Virus infection induces the development of T follicular helper (T) and T helper 1 (T1) cells. Although T cells are important in anti-viral humoral immunity, the contribution of T1 cells to a protective antibody response remains unknown. We found that IgG2 antibodies predominated in the response to vaccination with inactivated influenza A virus (IAV) and were responsible for protective immunity to lethal challenge with pathogenic H5N1 and pandemic H1N1 IAV strains, even in mice that lacked T cells and germinal centers. The cytokines interleukin-21 and interferon-γ, which are secreted from T1 cells, were essential for the observed greater persistence and higher titers of IgG2 protective antibodies. Our results suggest that T1 induction could be a promising strategy for producing effective neutralizing antibodies against emerging influenza viruses.

Hepatitis B virus (HBV) infects 240 million people worldwide. Current therapy profoundly suppresses HBV replication but requires long-term maintenance therapy. Therefore there is still a medical need for an efficient HBV cure. HBV enters host cells by binding via the preS1-domain of the viral L protein to the Na + /Taurocholate Cotransporting Polypeptide (NTCP). Thus, NTCP should be a key target for the development of anti-HBV therapeutics. Indeed, Myrcludex B, a synthetic form of the myristoylated preS1 peptide, effectively reduces HBV/HDV infection and has been approved as Hepcludex® in Europe for the treatment of patients with chronic hepatitis D virus (HDV) infection. We established a monoclonal antibody (mAb) N6HB426-20 that recognizes the extracellular domain of human NTCP and blocks HBV entry in vitro into human liver cells but has much less of an inhibitory effect on bile acid uptake. In vivo , administration of the N6HB426-20 mAb prevented HBV viremia for an extended period of time after HBV inoculation in a mouse model system without strongly inhibiting bile acid absorption. Among the extracellular loops (ECLs) of NTCP, regions of amino acids (aa) 84-87 in ECL1 and aa 157-165 near ECL2 of transmembrane domain 5 are critically important for HBV/HDV infection. Epitope-mapping and the 3D model of the NTCP structure suggested that the N6HB426-20 mAb may recognize aa 276/277 at the tip of ECL4 and interfere with an binding of HBV to the aa 84-87 region. In summary, we identified an in vivo neutralizing NTCP-targeting antibody capable of preventing HBV infection. Further improvements in efficacy of this drug will pave the way for its clinical applications. IMPORTANCE A number of entry inhibitors are being developed to enhance the treatment of HBV patients with oral nucleos(t)ide analogues (NA). To amplify the effectiveness of NA therapy, several efforts have been made to develop therapeutic mAbs with neutralizing activity against HBs antigens. However, the neutralizing effect of these mAbs may be muted by a large excess of HBsAg-positive noninfectious particles in the blood of infected patients. The advantage of NTCP-targeted HBV entry inhibitors is that they remain effective regardless of viral genotype, viral mutations and the presence of subviral particles. Although N6HB426-20 requires a higher dose than Myrcludex to obtain equivalent suppression of HBV in a model mouse system, it maintained the inhibitory effect for a long time post administration in proportion to the half-life of an IgG mAb. We believe that further improvements will make this antibody a promising treatment option for patients with chronic hepatitis B.

In T cell-dependent antibody responses, some of the activated B cells differentiate along extrafollicular pathways into low-affinity memory and plasma cells, whereas others are involved in subsequent GC formation in follicular pathways, in which somatic hypermutation and affinity maturation occur. The present study demonstrated that Bim, a proapoptotic BH3-only member of the Bcl-2 family, contributes to the establishment of the B cell repertoire from early to late stages of immune responses to T-cell dependent antigens. Extrafollicular plasma cells grew in the spleen during the early immune response, but their numbers rapidly declined with the appearance of GC-derived progeny in wild type mice. By contrast, conditional Bim deficiency in B cells resulted in expansion of extrafollicular IgG1 + antibody-forming cells (AFCs) and this expansion was sustained during the late response, which hampered the formation of GC-derived high-affinity plasma cells in the spleen. Approximately 10% of AFCs in mutant mice contained mutated VH genes, thus Bim deficiency appears not to impede the selection of high-affinity AFC precursor cells. These results suggest that Bim contributes to the replacement of low affinity antibody by high affinity antibody as the immune response progresses.