Influence of Mouse Strain Immunophenotype on Transfection Outcomes
The selection of a mouse strain is a foundational decision in in vivo transfection studies, directly impacting transfection efficiency, immune response, and data reproducibility. Each mouse strain possesses a unique immunophenotype that determines how it recognizes and processes foreign nucleic acids, how it responds to delivery vehicles, and how well transfected cells survive and function post-administration. These immunological and genetic differences become especially important when interpreting the effects of RNAi, plasmid DNA expression, or CRISPR-based editing in live animal models.
Immunocompetent strains like C57BL/6 and BALB/c are widely used due to their intact innate and adaptive immune systems, making them excellent models for studying immunological effects of gene modulation or vaccine candidates. However, these same immune functions present challenges for transfection. Cytosolic and endosomal RNA sensors such as Toll-like receptors (TLR3, TLR7, TLR9), RIG-I, and MDA5 detect foreign RNA or DNA and can trigger potent type I interferon responses. These responses can lead to inflammation, transgene silencing, or apoptosis of transfected cells. The strain-specific expression of these receptors, as well as cytokine profiles, can influence how a particular formulation is tolerated and how long the transgene remains active.
Immunodeficient strains such as NOD/SCID, NSG, and BALB/SCID mice are more permissive to transfection and are often preferred for xenograft studies or experiments involving human-derived cells. These models lack various components of the immune system—such as T cells, B cells, and/or natural killer (NK) cells—allowing exogenous gene delivery to occur with minimal immunogenicity. NOD/SCID mice, for example, lack functional lymphocytes but retain some innate immunity, while NSG mice are even more severely immunocompromised and lack mature NK cells as well as cytokine signaling pathways. These traits make them ideal for sustained gene expression and for evaluating tumor cell transfection without host rejection.
Outbred strains like CD1 or Swiss Nude mice introduce greater genetic variability and are often used in pharmacological studies for broader translatability. However, their unpredictable immune responses and variable transfection outcomes can complicate experimental interpretation. In contrast, inbred strains such as CB17 or C57BL/6 offer genetic consistency, improving reproducibility, but may exhibit heightened sensitivity to nucleic acid-induced inflammation depending on their baseline immune tone.
Other physiological factors tied to strain selection—including organ size, vascularization, and metabolic rate—also impact how transfection reagents distribute and function. For example, strains with faster clearance rates may show lower transgene expression due to rapid degradation or renal elimination of unencapsulated payloads. Variations in macrophage activity, splenic filtration, or hepatic uptake can further skew biodistribution profiles across strains.
To mitigate immune-related challenges, researchers often employ chemically modified nucleic acids (e.g., 2′-O-methyl or phosphorothioate backbones), use immune-tolerant delivery platforms (such as PEGylated liposomes), or include immunosuppressive agents in their dosing regimens. Nonetheless, the inherent strain-specific biology continues to play a major role in experimental design.
Ultimately, choosing the right mouse strain is not only about compatibility with the experimental payload but also about ensuring physiological relevance, reducing variability, and enabling accurate interpretation of gene modulation outcomes. A clear understanding of each strain’s immunophenotype, metabolism, and genetic background enhances the success of in vivo transfection studies and helps align model selection with the goals of preclinical research.