Creating effective biocontainment facilities and maintenance protocols for raising specific pathogen-free, severe combined immunodeficient (SCID) pigs

Abstract

Severe combined immunodeficiency (SCID) is defined by the lack of an adaptive immune system. Mutations causing SCID are found naturally in humans, mice, horses, dogs, and recently in pigs, with the serendipitous discovery of the Iowa State University SCID pigs. As research models, SCID animals are naturally tolerant of xenotransplantation and offer valuable insight into research areas such as regenerative medicine, cancer therapy, as well as immune cell signaling mechanisms. Large-animal biomedical models, particularly pigs, are increasingly essential to advance the efficacy and safety of novel regenerative therapies on human disease. Thus, there is a need to create practical approaches to maintain hygienic severe immunocompromised porcine models for exploratory medical research. Such research often requires stable genetic lines for replication and survival of healthy SCID animals for months post-treatment. A further hurdle in the development of the ISU SCID pig as a biomedical model involved the establishment of facilities and protocols necessary to obtain clean SPF piglets from the conventional pig farm on which they were discovered. A colony of homozygous SCID boars and SPF carrier sows has been created and maintained through selective breeding, bone marrow transplants, innovative husbandry techniques, and the development of biocontainment facilities.

Keywords: Severe combined immunodeficiency (SCID); colostrum; pig; snatch farrow; specific pathogen-free (SPF).

Figure 1.. General Bubble Components.

A) Entrance of long term bubble; pigs are housed on either side while middle section is designated for dressing in PPE. B) Staff shown collecting cord blood on newly snatch farrowed piglets in STB. C) HEPA filtration unit filters all incoming air that enters bubble. D) Water is filtered and irradiated before entering bubble. E) All staff don PPE prior to entering either bubble.

Figure 2.. Snatch Farrowed Piglet feeding apparatus.

A) A sterile urinary catheter tube is taped to a gloved finger and attached to a 60 ml tube for feeding. B) Porcine colostrum or milk replacer is administered as piglets suckle on the finger with tube attached.

Figure 3.. ELISA IgG and Growth Curve Data comparing naturally sucking and tube fed piglets.

A) The box and whisker plot shows serum levels of IgG (mg/mL) from cord blood of SCID (gray) and non-SCID(black) piglets prior to consumption of colostrum compared to SCID and non-SCID samples post colostrum delivery both from tube fed and naturally suckling piglets. (NS= non-SCID, S= SCID, NF= Naturally Farrowed, SF= Snatch Farrowed respectively). B) Weight (kg) over time for average of combined SCID and non-SCID piglets that were tube fed (gray) or naturally suckled (black) is shown. The gray vertical line denotes typical 35 day wean date (from sow or off milk replacer). Shaded region shows 95% confidence interval.

Figure 4.. Animal transfer through facilities.

A) The figure shows animal flow from farrowing through short (STB) and long term (LTB) bubbles. Litters are either naturally farrowed where SCID males are BMT rescued and used for subsequent breeding, or naturally farrowed where carrier females are kept SPF clean and moved to the LTB to sexually mature and ultimately be bred to BMT boars to produce naturally farrowed SPF litters in the LTB. B) HEPA filtered transfer cart used to move carrier female pigs from the STB into the LTB.