Method for screening influenza neutralizing antibodies in crude human plasma and its derivatives using SPR.

We applied Surface Plasmon Resonance (SPR) technology to develop a method for potency screening and quantification of anti-influenza antibodies in minimally processed human plasma samples and intravenous immunoglobulin (IGIV) products. We found that specific antibodies in human plasma or IGIV capable of inhibiting binding of influenza hemagglutinin to receptor-analogous glycans do so in concentration-dependent manner. We ranked the inhibitory activity of plasma samples from multiple donors and found a good correlation (r = 0.87) of SPR assay measurements and conventional hemagglutination inhibition (HAI) assay results. This method was also applied to screen for specific anti-influenza antibodies in IGIV lots manufactured pre- and post-2009 H1N1 pandemic. The SPR method was also applied to study binding inhibition of the intact A/California/04/2009 H1N1 and B/Victoria/504/2000 influenza viruses to α2,6 or α2,3-linked synthetic glycans. In contrast to recombinant H1 hemagglutinin, which was found to interact primarily with α2,6-linked terminal sialic acids, intact H1N1 or influenza B virus recognized both types of receptor analogs with different observed dissociation rates and the inhibitory activity of plasma antibodies was dependent on the type of sialic acid link. The SPR method can provide a high-throughput, time-saving and semi-automated alternative to conventional assays such as HAI or microneutralization in situations where screening of large numbers of plasma donations to identify high titer units is needed to product highly potent immunoglobulins.

Zika Virus Infection and Antibody Neutralization in FcRn Expressing Placenta and Engineered Cell Lines.

As a developmental toxicant, Zika virus (ZIKV) attacks both the growing nervous system, causing congenital Zika syndrome, and the placenta, resulting in pathological changes and associated adverse fetal outcomes. There are no vaccines, antibodies, or other treatments for ZIKV, despite the potential for its re-emergence. Multiple studies have highlighted the risk of antibodies for enhancing ZIKV infection, including during pregnancy, but the mechanisms for such effects are not fully understood. We have focused on the ability of the neonatal Fc receptor (FcRn) to interact with ZIKV in the presence and absence of relevant antibodies. We found that ZIKV replication was higher in Marvin Darby Canine Kidney (MDCK) cells that overexpress FcRn compared to those that do not, and knocking down FcRn decreased ZIKV RNA production. In the placenta trophoblast BeWo cell line, ZIKV infection itself downregulated FcRn at the mRNA and protein levels. Addition of anti-ZIKV antibodies to MDCK/FcRn cells resulted in non-monotonous neutralization curves with neutralization attenuation and even enhancement of infection at higher concentrations. Non-monotonous neutralization was also seen in BeWo cells at intermediate antibody concentrations. Our studies highlight the underappreciated role FcRn plays in ZIKV infection and may have implications for anti-ZIKV prophylaxis and therapy in pregnant women.

AFM Imaging Reveals Topographic Diversity of Wild Type and Z Variant Polymers of Human α1-Proteinase Inhibitor.

α1-Proteinase inhibitor (antitrypsin) is a canonical example of the serpin family member that binds and inhibits serine proteases. The natural metastability of serpins is crucial to carry out structural rearrangements necessary for biological activity. However, the enhanced metastability of the mutant Z variant of antitrypsin, in addition to folding defect, may substantially contribute to its polymerization, a process leading to incurable serpinopathy. The metastability also impedes structural studies on the polymers. There are no crystal structures of Z monomer or any kind of polymers larger than engineered wild type (WT) trimer. Our understanding of polymerization mechanisms is based on biochemical data using in vitro generated WT oligomers and molecular simulations. Here we applied atomic force microscopy (AFM) to compare topography of monomers, in vitro formed WT oligomers, and Z type polymers isolated from transgenic mouse liver. We found the AFM images of monomers closely resembled an antitrypsin outer shell modeled after the crystal structure. We confirmed that the Z variant demonstrated higher spontaneous propensity to dimerize than WT monomers. We also detected an unexpectedly broad range of different types of polymers with periodicity and topography depending on the applied method of polymerization. Short linear oligomers of unit arrangement similar to the Z polymers were especially abundant in heat-treated WT preparations. Long linear polymers were a prominent and unique component of liver extracts. However, the liver preparations contained also multiple types of oligomers of topographies undistinguishable from those found in WT samples polymerized with heat, low pH or guanidine hydrochloride treatments. In conclusion, we established that AFM is an excellent technique to assess morphological diversity of antitrypsin polymers, which is important for etiology of serpinopathies. These data also support previous, but controversial models of in vivo polymerization showing a surprising diversity of polymer topography.

Gestation age dependent transfer of human immunoglobulins across placenta in timed-pregnant guinea pigs.

INTRODUCTION: When administered during pregnancy, antibodies and other biologic drugs that contain the Fc part of the IgG molecule can traverse the placenta. Although it is generally accepted that the FcRn receptor mediates this process, gaps remain in our understanding of underlying details in humans and in common laboratory animal species. METHODS: We expanded our previous studies in timed-pregnant guinea pigs to both measure the transport of human (h) IgG at earlier gestation ages in vivo and evaluate FcRn function in vitro using Surface Plasmon Resonance (SPR) and Madin-Darby canine kidney cells (MDCK) that express guinea pig (gp) FcRn. RESULTS: In timed-pregnant guinea pigs both the average concentration of hIgG in the fetus and its ratio to maternal hIgG concentration increase exponentially with gestation age. Thus, hIgG fetal:maternal concentration ratios increase from an average of 1% to 3%, 17%, and 76% on GD ∼26, 35, 46, and 54, respectively. In vitro, gpFcRn immobilized on a solid surface can bind hIgG and gpIgG preparations in a similar manner. All engineered human Fc isotype-specific constructs were internalized by MDCK-gpFcRn cells at significant levels. While not significant, their recycling and hIgG transcytosis by this cell line also trend higher than background controls. DISCUSSION: Pregnant guinea pigs exhibit similarities with humans in the degree and timing of transplacental transfer as well as the ability of their FcRn to bind and internalize hIgG in vitro. Further studies are needed to guide building appropriate systems for the evaluation of FcRn mediated function of human immunoglobulin therapies.

Transplacental Transfer of Hepatitis B Neutralizing Antibody during Pregnancy in an Animal Model: Implications for Newborn and Maternal Health.

Despite the success of postexposure prophylaxis (PEP) of the newborn in preventing mother-to-child transmission of hepatitis B virus), in non-US clinical trials, administering hepatitis B immune globulin (HBIG) to mothers at the end of pregnancy (in addition to passive-active PEP of the newborn) only partially improved outcomes. That is, a significant percentage of newborns became infected during their first year of life. We used a relevant animal model for human IgG transplacental transfer to study dose, time and subclass dependence of HBV neutralizing antibody (nAb) maternal, and fetal levels at the end of pregnancy. Pregnant guinea pigs received 50 or 100 IU/kg HBIGIV 2-5 days before delivery. Human total IgG, IgG subclasses, and nAb in mothers and their litters were measured. In vitro analyses of guinea pig Fc neonatal receptor binding to HBIGIV, as well as to all human IgG subclasses, were also performed. Our study showed that nAb transferred transplacentally from the pregnant guinea pigs to their litters; no transfer occurred during parturition. The amount of the transferred nAb was dose and time dependent. Thus, selection of an efficacious dose in the clinic is important: microdosing may be underdosing, particularly in cases of high viraemia.