Generation of antibody- and B cell-deficient pigs by targeted disruption of the J-region gene segment of the heavy chain locus

Immune characterization of a xenogeneic human lung cross-circulation support system

Improved approaches to expanding the pool of donor lungs suitable for transplantation are critically needed for the growing population with end-stage lung disease. Cross-circulation (XC) of whole blood between swine and explanted human lungs has previously been reported to enable the extracorporeal recovery of donor lungs that declined for transplantation due to acute, reversible injuries. However, immunologic interactions of this xenogeneic platform have not been characterized, thus limiting potential translational applications. Using flow cytometry and immunohistochemistry, we demonstrate that porcine immune cell and immunoglobulin infiltration occurs in this xenogeneic XC system, in the context of calcineurin-based immunosuppression and complement depletion. Despite this, xenogeneic XC supported the viability, tissue integrity, and physiologic improvement of human donor lungs over 24 hours of xeno-support. These findings provide targets for future immunomodulatory strategies to minimize immunologic interactions on this organ support biotechnology.

Comparative Aspects of Immunoglobulin Gene Rearrangement Arrays in Different Species

Studies in humans and mice indicate the critical role of the surrogate light chain in the selection of the productive immunoglobulin repertoire during B cell development. However, subsequent studies using mutant mice have also demonstrated that alternative pathways are allowed. Our recent investigation has shown that some species, such as pig, physiologically use preferential rearrangement of authentic light chains, and become independent of surrogate light chains. Here we summarize the findings from swine and compare them with results in other species. In both groups, allelic and isotypic exclusions remain intact, so the different processes do not alter the paradigm of B-cell monospecificity. Both groups also retained some other essential processes, such as segregated and sequential rearrangement of heavy and light chain loci, preferential rearrangement of light chain kappa before lambda, and functional κ-deleting element recombination. On the other hand, the respective order of heavy and light chains rearrangement may vary, and rearrangement of the light chain kappa and lambda on different chromosomes may occur independently. Studies have also confirmed that the surrogate light chain is not required for the selection of the productive repertoire of heavy chains and can be substituted by authentic light chains. These findings are important for understanding evolutional approaches, redundancy and efficiency of B-cell generation, dependencies on other regulatory factors, and strategies for constructing therapeutic antibodies in unrelated species. The results may also be important for explaining interspecies differences in the proportional use of light chains and for the understanding of divergences in rearrangement processes. Therefore, the division into two groups may not be definitive and there may be more groups of intermediate species.

Unraveling the role of B cells in the pathogenesis of an oncogenic avian herpesvirus

Marek's disease virus (MDV) is a highly oncogenic alphaherpesvirus that causes immunosuppression, paralysis, and deadly lymphomas in chickens. In infected animals, B cells are efficiently infected and are thought to amplify the virus and transfer it to T cells. MDV subsequently establishes latency in T cells and transforms CD4⁺ T cells, resulting in fatal lymphomas. Despite many years of research, the exact role of the different B and T cell subsets in MDV pathogenesis remains poorly understood, mostly due to the lack of reverse genetics in chickens. Recently, Ig heavy chain J gene segment knockout (JH-KO) chickens lacking mature and peripheral B cells have been generated. To determine the role of these B cells in MDV pathogenesis, we infected JH-KO chickens with the very virulent MDV RB1B strain. Surprisingly, viral load in the blood of infected animals was not altered in the absence of B cells. More importantly, disease and tumor incidence in JH-KO chickens was comparable to wild-type animals, suggesting that both mature and peripheral B cells are dispensable for MDV pathogenesis. Intriguingly, MDV efficiently replicated in the bursa of Fabricius in JH-KO animals, while spread of the virus to the spleen and thymus was delayed. In the absence of B cells, MDV readily infected CD4⁺ and CD8⁺ T cells, allowing efficient virus replication in the lymphoid organs and transformation of T cells. Taken together, our data change the dogma of the central role of B cells, and thereby provide important insights into MDV pathogenesis.

