Sustained expression of CD154 (CD40L) and proinflammatory cytokine production by alloantigen-stimulated umbilical cord blood T cells

Immunological considerations regarding parental concerns on pediatric immunizations

Despite the fundamental role of vaccines in the decline of infant mortality, parents may decide to decline vaccination for their own children. Many factors may influence this decision, such as the belief that the infant immune system is weakened by vaccines, and concerns have been raised about the number of vaccines and the early age at which they are administered. Studies focused on the infant immune system and its reaction to immunizations, summarized in this review, show that vaccines can overcome those suboptimal features of infant immune system that render them more at risk of infections and of their severe manifestations. In addition, many vaccines have been shown to improve heterologous innate and adaptive immunity resulting in lower mortality rates for fully vaccinated children. Thus, multiple vaccinations are necessary and not dangerous, as infants can respond to several antigens as well as when responding to single stimuli. Current immunization schedules have been developed and tested to avoid vaccine interference, improve benefits and reduce side effects compared to single administrations. The infant immune system is therefore capable, early after birth, of managing several antigenic challenges and exploits them to prompt its development.

The difference in immune response and IL-12p35 methylation between newborns and adults

Background

The immune system of newborn is generally depressed by impaired production of Th1-cell associated cytokines, which results in increased susceptibility to intracellular pathogens and poor response to vaccinations. For avoiding abortion, the maternal and fetal immune systems tend to Th2-cell polarizing cytokines. Besides, IL-12p35 is a determining factor of the bioactivity of IL-12, which has an important role in the Th1 response. Recently methylated DNA is known to associate to inhibit transcription. Therefore, we explored the methylation status of CpG sites upstream of the coding sequence of the IL-12p35 gene to determine whether neonatal peripheral blood mononuclear cell (PBMC) synthesis lower level of IL-12 is related to methylated DNA.

Results

PBMCs from adults expressed higher levels of IL-12p40 (p = 0.303) and IL-12p70 (p = 0.045) and had a strong ability to produce IL-12p35 mRNA (p = 0.01). However, there was no difference in the methylation status of CpG sites in the promoter of IL-12p35 between adults and newborns.

Conclusions

We found that PBMC synthesis of bioactive IL-12p70 was significantly impaired in the neonatal period, potentially though a reduction in IL-12p35 production. The reeducation in IL-12p35 production might not be due to methylation of the promoter gene. But, the impairment of IL-12p35 expression during the neonatal period might be caused by other epigenetic regulation occurs in the chromatin level.

Perspectives on immunomodulation early in life

The immune system early in life is characterized by immature activation and function of immune cells and a preponderance of Th2 cytokines. Together with other factors such as genetics and epigenetics, these immature immune responses might prone newborns susceptible to severe infections as well as allergic diseases. Immunomodulation therapy may have potential as therapeutic strategy against those disorders and might have implication in early-life interventions in the future. In this review, we will focus on two immunomodulatory substance classes, Toll-like receptor (TLR) ligands and sphingolipids, which are the focus of extensive research to date. Both TLRs and sphingolipid receptors have a very distinct distribution pattern and function on immune cells. Therefore, they can potentially modulate and balance immune responses, which might be in particular beneficial for the immaturity of the immune response early in life.

Decreased expression of tumor necrosis factor family receptors involved in humoral immune responses in preterm neonates

Neonates have an increased rate of infection with encapsulated bacteria compared with older children and adults because of diminished antibody responses to T-independent (TI) antigens such as bacterial polysaccharides. Because the interactions of tumor necrosis factor (TNF) family ligands BAFF and APRIL with the TNF family receptors (TNFRs) TACI, BCMA, and BAFF-R are crucial to TI antibody responses, we measured the expression of these receptors on adult and cord blood-derived term and preterm neonatal B cells. Preterm neonatal B cells expressed less TACI, BCMA, and BAFF-R compared with adult B cells and had significantly less proliferation compared with adult B cells after stimulation with human recombinant BAFF and anti-IgM in an assay in which TACI-Fc fusion protein inhibits B-cell proliferation. In addition, neonatal dendritic cells had diminished expression of B7-1, B7-2, and CD40 compared with adult cells. Finally, neonatal B cells, particularly preterm B cells, exhibited markedly decreased production of IgG and IgA in response to CD40L and IL-10. Overall, this study shows that maturational delay in TNFR expression particularly by preterm neonatal B cells may interfere with effective antibody responses to TI antigens, cognate T- and B-cell interactions and normal isotype switching.

