IL-7 increases both thymic-dependent and thymic-independent T-cell regeneration after bone marrow transplantation

Kinetics of IL-7 and IL-15 levels after allogeneic peripheral blood stem cell transplantation following nonmyeloablative conditioning

BACKGROUND

We analysed kinetics of IL-7 and IL-15 levels in 70 patients given peripheral blood stem cells after nonmyeloablative conditioning.

METHODS

EDTA-anticoagulated plasma and serum samples were obtained before conditioning and about once per week after transplantation until day 100. Samples were aliquoted and stored at -80°C within 3 hours after collection until measurement of cytokines. IL-7 and IL-15 levels were measured by ELISAs.

RESULTS

Median IL-7 plasma levels remained below 6 pg/L throughout the first 100 days, although IL-7 plasma levels were significantly higher on days 7 (5.1 pg/mL, P=0.002), 14 (5.2 pg/mL, P<0.001), and 28 (5.1 pg/mL, P=0.03) (but not thereafter) than before transplantation (median value of 3.8 pg/mL). Median IL-15 serum levels were significantly higher on days 7 (12.5 pg/mL, P<0.001), 14 (10.5 pg/mL, P<0.001), and 28 (6.2 pg/mL, P<0.001) than before transplantation (median value of 2.4 pg/mL). Importantly, IL-7 and IL-15 levels on days 7 or 14 after transplantation did not predict grade II-IV acute GVHD.

CONCLUSIONS

These data suggest that IL-7 and IL-15 levels remain relatively low after nonmyeloablative transplantation, and that IL-7 and IL-15 levels early after nonmyeloablative transplantation do not predict for acute GVHD.

Decreased interleukin 7 responsiveness of T lymphocytes in patients with idiopathic CD4 lymphopenia

BACKGROUND

Elevated serum interleukin 7 (IL-7) levels are observed in lymphopenic conditions, including idiopathic CD4 lymphopenia (ICL), which is characterized by CD4 lymphopenia in the absence of human immunodeficiency virus infection or other known immunodeficiency.

METHODS

To test whether defective IL-7 signaling could be an etiologic or contributing factor in ICL, peripheral blood mononuclear cells from patients with ICL (median CD4 T-cell count, 160 cells/μL) and healthy controls (median CD4 T-cell count, 582 cells/μL) were evaluated for expression of IL-7Rα chain (CD127) and intracellular phosphorylated STAT-5 (a marker of γc cytokine signaling) after cytokine stimulation. Gene expression was analyzed by real-time polymerase chain reaction following IL-7 stimulation.

RESULTS

The percentage of CD4+CD127+ T cells was lower in patients with ICL, compared with controls (P < .001). Lower levels of STAT-5 phosphorylation after IL-7 stimulation were observed in both CD4 and CD8 T cells from patients with ICL, compared with controls (P < .001 and P = .017, respectively), that inversely correlated in CD4 T cells with serum IL-7 levels (r = -0.734, P = .013). Destabilization of p27(kip1), a critical step for IL-7-induced T-cell cycling, was decreased in patients with ICL, compared with controls (P = .004), after IL-7 stimulation.

CONCLUSIONS

These data suggest that diminished responsiveness to IL-7 in CD4 and CD8 T cells during ICL may be contributing to the dysregulation of T-cell homeostasis.

Effects of recombinant human interleukin 7 on T-cell recovery and thymic output in HIV-infected patients receiving antiretroviral therapy: results of a phase I/IIa randomized, placebo-controlled, multicenter study

BACKGROUND

The immune deficiency of human immunodeficiency virus (HIV) infection is not fully corrected with ARV therapy. Interleukin-7 (IL-7) can boost CD4 T-cell counts, but optimal dosing and mechanisms of cellular increases need to be defined.

METHODS

We performed a randomized placebo-controlled dose escalation (10, 20 and 30 µg/kg) trial of 3 weekly doses of recombinant human IL-7 (rhIL-7) in ARV-treated HIV-infected persons with CD4 T-cell counts between 101 and 400 cells/µL and plasma HIV levels <50 copies/mL. Toxicity, activity and the impact of rhIL-7 on immune reconstitution were monitored.

RESULTS

Doses of rhIL-7 up to 20 µg/kg were well tolerated. CD4 increases of predominantly naive and central memory T cells were brisk (averaging 323 cells/µL at 12 weeks) and durable (up to 1 year). Increased cell cycling and transient increased bcl-2 expression were noted. Expanded cells did not have the characteristics of regulatory or activated T cells. Transient low-level HIV viremia was seen in 6 of 26 treated patients; modest increases in total levels of intracellular HIV DNA were proportional to CD4 T-cell expansions. IL-7 seemed to increase thymic output and tended to improve the T-cell receptor (TCR) repertoire in persons with low TCR diversity.

CONCLUSIONS

Three weekly doses of rhIL-7 at 20 µg/kg are well tolerated and lead to a dose-dependent CD4 T-cell increase and the broadening of TCR diversity in some subjects. These data suggest that this rhIL-7 dose could be advanced in future rhIL-7 clinical studies.

CLINICAL TRIALS REGISTRATION

NCT0047732.

Preterm neonates show marked leukopenia and lymphopenia that are associated with increased regulatory T-cell values and diminished IL-7

INTRODUCTION

Current advances in neonatology have improved survival among preterm and low-birth-weight infants. However, the risk of neonatal death in preterm infants is much greater than in full-term neonates and is frequently associated with infections.