Antibody Repertoire Development in Swine

We describe the domestication of the species, explore its value to agriculture and bioscience, and compare its immunoglobulin (Ig) genes to those of other vertebrates. For encyclopedic information, we cite earlier reviews and chapters. We provide current gene maps for the heavy and light chain loci and describe their polygeny and polymorphy. B-cell and antibody repertoire development is a major focus, and we present findings that challenge several mouse-centric paradigms. We focus special attention on the role of ileal Peyer's patches, the largest secondary lymphoid tissues in newborn piglets and a feature of all artiodactyls. We believe swine fetal development and early class switch evolved to provide natural secretory IgA antibodies able to prevent translocation of bacteria from the gut while the bacterial PAMPs drive development of adaptive immunity. We discuss the value of using the isolator piglet model to address these issues.

Genome-editing technologies to improve research, reproduction, and production in pigs

The ability to directly manipulate the pig genome through genetic engineering has been available to the research community for over three decades. This technology has progressed from the random insertion of foreign DNA, via a variety of techniques (pronuclear microinjection, sperm mediated gene transfer, and integration of mobile genetic elements), to manipulation of endogenous genes, via homologous recombination in somatic cells followed by somatic cell nuclear transfer. Over the last few years, designer nucleases facilitated the development of techniques that provide efficient ways to introduce foreign DNA or to modify endogenous genes in eggs, zygotes, or somatic cells. Together, these genome-editing technologies have essentially removed the obstacles to gene manipulation in swine. Although the regulatory environment is still unclear for agricultural applications, genetic engineering of pigs will continue to advance biomedicine and biology. In addition, genetic engineering is now sufficiently simple and efficient that agricultural research can now ask basic and applied questions that are not hampered by limited funding.

Livestock in biomedical research: history, current status and future prospective

Livestock models have contributed significantly to biomedical and surgical advances. Their contribution is particularly prominent in the areas of physiology and assisted reproductive technologies, including understanding developmental processes and disorders, from ancient to modern times. Over the past 25 years, biomedical research that traditionally embraced a diverse species approach shifted to a small number of model species (e.g. mice and rats). The initial reasons for focusing the main efforts on the mouse were the availability of murine embryonic stem cells (ESCs) and genome sequence data. This powerful combination allowed for precise manipulation of the mouse genome (knockouts, knockins, transcriptional switches etc.) leading to ground-breaking discoveries on gene functions and regulation, and their role in health and disease. Despite the enormous contribution to biomedical research, mouse models have some major limitations. Their substantial differences compared with humans in body and organ size, lifespan and inbreeding result in pronounced metabolic, physiological and behavioural differences. Comparative studies of strategically chosen domestic species can complement mouse research and yield more rigorous findings. Because genome sequence and gene manipulation tools are now available for farm animals (cattle, pigs, sheep and goats), a larger number of livestock genetically engineered (GE) models will be accessible for biomedical research. This paper discusses the use of cattle, goats, sheep and pigs in biomedical research, provides an overview of transgenic technology in farm animals and highlights some of the beneficial characteristics of large animal models of human disease compared with the mouse. In addition, status and origin of current regulation of GE biomedical models is also reviewed.

Antibody repertoire development in fetal and neonatal piglets. XXIV. Hypothesis: The ileal Peyer patches (IPP) are the major source of primary, undiversified IgA antibodies in newborn piglets

The ileal Peyers patches (IPP) of newborn germfree (GF) piglets were isolated into blind loops and the piglets colonized with a defined probiotic microflora. After 5 weeks, IgA levels in the intestinal lavage (IL) of loop piglets remained at GF levels and IgM comprised ∼70% while in controls, IgA levels were elevated 5-fold and comprised ∼70% of total Igs. Loop piglets also had reduced serum IgA levels suggesting the source of serum IgA had been interrupted. The isotype profile for loop contents was intermediate between that in the IL of GF and probiotic controls. Surprisingly, colonization alone did not result in repertoire diversification in the IPP. Rather, colonization promoted pronounced proliferation of fully switched IgA(+)IgM(-) B cells in the IPP that supply early, non-diversified "natural" SIgA antibodies to the gut lumen and a primary IgA response in serum.

