HLA同胞全相合异基因造血干细胞移植后T细胞重建的规律

目的通过胸腺近输出功能和T细胞受体克隆谱型来研究同胞全相合骨髓移植后T细胞免疫重建。方法应用实时定量PCR的方法定量检测23例同胞全相合骨髓移植后不同时间及70例正常供者T细胞受体重排删除环（TRECs）水平;应用RT-PCR扩增其中10例患者骨髓移植后及5例正常供者外周血的T细胞受体β链可变区（TCRBV）24个家族的基因序列,通过基因扫描的方法判断TCRBV家族的克隆表达、互补决定区3（CDR3）克隆性质及计算TCRBV家族的利用率。结果70例正常人外周血单个核细胞中TRECs为（3351．1±3711．1）拷贝／10^5细胞,年龄与TRECs含量呈负相关。移植前患者TRECs定量检测结果为（307．9±433．3）拷贝／10^5细胞,明显低于正常人。移植后1～5个月患者TRECs水平均明显下降,部分患者未能检测到TRECs。移植后6个月TRECs明显升高并持续1年;移植后24个月TRECs水平有较大提高并接近移植前状态。移植后2～15个月,10例患者在7～16个BV家族有表达,且多克隆表达率为48％,单克隆及寡克隆分布在24个BV家族。结论在移植后早期TRECs为低水平并持续一段时间。移植后6个月,胸腺产生一定数量的初始T细胞并且TCRBV CDR3谱型显示BV家族的利用及多克隆的表达均在增加。     

Prediction of T-cell reconstitution by assessment of T-cell receptor excision circle before allogeneic hematopoietic stem cell transplantation in pediatric patients

The extent and rapidity with which T cells are regenerated from graft-derived precursor cells directly influences the incidence of infection and the T-cell-based graft-versus-tumor effect. Measurement of T-cell receptor excision circles (TRECs) in peripheral blood is a means of quantifying recent thymic T-cell production and has been used after transplantation in many studies to estimate thymus-dependent T-cell reconstitution. We hypothesized that the quality of thymic function before transplantation affects thymus-dependent T-cell reconstitution after transplantation. We used real-time polymerase chain reaction (PCR) to quantify signal-joint TRECs (sjTRECs) before and after transplantation. T-cell reconstitution was evaluated by T-cell receptor beta (TCRbeta) CDR3 size spectratyping. We tested 77 healthy sibling donors and 244 samples from 26 pediatric recipients of allogeneic hematopoietic stem cell transplantation (AHSCT). Blood from the healthy donors contained 1200 to 155,000 sjTREC copies/mL blood. Patients who had greater than 1200 copies/mL blood before transplantation showed early recovery of sjTREC numbers and TCRbeta repertoire diversity. In contrast, patients who had fewer than 1200 copies/mL blood before transplantation demonstrated significantly slower restoration of thymus-dependent T cells. We conclude that the rate of reconstitution of thymus-dependent T cells is dependent on the competence of thymic function in the recipients before transplantation. Therefore, pretransplantation measurement of sjTREC may provide an important tool for predicting thymus-dependent T-cell reconstitution after transplantation.     

Persistence of clonal T-cell expansions following high-dose chemotherapy and autologous peripheral blood progenitor cell rescue

Analysing the regeneration of T lymphocytes after high-dose chemotherapy with autologous peripheral blood progenitor cell rescue (PBPCR) may help elucidate the mechanisms of immune recovery. The T-cell receptor variable beta chain (TCRBV) repertoire of adult patients undergoing high-dose chemotherapy was analysed by flow cytometry, before and after treatment. Four patients were found to have a stable expansion present (TCRBV3, 17, 21 and 22) ranging from 8% to 42% of the CD4(+) or CD8(+) repertoire. We demonstrated that, in these patients, following high-dose chemotherapy and autologous stem cell transplantation, the clonal expansions reappeared in peripheral blood and returned to pretransplant levels. Three expansions (CD3(+)CD8(+)TCRBV3(+), CD3(+)CD4(+)TCRBV21(+) and CD3(+)CD8(+)TCRBV22(+)) were further defined by sequence analysis of the complementarity-determining region (CDR)3 portion within the TCR rearrangements. These were shown to be predominantly clonal, with the same sequences being identified in peripheral blood before and after PBPCR, providing evidence that the overwhelming majority of T cells in these expansions arise from mature lymphocytes. This study demonstrated that patients undergoing autologous PBPCR for high-dose chemotherapy regenerate clonal expansions, consistent with pretreatment levels. They also regenerate T-cell repertoires with each TCRBV family represented to a similar level as that prior to high-dose chemotherapy.     

