Generation of an Attenuated Chimeric Bat Influenza A Virus Live-Vaccine Prototype.

Recurring epizootic influenza A virus (IAV) infections in domestic livestock such as swine and poultry are associated with a substantial economic burden and pose a constant threat to human health. Therefore, universally applicable and safe animal vaccines are urgently needed. We recently demonstrated that a reassortment-incompatible chimeric bat H17N10 virus harboring the A/swan/Germany/R65/2006 (H5N1) surface glycoproteins hemagglutinin (HA) and neuraminidase (NA) can be efficiently used as a modified live influenza vaccine (MLIV). To ensure vaccine safety and, thus, improve the applicability of this novel MLIV for mammalian usage, we performed consecutive passaging in eggs and chickens. Following passaging, we identified mutations in the viral polymerase subunits PB2 (I382S), PB1 (Q694H and I695K), and PA (E141K). Strikingly, recombinant chimeric viruses encoding these mutations showed no growth deficiencies in avian cells but displayed impaired growth in human cells and mice. Homologous prime-boost immunization of mice with one of these avian-adapted chimeric viruses, designated rR65mono/H17N10EP18, elicited a strong neutralizing antibody response and conferred full protection against lethal highly pathogenic avian influenza virus (HPAIV) H5N1 challenge infection. Importantly, the insertion of the avian-adaptive mutations into the conventional avian-like A/SC35M/1980 (H7N7) and prototypic human A/PR/8/34 (H1N1) viruses led to attenuated viral growth in human cells and mice. Collectively, our data show that the polymerase mutations identified here can be utilized to further improve the safety of our novel H17N10-based MLIV candidates for future mammalian applications. IMPORTANCE Recurring influenza A virus outbreaks in livestock, particularly in swine and chickens, pose a constant threat to humans. Live attenuated influenza vaccines (LAIVs) might be a potent tool to prevent epizootic outbreaks and the resulting human IAV infections; however, LAIVs have several disadvantages, especially in terms of reassortment with circulating IAVs. Notably, the newly identified bat influenza A viruses H17N10 and H18N11 cannot reassort with conventional IAVs. Chimeric bat influenza A viruses encoding surface glycoproteins of conventional IAV subtypes might thus function as safe and applicable modified live influenza vaccines (MLIVs).

Dynamic regulation of TFH selection during the germinal centre reaction.

The germinal centre is a dynamic microenvironment in which B cells that express high-affinity antibody variants produced by somatic hypermutation are selected for clonal expansion by limiting the numbers of T follicular helper cells1,2. Although much is known about the mechanisms that control the selection of B cells in the germinal centre, far less is understood about the clonal behaviour of the T follicular helper cells that help to regulate this process. Here we report on the dynamic behaviour of T follicular helper cell clones during the germinal centre reaction. We find that, similar to germinal centre B cells, T follicular helper cells undergo antigen-dependent selection throughout the germinal centre reaction that results in differential proliferative expansion and contraction. Increasing the amount of antigen presented in the germinal centre leads to increased division of T follicular helper cells. Competition between T follicular helper cell clones is mediated by the affinity of T cell receptors for peptide-major-histocompatibility-complex ligands. T cells that preferentially expand in the germinal centre show increased expression of genes downstream of the T cell receptor, such as those required for metabolic reprogramming, cell division and cytokine production. These dynamic changes lead to marked remodelling of the functional T follicular helper cell repertoire during the germinal centre reaction.