Preformed CD40 ligand exists in secretory lysosomes in effector and memory CD4+ T cells and is quickly expressed on the cell surface in an antigen-specific manner

CD40 ligand (CD40L) is an essential effector cytokine for macrophage activation, dendritic cell licensing, and T-cell-dependent antibody responses. Although CD40L is known to be made de novo following antigen recognition, several reports have described surface mobilization of preformed, intracellular CD40L in certain CD4(+) effector T cells. Here we show that rapid surface expression of preformed CD40L following antigen recognition is a general property of both effector and memory CD4(+) T cells, including in vitro and in vivo activated T-cell-receptor transgenic T cells, memory phenotype CD4(+) T cells from pathogen-free naive mice, and polyclonal virus-specific effector and memory T cells. Intracellular CD40L is stored in secretory lysosomes, and colocalizes more strongly with Fas ligand than with CTLA-4, two other molecules that are delivered to the cell surface following antigen recognition. Stimulated surface expression of preformed CD40L is found in memory CD4(+) T cells from CD40-deficient mice, indicating that it does not depend on CD40-induced internalization for delivery to the secretory compartment. We suggest that delivery of preformed CD40L to antigen-presenting cells (APCs) could enable antigen-specific activation of APCs in transient interactions that are too brief to permit de novo synthesis of CD40L.

Impaired allogeneic activation and T-helper 1 differentiation of human cord blood naive CD4 T cells

CD4 T cells, particularly those of the T-helper 1 (Th1) subset, are important effectors in alloimmune diseases, such as graft-versus-host disease, and in controlling infections with intracellular pathogens. Thus, it is plausible that impaired neonatal CD4 T-cell immunity might contribute to the low incidence of acute graft-versus-host disease after allogeneic transplantation of hematopoietic stem cells using cord blood (CB) compared with adult sources of hematopoietic stem cells. In support of this hypothesis, we found that CB naive CD4 T cells had reduced activation and impaired early Th1 differentiation compared with adult peripheral blood naive CD4 T cells after stimulation by allogeneic dendritic cells derived from adult monocytes. Early Th1 polarization was dependent on interleukin-12 and CD154, and CB CD4 T cell/dendritic cell co-cultures had impaired expression of both proteins. CB naive CD4 T cells had low basal levels of signal transduction and activation of transcription 4 messenger RNA and protein, and, after alloantigen stimulation, reduced interleukin-12-induced signal transduction and activation of transcription 4 tyrosine phosphorylation, compared with adult peripheral blood naive T cells. Lastly, FoxP3 protein expression, a marker for regulatory CD25(high) CD4 T cells, was lower for naive CD4 T cells of CB compared with those of adult peripheral blood, which argued against increased T-regulatory activity as a mechanism for the decreased Th1 differentiation of CB CD4 T cells. Together, these intrinsic limitations in T-cell activation and Th1 differentiation may impair the ability of T cells in CB and the neonate to respond to allogeneic or infectious challenges.

Plasmacytoid dendritic cells induce a distinct cytokine pattern in virus-specific CD4+ memory T cells that is modulated by CpG oligodeoxynucleotides

Inherent properties of dendritic cell (DC) subsets are important in the regulation of naïve T-cell differentiation (e.g. Th1 versus Th2 cells), whereas effector memory T cells are believed to produce a fixed cytokine repertoire independent of the type of antigen presenting cell. Here we show that two distinct human DC subsets, plasmacytoid DC (PDC) and myeloid CD11c+ DC, induced autologous mumps virus-specific memory CD4(+) T cells to produce markedly different cytokine patterns upon antigen stimulation. PDC stimulated the T cells to produce gamma-interferon (IFN-gamma) and interleukin-(IL)-10, whereas CD11c+ DC induced lower levels of IFN-gamma, virtually no IL-10, but significant levels of IL-5. Analysis of intracellular cytokine production showed simultaneous production of IL-10 and IFN-gamma in mumps-specific T cells activated by PDC, a cytokine pattern similar to that described for Th1-like regulatory cells. Introduction of CpG oligodeoxynucleotides in PDC/T-cell co-cultures had synergistic effect on virus-dependent IFN-gamma production, whereas the other cytokines remained unchanged. Together, our results show that the type of DC involved in reactivation of previously primed T cells may have significant impact on the resulting cytokine response and suggest that targeting of viral antigens and adjuvant to specific DC subsets should be considered in the design of therapeutic antiviral vaccines.

