Neonatal CD4+ CD45RA+ T cells: precursors of adult CD4+ CD45RA+ T cells?

Human umbilical cord blood progenitor cells are attracted to infarcted myocardium and significantly reduce myocardial infarction size

We are investigating the effects of human umbilical cord blood mononuclear progenitor cells (HUCBC) for the treatment of acute myocardial infarction because human cord blood is a readily available and an abundant source of primitive cells that may be beneficial in myocardial repair. However, there is currently no scientific consensus on precisely when to inject stem/progenitor cells for the optimal treatment of acute myocardial infarction. We used an in vitro assay to determine the attraction of infarcted rat myocardium at 1, 2, 2.5, 3, 6, 12, 24, 48, and 96 h after left anterior descending coronary artery (LAD) occlusion from 45 rats for HUCBC in order to determine the optimal time to transplant HUCBC after myocardial infarction. Our assay is based on the migration of fluorescent DAPI-labeled HUCBC from wells in an upper chamber of a modified Boyden apparatus through a semiporous polycarbonate membrane into wells in a lower chamber that contain either normal or infarcted myocardium. DAPI-labeled HUCBC (100,000) were placed in each of the separate wells above the membrane that corresponded to normal or infarct homogenate in the lower wells. The greatest HUCBC migration to infarcted myocardium occurred at 2 h and 24 h after LAD occlusion in comparison with normal controls. A total of 76,331 +/- 3384 HUCBC migrated to infarcted myocardium at 2 h and 69,911 +/- 2732 at 24 h after LAD occlusion (both p < 0.001) and significantly exceeded HUCBC migration to normal heart homogenate. The HUCBC migration remained greatest at 2 and 24 h after LAD occlusion when the number of migrated cells was adjusted for the size of each myocardial infarction. Injection of 106 HUCBC in saline into infarcted myocardium of non immunosuppressed rats within 2 h (n=10) or at 24 h (n=5) after LAD occlusion resulted in infarction sizes 1 month later of 6.4 +/- 0.01% and 8.4 +/- 0.02% of the total left ventricular muscle area, respectively, in comparison with infarction sizes of 24.5 +/- 0.02% (n=10) in infarcted rat hearts treated with only saline (p < 0.005). Acute myocardial infarction in rats treated with only saline increased the myocardial concentration of tumor necrosis factor-alpha (TNF-alpha) from 6.9 +/- 0.8% to 51.3 +/- 4.6%, monocyte/macrophage chemoattractant protein (MCP-1) from 10.5 +/- 1.1% to 39.2 +/- 2.0%, monocyte inflammatory protein (MIP) from 10.6 +/- 1.6% to 23.1 +/- 1.5%, and interferon-gamma (INF-gamma) from 8.9 +/- 0.3% to 25.0 +/- 1.7% between 2 and 12 h after coronary occlusion in comparison with known controls (all p < 0.001). In contrast, the myocardial concentrations of these cytokines in rat hearts treated with HUCBC did not significantly change from the controls at 2, 6, 12, and 24 h after coronary occlusion. The present investigations suggest that infarcted myocardium significantly attracts HUCBC, that HUCBC can substantially reduce myocardial infarction size, and that HUCBC can limit the expression of TNF-alpha, MCP-1, MIP, and INF-gamma in acutely infarcted myocardium.

Rapid conversion of naive to effector T cell function counteracts diminished primary human newborn T cell responses

The reduced incidence of graft versus host disease following the use of human cord blood as a source of stem cells for bone marrow reconstitution challenges our understanding of the immunocompetence of newborn T cells. Newborn CD4+ T cells express mainly the CD45RA phenotype and have been considered to respond comparably to adult CD4+ T cells exhibiting the CD45RA phenotype. We compared the in vitro kinetics of phenotypic conversion of newborn and adult CD4+CD45RA+ T cells to CD4+CD45RO+ T cells. The cytokine profile and B cell helper activity of the converted CD4+CD45RO+ T cell population were also determined. Newborn CD4+CD45RA+ T cells were converted to CD4+CD45RO+ with significantly faster time kinetics than adult CD4+CD45RA+ T cells, following either phytohaemagglutinin (PHA) or anti-CD2 activation. Freshly purified newborn naive T cells did not produce IL-2, IL-4 or interferon-gamma (IFN-gamma) following stimulation, whereas adult naive T cells secreted IL-2 and adult-derived CD4+CD45RO+ T cells secreted all three cytokines under the same stimulatory conditions. However, newborn and adult CD4+CD45RA+ T cells, following primary stimulation and maturation in vitro, acquired the ability to secrete a Th1-type cytokine profile of IL-2 and IFN-gamma after secondary stimulation. Newborn CD4+ naive T cells that acquired the CD45RO phenotype in vitro also gained B cell helper activity equivalent to that of adult in vitro matured CD4+ naive T cells. These findings suggest that newborn and adult CD4+CD45RA+ T cell subsets are differentially responsive to various stimuli. They show that newborn CD4+CD45RA+ naive T cells can transform more quickly than their adult counterparts into functionally equivalent CD4+CD45RO+ T cells, a process that may be important to counteract the immature immune environment which exists in the newborn.

