castration sensitive prostate cancer

BACKGROUND

The standard treatment for non-metastatic castration sensitive prostate cancer (nmCSPC) is androgen deprivation therapy (ADT) or surveillance. This study evaluated the potential synergy of immunotherapy and enzalutamide (without ADT) in nmCSPC. In addition, the immunologic impact of enzalutamide was also evaluated in men with normal testosterone.

METHODS

Patients with rising prostate-specific antigen (PSA) after definitive therapy, normal testosterone and no radiographic metastasis were randomized to enzalutamide for 3 months with/without PROSTVAC for 6 months. Thereafter, patients could be retreated with another 3 month course of enzalutamide when PSA returned to baseline. Immune profiles were evaluated in these patients.

RESULTS

Thirty-eight patients were randomized with a median PSA=4.38 ng/dL and PSA doubling time=4.1 months. No difference was observed between the two groups for PSA growth kinetics, but PSA responses to enzalutamide were noteworthy regardless of PROSTVAC. The median PSA decline after short-course enzalutamide without ADT/testosterone lowering therapy was 99% in both courses. The median time to PSA recovery to baseline after each 84-day course of enzalutamide was also noteworthy because of the duration of response after enzalutamide was discontinued. After the first and second 3 month cycle of enzalutamide, PSA recovery to baseline took a median 224 (range 84-1246) and 189 days (78-400), respectively. The most common adverse events related to the enzalutamide were grade 1 fatigue (71%) and grade 1 breast pain/nipple tenderness (81%). The only grade 3 toxicity was aspartate aminotransferase (AST)/alanine aminotransferase (ALT) elevation in two patients. Enzalutamide was independently associated with immune changes, increasing natural killer cells, naïve-T cells, and decreasing myeloid-derived suppressor cells.

CONCLUSIONS

Three months of enzalutamide without ADT induced substantial PSA control beyond the treatment period and was repeatable, perhaps representing an alternative to intermittent ADT in nmCSPC. In addition, enzalutamide was associated with immune changes that could be relevant as future immune combinations are developed. TRAIL REGISTRATION NUMBER: clinicaltrials.gov (NCT01875250).

Newborn Screening through TREC, TREC/KREC System for Primary Immunodeficiency with limitation of TREC/KREC. Comprehensive Review

INTRODUCTION

Newborn screening (NBS) by quantifying T cell receptor excision circles (TRECs) and Kappa receptor excision circles in neonatal dried blood spots (DBS) enables early diagnosis of different types of primary immune deficiencies. Global newborn screening for PID, using an assay to detect T-cell receptor excision circles (TREC) in dried blood spots (DBS), is now being performed in all states in the United States. In this review, we discuss the development and outcomes of TREC, TREC/KREC combines screening, and continued challenges to implementation.

OBJECTIVE

To review the diagnostic performance of published articles for TREC and TREC/ KREC based NBS for PID and its different types.

METHODS

Different research resources were used to get an approach for the published data of TREС and KREC based NBS for PID like PubMed, Scopus, Google Scholar, Research gate EMBASE. We extracted TREC and KREC screening Publisher with years of publication, content and cut-off values, and a number of retests, repeat DBS, and referrals from the different published pilot, pilot cohort, Case series, and cohort studies.

RESULTS

We included the results of TREC, combined TREC/KREC system based NBS screening from different research articles, and divided these results between the Pilot studies, case series, and cohort. For each of these studies, different parameter data are excluded from different articles. Thirteen studies were included, re-confirming 89 known SCID cases in case series and reporting 53 new SCID cases in 3.15 million newborns. Individual TREC contents in all SCID patients were <25 TRECs/μl (except in those evaluated with the New York State assay).

CONCLUSION

TREC and KREC sensitivity for typical SCID and other types of PID was 100 %. It shows its importance and anticipating the significance of implementation in different undeveloped and developed countries in the NBS program in upcoming years. Data adapting the screening algorithm for pre-term/ill infants reduce the amount of false-positive test results.

A Multiplex, Droplet Digital PCR Assay for the Detection of T-Cell Receptor Excision Circles and Kappa-Deleting Recombination Excision Circles

BACKGROUND

T-cell receptor excision circles (TREC) and κ-deleting recombination receptor excision circles (KREC) concentrations can be used to assess and diagnose immune deficiencies, monitor thymic and bone marrow immune reconstitution, or follow responses to drug therapy. We developed an assay to quantify TREC, KREC, and a reference gene in a single reaction using droplet digital PCR (ddPCR).

METHODS

PCR was optimized for 3 targets: TREC, KREC, and ribonuclease P/MRP subunit p30 (RPP30) as the reference gene. Multiplexing was accomplished by varying the target's fluorophore and concentration. Correlation with clinical results was evaluated using 47 samples from healthy donors, 59 samples with T-cell and B-cell markers within the reference interval from the flow cytometry laboratory, 20 cord blood samples, and 34 samples submitted for exome sequencing for severe combined immunodeficiency disease (SCID).