Optimized clonotypic analysis of T-cell receptor repertoire in immune reconstitution

OBJECTIVE: In recent years, T-cell receptor (TCR) sequencing analysis has proven an effective technique for the identification of T-cell populations of interest in cancer and autoimmunity, as well as for the characterization of peripheral immune repertoire reconstitution after hematopoietic stem cell transplantation (HSCT). However, despite its increased utilization, to our knowledge no group has investigated the minimum number of sequences necessary to accurately and efficiently describe the composition of TCR repertoire. The primary aim of this study was to optimize a procedure for clonotypic analysis of the TCR repertoire in patients undergoing autologous HSCT. MATERIALS AND METHODS: TCR beta-chain diversity was analyzed by DNA sequencing and CDR3 spectratyping CD8(+) T cells isolated from three patients with multiple sclerosis undergoing autologous HSCT. Samples were collected at baseline and 1 or 2 years post-HSCT. RESULTS: Using DNA cloning and high throughput sequencing, we analyzed over 1500 in-frame TCR sequences, allowing us to evaluate how our measures of TCR repertoire diversity change with increasing numbers of sequences included in the analysis. Our findings show that by analyzing 75 to 100 in-frame sequences, we are able to estimate TCR diversity within 5.0% to 7.4% of the values obtained at endpoint analysis (213-312 sequences per sample). CONCLUSIONS: This study confirms the use of TCR sequencing as an effective technique for the characterization of immune renewal after autologous HSCT. In addition, we demonstrate for the first time convincing evidence to support the use of moderate sample sizes to accurately and efficiently evaluate TCR repertoire diversity.     

Quantitation of T-cell neogenesis in vivo after allogeneic bone marrow transplantation in adults

Following myeloablative therapy, it is unknown to what extent age-dependent thymic involution limits the generation of new T cells with a diverse repertoire. Normal T-cell receptor gene rearrangement in T-cell progenitors results in the generation of T-cell receptor rearrangement excision circles (TRECs). In this study, a quantitative assay for TRECs was used to measure T-cell neogenesis in adult patients with leukemia who received myeloablative therapy followed by transplantation of allogeneic hematopoietic stem cells. Although phenotypically mature T cells had recovered by 1 to 2 months after bone marrow transplantation (BMT), TREC levels remained low for 3 months after BMT. T-cell neogenesis became evident by 6 months, and normal levels of adult thymic function were restored at 6 to 12 months after BMT. Subsequent leukemia relapse in some patients was associated with reduced TREC levels, but infusion of mature donor CD4(+) T cells resulted in rapid restoration of thymic function. These studies demonstrate that T-cell neogenesis contributes to immune reconstitution in adult patients and suggest that thymic function can be manipulated in vivo. (Blood. 2001;98:1116-1121)     

T-Cell immune reconstitution in pediatric leukemia patients after allogeneic bone marrow transplantation with T-cell-depleted or unmanipulated grafts: evaluation of overall and antigen-specific T-cell repertoires

To evaluate the role of T-cell selection in the thymus and/or periphery in T-cell immune reconstitution after allogeneic bone marrow transplantation (allo-BMT), we have analyzed the overall and antigen-specific T-cell repertoires in pediatric allo-BMT recipients treated for leukemia. We observed a lack of overall T-cell receptor (TCR) diversity in the repopulating T cells at 3 months after allo-BMT, as was deduced from complementarity determining region 3 (CDR3) size distribution patterns displaying reduced complexity. This was noted particularly in recipients of a T-cell-depleted (TCD) graft and, to a lesser extent, also in recipients of unmanipulated grafts. At 1 year after allo-BMT, normalization was observed of TCR CDR3 size complexity in almost all recipients. Analysis of the antigen-specific T-cell repertoire at 1 year after BMT showed that the T cells responding to tetanus toxoid (TT) differed in TCR gene segment usage and in amino acid composition of the CDR3 region when comparing the recipient with the donor. Moreover, the TT-specific TCR repertoire was found to be stable within a given allo-BMT recipient, because TT-specific T cells with completely identical TCRs were found at 3 consecutive years after transplantation. These observations suggest an important role for T-cell selection processes in the complete restoration of the T-cell immune repertoire in children after allo-BMT.     