METHODS

Little is known about the immune status of preterm neonates; therefore, we analyzed the frequency and absolute counts of different immune populations in 211 cord blood samples taken from very-preterm to full-term neonates.

RESULTS

We found that absolute counts of all the immune subsets analyzed (i.e., monocytes, granulocytes, B cells, natural killer (NK) cells, CD4(+), and CD8(+) T cells) were markedly lower in preterm infants than in full-term infants. Surprisingly, we observed that regulatory T cells (Tregs) were the only cell subset that did not decrease in preterm infants, and their frequency was even higher than in full-term infants.

DISCUSSION

Tregs are crucial to maternal-fetal tolerance, but their suppressive role could be also implicated in the leukopenia observed in preterm infants. We did not observe differences in thymic function, but we found that plasma levels of interleukin (IL)-7 and the frequency of its receptor were significantly decreased in preterm infants. Our results could help to identify leukopenia and to implement immune therapies that significantly diminish mortality in preterm neonates.

HIV RNA suppression and immune restoration: can we do better?

HAART has significantly changed the natural history of HIV infection: patients receiving antiretrovirals are usually able to control viremia, even though not all virological responders adequately recover their CD4+ count. The reasons for poor immune restoration are only partially known and they include genetic, demographic and immunologic factors. A crucial element affecting immune recovery is immune activation, related to residual viremia; indeed, a suboptimal virological control (i.e., low levels of plasma HIV RNA) has been related with higher levels of chronic inflammation and all-cause mortality. The sources of residual viremia are not yet completely known, even though the most important one is represented by latently infected cells. Several methods, including 2-LTR HIV DNA and unspliced HIV RNA measurement, have been developed to estimate residual viremia and predict the outcome of antiretroviral therapy. Considering that poor immunologic responders are exposed to a higher risk of both AIDS-related and non-AIDS-related diseases, there is a need of new therapeutic strategies, including immunomodulators and drugs targeting the latent viral reservoirs, in order to face residual viremia but also to “drive” the host immunologic responses.

The influence of HIV on CD127 expression and its potential implications for IL-7 therapy

Interleukin-7 (IL-7) is critical for early T-cell development and plays an important role in T-cell homeostasis, differentiation and function. Signalling via the IL-7 receptor is dependent on the expression of its components, IL-7Rα (CD127) and IL-2Rγ (CD132) and is mediated in part by alterations in CD127 expression levels in different cell subsets. Naïve and memory T-cells express high levels of CD127, while effector cells are CD127(lo) and retention of the receptor is thought to influence the development of memory cells. Reduced expression of CD127 has been associated with markers of disease severity in HIV infection and other chronic viral infections as well as in various cancers. In HIV infection, decreased CD127 expression on T-cells is correlated with reduced CD4(+) T-cell counts, increased viral replication and immune activation. The loss of IL-7 activity, due to decreased CD127 expression, may contribute to the observed loss of CD8(+) cytotoxic T lymphocyte (CTL) activity in HIV infection. The downregulation of CD127 expression in HIV infection may be due to host (e.g. IL-7, IL-4, immune activation) and/or viral (e.g. HIV-tat) factors and mechanisms of receptor regulation may differ by cell type. In addition, the expression of a soluble form of CD127 (sCD127) has been shown to be increased in HIV infection. This protein may affect IL-7 activity in vivo and therefore may have implications for IL-7-based therapies which are currently being tested in clinical trials. Understanding how CD127 is regulated during HIV infection will provide insight for the development of novel therapeutics to improve immune function and anti-viral T-cell activity.

Mesenchymal stem cells inhibit thymic reconstitution after allogeneic cord blood transplantation

Cord blood (CB) as a source of stem cells has been a successful addition to the field of allogeneic stem cell transplantation (ASCT). The increased human leukocyte antigen (HLA) permissiveness of CB grafts has made it possible for more patients to undergo treatment. The drawback is that patients suffer from a longer period of compromised immunity. We analyzed T-cell receptor excision circles (TRECs), immunoglobulin G (IgG), and immunoglobulin M (IgM) levels after cord blood transplantation (CBT) in 50 patients transplanted at our center. These immunological parameters were compared retrospectively with clinical factors and complications. We found that TREC levels after CBT were lower in adults, patients with myeloablative conditioning, and in patients with a lower nucleated cell dose in the graft. In addition mesenchymal stem cells (MSC) as co-infusion at the time of CBT had a negative effect on TREC reconstitution. This was found to be associated with decreased overall survival for this patient category. Reduced IgM and IgG levels post-CBT were associated with a major AB0 mismatch, and infusion of MSCs. Our results highlight the importance of close monitoring of the immune reconstitution after CBT. In addition it shows a potentially new suppressive effect of MSCs on the immune system.

