Cell-associated transmission of HIV type 1 and other lentiviruses in small-animal models

Exogenous oestrogen inhibits genital transmission of cell-associated HIV-1 in DMPA-treated humanized mice

Introduction

HIV affects more women than any other life‐threatening infectious agent, and most infections are sexually transmitted. HIV must breach the female genital tract mucosal barrier to establish systemic infection, and clinical studies indicate virus more easily evades this barrier in women using depot‐medroxyprogesterone acetate (DMPA) and other injectable progestins for contraception. Identifying a potential mechanism for this association, we learned DMPA promotes susceptibility of wild‐type mice to genital herpes simplex virus type 2 (HSV‐2) infection by reducing genital tissue expression of the cell‐cell adhesion molecule desmoglein‐1 (DSG‐1) and increasing genital mucosal permeability. Conversely, DMPA‐mediated increases in genital mucosal permeability and HSV‐2 susceptibility were eliminated in mice concomitantly administered exogenous oestrogen (E). To confirm and extend these findings, herein we used humanized mice to define effects of systemic DMPA and intravaginal (ivag) E administration on susceptibility to genital infection with cell‐associated HIV‐1.

Methods

Effects of DMPA or an intravaginal (ivag) E cream on engraftment of NOD‐scid‐IL‐2Rgc^null (NSG) mice with human peripheral blood mononuclear cells (hPBMCs) were defined with flow cytometry. Confocal microscopy was used to evaluate effects of DMPA, DMPA and E cream, or DMPA and the pharmacologically active component of the cream on vaginal tissue DSG‐1 expression and genital mucosal permeability to low molecular weight (LMW) molecules and hPBMCs. In other studies, hPBMC‐engrafted NSG mice (hPBMC‐NSG) received DMPA or DMPA and ivag E cream before genital inoculation with 10⁶ HIV‐1‐infected hPBMCs. Mice were euthanized 10 days after infection, and plasma HIV‐1 load quantified by qRT‐PCR and splenocytes used to detect HIV‐1 p24 antigen via immunohistochemistry and infectious virus via TZM‐bl luciferase assay.

Results

Whereas hPBMC engraftment was unaffected by DMPA or E treatment, mice administered DMPA and E (cream or the pharmacologically active cream component) displayed greater vaginal tissue expression of DSG‐1 protein and decreased vaginal mucosal permeability to LMW molecules and hPBMCs versus DMPA‐treated mice. DMPA‐treated hPBMC‐NSG mice were also uniformly susceptible to genital transmission of cell‐associated HIV‐1, while no animal concomitantly administered DMPA and E cream acquired systemic HIV‐1 infection.

Conclusion

Exogenous E administration reduces susceptibility of DMPA‐treated humanized mice to genital HIV‐1 infection.

Neutralizing Antibody-Based Prevention of Cell-Associated HIV-1 Infection

Improved vaccine-mediated protection against HIV-1 requires a thorough understanding of the mode of HIV-1 transmission and how various immune responses control transmission. Cell-associated HIV-1 is infectious and contributes to HIV-1 transmission in humans. Non-human primate models of cell-associated SIV infection demonstrate that cell-associated SIV is more infectious than cell-free SIV. In a recently described chimeric simian–human immunodeficiency virus (SHIV) macaque model, it was demonstrated that an occult infection with cell-associated SHIV can be established that evades passive protection with a broadly neutralizing antibody (bnAb). Indeed, considerable in vitro data shows that bnAbs have less efficacy against cell-associated HIV-1 than cell-free HIV-1. Optimizing the protective capacity of immune responses such as bnAbs against cell-associated infections may be needed to maximize their protective efficacy.

Non-canonical function of Tat in regulating host microtubule dynamics: Implications for the pathogenesis of lentiviral infections

Lentiviruses are a class of genetically unique retroviruses that share similar features, despite their wide variety of host species. Transactivator of transcription (Tat) proteins of lentiviruses are critical for the regulation of viral transcription and replication. Recent studies demonstrate that in addition to mediating transactivation, Tat binds to the microtubule cytoskeleton of the host cell and interferes with microtubule dynamics, ultimately triggering apoptosis. This non-canonical function of Tat appears to be critical for the pathogenesis of lentiviral diseases, such as acquired immunodeficiency syndrome. Here, we compare the structure and activity of Tat proteins from three different types of lentiviruses, focusing on the roles of these proteins in the alteration of host microtubule dynamics and induction of apoptosis. We propose that further investigation of the Tat-microtubule interaction will provide important insight into the process of lentiviral pathogenesis and elucidate new avenues for the development of antiviral therapies.

