Protection of macaques from vaginal SHIV challenge by an orally delivered CCR5 inhibitor

Protection Efficacy of C5A Against Vaginal and Rectal HIV Challenges in Humanized Mice

Introduction:

In the absence of a vaccine, there is an urgent need for the identification of effective agents that prevent HIV transmission in uninfected individuals. Non-vaccine Biomedical Prevention (nBP) methods, such as topical or systemic pre-exposure prophylaxis (PrEP), are promising strategies to slow down the spread of AIDS.

Methods:

In this study, we investigated the microbicidal efficacy of the viral membrane-disrupting amphipathic SWLRDIWDWICEVLSDFK peptide called C5A. We chose the bone marrow/liver/thymus (BLT) humanized mouse model as vaginal and rectal HIV transmission models.

Results:

We found that the topical administration of C5A offers complete protection against vaginal and rectal HIV challenges in humanized mice. After demonstrating that C5A blocks genital HIV transmission in humanized mice, we examined the molecular requirements for its microbicidal property. We found that the removal of four amino acids on either end of C5A does not diminish its microbicidal efficacy. However, the removal of four amino acids at both the ends, abolishes its capacity to prevent vaginal or rectal HIV transmission, suggesting that the length of the peptide is a critical parameter for the microbicidal activity of C5A. Moreover, we demonstrated that the amphipathicity of the helical peptide as well as its hydrophobic surface represents key factors for the microbicidal activity of C5A in humanized mice.

Conclusion:

With its noncellular cytotoxic activity, its property of neutralizing both HSV and HIV, and its unique mechanism of action that disrupts the stability of the viral membrane, C5A represents an attractive multipurpose microbicidal candidate to be combined with other anti-HIV agents including antiretrovirals.

Prevention of vaginal and rectal HIV transmission by antiretroviral combinations in humanized mice

With more than 7,000 new HIV infections daily worldwide, there is an urgent need for non-vaccine biomedical prevention (nBP) strategies that are safe, effective, and acceptable. Clinical trials have demonstrated that pre-exposure prophylaxis (PrEP) with antiretrovirals (ARVs) can be effective at preventing HIV infection. In contrast, other trials using the same ARVs failed to show consistent efficacy. Topical (vaginal and rectal) dosing is a promising regimen for HIV PrEP as it leads to low systematic drug exposure. A series of titration studies were carried out in bone marrow/liver/thymus (BLT) mice aimed at determining the adequate drug concentrations applied vaginally or rectally that offer protection against rectal or vaginal HIV challenge. The dose-response relationship of these agents was measured and showed that topical tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) can offer 100% protection against rectal or vaginal HIV challenges. From the challenge data, EC50 values of 4.6 μM for TDF and 0.6 μM for FTC for HIV vaginal administration and 6.1 μM TDF and 0.18 μM for FTC for rectal administration were obtained. These findings suggest that the BLT mouse model is highly suitable for studying the dose-response relationship in single and combination ARV studies of vaginal or rectal HIV exposure. Application of this sensitive HIV infection model to more complex binary and ternary ARV combinations, particularly where agents have different mechanisms of action, should allow selection of optimal ARV combinations to be advanced into pre-clinical and clinical development as nBP products.

Brief Report: Pharmacokinetic/Pharmacodynamic Investigation of Single-Dose Oral Maraviroc in the Context of HIV-1 Pre-exposure Prophylaxis

To investigate the pharmacokinetics/pharmacodynamics of single-dose maraviroc 300 mg in HIV-1 exposure compartments. Maraviroc concentrations in blood, secretions (vaginal, urethral, oral, and rectal), and tissue (vaginal and rectal) were measured, and ex vivo challenge was performed in 54 healthy volunteers to study protection from HIV infection. Maraviroc Cmax occurred within 4 hours in most compartments. Concentrations from 4 to 72 hours were above intracellular (IC) IC90 in all compartments, range 15-8095 ng/mL. Mean AUC0-72 compartment-to-plasma ratios were highest in the rectum (45-819) and urethra (144) compared with the female genital tract (1.6-4.8) and saliva (0.2). No sex differences in AUC0-72 or Cmax were observed. No ex vivo protection from HIV-1BaL occurred in rectal or vaginal tissue. Despite high and sustained concentrations, single-dose maraviroc was not protective against ex vivo challenge of vaginal/rectal tissue.

Nonhuman Primate Models for Studies of AIDS Virus Persistence During Suppressive Combination Antiretroviral Therapy

Nonhuman primate (NHP) models of AIDS represent a potentially powerful component of the effort to understand in vivo sources of AIDS virus that persist in the setting of suppressive combination antiretroviral therapy (cART) and to develop and evaluate novel strategies for more definitive treatment of HIV infection (i.e., viral eradication "cure", or sustained off-cART remission). Multiple different NHP models are available, each characterized by a particular NHP species, infecting virus, and cART regimen, and each with a distinct capacity to recapitulate different aspects of HIV infection. Given these different biological characteristics, and their associated strengths and limitations, different models may be preferred to address different questions pertaining to virus persistence and cure research, or to evaluate different candidate intervention approaches. Recent developments in improved cART regimens for use in NHPs, new viruses, a wider array of sensitive virologic assay approaches, and a better understanding of pathogenesis should allow even greater contributions from NHP models to this important area of HIV research in the future.

Cabotegravir long-acting for HIV-1 prevention

PURPOSE OF REVIEW

Preexposure prophylaxis (PrEP) with daily Truvada has demonstrated clinical efficacy against HIV-1 acquisition that correlates with high adherence. Long-acting antiretroviral drugs offer an alternative to daily regimens and may improve PrEP adherence. This review summarizes the preclinical nonhuman primate studies for evaluating the efficacy of cabotegravir long-acting as PrEP and the ongoing phase 2a studies assessing safety, tolerability, and acceptability of cabotegravir long-acting.

RECENT FINDINGS

Cabotegravir is an HIV-1 integrase strand transfer inhibitor with intrinsic properties that permit its formulation as a long-acting injectable suspension. In clinical evaluation, cabotegravir long-acting has a half-life that permits infrequent dosing, possibly once every 3 months. In validated macaque models, cabotegravir long-acting demonstrated high protection against both rectal and vaginal transmission at clinically achievable drug concentrations.

SUMMARY

PrEP, after approval of Truvada, continues to evolve to address adherence limitations of daily dosing. As a long-acting injectable antiretroviral drug, cabotegravir long-acting permits quarterly dosing and demonstrated high efficacy in macaque models supporting dose selection and clinical development. Clinical studies have confirmed dose selection in phase 2a trials with cabotegravir long-acting to ultimately lead to phase 2b/3 PrEP efficacy trials.

