Exogenous IL-7 increases recent thymic emigrants in peripheral lymphoid tissue without enhanced thymic function

Interleukin 7 (IL-7) is critical in maintaining thymic-dependent and thymic-independent pathways of T-cell homeostasis. T-cell receptor (TCR) rearrangement excision circles (TRECs) have been used as markers for recent thymic emigrants (RTEs) in assessing human thymic function. To study the thymic and peripheral effects of IL-7 on RTEs, we measured TREC content and peripheral naive T-cell subsets and turnover in IL-7-treated mice. Short-term administration of IL-7 into thymus-intact mice resulted in increased total TREC numbers, consistent with RTE accumulation. Decreases in TREC frequency were attributable to dilution secondary to increased cell turnover. Significantly, IL-7 administration into thymectomized mice resulted in patterns of decreased TREC frequency and increased total TREC number similar to those in IL-7-treated thymus-intact mice. Distinct patterns of naive cell and RTE distribution among peripheral immune organs and altered expression of CD11a were observed following IL-7 treatment in thymus-intact and thymectomized mice. These results demonstrate (1) that total TREC number and not TREC frequency accurately reflects quantitative changes in RTEs; (2) that short-term IL-7 administration results in preferential accumulations of RTEs among peripheral immune organs, accounting for the increase in TRECs in the total peripheral lymphoid pool; and (3) no evidence for regulation of thymic function by short-term IL-7 administration.     

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 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)     

T-cell repopulation and thymic volume in HIV-1-infected adult patients after highly active antiretroviral therapy

The origin of T cells after highly active antiretroviral therapy (HAART) in patients infected with human immunodeficiency virus 1 (HIV-1) is now under discussion. The possibility of renewed lymphopoiesis in aged thymuses is still controversial. In this work we combine the analysis of na?ve T cells, T-cell receptor excision circles (TRECs), and computed tomography scanning of thymic tissue to further assess whether the thymus is involved in immune reconstitution. Fifteen antiretroviral-na?ve HIV-1-infected patients were evaluated during 48 weeks of HAART. At baseline, significant correlation was present among age and both thymic volume and TRECs, and between na?ve T cells and TRECs. After starting HAART, there was a significant increase at week 12 in na?ve CD4(+) and CD8(+) T cells, TRECs, and thymic volume. The initial net increases in na?ve T cells and TREC counts were significantly correlated. Changes in thymic volume and TRECs were also indirectly related; splitting the population into 2 groups of high and low baseline TREC levels, only the group with low TREC levels had significant increases in both TRECs and thymic volume. Thus, the increase in thymic volume might be functional, in response to depleted TREC levels. Taken together, our data strongly suggest a thymic role in immune reconstitution, at least in patients with depleted baseline TREC levels. (Blood. 2002;99:3702-3706)     

Long-term restoration of the human T-cell compartment after thymectomy during infancy: a role for thymic regeneration?

Thymectomy during early childhood is generally thought to have serious consequences for the establishment of the T-cell compartment. In the present study, we investigated the composition of the T-cell pool in the first 3 decades after thymectomy during infancy due to cardiac surgery. In the first 5 years after thymectomy, naive and total CD4(+) and CD8(+) T-cell numbers in the blood and T-cell receptor excision circle (TREC) levels in CD4(+) T cells were significantly lower than in healthy age-matched controls. In the first years after thymectomy, plasma IL-7 levels were significantly elevated and peripheral T-cell proliferation levels were increased by ～ 2-fold. From 5 years after thymectomy onward, naive CD4(+) and CD8(+) T-cell counts and TRECs were within the normal range. Because TREC levels are expected to decline continuously in the absence of thymic output, we investigated whether normalization of the naive T-cell pool could be due to regeneration of thymic tissue. In the majority of individuals who had been thymectomized during infancy, thymic tissue could indeed be identified on magnetic resonance imaging scans. Whereas thymectomy has severe effects on the establishment of the naive T-cell compartment during early childhood, our data suggest that functional regrowth of thymic tissue can limit its effects in subsequent years.     