Efficient identification of T-cell clones associated with graft-versus-host disease in target tissue allows for subsequent detection in peripheral blood

Graft-versus-host disease (GVHD) causes severe morbidity and mortality in allogeneic haematopoietic stem cell transplantation (HSCT) because of destruction of recipient tissues by donor alloreactive T cells. We hypothesized that GVHD-specific T-cell clones are expanded within affected tissue of HSCT patients and can also be detected in blood at the time of active disease. A multiplex polymerase chain reaction (PCR) was used to amplify T-cell receptor (TCR) variable beta (VB) chain rearrangements in skin biopsies from eight allogeneic HSCT patients. Molecular analysis of the complementarity-determining region 3 (CDR3) of amplified products defined expanded, potentially disease-associated 'clonotypes' and enabled the design of clonotype-specific PCR assays. We detected immunodominant clones in seven of eight GVHD-positive skin biopsies. In serial skin biopsies from the same patient, the identical clone was found in each biopsy. In a patient who underwent two successive HSCTs from different donors, distinct clones were identified for each engraftment. Using clonotypic PCR assays, individual tissue-derived clones could be identified in peripheral blood samples obtained during active GVHD. We hypothesize that clonotypic sequences derived from target tissue can serve as markers for GVHD and may have utility in diagnosis and monitoring response to therapy, as well as enable future therapies targeted against pathogenic clones.     

Reconstitution of T-cell receptor repertoire diversity following T-cell depleted allogeneic bone marrow transplantation is related to hematopoietic chimerism

CDR3 spectratyping was used to analyze the complexity of the T-cell repertoire and to define the mechanisms and kinetics of the reconstitution of T-cell immunity after allogeneic bone marrow transplantation (BMT). This method, which is based on polymerase chain reaction amplification of all CDR3 regions using the T-cell receptor (TCR) Vbeta genes, was used to examine serial samples of peripheral blood lymphocytes from 11 adult patients with chronic myelogenous leukemia (CML) who underwent T-cell-depleted allogeneic BMT. In contrast to 10 normal donors who display highly diverse and polyclonal spectratypes, patient samples before and early after BMT revealed markedly skewed repertoires, consisting of absent, monoclonal, or oligoclonal profiles for the majority of Vbeta subfamilies. To quantify changes in TCR repertoire over time, we established an 8-point scoring system for each Vbeta subfamily. The mean complexity score for patient samples before transplant (130.8) was significantly lower than that for normal donors (183; P = 0. 0007). TCR repertoire complexity was abnormal in all patients at 3 months after BMT (mean score = 87). Normalization of repertoire began in 4 patients at 6 months after BMT, but the majority of patients continued to display abnormal repertoires for up to 3 years after BMT. To determine whether the reconstituted T-cell repertoire was derived from the donor or recipient, unique microsatellite loci were examined to establish chimeric status. At 3 months after BMT, 7 patients demonstrated mixed chimerism; 4 had complete donor hematopoiesis (CDH). CDH strongly correlated with likelihood of restoration of T-cell repertoire complexity (P = 0.003). In contrast, patients who demonstrated persistence of recipient hematopoiesis failed to reconstitute a diverse TCR repertoire. These findings suggest that the reconstitution of a normal T-cell repertoire from T-cell progenitors in adults is influenced by interactions between recipient and donor hematopoietic cells. (Blood. 2000;95: 352-359)     

Direct evidence for new T-cell generation by patients after either T-cell-depleted or unmodified allogeneic hematopoietic stem cell transplantations

