Broadly neutralizing antibodies reactive against most and even all variants of the same viral species have been described for influenza and HIV-1 (ref. 1). However, whether a neutralizing antibody could have the breadth of range to target different viral species was unknown. Human respiratory syncytial virus (HRSV) and human metapneumovirus (HMPV) are common pathogens that cause severe disease in premature newborns, hospitalized children and immune-compromised patients, and play a role in asthma exacerbations. Although antisera generated against either HRSV or HMPV are not cross-neutralizing, we speculated that, because of the repeated exposure to these viruses, cross-neutralizing antibodies may be selected in some individuals. Here we describe a human monoclonal antibody (MPE8) that potently cross-neutralizes HRSV and HMPV as well as two animal paramyxoviruses: bovine RSV (BRSV) and pneumonia virus of mice (PVM). In its germline configuration, MPE8 is HRSV-specific and its breadth is achieved by somatic mutations in the light chain variable region. MPE8 did not result in the selection of viral escape mutants that evaded antibody targeting and showed potent prophylactic efficacy in animal models of HRSV and HMPV infection, as well as prophylactic and therapeutic efficacy in the more relevant model of lethal PVM infection. The core epitope of MPE8 was mapped on two highly conserved anti-parallel ?-strands on the pre-fusion viral F protein, which are rearranged in the post-fusion F protein conformation. Twenty-six out of the thirty HRSV-specific neutralizing antibodies isolated were also found to be specific for the pre-fusion F protein. Taken together, these results indicate that MPE8 might be used for the prophylaxis and therapy of severe HRSV and HMPV infections and identify the pre-fusion F protein as a candidate HRSV vaccine.
TCR signal strength instructs ?? versus ?? lineage decision in immature T cells. Increased signal strength of ??TCR with respect to pre-TCR results in induction of the ?? differentiation program. Extracellular ATP evokes physiological responses through purinergic P2 receptors expressed in the plasma membrane of virtually all cell types. In peripheral T cells, ATP released upon TCR stimulation enhances MAPK activation through P2X receptors. We investigated whether extracellular ATP and P2X receptors signaling tuned TCR signaling at the ??/?? lineage bifurcation checkpoint. We show that P2X7 expression was selectively increased in immature ??(+)CD25(+) cells. These cells were much more competent to release ATP than pre-TCR-expressing cells following TCR stimulation and Ca(2+) influx. Genetic ablation as well as pharmacological antagonism of P2X7 resulted in impaired ERK phosphorylation, reduction of early growth response (Egr) transcripts induction, and diversion of ??TCR-expressing thymocytes toward the ?? lineage fate. The impairment of the ERK-Egr-inhibitor of differentiation 3 (Id3) signaling pathway in ?? cells from p2rx7(-/-) mice resulted in increased representation of the Id3-independent NK1.1-expressing ?? T cell subset in the periphery. Our results indicate that ATP release and P2X7 signaling upon ??TCR expression in immature thymocytes constitutes an important costimulus in T cell lineage choice through the ERK-Egr-Id3 signaling pathway and contributes to shaping the peripheral ?? T cell compartment.
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