Selection of Recombinant Human Antibodies

Since the development of therapeutic antibodies the demand of recombinant human antibodies is steadily increasing. Traditionally, therapeutic antibodies were generated by immunization of rat or mice, the generation of hybridoma clones, cloning of the antibody genes and subsequent humanization and engineering of the lead candidates. In the last few years, techniques were developed that use transgenic animals with a human antibody gene repertoire. Here, modern recombinant DNA technologies can be combined with well established immunization and hybridoma technologies to generate already affinity maturated human antibodies. An alternative are in vitro technologies which enabled the generation of fully human antibodies from antibody gene libraries that even exceed the human antibody repertoire. Specific antibodies can be isolated from these libraries in a very short time and therefore reduce the development time of an antibody drug at a very early stage.In this review, we describe different technologies that are currently used for the in vitro and in vivo generation of human antibodies.

Establishment of cell-based transposon-mediated transgenesis in cattle

Transposon-mediated transgenesis is a well-established tool for genome modification in small animal models. However, translation of this active transgenic method to large animals warrants further investigations. Here, the piggyBac (PB) and sleeping beauty (SB) transposon systems were assessed for stable gene transfer into the cattle genome. Bovine fibroblasts were transfected either with a helper-independent PB system or a binary SB system. Both transposons were highly active in bovine cells increasing the efficiency of DNA integration up to 88 times over basal nonfacilitated integrations in a colony formation assay. SB transposase catalyzed multiplex transgene integrations in fibroblast cells transfected with the helper vector and two donor vectors carrying different transgenes (fluorophore and neomycin resistance). Stably transfected fibroblasts were used for SCNT and on in vitro embryo culture, morphologically normal blastocysts that expressed the fluorophore were obtained with both transposon systems. The data indicate that transposition is a feasible approach for genetic engineering in the cattle genome.

Respiratory nanoparticle-based vaccines and challenges associated with animal models and translation

Vaccine development has had a huge impact on human health. However, there is a significant need to develop efficacious vaccines for several existing as well as emerging respiratory infectious diseases. Several challenges need to be overcome to develop efficacious vaccines with translational potential. This review focuses on two aspects to overcome some barriers - 1) the development of nanoparticle-based vaccines, and 2) the choice of suitable animal models for respiratory infectious diseases that will allow for translation. Nanoparticle-based vaccines, including subunit vaccines involving synthetic and/or natural polymeric adjuvants and carriers, as well as those based on virus-like particles offer several key advantages to help overcome the barriers to effective vaccine development. These include the ability to deliver combinations of antigens, target the vaccine formulation to specific immune cells, enable cross-protection against divergent strains, act as adjuvants or immunomodulators, allow for sustained release of antigen, enable single dose delivery, and potentially obviate the cold chain. While mouse models have provided several important insights into the mechanisms of infectious diseases, they are often a limiting step in translation of new vaccines to the clinic. An overview of different animal models involved in vaccine research for respiratory infections, with advantages and disadvantages of each model, is discussed. Taken together, advances in nanotechnology, combined with the right animal models for evaluating vaccine efficacy, has the potential to revolutionize vaccine development for respiratory infections.

Generation of B cell-deficient pigs by highly efficient CRISPR/Cas9-mediated gene targeting

Generating B cell-deficient mutant is the first step to produce human antibody repertoires in large animal models. In this study, we applied the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated (Cas) system to target the JH region of the pig IgM heavy chain gene which is crucial for B cell development and differentiation. Transfection of IgM-targeting Cas9 plasmid in primary porcine fetal fibroblasts (PFFs) enabled inducing gene knock out (KO) in up to 53.3% of colonies analyzed, a quarter of which harbored biallelic modification, which was much higher than that of the traditional homologous recombination (HR). With the aid of somatic cell nuclear transfer (SCNT) technology, three piglets with the biallelic IgM heavy chain gene mutation were produced. The piglets showed no antibody-producing B cells which indicated that the biallelic mutation of the IgM heavy chain gene effectively knocked out the function of the IgM and resulted in a B cell-deficient phenotype. Our study suggests that the CRISPR/Cas9 system combined with SCNT technology is an efficient genome-editing approach in pigs.