A long-acting integrase inhibitor protects female macaques from repeated high-dose intravaginal SHIV challenge

Long-acting GSK1265744 (GSK744 LA) is a strand transfer inhibitor of the HIV/SIV (simian immunodeficiency virus) integrase and was shown to be an effective preexposure prophylaxis (PrEP) agent in a low-dose intrarectal SHIV (simian-human immunodeficiency virus) rhesus macaque challenge model. We examined the pharmacokinetics and efficacy of GSK744 LA as PrEP against repeat high-dose intravaginal SHIV challenge in female rhesus macaques treated with Depo-Provera (depot medroxyprogesterone acetate), which promotes viral transmission vaginally. When Depo-Provera-treated female rhesus macaques were dosed with GSK744 LA (50 mg/kg) monthly, systemic and tissue drug concentrations were lower than previously observed in male rhesus macaques. GSK744 concentrations were fivefold lower on average in cervical tissues than in rectal tissues. Eight female rhesus macaques were treated with GSK744 LA at week 0, and four female rhesus macaques served as controls. All animals received a high-dose challenge of SHIV162P3 at week 1. No infection was detected in GSK744 LA-treated rhesus macaques, whereas viremia was detected 1 to 2 weeks after SHIV challenge in all control animals. The GSK744 LA-treated rhesus macaques were given a second administration of drug at week 4 and further challenged at weeks 5 and 7. GSK744 LA treatment protected six of eight female rhesus macaques against three high-dose SHIV challenges, whereas all control animals became infected after the first challenge (P = 0.0003, log-rank test). These results support further clinical development of GSK744 LA for PrEP.

Preclinical assessments of vaginal microbicide candidate safety and efficacy

Sexually transmitted infections like HIV, HPV, and HSV-2, as well as unplanned pregnancy, take a huge toll on women worldwide. Woman-initiated multipurpose prevention technologies that contain antiviral/antibacterial drugs (microbicides) and a contraceptive to simultaneously target sexually transmitted infections and unplanned pregnancy are being developed to reduce these burdens. This review will consider products that are applied topically to the vagina. Rectally administered topical microbicides in development for receptive anal intercourse are outside the scope of this review. Microbicide and microbicide/contraceptive candidates must be rigorously evaluated in preclinical models of safety and efficacy to ensure that only candidates with favorable risk benefit ratios are advanced into human clinical trials. This review describes the comprehensive set of in vitro, ex vivo, and in vivo models used to evaluate the preclinical safety and antiviral efficacy of microbicide and microbicide/contraceptive candidates.

The role of chance in primate lentiviral infectivity: from protomer to host organism

Infection is best described as a stochastic process. Whether a host becomes infected upon exposure has a strong random element. The same applies to cells exposed to virions. In this review, we show how the mathematical formalism for stochastic processes has been used to describe and understand the infection by the Human and Simian Immunodeficiency Virus on different levels. We survey quantitative studies on the establishment of infection in the host (the organismal level) and on the infection of target cells (the cellular and molecular level). We then discuss how a synthesis of the approaches across these levels could give rise to a predictive framework for assessing the efficacy of microbicides and vaccines.

Pre-exposure prophylaxis for human immunodeficiency virus: the past, present, and future

This article presents an overview of pre-exposure prophylaxis (PrEP) for human immunodeficiency virus (HIV) prevention. The authors describe the past animal and human research that has been conducted that informs our current understanding of PrEP; summarize ongoing research in the area, including describing new regimens and delivery mechanisms being studied for PrEP; and highlight key issues that must be addressed in order to implement and optimize the use of this HIV prevention tool.

Pharmacokinetics of a CCR5 inhibitor in rhesus macaques following vaginal, rectal and oral application

OBJECTIVES

This study measured and compared the pharmacokinetics of CMPD167, a small molecule antiretroviral CCR5 inhibitor with potential as an HIV microbicide, following vaginal, rectal and oral administration in rhesus macaques.

METHODS

A vaginal hydroxyethylcellulose (HEC) gel, a rectal HEC gel, a silicone elastomer matrix-type vaginal ring and an oral solution, each containing CMPD167, were prepared and administered to rhesus macaques pretreated with Depo-Provera. CMPD167 concentrations in vaginal fluid, vaginal tissue (ring only), rectal fluid and blood plasma were quantified by HPLC-mass spectrometry.

RESULTS

CMPD167 concentrations measured in rectal fluid, vaginal fluid and blood plasma were highly dependent on both the route of administration and the formulation type. Although rectal and vaginal fluid concentrations were highest when CMPD167 was administered locally (via either gel or ring), lower concentrations of the drug were also measured in these compartments following administration at the remote mucosal site or orally. CMPD167 levels in the vaginal and rectal fluid following oral administration were relatively low compared with local administration.

CONCLUSIONS

The study provides clear evidence for vaginal-rectal and rectal-vaginal drug transfer pathways and suggests that oral pre-exposure prophylaxis with CMPD167 may be less efficacious at preventing sexual transmission of HIV-1 than topically applied products.

Animal models for microbicide safety and efficacy testing

PURPOSE OF REVIEW

Early studies have cast doubt on the utility of animal models for predicting success or failure of HIV-prevention strategies, but results of multiple human phase 3 microbicide trials, and interrogations into the discrepancies between human and animal model trials, indicate that animal models were, and are, predictive of safety and efficacy of microbicide candidates.

RECENT FINDINGS

Recent studies have shown that topically applied vaginal gels, and oral prophylaxis using single or combination antiretrovirals are indeed effective in preventing sexual HIV transmission in humans, and all of these successes were predicted in animal models. Further, prior discrepancies between animal and human results are finally being deciphered as inadequacies in study design in the model, or quite often, noncompliance in human trials, the latter being increasingly recognized as a major problem in human microbicide trials.

SUMMARY

Successful microbicide studies in humans have validated results in animal models, and several ongoing studies are further investigating questions of tissue distribution, duration of efficacy, and continued safety with repeated application of these, and other promising microbicide candidates in both murine and nonhuman primate models. Now that we finally have positive correlations with prevention strategies and protection from HIV transmission, we can retrospectively validate animal models for their ability to predict these results, and more importantly, prospectively use these models to select and advance even safer, more effective, and importantly, more durable microbicide candidates into human trials.

HIV prevention by oral preexposure prophylaxis

The impressive advances in antiretroviral (ARV) therapy of chronic human immunodeficiency virus (HIV) infections during the last decade and the availability of potent ARV drugs have fueled interest in using chemoprophylaxis as a novel HIV prevention strategy. Preexposure prophylaxis (PrEP) refers to the use of ARV drugs in HIV-negative persons to prevent HIV infection. The rationale for PrEP builds on the success of ARV prophylaxis in preventing mother-to-child transmission of HIV and on a large body of animal studies that show the efficacy of PrEP against mucosal and parenteral infection. We focus on oral administration of ARV drugs for prevention of HIV infection. Identifying an effective prophylactic pill that individuals can take outside the setting of sexual intercourse precludes the necessity to disclose such use to their partners, thereby empowering those who might not be in a position to negotiate with their partners. Several human clinical trials evaluating the efficacy of daily regimens of the HIV reverse-transcriptase (RT) inhibitors tenofovir disoproxil fumarate (TDF) or Truvada (TDF and emtricitabine [FTC]) are under way among high-risk populations. The results of one trial among men who have sex with men showed that daily Truvada was safe and effective, providing the first support for oral PrEP as a prevention strategy. Here we outline the preclinical and clinical research on oral PrEP, pharmacologic considerations, and future directions and challenges.

