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2020-

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Browsing 2020- by Author "Aboellail, Tawfik, committee member"

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    Modeling the evolution of SIV progenitor viruses towards HIV-1 and HIV-2 in a humanized mouse surrogate model
    (Colorado State University. Libraries, 2020) Curlin, James Zachary, author; Akkina, Ramesh, advisor; Aboellail, Tawfik, committee member; Stenglein, Mark, committee member; Wiese, Claudia, committee member
    Human Immunodeficiency Virus Type 1 (HIV-1) and Type 2 (HIV-2), the causative agents of Acquired Immunodeficiency Syndrome (AIDS) first emerged in humans over the past century. Despite significant advances in treatment options, the pandemics continue with millions of new infections every year. Both HIV-1 and HIV-2 likely emerged through the cross-species transmission of primate lentiviruses originating from nonhuman primates (NHPs) including chimpanzees (SIVcpz), gorillas (SIVgor), and sooty mangabeys (SIVsm). SIVsm shares a remarkable degree of homology with HIV-2, while SIVcpz and SIVgor are most closely related to HIV-1. Nonhuman primates infected with these lentiviruses frequently come into contact with humans due to the prevalence of bushmeat hunting practices in various African countries. Other lentiviruses such as SIVmac239 represent independent instances of primate lentiviruses crossing into novel host species. The repeated exposure of primate lentiviruses to a human immune environment allowed the accumulation of adaptive genetic changes uniquely suited to overcoming the evolutionary pressures of a new host. Host-restriction factors such as tetherin, SAMHD1, APOBEC3G and SERINC3/5 exert species-specific antiviral activity and must be overcome for a virus to adapt to a new host cell. These evolutionary pressures could be a guiding force in the direction that these viruses adapt. In order to recapitulate these genomic cross-species adaptations, we used humanized mice engrafted with human hematopoietic stem cells (hu-HSC mice). These mice produce a full spectrum of human immune cells such as B cells, T cells, macrophages, monocytes, and dendritic cells, and are susceptible to HIV infection. Representative progenitor viruses of both HIV-1 (SIVcpzEK505, SIVcpzMB897, and SIVcpzLB715) and HIV-2 (SIVsmE041) as well as other viruses of interest, namely, SIVmac239, SIVhu and SIVB670 lineages were intraperitoneally injected into hu-HSC mice. Following successful infections, the derivative viruses were subsequently passaged serially through multiple generations to simulate the repeated exposures that originally produced HIV-1 and HIV-2. Viral adaptation was assessed primarily through three different criteria. Plasma viral RNA levels were measured on a weekly basis using qRT-PCR to determine changes in viral replication kinetics over time. We found that the plasma viral loads of the viruses tested varied during serial passages, and mostly increased over time in many cases. Human CD4+ T cell engraftment decline as assessed by flow cytometry biweekly acts as a measure of AIDS progression in cases of human infection. CD4+ T cell levels declined over time with increasing rapidity upon further passaging in many cases. Additionally, viral RNA collected from the infected mice at multiple timepoints in each generation was used to generate overlapping amplicons spanning the length of the viral genome in order to be used with Illumina-based deep sequencing. Numerous nonsynonymous mutations arose in the first generation of passaging and were maintained across multiple sequential passages. While the mutations occurred throughout the viral genome, the bulk of the mutations were found in env and nef. Many of these mutations were present in known CD4+ binding sites, motifs involved in protein interactions, and other areas involved in host-restriction factor antagonism. While these results are revealing, further inquiry is needed to determine the true functionality of these genetic changes. These data showcase the value of using humanized mice to model lentiviral evolution and provide important insights into understanding the origin of HIVs.