Systemic and mucosal immunological responses during repeated mucosal SHIV(162P3) challenges prior to and following infection in pigtailed macaques.

Local and systemic immunological changes following vaginal HIV-1 exposures are poorly characterized and may influence susceptibility to infection. Therefore, we examined longitudinal mucosal, plasma cytokine profiles and viral-specific T-cell responses (vSTRs) before and during weekly repeated low-dose SHIV(SF162P3) viral challenges in six female pigtailed macaques, even in the absence of overt systemic infection. Following a single viral challenge, induction of several cytokines was detected consistently in cervico-vaginal lavages (CVL). With additional exposure and documented systemic infection, a hallmark of response profile was defined as peak levels in both CVL (MCP-1, MIP-1alpha, TNF-alpha, IL-1beta, IL-1RA and IL-8) and plasma cytokines (MCP-1, eotaxin and IL-1RA) in the macaques. In the periphery, vSTRs were observed within the first one or two viral challenges, but prior to the detection of systemic infection in 5/6 exposed pigtailed macaques. These findings provide valuable information regarding mucosal HIV-1 infection that may benefit microbicide research and development.

Prevention of rectal SHIV transmission in macaques by daily or intermittent prophylaxis with emtricitabine and tenofovir.

BACKGROUND: In the absence of an effective vaccine, HIV continues to spread globally, emphasizing the need for novel strategies to limit its transmission. Pre-exposure prophylaxis (PrEP) with antiretroviral drugs could prove to be an effective intervention strategy if highly efficacious and cost-effective PrEP modalities are identified. We evaluated daily and intermittent PrEP regimens of increasing antiviral activity in a macaque model that closely resembles human transmission. METHODS AND FINDINGS: We used a repeat-exposure macaque model with 14 weekly rectal virus challenges. Three drug treatments were given once daily, each to a different group of six rhesus macaques. Group 1 was treated subcutaneously with a human-equivalent dose of emtricitabine (FTC), group 2 received orally the human-equivalent dosing of both FTC and tenofovir-disoproxil fumarate (TDF), and group 3 received subcutaneously a similar dosing of FTC and a higher dose of tenofovir. A fourth group of six rhesus macaques (group 4) received intermittently a PrEP regimen similar to group 3 only 2 h before and 24 h after each weekly virus challenge. Results were compared to 18 control macaques that did not receive any drug treatment. The risk of infection in macaques treated in groups 1 and 2 was 3.8- and 7.8-fold lower than in untreated macaques (p = 0.02 and p = 0.008, respectively). All six macaques in group 3 were protected. Breakthrough infections had blunted acute viremias; drug resistance was seen in two of six animals. All six animals in group 4 that received intermittent PrEP were protected. CONCLUSIONS: This model suggests that single drugs for daily PrEP can be protective but a combination of antiretroviral drugs may be required to increase the level of protection. Short but potent intermittent PrEP can provide protection comparable to that of daily PrEP in this SHIV/macaque model. These findings support PrEP trials for HIV prevention in humans and identify promising PrEP modalities.

Direct stringency comparison of two macaque models (single-high vs. repeat-low) for mucosal HIV transmission using an identical anti-HIV chemoprophylaxis intervention.

BACKGROUND: In our previous work, oral chemoprophylaxis with tenofovir disoproxil fumarate (TDF) provided partial protection in rhesus macaques against repeated low-dose (RL) intrarectal SHIV162p3 exposure. METHODS: Here, we make a direct comparison of these previous findings with data generated using a single high (SH)-dose challenge strategy. RESULTS: All 5 (100%) control macaques were infected after a SH challenge and only three of five (60%) TDF-treated macaques became infected. The remaining two TDF-treated macaques remained virus-negative and were susceptible to virus infection upon re-challenge in the absence of oral TDF. Thus, two of five (40%) TDF-treated macaques were protected by the pre-exposure chemoprophylaxis regimen. By comparison with the RL challenge system, only one of four (25%) of TDF-treated macaques were protected from infection, whereas four of four (100%) control macaques became infected using RL challenges. CONCLUSION: Taken together, these findings indicate that the stringency of the RL challenge model for testing antiretroviral interventions is not lower and possibly greater than that of the SH challenge model.

Chemoprophylaxis with tenofovir disoproxil fumarate provided partial protection against infection with simian human immunodeficiency virus in macaques given multiple virus challenges.

We examined the efficacy of tenofovir disoproxil fumarate (TDF) in blocking simian human immunodeficiency virus (SHIV) infection in Chinese rhesus macaques. Once weekly for 14 weeks or until a macaque became infected, 12 male macaques were inoculated intrarectally with amounts of SHIV(SF162P3) (10 median tissue culture infective doses; 3.8 x 10(5) virus particles) that were approximately 5-fold higher than the human immunodeficiency virus type 1 RNA levels noted in human semen during an acute infection. Of the 12 macaques, 4 received oral TDF daily, 4 received oral TDF once weekly, and 4 (control animals) received no TDF. The control animals became infected after receiving a median of 1.5 virus inoculations; macaques receiving TDF daily (1 macaque remained uninfected after 14 inoculations) and those receiving TDF weekly became infected after a median duration of 6.0 and 7.0 weeks, respectively. Although infection was delayed in treated macaques, compared with control macaques, the differences were not statistically significant (P=.315); however, the study was limited by the small numbers of animals evaluated and the variability in blood levels of TDF that resulted from oral dosing. These data demonstrate that treatment with oral TDF provided partial protection against SHIV infection but ultimately did not protect all TDF treated animals against multiple virus challenges.