Evidence for adequate thymic function but impaired naive T-cell survival following allogeneic hematopoietic stem cell transplantation in the absence of chronic graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (AHSCT) leads to a prolonged state of immunodeficiency characterized by low peripheral naive T-cell counts. To identify the mechanisms leading to this defect we quantitatively and qualitatively analyzed thymic function through quantification of T-cell receptor excision circle (TREC) frequencies (both the signal-joint TREC [sjTREC] and 6 different DbetaJbeta TRECs, by-products of T-cell receptor [TCR] alpha and beta gene rearrangement, respectively), in conjunction with immunophenotype and spectratype analyses in a cohort of patients sampled from 1 to 10 years following AHSCT. In this cohort, reduced thymic function was associated only with ongoing clinical chronic graft-versus-host disease (cGVHD). Nonetheless, the diversity of thymic production remained unchanged irrespective of the patient's cGVHD status. Interestingly, increased homeostatic proliferation was found in the naive T-cell compartment of cGVHD- patients who underwent transplantation. However, reduced expression of both the interleukin-7 receptor alpha (IL-7Ralpha) (CD127) chain and the antiapoptotic protein Bcl-2 was observed. Taken together, these data indicate that the inability to reconstitute the naive T-cell compartment for several years after AHSCT, in the absence of cGVHD, is a consequence of impaired naive T-cell survival rather than thymic dysfunction.     

Distinct homeostatic requirements of CD4+ and CD4- subsets of Valpha24-invariant natural killer T cells in humans

CD1d-restricted Valpha24-invariant natural killer T cells (iNKTs) are important in immunoregulation. CD4(+) and CD4(-) iNKTs develop with similar frequencies in murine thymus and depend on interleukin-15 (IL-15) in periphery. However, homeostatic requirements of iNKTs have not been analyzed in humans. We evaluated thymic production, peripheral dynamics, and functional maturation of human iNKTs. CD4(+) subset comprises 90% of iNKTs in mature thymocytes and cord blood (CB) but only 40% in adult blood. Using T-cell receptor excision circle (TREC) analysis, we directly measured in vivo replicative history of CD4(+) and CD4(-) iNKT cells. Compared to CD4(+), CD4(-) iNKTs contain fewer TRECs, express higher levels of IL-2Rbeta, and proliferate with higher rate in response to IL-15. In contrast, CD4(+) cells express higher levels of IL-7Ralpha and better respond to IL-7. Neither thymic nor CB iNKTs are able to produce cytokines unless they are induced to proliferate. Therefore, unlike in the mouse, human CD4(+) iNKTs are mainly supported by thymic output and limited peripheral expansion, whereas CD4(-) cells undergo extensive peripheral expansion, and both subsets develop their functions in periphery. These findings reveal important differences in homeostatic requirements and functional maturation between murine and human iNKTs that are to be considered for clinical purposes.     

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.     

Stromal cell-derived factor 1/CXCR4 signaling is critical for early human T-cell development.

The present study investigated the potential role of stromal cell-derived factor 1 (SDF-1) in human intrathymic T-cell differentiation. Results show that SDF-1 is produced by human thymic epithelial cells from the subcapsular and medullary areas, and its receptor, CXCR4, is up-regulated on CD34(+) precursor cells committed to the T-cell lineage. Chimeric human-mouse fetal thymus organ culture (FTOC) seeded with purified CD34(+) thymic progenitors and treated with neutralizing antibodies against SDF-1 or CXCR4 showed a significant reduction of the number of human thymocytes and an arrested thymocyte differentiation in the transition between CD34(+) precursor cells and CD4(+) immature thymocytes. SDF-1-treated FTOC showed an increase of human thymocyte numbers, mainly affecting the most immature subpopulations. Moreover, these results suggest that CXCR4/SDF-1 signaling is not critical for the CD34(+) cell precursor recruitment to the thymus. On the other hand, SDF-1 significantly increased the viability of CD34(+) T-cell precursors modulating the expression of BCL-2 and BAX genes, and stimulated the proliferation of CD34(+) thymic precursor cells, particularly in synergy with interleukin 7 (IL-7), but not with other cytokines, such as stem cell factor or flt3-ligand. Accordingly, only IL-7 was able to up-regulate CXCR4 expression on CD34(+) thymic progenitors. In addition, deprivation of SDF-1 partially inhibited human thymocyte expansion induced by IL-7 in human-mouse FTOC. This study indicates that SDF-1/CXCR4 signaling is required for the survival, expansion, and subsequent differentiation of human early thymocytes and identifies a new mechanism by which IL-7 mediates its effects on human thymopoiesis.     