IL-7 promotes the survival and maturation but not differentiation of human post-thymic CD4+ T cells

This study examines the influence of IL-7 on post-thymic CD4+ T cells using cord blood as a model system. Survival of naive cord blood T cells in the presence of IL-7 alone was significantly prolonged by up-regulating bcl-2, thereby preventing apoptosis while maintaining maximal cell viability. Cultures without IL-7 showed high rates of apoptosis resulting in 50% cell death by day 5 of culture. Upon phorbol 12-myristate 13-acetate + ionomycin stimulation, accumulation of cytoplasmic IL-2 was similar to that observed in freshly isolated cells, but no IL-4- or IFN-gamma-positive cells were detected. IL-7 maintained the naive T cells in a quiescent state expressing the CD45RA antigen. A significant finding was the loss of CD38 antigen expression on the naive cord blood T cells to levels similar to that observed on adult naive T cells. In contrast to the reduced proliferative response of fresh cord blood T cells to anti-CD2 + CD28 stimulation, the proliferative response of IL-7-treated cells was similar to that of adult naive T cells. This study shows that as well as maintaining the naive T cell pool by enhancing cell survival and up-regulating bcl-2 expression, IL-7 also functions as a maturation factor for post-thymic naive T cells.

Post-Thymic Maturation of Migrating Human Thymic Single-Positive T Cells: Thymic CD1a− CD4+ T Cells Are More Susceptible to Anergy Induction by Toxic Shock Syndrome Toxin-1 than Cord Blood CD4+ T Cells

To determine whether human CD4+ T cells undergo post-thymic maturation, we compared the susceptibility to anergy induction in human thymic CD1a− CD4+ single-positive (CD4+), cord blood (CB) CD4+, and adult peripheral blood (APB) CD4+ T cells by stimulation with toxic shock syndrome toxin-1 (TSST-1). Most TSST-1-induced T cell blasts derived from either T cell preparation expressed TCR Vβ2, which determines the potential reactivity to TSST-1. Most thymic CD4+ T cell blast preparations exhibited little or no production of IL-2 and IL-4 after restimulation with TSST-1 and only marginal responses after stimulation with rIL-2 or a combination of PMA and calcium ionophore, while the APB CD4+ T cell blasts showed high responses to these stimuli. The responses of CB CD4+ T cell blasts to these stimuli varied, ranging from minimal to relatively high. Studies of DNA fragmentation showed that there was no significant cell death of thymic CD4+ T cell blasts. Most thymic CD1a− CD4+ and CB CD4+ T cells were CD38 positive. APB CD4+ T cell blasts derived from the CD38+ fraction and from the CD38− fraction exhibited equally high responses to restimulation with TSST-1. These results indicate that thymic CD1a− CD4+ and CB CD4+ T cells are inherently highly susceptible to anergy induction by bacterial superantigens and that thymic CD1a− CD4+ T cells are less mature than CB CD4+ T cells, suggesting that post-thymic maturation in thymic T cells migrating to the periphery is required for acquisition of full reactivity to antigenic stimulation.