Primary alloproliferative TH1 response induced by immature plasmacytoid dendritic cells in collaboration with myeloid DCs

The role played by dendritic cell (DC) subsets in the immune response to alloantigens is not well defined. In vitro experiments have extensively shown that freshly isolated myeloid (M)DCs induce a strong T lymphocyte proliferation whereas plasmacytoid (P)DCs do not, unless activated by CD40 ligation. The aim of these studies was to explore whether the interplay among PDCs, MDCs and T cells modulates alloresponse. Freshly isolated MDCs and PDCs were merged in different proportions and used as antigen presenting cells (APCs) in mixed lymphocyte cultures (MLC). As described, isolated PDCs only induced a mild alloresponse, while MDCs were potent inducers of alloproliferation. Unexpectedly, when PDCs were merged with even low numbers of MDCs (down to 100 cells) and used as APCs, a potent Th1 cell proliferation was detected. Survival and maturation of PDCs was increased in these MLC conditions, which could partially explain the magnitude of the T-cell response. Interestingly, the proportion of IFNgamma-producing cells generated in such cultures was higher compared to MDC-stimulated cultures. These data suggest that the interaction between both DC subsets is determinant to generate a potent Th1 response, at least in an allogeneic situation, and may be relevant to the outcome of allogeneic stem cell transplantation.

Naive CD4+ Cells from Cord Blood Can Generate Competent Th Effector Cells

BACKGROUND

Umbilical cord blood (UCB) cells have been increasingly used as a source of hematopoietic stem cells for allogeneic transplantation. Previous reports suggest that the low risk of graft-versus-host disease in patients that received cord blood cells seems related to the distinctive nature of cord blood T cells.

METHODS

To analyze the maturation of CD4+CD45RA+ cord blood cells, we performed an in vitro differentiation assay to compare the generation of Th effector cells strictly from UCB and adult peripheral blood (APB) CD4+CD45RA+ cells.

RESULTS

During the maturation into effector cells, UCB and APB cells acquired a comparable activation level determined by the expression pattern of CD69, CD40L, OX40 and CD62L as well as PD1 and CTLA-4 molecules. Moreover, the expression of CD45RO isoform was induced in most activated effector cells from both UCB and APB. OKT3-restimulated effector cells generated from naive UCB expressed higher levels of CD25 coinciding with the secretion of higher amounts of IL-2. Effector cells from both origins consisted of heterogeneous populations with similar frequencies of Th1 and Th2 cytokine producing cells, secreting equivalent levels of IL-4, IL-5 and IFNgamma. Although, higher levels of IL-10 were detected in the cytokine mRNA profile and in the supernatants of OKT3-restimulated UCB effector cells, blocking endogenous IL-10 with anti-IL-10 mAbs enhanced significantly the proliferative response of UCB as well as APB effector cells (P < 0.05).

CONCLUSIONS

These results indicated that Th effector cells generated from naive UCB cells were intrinsically as competent as naive APB to respond to TCR-mediated stimulation. In addition, UCB effector cells produced higher IL-10 but its inhibitory effect on proliferation may be partially compensated by the higher production of IL-2 and enhanced expression of CD25.

Differential expression of the cytokine receptors for human interleukin (IL)-12 and IL-18 on lymphocytes of both CD45RA and CD45RO phenotype from tonsils, cord and adult peripheral blood