The Mammary Gland in Mucosal and Regional Immunity

The mammary gland (MG) lacks a mucosa but is part of the mucosal immune system because of its role in passive mucosal immunity. The MG is not an inductive site for mucosal immunity. Rather, synthesis of immunoglobulin (Ig)A by plasma cells stimulated at distal inductive sites dominate in the milk of rodents, humans, and swine whereas IgG1 derived from serum predominates in ruminants. Despite the considerable biodiversity in the role of the MG, IgG passively transfers the maternal systemic immunological experience whereas IgA transfers the mucosal immunological experience. Although passive antibodies are protective, they and other lacteal constituents can be immunoregulatory. Immune protection of the MG largely depends on the innate immune system; the monocytes–macrophages group together with intraepithelial lymphocytes is dominant in the healthy gland. An increase in somatic cells (neutrophils) and various interleukins signal infection (mastitis) and a local immune response in the MG. The major role of the MG to mucosal immunity is the passive immunity supplied to the suckling neonate.

Current progress of genetically engineered pig models for biomedical research

The first transgenic pigs were generated for agricultural purposes about three decades ago. Since then, the micromanipulation techniques of pig oocytes and embryos expanded from pronuclear injection of foreign DNA to somatic cell nuclear transfer, intracytoplasmic sperm injection-mediated gene transfer, lentiviral transduction, and cytoplasmic injection. Mechanistically, the passive transgenesis approach based on random integration of foreign DNA was developed to active genetic engineering techniques based on the transient activity of ectopic enzymes, such as transposases, recombinases, and programmable nucleases. Whole-genome sequencing and annotation of advanced genome maps of the pig complemented these developments. The full implementation of these tools promises to immensely increase the efficiency and, in parallel, to reduce the costs for the generation of genetically engineered pigs. Today, the major application of genetically engineered pigs is found in the field of biomedical disease modeling. It is anticipated that genetically engineered pigs will increasingly be used in biomedical research, since this model shows several similarities to humans with regard to physiology, metabolism, genome organization, pathology, and aging.

Generation of recombination activating gene-1-deficient neonatal piglets: a model of T and B cell deficient severe combined immune deficiency

Although severe combined immune deficiency (SCID) is a very important research model for mice and SCID mice are widely used, there are only few reports describing the SCID pig models. Therefore, additional research in this area is needed. In this study, we describe the generation of Recombination activating gene-1 (Rag-1)-deficient neonatal piglets in Duroc breed using somatic cell nuclear transfer (SCNT) with gene targeting and analysis using fluorescence-activated cell sorting (FACS) and histology. We constructed porcine Rag-1 gene targeting vectors for the Exon 2 region and obtained heterozygous/homozygous Rag-1 knockout cell colonies using SCNT. We generated two Rag-1-deficient neonatal piglets and compared them with wild-type neonatal piglets. FACS analysis showed that Rag-1 disruption causes a lack of Immunoglobulin M-positive B cells and CD3-positive T cells in peripheral blood mononuclear cells. Consistent with FACS analysis, histological analysis revealed structural defects and an absence of mature lymphocytes in the spleen, mesenteric lymph node (MLNs), and thymus in Rag-1-deficient piglets. These results confirm that Rag-1 is necessary for the generation of lymphocytes in pigs, and Rag-1-deficient piglets exhibit a T and B cell deficient SCID (T-B-SCID) phenotype similar to that of rodents and humans. The T-B-SCID pigs with Rag-1 deficiency generated in this study could be a suitably versatile model for laboratory, translational, and biomedical research, including the development of a humanized model and assessment of pluripotent stem cells.

The porcine innate immune system: an update

Over the last few years, we have seen an increasing interest and demand for pigs in biomedical research. Domestic pigs (Sus scrofa domesticus) are closely related to humans in terms of their anatomy, genetics, and physiology, and often are the model of choice for the assessment of novel vaccines and therapeutics in a preclinical stage. However, the pig as a model has much more to offer, and can serve as a model for many biomedical applications including aging research, medical imaging, and pharmaceutical studies to name a few. In this review, we will provide an overview of the innate immune system in pigs, describe its anatomical and physiological key features, and discuss the key players involved. In particular, we compare the porcine innate immune system to that of humans, and emphasize on the importance of the pig as model for human disease.