Greater than the sum of their parts: combination strategies for immune regeneration following allogeneic hematopoietic stem cell transplantation

Cytoreductive conditioning regimes designed to allow for successful allogeneic hematopoietic stem cell transplantation (allo-HSCT) paradoxically are also detrimental to recovery of the immune system in general but lymphopoiesis in particular. Post-transplant immune depletion is particularly striking within the T cell compartment which is exquisitely sensitive to negative regulation, evidenced by the profound decline in thymic function with age. As a consequence, regeneration of the immune system remains a significant unmet clinical need. Over the past decade studies have revealed several promising therapeutic strategies to address ineffective lymphopoiesis and post-transplant immune deficiency. These include the use of cytokines such as IL-7, IL-12 and IL-15; growth factors and hormones like keratinocyte growth factor (KGF), insulin-like growth factor (IGF)-1 and growth hormone (GH); adoptive transfer of ex vivo-generated precursor T cells (pre-T) and sex steroid ablation (SSA). Moreover, recently several novel approaches have been proposed to generate whole thymii ex vivo using stem cell technologies and bioscaffolds. Increasingly, however, when transferred to the clinic, these strategies alone are not sufficient to restore thymopoiesis in all patients leading to the potential of combination strategies as a way to reign in non-responders. Synergistic enhancement in combination may be due to differential targets may therefore be effective in improving clinical outcomes in the transplant settings as well as in other lymphopenic states induced by high dose chemotherapy/radiation therapy or HIV, and may also be useful in improving responses to vaccination and augmenting anti-tumor immunotherapy.

Harnessing the biology of IL-7 for therapeutic application

Interleukin-7 (IL-7) is required for T cell development and for maintaining and restoring homeostasis of mature T cells. IL-7 is a limiting resource under normal conditions, but it accumulates during lymphopaenia, leading to increased T cell proliferation. The administration of recombinant human IL-7 to normal or lymphopenic mice, non-human primates and humans results in widespread T cell proliferation, increased T cell numbers, modulation of peripheral T cell subsets and increased T cell receptor repertoire diversity. These effects raise the prospect that IL-7 could mediate therapeutic benefits in several clinical settings. This Review summarizes the biology of IL-7 and the results of its clinical use that are available so far to provide a perspective on the opportunities for clinical application of this cytokine.

A challenge for the future: aging and HIV infection

Older individuals (≥50 years of age) are increasingly becoming a new at-risk group for HIV-1 infection and, together with those surviving longer due to the introduction of anti-retroviral therapy (ART), it is predicted that more than half of all HIV-1-infected individuals in the United States will be greater than 50 years of age in the year 2015. Older individuals diagnosed with HIV-1 are prone to faster disease progression and reduced T-cell reconstitution despite successful virologic control with anti-retroviral therapy (ART). There is also growing evidence that the T-cell compartment in HIV-1(+) adults displays an aged phenotype, and HIV-1-infected individuals are increasingly diagnosed with clinical conditions more commonly seen in older uninfected persons. As aging in the absence of HIV infection is associated with alterations in T-cell function and immunosenescence, the combined impact of both HIV-1 infection and aging may provide an explanation for poorer clinical outcomes observed in older HIV-1-infected individuals. Thus, the development of novel therapeutics to stimulate immune function and delay immunosenescence is critical and would be beneficial to both the elderly and HIV-1-infected individuals.

Interactions between the immune system and bone

The relationship between the immune system, estrogen deficiency and bone loss is an intriguing and, as yet, unexplained challenge of the past two decades. Here we summarize the evidence that links immune cells, inflammation, cytokine production and osteoclast formation and activity with particular regard to humans.

The thymus and the immune system: layered levels of control

Control points of normal thymopoiesis may provide insights into strategies for interrupting cell interactions in thymomas which appear to maintain active T cell production. Thymus production of T cells represents one of two pathways by which peripheral T cell populations are maintained or, if lost, regenerated. The production of T cells by the thymus results from a series of thymus epithelial cell (TEC) - thymocyte interactions from entry of thymocyte precursors into the thymus to release of mature naïve single positive T cells into the periphery. Within this series of interactions, certain control points have been identified, all of which act through TEC to modulate thymopoiesis.

Advances in adoptive immunotherapy to accelerate T-cellular immune reconstitution after HLA-incompatible hematopoietic stem cell transplantation

Although partially HLA-mismatched hematopoietic stem cell transplantation (HSCT) has become an important therapeutic option for children with primary immunodeficiencies, delayed reconstitution of the T-cell compartment remains a major clinical concern. Adoptive immunotherapies to provide recipients with a protective and diverse T-cell repertoire in the months following HSCT are warranted. In order to improve T-cell reconstitution after T-cell-depleted HSCT, different strategies are currently being studied. Some are based on administration of modified mature T cells (e.g., allodepleted T cells or pathogen-specific T cells). Others aim at accelerating de novo thymopoiesis from donor-derived hematopoietic stem cells in vivo via the administration of thymopoietic agents or the transfer of large numbers of T-cell precursors generated ex vivo. The present article will provide a brief summary of recent advances in the field of allodepletion and adoptive transfer of pathogen-specific T cells and a detailed discussion of strategies for enhancing thymopoiesis in vivo.

IL-7 and lymphopenia

Interleukin-7 (IL-7) is a growth and anti-apoptotic factor for T-lymphocytes, with potential for clinical use in the treatment of immunodeficiencies due to loss of T-cells. Lymphopenia induced by disease (HIV infection, hemodialysis or Idiopathic CD4+ lymphopenia) or by treatment (high dose chemotherapy or depleting antibodies) for cancer or auto-immune diseases results in increased circulating levels of IL-7 which decline with T-cell recovery, however, the mechanism of such response remains to be elucidated. Furthermore, IL-7 is a major player in the regulation of peripheral T-cell homeostasis and as such is an important candidate cytokine for therapy aimed at improving T-cell reconstitution following lymphopenia. Anti- IL-7 is on the other hand proposed to treat conditions where IL-7 may play a more direct role in pathogenesis such as autoimmune disease like Rheumatoid Arthritis, Multiple Sclerosis or Inflammatory Bowel disease.