The objective of this study was to demonstrate the variable expression of cytokine receptors on naive versus memory human CD4+ T cell subpopulations in tonsillar tissue, cord blood and adult blood. We prove that the receptors for both interleukin (IL)-12 and IL-18 are expressed exclusively on memory T cells. This observation was seen not only on the CD45RO+ memory T cells but also on a significant percentage of the CD45RA+, CD62L-, CD27- and CCR7- populations. Furthermore, CD45RA+ CD62L+, CD27+ or CCR7+ CD4+ T cells that expressed IL-12Rbeta1 and IL-18Ralpha did not express CD31, a marker for recent thymic emigrants. We reveal that cord blood lymphocytes do not express IL-12Rbeta1 whereas IL-18Ralpha expression was detected at low levels. Importantly, the IL-12Rbeta2 signalling chain, which is absent in all resting T cells, was up-regulated in both CD45RA+ and CD45RO+ T cells as a result of stimulation with anti-CD3 and anti-CD28 in vitro. This observed up-regulation was, however, restricted to 80% of the total CD4+ population. Finally, a very small proportion of the CD4+ CD45RO+ tonsillar T cells expressed the IL-12 and IL-18 receptors, thereby establishing the differential expression of these receptors between peripheral and tonsillar memory T cell subpopulations.

Potential immaturity of the T-cell and antigen-presenting cell interaction in cord blood with particular emphasis on the CD40-CD40 ligand costimulatory pathway

There are reports of immaturity of the neonatal immune system, which may explain the low incidence of graft-versus-host-disease (GVHD) after cord blood transplantation. The CD40 ligand (CD40L)-CD40 interaction is important in regulating the cellular immune response. We hypothesized that the neonatal immune system may show immaturity in this interaction. We studied the function of the CD40L-CD40 interaction in the T-cell interaction with B cells and monocytes in cord blood compared with adult blood in vitro. Consistent with previous reports, CD4+ T cells do not express CD40L after T-cell activation. In whole blood, adult monocytes, but not neonatal monocytes, were activated following T-cell activation. However, the activation of adult monocytes was not dependent on the CD40L-CD40 interaction. Using the CD40L trimer (Lt), we showed that cord B cells have comparable responses to CD40 ligation to those of the adult B cells. Both cord and adult monocytes do not respond as well as B cells and this is probably related to low density of expression of CD40. However, interferon-gamma up-regulated CD40 on adult monocytes but not on cord monocytes. This potentiated the adult monocyte response to CD40 ligation by CD40Lt. Our findings suggest that the neonatal CD40L-CD40 pair is immature in the cellular immune response involving monocytes and that interferon-gamma fails to activate neonatal monocytes for a response to CD40L. These findings suggest that in the inflammatory microenvironment of cord blood transplantation neonatal monocytes may play a minor role in the effector arm of the immune response. This finding may be one of several mechanisms for the low incidence of GVHD that is observed following cord blood transplantation. Also the ligand-receptor immaturity may contribute to the increased susceptibility of newborns to certain infections.

Tolerance associated with cord blood transplantation may depend on the state of host dendritic cells

Allogeneic cord blood (CB) transplantation is associated with less severe graft-versus-host disease (GvHD), thought to be due to the immaturity of CB T cells, but how T cells interact with host and donor-derived dendritic cells (DCs) to initiate GvHD has not been elucidated. We therefore investigated the responses of CB and adult blood CD4(+) T cells co-cultured with adult host DCs of different maturities. Primed by adult host DCs, CB and adult blood CD4(+) T cells underwent similar changes in the expression of CD45RA/45RO, CD25, CD40L and CTLA-4. However, CB CD4(+) T cells, when primed by either immature or Bacillus Calmette-Guerin mycobacteria-treated adult host DCs, produced lower interferon-gamma (IFN-gamma) and higher interleukin-10 (IL-10), which is a regulatory T cell-like cytokine profile, as compared with adult blood CD4(+) T cells. In contrast, lipopolysaccharide (LPS)-treated adult host DCs significantly up-regulated IFN-gamma and down-regulated IL-10 production levels from CB CD4(+) T cells to that from adult blood CD4(+) T cells. The sustained low IFN-gamma and high IL-10 production from CB CD4(+) T cells co-cultured with adult blood DCs might account for the less severe GvHD occurrence after CB transplantation, which could be reversed by LPS-treated adult blood DCs.