Lack of prophylactic efficacy of oral maraviroc in macaques despite high drug concentrations in rectal tissues

Maraviroc (MVC) is a potent CCR5 coreceptor antagonist that is in clinical testing for daily oral pre-exposure prophylaxis (PrEP) for HIV prevention. We used a macaque model consisting of weekly SHIV162p3 exposures to evaluate the efficacy of oral MVC in preventing rectal SHIV transmission. MVC dosing was informed by the pharmacokinetic profile seen in blood and rectal tissues and consisted of a human-equivalent dose given 24 h before virus exposure, followed by a booster postexposure dose. In rectal secretions, MVC peaked at 24 h (10,242 ng/ml) with concentrations at 48 h that were about 40 times those required to block SHIV infection of peripheral blood mononuclear cells (PBMCs) in vitro. Median MVC concentrations in rectal tissues at 24 h (1,404 ng/g) were 30 and 10 times those achieved in vaginal or lymphoid tissues, respectively. MVC significantly reduced macrophage inflammatory protein 1β-induced CCR5 internalization in rectal mononuclear cells, an indication of efficient binding to CCR5 in rectal lymphocytes. The half-life of CCR5-bound MVC in PBMCs was 2.6 days. Despite this favorable profile, 5/6 treated macaques were infected during five rectal SHIV exposures as were 3/4 controls. MVC treatment was associated with a significant increase in the percentage of CD3(+)/CCR5(+) cells in blood. We show that high and durable MVC concentrations in rectal tissues are not sufficient to prevent SHIV infection in macaques. The increases in CD3(+)/CCR5(+) cells seen during MVC treatment point to unique immunological effects of CCR5 inhibition by MVC. The implications of these immunological effects on PrEP with MVC require further evaluation.

CCR5 inhibitors in HIV-1 therapy

BACKGROUND

The human immunodeficiency virus 1 (HIV-1) is the causative pathogen of AIDS, the world's biggest infectious disease killer. About 33 million people are infected worldwide, with 2.1 million deaths a year as a direct consequence. The devastating nature of AIDS has prompted widespread research, which has led to an extensive array of therapies to suppress viral replication and enable recovery of the immune system to prolong and improve patient life substantially. However, the genetic plasticity and replication rate of HIV-1 are considerable, which has lead to rapid drug resistance. This, together with the need for reducing drug side effects and increasing regimen compliance, has led researchers to identify antiretroviral drugs with new modes of action.

OBJECTIVE

This review describes the discovery and clinical development of CCR5 antagonists and the recent approval of maraviroc as a breakthrough in anti-HIV-1 therapy.

CONCLUSION

CCR5 inhibitors target a human cofactor to disable HIV-1 entry into the cells, and thereby provide a new hurdle for the virus to overcome. The status and expert opinion of CCR5 antagonists for the treatment of HIV-1 infection are detailed.

Use of G-protein-coupled and -uncoupled CCR5 receptors by CCR5 inhibitor-resistant and -sensitive human immunodeficiency virus type 1 variants

Small-molecule CCR5 inhibitors such as vicriviroc (VVC) and maraviroc (MVC) are allosteric modulators that impair HIV-1 entry by stabilizing a CCR5 conformation that the virus recognizes inefficiently. Viruses resistant to these compounds are able to bind the inhibitor-CCR5 complex while also interacting with the free coreceptor. CCR5 also interacts intracellularly with G proteins, as part of its signal transduction functions, and this process alters its conformation. Here we investigated whether the action of VVC against inhibitor-sensitive and -resistant viruses is affected by whether or not CCR5 is coupled to G proteins such as Gαi. Treating CD4(+) T cells with pertussis toxin to uncouple the Gαi subunit from CCR5 increased the potency of VVC against the sensitive viruses and revealed that VVC-resistant viruses use the inhibitor-bound form of Gαi-coupled CCR5 more efficiently than they use uncoupled CCR5. Supportive evidence was obtained by expressing a signaling-deficient CCR5 mutant with an impaired ability to bind to G proteins, as well as two constitutively active mutants that activate G proteins in the absence of external stimuli. The implication of these various studies is that the association of intracellular domains of CCR5 with the signaling machinery affects the conformation of the external and transmembrane domains and how they interact with small-molecule inhibitors of HIV-1 entry.

A silicone elastomer vaginal ring for HIV prevention containing two microbicides with different mechanisms of action

Vaginal rings are currently being developed for the long-term (at least 30 days) continuous delivery of microbicides against human immunodeficiency virus (HIV). Research to date has mostly focused on devices containing a single antiretroviral compound, exemplified by the 25mg dapivirine ring currently being evaluated in a Phase III clinical study. However, there is a strong clinical rationale for combining antiretrovirals with different mechanisms of action in a bid to increase breadth of protection and limit the emergence of resistant strains. Here we report the development of a combination antiretroviral silicone elastomer matrix-type vaginal ring for simultaneous controlled release of dapivirine, a non-nucleoside reverse transcriptase inhibitor, and maraviroc, a CCR5-targeted HIV-1 entry inhibitor. Vaginal rings loaded with 25mg dapivirine and various quantities of maraviroc (50-400mg) were manufactured and in vitro release assessed. The 25mg dapivirine and 100mg maraviroc formulation was selected for further study. A 24-month pharmaceutical stability evaluation was conducted, indicating good product stability in terms of in vitro release, content assay, mechanical properties and related substances. This combination ring product has now progressed to Phase I clinical testing.

Pharmacokinetics and efficacy of a vaginally administered maraviroc gel in rhesus macaques

OBJECTIVES

To investigate the pharmacokinetics (PK) of maraviroc, a CCR5-targeted HIV-1 entry inhibitor, in rhesus macaques following vaginal administration of various maraviroc-loaded aqueous hydroxyethylcellulose (HEC) gels, and to correlate the PK data with efficacy in a single high-dose vaginal SHIV-162P3 challenge model.

METHODS

Maraviroc concentrations in vaginal fluid (Weck-Cel(®) sponge), vaginal tissue (punch biopsy) and plasma were assessed over 72 h following single-dose vaginal application of various maraviroc-loaded HEC gels. The range of maraviroc gel concentrations was sufficiently broad (0.003%-3.3% w/w) that test gels included both fully solubilized and predominantly dispersed formulations. The efficacy of the HEC gels against a single high-dose vaginal SHIV-162P3 challenge was also measured, and correlated with the PK concentrations.

RESULTS

Maraviroc concentrations in vaginal fluid (range 10(4)-10(7) ng/mL), vaginal tissue (100-1200 ng/g) and plasma (<10(2) ng/mL) were highly dependent on maraviroc gel loading, irrespective of the form of the maraviroc component within the gel (solubilized versus dispersed). Fluid and plasma concentrations were generally highest 0.5 or 2 h after gel application, before declining steadily through to 72 h. Maraviroc concentrations in the various biological compartments correlated strongly with the extent of protection against vaginal SHIV-162P3 challenge. Complete protection was achieved with a 3.3% w/w maraviroc gel.

CONCLUSIONS

A high degree of correlation between PK and efficacy was observed. Based on the data obtained with the 3.3% w/w maraviroc gel, maintenance of vaginal fluid and tissue levels in the order of 10(7) ng/mL and 10(3) ng/g, respectively, are required for complete protection with this compound.