The immune system and bone

T cells and B cells produce large amounts of cytokines which regulate bone resorption and bone formation. These factors play a critical role in the regulation of bone turnover in health and disease. In addition, immune cells of the bone marrow regulate bone homeostasis by cross-talking with bone marrow stromal cells and osteoblastic cells via cell surface molecules. These regulatory mechanisms are particularly relevant for postmenopausal osteoporosis and hyperparathyroidism, two common forms of bone loss caused primarily by an expansion of the osteoclastic pool only partially compensated by a stimulation of bone formation. This article describes the cytokines and immune factors that regulate bone cells, the immune cells relevant to bone, examines the connection between T cells and bone in health and disease, and reviews the evidence in favor of a link between T cells and the mechanism of action of estrogen and PTH in bone.

Interleukin-7 permits Th1/Tc1 maturation and promotes ex vivo expansion of cord blood T cells: a critical step toward adoptive immunotherapy after cord blood transplantation

Donor leukocyte infusions (DLI) in the allogeneic hematopoietic transplant setting can provide a clinically relevant boost of immunity to reduce opportunistic infections and to increase graft-versus-leukemia activity. Despite significant advances in applicability, DLI has not been available for single-unit recipients of unrelated cord blood transplant. Ex vivo expansion of cord blood T cells can be achieved with interleukin (IL)-2 and CD3/CD28 costimulatory beads. However, significant apoptosis occurs in proliferating T cells, diminishing the yield and skewing the CD4/CD8 ratio in the T-cell population, jeopardizing the potential efficacy of DLI. In this study, we show that interleukin (IL)-7 not only reduces apoptosis of activated T lymphocytes and enhances their proliferation but also promotes functional maturation, leading to secretion of IFN-gamma and other key cytokines. Recognizing that infused T lymphocytes will need to meet microbial antigens in secondary lymphoid organs to generate effectors, we also show that expansion with IL-7 promotes the preservation of a polyclonal broad T-cell receptor repertoire and a surface phenotype that favors lymph node homing. Expanded lymphocytes lack alloreactivity against recipient and other allogeneic cells, indicating a favorable safety profile from graft-versus-host disease. Nevertheless, expanded T cells can be primed subsequently against lymphoid and myeloid leukemia cells to generate tumor-specific cytotoxic T cells. Taken together, our findings offer a major step in fulfilling critical numerical and biological requirements to quickly generate a DLI product ex vivo using a negligible fraction of a cord blood graft that provides a flexible adoptive immunotherapy platform for both children and adults.

Increased generation of CD8 single positive cells in SOCS1-deficient thymus does not proportionately increase their export

Mice lacking suppressor of cytokine signaling 1 (SOCS1) accumulate CD8(+) T lymphocytes in the thymus and in the periphery. Whereas IL-7 and IL-15 promote the generation of CD8 single positive (SP) thymocytes, IL-15 drives the expansion of CD8 T cells in the periphery. Here, we investigated whether increased production of CD8 SP thymocytes is accompanied by their increased export in SOCS1-deficient mice. In vivo labeling with bromodeoxyuridine showed increased cycling of CD8 SP thymocytes in SOCS1-deficient mice. However, SOCS1-deficient thymi contained increased proportion of CD24(lo)CD69(lo) SP thymocytes as well as increased expression of Qa-2 in both CD4 and CD8 SP compartments. Analysis of recent thymic emigrants (RTE) following intrathymic labeling with fluorescein isothiocyanate revealed less efficient export of CD8 RTEs from SOCS1-deficient thymi and comparable CD4:CD8 ratio among RTEs in SOCS1-null and control mice. These findings show that the rate of export of CD8 SP thymocytes is not proportional to their generation in SOCS1-deficient thymi and suggest the existence of homeostatic mechanisms controlling the egress of CD8 T cells.

Sex steroid ablation enhances immune reconstitution following cytotoxic antineoplastic therapy in young mice

Cytotoxic antineoplastic therapy is used to treat malignant disease but results in long-term immunosuppression in postpubertal and adult individuals, leading to increased incidence and severity of opportunistic infections. We have previously shown that sex steroid ablation (SSA) reverses immunodeficiencies associated with age and hematopoietic stem cell transplantation in both autologous and allogeneic settings. In this study, we have assessed the effects of SSA by surgical castration on T cell recovery of young male mice following cyclophosphamide treatment as a model for the impact of chemotherapy. SSA increased thymic cellularity, involving all of the thymocyte subsets and early T lineage progenitors. It also induced early repair of damage to the thymic stromal microenvironment, which is crucial to the recovery of a fully functional T cell-based immune system. These functional changes in thymic stromal subsets included enhanced production of growth factors and chemokines important for thymopoiesis, which preceded increases in both thymocyte and stromal cellularity. These effects collectively translated to an increase in peripheral and splenic naive T cells. In conclusion, SSA enhances T cell recovery following cyclophosphamide treatment of mice, at the level of the thymocytes and their stromal niches. This provides a new approach to immune reconstitution following antineoplastic therapy.

