A second model recently developed using CRISPR Cas is the
A second model recently developed using CRISPR/Cas9 is the CF rabbit, both CFTR null or carrying the ΔF508 mutation . This model was also generated because of the need of an easy animal model that reproduces the lung phenotype. The CF rabbit is still at the initial characterization stage, but preliminary evidence shows development of a lung phenotype including the presence of bacterial infection in the airways.
More recently CF researchers have been trying to generate a humanized mouse model that expresses the human CFTR gene . This has been possible by using bacteria artificial chromosomes (BAC) or yeast artificial chromosome (YAC) that allow the transfer of a large genomic sequence, including regulatory elements such as promoters, introns and flanking regions [52,53]. In the future, it will be likely possible to use the CRISP/Cas9 gene editing technology to introduce specific CFTR mutations and use this system for testing new treatments.
Conclusions CF is a multi-organ disease and the use of in-vivo animal models is necessary to have a more comprehensive understanding of the disease to apply for the search of new therapies. Both small animal models (i.e. mouse, rat) and larger mammals (i.e. rabbit, ferret, pig) have been developed. Although all of these models have limitations and do not fully recapitulate the human disease, the comparative analysis of CF biology among species has been the most useful tool to understand the pathophysiologic processes of CFTR in different organs (see Table 1).
Funding This work was supported by the National Institutes of Health (RO1DK096096, RO1DK-079005-07, RO1DK101528, DK034989 Silvio O. Conte Digestive Diseases Research Core Center); by Partners Seeking a Cure Foundation and a grant from Connecticut Innovations (16-RMA-YALE-26).
Introduction To achieve the first goal, it is important to use components that have been already characterized and allow for precise tracking of the immune response. Thus, many research groups used well-characterized model Malonyl Coenzyme A that are transgenically expressed as targets in the liver. In addition, a transfer of a defined T cell population isolated from TcR-transgenic mice facilitates the tracking and characterization of autoaggressive T cells after adoptive transfer. The problem with such transgenic approaches using model antigens is its feasibility as they are often not related to the human disease. Yet, to be able to investigate basic mechanisms involved in liver cell destruction and if present hepatic fibrosis, it is of course important to be successful in breaking immune tolerance in the liver. Thus, many of these transgenic models revealed novel mechanisms of immune activation as well as immune regulation. To be sure to elicit a strong immune response in the liver, several aspects would have to be fulfilled. First, a certain degree of susceptibility, which may include the ideal MHC haplotype fit for presenting critical epitopes of an autoantigen or a defect in immune regulation as occurring in spontaneous disease models like the non-obese diabetic (NOD) mouse that is predominantly used to study type 1 diabetes (T1D) . Second, a target autoantigen whose expression is transgenically controlled and restricted to the liver. Third, the presence of a strong T cell response with specificity to the target autoantigen. This can be accomplished by either directly using TcR-transgenic mice as model system or by adoptively transferring T cells isolated from TcR-transgenic mice. Forth, a strong inflammation of the liver that provides critical inflammatory factors that ensure activation and proliferation of autoantigen-specific T cells. To achieve the second goal, namely the generation of a model that is as close as possible to the human disease in order to have a tool for evaluating possible therapies, it is important that the path of disease induction is feasible and that the clinical phenotype, including serology and histology is similar to the one found in patients. A realistic scenario for the development of AIH in patients would be one or a series of triggering event(s) that would induce liver autoimmunity in susceptible individuals. It is the current opinion that most autoimmune diseases develop due to a combination of genetic and environmental factors . Molecular mimicry has been proposed as a concept by which the impact of environmental factors might be potentiated and autoimmune processes accelerated. Thus, the molecular mimicry hypothesis has been used as a basis for experimental animal models for many autoimmune diseases.