IL-2 therapy and thymic production of naive CD4 T cells in HIV-infected patients with severe CD4 lymphopenia

OBJECTIVES: IL-2 therapy increases memory and naive CD4 T cells in HIV-infected patients, but its effect on thymopoiesis is unknown. To investigate this effect, we quantified T-cell receptor rearrangement excision circles (TREC) in CD4 T cells from lymphopenic AIDS patients treated with highly active antiretroviral therapy and IL-2. METHODS: CD4 cell subsets were evaluated by flow cytometry using anti-CD45RO/RA, CD62L, Ki67 and CD95 monoclonal antibodies. The proportion of recent thymic emigrant had been quantified by a real-time polymerase chain reaction assay for signal joint TREC in peripheral blood mononuclear and purified CD4 T cells. RESULTS: At initiation of IL-2, TREC copies/microl of blood were correlated with naive T cell numbers and age. Both naive and TREC numbers/microl significantly increased over time in all patients, with a wide range of TREC increases. Higher percentages of CD4+CD45RO-negative cells positive for the Ki67 cell-cycle marker were found in patients with a low TREC increase, but remained stable under IL-2. TREC and naive cell recovery were correlated; they also correlated with the numbers of TREC and naive cells at the start of IL-2, and with age, suggesting a thymic origin for naive T-cell recovery. A mathematical model showing the linear recovery of naive cells and TREC under IL-2 also strongly suggested that a naive T-cell increase reflects thymic export and involves little net death and proliferation. CONCLUSION: Although we cannot rule out a mechanism of altered proliferation or death rate, the thymus plays an important role in the long-term recovery of naive T cells under IL-2 therapy.     

De novo T-cell generation in patients at different ages and stages of HIV-1 disease

We assessed de novo T-cell generation by determining T-cell receptor-rearrangement excision circles (TRECs) based on patient age and on stage of HIV-1 infection. TRECs were measured in purified CD4 and CD8 T cells of a large cohort of HIV-1-infected subjects (n = 297) with chronic infection but no previous antiretroviral treatment and of a control group of HIV-negative subjects (n = 120). HIV-1-infected subjects were stratified on the basis of CD4 T-cell counts in 3 groups, early-stage disease (more than 500 CD4 T cells), intermediate-stage disease (200-500 CD4 T cells), and late-stage disease (fewer than 200 CD4 T cells). Compared with the control group, CD8 TREC contents were severely reduced (P <.001) in HIV-1-infected subjects regardless of the stage of HIV disease. In contrast, CD4 TREC contents were significantly increased (P =.003) in HIV-1-infected subjects during early-stage disease, similar at intermediate-stage disease, and severely reduced only at late-stage disease. We show that the increase in CD4 TRECs was mostly limited to younger (younger than 45 years) patients at early-stage disease. Our results demonstrate a dichotomy between TREC contents in CD4 and CD8 T-cell populations in HIV-1 infection and indicate that thymus function in younger subjects is preserved at early and intermediate stages of HIV infection.     