Impact of gamma-chain cytokines on T cell homeostasis in HIV-1 infection: therapeutic implications

CD4(+) T cell lymphocytes are a major target for human immunodeficiency virus type-1 (HIV-1) infection. During this chronic infection, CD4(+) T cell loss (induced through direct viral replication), generalized immune activation and increased susceptibility to apoptosis result in impaired T cell homeostasis with subsequent development of opportunistic infections and cancers. Highly active antiretroviral therapy (HAART) has a well-defined, beneficial effect on HIV-1-related clinical outcome; however, it does not lead to normalization of immune dysregulation. In order to boost both CD4(+) T cell restoration and HIV-1 specific immunity, immunotherapy with gamma-chain cytokines has been used in HIV-1-infected patients during concomitant HAART. In this review, we summarize the role of gamma-chain cytokines, especially interleukin (IL)-2 and IL-7, in influencing T cell homeostasis and proliferation, and discuss how immunotherapy with these cytokines may be beneficial to reconstitute the T cell compartment in the context of HIV-1 infection. The intriguing results of two large trials evaluating the efficacy of IL-2 in restoring immune function during HIV-1 infection are also discussed. In addition, we consider the promises and caveats of the first phase I/II clinical trials with IL-7 in HIV-1-infected patients and the knowledge that is still lacking in the field of T cell reconstitution through gamma-chain cytokines.

Cord blood transplantation: evolving strategies to improve engraftment and immune reconstitution

PURPOSE OF REVIEW

For many patients with relapsed or high-risk hematologic malignancies, allogeneic stem cell transplantation offers the best hope for cure. For patients lacking a suitable family or unrelated donor, umbilical cord blood provides a promising alternative graft source. Dramatic advances in cord blood transplantation (CBT) have been made in the past 2 decades, leading to a rapid expansion of CBT programs worldwide.

RECENT FINDINGS

Promising new strategies, including double CBT and ex-vivo graft engineering, have improved myeloid and platelet engraftment rates and kinetics. However, delayed immune reconstitution and associated infectious morbidity and mortality remain a significant challenge, especially in adult CBT recipients. In adults, both impaired recipient thymopoiesis and the lack of transferred memory cells contribute to delayed T cell recovery, resulting in an increased risk of opportunistic infections.

SUMMARY

Novel clinical approaches in CBT have improved outcomes, especially those associated with delays in myeloid and platelet engraftment. However, delayed immune reconstitution remains a great challenge. Novel strategies, including graft engineering approaches capable of improving T cell recovery, and pharmacologic interventions capable of preserving thymopoiesis and facilitating the recovery of a diverse functional T cell repertoire are being pursued; these approaches have great potential to further improve outcomes after CBT.

Immune reconstitution after allogeneic transplantation and expanding options for immunomodulation: an update

Allogeneic hematopoietic stem cell transplantation (HSCT) has advanced to a common procedure for treating also older patients with malignancies and immunodeficiency disorders by redirecting the immune system. Unfortunately, cure is often hampered by relapse of the underlying disease, graft-versus-host disease, or severe opportunistic infections, which account for the majority of deaths after HSCT. Enhancing immune reconstitution is therefore an area of intensive research. An increasing variety of approaches has been explored preclinically and clinically: the application of cytokines, keratinocyte growth factor, growth hormone, cytotoxic lymphocytes, and mesenchymal stem cells or the blockade of sex hormones. New developments of allogeneic HSCT, for example, umbilical cord blood or haploidentical graft preparations leading to prolonged immunodeficiency, have further increased the need to improve immune reconstitution. Although a slow T-cell reconstitution is regarded as primarily responsible for deleterious infections with viruses and fungi, graft-versus-host disease, and relapse, the importance of innate immune cells for disease and infection control is currently being reevaluated. The groundwork has been prepared for the creation of individualized therapy partially based on genetic features of the underlying disease. We provide an update on selected issues of development in this fast evolving field; however, we do not claim completeness.

Phase I study of recombinant human interleukin-7 administration in subjects with refractory malignancy

PURPOSE

Interleukin-7 (IL-7) has critical and nonredundant roles in T-cell development, hematopoiesis, and postdevelopmental immune functions as a prototypic homeostatic cytokine. Based on a large body of preclinical evidence, it may have multiple therapeutic applications in immunodeficiency states, either physiologic (immunosenescence), pathologic (HIV), or iatrogenic (postchemotherapy and posthematopoietic stem cell transplant), and may have roles in immune reconstitution or enhancement of immunotherapy. We report here on the toxicity and biological activity of recombinant human IL-7 (rhIL-7) in humans.

DESIGN

Subjects with incurable malignancy received rhIL-7 subcutaneously every other day for 2 weeks in a phase I interpatient dose escalation study (3, 10, 30, and 60 microg/kg/dose). The objectives were safety and dose-limiting toxicity determination, identification of a range of biologically active doses, and characterization of biological and, possibly, antitumor effects.

RESULTS

Mild to moderate constitutional symptoms, reversible spleen and lymph node enlargement, and marked increase in peripheral CD3(+), CD4(+), and CD8(+) lymphocytes were seen in a dose-dependent and age-independent manner in all subjects receiving >or=10 microg/kg/dose, resulting in a rejuvenated circulating T-cell profile, resembling that seen earlier in life. In some subjects, rhIL-7 induced in the bone marrow a marked, transient polyclonal proliferation of pre-B cells showing a spectrum of maturation as well as an increase in circulating transitional B cells.

CONCLUSION

This study shows the potent biological activity of rhIL-7 in humans over a well-tolerated dose range and allows further exploration of its possible therapeutic applications.

