Fetal public Vγ9Vδ2 T cells expand and gain potent cytotoxic functions early after birth.

Vγ9Vδ2 T cells are a major human blood γδ T cell population that respond in a T cell receptor (TCR)-dependent manner to phosphoantigens which are generated by a variety of microorganisms. It is not clear how Vγ9Vδ2 T cells react toward the sudden microbial exposure early after birth. We found that human Vγ9Vδ2 T cells with a public/shared fetal-derived TCR repertoire expanded within 10 wk postpartum. Such an expansion was not observed in non-Vγ9Vδ2 γδ T cells, which possessed a private TCR repertoire. Furthermore, only the Vγ9Vδ2 T cells differentiated into potent cytotoxic effector cells by 10 wk of age, despite their fetal origin. Both the expansion of public fetal Vγ9Vδ2 T cells and their functional differentiation were not affected by newborn vaccination with the phosphoantigen-containing bacillus Calmette-Guérin (BCG) vaccine. These findings suggest a strong and early priming of the public fetal-derived Vγ9Vδ2 T cells promptly after birth, likely upon environmental phosphoantigen exposure.

Differential leukocyte counting and immunophenotyping in cryopreserved ex vivo whole blood.

Absolute cell counts are typically measured in fresh samples, but this is impractical in large field studies. We compared quantification of leukocyte proportions and absolute counts using reference real-time methods (stain and lyse/no-wash (LNW) or hematology analyser) with a novel assay that allows long-term cryopreservation of fixed leukocytes for later counting (DLC-ICE: differential leukocyte count and immunophenotype in cryopreserved ex vivo whole blood). For the LNW method, whole blood (WB) was stained with fluorescent antibodies, then erythrocytes were lysed, and leukocytes fixed prior to flow cytometry. Alternatively, our novel DLC-ICE method entailed erythrocyte lysis and leukocyte fixation, cryopreservation and later staining of permeabilized cells prior to flow cytometry. Outcomes were proportions and absolute counts of granulocytes, lymphocytes, monocytes, T cells, B cells, and activated T cells within the leukocyte population. We also compared leukocyte subset counts in fresh WB from 51 healthy infants measured by hematology analyser at a rural clinical site or by DLC-ICE method after 2 years of cryopreservation. We observed excellent agreement and strong correlations between absolute counts or cell proportions measured by the LNW and DLC-ICE methods on fresh WB from 10 healthy adults. Compared to LNW, DLC-ICE yielded similar or brighter staining even after cryopreservation. Duration of cryopreservation, assessed monthly for 1 year, had little effect on cell enumeration: median coefficients of variation were below 15% for all outcomes. Under field site conditions, we observed strong correlations between infant leukocyte numbers measured in fresh samples by hematology analyser and those measured by DLC-ICE up to 2 years of cryopreservation. Our novel DLC-ICE method allows accurate flow cytometric quantification of cell subsets from fixed WB even after long-term cryopreservation. This method is ideal for batched, retrospective analysis of samples from large field studies, or when advanced flow cytometry equipment is not available for clinical research purposes. © 2014 International Society for Advancement of Cytometry.

Newborn bacille Calmette-Guérin vaccination induces robust infant interferon-γ-expressing natural killer cell responses to mycobacteria.

OBJECTIVES: The bacille Calmette-Guérin (BCG) vaccine is usually administered at birth to protect against severe forms of tuberculosis in children. BCG also confers some protection against other infections, possibly mediated by innate immune training. We investigated whether newborn BCG vaccination modulates myeloid and natural killer (NK) cell responses to mycobacteria. METHODS: BCG vaccination was either administered at birth or delayed to 6 or 10 weeks of age in 130 South African infants. Whole blood was stimulated with BCG and clusters of differentiation (CD)4+ T, myeloid, and NK cell responses were measured by flow cytometry; the levels of secreted cytokines were measured by a multiplex bead array. RESULTS: Newborn BCG vaccination was associated with significantly higher frequencies of BCG-reactive, cytokine-expressing CD4+ T cells, and interferon (IFN)-γ-expressing NK cells than in unvaccinated infants but no differences in cytokine-expressing CD33+ myeloid cells were observed. The induction of BCG-reactive IFN-γ-expressing NK cells was not associated with the markers of NK cell maturation, differentiation, or cytokine receptor expression. BCG-reactive NK cell responses correlated directly with the levels of secreted interleukin (IL)-2 and IFN-γ and the innate pro-inflammatory cytokines IL-6, IL-1ß, and tumor necrosis factor (TNF) in BCG-vaccinated infants only. CONCLUSION: We showed that BCG-reactive IFN-γ-expressing NK cells are strongly induced by BCG vaccination in infants and are likely amplified through bystander cytokines.

Effects of BCG vaccination on donor unrestricted T cells in two prospective cohort studies.

BACKGROUND: Non-protein antigen classes can be presented to T cells by near-monomorphic antigen-presenting molecules such as CD1, MR1, and butyrophilin 3A1. Such T cells, referred to as donor unrestricted T (DURT) cells, typically express stereotypic T cell receptors. The near-unrestricted nature of DURT cell antigen recognition is of particular interest for vaccine development, and we sought to define the roles of DURT cells, including MR1-restricted MAIT cells, CD1b-restricted glucose monomycolate (GMM)-specific T cells, CD1d-restricted NKT cells, and γδ T cells, in vaccination against Mycobacterium tuberculosis. METHODS: We compared and characterized DURT cells following primary bacille Calmette-Guerin (BCG) vaccination in a cohort of vaccinated and unvaccinated infants, as well as before and after BCG-revaccination in adults. FINDINGS: BCG (re)vaccination did not modulate peripheral blood frequencies, T cell activation or memory profiles of MAIT cells, CD1b-restricted GMM-specific and germline-encoded mycolyl-reactive (GEM) cells or CD1d-restricted NKT cells. By contrast, primary BCG vaccination was associated with increased frequencies of γδ T cells as well as a novel subset of CD26+CD161+TRAV1-2- IFN-γ-expressing CD4+ T cells in infants. INTERPRETATION: Our findings, that most DURT cell populations were not modulated by BCG, do not preclude a role of BCG in modulating other qualitative aspects of DURT cells. More studies are required to understand the full potential of DURT cells in new TB vaccine strategies. FUNDING: Aeras, the National Institutes of Health, and the Bill and Melinda Gates Foundation.

Inflammatory Determinants of Differential Tuberculosis Risk in Pre-Adolescent Children and Young Adults.

The risk of progression from Mycobacterium tuberculosis (M.tb) infection to active tuberculosis (TB) disease varies markedly with age. TB disease is significantly less likely in pre-adolescent children above 4 years of age than in very young children or post-pubescent adolescents and young adults. We hypothesized that pro-inflammatory responses to M.tb in pre-adolescent children are either less pronounced or more regulated, than in young adults. Inflammatory and antimicrobial mediators, measured by microfluidic RT-qPCR and protein bead arrays, or by analyzing published microarray data from TB patients and controls, were compared in pre-adolescent children and adults. Multivariate analysis revealed that M.tb-uninfected 8-year-old children had lower levels of myeloid-associated pro-inflammatory mediators than uninfected 18-year-old young adults. Relative to uninfected children, those with M.tb-infection had higher levels of similar myeloid inflammatory responses. These inflammatory mediators were also expressed after in vitro stimulation of whole blood from uninfected children with live M.tb. Our findings suggest that myeloid inflammation is intrinsically lower in pre-pubescent children than in young adults. The lower or more regulated pro-inflammatory responses may play a role in the lower risk of TB disease in this age group.