Controlled-release vaginal ring drug-delivery systems: a key strategy for the development of effective HIV microbicides

BACKGROUND

Over half of all HIV-infected adults are women and heterosexual intercourse is a significant mode of viral transmission. This review examines the potential for using polymeric vaginal ring systems to provide controlled delivery of HIV microbicides in order to prevent heterosexual transmission of the virus.

DISCUSSION

Continuous delivery of microbicides has the potential to be more effective than one-off dosing. Thus, controlled-release vaginal delivery devices are now a key area of HIV prevention research. Initial clinical trials on vaginal rings loaded with dapivirine (a candidate microbicide) have indicated that these products are safe and well tolerated by women. These devices are female-initiated, robust and capable of long-term delivery of the active agent.

CONCLUSIONS

Vaginal rings may offer an effective system for the controlled delivery of microbicides to prevent heterosexual transmission of HIV. Candidate vaginal ring microbicide products are now in clinical trials.

The use of preexposure treatments for HIV prophylaxis

Infection with human immunodeficiency virus remains a global concern with a significant number of incident infections still reported worldwide. The use of prophylaxis prior to exposure to the virus to prevent infection has been a growing area of recent research. Results in nonhuman primates and clinical trials in high-risk patient populations using preexposure prophylaxis have shown promising results in terms of efficacy and safety, especially relating to oral preexposure prophylaxis. The potential use of oral antiretroviral agents traditionally used for human immunodeficiency virus treatment as prophylaxis raises interesting considerations, such as the best agents available for such a role, long-term safety in healthy individuals, and the potential development of resistance to these agents should infection occur. From a public health perspective, the cost-effectiveness of implementing this preventive strategy has not been fully defined at this point in time.

The use of nonhuman primate models of HIV infection for the evaluation of antiviral strategies

Several nonhuman primate models are used in HIV/AIDS research. In contrast to natural host models, infection of macaques with virulent simian immunodeficiency virus (SIV) isolates results in a disease (simian AIDS) that closely resembles HIV infection and AIDS. Although there is no perfect animal model, and each of the available models has its limitations, a carefully designed study allows experimental approaches that are not feasible in humans, but that can provide better insights in disease pathogenesis and proof-of-concept of novel intervention strategies. In the early years of the HIV pandemic, nonhuman primate models played a minor role in the development of antiviral strategies. Since then, a better understanding of the disease and the development of better compounds and assays to monitor antiviral effects have increased the usefulness and relevance of these animal models in the preclinical development of HIV vaccines, microbicides, and antiretroviral drugs. Several strategies that were first discovered to have efficacy in nonhuman primate models are now increasingly used in humans. Recent trends include the use of nonhuman primate models to explore strategies that could reduce viral reservoirs and, ultimately, attempt to cure infection. Ongoing comparison of results obtained in nonhuman primate models with those observed in human studies will lead to further validation and improvement of these animal models so they can continue to advance our scientific knowledge and guide clinical trials.

Barriers of the Human Organism and Their Achilles’ Heels

The human body is covered by barriers separating it from the external and internal surroundings. The “milieu enterieur” has to be stabilised in spite of the variable external and internal conditions of toxic, osmotic, microbial and climatic environmental circumstances. This first line of barriers is composed of skin and mucous membranes of complicated structures.

A second line of barrier system is present in our organisms. Certain organs have to be separated from the immune system and other parts of the body because of evolutionary reasons (eye-bulb and testicles) because of unique proteins “unknown” for the acquired immune system. The blood-brain barrier (BBB) is providing enhanced safety circumstances for the central nervous system. The second line of barriers is represented by the special properties of the capillary endothelial system.

The maternal-fetal barrier is the most complex. At the maternal fetal interface two individuals of two different haplotypes has to be live 9 months separated by a very complicated dynamic barrier.

The placenta is the organ, which is separating the maternal and fetal tissues. Similar to others the bidirectional transport of gasses, metabolites, cells, proteins, regulatory substances, are transported by active or passive transcellular and intercellular mechanisms.

The fetal immune system develops immunotolerance to all maternal cells and antigens transferred transplacentally. The problem is to mitigate the maternal immune system to tolerate the paternal haplotype of the fetus. In the case of normal pregnancy a complex series of physiological modifications can solve the problem without harmful consequences to the mother and fetus.

The outermost contact cells of trophoblasts express instead of HLA-class Ia and class II antigens non-variable HLA-C, HLA-E, HLA-F and HLA-G antigens. The first consequence of this is reduction of the activity of maternal natural killer cells and maternal dendritic cells;

Progesteron, micro-RNA and mediators influence the development of T effector-cells. The production of soluble HLA-G(5 and 6) and IL-10 supports the differentiation of Th-2 CD4⁺ helper cells, reducing the ability of maternal cells to kill fetal cells.

Series of receptors and costimulators are expressed by the different lines of semi-allogenic trophoblast cells to bind HLA-G and mitigate maternal immune response;

The maternal immunotolerance is further facilitated by the activation of CD4⁺CD25^brightFoxp3⁺ regulatory T (T_REG) cells.

Infections have to be prevented during pregnancy. The cells of placenta express 10 Toll-like receptors a group of pattern recognition receptors responsible for innate immunity. The interferon level is also higher in the placental tissues than in the somatic fetal or maternal cells.

The complement system is also adapted to the requirements of the pregnancy and fetal damage is inhibited by the production of “assymmetric IgG antibodies” under hormonal and placental-regulation. These modifications prevent the activation of complement, cytotoxic activity, opsonising ability, antigen clearance and precipitating activity of the molecules.

The Achilles’ heels of the different barriers are regularly found by virus infections. Lamina cribrosa of the blood-brain barrier, optical nerve of the eyes, etc. the risk factors of the maternal-fetal barrier has been summarised in Table 1.1.

Incorporation of the HIV-1 microbicide cyanovirin-N in a food product

An urgent need exists for HIV-1 microbicides. Here, we describe the in vivo testing of lactic acid bacteria bioengineered to secrete cyanovirin-N. We fed pigtail macaques a yogurt formulation that used bioengineered strains as a starter culture. Cyanovirin-N expression could be detected in the rectal vault during and immediately after feeding. Ex vivo viral challenge of rectal tissue biopsies revealed that peak viral burden was significantly lower in tissue obtained from experimental animals compared with control animals. Formulation of candidate compounds in lactic acid bacteria and their oral administration seems to be a feasible strategy for mucosal delivery of microbicides.

Modeling dynamic interactions between pre-exposure prophylaxis interventions & treatment programs: predicting HIV transmission & resistance

Clinical trials have recently demonstrated the effectiveness of Pre-Exposure Prophylaxis (PrEP) in preventing HIV infection. Consequently, PrEP may soon be used for epidemic control. We model the dynamic interactions that will occur between treatment programs and potential PrEP interventions in resource-constrained countries. We determine the consequences for HIV transmission and drug resistance. We use response hypersurface modeling to predict the effect of PrEP on decreasing transmission as a function of effectiveness, adherence and coverage. We predict PrEP will increase need for second-line therapies (SLT) for treatment-naïve individuals, but could significantly decrease need for SLT for treatment-experienced individuals. If the rollout of PrEP is carefully planned it could increase the sustainability of treatment programs. If not, need for SLT could increase and the sustainability of treatment programs could be compromised. Our results show the optimal strategy for rolling out PrEP in resource-constrained countries is to begin around the "worst" treatment programs.