A validated assay to measure soluble IL-7 receptor shows minimal impact of IL-7 treatment

IL-7 is a crucial cytokine for T cell hematopoiesis and peripheral homeostasis which by signaling through its receptor alpha chain (CD127) is essential for inducing T cell proliferation and survival. Since the specific CD127 alpha chain is found in a soluble state (sCD127) and at a high level in plasma (ng/mL), it is important to develop a sensitive and reliable assay in order to investigate the potential role of this receptor in the regulation of IL-7 physiologic, physipathologic and therapeutic effects. We here report a fully validated method to measure sCD127 in human and simian plasma using a method based on ELISA MSD technology. We demonstrate that sCD127 is detectable at various levels in the plasma of healthy humans as well as in that of healthy Rhesus and Cynomolgus macaques (106.72, 205.26 and 366.95 ng/mL respectively). Moreover, as opposed to the sCD25/IL-2 tandem, we demonstrate that IL-7 treatment has no impact on sCD127 plasma concentration in patients infected by HIV.

Increased numbers of IL-7 receptor molecules on CD4+CD25-CD107a+ T-cells in patients with autoimmune diseases affecting the central nervous system

Background

High content immune profiling in peripheral blood may reflect immune aberrations associated with inflammation in multiple sclerosis (MS) and other autoimmune diseases affecting the central nervous system.

Methods and Findings

Peripheral blood mononuclear cells from 46 patients with multiple sclerosis (MS), 9 patients diagnosed with relapsing remitting MS (RRMS), 13 with secondary progressive multiple sclerosis (SPMS), 9 with other neurological diseases (OND) and well as 15 healthy donors (HD) were analyzed by 12 color flow cytometry (TCRαβ, TCRγδ, CD4, CD8α, CD8β, CD45RA, CCR7, CD27, CD28, CD107a, CD127, CD14) in a cross-sectional study to identify variables significantly different between controls (HD) and patients (OND, RRMS, SPMS). We analyzed 187 individual immune cell subsets (percentages) and the density of the IL-7 receptor alpha chain (CD127) on 59 individual immune phenotypes using a monoclonal anti-IL-7R antibody (clone R34.34) coupled to a single APC molecule in combination with an APC-bead array. A non-parametric analysis of variance (Kruskal-Wallis test) was conducted in order to test for differences among the groups in each of the variables. To correct for the multiplicity problem, the FDR correction was applied on the p-values. We identified 19 variables for immune cell subsets (percentages) which allowed to segregate healthy individuals and individuals with CNS disorders. We did not observe differences in the relative percentage of IL-7R-positive immune cells in PBMCs. In contrast, we identified significant differences in IL-7 density, measured on a single cell level, in 2/59 variables: increased numbers of CD127 molecules on TCRαβ+CD4+CD25 (intermed) T-cells and on TCRαβ+CD4+CD25−CD107a+ T-cells (mean: 28376 Il-7R binding sites on cells from HD, 48515 in patients with RRMS, 38195 in patients with SPMS and 33692 IL-7 receptor binding sites on cells from patients with OND).

Conclusion

These data show that immunophenotyping represents a powerful tool to differentiate healthy individuals from individuals suffering from neurological diseases and that the number of IL-7 receptor molecules on differentiated TCRαβ+CD4+CD25−CD107a+ T-cells, but not the percentage of IL-7R-positive cells, segregates healthy individuals from patients with neurological disorders.

Modulating T-cell homeostasis with IL-7: preclinical and clinical studies

Interleukin-7 (IL-7) is required for the development and survival of T cells and plays a critical role in modulating T-cell homeostasis. This review will address current understanding of IL-7 biology, review recent clinical experiences and discuss potential future clinical applications of IL-7, or IL-7 blockade, in the setting of disease.

Rejuvenation of the aging T cell compartment

The elderly face significant risk for susceptibility to infection and cancer because of declining immune function. Various agents used in the setting of bone marrow transplantation and aging studies represent promising approaches to combating T cell defects in the aging population. Preclinical and clinical studies on the T cell reconstitution effects of sex steroid ablation, keratinocyte growth factor, the growth hormone pathway, and the cytokines interleukin-7, interleukin-12, and interleukin-15 indicate that these strategies may be used to alleviate the effects of T cell deficiencies in the elderly.

Thymic involution and immune reconstitution

Chronic thymus involution associated with aging results in less efficient T-cell development and decreased emigration of naïve T cells to the periphery. Thymic decline in the aged is linked to increased morbidity and mortality in a wide range of clinical settings. Negative consequences of these effects on global health make it of paramount importance to understand the mechanisms driving thymic involution and homeostatic processes across the lifespan. There is growing evidence that thymus tissue is plastic and that the involution process might be therapeutically halted or reversed. We present here progress on the exploitation of thymosuppressive and thymostimulatory pathways using factors such as keratinocyte growth factor, interleukin 7 or sex steroid ablation for therapeutic thymus restoration and peripheral immune reconstitution in adults.