Single-institute comparative analysis of unrelated bone marrow transplantation and cord blood transplantation for adult patients with hematologic malignancies

Unrelated cord blood transplantation (CBT) has now become more common, but as yet there have been only a few reports on its outcome compared with bone marrow transplantation (BMT), especially for adults. We studied the clinical outcomes of 113 adult patients with hematologic malignancies who received unrelated BM transplants (n = 45) or unrelated CB transplants (n = 68). We analyzed the hematopoietic recovery, rates of graft-versus-host disease (GVHD), risks of transplantation-related mortality (TRM) and relapse, and disease-free survival (DFS) using Cox proportional hazards models. The time from donor search to transplantation was significantly shorter among CB transplant recipients (median, 2 months) than BM transplant recipients (median, 11 months; P < .01). Multivariate analysis demonstrated slow neutrophil (P < .01) and platelet (P < .01) recoveries in CBT patients compared with BMT patients. Despite rapid tapering of immunosuppressants after transplantation and infrequent use of steroids to treat severe acute GVHD, there were no GVHD-related deaths among CB transplant recipients compared with 10 deaths of 24 among BM transplant recipients. Unrelated CBT showed better TRM and DFS results compared with BMT (P = .02 and P < .01, respectively), despite the higher human leukocyte antigen mismatching rate and lower number of infused cells. These data strongly suggest that CBT could be safely and effectively used for adult patients with hematologic malignancies.

A kinetic study of the murine mixed lymphocyte reaction by 5,6-carboxyfluorescein diacetate succinimidyl ester labeling

Alternatives to the use of radioisotopes to measure cell proliferation in mixed lymphocyte reactions (MLR) are desirable to avoid the hazards and costs associated with radioisotope use. The versatile fluorochrome 5,6-carboxyfluorescein diacetate succinimidyl ester (CFSE) has been used to measure MLR and provides the opportunity to measure several different growth parameters. This study was aimed at determining which growth parameter is most practical and suitable for measuring murine MLR. The parameters measured were: the relative number of daughter T-cells, the relative number and frequency of reactive T-cell precursors and the relative number of mitotic events. Responder cells were CFSE-labeled unfractionated splenocytes from C57BL/6 mice. Stimulator cells included irradiated splenocytes from C57BL/6 (control), B6D2F(1) (haplo-allogeneic) or FVB/N (allogeneic) mice. Cultures were harvested daily for 1 week. Stimulator T-cells rapidly declined to less than 0.2-0.3% of the mixed population by day 2 of culture. Experimental groups had a significantly higher number of daughter T-cells and mitotic events after 2 days of culture with the number of daughter T-cells climbing exponentially after 5 days of culture. The number and frequency of reactive T-cell precursors were significantly higher in experimental groups on days 2-3, but this difference became insignificant by day 4. Among all the parameters, the relative number of daughter T-cells was the most practical for measuring MLR, after 5 days of culture, based upon the growth kinetics of responder T-cells and the survival of the stimulator cells.

A new approach for evaluating antigen-specific T cell responses to myelin antigens during the course of multiple sclerosis

We used a flow cytometry assay to measure proliferation and cytokine production of self-antigen-specific T cells in individual patients during the clinical course of multiple sclerosis (MS). Myelin-associated oligodendrocytic basic protein (MOBP) was selected for proof of principles in the assay, along with myelin basic protein (MBP) to assess specific activated T cells in 10 MS patients over an 18-month period, in parallel with brain magnetic resonance imaging (MRI) scans and clinical rating scale. A positive correlation occurred between antigen-specific T cell proliferation and interferon-gamma production with clinical relapses and MRI lesion activity that was absent when the same patients were in remission.

Activation of alloreactive CD8+ T cells operates via CD4-dependent and CD4-independent mechanisms and is CD154 blockade sensitive

CD154, one of the most extensively studied T cell costimulation molecules, represents a promising therapeutic target in organ transplantation. However, the immunological mechanisms of CD154 blockade that result in allograft protection, particularly in the context of alloreactive CD4/CD8 T cell activation, remain to be elucidated. We now report on the profound inhibition of alloreactive CD8(+) T cells by CD154 blockade via both CD4-dependent and CD4-independent activation pathways. Using CD154 KO recipients that are defective in alloreactive CD8(+) T cell activation and unable to reject cardiac allografts, we were able to restore CD8 activation and graft rejection by adoptively transferring CD4(+) or CD8(+) T cells from wild-type syngeneic donor mice. CD4-independent activation of alloreactive CD8(+) T cells was confirmed following treatment of wild-type recipients with CD4-depleting mAb, and by using CD4 KO mice. Comparable levels of alloreactive CD8(+) T cell activation was induced by allogenic skin engraftment in both animal groups. CD154 blockade inhibited CD4-independent alloreactive CD8(+) T cell activation. Furthermore, we analyzed whether disruption of CD154 signaling affects cardiac allograft survival in skin-sensitized CD4 KO and CD8 KO recipients. A better survival rate was observed consistently in CD4 KO, as compared with CD8 KO recipients. Our results document CD4-dependent and CD4-independent activation pathways for alloreactive CD8(+) T cells that are both sensitive to CD154 blockade. Indeed, CD154 blockade was effective in preventing CD8(+) T cell-mediated cardiac allograft rejection.

