Humanized Bone marrow/Liver/Thymus (BLT) mice recapitulate the mucosal transmission of HIV, permitting study of early events in HIV pathogenesis and evaluation of preexposure prophylaxis methods to inhibit HIV transmission. Human hematopoiesis is reconstituted in NOD-scid mice by implantation of human fetal liver and thymus tissue to generate human T cells plus intravenous injection of autologous liver-derived CD34+ hematopoietic stem cells to engraft the mouse bone marrow. In side-by-side comparisons, we show that NOD-scid mice homozygous for a deletion of the IL-2Rγ-chain (NOD-scid IL-2Rγ−/−) are far superior to NOD-scid mice in both their peripheral blood reconstitution with multiple classes of human leukocytes (e.g., a mean of 182 versus 14 CD4+ T cells per μl 12 weeks after CD34+ injection) and their susceptibility to intravaginal HIV exposure (84% versus 11% viremic mice at 4 weeks). These results should speed efforts to obtain preclinical animal efficacy data for new HIV drugs and microbicides.

Like normal cellular nucleosides, the nucleoside reverse transcriptase (RT) inhibitor (NRTI) 4=-ethynyl-2-fluoro-2=-deoxyadenosine (EFdA) has a 3=-hydroxyl moiety, and yet EFdA is a highly potent inhibitor of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) replication with activity against a broad range of clinically important drug-resistant HIV isolates. We evaluated the anti-HIV activity of EFdA in primary human cells and in HIV-infected humanized mice. EFdA exhibited excellent potency against HIV JR-CSF in phytohemagglutinin-stimulated peripheral blood mononuclear cells (PBMCs), with a 50% inhibitory concentration of 0.25 nM and a selectivity index of 184,000; similar antiviral potency was found against 12 different HIV clinical isolates from multiple clades (A, B, C, D, and CRF01_AE). EFdA was readily absorbed after oral dosing (5 mg/kg of body weight) in both mice and the rhesus macaque, with micromolar levels of the maximum concentration of drug in serum (C max ) attained at 30 min and 90 min, respectively. Trough levels were at or above 90% inhibitory concentration (IC 90 ) levels in the macaque at 24 h, suggesting once-daily dosing. EFdA showed reasonable penetration of the blood-brain barrier in the rhesus macaque, with cerebrospinal fluid levels at approximately 25% of plasma levels 8 h after single oral dosing. Rhesus PBMCs isolated 24 h following a single oral dose of 5 mg/kg EFdA were refractory to SIV infection due to sufficiently high intracellular EFdA-triphosphate levels. The intracellular half-life of EFdA-triphosphate in PBMCs was determined to be >72 h following a single exposure to EFdA. Daily oral administration of EFdA at low dosage levels (1 to 10 mg/kg/day) was highly effective in protecting humanized mice from HIV infection, and 10 mg/kg/day oral EFdA completely suppressed HIV RNA to undetectable levels within 2 weeks of treatment. N ucleoside/nucleotide reverse transcriptase (RT) inhibitors (NRTIs) are highly effective for both first-line therapy and preexposure prophylaxis (PrEP) of human immunodeficiency virus (HIV) infection. There are seven FDA-licensed single NRTIs, including the nucleoside emtricitabine (FTC) and the nucleotide tenofovir (TFV). Long-term use of these drugs has resulted in the emergence of drug-resistant variants in treated patients as well as in treatment-naive individuals due to transmission of these drugresistant variants (1, 2). New, more-potent compounds with activity against NRTI-resistant strains are needed. All currently approved anti-HIV NRTIs lack the 3=-hydroxyl group and therefore inhibit further DNA polymerization by HIV RT through immediate chain termination after incorporation into the nascent DNA. The absence of a 3=-OH, however, imparts unfavorable properties to these NRTIs by negatively impacting their binding affinity for RT compared to the natural deoxynucleoside triphosphate (dNTP) substrates and by reducing their binding affinity for the cellular nucleoside/nucleotide kinases responsible for intracellular phosphoryl...

SUMMARY Paradoxically, early host responses to infection include the upregulation of the antiphagocytic molecule, CD47. This suggests that CD47 blockade could enhance antigen presentation and subsequent immune responses. Indeed, mice treated with anti-CD47 monoclonal antibody following lymphocytic choriomeningitis virus infections show increased activation of both macrophages and dendritic cells (DCs), enhancement of the kinetics and potency of CD8 + T cell responses, and significantly improved virus control. Treatment efficacy is critically dependent on both APCs and CD8 + T cells. In preliminary results from one of two cohorts of humanized mice infected with HIV-1 for 6 weeks, CD47 blockade reduces plasma p24 levels and restores CD4 + T cell counts. The results indicate that CD47 blockade not only enhances the function of innate immune cells but also links to adaptive immune responses through improved APC function. As such, immunotherapy by CD47 blockade may have broad applicability to treat a wide range of infectious diseases.