Successful allogeneic hematopoietic stem cell transplantation (HSCT) requires reconstitution of normal T-cell immunity. Recipient thymic activity, biologic features of the allograft, and preparative regimens all contribute to immune reconstitution. We evaluated circulating T-cell phenotypes and T-cell receptor rearrangement excision circles (TRECs) in 331 blood samples from 158 patients who had undergone allogeneic HSCTs. All patients had received myeloablative conditioning regimens and were full donor chimeras in remission. Younger patients exhibited more rapid recovery and higher TRECs (P =.02). Recipients of T-cell-depleted allografts initially had lower TRECs than unmodified allograft recipients (P <.01), but the difference abated beyond 9 months. TREC level disparities did not achieve significance among adults with respect to type of allograft. Measurable, albeit low, TREC values correlated strongly with severe opportunistic infections (P <.01). This finding was most notable during the first 6 months after transplantation, when patients are at greatest risk but before cytofluorography can detect circulating CD45RA(+) T cells. Low TRECs also correlated strongly with extensive chronic graft-versus-host disease (P <.01). Recipients of all ages of either unmodified or T-cell-depleted allografts therefore actively generate new T cells. This generation is most notable among adult recipients of T-cell-depleted allografts, most of whom had also received antithymocyte globulin for rejection prophylaxis. Low TREC values are significantly associated with morbidity and mortality after transplantation. T-cell neogenesis, appropriate to age but delayed in adult recipients of T-cell-depleted allografts, justifies interventions to hasten this process and to stimulate desirable cellular immune responses.     

Initiation of antiretroviral therapy during primary HIV-1 infection induces rapid stabilization of the T-cell receptor beta chain repertoire and reduces the level of T-cell oligoclonality

Major T-cell receptor beta chain variable region (TCRBV) repertoire perturbations are temporally associated with the down-regulation of viremia during primary human immunodeficiency virus (HIV) infection and with oligoclonal expansion and clonal exhaustion of HIV-specific cytotoxic T lymphocytes (CTLs). To determine whether initiation of antiretroviral therapy (ART) or highly active antiretroviral therapy (HAART) during primary infection influences the dynamics of T-cell-mediated immune responses, the TCRBV repertoire was analyzed by semiquantitative polymerase chain reaction in serial blood samples obtained from 11 untreated and 11 ART-treated patients. Repertoire variations were evaluated longitudinally. Stabilization of the TCRBV repertoire was more consistently observed in treated as compared with untreated patients. Furthermore, the extent and the rapidity of stabilization were significantly different in treated versus untreated patients. TCRBV repertoire stabilization was positively correlated with the slope of HIV viremia in the treated group, suggesting an association between repertoire stabilization and virologic response to treatment. To test whether stabilization was associated with variations in the clonal complexity of T-cell populations, T-cell receptor (TCR) heteroduplex mobility shift assays (HMAs) were performed on sequential samples from 4 HAART-treated subjects. Densitometric analysis of HMA profiles showed a reduction in the number of TCR clonotypes in most TCRBV families and a significant decrease in the total number of clonotypes following 7 months of HAART. Furthermore, a biphasic decline in HIV-specific but not heterologous CTL clones was observed. This indicates that ART leads to a global reduction of CD8(+) T-cell oligoclonality and significantly modulates the mobilization of HIV-specific CTL during primary infection. (Blood. 2000;95:1743-1751)     

T lymphocytes of recipient origin may contribute to the recovery of specific immune response toward viruses and fungi in children undergoing cord blood transplantation

Patients undergoing allogeneic cord blood transplantation (CBT) benefit from a low risk of graft-versus-host disease (GVHD), but there are still concerns that they be able to recover an effective immune capacity early after transplantation. We investigated the ability to develop in vitro T-lymphocyte-mediated immune response toward human cytomegalovirus and Candida albicans antigens, early and late after transplantation, in children given cord blood transplants from either an HLA-identical sibling or an unrelated donor. Proliferative capacity and frequency of antigen-specific T cells were evaluated; antigen-specific CD4(+) T-cell clones were also generated and characterized for T-cell receptor repertoire diversity, cytokine phenotype, and their origin (either from donor or patient). We found that the majority of recipients can develop a specific response to viral or fungal antigens already early after transplantation. Antigen-specific T-cell clones of both donor and recipient origin contributed to the reconstitution of immune response. Antigen-specific T lymphocytes of recipient origin were detected in patients receiving a transplant from a relative, after a chemotherapy-based conditioning regimen, and who did not have GVHD. Our results document, at a clonal level, that after CBT recovery of either polyclonal or pauciclonal T-cell response toward widespread pathogens is prompt, with some patients benefiting from a contribution of recipient-derived cells.     