Development of interleukin-12-producing capacity throughout childhood

Increasing evidence indicates that the capacity to induce protective Th1 immune responses is impaired in early childhood, an observation that can be partially attributed to deficiencies in antigen-presenting-cell function. Synthesis of interleukin 12 (IL-12), a key Th1-trophic cytokine, is markedly reduced in the neonatal period, though there is a paucity of knowledge concerning the ontogeny of IL-12-synthetic capacity throughout the childhood years. Hence, we examined the production of bioactive IL-12 p70 by circulating mononuclear cells in a population of healthy individuals. As expected, the capacity to synthesize IL-12 p70 in response to either lipopolysaccharide or heat-killed Staphylococcus aureus was markedly impaired at birth, even after priming of cells with gamma interferon. Surprisingly however, IL-12 p70 synthesis by peripheral blood mononuclear cells from both 5- and 12-year-old children was still substantially below that seen in adults, and this did not appear to be related to excessive production of IL-10. In contrast, dendritic cells from adults and neonates, derived from monocytes with granulocyte-macrophage colony-stimulating factor and IL-4, synthesized equivalent amounts of IL-12 p70 in response to microbial stimulation. This indicates that the impaired capacity for IL-12 synthesis in childhood is not an intrinsic property of circulating mononuclear cells but rather can be readily overcome in response to appropriate maturational stimuli. Because IL-12 arose predominantly from circulating HLA-DR(+) cells that lacked B-cell- and monocyte-specific markers, we propose that the slow maturation of IL-12-synthetic capacity in the childhood years can be attributed to deficiencies in the number and/or function of dendritic cells.

Dendritic cell-associated lectin-1: a novel dendritic cell-associated, C-type lectin-like molecule enhances T cell secretion of IL-4

We have characterized dendritic cell (DC)-associated lectin-1 (DCAL-1), a novel, type II, transmembrane, C-type lectin-like protein. DCAL-1 has restricted expression in hemopoietic cells, in particular, DCs and B cells, but T cells and monocytes do not express it. The DCAL-1 locus is within a cluster of C-type lectin-like loci on human chromosome 12p12-13 just 3' to the CD69 locus. The consensus sequence of the DCAL-1 gene was confirmed by RACE-PCR; however, based on sequence alignment with genomic DNA and with various human expressed sequence tags, we predict that DCAL-1 has two splice variants. C-type lectins share a common sequence motif of 14 invariable and 18 highly conserved aa residues known as the carbohydrate recognition domain. DCAL-1, however, is missing three of the cysteine residues required to form the standard carbohydrate recognition domain. DCAL-1 mRNA and protein expression are increased upon the differentiation of monocytes to CD1a(+) DCs. B cells also express high levels of DCAL-1 on their cell surface. Using a DCAL-1 fusion protein we identified a population of CD4(+) CD45RA(+) T cells that express DCAL-1 ligand. Coincubation with soluble DCAL-1 enhanced the proliferation of CD4(+) T cells in response to CD3 ligation and significantly increased IL-4 secretion. In contrast, coincubation with soluble DC-specific ICAM-3-grabbing nonintegrin (CD209) fusion protein as a control had no effect on CD4(+) T cell proliferation or IL-4 and IFN-gamma secretion. Therefore, the function of DCAL-1 on DCs and B cells may act as a T cell costimulatory molecule, which skews CD4(+) T cells toward a Th2 response by enhancing their secretion of IL-4.