Linkage of protein kinase C-beta activation and intracellular interleukin-2 accumulation in human naive CD4 T cells

A critical role for protein kinase C (PKC) in signal transduction events has been well established. Moreover, studies of regulation in PKC levels suggest participation in mediating long-term cellular functions. Protein kinase C-beta (PKC-beta) has been reported to be involved in interleukin-2 (IL-2) synthesis in T lymphocytes. In this study, the role of PKC-beta in intracellular accumulation of IL-2 was investigated using specific inhibitors. Preincubation with two different PKC inhibitors, one specific for classical isotypes (alpha and beta I) Go6976, and one which inhibits both classical and non-classical isotypes, GF109203X, caused a complete block in cytoplasmic IL-2 accumulation when naive CD4 T cells were stimulated in the presence of CD2+CD28+phorbol myristate acetate (PMA). In contrast, preincubation with up to 1000 ng/ml of cyclosporin A (CsA) resulted in a reduction in the intracellular IL-2 detected, as observed by a decrease in the proportion of positive cells as well as a fall in the mean fluorescence intensity (MFI). CsA did not influence PKC-beta translocation. Flow cytometric assessments of PKC-beta and its isoforms beta I and beta II correlated with Western blotting analysis and these results were further supported by the use of PKC-beta-positive (HUT 78) and -negative (BW5147) T-cell lines. Using the specific inhibitors, Go6976 and GF109203X, the findings in this study suggest that activation and translocation of PKC-beta is critical for accumulation of intracellular IL-2. The influence of CsA in reducing but not blocking IL-2 synthesis is discussed. PMA-induced down-regulation of the CD4 antigen was observed in the presence of Go6976 and but not GF109203X, suggesting regulation by non-classical PKC isoforms.

Cord blood CD4+ CD45RA+ T cells achieve a lower magnitude of activation when compared with their adult counterparts

Highly purified CD4+ CD45RA+ cells from cord blood and peripheral blood from healthy adults were studied. The levels of expression of the CD2, CD3, CD4 and CD28 antigens were similar; however, CD45 and CD45RA antigen expression were slightly lower in cord cells. The reduced expression of the CD45RA antigen on cord CD4+ T cells was confirmed in whole blood. Functional assessment revealed deficiencies in cord CD4+ CD45RA+ T cells. Interleukin-2 (IL-2) production in response to specific triggering via CD2 monoclonal antibody (mAb) alone, or CD2 mAb in combination with CD28 mAb showed marked underproduction (about 10% of adult production). When CD25 expression was examined, it was observed that the proportion of activated CD4+ CD45RA+ T cells in cord blood was lower than in adult (about 20% of adult expression). Proliferation to CD2 mAbs or CD2 + 28 mAbs of cord blood native cells was similarly depressed. Investigation of IL-2 mRNA expression under these stimulatory conditions paralleled the results observed for CD25 expression, IL-2 production and proliferation. When phorbol 12-myristate 13-acetate (PMA) was added to the cells triggered with CD2 + 28mAbs, the responses examined were enhanced in both cord and adult blood with no significant differences between the groups. These findings suggest that under identical conditions of stimulation, purified cord blood CD4+ CD45RA+ T cells do not acquire similar activation status as their adult counterparts. These findings may help in understanding the reduced graft-versus-host disease (GVHD) observed in cord blood stem cell transplantation.

Stimulation of blood mononuclear cells of atopic children with the relevant allergen induces the release of eosinophil chemotaxins such as IL-3, IL-5, and GM-CSF

Peripheral blood mononuclear cells (PBMC) from 10 atopic asthmatic children (atopics), sensitized to Dermatophagoides pteronyssinus (Dp), and from 5 nonatopic healthy children (controls) were stimulated with Dp extract or with birch extract (Be). After 6 days we tested the supernatant's (Sn) chemotactic activity toward purified blood eosinbnophils and T-lymphocyte proliferation. Dp induced a statistically significant T-cell proliferation from atopics as compared to controls (p < 0.05), which correlated with the levels of eosinophil chemotactic activity in the Sn (r = 0.713; p < 0.05). Measurable levels of IL-3, IL-5, and GM-CSF were demonstrated in the Sn of Dp-stimulated PBMC from atopics, while eosinophil locomotion toward different concentrations of recombinant human (rh) IL-3, rhIL-5, and rhGM-CSF confirmed that these cytokines were able to stimulate eosinophil chemotaxis in a close concentration range. Preincubation of different concentrations of the same Sn with blocking antisera demonstrated that anti-human (ah) IL-3, ahIL-5, and ahGM-CSF effectively decreased eosinophil chemotaxis (p < 0.05; each comparison). Thus PBMC activation with the relevant allergen induces the release by T cells with a Th2 phenotype of chemotactic factors for eosinophils.

