It is widely accepted that humanized rat models offer distinct advantages in biomedical research, drug discovery and preclinical trials when compared to their mouse counterparts – the rat is genetically and physiologically more similar to humans and their larger body mass allows for more biological material to be harvested for evaluation. However, until recently, BAC (bacterial artificial chromosome) transgeneis in rats has been less successful than in mice, making it difficult to use rats to study the engraftment potential of human cells and tissues as well as for reproducing human immune diseases and evaluating therapeutic strategies.

As reported in a study recently published in Scientific Reports, Jung et al were successfully able to generate BAC transgenic rats that faithfully expressed human SIRPA, which allow for “improved human cell engraftment and improved functionality of human adaptive immune system in vivo.” As part of this their process, they evaluated piggyBac transposon, CRISPR/Cas9 and TALEN mediated approaches. The piggyBac approach was found to be more efficient than classical BAC transgenesis (embryonic injection of BACs), with a better success rate for complete BAC integration with predictable end sequences that provided the added benefit of being able to readily identify the insertion sites using a simple PCR approach. Neither CRISPR nor TALEN facilitated targeted knock-in or proved to be effective methods for the large targeted insertions associated with BAC-based transgenics.

Based on their research, Jung et al suggest that rapidly advancing genome engineering technologies will likely allow for efficient targeting of BACs into specific loci in the genome for production of rat transgenics in the near future. This increasingly effective generation of human SIRPA transgenic rats using piggyBac has the potential to significantly impact biomedical and translational research, as well as therapeutic applications, related to human immune diseases, inflammation, stem cells, cancer and cycle cell regulation.