Expression of recombinant antibodies

Recombinant antibodies are highly specific detection probes in research, diagnostics, and have emerged over the last two decades as the fastest growing class of therapeutic proteins. Antibody generation has been dramatically accelerated by in vitro selection systems, particularly phage display. An increasing variety of recombinant production systems have been developed, ranging from Gram-negative and positive bacteria, yeasts and filamentous fungi, insect cell lines, mammalian cells to transgenic plants and animals. Currently, almost all therapeutic antibodies are still produced in mammalian cell lines in order to reduce the risk of immunogenicity due to altered, non-human glycosylation patterns. However, recent developments of glycosylation-engineered yeast, insect cell lines, and transgenic plants are promising to obtain antibodies with "human-like" post-translational modifications. Furthermore, smaller antibody fragments including bispecific antibodies without any glycosylation are successfully produced in bacteria and have advanced to clinical testing. The first therapeutic antibody products from a non-mammalian source can be expected in coming next years. In this review, we focus on current antibody production systems including their usability for different applications.

Antibody repertoire development in fetal and neonatal piglets. XII. Three IGLV genes comprise 70% of the pre-immune repertoire and there is little junctional diversity

We characterized 239 lambda rearrangements from fetal and germfree (GF) piglets to: (1) determine if transcripts recovered from the earliest sites of B cell lymphogenesis were unique (2) determine what proportion of the genome is used to form the pre-immune repertoire (3) estimate the degree of somatic hypermutation and junctional diversity during ontogeny and (4) test whether piglets maintained germfree in isolators (GF piglets) have a more diversified repertoire than fetal piglets. We show that all expressed lambda genes belong to the IGLV3 and IGLV8 families and only IGLJ2 and IGLJ3 were expressed and used equally throughout fetal and neonatal life. Only genes of the IGLV8 family were used in yolk sac and fetal liver and in these tissues, IGLV8-10 comprised >50%. However, the IGLV8 genes recovered at these early sites of B cell lymphogenesis were recovered at all stages of development. Thus, no unique lambda rearrangement was recovered at the first sites of B cell development. The frequency of somatic hypermutation (SHM) in fetal piglets was ~5.9 per Kb equivalent, mutation were concentrated in CDR regions and did not increase in GF piglets. The average CDR3 length was 30 nt ± 2.7 and did not change in GF piglets. Similar to the heavy chain pre-immune repertoire in this species, three IGLV genes account for ~70% of the repertoire. Unlike the heavy chain repertoire, junctional diversity was very limited.

Domestic animal models for biomedical research

Experimental animals in biomedical research provide insights into disease mechanisms and models for determining the efficacy and safety of new therapies and for discovery of corresponding biomarkers. Although mouse and rat models are most widely used, observations in these species cannot always be faithfully extrapolated to human patients. Thus, a number of domestic species are additionally used in specific disease areas. This review summarizes the most important applications of domestic animal models and emphasizes the new possibilities genetic tailoring of disease models, specifically in pigs, provides.

Completion of the swine genome will simplify the production of swine as a large animal biomedical model

Background

Anatomic and physiological similarities to the human make swine an excellent large animal model for human health and disease.

Methods

Cloning from a modified somatic cell, which can be determined in cells prior to making the animal, is the only method available for the production of targeted modifications in swine.

Results

Since some strains of swine are similar in size to humans, technologies that have been developed for swine can be readily adapted to humans and vice versa. Here the importance of swine as a biomedical model, current technologies to produce genetically enhanced swine, current biomedical models, and how the completion of the swine genome will promote swine as a biomedical model are discussed.

Conclusions

The completion of the swine genome will enhance the continued use and development of swine as models of human health, syndromes and conditions.

Assessment of fecundity and germ line transmission in two transgenic pig lines produced by sleeping beauty transposition

Recently, we described a simplified injection method for producing transgenic pigs using a non-autonomous Sleeping Beauty transposon system. The founder animals showed ubiquitous expression of the Venus fluorophore in almost all cell types. To assess, whether expression of the reporter fluorophore affects animal welfare or fecundity, we analyzed reproductive parameters of two founder boars, germ line transmission, and organ and cell specific transgene expression in animals of the F1 and F2 generation. Molecular analysis of ejaculated sperm cells suggested three monomeric integrations of the Venus transposon in both founders. To test germ line transmission of the three monomeric transposon integrations, wild-type sows were artificially inseminated. The offspring were nursed to sexual maturity and hemizygous lines were established. A clear segregation of the monomeric transposons following the Mendelian rules was observed in the F1 and F2 offspring. Apparently, almost all somatic cells, as well as oocytes and spermatozoa, expressed the Venus fluorophore at cell-type specific levels. No detrimental effects of Venus expression on animal health or fecundity were found. Importantly, all hemizygous lines expressed the fluorophore in comparable levels, and no case of transgene silencing or variegated expression was found after germ line transmission, suggesting that the insertions occurred at transcriptionally permissive loci. The results show that Sleeping Beauty transposase-catalyzed transposition is a promising approach for stable genetic modification of the pig genome.