Rapid immune reconstitution after a reduced-intensity conditioning regimen and a CD3-depleted haploidentical stem cell graft for paediatric refractory haematological malignancies

The main obstacles to successful haploidentical haematopoietic stem cell transplantation from a mismatched family member donor are delayed immune reconstitution, vulnerability to infections and severe graft-versus-host disease (GvHD). We designed a reduced-intensity conditioning regimen that excluded total body irradiation and anti-thymocyte globulin in order to expedite immune reconstitution after a CD3-depleted haploidentical stem cell transplant. This protocol was used to treat 22 paediatric patients with refractory haematological malignancies. After transplantation, 91% of the patients achieved full donor chimaerism. They also showed rapid recovery of CD3(+) T-cells, T-cell receptor (TCR) excision circle counts, TCRbeta repertoire diversity and natural killer (NK)-cells during the first 4 months post-transplantation, compared with those results from a group of patients treated with a myeloablative conditioning regimen. The incidence and extent of viremia were limited and no lethal infection was seen. Only 9% of patients had grade 3 acute GvHD, while 27% patients had grade 1 and another 27% had grade 2 acute GvHD. This well-tolerated regimen appears to accelerate immune recovery and shorten the duration of early post-transplant immunodeficiency, thereby reducing susceptibility to viral infections. Rapid T-cell reconstitution, retention of NK-cells in the graft and induction of low grade GvHD may also enhance the potential anti-cancer immune effect.     

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

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.Hematopoietic stem cell transplantation (HSCT) has become common clinical practice in the treatment of leukemia, lymphoma, and certain inherited immune and metabolic disorders. After transplantation there is an immediate need for de novo production of granulocytes, erythrocytes, and platelets, referred to as “hematopoietic reconstitution,” later followed by recovery of lymphocyte numbers, termed “immune reconstitution.” Although often successful, HSCT is associated with a number of complications arising from poor immune reconstitution, which presents one of the most important causes of morbidity after HSCT (1, 2). Poor myeloid reconstitution is directly linked to low numbers of HSCs in the transplant, but the reasons for poor immune and, in particular, T-lymphocyte reconstitution are much less clear.A study on the application of antithymocyte globulin in cord blood transplantation showed that antithymocyte globulin administration in pretransplantation conditioning results in decreased T-cell reconstitution and survival (3), indicating the need for a better understanding of de novo T-cell development after HSCT. As T cells develop in the thymus, in contrast to all other blood lineages that develop in the bone marrow (BM), HSC-derived progenitors need to seed the thymus. Earlier work in mice has indicated that relatively few progenitors seed the thymus (4, 5), yet their numbers and the subsequent fate of the progeny derived from an HSC clone has remained elusive. The nature of the thymus-seeding cell has been subject of much debate, certainly in humans. CD34⁺CD38⁻CD7⁺ cells (6, 7), CD34⁺CD38⁻CD10⁻CD62L⁺ cells (8), and others have been proposed as thymus-seeding cells in the human situation. In contrast to mice, the earliest human thymocytes show a much broader lineage developmental potential, including low levels of erythroid and megakaryocytic potential (9), and may therefore be much closer related to HSCs or the proposed myeloid lymphoid precursors.In this study, we aimed to address the functional relationship between HSCs and developing T cells by using DNA barcoding. This method allows marking of each stem cell and its progeny by a unique, neutral DNA sequence that can be retrieved by next-generation sequencing. Here we used replication-deficient lentiviruses to transfer a DNA barcode and the GFP into phenotypically defined human HSCs. These marked HSCs were transplanted, using an optimized protocol (10), into NOD/SCID/Il-2Rγ^−/− (NSG) mice (11), which allowed us to determine the dynamics of clonal reconstitution in the thymus in great detail. We used umbilical cord blood (UCB) as source of human stem cells, because UCB is frequently used as a readily available HSC source with less stringent HLA (human leukocyte antigen)-matching requirements (12). However, T-cell immune reconstitution, a general problem in allogeneic HSCT, is more problematic in UCB. Therefore, UCB provides an appropriate HSC source to address questions of lineage tracing and clonality in the blood and immune system. As we demonstrate here, only a fraction of HSC clones in UCB contributes to the T-cell pool, yet a fully diverse T-cell receptor (TCR) repertoire can be generated in the thymus.     