Phenotype of fetal monocytes and B lymphocytes during the third trimester of pregnancy

The neonate typically exhibits an immature immune response compared with the adult, yet the fetus is able to generate antigen-specific responses from around 20-22 weeks of gestation. Although antigen-presenting cells (APCs) must have attained the necessary level of maturity to support this, very little is known about the phenotype and function of these populations during human fetal development. Whole blood flow cytometry was, therefore, utilised to phenotype fetal/neonatal circulating monocytes and B cells throughout the third trimester of pregnancy. The percentage of B cells (CD19+) expressing MHC Class II was comparable to the adult at all gestations, whereas the percentage of MHC Class II-positive monocytes (CD14+) increased significantly over gestation (P=0.0008) but remained lower than the adult at term. In contrast, the percentage of CD40+ or CD86+ fetal/neonatal monocytes at all gestations was comparable to the adult, but there was a maturational increase in the percentage of CD40+ or CD86+ B cells (P=0.007) to adult levels by term. The expression of CD14 itself (mean fluorescence intensity, MFI) showed a trend to increase over gestation (P=0.062) and, although all CD14+ cells expressed other receptors associated with innate immune responses (CD11b and CD35), there was fluctuation in the intensity of expression over gestation. Functional immaturity of neonatal antigen-specific immune responses could be associated with reduced co-stimulation provided by both monocytes (via reduced MHC Class II) and B cells (via reduced CD40 and CD86); altered innate responsiveness of monocytes could also contribute.

Phenotypic and functional comparison of monocytes from cord blood and granulocyte colony-stimulating factor-mobilized apheresis products

OBJECTIVE

It is well established that T cells are effector cells in graft-vs-host disease (GVHD), yet the contribution of graft monocytes is less well characterized. Therefore, monocytes in cord blood (CB) and granulocyte colony-stimulating factor-mobilized apheresis products (G-AP), two stem cell grafts associated with reduction of acute and chronic GVHD and relative reduction of acute GVHD, respectively, were compared phenotypically and functionally.

MATERIALS AND METHODS

The frequencies, phenotypes, and pinocytosis activities of monocytes from CB and G-AP were determined by flow cytometry and their allostimulatory potential in a primary mixed leukocyte reaction.

RESULTS

G-AP contained significantly more monocytes than CB (24.9% +/- 7.1% vs 8.8% +/- 1.5% CD14+ and 62.4 +/- 27.5 x 10(6) vs 0.9 +/- 0.2 x 10(6) CD14+ cells/mL). Monocytes from both sources revealed similar phenotypes. They expressed CD4, CD11a, CD11b, CD11c, CD18, CD32, CD33, CD45R0, CD48, CD50, CD54, CD58, CD64, CD86, CD102, CD116, CD123, and HLA-DR; showed no expression of CD1a and CD83; and weak expression of CD16, CD45RA, and CD80. The levels of CD80 and CD86 expression were comparable; however, in contrast to G-AP monocytes, CB monocytes lacked CD40. There was no difference in pinocytosis activity and allostimulatory capacity of CB and G-AP monocytes.

CONCLUSIONS

Monocytes in CB and G-AP are phenotypically and functionally comparable. The only difference observed is the lack of CD40 on CB monocytes.

Neonatal and early life vaccinology

Preclinical and human vaccine studies indicate that, although neonatal immunisation does not generally lead to rapid and strong antibody responses, it may result in an efficient immunological priming, which can serve as an excellent basis for future responses. The apparent impairment of CD4 and CD8 T-cell function in early life seems to result from suboptimal antigen-presenting cells-T cell interactions, which can be overcome by use of specific adjuvants or delivery systems. Although persistence of maternal antibodies may limit infant antibody responses, induction of T-cell responses largely remain unaffected by these passively transferred antibodies. Thus, neonatal priming and early boosting with vaccine formulations optimised for sufficient early life immunogenicity and maximal safety profiles, could allow better control of the huge infectious disease burden in early life.

