Role of Mouse Strain Selection in In Vivo Transfection Efficiency

The genetic background and immunological status of mouse strains play a crucial role in determining the success of in vivo transfection experiments. When delivering nucleic acids such as plasmid DNA, mRNA, siRNA, or shRNA into living mice, researchers must account for variations in tissue physiology, immune response, and cellular uptake mechanisms that can dramatically affect the distribution, stability, and gene expression of the introduced material. Strain-specific differences in transfection efficiency, toxicity tolerance, and pharmacokinetics have made mouse model selection a central consideration in preclinical gene delivery research.

Immunocompromised mouse strains, such as NOD/SCID and NSG (NOD scid gamma), are frequently used for in vivo nucleic acid delivery due to their profound lack of adaptive immunity. These mice do not mount strong responses to foreign genetic material, which allows for extended gene expression, reduced clearance of delivery vectors, and enhanced reproducibility. NSG mice are particularly suitable for xenograft studies involving human cells, as their complete absence of T, B, and NK cells provides an immunologically permissive environment. For siRNA or CRISPR delivery in cancer research, NSG mice provide an ideal host for testing targeted gene silencing in tumor xenografts without complications from immune surveillance or inflammation.

Inbred immunocompetent strains like C57BL/6 (B6) and BALB/c are widely used in studies of immunology, oncology, and metabolic disease. These strains retain full immune functionality, which means nucleic acid delivery can trigger innate immune pathways, particularly through pattern recognition receptors such as TLR3, TLR7, and RIG-I. These pathways can result in inflammatory cytokine production, degradation of the delivered nucleic acids, and activation of interferon responses that interfere with experimental endpoints. However, using these strains is essential when immune system interactions are part of the experimental design, such as in vaccine development or autoimmune disease models. Optimizing delivery methods—through the use of chemically modified nucleic acids or immunosuppressive agents—can mitigate these challenges and allow for successful transfection in immunocompetent mice.

Outbred strains like CD1 or Swiss Nude provide genetic diversity and often exhibit greater resistance to toxicity, making them suitable for toxicity screening or dose-ranging studies. Swiss Nude mice, which lack a thymus and are T-cell deficient, represent a middle ground between fully immunodeficient and immunocompetent models. These mice are often used for subcutaneous tumor xenografts and can support moderate levels of transgene expression without the complete absence of immune regulation. This makes them a valuable model for moderate-duration studies where some degree of immune interaction is desirable.

Certain strains, such as BALB/c and CB17, are preferred in organ-specific targeting studies due to their predictable physiological traits and compatibility with established experimental protocols. BALB/c mice, for instance, are frequently used in respiratory and gastrointestinal transfection models, while CB17 mice serve as hosts for hybridoma development and therapeutic antibody research. Meanwhile, B6 mice are genetically amenable to knock-in and knock-out models, making them a foundational strain for genetic engineering and transgenic lines.

Ultimately, successful in vivo transfection depends on harmonizing vector design, administration route, and mouse model. Choosing the correct mouse strain not only improves transfection efficiency and tissue specificity but also ensures that immune responses, gene silencing kinetics, and transgene expression align with the biological questions being addressed. This selection process should be informed by the goals of the study, the nature of the genetic payload, and the delivery platform used, ensuring high fidelity in gene modulation studies conducted in mouse models.