Antigen-independent responsiveness to interleukin-4 demonstrates differential regulation of newborn human T cells

The low incidence of graft-versus-host disease following clinical use of umbilical cord blood compared to adult bone marrow as a source of stem cells for bone marrow reconstitution, leads to questions concerning the level of immunocompetence of newborn T cells. The maturation and functional status of newborn CD4+ T cells, which are almost exclusively CD45RA+ naive T cells, compared with their adult phenotypic counterparts, is poorly understood. We examined the proliferative response to mitogens and cytokines of CD4/CD45RA+ T cells from adults and newborns, with and without accessory cells. Newborn CD4/CD45RA+ T cells demonstrated a distinct proliferative response profile which was determined by the number of accessory cells present in co-cultures with various stimuli. Newborn CD4/CD45RA+ T cells were particularly responsive to interleukin (IL)-4, IL-4 plus anti-CD2 monoclonal antibodies (mAb) and IL-4 plus phytohemagglutinin (PHA), whereas adult CD4/CD45RA+ T cells were unresponsive under similar conditions. The mitogenic responses of newborn and adult CD4/CD45RA+ T cells to PHA and anti-CD2 mAb, which were equivalent, were directly proportional to the number of accessory cells present, whereas the responsiveness to cytokines was inversely proportional to the number of co-cultured accessory cells. Anti-CD2 responses were much more sensitive to low numbers of accessory cells than PHA. The particular sensitivity of newborn CD4/CD45RA+ T cells to IL-4 represents an antigen-independent T cell activation response which could help promote a Th2 immune response resulting in the newborn.

Reduced primary antigen-specific T-cell precursor frequencies in neonates is associated with deficient interleukin-2 production

Clinical evidence has indicated that the neonatal cell-mediated immune response to primary infection is delayed when compared to that of adults with the same primary infection. The mechanisms regulating the development of antigen-specific T-cell immunity in neonates remain to be elucidated. We examined the primary immune response to the non-recall antigen, keyhole limpet haemocyanin (KLH) in adults and neonates in vitro. We report here that conventional bulk culture methods show reduced proliferative responses in neonates although statistical significance was not achieved. Using limiting dilution analysis, the frequencies of KLH-specific T lymphocytes were 10-100-fold lower in neonates when compared to adults. Interleukin-2 (IL-2) production was significantly lower in the supernatants of neonatal mononuclear cells (MNC) stimulated with KLH when compared to adults. Addition of exogenous IL-2 increased precursor frequencies twofold in both adult and newborn cultures. In contrast to the secreted IL-2 levels, IL-2 mRNA expression was higher in antigen-stimulated neonatal MNC preparations, even though proliferation was lower. These observations indicate differential in vitro responsiveness in neonates and adults to primary antigenic challenge. Since no IL-2 was detected in cell lysates, the presence of high levels of IL-2 mRNA and low IL-2 production suggests inability by neonatal MNC to translate IL-2. This deficiency in IL-2 production may explain the reduced precursor frequencies, suggesting failure to recruit T lymphocytes in order to expand the KLH-specific T-cell response. These observations are important for the understanding of the development of primary immune responses and immunological maturation in neonates.

Signalling via CD28 of human naive neonatal T lymphocytes

Accessory molecules play a crucial role in the development of the T cell response to antigenic challenge. We have examined the role of CD28 in modulating the 'naive' neonatal T cell response to anti-CD2-mediated activation. To compare the role of CD28, neonatal and adult T cells were stimulated with a pair of mitogenic anti-CD2 antibodies in the presence or absence of anti-CD28 MoAb. With anti-CD2 alone, neonatal T cells proliferated slightly but produced no detectable IL-2, whereas adult T cells proliferated vigorously, with significant IL-2 production. Costimulation with anti-CD28 MoAb greatly enhanced the proliferative response of neonatal T cells to levels equivalent to those of adult T cells, whereas adult T cells showed only slight increases. Although IL-2 secretion was increased in the presence of anti-CD28 MoAb, neonatal T cell IL-2 production remained lower than in adults. In contrast, enhancement of IL-2 mRNA expression in neonates was similar to adult levels. Anti-CD28 MoAb costimulation increased NF kappa B levels in neonates, albeit to levels lower than that of adults. The cellular mechanism governing the diminished proliferative response of neonatal T lymphocytes to anti-CD2 may therefore be due to decreased NF kappa B induction, reduced IL-2 mRNA expression and deficient IL-2 production. Although anti-CD28 MoAb costimulation enhances all of the above signals, NF kappa B and IL-2 levels remain lower than in adults, suggesting the need for further activation requirements in the neonate.

