The respiratory syncytial virus (RSV) prefusion F-protein functional antibody repertoire in adult healthy donors

Respiratory syncytial virus (RSV) is the leading cause of death from lower respiratory tract infection in infants and children, and is responsible for considerable morbidity and mortality in older adults. Vaccines for pregnant women and elderly which are in phase III clinical studies target people with pre-existing natural immunity against RSV. To investigate the background immunity which will be impacted by vaccination, we single cell-sorted human memory B cells and dissected functional and genetic features of neutralizing antibodies (nAbs) induced by natural infection. Most nAbs recognized both the prefusion and postfusion conformations of the RSV F-protein (cross-binders) while a smaller fraction bound exclusively to the prefusion conformation. Cross-binder nAbs used a wide array of gene rearrangements, while preF-binder nAbs derived mostly from the expansion of B-cell clonotypes from the IGHV1 germline. This latter class of nAbs recognizes an epitope located between Site Ø, Site II, and Site V on the F-protein, identifying an important site of pathogen vulnerability.

Vaccine adjuvant MF59 promotes the intranodal differentiation of antigen-loaded and activated monocyte-derived dendritic cells

MF59 is an oil-in-water emulsion adjuvant approved for human influenza vaccination in European Union. The mode of action of MF59 is not fully elucidated yet, but results from several years of investigation indicate that MF59 establishes an immunocompetent environment at injection site which promotes recruitment of immune cells, including antigen presenting cells (APCs), that are facilitated to engulf antigen and transport it to draining lymph node (dLN) where the antigen is accumulated. In vitro studies showed that MF59 promotes the differentiation of monocytes to dendritic cells (Mo-DCs). Since after immunization with MF59, monocytes are rapidly recruited both at the injection site and in dLN and appear to have a morphological change toward a DC-like phenotype, we asked whether MF59 could play a role in inducing differentiation of Mo-DC in vivo. To address this question we immunized mice with the auto-fluorescent protein Phycoerythrin (PE) as model antigen, in presence or absence of MF59. We measured the APC phenotype and their antigen uptake within dLNs, the antigen distribution within the dLN compartments and the humoral response to PE. In addition, using Ovalbumin as model antigen, we measured the capacity of dLN APCs to induce antigen-specific CD4 T cell proliferation. Here, we show, for the first time, that MF59 promotes differentiation of Mo-DCs within dLNs from intranodal recruited monocytes and we suggest that this differentiation could take place in the medullary compartment of the LN. In addition we show that the Mo-DC subset represents the major source of antigen-loaded and activated APCs within the dLN when immunizing with MF59. Interestingly, this finding correlates with the enhanced triggering of antigen-specific CD4 T cell response induced by LN APCs. This study therefore demonstrates that MF59 is able to promote an immunocompetent environment also directly within the dLN, offering a novel insight on the mechanism of action of vaccine adjuvants based on emulsions.

In vivo characterization of the immune response towards the pathogenic Escherichia coli antigen SslE and modulation of the intestinal microbiota

Pathogenic E. coli, both intestinal (InPEC) and extraintestinal (ExPEC), account for a wide range of diseases, which can be fatal, across developing and developed countries. The vast array of virulence factors they can acquire may dramatically increase the severity of the infection. Emergence of resistant strains often renders antibiotics inefficient; in the case of Shiga toxin-producing E. coli, antibiotics can even be detrimental. Hence, a broad spectrum E. coli vaccine could be a promising alternative to prevent the spread of such diseases, while offering the potential for covering against several InPEC and ExPEC at once.

Using the «reverse vaccinology» approach on an ExPEC strain, nine antigens were identified as protective against a mouse sepsis model. With 82% protective efficacy, SslE (Secreted and Surface-associated Lipoprotein of E. coli) was the most potent candidate; additional models demonstrated that SslE was also cross-protective against other ExPEC strains. Functional assays have demonstrated in vitro and in vivo that SslE is a mucinase which plays an important role for colonization and virulence of E. coli.

To better understand the mechanism behind such protection, particularly at the mucosa, we are investigating the intestinal immune response obtained after immunizations with SslE using different routes of injection. In-depth analysis of each regimen will allow us to determine the most efficient method of immunization and adjuvant choice for SslE to be protective. Further, using this model of immunization, we will evaluate the potential perturbation caused by SslE on a human intestinal microbiota. These findings will be important to help us optimize the development of a potential broad spectrum vaccine.

Cutting Edge: The CD45 Tyrosine Phosphatase Is an Inhibitor of Lck Activity in Thymocytes

A widely accepted model for regulation of the Lck tyrosine kinase is that it is activated by CD45-mediated dephosphorylation of its COOH-terminal negative regulatory tyrosine (Tyr505). Previous work from our laboratory, however, found that despite hyperphosphorylation of Tyr505, the activity of Lck from CD45− T cell lines was actually increased due to hyperphosphorylation of the positive regulatory tyrosine, residue 394. To avoid potential complications introduced by transformed cells, in this study we have characterized the effect of CD45 on Lck activity in normal cells. Lck in thymocytes from CD45−/− mice was hyperphosphorylated on tyrosine residues. Importantly, and in disagreement with the model that CD45 only activates Lck in vivo, the kinase activity of Lck from cells lacking CD45 was substantially increased. These results support a model in which CD45 dephosphorylates both Tyr505 and Tyr394, the net effect in normal thymocytes being a decrease in enzymatic activity.