CCR5 antagonism in HIV infection: current concepts and future opportunities

CCR5 antagonists inhibit HIV-1 entry by blocking the interaction of HIV-1 with the CCR5 cellular receptor. In patients with established HIV-1 infection, some viral strains use an alternative coreceptor for HIV-1 entry, CXCR4; CCR5 antagonists are not effective in patients harboring these viral strains. Coreceptor tropism testing of viral strains in an individual patient is necessary prior to treating with a CCR5 antagonist. There is one CCR5 antagonist, maraviroc, that is FDA-approved for treatment of HIV-1 infection. This drug is used most commonly for the treatment of HIV-1 infection in patients who have failed other antiretroviral regimens. In addition to virologic effects, CCR5 antagonists are under investigation for immune-modulating effects and for HIV-1 prevention. Ongoing research will further elucidate the role of CCR5 antagonists in combating HIV disease.

Topical nonnucleoside reverse transcriptase inhibitor MC 1220 partially prevents vaginal RT-SHIV infection of macaques

The availability of an effective vaginal microbicide would be a major step toward containment of HIV transmission as well as allowing women self-protection against HIV infection. Here we evaluated the efficacy of vaginal application of the potent nonnucleoside reverse transcriptase inhibitor (NNRTI) MC 1220 against vaginal challenge of macaques with RT-SHIV, a chimeric simian immunodeficiency virus (SIV) containing the reverse transcriptase (RT) gene of HIV-1. Challenge infection of monkeys with RT-SHIV currently represents the only nonhuman primate model available to test the anti-HIV-1 effects of NNRTIs. Two different gel formulations containing different MC 1220 concentrations were evaluated for efficacy in female rhesus macaques exposed to RT-SHIV. Five groups of five animals each were treated with two different gel compositions containing no drug, 0.1% or 0.5% MC 1220, followed by vaginal RT-SHIV challenge 30 min later. One animal in each group treated with the low concentration of MC 1220 as well as one control animal remained uninfected after vaginal challenge. By contrast, three of the animals receiving 0.5% MC 1220 remained uninfected, suggesting a threshold of the drug. Despite being negative for plasma viral RNA and absence of seroconversion, almost all uninfected animals exhibited SIV-specific T cells, either in the periphery or in lymph nodes draining the portal of virus entry. Our results make MC 1220 a promising compound for further development as a topical microbicide and warrant additional testing with improved formulation, long-lasting vaginal delivery systems, or even combinations with other inhibitors.

Preexposure prophylaxis for HIV prevention

Reducing the incidence of HIV remains one of our greatest public health challenges. However, there is growing optimism that preexposure prophylaxis (PrEP) could have a major impact on preventing incident HIV infection. Recently presented data on the use of oral PrEP in men who have sex with men (MSM) have provided proof-of-principle for this strategy. Additional clinical trials are evaluating whether PrEP provides similar protection to risk groups other than MSM, such as heterosexual persons and injection drug users. Still unanswered questions include optimal dosing strategies, long-term safety, maximizing adherence and minimizing costs, addressing drug resistance in the face of PrEP failure, optimizing access, and assessing effects on risk behavior. Future implementation will be guided by the results of clinical trials in progress. This article provides a review of the data on the potential strengths and limitations of PrEP as an HIV prevention strategy, identifies challenges to implementation of this approach, and outlines knowledge gaps.

Resistance to the CCR5 inhibitor 5P12-RANTES requires a difficult evolution from CCR5 to CXCR4 coreceptor use

Viral resistance to small molecule allosteric inhibitors of CCR5 is well documented, and involves either selection of preexisting CXCR4-using HIV-1 variants or envelope sequence evolution to use inhibitor-bound CCR5 for entry. Resistance to macromolecular CCR5 inhibitors has been more difficult to demonstrate, although selection of CXCR4-using variants might be expected. We have compared the in vitro selection of HIV-1 CC1/85 variants resistant to either the small molecule inhibitor maraviroc (MVC) or the macromolecular inhibitor 5P12-RANTES. High level resistance to MVC was conferred by the same envelope mutations as previously reported after 16–18 weeks of selection by increasing levels of MVC. The MVC-resistant mutants were fully sensitive to inhibition by 5P12-RANTES. By contrast, only transient and low level resistance to 5P12-RANTES was achieved in three sequential selection experiments, and each resulted in a subsequent collapse of virus replication. A fourth round of selection by 5P12-RANTES led, after 36 weeks, to a “resistant” variant that had switched from CCR5 to CXCR4 as a coreceptor. Envelope sequences diverged by 3.8% during selection of the 5P12-RANTES resistant, CXCR4-using variants, with unique and critical substitutions in the V3 region. A subset of viruses recovered from control cultures after 44 weeks of passage in the absence of inhibitors also evolved to use CXCR4, although with fewer and different envelope mutations. Control cultures contained both viruses that evolved to use CXCR4 by deleting four amino acids in V3, and others that maintained entry via CCR5. These results suggest that coreceptor switching may be the only route to resistance for compounds like 5P12-RANTES. This pathway requires more mutations and encounters more fitness obstacles than development of resistance to MVC, confirming the clinical observations that resistance to small molecule CCR5 inhibitors very rarely involves coreceptor switching.

Attachment and fusion inhibitors potently prevent dendritic cell-driven HIV infection

Dendritic cells (DCs) efficiently transfer captured (trans) or de novo-produced (cis) virus to CD4 T cells. Using monocyte-derived DCs, we evaluated entry inhibitors targeting HIV envelope (BMS-C, T-1249) or CCR5 (CMPD167) for their potency to prevent DC infection, DC-driven infection in T cells in trans and cis, and direct infection of DC-T-cell mixtures. Immature DC-T-cell cultures with distinct mechanisms of viral transfer yielded similar levels of infection and produced more proviral DNA compared with matched mature DC-T-cell cultures or infected immature DCs. Although all compounds completely blocked HIV replication, 16 times more of each inhibitor (250 vs 15.6 nM) was required to prevent low-level infection of DCs compared with the productive DC-T-cell cocultures. Across all cell systems tested, BMS-C blocked infection most potently. BMS-C was significantly more effective than CMPD167 at preventing DC infection. In fact, low doses of CMPD167 significantly enhanced DC infection. Elevated levels of CCL4 were observed when immature DCs were cultured with CMPD167. Viral entry inhibitors did not interfere with Candida albicans-specific DC cytokine/chemokine responses. These findings indicate that an envelope-binding small molecule is a promising tool for topical microbicide design to prevent the infection of early targets needed to establish and disseminate HIV infection.