T-cell receptor repertoire and function in umbilical cord blood lymphocytes from newborns of type 1 diabetic mothers

Abstract Recent observations show that the development of the human fetal immune system is susceptible to conditions of the maternal immune system and vice versa. To investigate the impact of type 1 diabetes mellitus in pregnant women on the maturation of the immune system of their newborn infants, the umbilical cord blood (UCB) T-cell repertoire at birth was analysed for clonal or oligoclonal expansions and TCRBV gene usage. Quantitative PCR using TCRBV family-specific probes and the spectratyping method were used. The extent of oligoclonal expansions observed in cord blood was markedly lower than in peripheral blood of the diabetic mothers and healthy adults. Functional analysis revealed that UCB T cells from newborns of both type 1 diabetic and gestational diabetic mothers are mature and can be readily stimulated by superantigens and phytohemagglutinin in vitro. No significant differences of the clonal contingent and the TCRBV usage were found in newborns of type 1 diabetic mothers when compared to newborns of gestational diabetic mothers, independent from the presence or absence of islet autoantigens. Our findings indicate that the immune system of type 1 diabetic mothers has no major effects on the TCR repertoire of the newborn infants. In that respect, no evidence was found for superantigen-activated T cells, nor was chronic hyperglycaemia per se found to alter either T-cell repertoire or functional activity.     

Early determinants of long-term T-cell reconstitution after hematopoietic stem cell transplantation for severe combined immunodeficiency

The immune system of patients with severe combined immunodeficiency (SCID) reconstitutes to a large extent during the first years after hematopoietic stem cell transplantation (HSCT). It was suggested, however, that accelerated loss of thymus output may cause impaired immune function at the long term. To address this issue, we studied patients with SCID who underwent allogeneic HSCT 5 to 32 years earlier and identified early determinants of long-term T-cell reconstitution. A variety of immune parameters were analyzed both early (1-4 years) and late (5-32 years) after HSCT. Late after HSCT, a clear distinction could be made between a group of 8 patients with impaired T-cell reconstitution and 11 patients with good immune reconstitution. Importantly, in patients with decreased long-term T-cell reconstitution, T-cell recovery was already poor early after HSCT, demonstrating that long-term immune failure was not caused by accelerated loss of thymus output or long-term graft failure, but resulted from poor early grafting. The number of T-cell receptor excision circles (TRECs) early after HSCT was most predictive for long-term T-cell reconstitution. Frequent monitoring of T-cell immunity and TREC numbers early after HSCT may thus serve to timely identify patients who will fail to reconstitute properly and who may need additional treatment.      

Incomplete T-cell immune reconstitution in two major histocompatibility complex class II-deficiency/bare lymphocyte syndrome patients after HLA-identical sibling bone marrow transplantation.

To study the effects of major histocompatibility complex (MHC) class II expression on T-cell development, we have investigated T-cell immune reconstitution in two MHC class II-deficiency patients after allogeneic bone marrow transplantation (allo-BMT). Our study showed that the induction of MHC class II antigen expression on BM graft-derived T cells in these allo-BMT recipients was hampered upon T-cell activation. This reduction was most striking in the CD8(+) T-cell subset. Furthermore, the peripheral T-cell receptor (TCR) repertoire in these graft-derived MHC class II-expressing CD4(+) and in the CD8(+) T-cell fractions was found to be restricted on the basis of TCR complementarity determining region 3 (CDR3) size profiles. Interestingly, the T-cell immune response to tetanus toxoid (TT) was found to be comparable to that of the donor. However, when comparing recipient-derived TT-specific T cells with donor-derived T cells, differences were observed in TCR gene segment usage and in the hydropathicity index of the CDR3 regions. Together, these results reveal the impact of an environment lacking endogenous MHC class II on the development of the T-cell immune repertoire after allo-BMT.     