Antibody repertoire development in fetal and neonatal piglets. XXII. λ Rearrangement precedes κ rearrangement during B-cell lymphogenesis in swine

VDJ and VJ rearrangements, expression of RAG-1, Tdt and VpreB, and the presence of signal joint circles (SJC) were used to identify sites of B-cell lymphogenesis. VDJ, VλJλ but not VκJκ rearrangements or SJC were recovered from yolk sac (YS) at 20 days of gestation (DG) along with strong expression of VpreB and RAG-1 but weak Tdt expression. VλJλ rearrangements but not VκJκ rearrangements were recovered from fetal liver at 30-50 DG. SJC were pronounced in bone marrow at 95 DG where VκJκ rearrangements were first recovered. The VλJλ rearrangements recovered at 20-50 DG used some of the same Vλ and Jλ segments seen in older fetuses and adult animals. Hence the textbook paradigm for the order of light-chain rearrangement does not apply to swine. Consistent with weak Tdt expression in early sites of lymphogenesis, N-region additions in VDJ rearrangements were more frequent at 95 DG. Junctional diversity in VλJλ rearrangement was limited at all stages of development. There was little evidence for B-cell lymphogenesis in the ileal Peyer's patches. The widespread recovery of VpreB transcripts in whole, non-lymphoid tissue was unexpected as was its recovery from bone marrow and peripheral blood monocytes. Based on recovery of SJC, B-cell lymphogenesis continues for at least 5 weeks postpartum.

Resolution of an immunodiagnostic dilemma: heavy chain chimeric antibodies for species in which plasmocytomas are unknown

The immunoglobulin (Ig) genes of many vertebrates have been characterized but IgG subclasses, IgD and IgE proteins are only available for three species in which plasmacytomas occur. This creates a major problem in the production and specificity verification of diagnostic anti-Ig reagents for the vast majority of mammals. We describe a novel solution using the swine system with its eleven different variants of IgG. It involves the in vitro synthesis of chimeric porcine-camelid heavy chain antibodies (HCAbs) that do not require light chains and therefore only a single transfection vector. The expressed chimeric HCAbs are comprised of the camelid VHH domain encoding specificity for lysozyme and the hinge, CH2 and CH3 domains of the various porcine IgGs. These HCAb retain their antigenic integrity and their ability to recognize lysozyme. The engineered specificity assures that these HCAb can be immobilized in native configuration when used for testing the specificity of anti-swine IgG antibodies. Comparative data to illustrate the importance of this point are provided. These are now available for use in hybridoma selection and as reference standards for evaluating the specificity of currently available anti-swine IgG antibodies.

Linkage haplotype for allotypic variants of porcine IgA and IgG subclass genes

Six putative subclasses of expressed porcine IgG have been described from gene sequences and allotypic variants for five of these have been proposed. We tested this hypothesis by studying the transcription of these 11 variants in outbred hemizygous farm pigs. Since Cγ subclass genes are closely linked, they are most likely inherited as a haplotype. Since hemizygous pigs can only express genes encoded on one chromosome, identifying the expressed genes can indicate which allelic variants are linked as well as testing whether the putative alleles are indeed alleles or separate subclass genes. The procedure for producing B cell knockout pigs has recently been described; our study examines transcripts from the hemizygous parents and offspring generated by this technology. More than 570 Cγ gene clones from hemizygous animals were identified according to subclass and allotype by a combination of clone hybridization and sequencing. IgG3 accounted for 80% in newborn animals but <5% in adults. IgG1 accounted for ~50% of all clones recovered from adults and IgG4 was the least frequently recovered (4%). Results indicate that IgG1(b), IgG2(a), IgG3, IgG4(a), IgG5(a), and IgG6(a) are linked and also linked to IgA(a). This comprises a haplotype for domesticated swine. For simplicity, we propose that the current nomenclature for the allotypes of IgG1 be reversed so that all genes in the Cγ(a)-Cα(a) haplotype are designated "a".