RESULTS

The limit of the blank was 4 positive droplets, limit of detection 9 positive droplets, and limit of quantification 25 positive droplets, or 2.0 copies/μL. TREC and KREC copies/μL were as expected in the healthy donors and cord blood samples and concordant with the healthy flow cytometry results. Of the samples from the SCID Panel, 56.5% had a TREC count <20 copies/μL and 17.7% had a KREC count <20 copies/μL, suggestive of low T- and B-cell numbers, respectively.

CONCLUSIONS

Our multiplex ddPCR assay is an analytically sensitive and specific method for the absolute quantification of TREC and KREC. To the best of our knowledge, this paper is the first to describe the simultaneous quantification of TREC, KREC, and a reference gene by use of ddPCR.

Reconstitution of T Cell Subsets Following Allogeneic Hematopoietic Cell Transplantation

Allogeneic (allo) hematopoietic cell transplantation (HCT) is the only curative treatment option for patients suffering from chemotherapy-refractory or relapsed hematological malignancies. The occurrence of morbidity and mortality after allo-HCT is still high. This is partly correlated with the immunological recovery of the T cell subsets, of which the dynamics and relations to complications are still poorly understood. Detailed information on T cell subset recovery is crucial to provide tools for better prediction and modulation of adverse events. Here, we review the current knowledge regarding CD4+ and CD8+ T cells, γδ T cells, iNKT cells, Treg cells, MAIT cells and naive and memory T cell reconstitution, as well as their relations to outcome, considering different cell sources and immunosuppressive therapies. We conclude that the T cell subsets reconstitute in different ways and are associated with distinct adverse and beneficial events; however, adequate reconstitution of all the subsets is associated with better overall survival. Although the exact mechanisms involved in the reconstitution of each T cell subset and their associations with allo-HCT outcome need to be further elucidated, the data and suggestions presented here point towards the development of individualized approaches to improve their reconstitution. This includes the modulation of immunotherapeutic interventions based on more detailed immune monitoring, aiming to improve overall survival changes.

Establishing Simultaneous T Cell Receptor Excision Circles (TREC) and K-Deleting Recombination Excision Circles (KREC) Quantification Assays and Laboratory Reference Intervals in Healthy Individuals of Different Age Groups in Hong Kong

The clinical experience gathered throughout the years has raised awareness of primary immunodeficiency diseases (PIDD). T cell receptor excision circles (TREC) and kappa-deleting recombination excision circles (KREC) assays for thymic and bone marrow outputs measurement have been widely implemented in newborn screening (NBS) programs for Severe Combined Immunodeficiency. The potential applications of combined TREC and KREC assay in PIDD diagnosis and immune reconstitution monitoring in non-neonatal patients have been suggested. Given that ethnicity, gender, and age can contribute to variations in immunity, defining the reference intervals of TREC and KREC levels in the local population is crucial for setting up cut-offs for PIDD diagnosis. In this retrospective study, 479 healthy Chinese sibling donors (240 males and 239 females; age range: 1 month-74 years) from Hong Kong were tested for TREC and KREC levels using a simultaneous quantitative real-time PCR assay. Age-specific 5th-95th percentile reference intervals of TREC and KREC levels (expressed in copies per μL blood and copies per 106 cells) were established in both pediatric and adult age groups. Significant inverse correlations between age and both TREC and KREC levels were observed in the pediatric age group. A significant higher KREC level was observed in females than males after 9-12 years of age but not for TREC. Low TREC or KREC levels were detected in patients diagnosed with mild or severe PIDD. This assay with the established local reference intervals would allow accurate diagnosis of PIDD, and potentially monitoring immune reconstitution following haematopoietic stem cell transplantation or highly active anti-retroviral therapy in the future.

Human Thymic Involution and Aging in Humanized Mice

Thymic involution is an important factor leading to the aging of the immune system. Most of what we know regarding thymic aging comes from mouse models, and the nature of the thymic aging process in humans remains largely unexplored due to the lack of a model system that permits longitudinal studies of human thymic involution. In this study, we sought to explore the potential to examine human thymic involution in humanized mice, constructed by transplantation of fetal human thymus and CD34⁺ hematopoietic stem/progenitor cells into immunodeficient mice. In these humanized mice, the human thymic graft first underwent acute recoverable involution caused presumably by transplantation stress, followed by an age-related chronic form of involution. Although both the early recoverable and later age-related thymic involution were associated with a decrease in thymic epithelial cells and recent thymic emigrants, only the latter was associated with an increase in adipose tissue mass in the thymus. Furthermore, human thymic grafts showed a dramatic reduction in FOXN1 and AIRE expression by 10 weeks post-transplantation. This study indicates that human thymus retains its intrinsic mechanisms of aging and susceptibility to stress-induced involution when transplanted into immunodeficient mice, offering a potentially useful in vivo model to study human thymic involution and to test therapeutic interventions.