Repetitive exposures with simian/human immunodeficiency viruses: strategy to study HIV pre-clinical interventions in non-human primates.

BACKGROUND: Non-human primate models for human immunodeficiency virus (HIV) infection represent a valuable pre-clinical tool to evaluate interventions (e.g., topical microbicides, vaccines, and chemoprophylaxis) designed to prevent transmission or slow disease progression after infection. Standard transmission models use a single-dose exposure with high, non-physiologic levels of virus to approach 100% infection rates of control animals. These single-exposure models do not represent the circumstances of mucosal HIV transmission in humans and may result in misleading data with regard to intervention efficacy. Therefore, we have developed a repetitive mucosal exposure model using doses of virus that better reflects human exposures. METHODS: The virus used for these evaluations was simian-human immunodeficiency virus [SHIVSF162P3 (R5-using, subtype B HIV-1 envelope)] and the virus dose used (approximately 10(5)-10(6) viral particle equivalents or approximately 10 tissue culture infectious doses per exposure) approximates viral loads observed in the semen during acute HIV-1 infection. Using the repeated mucosal exposure approach, we have evaluated a candidate vaginal microbicide (cellulose acetate phthalate, CAP) given 15 minutes prior to each weekly virus exposure. Pig-tailed macaques were exposed weekly by vaginal inoculations with and without microbicide until systemic viral RNA was detected. RESULTS: Groups of naïve control monkeys were infected after an average of three to four exposures for the vaginal route of inoculation. Data from the first application of this monkey model to evaluate the topical microbicide CAP suggested that protection from SHIV infection was possible with three of four CAP-treated monkeys remaining uninfected after 12 exposures (P = 0.015). CAP efficacy was markedly improved from 66% in a previous single-dose virus exposure study to 92% in this repeated exposure system. CONCLUSIONS: Our experience with using repetitive virus exposures to study topical microbicides and the findings to date from this study provides a basis to refine monkey models to more closely resemble human exposure during HIV transmission. This model may be highly relevant to pre-clinical evaluation for a variety of therapeutic interventions which is discussed here.

Multiple vaginal exposures to low doses of R5 simian-human immunodeficiency virus: strategy to study HIV preclinical interventions in nonhuman primates.

A nonhuman-primate model of human immunodeficiency virus type 1 (HIV-1) infection that more closely emulates human heterosexual transmission by use of multiple exposures to low doses of virus is critical to better evaluate intervention strategies that include microbicides or vaccines. In this report, we describe such a system that uses female pig-tailed macaques exposed vaginally to a CCR5-using simian-human immunodeficiency virus (SHIV(SF162P3)) at weekly intervals. Results of dose-titration experiments indicated that 3 once-weekly exposures to 10 tissue culture infectious doses of SHIV(SF162P3) resulted in consistent transmission of virus and establishment of systemic infection. The efficacy of cellulose acetate phthalate (CAP) as a vaginal microbicide was evaluated by applying it to the vaginal vault of macaques (n = 4) 15 min before each weekly exposure to SHIV(SF162P3). One conclusion that can be drawn from the data derived from multiple exposures to virus is that CAP prevented infection in 12 of 13 possible chances for infection, over the course of 39 total exposures. Our findings provide a basis to refine monkey models for transmission of HIV-1, which may be relevant to preclinical evaluation for therapeutic interventions.

Chronic HIV-2 infection protects against total CD4+ cell depletion and rapid disease progression induced by SHIV89.6p challenge.

OBJECTIVE: To better understand HIV-1 sexual transmission risk, we have studied the susceptibility of HIV-2-exposed, uninfected (EU) female pig-tailed macaques to intravaginal (IVAG) re-challenge with the homologous HIV-2 strain, followed by heterologous SHIV89.6p. METHODS: Nine female macaques, previously protected by a post-exposure prophylaxis (PEP) regimen, along with one mock-treated EU animal, were re-exposed to HIV-2 by the IVAG route approximately 1.5 years later. A single follow-up challenge was performed approximately 1 year later with SHIV89.6p to assess susceptibility of chronic HIV-2-infected animals to further re-infection and pathogenic effects with a heterologous virus, somewhat mimicking HIV-1. RESULTS: Eight of ten macaques (80%) became infected systemically with HIV-2, and plasma or cervicovaginal vRNA levels did not appreciably differ from prior historic non-PEP control macaques. Interestingly, all eight HIV-2-infected females were susceptible to SHIV89.6p infection by either intravenous (n = 4) or IVAG exposure (n = 4) after one inoculation. Plasma vRNA levels in these groups were controlled by week 8 and there were no decrease in CD4+ T cells > 50%. The remaining two HIV-2 EU macaques, inoculated intrarectally with SHIV89.6p, were unable to control virus replication and succumbed to disease by week 25 or week 61. CONCLUSIONS: Our findings demonstrate that successful PEP regimens to prevent an initial infection do not have any lasting protective effects. The observed lack of cross-protection against SHIV89.6p transmission among chronic HIV-2-infected macaques provides modeling support for limited epidemiologic data indicating that human HIV-2 infection does not protect against HIV-1 infection, but may serve to alter overt clinical outcome.