Abstract
Mice cannot be used to evaluate HIV-1 therapeutics and vaccines because they are not infectible by HIV-1 due to structural differences between several human and mouse proteins required for HIV-1 entry and replication including CD4, CCR5 and cyclin T1. We overcame this limitation by constructing mice with CD4 enhancer/promoter-regulated human CD4, CCR5 and cyclin T1 genes integrated as tightly linked transgenes (hCD4/R5/cT1 mice) promoting their efficient co-transmission and enabling the murine CD4-expressing cells to support HIV-1 entry and Tat-mediated LTR transcription. All of the hCD4/R5/cT1 mice developed disseminated infection of tissues that included the spleen, small intestine, lymph nodes and lungs after intravenous injection with an HIV-1 infectious molecular clone (HIV-IMC) expressing Renilla reniformis luciferase (LucR). Furthermore, localized infection of cervical-vaginal mucosal leukocytes developed after intravaginal inoculation of hCD4/R5/cT1 mice with the LucR-expressing HIV-IMC. hCD4/R5/cT1 mice reproducibly developed in vivo infection after inoculation with LucR-expressing HIV-IMC which could be bioluminescently quantified and visualized with a high sensitivity and specificity which enabled them to be used to evaluate the efficacy of HIV-1 therapeutics. Treatment with highly active anti-retroviral therapy or one dose of VRC01, a broadly neutralizing anti-HIV-1 antibody, almost completed inhibited acute systemic HIV-1 infection of the hCD4/R5/cT1 mice. hCD4/R5/cT1 mice could also be used to evaluate the capacity of therapies delivered by gene therapy to inhibit in vivo HIV infection. VRC01 secreted in vivo by primary B cells transduced with a VRC01-encoding lentivirus transplanted into hCD4/R5/cT1 mice markedly inhibited infection after intravenous challenge with LucR-expressing HIV-IMC. The reproducible infection of CD4/R5/cT1 mice with LucR-expressing HIV-IMC after intravenous or mucosal inoculation combined with the availability of LucR-expressing HIV-IMC expressing transmitted/founder and clade A/E and C Envs will provide researchers with a highly accessible pre-clinical in vivo HIV-1-infection model to study HIV-1 acquisition, treatment, and prevention.
Highlights
Two major restrictions prevent HIV-1 from infecting mouse cells
Mice transplanted with human peripheral blood lymphocytes [5] or implanted with human fetal thymus and liver [6], Rag22/2cc2/ 2 mice injected with human hematopoietic stem cells [7,8], NOD/severe combined immunodeficient (SCID)/IL2Rcnull mice injected with hHSC [9] or NOD/SCID mice transplanted with human fetal thymus and liver tissue and injected with syngeneic hHSC [10]
Co-injecting this construct into fertilized mouse eggs along with a human cyclin T1 expression plasmid regulated by the same CD4 promoter/enhancer [16,36] resulted in successful tandem integration and the generation of some founder mice that transmitted these transgenes as a single allele (Figure 1B) [37]
Summary
Two major restrictions prevent HIV-1 from infecting mouse cells. First, HIV-1 is unable to enter mouse cells because its envelope glycoprotein, gp120, does not engage mouse CD4 and CCR5 [1]. HIV-1 Tat does not function in mouse cells because it does not bind to mouse cyclin T1 and cannot activate HIV-1 transcription by recruiting the positive transcription elongation factor b (P-TEFb) complex to the HIV-1 TAR RNA target element [2,3,4] To circumvent this restriction, humanized mouse models have been developed and used for HIV-. Mice transplanted with human peripheral blood lymphocytes [5] or implanted with human fetal thymus and liver [6], Rag22/2cc2/ 2 mice injected with human hematopoietic stem cells (hHSC) [7,8], NOD/SCID/IL2Rcnull mice injected with hHSC [9] or NOD/SCID mice transplanted with human fetal thymus and liver tissue and injected with syngeneic hHSC [10] These humanized mouse models cannot take advantage of the wide array of available transgenic and gene-deleted mouse lines to apply genetic approaches to investigate HIV-1 transmission. They do not generate potent HIV-1-specific human immune responses which limit their usefulness for evaluating HIV1 vaccines and HIV-1 immunopathogenesis
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