Homeostatic control of T-cell generation in neonates

T cells are produced through 2 mechanisms, thymopoiesis and proliferative expansion of postthymic T cells. Thymic output generates diversity of the pool, and proliferation achieves optimal clonal size of each individual T cell. To determine the contribution of these 2 mechanisms to the formation of the initial T-cell repertoire, we examined neonates of 30 to 40 weeks' gestation. Peripheral T cells were in a state of high proliferative turnover. In premature infants, 10% of T cells were dividing; the proliferation rates then declined but were still elevated in mature newborns. Throughout the third trimester, concentrations of T-cell-receptor excision circles (TRECs) were 10 per 100 T cells. Stability of TREC frequencies throughout the period of repertoire generation suggested strict regulation of clonal size to approximately 10 to 20 cells. Neonatal naive CD4+ and CD8+ T cells were explicitly responsive to IL-7; growth-promoting properties of IL-15 were selective for newborn CD8+ T cells. Neonatal T cells expressed telomerase and, in spite of the high turnover, built up a telomeric reserve. Thus, proliferative expansion, facilitated by increased cytokine responsiveness, and thymopoiesis complement each other as mechanisms of T-cell production in neonates. Maintaining optimal clonal size instead of filling the space in a lymphopenic host appears to regulate homeostatic T-cell proliferation during fetal development.     

Factors affecting thymic function after allogeneic hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is followed by profound immunodeficiency. Thymic function is necessary for de novo generation of T cells after HSCT. Circulating CD45RA(+) naive T-cell levels are predictive of antigen-specific T-cell responses in the absence of graft-versus-host disease (GVHD). These T cells may not represent recent thymic emigrants, since naive T cells may maintain this phenotype if not antigen-activated. To accurately measure thymic output after HSCT and determine the factors that influence thymic function, T-cell receptor excision circles (TRECs) were examined in CD4(+) and CD8(+) cells from a cross-section of patients following HSCT. TREC levels rose weeks after HSCT and could be detected in patients 6 years after HSCT. TREC levels correlated with the frequency of phenotypically naive T cells, indicating that such cells were not expanded progeny of naive T cells present in the donor graft. Chronic GVHD was the most important factor that predicted low TREC levels even years after HSCT. Patients with a history of resolved GVHD had decreased numbers of TREC, compared with those with no GVHD. Because few adults had no history of GVHD, it was not possible to determine whether age alone inversely correlated with TREC levels. Recipients of cord blood grafts had no evidence of decreased TREC induced by immunosuppressive prophylaxis drugs. Compared with unrelated donor grafts, recipients of matched sibling grafts had higher TREC levels. Collectively, these data suggest that thymopoiesis is inhibited by GVHD. Larger studies will be needed to determine the independent contributions of age and preparative regimen to post-transplant thymopoietic capacity.     

Features of 'CD4-exploders', HIV-positive patients with an optimal immune reconstitution after potent antiretroviral therapy

OBJECTIVE: To identify crucial immunological characteristics of a group of patients, defined 'CD4-exploders', who were able to fully reconstitute their immune system after receiving highly active antiretroviral therapy (HAART). PATIENTS: Among a population of 540 HIV-positive patients treated with HAART, six individuals were identified who experienced a nadir of less than 85 x 106 CD4+ cells/l, had major opportunistic infections (four out of six), started HAART in 1996 or 1997, and showed a rapid and relevant CD4+ lymphocyte increase (mainly due to virgin cells), in some cases regardless of virological control. METHODS: Enzyme-linked immunosorbent assay for the determination of interleukin (IL)-7 plasma levels; flow cytometry to analyse surface antigens and CD127 (IL-7 receptor alpha-chain) expression; quantitative-competitive (QC) PCR for detecting cells containing T-cell receptor rearrangement excision circles (TREC); chest-computed tomography (CT) to analyse thymus volume and content. RESULTS: In 'CD4-exploders', high levels of TREC+ lymphocytes were found among CD4+ T cells, which also contained a high percentage of naive cells. However, CT revealed a dramatic depletion of intrathymic lymphoid tissue. Plasma levels of IL-7 were significantly high. Most CD4+ and CD8+ T lymphocytes expressed CD127, whose level was similar to that of healthy donors. CD127 expression on CD8+ lymphocytes was markedly higher than in HIV-positive individuals treated with the same therapy or in patients with AIDS. CONCLUSION: In 'CD4-exploders', HAART-induced reconstitution of the T-cell compartment is independent from thymus volume, and is favoured by the upregulation of the IL-7/IL-7 receptor system.     