Identification of both myeloid CD11c+ and lymphoid CD11c- dendritic cell subsets in cord blood

Dendritic cells (DCs) are the most potent antigen-presenting cells described to date. In human peripheral blood, both myeloid and lymphoid subsets of DCs have been identified. In contrast, cord blood (CB) DCs have recently been described as being exclusively of the immature CD11c- lymphoid DC subset. Using an alternative method of enrichment, based on a negative selection system, both lymphoid (HLA-DR+ CD123+++ CD11c- CD33-) and myeloid (HLA-DR++ CD123+ CD11c+ CD33+) DCs were identified in CB. Although the majority of CB DCs showed a lymphoid phenotype, a significant number of CD11c+ myeloid DCs (25.6% +/- 14.5%, n = 13) were also present. Other markers, such as CD80 and CD83, were negative in both subsets. Analyses of the allostimulatory capacity of both subsets showed that freshly isolated CB lymphoid DCs failed to induce a potent allostimulation of naive CB T cells. These features are therefore consistent with previous work reporting an immature phenotype for lymphoid DCs in adult blood. The significance of the inverted CD11c+/CD11c- ratio observed in CB DCs (1:3) with respect to adult blood DCs (3:1) remains to be explained.

Analysis of immune reconstitution in children undergoing cord blood transplantation

OBJECTIVE

The aim of this study was to investigate and compare immune reconstitution in allogeneic cord blood transplantation (CBT) and bone marrow transplantation (BMT) recipients.

MATERIALS AND METHODS

Twenty-three children underwent CBT from either human leukocyte antigen-identical siblings (11 cases) or unrelated donors (12 cases) were enrolled in the study, together with 23 matched children receiving BMT. Patients were analyzed 2-3 and 12-15 months after transplant. Recovery of T-, B-, and NK-lymphocyte subsets, proliferative in vitro response to mitogens, as well as cytotoxic activities, were investigated.

RESULTS

CBT recipients showed a marked increase in the number of B lymphocytes as compared with patients who underwent BMT (p < 0.001). The absolute number of CD3(+) and CD8(+) T cells, as well as the proliferative response to T-cell mitogens, recovered with time after transplantation, irrespective of the source of stem cells used. Recipients of unrelated CBT had a better recovery of CD4(+) T lymphocytes (p < 0.01). Among patients experiencing acute graft-versus-host disease (GVHD), children given CBT had a much greater production of CD4(+) CD45RA(+) T cells than BMT recipients (p < 0.005). Recovery of NK cell number and innate cytotoxic activities was fast, irrespective of the source of stem cells used.

CONCLUSIONS

Despite the much lower number of lymphocytes transferred with the graft, recovery of lymphocyte number and function toward normal in CBT recipients was rapid and comparable to that observed after transplantation of bone marrow progenitors. This prompt immune recovery possibly was favored by the reduced incidence and severity of GVHD observed in children who underwent CBT.

Immunofluorescence analysis of T-cell responses in health and disease

The use of flow cytometry to study the functional responses of T cells by immunofluorescent staining for intracellular cytokines and other markers is a growing field of clinical interest. In this article, we describe methods for the rapid evaluation of T-cell responses to mitogens and specific antigens and explore how these assays might be valuable in various clinical settings.

Neonatal (cord blood) T cells can competently raise type 1 and 2 immune responses upon polyclonal activation

In the neonate, cellular immunity has generally been hypothesized as being incompetent. Accumulating evidence from several recent studies, together with our present report, contradicts this hypothesis. T-helper cell and T cytotoxic type 1 and 2 (Th1/Th2 and Tc1/Tc2, respectively) cytokine responses to polyclonal T cell receptor (TCR) activation were assessed in medium-term cultures of human cord blood T cells using intracellular cytokine staining, which could measure the frequencies of cytokine-producing cells. In this study, we examined the responses of cord blood CD4(+) and CD8(+) T cells in regard to the production of interferon (IFN)-gamma and interleukin (IL)-4 and compared the responses with those obtained from T cells of healthy adults. We found that the responses in cord blood T cells activated with TCR stimulation were comparable to those of their adult counterparts. Moreover, the Th/Tc cells that developed in cord blood were as competent as adult cells for both IFN-gamma and IL-4 secretion. In addition, IL-12 production, which is critical for both Th1 and Tc1 responses, was equally comparable in the two groups. The production of two major cross-regulatory cytokines, tumor necrosis factor-alpha and IL-10, was similarly comparable and not significantly different between the two groups. Taken together, these results indicate that, though naive, the neonatal T cell is competent to respond to TCR-mediated stimulation and to produce both type 1 and type 2 cytokines.