Characterization of the rabbit neonatal Fc receptor (FcRn) and analyzing the immunophenotype of the transgenic rabbits that overexpresses FcRn

The neonatal Fc receptor (FcRn) regulates IgG and albumin homeostasis, mediates maternal IgG transport, takes an active role in phagocytosis, and delivers antigen for presentation. We have previously shown that overexpression of FcRn in transgenic mice significantly improves the humoral immune response. Because rabbits are an important source of polyclonal and monoclonal antibodies, adaptation of our FcRn overexpression technology in this species would bring significant advantages. We cloned the full length cDNA of the rabbit FcRn alpha-chain and found that it is similar to its orthologous analyzed so far. The rabbit FcRn - IgG contact residues are highly conserved, and based on this we predicted pH dependent interaction, which we confirmed by analyzing the pH dependent binding of FcRn to rabbit IgG using yolk sac lysates of rabbit fetuses by Western blot. Using immunohistochemistry, we detected strong FcRn staining in the endodermal cells of the rabbit yolk sac membrane, while the placental trophoblast cells and amnion showed no FcRn staining. Then, using BAC transgenesis we generated transgenic rabbits carrying and overexpressing a 110 kb rabbit genomic fragment encoding the FcRn. These transgenic rabbits--having one extra copy of the FcRn when hemizygous and two extra copies when homozygous--showed improved IgG protection and an augmented humoral immune response when immunized with a variety of different antigens. Our results in these transgenic rabbits demonstrate an increased immune response, similar to what we described in mice, indicating that FcRn overexpression brings significant advantages for the production of polyclonal and monoclonal antibodies.

Use of single stranded targeting DNA or negative selection does not further increase the efficiency of a GGTA1 promoter trap

Although several techniques have been developed to create gene knockouts in pigs, homologous recombination will continue to be required for site-specific genome modifications that are more sophisticated than gene disruption (base changes, domain exchanges, conditional knockouts). The objective of the present paper was to improve the efficiency of homologous recombination in porcine fetal fibroblasts, which would be used to produce gene knockout pigs by somatic cell nuclear transfer. A promoter-trap was used to enable selection of GGTA1 targeted cells. Cells were transfected with either a single stranded or double stranded targeting vector, or a vector, with or without a negative selectable marker gene (diphtheria toxin-A). Although targeting efficiencies were numerically lower for single stranded targeting vectors, statistical differences could not be detected. Similarly, the use of a negative selectable marker (in cis or trans) provided numerically lower targeting efficiencies, statistical differences again could not be detected. Overall, the targeting efficiencies ranged from 1.5×10-5 to 2.5×10-6 targeting events per transfected cell. Given the results, it may be applicable to investigate multiple enrichment techniques for homologous recombination, given that every targeted locus is different.

Precision editing of large animal genomes

Transgenic animals are an important source of protein and nutrition for most humans and will play key roles in satisfying the increasing demand for food in an ever-increasing world population. The past decade has experienced a revolution in the development of methods that permit the introduction of specific alterations to complex genomes. This precision will enhance genome-based improvement of farm animals for food production. Precision genetics also will enhance the development of therapeutic biomaterials and models of human disease as resources for the development of advanced patient therapies.

PB, Butler J, Uc A. An activated immune and inflammatory response targets the pancreas of newborn pigs with cystic fibrosis

BACKGROUND/AIMS

In cystic fibrosis (CF), pancreatic disease begins in utero and progresses over time to complete destruction of the organ. Although inflammatory cells have been detected in the pancreas of humans and pigs with CF, their subtypes have not been characterized.

METHODS

Using four-color flow cytometry, we analyzed the surface antigens of leukocytes in pancreas, blood, and mesenteric lymph nodes (MLN) of newborn pigs with CF (CFTR(-/-) and CFTR(Δ)(F508/)(Δ)(F508)) and in those without CF (CFTR(+/-), CFTR(+/)(Δ)(F508), CFTR(+/+)). Pancreatic histopathology was examined with HE stain.