Clinical use of CCR5 inhibitors in HIV and beyond

Since the discovery of CCR5 as a coreceptor for HIV entry, there has been interest in blockade of the receptor for treatment and prevention of HIV infection. Although several CCR5 antagonists have been evaluated in clinical trials, only maraviroc has been approved for clinical use in the treatment of HIV-infected patients. The efficacy, safety and resistance profile of CCR5 antagonists with a focus on maraviroc are reviewed here along with their usage in special and emerging clinical situations. Despite being approved for use since 2007, the optimal use of maraviroc has yet to be well-defined in HIV and potentially in other diseases. Maraviroc and other CCR5 antagonists have the potential for use in a variety of other clinical situations such as the prevention of HIV transmission, intensification of HIV treatment and prevention of rejection in organ transplantation. The use of CCR5 antagonists may be potentiated by other agents such as rapamycin which downregulate CCR5 receptors thus decreasing CCR5 density. There may even be a role for their use in combination with other entry inhibitors. However, clinical use of CCR5 antagonists may have negative consequences in diseases such as West Nile and Tick-borne encephalitis virus infections. In summary, CCR5 antagonists have great therapeutic potential in the treatment and prevention of HIV as well as future use in novel situations such as organ transplantation. Their optimal use either alone or in combination with other agents will be defined by further investigation.

Pharmacologic opportunities for HIV prevention

Innovations in antiretroviral (ARV) treatment strategies have resulted in treated HIV-infected patients having life expectancies similar to those of uninfected individuals. Yet the number of individuals capable of HIV transmission is increasing-for every person in whom ARV treatment is initiated, four others are becoming newly infected with HIV. The limited progress with microbicides and vaccines for HIV prevention reinforce the need for a concentrated exploration of the utility of ARVs. Preliminary animal studies with topical and systemic ARVs show promising results. However, current clinical trials were designed without a comprehensive understanding of ARV pharmacokinetic-pharmacodynamic relationships in HIV prevention. This review focuses on current strategies for the prevention of HIV infection and on the ways in which the tools of pharmacology can be a valuable resource for determining pharmacodynamic targets, providing interspecies scaling of exposures, identifying the optimal drugs/drug combinations, doses, and dosing regimens, and designing efficient clinical trials.

Protection of rhesus macaques from vaginal infection by vaginally delivered maraviroc, an inhibitor of HIV-1 entry via the CCR5 co-receptor

An effective vaginal microbicide could reduce human immunodeficiency virus type 1 (HIV-1) transmission to women. Among microbicide candidates in clinical development is Maraviroc (MVC), a small-molecule drug that binds the CCR5 co-receptor and impedes HIV-1 entry into cells. Delivered systemically, MVC reduces viral load in HIV-1-infected individuals, but its ability to prevent transmission is untested. We have now evaluated MVC as a vaginal microbicide with use of a stringent model that involves challenge of rhesus macaques with a high-dose of a CCR5-using virus, SHIV-162P3. Gel-formulated, prescription-grade MVC provided dose-dependent protection, half-maximally at 0.5 mM (0.25 mg/mL). The duration of protection was transient; the longer the delay between MVC application and virus challenge, the less protection (half life of approximately 4 h). As expected, MVC neither protected against challenge with a CXCR4-using virus, SHIV-KU1, nor exacerbated postinfection viremia. These findings validate MVC development as a vaginal microbicide for women and should guide clinical programs.

HIV, transmitted drug resistance, and the paradox of preexposure prophylaxis

The administration of antiretrovirals before HIV exposure to prevent infection (i.e., preexposure prophylaxis; PrEP) is under evaluation in clinical trials. Because PrEP is based on antiretrovirals, there is considerable concern that it could substantially increase transmitted resistance, particularly in resource-rich countries. Here we use a mathematical model to predict the effect of PrEP interventions on the HIV epidemic in the men-who-have-sex-with-men community in San Francisco. The model is calibrated using Monte Carlo filtering and analyzed by constructing nonlinear response hypersurfaces. We predict PrEP interventions could substantially reduce transmission but significantly increase the proportion of new infections caused by resistant strains. Two mechanisms can cause this increase. If risk compensation occurs, the proportion increases due to increasing transmission of resistant strains and decreasing transmission of wild-type strains. If risk behavior remains stable, the increase occurs because of reduced transmission of resistant strains coupled with an even greater reduction in transmission of wild-type strains. We define this as the paradox of PrEP (i.e., resistance appears to be increasing, but is actually decreasing). We determine this paradox is likely to occur if the efficacy of PrEP regimens against wild-type strains is greater than 30% and the relative efficacy against resistant strains is greater than 0.2 but less than the efficacy against wild-type. Our modeling shows, if risk behavior increases, that it is a valid concern that PrEP could significantly increase transmitted resistance. However, if risk behavior remains stable, we find the concern is unfounded and PrEP interventions are likely to decrease transmitted resistance.

HIV-1 Entry, Inhibitors, and Resistance

Entry inhibitors represent a new class of antiretroviral agents for the treatment of infection with HIV-1. While resistance to other HIV drug classes has been well described, resistance to this new class is still ill defined despite considerable clinical use. Several potential mechanisms have been proposed: tropism switching (utilization of CXCR4 instead of CCR5 for entry), increased affinity for the coreceptor, increased rate of virus entry into host cells, and utilization of inhibitor-bound receptor for entry. In this review we will address the development of attachment, fusion, and coreceptor entry inhibitors and explore recent studies describing potential mechanisms of resistance.

CCR5 antagonists: host-targeted antiviral agents for the treatment of HIV infection, 4 years on

The chemokine coreceptor 5 (CCR5) antagonists are antiretroviral agents with an extracellular, host-targeted mechanism of action against HIV. Maraviroc, the first-in-class CCR5 antagonist, received regulatory approval in 2007, becoming the first oral antiretroviral from a new class in more than 10 years. Other compounds in this class are in various stages of clinical development. In 2005, we reviewed the limited clinical data then available on CCR5 antagonists. In this follow-up review, we revisit the field and assess the clinical and virological data that have emerged in the 4 years since, with particular reference to maraviroc for which the most comprehensive data currently exist.

Systemic administration of antiretrovirals prior to exposure prevents rectal and intravenous HIV-1 transmission in humanized BLT mice

Successful antiretroviral pre-exposure prophylaxis (PrEP) for mucosal and intravenous HIV-1 transmission could reduce new infections among targeted high-risk populations including discordant couples, injection drug users, high-risk women and men who have sex with men. Targeted antiretroviral PrEP could be particularly effective at slowing the spread of HIV-1 if a single antiretroviral combination were found to be broadly protective across multiple routes of transmission. Therefore, we designed our in vivo preclinical study to systematically investigate whether rectal and intravenous HIV-1 transmission can be blocked by antiretrovirals administered systemically prior to HIV-1 exposure. We performed these studies using a highly relevant in vivo model of mucosal HIV-1 transmission, humanized Bone marrow/Liver/Thymus mice (BLT). BLT mice are susceptible to HIV-1 infection via three major physiological routes of viral transmission: vaginal, rectal and intravenous. Our results show that BLT mice given systemic antiretroviral PrEP are efficiently protected from HIV-1 infection regardless of the route of exposure. Specifically, systemic antiretroviral PrEP with emtricitabine and tenofovir disoproxil fumarate prevented both rectal (Chi square = 8.6, df = 1, p = 0.003) and intravenous (Chi square = 13, df = 1, p = 0.0003) HIV-1 transmission. Our results indicate that antiretroviral PrEP has the potential to be broadly effective at preventing new rectal or intravenous HIV transmissions in targeted high risk individuals. These in vivo preclinical findings provide strong experimental evidence supporting the potential clinical implementation of antiretroviral based pre-exposure prophylactic measures to prevent the spread of HIV/AIDS.