Lymphocyte Subgroups and KREC Numbers in Common Variable Immunodeficiency: A Single Center Study

Common variable immunodeficiency (CVID) results in defective B cell differentiation and impaired antibody production and is the most common symptomatic primary immunodeficiency. Our aim was to evaluate the correlation among B cell subgroups, κ-deleting recombination excision circle (KREC) copy numbers, and clinical and immunological data of the patients with CVID, and evaluate the patients according to classifications currently available to define the role of KREC copy numbers in the diagnosis of CVID. KREC analysis was performed using a quantitative real-time polymerase chain reaction assay, and B cell subgroups were measured by flow cytometry. The median age of the patients (n = 30) was 25 (6-69) years. Parental consanguinity ratio was 33%. The median age at diagnosis was 15 (4-59), and follow-up period was 6 (1-37) years. CD19⁺ and CD4⁺ cell counts at the time of diagnosis were low in 66.7% and 46.7% of the patients, respectively. CD19⁺ cell counts were positively correlated with KREC copy numbers in patients and healthy controls. CD19⁺ cell counts and KREC copy numbers were significantly reduced in CVID patients compared to healthy controls as expected. KRECs are quantitative markers for B cell defects. We found low CD4⁺ cell numbers, recent thymic emigrants, and lymphopenia in some of the patients at diagnosis, which reminds the heterogeneity of CVID's etiology. In this study, a positive correlation was shown between CD19⁺ cell counts and KREC copy numbers. Low KREC copy numbers indicated B cell deficiency; however, high KREC copy numbers were not sufficient to rule out CVID.

Immune reconstitution after HSCT in SCID-a cohort of conditioned and unconditioned patients

Allogeneic hematopoietic stem cell transplantation (HSCT) is the effective mean of immune restoration in severe combined immunodefiency (SCID). Usually, HSCT without cytoreductive conditioning is attempted. Nevertheless, conditioning procedures are still preferred in a subset of patients. Herein, we describe the immunological outcome in a cohort of conditioned and unconditioned patients, from diagnosis, through transplantation, to follow-up. This retrospective study was conducted on 17 patients with SCID (10 conditioned, 7 unconditioned) who later underwent HSCT. Immune reconstitution was assessed in the post-transplant year by quantification of T cell receptor excision circles (TRECs) and kappa-deleting recombination excision circles (KRECs), among additional laboratory and clinical evaluations. Unconditioned patients were diagnosed and transplanted earlier. TREC and KREC quantification showed a gradual increase in both groups, with higher levels in the conditioned group. Engraftment percentages differed drastically between groups, favoring the conditioned group. Unconditioned patients were significantly more dependent on intravenous immunoglobulins (IVIGs). One patient from each group succumbed to disease complications. Conditioning demonstrated superior laboratorial outcomes. Patients with unique characteristics (i.e., consanguinity, Bacillus Calmette-Guérin vaccination, impaired access to IVIG) may require personalized considerations. The effort to implement secondary prevention of SCID with newborn screening should continue.

Development of a Multiplex Real-Time PCR Assay for the Newborn Screening of SCID, SMA, and XLA

Numerous studies have shown evidence supporting the benefits of universal newborn screening for primary immunodeficiencies (PID) and for Spinal Muscular Atrophy (SMA). We have developed a four-plex, real-time PCR assay to screen for Severe Combined Immune Deficiencies (SCID), X-linked agammaglobulinemia (XLA), and SMA in DNA extracted from a single 3.2 mm punch of a dried blood spot (DBS). A simple, high-throughput, semi-automated DNA extraction method was developed for a Janus liquid handler that can process 384 DBS punches in four 96-well plates in just over one hour with sample tracking capability. The PCR assay identifies the absence of exon 7 in the SMN1 gene, while simultaneously evaluating the copy number of T-cell receptor excision circles (TREC) and Kappa-deleting recombination excision circles (KREC) molecules. Additionally, the amplification of a reference gene, RPP30, was included in the assay as a quality/quantity indicator of DNA isolated from the DBS. The assay performance was demonstrated on over 3000 DNA samples isolated from punches of putative normal newborn DBS. The reliability and analytical accuracy were further evaluated using DBS controls, and contrived and confirmed positive samples. The results from this study demonstrate the potential of future molecular DBS assays, and highlight how a multiplex assay could benefit newborn screening programs.

Immune recovery after in vivo T-cell depletion myeloablative conditioning hematopoietic stem cell transplantation in severe beta-thalassemia children

BACKGROUND

The clinical outcome of hematopoietic stem cell transplantation (HSCT) in those with severe beta-thalassemia (β-TM) is closely related to post-transplantation immune reconstitution (IR). However, the data on the IR in these settings are scarce.

METHODS

A prospective analysis of the clinical outcome and IR in 47 children with severe β-TM who underwent in vivo T-cell depletion myeloablative conditioning and matched sibling donor HSCT was performed. Immune reconstitution, including immune cell subset counts, as well as the generation of new T and B cells assays after HSCT, was measured.

RESULTS

In the first year after HSCT, bacterial infections and cytomegalovirus (CMV) reactivation were observed in 70.2% and 36.2% of the patients, respectively. In the same period, poor CD4⁺ T-cell recovery was observed. The B cells recovered within 6 months. Natural killer (NK) cells recovered as early as 1 month, but their function was defective. Cord blood and bone marrow (CB + BM) group had slower T-cell recovery, and higher B cells and NK cells in comparison with peripheral blood and bone marrow (PB + BM) group.