Enhanced T cell recovery in HIV-1-infected adults through IL-7 treatment

HIV infection results in CD4+ T cell deficiency, but efficient combination antiretroviral therapy (c-ART) restores T cells and decreases morbidity and mortality. However, immune restoration by c-ART remains variable, and prolonged T cell deficiency remains in a substantial proportion of patients. In a prospective open-label phase I/IIa trial, we evaluated the safety and efficacy of administration of the T cell regulator IL-7. The trial included 13 c-ART-treated HIV-infected patients whose CD4+ cell counts were between 100 and 400 cells/microl and plasma HIV RNA levels were less than 50 copies/ml. Patients received a total of 8 subcutaneous injections of 2 different doses of recombinant human IL-7 (rhIL-7; 3 or 10 microg/kg) 3 times per week over a 16-day period. rhIL-7 was well tolerated and induced a sustained increase of naive and central memory CD4+ and CD8+ T cells. In the highest dose group, 4 patients experienced transient increases in viral replication. However, functional assays showed that the expanded T cells responded to HIV antigen by producing IFN-gamma and/or IL-2. In conclusion, in lymphopenic HIV-infected patients, rhIL-7 therapy induced substantial functional and quantitative changes in T cells for 48 weeks. Therefore, patients may benefit from intermittent therapy with IL-7 in combination with c-ART.

T lymphocyte maturation is impaired in healthy young individuals carrying trisomy 21 (Down syndrome)

Cytokine production, immune activation, T lymphocytes maturation, and serum IL-7 concentration were examined in 24 youngsters with Down syndrome and no acquired diseases (healthy Down syndrome [12 prepubertal, 13 pubertal]) and 42 age- and gender-matched controls (20 prepubertal, 22 pubertal). Results showed that a complex immune and impairment is present in healthy individuals with Down syndrome in whom interferon gamma, interleukin (IL) IL-10 production, as well as serum IL-7 concentrations and activation markers-bearing T lymphocytes were significantly augmented. Additionally, a complex skewing of post-thymic lymphocyte maturation pathways was observed in patients: significant reduction of CD4+ and CD8+ naive (RA+CCR7+) lymphocytes, significant increase of CD4+ and CD8+ central memory (RA-CCR7+), and terminally differentiated (TD) (RA+CCR7-) lymphocytes.

Clonal expansions and loss of receptor diversity in the naive CD8 T cell repertoire of aged mice

There are well-characterized age-related changes in the peripheral repertoire of CD8 T cells characterized by reductions in the ratio of naive:memory T cells and the development of large clonal expansions in the memory pool. In addition, the TCR repertoire of naive T cells is reduced with aging. Because a diverse repertoire of naive T cells is essential for a vigorous response to new infections and vaccinations, there is much interest in understanding the mechanisms responsible for declining repertoire diversity. It has been proposed that one reason for declining repertoire diversity in the naive T cell pool is an increasing dependence on homeostatic proliferation in the absence of new thymic emigrants for maintenance of the naive peripheral pool. In this study, we have analyzed the naive CD8 T cell repertoire in young and aged mice by DNA spectratype and sequence analysis. Our data show that naive T cells from aged mice have perturbed spectratype profiles compared with the normally Gaussian spectratype profiles characteristic of naive CD8 T cells from young mice. In addition, DNA sequence analysis formally demonstrated a loss of diversity associated with skewed spectratype profiles. Unexpectedly, we found multiple repeats of the same sequence in naive T cells from aged but not young mice, consistent with clonal expansions previously described only in the memory T cell pool. Clonal expansions among naive T cells suggests dysregulation in the normal homeostatic proliferative mechanisms that operate in young mice to maintain diversity in the naive T cell repertoire.

Immune deficits in allogeneic hematopoietic stem cell transplant (HSCT) recipients

Immune deficits account for the high frequency of life threatening bacterial, viral, and fungal opportunistic infections seen in allogeneic HSCT recipients. Despite advances in infectious disease management, the integrity of host defenses remains the mainstay of defense. The intensity of the preparative regimen, degree of HLA matching, source of stem cells (marrow, blood, or cord), extent of T-cell depletion, and immunosuppressive therapy are some of the factors that impact the kinetics, characteristics, and quality of immune reconstitution. Graft-versus-host disease and its prophylaxis or treatment produce a host environment that is particularly vulnerable to infections. Mucosal disruption and prolonged severe neutropenia usually confine their impact to the early course of transplant. After initial engraftment, HSCT recipients remain at great risk for opportunistic infections and this is related to prolonged and severe T-lymphocyte dysfunction of a complex multifactorial nature. B cell dysfunction is less problematic clinically, but includes deficiencies of immunoglobulin subclasses and impaired ability to mount a vaccine response. Advances in understanding of these immune deficits have resulted in successful strategies including revaccination, growth factors, thymic protection, and adoptive cellular therapy with antigen-specific cells.

Interleukin 7 signaling in dendritic cells regulates the homeostatic proliferation and niche size of CD4+ T cells

Interleukin 7 (IL-7) and T cell receptor (TCR) signals have been proposed to be the primary drivers of homeostatic T cell proliferation. However, it is not known why CD4⁺ T cells undergo less efficient homeostatic proliferation than CD8⁺ T cells. Here we showed that systemic IL-7 concentrations rise during lymphopenia due to diminished IL-7 utilization, but that IL-7 signaling on IL-7Rα⁺ dendritic cells (DCs) in lymphopenic settings paradoxically diminishes CD4⁺ T cell homeostatic proliferation. This effect is mediated, at least in part, by IL-7-mediated downregulation of MHC class II expression on IL-7Rα⁺ DCs. These results implicate IL-7Rα⁺ DCs as regulators of the peripheral CD4⁺ T cell niche, and indicate that IL-7 signals in DCs prevent uncontrolled CD4⁺ T cell expansion in vivo.

