Dectin-1 activation unlocks IL12A expression and reveals the TH1 potency of neonatal dendritic cells.

BACKGROUND: Early life is characterized by a high susceptibility to infection and a TH2-biased CD4 T-cell response to vaccines. Toll-like receptor (TLR) agonists are currently being implemented as new vaccine adjuvants for TH1 activation, but their translation to the field of pediatric vaccines is facing the impairment of neonatal innate TLR responses. OBJECTIVE: We sought to analyze C-type lectin receptor pathways as an alternative or a coactivator to TLRs for neonatal dendritic cell activation for TH1 polarization. METHODS: Neonatal monocyte-derived dendritic cells (moDCs) were exposed to various combinations of TLR agonists with or without Dectin-1 agonist. IL-12 and IL-23 responses were analyzed at the transcriptional and protein levels after stimulation. The intracellular pathways triggered by combined TLR plus Dectin-1 stimulation was determined by using pharmacologic inhibitors. The capacity of neonatal moDCs to differentiate naive CD4 TH cells was evaluated in cocultures with heterologous neonatal naive T cells. Curdlan was finally tested as an adjuvant within a subunit tuberculosis vaccine in neonatal mice. RESULTS: Simultaneous coactivation through Dectin-1 and TLRs induced robust secretion of IL-12p70 by neonatal moDCs by unlocking transcriptional control on the p35 subunit of IL-12. Both the spleen tyrosine kinase and Raf-1 pathways were involved in this process, allowing differentiation of neonatal naive T cells toward IFN-γ-producing TH1 cells. In vivo a Dectin-1 agonist as adjuvant was sufficient to induce TH1 responses after vaccination of neonatal mice. CONCLUSION: Coactivation of neonatal moDCs through Dectin-1 allows TLR-mediated IL-12p70 secretion and TH1 polarization of neonatal T cells. Dectin-1 agonists represent a promising TH1 adjuvant for pediatric vaccination.

IL-15 trans-presentation promotes human NK cell development and differentiation in vivo.

The in vivo requirements for human natural killer (NK) cell development and differentiation into cytotoxic effectors expressing inhibitory receptors for self-major histocompatibility complex class I (MHC-I; killer Ig-like receptors [KIRs]) remain undefined. Here, we dissect the role of interleukin (IL)-15 in human NK cell development using Rag2(-/-)gamma c(-/-) mice transplanted with human hematopoietic stem cells. Human NK cell reconstitution was intrinsically low in this model because of the poor reactivity to mouse IL-15. Although exogenous human IL-15 (hIL-15) alone made little improvement, IL-15 coupled to IL-15 receptor alpha (IL-15R alpha) significantly augmented human NK cells. IL-15-IL-15R alpha complexes induced extensive NK cell proliferation and differentiation, resulting in accumulation of CD16(+)KIR(+) NK cells, which was not uniquely dependent on enhanced survival or preferential responsiveness of this subset to IL-15. Human NK cell differentiation in vivo required hIL-15 and progressed in a linear fashion from CD56(hi)CD16(-)KIR(-) to CD56(lo)CD16(+)KIR(-), and finally to CD56(lo)CD16(+)KIR(+). These data provide the first evidence that IL-15 trans-presentation regulates human NK cell homeostasis. Use of hIL-15 receptor agonists generates a robust humanized immune system model to study human NK cells in vivo. IL-15 receptor agonists may provide therapeutic tools to improve NK cell reconstitution after bone marrow transplants, enhance graft versus leukemia effects, and increase the pool of IL-15-responsive cells during immunotherapy strategies.

Effect of attenuation of Treg during BCG immunization on anti-mycobacterial Th1 responses and protection against Mycobacterium tuberculosis.

BACKGROUND: The functional equilibrium between natural regulatory T cells (Treg) and effector T cells can affect the issue of numerous infections. In unvaccinated mice, the influence of Treg in the control of primary infection with mycobacteria remains controversial. METHODOLOGY: Here, we evaluated the role of Treg during prophylactic vaccination with Mycobacterium bovis BCG (Bacillus Calmette-Guérin) on the induction of T cell responses and on the protective effect against subsequent M. tuberculosis challenge in mice. PRINCIPAL FINDINGS: We demonstrated that, subsequent to BCG injection, Treg were recruited to the draining lymph nodes and negatively control anti-mycobacterial CD4(+)--but not CD8(+)--T-cell responses. Treatment of BCG-immunized mice with an anti-CD25 mAb (PC61) induced an increase IFN-gamma response against both subdominant and immunodominant regions of the protective immunogen TB10.4. In Treg-attenuated, BCG-immunized mice, which were then infected with M. tuberculosis, the lung mycobacterial load was significantly, albeit moderately, reduced compared to the control mice. CONCLUSIONS: Our results provide the first demonstration that attenuation of Treg subset concomitant to BCG vaccination has a positive, yet limited, impact on the protective capacity of this vaccine against infection with M. tuberculosis. Thus, for rational design of improved BCG, it should be considered that, although the action of Treg does not represent the major cause of the limited efficiency of BCG, the impact of this cell population on the subsequent control of M. tuberculosis growth is significant and measurable.