CONCLUSIONS

The high incidence of infection within 1 year after in vivo T-cell depletion myeloablative conditioning HSCT in severe β-TM was consistent with poor IR.

The ESC: The Dangerous By-Product of V(D)J Recombination

V(D)J recombination generates antigen receptor diversity by mixing and matching individual variable (V), diversity (D), and joining (J) gene segments. An obligate by-product of many of these reactions is the excised signal circle (ESC), generated by excision of the DNA from between the gene segments. Initially, the ESC was believed to be inert and formed to protect the genome from reactive broken DNA ends but more recent work suggests that the ESC poses a substantial threat to genome stability. Crucially, the recombinase re-binds to the ESC, which can result in it being re-integrated back into the genome, to cause potentially oncogenic insertion events. In addition, very recently, the ESC/recombinase complex was found to catalyze breaks at recombination signal sequences (RSSs) throughout the genome, via a “cut-and-run” mechanism. Remarkably, the ESC/recombinase complex triggers these breaks at key leukemia driver genes, implying that this reaction could be a significant cause of lymphocyte genome instability. Here, we explore these alternate pathways and discuss their relative dangers to lymphocyte genome stability.

B Cell Reconstitution and Influencing Factors After Hematopoietic Stem Cell Transplantation in Children

B cell reconstitution after hematopoietic stem cell transplantation (HSCT) is variable and influenced by different patient, donor, and treatment related factors. In this review we describe B cell reconstitution after pediatric allogeneic HST, including the kinetics of reconstitution of the different B cell subsets and the development of the B cell repertoire, and discuss the influencing factors. Observational studies show important roles for stem cell source, conditioning regimen, and graft vs. host disease in B cell reconstitution. In addition, B cell recovery can play an important role in post-transplant infections and vaccine responses to encapsulated bacteria, such as pneumococcus. A substantial number of patients experience impaired B cell function and/or dependency on Ig substitution after allogeneic HSCT. The underlying mechanisms are largely unresolved. The integrated aspects of B cell recovery after HSCT, especially BCR repertoire reconstitution, are awaiting further investigation using modern techniques in order to gain more insight into B cell reconstitution and to develop strategies to improve humoral immunity after allogeneic HSCT.

TREC and KREC Levels as a Predictors of Lymphocyte Subpopulations Measured by Flow Cytometry

Primary immunodeficiency diseases (PID) is a heterogeneous group of disorders caused by genetic defects of the immune system, which manifests clinically as recurrent infections, autoimmune diseases, or malignancies. Early detection of other PID remains a challenge, particularly in older children due to milder and less specific symptoms, a low level of clinician PID awareness and poor provision of hospital laboratories with appropriate devices. T-cell recombination excision circles (TREC) and kappa-deleting element recombination circle (KREC) in a dried blood spot and in peripheral blood using real-time polymerase chain reaction (PCR) are used as a tool for severe combined immune deficiency but not in PID. They represent an attractive and cheap target for a more extensive use in clinical practice. This study aimed to assess TREC/KREC correspondence with lymphocyte subpopulations, measured by flow cytometry and evaluate correlations between TREC/KREC, lymphocyte subpopulations and immunoglobulins. We carried out analysis of data from children assessed by clinical immunologists at Speransky Children's Hospital, Moscow, Russia with suspected immunodeficiencies between May 2013 and August 2016. Peripheral blood samples were sent for TREC/KREC, flow cytometry (CD3, CD4, CD8, and CD19), IgA, IgM, and IgG analysis. A total of 839 samples were analyzed for using TREC assay and flow cytometry and 931 KREC/flow cytometry. TREC demonstrated an AUC of 0.73 (95% CI 0.70-0.76) for CD3, 0.74 (95% CI 0.71-0.77) for CD4 and 0.67 (95% CI 0.63-0.70) for CD8, respectively, while KREC demonstrated an AUC of 0.72 (95% CI 0.69-0.76) for CD19. Moderate correlation was found between the levels of TREC and CD4 (r = 0.55, p < 0.01) and KREC with CD19 (r = 0.56, p < 0.01). In this study, promising prediction models were tested. We found that TREC and KREC are able to moderately detect abnormal levels of individual lymphocyte subpopulations. Future research should assess associations between TREC/KREC and other lymphocyte subpopulations and approach TREC/KREC use in PID diagnosis.

Naive B Cell Output in HIV-Infected and HIV-Uninfected Children

In this study, we aimed to quantify KREC (kappa-deleting recombination excision circle) levels and naive B cell output in healthy HIV-uninfected children, compared with HIV-infected South African children, before and after starting ART (antiretroviral therapy). Samples were acquired from a Child Wellness Clinic (n = 288 HIV-uninfected South African children, 2 weeks-12 years) and the Children with HIV Early Antiretroviral Therapy (CHER) trial (n = 153 HIV-infected South African children, 7 weeks-8 years). Naive B cell output was estimated using a mathematical model combining KREC levels to reflect B cell emigration into the circulation, flow cytometry measures of naive unswitched B cells to quantify total body naive B cells, and their rates of proliferation using the intracellular marker Ki67. Naive B cell output increases from birth to 1 year, followed by a decline and plateau into late childhood. HIV-infected children on or off ART had higher naive B cell outputs than their uninfected counterparts (p = .01 and p = .04). This is the first study to present reference ranges for measurements of KRECs and naive B cell output in healthy and HIV-infected children. Comparison between HIV-uninfected healthy children and HIV-infected children suggests that HIV may increase naive B cell output. Further work is required to fully understand the mechanisms involved and clinical value of measuring naive B cell output in children.