Cytokines as Adjuvants for Vaccine and Cellular Therapies for Cancer

PROBLEM STATEMENT: The development of a potent vaccine that can help treat tumors resistant to conventional cytotoxic therapies remains elusive. While part of the problem may be that trials have focused on patients with bulky residual disease, the desire to maximize responses to the vaccine remains. APPROACH: The gamma(c) family of cytokines offer a unique opportunity to support the expansion and effector potential of vaccine-responding T-cells, as well as stimulate other effectors, such as natural killer (NK) cells, to become activated. RESULTS: Combining vaccines with cytokines seems logical but can bring unwanted toxicity, as has been observed with interleukin (IL)-2. In addition, the nonspecific activation or expansion of unwanted cell subsets, such as regulatory T-cells, can contribute to global immunosuppression and limit vaccine responses. The development of IL-7 and IL-21 for the clinic offers the promise of enhancing anti-tumor responses but with far less systemic toxicity and no expansion of regulatory T cells. Preclinical studies demonstrate that IL-15 could also improve T-cell, and especially NK-cell, responses as well. CONCLUSIONS/RECOMMENDATIONS: Future work should expand the use of vaccines with IL-7, IL-21 and hopefully IL-15 in high-risk patients, and consider treatment while in a state of minimal residual disease to maximize benefit. Identifying tumors that can signal through gamma(c) cytokines will also be essential so that induction of relapse will be avoided.

Immune reconstitution and implications for immunotherapy following haematopoietic stem cell transplantation

Recovery of a fully functional immune system is a slow and often incomplete process following allogeneic stem cell transplantation. While innate immunity reconstitutes quickly, adaptive B- and especially T-cell lymphopoeisis may be compromised for years following transplantation. In large part, these immune system deficits are due to the decrease, or even absence, of thymopoiesis following transplantation. Thereby, T-cell reconstitution initially relies upon expansion of mature donor T cells; a proliferation driven by high cytokine levels and the presence of allo-reactive antigens. This peripheral mechanism of T-cell generation may have important clinical consequences. By expanding tumouricidal T cells, it may provide a venue to enhance T-cellular immunotherapy following transplantation. Alternatively, decreased thymic function may impair long-term anti-tumour immunity and increase the likelihood of graft-versus-host disease.

IL-7 sustains CD31 expression in human naive CD4+ T cells and preferentially expands the CD31+ subset in a PI3K-dependent manner

The CD31(+) subset of human naive CD4(+) T cells is thought to contain the population of cells that have recently emigrated from the thymus, while their CD31(-) counterparts have been proposed to originate from CD31(+) cells after homeostatic cell division. Naive T-cell maintenance is known to involve homeostatic cytokines such as interleukin-7 (IL-7). It remains to be investigated what role this cytokine has in the homeostasis of naive CD4(+) T-cell subsets defined by CD31 expression. We provide evidence that IL-7 exerts a preferential proliferative effect on CD31(+) naive CD4(+) T cells from adult peripheral blood compared with the CD31(-) subset. IL-7-driven proliferation did not result in loss of CD31 expression, suggesting that CD31(+) naive CD4(+) T cells can undergo cytokine-driven homeostatic proliferation while preserving CD31. Furthermore, IL-7 sustained or increased CD31 expression even in nonproliferating cells. Both proliferation and CD31 maintenance were dependent on the activation of phosphoinositide 3-kinase (PI3K) signaling. Taken together, our data suggest that during adulthood CD31(+) naive CD4(+) T cells are maintained by IL-7 and that IL-7-based therapies may exert a preferential effect on this population.

Association of serum interleukin-7 levels with the development of acute graft-versus-host disease

PURPOSE

Morbidity from acute graft-versus-host disease (GVHD) limits the success of allogeneic hematopoietic stem-cell transplantation (HSCT) to treat malignancy. Interleukin-7 (IL-7), the principal homeostatic cytokine for T cells, is required for acute GVHD in murine models. In contrast to inflammatory cytokines (eg, IL-2, tumor necrosis factor alpha), IL-7 has not been studied extensively in the clinical transplant setting relative to its relationship with acute GVHD.

PATIENTS AND METHODS

We evaluated the association of serum IL-7 levels with acute GVHD in 31 patients who were uniformly treated in a prospective clinical trial with reduced-intensity allogeneic HSCT from human leukocyte antigen-identical siblings. GVHD prophylaxis consisted of cyclosporine and methotrexate. Serum IL-7 levels and lymphocyte populations were determined at enrollment, the day of transplantation before the allograft infusion, and at specified intervals through 12 months post-transplantation.

RESULTS

As expected, IL-7 levels were inversely correlated with T-cell populations (P < .00001). Acute GVHD was significantly associated with higher IL-7 levels at day +7 (P = .01) and day +14 (P = .00003) post-transplantation as well as with the allograft CD34(+) cell dose (P = .01). IL-7 levels at day +14 also correlated with the severity of acute GVHD (P < .0001). In logistic regression models, these factors were highly sensitive (up to 86%) and specific (100%) for classifying whether patients developed acute GVHD.

CONCLUSION

These data support preclinical observations that IL-7 plays a critical role in inducing acute GVHD and provide a rational basis for novel approaches to prevent and treat acute GVHD through modulation of the IL-7 pathway.