The humanized NOD/SCID/interleukin (IL)-2 receptor γ-chainnull (hereafter referred to as huNS γ-chainnull) mouse model has been widely used for studying the pathogenesis of infections, autoimmunity, and cancer, as well as for pre-clinical studies of drugs and human cell-based therapies1,2. These mice are based on a non-obese diabetic (NOD) background, with the scid mutation and targeted mutation at the IL-2 receptor γ-chain locus (common γ-chain for IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21), which induce a severe impairment in the development of mouse T-, B-, and natural killer (NK) cells1. Thus, they support the engraftment of human tissue, human CD34+ hematopoietic stem cells (HSCs), and human peripheral blood mononuclear cells (PBMCs)3,4,5. In addition, transgenic expression of human hematopoietic factors, such as stem cell factor (SCF), granulocyte/macrophage colony-stimulating factor (GM-CSF), and IL-3 promotes the engraftment of human myeloid populations6,7,8.
For HIV studies, several huNS γ-chainnull mouse models have been described, which differ in the mouse strain, type of human cells used, type of tissues for the engraftment, and origin of cells (i.e., healthy vs. HIV-infected donor)9,10. The original strain, however, is widely used due to the high levels of human cells engraftment and viral replication following infection with a reference HIV strain11,12,13. Similar immunodeficient mouse strains with transgenic expression of human hematopoietic factors (e.g., NOG-EXL or NSG-SGM3) or with implants of human liver and thymus tissues (bone marrow-liver-thymus [BLT] mice) are useful for evaluating the role of myeloid populations in the anti-HIV immune response, effects of HIV on these tissues, and their participation as viral reservoirs14,15. Furthermore, some strains with transgenic expression of human leukocyte antigen (HLA) molecules, as well as BLT mice, can be used for studying the T-cell response to HIV infection16,17.
In general, in these mice, humanization depends on the cellular origin, delivery route (intraperitoneal, intrahepatic, intravenous, intracardiac) and mouse age at the time of engraftment18,19,20. Regarding the cell origin, human CD34+ HSC derived from cord blood, fetal liver, or mobilized peripheral blood can be injected in newborn or young mice3,21. In addition, adult γ-chainnull mice can be humanized by the injection of PBMC (here, referred to as hu-PBL-NS γ-chainnull mice), allowing the temporal circulation of these cells in the blood, secondary lymphoid organs, and inflamed tissues22,23,24.
Described here is a detailed protocol for the establishment of huNS γ-chainnull mouse models for the study of HIV infection. The first is the chronic model, in which human CD34+ HSCs derived from cord blood from a healthy donor are injected in newborn mice, followed by infection with a reference HIV strain after 14 weeks of human immune system reconstitution. This model allows monitoring of mice for up to ~36 weeks after infection. The second model is an acute model, in which PBMCs derived from a healthy donor are injected in adult NS γ-chainnull mice, followed by infection with a reference HIV strain after 3 weeks of human T-cell expansion in the mouse. Finally, the third model is the reactivation model, in which PBMCs derived from an HIV-infected donor under suppressive antiretroviral therapy (ART) are injected in adult NS γ-chainnull mice. In this case, a drug-free environment allows for viral reactivation and increase in the viral load. The two latter models allow monitoring for up to ~9 weeks after engraftment.
Overall, these three models are useful for virological studies, pre-clinical studies of novel drugs, and evaluation of HIV infection effects on the global immune response. It is also important to consider that use of HIV-infected humanized mice requires review and approval by the Institutional Biosafety Committee (IBC) as well as by the Institutional Animal Care and Use Committee (IACUC) before any experiment. This ensures that the study follows all internal and external institutional regulations for the use of hazardous biological material and humane handling of experimental animals.