Microbicide safety/efficacy studies in animals: macaques and small animal models

PURPOSE OF REVIEW

A number of microbicide candidates have failed to prevent HIV transmission in human clinical trials, and there is uncertainty as to how many additional trials can be supported by the field. Regardless, there are far too many microbicide candidates in development, and a logical and consistent method for screening and selecting candidates for human clinical trials is desperately needed. The unique host and cell specificity of HIV, however, provides challenges for microbicide safety and efficacy screening, that can only be addressed by rigorous testing in relevant laboratory animal models.

RECENT FINDINGS

A number of laboratory animal model systems ranging from rodents to nonhuman primates, and single versus multiple dose challenges have recently been developed to test microbicide candidates. These models have shed light on both the safety and efficacy of candidate microbicides as well as the early mechanisms involved in transmission. This article summarizes the major advantages and disadvantages of the relevant animal models for microbicide safety and efficacy testing.

SUMMARY

Currently, nonhuman primates are the only relevant and effective laboratory model for screening microbicide candidates. Given the consistent failures of prior strategies, it is now clear that rigorous safety and efficacy testing in nonhuman primates should be a prerequisite for advancing additional microbicide candidates to human clinical trials.

Recent advances of CCR5 antagonists

PURPOSE OF REVIEW

The interaction of the beta-chemokine receptor CCR5 with the HIV-1 envelope glycoprotein gp120 is critical for viral entry. Therefore, CCR5 seems to be a promising target for inhibition of HIV-1 replication. A number of attempts have been made to identify small-molecule CCR5 antagonists as novel antiretroviral agents. This review focuses on recent advances of CCR5 antagonists in antiviral activity, safety, and pharmacokinetics in vitro and in vivo.

RECENT FINDINGS

Following the discovery of the first small-molecule CCR5 antagonist, TAK-779, a variety of molecules have been identified as novel CCR5 antagonists, such as SCH-C, vicriviroc, maraviroc, aplaviroc, TAK-220, and TAK-652. All compounds are orally bioavailable and have proved to be highly potent and selective inhibitors of CCR5 using (R5) HIV-1 replication in cell cultures. Their biochemical and pharmacokinetic profiles, however, differ. Clinical studies of three compounds (vicriviroc, maraviroc, and aplaviroc) have been performed, and considerable reduction of plasma viral load in R5 HIV-1-infected patients has been achieved.

SUMMARY

CCR5 antagonists are a novel class of antiretroviral agents and they are active against a wide range of R5 HIV-1. Most of the CCR5 antagonists subjected to clinical trials are well tolerated and have shown efficacy in HIV-1-infected patients.

Pharmacotherapy of HIV-1 Infection: Focus on CCR5 Antagonist Maraviroc

Sustained inhibition of HIV-1, the goal of antiretroviral therapy, is often impeded by the emergence of viral drug resistance. For patients infected with HIV-1 resistant to conventional drugs from the viral reverse transcriptase and protease inhibitor classes, the recently approved entry and integration inhibitors effectively suppress HIV-1 and offer additional therapeutic options. Entry inhibitors are particularly attractive because, unlike conventional antiretrovirals, they target HIV-1 extracellularly, thereby sparing cells from both viral- and drug-induced toxicities. The fusion inhibitor enfuvirtide and the CCR5 antagonist maraviroc are the first entry inhibitors licensed for patients with drug-resistant HIV-1, with maraviroc restricted to those infected with CCR5-tropic HIV-1 (R5 HIV-1) only. Vicriviroc (another CCR5 antagonist) is in Phase III clinical trials, whereas the CCR5 antibodies PRO 140 and HGS 004 are in early stages of clinical development. Potent antiviral synergy between maraviroc and CCR5 antibodies, coupled with distinct patterns of resistance, suggest their combinations might be particularly effective in patients. In addition, given that oral administration of maraviroc achieves high drug levels in cervicovaginal fluid, combinations of maraviroc and other CCR5 inhibitors could be effective in preventing HIV-1 transmission. Moreover, since CCR5 antagonists prevent rejection of transplanted organs, maraviroc could both suppress HIV-1 and prolong organ survival for the growing number of HIV-1 patients with kidney or liver failure necessitating organ transplantation. Thus, maraviroc offers an important treatment option for patients with drug-resistant R5 HIV-1, who presently account for >50% of drug-resistance cases.

Maraviroc concentrates in the cervicovaginal fluid and vaginal tissue of HIV-negative women

OBJECTIVE

To compare single- and multiple-dose maraviroc exposures in cervicovaginal fluid (CVF) and vaginal tissue (VT) with blood plasma (BP) and quantify maraviroc protein binding in CVF.

DESIGN

Open-label pharmacokinetic study.

METHODS

In 12 HIV-negative women, 7 paired CVF and BP samples were collected over 12 hours after 1 maraviroc dose. Subjects then received maraviroc twice daily for 7 days. After the last dose, subjects underwent CVF and BP sampling as on day 1, with additional sampling during terminal elimination. VT biopsies were obtained at steady state.

RESULTS

Day 1 and day 7 median maraviroc CVF AUCtau were 1.9- and 2.7-fold higher, respectively, than BP. On day 1, 6 of 12 subjects had detectable maraviroc CVF concentrations within 1 hour; 12 of 12 were detectable within 2 hours, and all exceeded the protein-free IC90. On day 7, maraviroc CVF protein binding was 7.6% and the VT AUCtau was 1.9-fold higher than BP. Maraviroc CVF concentrations 72 hours after dose and BP concentrations 12 hours after dose were similar.

CONCLUSIONS

Higher maraviroc exposure in the female genital tract provides a pharmacologic basis for further evaluation of chemokine receptor 5 antagonists in HIV infection prophylaxis. This is the first study to report antiretroviral VT concentrations, CVF protein binding, and CVF terminal elimination.

Evaluation of antiretrovirals in animal models of HIV infection

Animal models of HIV infection have played an important role in the development of antiretroviral drugs. Although each animal model has its limitations and never completely mimics HIV infection of humans, a carefully designed study allows experimental approaches that are not feasible in humans, but that can help to better understand disease pathogenesis and to provide proof-of-concept of novel intervention strategies. While rodent and feline models are useful for initial screening, further testing is best done in non-human primate models, such as simian immunodeficiency virus (SIV) infection of macaques, because they share more similarities with HIV infection of humans. In the early years of the HIV pandemic, non-human primate models played a relatively minor role in the antiretroviral drug development process. Since then, a better understanding of the disease and the development of better drugs and assays to monitor antiviral efficacy have increased the usefulness of the animal models. In particular, non-human primate models have provided proof-of-concept for (i) the benefits of chemoprophylaxis and early treatment, (ii) the preclinical efficacy of novel drugs such as tenofovir, (iii) the virulence and clinical significance of drug-resistant viral mutants, and (iv) the role of antiviral immune responses during drug therapy. Ongoing comparison of results obtained in animal models with those observed in human studies will further validate and improve these animal models so they can continue to help advance our scientific knowledge and to guide clinical trials. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

A pièce de resistance: how HIV-1 escapes small molecule CCR5 inhibitors

PURPOSE OF REVIEW

Small molecule inhibitors targeting the CCR5 coreceptor represent a new class of drugs for treating HIV-1 infection. Maraviroc has received regulatory approvals, and vicriviroc is in phase 3 trials. Understanding how resistance to these drugs develops and is diagnosed is essential to guide clinical practice. We review what has been learned from in-vitro resistance studies, and how this relates to what is being seen, or can be anticipated, in clinical studies.