Impaired production of naive T lymphocytes in human T-cell leukemia virus type I-infected individuals: its implications in the immunodeficient state

Opportunistic infections frequently occur in patients with adult T-cell leukemia (ATL) and human T-cell leukemia virus type I (HTLV-I) carriers. However, the underlying mechanisms of such infections remain unknown. To clarify the mechanism of immunodeficiency in those infected with HTLV-I, this study analyzed the T-cell subsets in HTLV-I carriers and patients with HTLV-I-associated myelopathy/tropical spastic paraparesis and ATL using 3-color fluorescence with CD62L and CD45RA coexpression either with CD4(+) or CD8(+) T cells. The number of naive T lymphocytes was markedly suppressed in patients with ATL, particularly in those with acute form, compared with uninfected control individuals. The number of naive T cells was low in HTLV-I-infected individuals under 50 years old compared with uninfected individuals, whereas the number of memory T lymphocytes was greater in HTLV-I-infected individuals. Although the increase of memory T lymphocytes correlated with HTLV-I provirus loads, no relationship was found between naive T-cell counts and provirus loads. T-cell receptor rearrangement excision circles (TRECs), which are generated by DNA recombination during early T lymphopoiesis, were quantified to evaluate thymic function in HTLV-I-infected individuals. TREC levels were lower in HTLV-I-infected individuals than in uninfected individuals. In HTLV-I carriers less than 70 years old, an increase of Epstein-Barr virus DNA in peripheral blood mononuclear cells was observed in 6 of 16 (38%) examined, whereas it was detectable in only 1 of 11 uninfected controls. These results suggested that the low number of naive T lymphocytes was due to suppressed production of T lymphocytes in the thymus, which might account for immunodeficiency observed in HTLV-I-infected individuals.     

IL-7 therapy dramatically alters peripheral T-cell homeostasis in normal and SIV-infected nonhuman primates

Interleukin-7 (IL-7) is important for thymopoiesis in mice and humans because IL-7 receptor alpha (IL-7Ralpha) mutations result in a severe combined immunodeficiency phenotype with severe thymic hypoplasia. Recent evidence has indicated that IL-7 also plays an important role as a regulator of T-cell homeostasis. Here we report the immunologic effects of recombinant human IL-7 (rhIL-7) therapy in normal and simian immunodeficiency virus (SIV)-infected nonhuman primates. Cynomolgus monkeys receiving 10 days of rhIL-7 showed substantial, reversible increases in T-cell numbers involving a dramatic expansion of both naive and nonnaive phenotype CD4(+) and CD8(+) subsets. Although IL-7 is known to have thymopoietic effects in mice, we observed marked declines in the frequency and absolute number of T-cell receptor excision circle-positive (TREC(+)) cells in the peripheral blood and dramatic increases in the percentage of cycling T cells in the peripheral blood as measured by Ki-67 expression (baseline less than 5% to approximately 50% after 6 days of therapy) and ex vivo bromodeoxyuridine (BrdU) incorporation. Similarly, moderately CD4- depleted SIV-infected macaques treated with rhIL-7 also had significant increases in peripheral blood CD4(+) and CD8(+) T cells following rhIL-7 therapy. Thus, rhIL-7 induces dramatic alterations in peripheral T-cell homeostasis in both T-cell-replete and T-cell-depleted nonhuman primates. These results further implicate IL-7 as a promising immunorestorative agent but illustrate that a major component of its immunorestorative capacity reflects effects on mature cells. These results also raise the possibility that IL-7 therapy could be used to temporarily modulate T-cell cycling in vivo in the context of immunotherapies such as vaccination.     