RESULTS

CF pig pancreas had patchy distribution of inflammatory cells with neutrophils/macrophages in dilated acini, and lymphocytes in the interstitium compared to non-CF. B cells, effector (MHC-II(+)) and cytotoxic (CD2(+)CD8(+)) γδ T cells, activated (MHC-II(+) and/or CD25(+)) and effector (CD4(+)CD8(+)) αβ T helper cells, effector natural killer cells (MHC-II(+)CD3(-)CD8(+)), and monocytes/macrophages and neutrophils were increased in the CF pig pancreas compared to pigs without CF. Blood and MLN leukocyte populations were not different between CF and non-CF pigs.

CONCLUSIONS

We discovered an activated immune response that was specific to the pancreas of newborn CF pigs; inflammation was not systemic. The presence of both innate and adaptive immune cells suggests that the disease process is complex and extensive.

Antibody repertoire development in fetal and neonatal piglets XXI. Usage of most VH genes remains constant during fetal and postnatal development

Usage of variable region gene segments during development of the antibody repertoire in mammals is unresolved in part because of the complexity of the locus in mice and humans and the difficulty of distinguishing intrinsic from extrinsic influences in these species. We present the first vertical studies on VH usage that spans the fetal and neonatal period using the piglet model. We tracked VH usage in DNA rearrangements and in VDJ transcripts throughout 75 days of gestation (DG) in outbred fetuses, thereafter in outbred germfree and colonized isolator piglets, isolator piglets infected with swine influenza and in conventionally reared nematode-infected adults. Seven VH genes account for >90% of the pre-immune repertoire which is the same among tissues and in both transcripts and DNA rearrangements. Statistical modeling supports the view that proportional usage of the major genes remains constant during fetal life and that postnatal usage ranking is similar to that during fetal life. Changes in usage ranking are developmental not antigen dependent. In this species exposure to environmental antigens results in diversification of the repertoire by somatic hypermutation of the same small number of VH genes that comprise the pre-immune repertoire, not by using other VH gene available in the germline. Therefore in swine a small number of VH genes shape the antibody repertoire throughout life questioning the need for extensive VH polygeny.

Genetic modifications of pigs for medicine and agriculture

Genetically modified swine hold great promise in the fields of agriculture and medicine. Currently, these swine are being used to optimize production of quality meat, to improve our understanding of the biology of disease resistance, and to reduced waste. In the field of biomedicine, swine are anatomically and physiologically analogous to humans. Alterations of key swine genes in disease pathways provide model animals to improve our understanding of the causes and potential treatments of many human genetic disorders. The completed sequencing of the swine genome will significantly enhance the specificity of genetic modifications, and allow for more accurate representations of human disease based on syntenic genes between the two species. Improvements in both methods of gene alteration and efficiency of model animal production are key to enabling routine use of these swine models in medicine and agriculture.

Efficient immunoglobulin gene disruption and targeted replacement in rabbit using zinc finger nucleases

Rabbits are widely used in biomedical research, yet techniques for their precise genetic modification are lacking. We demonstrate that zinc finger nucleases (ZFNs) introduced into fertilized oocytes can inactivate a chosen gene by mutagenesis and also mediate precise homologous recombination with a DNA gene-targeting vector to achieve the first gene knockout and targeted sequence replacement in rabbits. Two ZFN pairs were designed that target the rabbit immunoglobulin M (IgM) locus within exons 1 and 2. ZFN mRNAs were microinjected into pronuclear stage fertilized oocytes. Founder animals carrying distinct mutated IgM alleles were identified and bred to produce offspring. Functional knockout of the immunoglobulin heavy chain locus was confirmed by serum IgM and IgG deficiency and lack of IgM(+) and IgG(+) B lymphocytes. We then tested whether ZFN expression would enable efficient targeted sequence replacement in rabbit oocytes. ZFN mRNA was co-injected with a linear DNA vector designed to replace exon 1 of the IgM locus with ∼1.9 kb of novel sequence. Double strand break induced targeted replacement occurred in up to 17% of embryos and in 18% of fetuses analyzed. Two major goals have been achieved. First, inactivation of the endogenous IgM locus, which is an essential step for the production of therapeutic human polyclonal antibodies in the rabbit. Second, establishing efficient targeted gene manipulation and homologous recombination in a refractory animal species. ZFN mediated genetic engineering in the rabbit and other mammals opens new avenues of experimentation in immunology and many other research fields.