Human antibodies can cross guinea pig placenta and bind its neonatal Fc Receptor: implications for studying immune prophylaxis and therapy during pregnancy

Abstract

Despite increased use of monoclonal and polyclonal antibody therapies, including during pregnancy, there is little data on appropriate animal models that could humanely be used to understand determinants of protection and to evaluate safety of these biologics in the mother and the developing fetus. Here, we demonstrate that pregnant guinea pigs can transport human IgG transplacentally at the end of pregnancy. We also observe that human IgG binds to an engineered soluble variant of the guinea pig neonatal Fc receptor in vitro in a manner similar to that demonstrated for the human variant, suggesting that this transplacental transport mirrors the receptor-based mechanism seen in humans. Using an intravenous antihepatitis B-specific immune globulin preparation as an example, we show that this transport results in neutralizing activity in the mother and the newborn that would potentially be prophylactic against hepatitis B viral infection. These preliminary data lay the groundwork for introducing pregnant guinea pigs as an appropriate model for the evaluation of antibody therapies and advancing the health of women and neonates.

Figure 1

Human IgG transfer to the piglets of pregnant guinea pigs injected with a human immune globulin preparation. Two pregnant sows, numbered 4 and 7, were injected with HBIGIV on days 62 and 66 of pregnancy, respectively. Total and neutralizing human IgG, and the IgG subclasses ((a), (b), and (c), resp.) in the serum of the dams and the piglets (Pg1–5 and Pg1-2, resp.) soon after farrowing (on days 67 and 68, resp.) was quantified with commercial kits. All the piglets had human IgG in their blood stream. The concentrations for total (a) and neutralizing (b) antibody as well as for all the subtypes (c) were higher in the progeny of dam number 4, which delivered five days after the HBIGIV administration, than in that of dam number 7, which delivered two days following administration.

Figure 2

Expression and binding of engineered guinea pig soluble FcRn receptor. (a) This western blot confirms secretion of the guinea pig soluble FcRn by the Huh7 human liver cell line transiently transfected with pFUSE containing soluble FcRn. Shown are reduced (lane 1) and nonreduced (lane 2) guinea pig soluble receptor conjugated to Fc and blotted with rabbit anti-FCGRT polyclonal primary antibody specific for a FcRn alpha chain peptide partially conserved in the guinea pig sequence (see Figure 3(a) for the sequence). (b) Images of Coomassie stained gel (left) and a western blot demonstrating binding of the engineered guinea pig soluble FcRn receptor to a commercial human IgG column. Shown are the molecular weight markers (lane 1, with the respective mass shown), cell culture medium, column load (lane 2), column flow-through (lane 3), and column eluate (lane 4). The apparent molecular mass is lower than 50 kDa, whereas the theoretical molecular mass without glycosylation is ~43 kDa. The column binding and elution was repeated three times with similar results.

Figure 3

Alignment of human and guinea pig FCGRT (a) and B2M (b) chains of the FcRn receptor. Program LALIGN with matrix BLOSUM50, as described [48] was used. Similar results were obtained using BLAST. Regions highlighted in yellow correspond to signal and transmembrane domains of these chains and were not included in the engineered soluble receptor. The immunogen used for polyclonal anti-FCGRT antibody production is highlighted in cyan.