Interleukin-7 improves T-cell recovery after experimental T-cell-depleted bone marrow transplantation in T-cell-deficient mice by strong expansion of recent thymic emigrants

Interleukin-7 (IL-7) has been shown to enhance thymic output of newly developed T cells following bone marrow transplantation (BMT) in mice. In addition, IL-7 may affect peripheral expansion of T cells. In order to study the relative contribution of thymopoiesis versus peripheral T-cell expansion in the setting of compromised thymopoiesis, we have applied IL-7 in an experimental stem cell transplantation model using T cell-deficient RAG-1(-/-) mice. C57BL/6 RAG-1(-/-) mice received transplants of syngeneic T-cell-depleted (TCD) bone marrow (Ly5.1) with or without supplemented T cells (Ly5.2). IL-7 was administered until day 63 after BMT. Peripheral blood T- and B-cell recovery was quantified by flow cytometry and thymopoiesis was studied by quantification of T-cell receptor rearrangement excision circles (TRECs). In mice receiving a T-cell-replete BMT, IL-7 selectively expanded mature CD45.2+ T cells without affecting the recovery of new bone marrow-derived CD45.1+ T cells. In contrast, IL-7 significantly enhanced the recovery of bone marrow-derived T cells after TCD BMT. Quantification of TRECs in mice receiving a TCD BMT revealed that enhanced T-cell recovery following IL-7 treatment resulted from a strong expansion of newly developed naive T cells. These results suggest that peripheral expansion of recent thymic emigrants or mature T cells may be a preferential mechanism by which IL-7 enhances T-cell recovery after BMT.     

Quantification of T cell receptor rearrangement excision circles to estimate thymic function: an important new tool for endocrine-immune physiology

Although the thymus constitutes a target organ for most protein and steroid hormones, it has been quite difficult to determine the precise control exerted in vivo by the endocrine system upon thymic function. The biological role of the thymus is to ensure the generation of a diversified population of peripheral T cells able to respond to non-self-antigens but nevertheless tolerant to self-antigens. For a long time, thymic function could not be monitored, as a consequence of the absence of adequate technology to differentiate recent thymic emigrants from naive T cells. The generation of T cell receptor (TCR) diversity occurs in the thymus through recombination of gene segments encoding the variable parts of the TCR alpha and beta chains. During these processes, by-products of the rearrangements are generated in the form of TCR excision circles (TRECs). As these molecules are lost upon further cell division, their quantification is actually considered as a very valuable tool to estimate thymic function. The most appropriate TREC is deltaRec-Psi(J)alpha TREC or signal joint TREC resulting from deltaRec-Psi(J)alpha rearrangement (TCRD deletion) that occurs late during thymopoiesis, before V(alpha)-J(alpha) rearrangement. Here we describe how TREC quantification is a powerful and reliable method to evaluate the impact of hormones and endocrine disorders upon thymic function.     

Immunologic effects of prophylactic donor lymphocyte infusion after allogeneic marrow transplantation for multiple myeloma

Reconstitution of T-cell immunity after bone marrow transplantation (BMT) is often delayed, resulting in a prolonged period of immunodeficiency. Donor lymphocyte infusion (DLI) has been used to enhance graft-versus-leukemia activity after BMT, but the effects of DLI on immune reconstitution have not been established. We studied 9 patients with multiple myeloma who received myeloablative therapy and T-cell-depleted allogeneic BMT followed 6 months later by infusion of lymphocytes from the same donor. DLI consisted of 3 x 10(7) CD4(+) donor T cells per kilogram obtained after in vitro depletion of CD8(+) cells. Cell surface phenotype of peripheral lymphocytes, T-cell receptor (TCR) V beta repertoire, TCR rearrangement excision circles (TRECs), and hematopoietic chimerism were studied in the first 6 months after BMT and for 1 year after DLI. These studies were also performed in 7 patients who received similar myeloablative therapy and BMT but without DLI. Phenotypic reconstitution of T and natural killer cells was similar in both groups, but patients who received CD4(+) DLI developed increased numbers of CD20(+) B cells. TCR V beta repertoire complexity was decreased at 3 and 6 months after BMT but improved more rapidly in patients who received DLI (P =.01). CD4(+) DLI was also associated with increased numbers of TRECs in CD3(+) T cells (P <.001) and with conversion to complete donor hematopoiesis (P =.05). These results provide evidence that prophylactic infusion of CD4(+) donor lymphocytes 6 months after BMT enhances reconstitution of donor T cells and conversion to donor hematopoiesis as well as promoting antitumor immunity.