Early phase dynamics of traceable mCherry fluorescent protein-carrying HIV-1 infection in human peripheral blood mononuclear cells-transplanted NOD/SCID/Jak3-/- mice

We attempted to elucidate early-phase dynamics of HIV-1 infection using replication-competent, red-fluorescent-protein (mCherry)-labeled HIV-1JR-FL (HIVJR-FLmC) and NOD/SCID/Jak3-/- mice transplanted with Individual-A's human peripheral blood mononuclear cells (hPBMC)(hNOJ mice). On day 7 following HIVJR-FLmC inoculation, mCherry-signal-emitting infection foci were readily identified in the subserosa of 10 of 10 HIVJR-FLmC-inoculated hNOJ mice, although infection foci were not located without the mCherry signal in unlabeled HIV-1JR-FL-inoculated mice (n = 6). Even on day 14, infection foci were hardly located in the unlabeled HIV-1JR-FL-inoculated mice, while in all of 7 HIVJR-FLmC-inoculated hNOJ mice examined, mCherry-signal-emitting lymph nodes were easily identified, in which active viral replication was present. On day 14, a significantly larger number of mesenteric lymph nodes were seen in HIVJR-FLmC-exposed hNOJ mice than in HIVJR-FLmC-unexposed mice (P = 0.0025). The weights of mesenteric lymph nodes of those HIVJR-FLmC-exposed hNOJ mice were also greater than those of HIVJR-FLmC-unexposed mice (P = 0.0005). When hNOJ mice were inoculated with HIVJR-FLmC-exposed hPBMC from Individual-B, significantly greater viremia was seen than in cell-free HIVJR-FLmC-inoculated hNOJ mice as examined on day 7. In the lymph nodes of those mice inoculated with HIVJR-FLmC-exposed hPBMC from Individual-B, a substantial number of Individual-B's HIVJR-FLmC-infected cells were identified together with Individual-A's cells as examined on day 14. The present HIVJR-FLmC-infected mouse model represents the first system reported using traceable HIVJR-FLmC and human target cells, not using SIV or simian cells, which should be of utility in studies of early-phases of HIV-1 transmission and in evaluating the effects of potential agents for post-exposure and pre-exposure prophylaxis.

Feline Immunodeficiency Virus Neuropathogenesis: A Model for HIV-Induced CNS Inflammation and Neurodegeneration

Feline Immunodeficiency virus (FIV), similar to its human analog human immunodeficiency virus (HIV), enters the central nervous system (CNS) soon after infection and establishes a protected viral reservoir. The ensuing inflammation and damage give rise to varying degrees of cognitive decline collectively known as HIV-associated neurocognitive disorders (HAND). Because of the similarities to HIV infection and disease, FIV has provided a useful model for both in vitro and in vivo studies of CNS infection, inflammation and pathology. This mini review summarizes insights gained from studies of early infection, immune cell trafficking, inflammation and the mechanisms of neuropathogenesis. Advances in our understanding of these processes have contributed to the development of therapeutic interventions designed to protect neurons and regulate inflammatory activity.

HIV transmission biology: translation for HIV prevention

Rigorous testing of new HIV-prevention strategies is a time-consuming and expensive undertaking. Thus, making well informed decisions on which candidate-prevention approaches are most likely to provide the most benefit is critical to appropriately prioritizing clinical testing. In the case of biological interventions, the decision to test a given prevention approach in human trials rests largely on evidence of protection in preclinical studies. The ability of preclinical studies to predict efficacy in humans may depend on how well the model recapitulates key biological features of HIV transmission relevant to the question at hand. Here, we review our current understanding of the biology of HIV transmission based on data from animal models, cell culture, and viral sequence analysis from human infection. We summarize studies of the bottleneck in viral transmission; the characteristics of transmitted viruses; the establishment of infection; and the contribution of cell-free and cell-associated virus. We seek to highlight the implications of HIV-transmission biology for development of prevention interventions, and to discuss the limitations of existing preclinical models.

Cell-associated HIV mucosal transmission: the neglected pathway

This supplement to The Journal of Infectious Diseases is devoted to the important and understudied topic of cell-associated human immunodeficiency virus Type 1 (HIV) mucosal transmission. It stems from a workshop held in Boston, Massachusetts, in October 2013, in which scientists discussed their research and insights regarding cell-associated HIV mucosal transmission. The 10 articles in this supplement present the case for cell-associated HIV transmission as an important element contributing to the HIV epidemic, review evidence for the efficacy of current HIV prevention strategies against cell-associated HIV transmission and opportunities for further development, and describe in vitro, ex vivo, and animal cell-associated transmission models that can be used to further elucidate the molecular mechanisms of cell-associated HIV mucosal transmission and test HIV prevention strategies. We hope that these articles will help to inform and invigorate the HIV prevention field and contribute to the development of more-effective vaccine, treatment, and microbicide strategies for HIV prevention.