T-cell receptor excision circle and T-cell dynamics after allogeneic stem cell transplantation are related to clinical events

It is generally believed that homeostatic responses regulate T-cell recovery after peripheral stem cell transplantation (PSCT). We studied in detail immune recovery in relation to T-cell depletion and clinical events in a group of adult patients who underwent PSCT because of hematologic malignancies. Initially, significantly increased proportions of dividing naive, memory, and effector CD4(+) and CD8(+) T cells were found that readily declined, despite still very low numbers of CD4(+) and CD8(+) T cells. After PSCT, increased T-cell division rates reflected immune activation because they were associated with episodes of infectious disease and graft-versus-host disease (GVHD). T-cell receptor excision circles (TRECs) were measured to monitor thymic output of naive T cells. Mean TREC content normalized rapidly after PSCT, long before naive T-cell numbers had significantly recovered. This is compatible with the continuous thymic production of TREC(+) naive T cells and does not reflect homeostatic increases of thymic output. TREC content was decreased in patients with GVHD and infectious complications, which may be explained by the dilution of TRECs resulting from increased proliferation. Combining TREC and Ki67 analysis with repopulation kinetics led to the novel insight that recovery of TREC content and increased T-cell division during immune reconstitution after transplantation are related to clinical events rather than to homeostatic adaptation to T-cell depletion. (Blood. 2002;99:3449-3453)     

Long-term T-cell reconstitution after hematopoietic stem-cell transplantation in primary T-cell-immunodeficient patients is associated with myeloid chimerism and possibly the primary disease phenotype

We studied T-cell reconstitution in 31 primary T-cell-immunodeficient patients who had undergone hematopoietic stem-cell transplantation (HSCT) over 10 years previously. In 19 patients, there was no evidence of myeloid chimerism because little or no myeloablation had been performed. Given this context, we sought factors associated with good long-term T-cell reconstitution. We found that all patients having undergone full myeloablation had donor myeloid cells and persistent thymopoiesis, as evidenced by the presence of naive T cells carrying T-cell receptor excision circles (TRECs). In 9 patients with host myeloid chimerism, sustained thymic output was also observed and appeared to be associated with gammac deficiency. It is therefore possible that the complete absence of thymic progenitors characterizing this condition created a more favorable environment for thymic seeding by a population of early progenitor cells with the potential for self-renewal, thus enabling long-term (> 10 years) T-cell production.     

T-cell receptor excision circles: a novel prognostic parameter for the outcome of transplantation in multiple myeloma patients

This study investigated whether T-cell receptor excision circles (TRECs) are a prognostic marker for the outcome of myeloma patients undergoing a tandem autologous peripheral blood stem cell transplantation (PBSCT). Twenty-five patients were enrolled. Samples were obtained at study enrollment, after conventional therapy, between first and second transplantation and 3, 6, 12 and 24 months after the second PBSCT. TRECs were quantified using real-time polymerase chain reaction. A high variation in TREC levels was found at diagnosis (median TREC level 136/10(5) peripheral blood mononuclear cells (PBMCs); range 1-1729), suggesting individual differences in thymic output of naive T cells. Patients with more than 136 TRECs/10(5) P BMCs at diagnosis had a statistically significant better overall survival (P=0.05) and event-free survival (P=0.045), whereas low TREC levels correlated with a higher incidence of infectious complications. Median TREC values were lowest after the first PBSCT (52/10(5) PBMCs) and reached the baseline 12 months after the second transplantation. Patients with high TREC levels after the second PBSCT had a significantly higher probability of being in complete or partial remission 30 months after the second PBSCT. TREC levels were not correlated with beta2-microglobulin and C-reactive protein levels at diagnosis. These data suggest that TRECs could be a relevant prognostic factor for patients who receive high-dose chemotherapy and autologous PBSCT.