IgG trafficking in the adult pig small intestine: one- or bidirectional transfer across the enterocyte brush border?

Short FcRn-Binding Peptides Enable Salvage and Transcytosis of scFv Antibody Fragments

Therapeutic antibodies have become one of the most widely used classes of biotherapeutics due to their unique antigen specificity and their ability to be engineered against diverse disease targets. There is significant interest in utilizing truncated antibody fragments as therapeutics, as their small size affords favorable properties such as increased tumor penetration as well as the ability to utilize lower-cost prokaryotic production methods. Their small size and simple architecture, however, also lead to rapid blood clearance, limiting the efficacy of these potentially powerful therapeutics. A common approach to circumvent these limitations is to enable engagement with the half-life extending neonatal Fc receptor (FcRn). This is usually achieved via fusion with a large Fc domain, which negates the benefits of the antibody fragment's small size. In this work, we show that modifying antibody fragments with short FcRn-binding peptide domains that mimic native IgG engagement with FcRn enables binding and FcRn-mediated recycling and transmembrane transcytosis in cell-based assays. Further, we show that rational, single amino acid mutations to the peptide sequence have a significant impact on the receptor-mediated function and investigate the underlying structural basis for this effect using computational modeling. Finally, we report the identification of a short peptide from human serum albumin that enables FcRn-mediated function when grafted onto a single-chain variable fragment (scFv) scaffold, establishing an approach for the rational selection of short-peptide domains from full-length proteins that could enable the transfer of non-native functions to small recombinant proteins without significantly impacting their size or structure.

Maternal Vaccination. Immunization of Sows during Pregnancy against ETEC Infections

The immunology of pregnancy is an evolving consequence of multiple reciprocal interactions between the maternal and the fetal-placental systems. The immune response must warrant the pregnancy outcome (including tolerance to paternal antigens), but at the same time, efficiently respond to pathogenic challenges. Enterotoxigenic Escherichia coli (ETEC) strains are a major cause of illness and death in neonatal and recently weaned pigs. This review aims to give an overview of the current rationale on the maternal vaccination strategies for the protection of the newborn pig against ETEC. Newborn piglets are immunodeficient and naturally dependent on the maternal immunity transferred by colostrum for protection—a maternal immunity that can be obtained by vaccinating the sow during pregnancy. Our current knowledge of the interactions between the pathogen strategies, virulence factors, and the host immune system is aiding the better design of vaccination strategies in this particular and challenging host status. Challenges include the need for better induction of immunity at the mucosal level with the appropriate use of adjuvants, able to induce the most appropriate and long-lasting protective immune response. These include nanoparticle-based adjuvants for oral immunization. Experiences can be extrapolated to other species, including humans.