09 March, 2020

Care and husbandry for immunodeficient rodents: guidance to reduce risks in your research

By Jamie Naden

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Immunodeficient rodents can serve as a valuable part of basic research studies to help researchers better understand immune-related diseases and immune response. Use of these unique models have driven medical advances in the development of chemotherapies, immunotherapies, biologics and CAR T-cell therapies and even contributed to imaging techniques and personalized medicines.

While these rodent models can be very powerful in research, they understandably require very special care to maintain their health status and reduce the risk of pathogens and infections that can derail research results.

This blog discusses how immunodeficient rodents can be bred and housed along with the considerations for bedding, enrichment, packing and shipping to ensure that these rodents have the care they require to remain healthy throughout their lives.  

Understanding the importance of care and husbandry

For all research models, and especially immunodeficient rodents, it is critical to keep animals healthy and ensure that procedures are in place to eliminate any opportunistic agents, pathogens and parasites that can cause disease and compromise research results. In immunodeficient models, one critical challenge is avoiding Corynebacterium bovis or C. bovis, a common pathogen found in some immunodeficient mouse colonies, which may be carried by immunocompetent mice and can be transmitted by other infected animals or fomites.

In conjunction with the health status of the animals, it is essential that animals are well-nourished, safe, able to express innate behavior, given appropriate care and shelter, handled in a humane manner and free from pain, fear and distress. Following these welfare principles not only supports the 3Rs but also maintains the health of models – a key part of obtaining robust and consistent research results.

Commercial breeding and breeding schemes

In a commercial breeding facility, mating cages for mice are set up at 7-8 weeks of age; rat mating cages are set up at 9-10 weeks of age. These cages remain together until retirement of the breeders, around 8-10 months of age. The pups are weaned at 3-4 weeks of age.

The specific breeding schemes are model dependent and vary by region*. For North American (NA) colonies, the schemes are:

Table 1: 

Hsd:Athymic Nude-Foxn1nu

Heterozygous female x Homozygous male

1x3

NOD.CB17-Prkdcscid/NCrHsd

Homozygous female x Homozygous male

FC: 1 x 1, PEC: 1 x 2, PC: 1 x 2

C.B-17/IcrHsd-Prkdcscid 

Homozygous female x Homozygous male

FC: 1 x 1, PEC: 1 x 2, PC: 1 x 3

C.B-17/IcrHsd-Prkdcscid Lystbg-J 

Homozygous female x Homozygous male

FC: 1 x 1, PEC: 1 x 2, PC: 1 x 2

B6;129- Rag2tm1FwaIL2rgtm1Rsky/DwlHsd

Homozygous female x Homozygous male

1x2

Hsd:RH-Foxn1rnu 

Heterozygous female x Homozygous male

1x1

Table 1: Breeding for NA rodents
FC: Foundation Colony; PEC: Pedigreed Expansion Colony; PC: Production Colony
*
EU differences may apply following EEC/2010/63 guidelines

It should be noted that the athymic nude rat and mouse are unable to produce T cells. They can be used as controls, depending on the type of study.

Housing guidelines

Keeping surroundings clean for immunodeficient rodents is an involved process. Every touchpoint – feed, bedding, enrichment and housing – must be sterilized in some fashion. To ensure a clean environment, feed is irradiated, bedding is autoclaved and water is chlorinated and acidified.

While barrier housing is suitable for most immunocompetent rodents, immunodeficient rodents are housed in flexible film isolators with individual air sources. In both housing configurations, incoming clean air is HEPA-filtered and dirty air is sent out through a separate exhaust.

Within the isolators, the movement of supplies and animals requires careful sanitization processes. Any supplies that enter the isolator must be sterilized. Chlorine dioxide is sprayed through an atomizer to sanitize the port of the isolator prior to opening. Cage cleaning is also required following detailed steps that keep clean supplies separate from dirty supplies.

Biosecurity measures

Employees within the facility also contribute to maintaining the health status of the immunocompromised models. Technicians wear head-to-toe personal protection equipment with as little skin exposed as possible.

Technicians must comply with a pet policy that ensures they do not introduce pathogens from their home environment. Technicians cannot own any rodents, rabbits, gerbils, hamsters and are not allowed to visit pet stores. This policy reduces the possibility transmitting fomites, which can have devastating effects within any highly-controlled facility.

Bedding and enrichment considerations

Enrichment products enhance the welfare of research animals but only those that are irradiated and can be sterilized should be used for immunodeficient rodents. The materials must be free of heavy metals and pesticides, both of which could be harmful for the animals. Nude rodents also need low dust, non-irritating materials to ensure they do not experience discomfort from the enrichment materials.

Packing and shipping

Finally, to ensure that immunodeficient rodents bred in a commercial facility arrive disease-free at a customer’s site, the packing and shipping of the animals follows very detailed procedures. Boxes are first autoclaved and then three minutes before the animals are retrieved, the boxes are sanitized again with chlorine dioxide within a laminar flow hood with HEPA-filtered air. Within the flow hood, the animals are placed into the box, which is then sealed and has several filtered air vents. By flipping back a tab on the top of the box, technicians can peer through a mylar window to perform visual health checks on the animals before they are shipped.

Maintaining healthy immunodeficient rodents

With rigorous health testing, strong biosecurity measures and proper training programs, researchers working with immunodeficient rodents can implement the principles of 3R, ensure ongoing health of their animals and help reduce study risks by systematically eliminating all sources of potential pathogens.   

If you would like to learn more about care and husbandry for immunodeficient rodents, read the full panel presentation that was delivered at AALAS 2019 or speak to an expert today

Category // Research models and services, immunodeficient research models, animal research, immunodeficient rodents