RECENT FINDINGS

The principal resistance pathway in vitro involves continued use of CCR5 in an inhibitor-insensitive manner; the resistant viruses recognize the inhibitor-CCR5 complex, as well as free CCR5. Switching to use the CXCR4 coreceptor is rare. The principal genetic pathway involves accumulating 2-4 sequence changes in the gp120 V3 region, but a non-V3 pathway is also known. The limited information available from clinical studies suggests that a similar escape process is followed in vivo. However, the most common change associated with virologic failure involves expansion of pre-existing, CXCR4-using viruses that are insensitive to CCR5 inhibitors.

SUMMARY

HIV-1 escapes small molecule CCR5 inhibitors by continuing to use CCR5 in an inhibitor-insensitive manner, or evades them by expanding naturally insensitive, CXCR4-using variants.

Macrophages in vaginal but not intestinal mucosa are monocyte-like and permissive to human immunodeficiency virus type 1 infection

Mucosal surfaces play a major role in human immunodeficiency virus type 1 (HIV-1) transmission and pathogenesis, and yet the role of lamina propria macrophages in mucosal HIV-1 infection has received little investigative attention. We report here that vaginal and intestinal macrophages display distinct phenotype and HIV-1 permissiveness profiles. Vaginal macrophages expressed the innate response receptors CD14, CD89, CD16, CD32, and CD64 and the HIV-1 receptor/coreceptors CD4, CCR5, and CXCR4, similar to monocytes. Consistent with this phenotype, green fluorescent protein-tagged R5 HIV-1 entered macrophages in explanted vaginal mucosa as early as 30 min after inoculation of virus onto the epithelium, and purified vaginal macrophages supported substantial levels of HIV-1 replication by a panel of highly macrophage-tropic R5 viruses. In sharp contrast, intestinal macrophages expressed no detectable, or very low levels of, innate response receptors and HIV-1 receptor/coreceptors and did not support HIV-1 replication, although virus occasionally entered macrophages in intestinal tissue explants. Thus, vaginal, but not intestinal, macrophages are monocyte-like and permissive to R5 HIV-1 after the virus has translocated across the epithelium. These findings suggest that genital and gut macrophages have different roles in mucosal HIV-1 pathogenesis and that vaginal macrophages play a previously underappreciated but potentially important role in mucosal HIV-1 infection in the female genital tract.

Selection of a simian-human immunodeficiency virus strain resistant to a vaginal microbicide in macaques

PSC-RANTES binds to CCR5, inhibits human immunodeficiency virus type 1 (HIV-1) entry, and has been shown as a vaginal microbicide to protect rhesus macaques from a simian-human immunodeficiency virus chimera (SHIV(SF162-p3)) infection in a dose-dependent manner. In this study, env gene sequences from SHIV(SF162-p3)-infected rhesus macaques treated with PSC-RANTES were analyzed for possible drug escape variants. Two specific mutations located in the V3 region of gp120 (K315R) and C-helical domain of gp41 (N640D) were identified in a macaque (m584) pretreated with a 100 microM dose of PSC-RANTES. These two env mutations were found throughout infection (through week 77) but were found at only low frequencies in the inoculating SHIV(SF162-p3) stock and in the other SHIV(SF162-p3)-infected macaques. HIV-1 env genes from macaque m584 (env(m584)) and from inoculating SHIV(SF162-p3) (env(p3)) were cloned into an HIV-1 backbone. Increases in 50% inhibitory concentrations to PSC-RANTES with env(m584) were modest (sevenfold) and most pronounced in cells expressing rhesus macaque CCR5 as compared to human CCR5. Nonetheless, virus harboring env(m584), unlike inoculating virus env(p3), could replicate even at the highest tissue culture PSC-RANTES concentrations (100 nM). Dual-virus competitions revealed a dramatic increase in fitness of chimeric virus containing env(m584) (K315R/N640D) over that containing env(p3), but again, only in rhesus CCR5-expressing cells. This study is the first to describe the immediate selection and infection of a drug-resistant SHIV variant in the face of a protective vaginal microbicide, PSC-RANTES. This rhesus CCR5-specific/PSC- RANTES resistance selection is particularly alarming given the relative homogeneity of the SHIV(SF162-p3) stock compared to the potential exposure to a heterogeneous HIV-1 population in human transmission.

Multiple roles for chemokines in the pathogenesis of SIV infection

Chemokines are small chemoattractant cytokines involved in homeostatic and inflammatory immune cell migration. These small proteins have multiple functional properties that extend beyond their most recognized role in controlling cellular migration. The complex immunobiology of chemokines, coupled with the use of subsets of chemokine receptors as HIV-1 and SIV entry co-receptors, suggests that these immunomodulators could play important roles in the pathogenesis associated with infection by HIV-1 or SIV. This review provides an overview of the effects of pathogenic infection on chemokine expression in the SIV/macaque model system, and outlines potential mechanisms by which changes in these expression profiles could contribute to development of disease. Key challenges faced in studying chemokine function in vivo and new opportunities for further study and development of therapeutic interventions are discussed. Continued growth in our understanding of the effects of pathogenic SIV infection on chemokine expression and function and the continuing development of chemokine receptor targeted therapeutics will provide the tools and the systems necessary for future studies of the roles of chemokines in HIV-1 pathogenesis.

Tropism-independent protection of macaques against vaginal transmission of three SHIVs by the HIV-1 fusion inhibitor T-1249

We have assessed the potential of the fusion inhibitory peptide T-1249 for development as a vaginal microbicide to prevent HIV-1 sexual transmission. When formulated as a simple gel, T-1249 provided dose-dependent protection to macaques against high-dose challenge with three different SHIVs that used either CCR5 or CXCR4 for infection (the R5 virus SHIV-162P3, the X4 virus SHIV-KU1 and the R5X4 virus SHIV-89.6P), and it also protected against SIVmac251 (R5). Protection of half of the test animals was estimated by interpolation to occur at T-1249 concentrations of approximately 40-130 muM, whereas complete protection was observed at 0.1-2 mM. In vitro, T-1249 had substantial breadth of activity against HIV-1 strains from multiple genetic subtypes and in a coreceptor-independent manner. Thus, at 1 muM in a peripheral blood mononuclear cell-based replication assay, T-1249 inhibited all 29 R5 viruses, all 12 X4 viruses and all 7 R5X4 viruses in the test panel, irrespective of their genetic subtype. Combining lower concentrations of T-1249 with other entry inhibitors (CMPD-167, BMS-C, or AMD3465) increased the proportion of test viruses that could be blocked. In the PhenoSense assay, T-1249 was active against 636 different HIV-1 Env-pseudotyped viruses of varying tropism and derived from clinical samples, with IC(50) values typically clustered in a 10-fold range approximately 10 nM. Overall, these results support the concept of using T-1249 as a component of an entry inhibitor-based combination microbicide to prevent the sexual transmission of diverse HIV-1 variants.