Change of apheresis device decreased the incidence of severe acute graft-versus-host disease among patients after allogeneic stem cell transplantation with sibling donors

BACKGROUND

The composition of the graft used for allogeneic hematopoietic stem cell transplantation (HSCT) is important for the treatment outcome. Different apheresis devices may yield significant differences in peripheral blood stem cell graft cellular composition. We compared stem cell grafts produced by Cobe Spectra (Cobe) and Spectra Optia (Optia) with use of the mononuclear cell (MNC) protocol, and evaluated clinical outcome parameters such as graft-versus-host disease (GvHD), transplant-related mortality (TRM), relapse, and overall survival.

STUDY DESIGN AND METHODS

During 5 years, 31 Cobe Spectra and 40 Spectra Optia grafts were analyzed for CD34, CD3, CD4, CD8, CD19, and CD56 cell content. Clinical outcome parameters were correlated and compared between the two patient groups using different apheresis devices.

RESULTS

Optia grafts contained fewer lymphocytes compared to Cobe (p < 0.001). Optia grafts had a significantly lower incidence of acute GvHD Grades II through IV (Cobe 45% vs. Optia 23%; p = 0.039) and TRM (16% vs. 2.5%; p < 0.05) but higher chronic GvHD (32% vs. 67%; p = 0.005) compared to Cobe grafts. Finally, the multivariate analysis showed a significant correlation among the different apheresis devices and both acute GvHD II through IV and severe chronic GvHD. The multivariate analysis also showed a significant correlation between the CD3+ cell dose and the incidence of severe acute GvHD.

CONCLUSION

Optia-obtained grafts yielded a lower acute GvHD Grades II-IV and TRM risk, but had no impact on relapse or overall survival in this study. Understanding and further improvement of peripheral blood stem cell (PBSC) apheresis techniques may be used in the future to personalize HSCT by, for example, fine-tuning the GvHD incidence.

Immunological effects of nilotinib prophylaxis after allogeneic stem cell transplantation in patients with advanced chronic myeloid leukemia or philadelphia chromosome-positive acute lymphoblastic leukemia

Allogeneic stem cell transplantation remains the standard treatment for resistant advanced chronic myeloid leukemia and Philadelphia chromosome–positive acute lymphoblastic leukemia. Relapse is the major cause of treatment failure in both diseases. Post-allo-SCT administration of TKIs could potentially reduce relapse rates, but concerns regarding their effect on immune reconstitution have been raised. We aimed to assess immune functions of 12 advanced CML and Ph+ ALL patients who received post-allo-SCT nilotinib. Lymphocyte subpopulations and their functional activities including T-cell response to mitogens, NK cytotoxic activity and thymic function, determined by quantification of the T cell receptor (TCR) excision circles (TREC) and TCR repertoire, were evaluated at several time points, including pre-nilotib-post-allo-SCT, and up to 365 days on nilotinib treatment. NK cells were the first to recover post allo-SCT. Concomitant to nilotinib administration, total lymphocyte counts and subpopulations gradually increased. CD8 T cells were rapidly reconstituted and continued to increase until day 180 post SCT, while CD4 T cells counts were low until 180−270 days post nilotinib treatment. T-cell response to mitogenic stimulation was not inhibited by nilotinib administration. Thymic activity, measured by TREC copies and surface membrane expression of 24 different TCR Vβ families, was evident in all patients at the end of follow-up after allo-SCT and nilotinib treatment. Finally, nilotinib did not inhibit NK cytotoxic activity. In conclusion, administration of nilotinib post allo-SCT, in attempt to reduce relapse rates or progression of Ph+ ALL and CML, did not jeopardize immune reconstitution or function following transplantation.

Assessment of TREC, KREC and telomere length in long-term survivors after allogeneic HSCT: the role of GvHD and graft source and evidence for telomere homeostasis in young recipients

Reconstitution of the adaptive immune system following allogeneic hematopoietic stem cell transplantation is crucial for beneficial outcome and is affected by several factors, such as GvHD and graft source. The impact of these factors on immune reconstitution has been thoroughly investigated during the early phase after transplantation. However, little is known about their long-term effect. Similarly, leukocyte telomere length (TL) shortening has been reported shortly after transplantation. Nevertheless, whether TL shortening continues in long-term aspect is still unsettled. Here, we assessed T-cell receptor excision circle (TREC), kappa deleting recombination excision circle (KREC) and leukocyte TL in recipients and donors several years post transplantation (median 17 years). Our analysis showed that, recipients who received bone marrow (BM) as the graft source have higher levels of both TREC and KREC. Also, chronic GvHD affected TREC levels and TL but not KREC levels. Finally, we show that recipient's TL was longer than respective donors in a group of young age recipients with high KREC levels. Our results suggest that BM can be beneficial for long-term adaptive immune recovery. We also present supporting evidence for recipient telomere homeostasis, especially in young age recipients, rather than telomere shortening.

