Housing and Breeding Considerations for NSG™ Mice

NSG™ mice are severely immunodeficient and sensitive to infection by a wide range of normal pathogens, opportunistic pathogens, and commensal organisms (Foreman, et al. 2011). Barrier practices that are sufficient to maintain nude and scid colonies may not be adequate for NSG™ mice, however, with the implementation of strict barrier practices and aseptic technique, maintenance of pathogen-free NSG mice is possible and attainable.

Below are some suggestions for ensuring the health status of NSG™ and related immunodeficient strains:

• All food, water, bedding, and cages entering the room should be autoclaved or sterilized in some way
• Microisolator or pressurized individually ventilated (PIV) caging is recommended
• Acidification of water to pH 2.5 – 3.0 helps to prevent infection by Pseudomonas species
• Personal protective equipment (sterile scrubs, frocks, gloves, masks, and hair coverings) should be worn at all times to cover your skin and minimize chances of spreading bacteria to the mice
• Handle mice with forceps that have disinfected, and/or with gloved hands that have been sterilized with ethanol
• Change cages under a laminar flow hood.  Disinfect hands after opening the ventilated cage top, reaching within the cage, or removing your gloved hands from the hood.  Disinfect the hood in between changes
• In a strict barrier environment (such as the maximum barrier rooms at JAX) biweekly changes are sufficient to maintain healthy mice. However, research facilities may want to consider changing cages weekly to prevent the introduction of minimal inoculating doses of opportunistic or commensal organisms in the cage environment (Foreman et al. 2011)
• Kinked tail, head tilt, circling, and hind limb lameness are observed at low frequency. These conditions are very infrequent (<0.01% incidence) in young, experimentally naïve mice. Incidence is estimated at <0.5% in older mice used for humanization and other studies.

Breeding considerations for NOD scid gamma (NSG™) immunodeficient mice

NSG™ mice are good breeders if they are maintained under optimal housing conditions that ensure their health status. Breeding characteristics of our NSG™ colony include:

• Litter sizes are large (averaging 8 pups per litter) and frequent (most females deliver 7-8 litters over the course of 6 month breeding period) 
• Breeding performance of NSG™ mice improves when breeding pairs or trios are established at the age of 8 weeks 
• The breeding lifespan of NSG™ mice is not limited by the development of thymic lymphoma as in other scid strains. NSG™ mice can remain productive breeders for as long as one year, and some older breeders can occasionally develop osteosarcomas and mammary carcinomas (Kavirayani and Foreman, 2010). Approximately 90-95% of breeders in our NSG™ colony reach the end of the breeding period at the age of 7-8 months