Relationships between maternal malaria and malarial immune responses in mothers and neonates

Immune responses of 97 Gambian women and their neonates were studied. New methods distinguished between active and previous placental malaria, were used to examine relationships between maternal malaria and neonatal immune responses. Many placentas (61%) had active or previous malarial infection. Maternal and cord malarial IgG levels correlated (P < 0.001). Malarial IgG was raised in cord blood in active placental malaria; IgM was not detected. Mean lymphoproliferation and the proportion of responders to soluble P. falciparum antigens (F32) and conserved regions of p190 expressed on trophozoites and schizonts (190L and 190N) were higher in neonates than mothers. There was no clear relationship between maternal malaria and neonatal mean lymphoproliferation to malarial antigens, although fewer neonates responded when mothers were actively infected. Matched maternal and neonatal lymphoproliferation responses did not correlate. However, first born neonatal lymphoproliferation to PPD and malarial antigens appeared lower than other neonates, in agreement with lower lymphoproliferation in primigravidae compared with multigravidae. Also in common with mothers, autologous plasma suppressed neonatal lymphoproliferation to PPD and malarial antigens, suggesting common immunoregulation. Higher cortisol or other circulating factors in first pregnancies may be implicated. The relevance of cell-mediated malarial immune responses detected at birth remains to be established.

Comparison of cord blood and adult blood lymphocyte normal ranges: a possible explanation for decreased severity of graft versus host disease after cord blood transplantation

Lymphocyte subpopulations in cord blood (CB; collected at birth from full-term babies) were compared with that of adult blood (AB) and found to contain significantly different numbers and percentages of lymphocyte subpopulations. The absolute lymphocyte count was greater in CB (4.8 +/- 1.1 x 10(9)/L) than in AB (1.69 +/- 0.38 x 10(9)/L), with CB having significantly higher absolute numbers of lymphocyte subsets even though CB percentages were significantly lower. Significant differences in percentages were found between cord and adult T cells (CB 58% vs AB 74%), NK cells (CB 19% vs AB 7%) and their subsets. CD38, a marker of activation and immaturity, was present on virtually all cord T cells and approximately half the adult T cells. CD45RA, a marker considered to define unprimed or naive cells, was expressed on 82% of cord lymphocytes as compared with 48% in AB. CD45RO was expressed on 16% of CB lymphocytes and 49% of AB lymphocytes. Cord blood contains a higher percentage and total number of immature and immunologically naive lymphocytes than AB.

Interleukin-1 augments the diminished interleukin-2 mRNA expression and proliferative response of neonatal T lymphocytes to anti-CD2 antibodies

Expression of IL-2 mRNA by unstimulated and stimulated purified T cells and mononuclear cells from adult and cord blood was investigated in an attempt to better understand the underlying defective neonatal host immune defense system. Using RNA dot-blot analysis, IL-2 mRNA expression in anti-CD2-stimulated neonatal T cells revealed significantly reduced levels when compared to adult T cells (P < 0.01). Purified neonatal T cells also showed a significantly reduced proliferative response to anti-CD2 antibodies (P < 0.01). Addition of IL-1 beta enhanced the hyporesponsiveness of neonatal T cells at both the level of proliferation and IL-2 mRNA expression. Unseparated mononuclear cells from adult and cord blood revealed similar IL-2 mRNA levels and proliferation when activated by anti-CD2 stimulation. The reduced IL-2 mRNA expression observed in neonatal T cells may explain, in part, the difference in host defense between the newborn and adult during states of increased demand such as infection.

Maternal infections influence infection susceptibility in childhood

The proposed hypothesis suggests that the types of infections commonly experienced in pregnancy and in childhood are linked. The suggestion is made that maternal infections leave an impression on the developing fetal immune system and modulate future responsiveness to infection and/or vaccination challenge. A number of factors are explored which may influence this process, namely immunoregulation in pregnancy and infection type, gestation, maturity of the fetal immune system, and parity.