Sequential monitoring of lymphocyte subsets and of T-and-B cell neogenesis indexes to identify time-varying immunologic profiles in relation to graft-versus-host disease and relapse after allogeneic stem cell transplantation

T and B lymphocyte subsets have been not univocally associated to Graft-versus-host disease (GVHD) and relapse of hematological malignancies after stem cell transplantation (SCT). Their sequential assessment together with B and T cell neogenesis indexes has been not thoroughly analysed in relation to these changing and interrelated immunologic/clinic events yet.

Lymphocyte subsets in peripheral blood (PB) and B and T cell neogenesis indexes were analysed together at different time points in a prospective study of 50 patients. Principal component analysis (PCA) was used as first step of multivariate analysis to address issues related to a high number of variables versus a relatively low number of patients. Multivariate analysis was completed by Fine-Gray proportional hazard regression model. PCA identified 3 clusters of variables (PC1-3), which correlated with acute GVHD: PC1 (pre-SCT: KRECs≥6608/ml, unswitched memory B <2.4%, CD4+T_CM cells <45%; HR 0.5, p = 0.001); PC2 (at aGVHD onset: CD4+>44%, CD8+T_CM cells>4%; HR 1.9, p = 0.01), and PC3 (at aGVHD onset: CD4+TEM_RA<1, total Treg<4, Treg_EM <2 cells/μl; HR 0.5, p = 0.002). Chronic GVHD was associated with one PC (Treg_EM <2 cells/μl at day+28, CD8+TEM_RA<43% at day+90, immature B cells<6 cells/μl and KRECs<11710/ml at day+180; HR 0.4, P = 0.001). Two PC correlated with relapse: PC1 (pre-SCT: CD4+ <269, CD4+T_CM <120, total Treg <18, Treg_CM <8 cells/μl; HR 4.0, p = 0.02); PC2 (pre-SCT mature CD19+ >69%, switched memory CD19+ = 0 cells and KRECs<6614/ml at +90; HR 0.1, p = 0.008). All these immunologic parameters were independent indicators of chronic GVHD and relapse, also considering the possible effect of previous steroid-therapy for acute GVHD. Specific time-varying immunologic profiles were associated to GVHD and relapse. Pre-SCT host immune-microenvironment and changes of B cell homeostasis could influence GVH- and Graft-versus-Tumor reactions. The paradoxical increase of EM Treg in PB of patients with GVHD could be explained by their compartmentalization outside lymphoid tissues, which are of critical relevance for regulation of GVH reactions.

Newborn Screening for Severe Primary Immunodeficiency Diseases in Sweden-a 2-Year Pilot TREC and KREC Screening Study

Newborn screening for severe primary immunodeficiencies (PID), characterized by T and/or B cell lymphopenia, was carried out in a pilot program in the Stockholm County, Sweden, over a 2-year period, encompassing 58,834 children. T cell receptor excision circles (TREC) and kappa-deleting recombination excision circles (KREC) were measured simultaneously using a quantitative PCR-based method on DNA extracted from dried blood spots (DBS), with beta-actin serving as a quality control for DNA quantity. Diagnostic cutoff levels enabling identification of newborns with milder and reversible T and/or B cell lymphopenia were also evaluated. Sixty-four children were recalled for follow-up due to low TREC and/or KREC levels, and three patients with immunodeficiency (Artemis-SCID, ATM, and an as yet unclassified T cell lymphopenia/hypogammaglobulinemia) were identified. Of the positive samples, 24 were associated with prematurity. Thirteen children born to mothers treated with immunosuppressive agents during pregnancy (azathioprine (n = 9), mercaptopurine (n = 1), azathioprine and tacrolimus (n = 3)) showed low KREC levels at birth, which spontaneously normalized. Twenty-nine newborns had no apparent cause identified for their abnormal results, but normalized with time. Children with trisomy 21 (n = 43) showed a lower median number of both TREC (104 vs. 174 copies/μL blood) and KREC (45 vs. 100 copies/3.2 mm blood spot), but only one, born prematurely, fell below the cutoff level. Two children diagnosed with DiGeorge syndrome were found to have low TREC levels, but these were still above the cutoff level. This is the first large-scale screening study with a simultaneous detection of both TREC and KREC, allowing identification of newborns with both T and B cell defects.

T Cell Receptor Excision Circle (TREC) Monitoring after Allogeneic Stem Cell Transplantation; a Predictive Marker for Complications and Clinical Outcome

Allogeneic hematopoietic stem cell transplantation (HSCT) is a well-established treatment modality for a variety of malignant diseases as well as for inborn errors of the metabolism or immune system. Regardless of disease origin, good clinical effects are dependent on proper immune reconstitution. T cells are responsible for both the beneficial graft-versus-leukemia (GVL) effect against malignant cells and protection against infections. The immune recovery of T cells relies initially on peripheral expansion of mature cells from the graft and later on the differentiation and maturation from donor-derived hematopoietic stem cells. The formation of new T cells occurs in the thymus and as a byproduct, T cell receptor excision circles (TRECs) are released upon rearrangement of the T cell receptor. Detection of TRECs by PCR is a reliable method for estimating the amount of newly formed T cells in the circulation and, indirectly, for estimating thymic function. Here, we discuss the role of TREC analysis in the prediction of clinical outcome after allogeneic HSCT. Due to the pivotal role of T cell reconstitution we propose that TREC analysis should be included as a key indicator in the post-HSCT follow-up.

Lymphoid and Myeloid Recovery in Rhesus Macaques Following Total Body X-Irradiation

Recovery from severe immunosuppression requires hematopoietic stem cell reconstitution and effective thymopoiesis to restore a functional immune cell repertoire. Herein, a model of immune cell reconstitution consequent to potentially lethal doses of irradiation is described, which may be valuable in evaluating potential medical countermeasures. Male rhesus macaques were total body irradiated by exposure to 6.00 Gy 250 kVp x-radiation (midline tissue dose, 0.13 Gy min), resulting in an approximate LD10/60 (n = 5/59). Animals received medical management, and hematopoietic and immune cell recovery was assessed (n ≤ 14) through 370 d post exposure. A subset of animals (n ≤ 8) was examined through 700 d. Myeloid recovery was assessed by neutrophil and platelet-related parameters. Lymphoid recovery was assessed by the absolute lymphocyte count and FACS-based phenotyping of B- and T-cell subsets. Recent thymic emigrants were identified by T cell receptor excision circle quantification. Severe neutropenia, lymphopenia, and thrombocytopenia resolved within 30 d. Total CD3+ cells μL required 60 d to reach values 60% of normal, followed by subsequent slow recovery to approximately normal by 180 d post irradiation. Recovery of CD3+4+ and CD3+8+ cell memory and naïve subsets were markedly different. Memory populations were ≥ 100% of normal by day 60, whereas naïve populations were only 57% normal at 180 d and never fully recovered to baseline post irradiation. Total (CD20+) B cells μL were within normal levels by 77 d post exposure. This animal model elucidates the variable T- and B-cell subset recovery kinetics after a potentially lethal dose of total-body irradiation that are dependent on marrow-derived stem and progenitor cell recovery, peripheral homeostatic expansion, and thymopoiesis.

Thymic and bone marrow output in individuals with 22q11.2 deletion syndrome

BACKGROUND

The 22q11.2 deletion syndrome (22q11.2DS) is a congenital multisystem anomaly characterized by typical facial features, palatal anomalies, congenital heart defects, hypocalcemia, immunodeficiency, and cognitive and neuropsychiatric symptoms. The aim of our study was to investigate T- and B-lymphocyte characteristics associated with 22q11.2DS.

METHODS

Seventy-five individuals with 22q11.2DS were tested for T and B lymphocytes by examination of T-cell receptor rearrangement excision circles (TRECs) and B-cell κ-deleting recombination excision circles (KRECs), respectively.

RESULTS

The 22q11.2DS individuals displayed low levels of TRECs, while exhibiting normal levels of KRECs. There was a significant positive correlation between TREC and KREC in the 22q11.2DS group, but not in controls. Both TREC and KREC levels showed a significant decrease with age and only TREC was low in 22q11.2DS individuals with recurrent infections. No difference in TREC levels was found between 22q11.2DS individuals who underwent heart surgery (with or without thymectomy) and those who did not.

CONCLUSION

T-cell immunodeficiency in 22q11.2DS includes low TREC levels, which may contribute to recurrent infections in individuals with this syndrome. A correlation between T- and B-cell abnormalities in 22q11.2DS was identified. The B-cell abnormalities could account for part of the immunological deficiency seen in 22q11.2DS.

Simultaneous quantification of T-cell receptor excision circles (TRECs) and K-deleting recombination excision circles (KRECs) by real-time PCR

T-cell receptor excision circles (TRECs) and K-deleting recombination excision circles (KRECs) are circularized DNA elements formed during recombination process that creates T- and B-cell receptors. Because TRECs and KRECs are unable to replicate, they are diluted after each cell division, and therefore persist in the cell. Their quantity in peripheral blood can be considered as an estimation of thymic and bone marrow output. By combining well established and commonly used TREC assay with a modified version of KREC assay, we have developed a duplex quantitative real-time PCR that allows quantification of both newly-produced T and B lymphocytes in a single assay. The number of TRECs and KRECs are obtained using a standard curve prepared by serially diluting TREC and KREC signal joints cloned in a bacterial plasmid, together with a fragment of T-cell receptor alpha constant gene that serves as reference gene. Results are reported as number of TRECs and KRECs/10(6) cells or per ml of blood. The quantification of these DNA fragments have been proven useful for monitoring immune reconstitution following bone marrow transplantation in both children and adults, for improved characterization of immune deficiencies, or for better understanding of certain immunomodulating drug activity.

Long-lasting production of new T and B cells and T-cell repertoire diversity in patients with primary immunodeficiency who had undergone stem cell transplantation: a single-centre experience

Levels of Kappa-deleting recombination excision circles (KRECs), T-cell receptor excision circles (TRECs), and T-cell repertoire diversity were evaluated in 1038 samples of 124 children with primary immunodeficiency, of whom 102 (54 with severe combined immunodeficiency and 48 with other types of immunodeficiency) underwent hematopoietic stem cell transplantation. Twenty-two not transplanted patients with primary immunodeficiency were used as controls. Only data of patients from whom at least five samples were sent to the clinical laboratory for routine monitoring of lymphocyte reconstitutions were included in the analysis. The mean time of the follow-up was 8 years. The long-lasting posttransplantation kinetics of KREC and TREC production occurred similarly in patients with severe combined immunodeficiency and with other types of immunodeficiency and, in both groups, the T-cell reconstitution was more efficient than in nontransplanted children. Although thymic output decreased in older transplanted patients, the degree of T-cell repertoire diversity, after an initial increase, remained stable during the observation period. However, the presence of graft-versus-host disease and ablative conditioning seemed to play a role in the time-related shaping of T-cell repertoire. Overall, our data suggest that long-term B- and T-cell reconstitution was equally achieved in children with severe combined immunodeficiency and with other types of primary immunodeficiency.

SCT for severe autoimmune diseases: consensus guidelines of the European Society for Blood and Marrow Transplantation for immune monitoring and biobanking

Over the past 15 years, SCT has emerged as a promising treatment option for patients with severe autoimmune diseases (ADs). Mechanistic studies recently provided the proof-of-concept that restoration of immunological tolerance can be achieved by haematopoietic SCT in chronic autoimmunity through eradication of the pathologic, immunologic memory and profound reconfiguration of the immune system, that is, immune ‘resetting'. Nevertheless, a number of areas remain unresolved and warrant further investigation to refine our understanding of the underlying mechanisms of action and to optimize clinical SCT protocols. Due to the low number of patients transplanted in each centre, it is essential to adequately collect and analyse biological samples in a larger cohort of patients under standardized conditions. The European society for blood and marrow transplantation Autoimmune Diseases and Immunobiology Working Parties have, therefore, undertaken a joint initiative to develop and implement guidelines for ‘good laboratory practice' in relation to procurement, processing, storage and analysis of biological specimens for immune reconstitution studies in AD patients before, during and after SCT. The aim of this document is to provide practical recommendations for biobanking of samples and laboratory immune monitoring in patients with ADs undergoing SCT, both for routine supportive care purposes and investigational studies.

Impact of acute and chronic graft-versus-host disease on human B-cell generation and replication

Using B-cell rearrangement excision circle measurements, we analyzed B-cell reconstitution in a cohort of 243 patients who underwent allogeneic stem cell transplantation. Acute and chronic graft-versus-host disease (aGVHD and cGVHD, respectively) transiently increased B-cell replication but decreased overall B-cell neogenesis with a clear difference in terms of kinetics. Moreover, the impact of aGVHD in the absence of cGVHD was transient, recovering at month 6 similar values as in patients who did not suffer from GVHD. Conversely, impact of cGVHD at month 12 in multivariate analysis was independent of the previous aGVHD effect on B-cell output. Finally, we showed in patients affected with cGVHD a higher B-cell division rate that correlates with an elevated BAFF/CD19(+) B-cell ratio, supporting a B-cell hyperactivation state in vivo.

Bone marrow T-cell infiltration during acute GVHD is associated with delayed B-cell recovery and function after HSCT

B-cell immune dysfunction contributes to the risk of severe infections after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Delayed B-cell regeneration is found in patients with systemic graft-versus-host disease (GVHD) and is often accompanied by bone marrow (BM) suppression. Little is known about human BM GVHD. We analyzed the reconstitution kinetics of B-cell subsets in adult leukemic patients within 6 months after allo-HSCT. B-cell deficiency already existed before transplant and was aggravated after transplant. Onset of B-cell reconstitution characterized by transitional B-cell recovery occurred either early (months 2-3) or late (from month 6 on) and correlated highly positively with reverse transcription-polymerase chain reaction quantified numbers of κ-deleting recombination excision circles (KRECs). Delayed recovery was associated with systemic acute GVHD and full-intensity conditioning therapy. Histological analysis of BM trephines revealed increased T-cell infiltration in late recovering patients, which was associated with reduced numbers of osteoblasts. Functionally, late recovering patients displayed less pneumococcal polysaccharide-specific immunoglobin M-producing B cells on ex vivo B-cell activation than early recovering patients. Our results provide evidence for acute BM GVHD in allo-HSCT patients with infiltrating donor T cells and osteoblast destruction. This is associated with delayed B-cell reconstitution and impaired antibody response. Herein, KREC appears suitable to monitor BM B-cell output after transplant.