The HIV Env variant N283 enhances macrophage tropism and is associated with brain infection and dementia

The effects of cocaine on HIV transcription

Illicit drug users are a high-risk population for infection with the human immunodeficiency virus (HIV). A strong correlation exists between prohibited drug use and an increased rate of HIV transmission. Cocaine stands out as one of the most frequently abused illicit drugs, and its use is correlated with HIV infection and disease progression. The central nervous system (CNS) is a common target for both drugs of abuse and HIV, and cocaine intake further accelerates neuronal injury in HIV patients. Although the high incidence of HIV infection in illicit drug abusers is primarily due to high-risk activities such as needle sharing and unprotected sex, several studies have demonstrated that cocaine enhances the rate of HIV gene expression and replication by activating various signal transduction pathways and downstream transcription factors. In order to generate mature HIV genomic transcript, HIV gene expression has to pass through both the initiation and elongation phases of transcription, which requires discrete transcription factors. In this review, we will provide a detailed analysis of the molecular mechanisms that regulate HIV transcription and discuss how cocaine modulates those mechanisms to upregulate HIV transcription and eventually HIV replication.

Phenotypic Correlates of HIV-1 Macrophage Tropism

HIV-1 is typically CCR5 using (R5) and T cell tropic (T-tropic), targeting memory CD4(+) T cells throughout acute and chronic infections. However, viruses can expand into alternative cells types. Macrophage-tropic (M-tropic) HIV-1 variants have evolved to infect macrophages, which have only low levels of surface CD4. Most M-tropic variants have been isolated from the central nervous system during late-stage chronic infection. We used the HIV-1 env genes of well-defined, subject-matched M-tropic and T-tropic viruses to characterize the phenotypic features of the M-tropic Env protein. We found that, compared to T-tropic viruses, M-tropic viruses infect monocyte-derived macrophages (MDMs) on average 28-fold more efficiently, use low-density CD4 more efficiently, have increased sensitivity to soluble CD4 (sCD4), and show trends toward sensitivity to some CD4 binding site antibodies but no difference in sensitivity to antibodies targeting the CD4-bound conformation. M-tropic viruses also displayed a trend toward resistance to neutralization by monoclonal antibodies targeting the V1/V2 region of Env, suggesting subtle changes in Env protein conformation. The paired M- and T-tropic viruses did not differ in autologous serum neutralization, temperature sensitivity, entry kinetics, intrinsic infectivity, or Env protein incorporation. We also examined viruses with modestly increased CD4 usage. These variants have significant sensitivity to sCD4 and may represent evolutionary intermediates. CD4 usage is strongly correlated with infectivity of MDMs over a wide range of CD4 entry phenotypes. These data suggest that emergence of M-tropic HIV-1 includes multiple steps in which a phenotype of increased sensitivity to sCD4 and enhanced CD4 usage accompany subtle changes in Env conformation.

IMPORTANCE

HIV-1 typically replicates in CD4(+) T cells. However, HIV-1 can evolve to infect macrophages, especially within the brain. Understanding how CCR5-using macrophage-tropic viruses evolve and differ from CCR5-using T cell-tropic viruses may provide insights into viral evolution and pathogenesis within the central nervous system. We characterized the HIV-1 env viral entry gene from subject-matched macrophage-tropic and T cell-tropic viruses to identify entry features of macrophage-tropic viruses. We observed several differences between T cell-tropic and macrophage-tropic Env proteins, including functional differences with host CD4 receptor engagement and possible changes in the CD4 binding site and V1/V2 region. We also identified viruses with phenotypes between that of "true" macrophage-tropic and T cell-tropic viruses, which may represent evolutionary intermediates in a multistep process to macrophage tropism.

Envelope gene evolution and HIV-1 neuropathogenesis

In the era of combined antiretroviral therapy (cART), HIV-associated neurocognitive disorders (HAND) account for 40 to 56% of all HIV⁺ cases. During the acute stage of HIV-1 infection (<6 months), the virus invades and replicates within the central nervous system (CNS). Compared to peripheral tissues, the local CNS cell population expresses distinct levels of chemokine receptors, which levels exert selective pressure on the invading virus. HIV-1 envelope (env) sequences recovered from the brains and cerebrospinal fluid (CSF) of neurocognitively impaired HIV⁺ subjects often display higher nucleotide variability as compared to non-impaired HIV⁺ subjects. Specifically, env evolution provides HIV-1 with the strategies to evade host immune response, to reduce chemokine receptor dependence, to increase co-receptor binding efficiency, and to potentiate neurotoxicity. The evolution of env within the CNS leads to changes that may result in the emergence of novel isolates with neurotoxic and neurovirulent features. However, whether specific factors of HIV-1 evolution lead to the emergence of neurovirulent and neurotropic isolates remains ill-defined. HIV-1 env evolution is an ongoing phenomenon that occurs independently of neurological and neurocognitive disease severity; thus HIV env evolution may play a pivotal and reciprocal role in the etiology of HAND. Despite the use of cART, the reactivation of latent viral reservoirs represents a clinical challenge because of the replenishment of the viral pool that may subsequently lead to persistent infection. Therefore, gaining a more complete understanding of how HIV-1 env evolves over the course of the disease should be considered for the development of future therapies aimed at controlling CNS burden, diminishing persistent viremia, and eradicating viral reservoirs. Here we review the current literature on the role of HIV-1 env evolution in the setting of HAND disease progression and on the impact of cART on the dynamics of viral evolution.

A single-residue change in the HIV-1 V3 loop associated with maraviroc resistance impairs CCR5 binding affinity while increasing replicative capacity

Background

Maraviroc (MVC) is an allosteric CCR5 inhibitor used against HIV-1 infection. While MVC-resistant viruses have been identified in patients, it still remains incompletely known how they adjust their CD4 and CCR5 binding properties to resist MVC inhibition while preserving their replicative capacity. It is thought that they maintain high efficiency of receptor binding. To date however, information about the binding affinities to receptors for inhibitor-resistant HIV-1 remains limited.

Results

Here, we show by means of viral envelope (gp120) binding experiments and virus-cell fusion kinetics that a MVC-resistant virus (MVC-Res) that had emerged as a dominant viral quasispecies in a patient displays reduced affinities for CD4 and CCR5 either free or bound to MVC, as compared to its MVC-sensitive counterpart isolated before MVC therapy. An alanine insertion within the GPG motif (G310_P311insA) of the MVC-resistant gp120 V3 loop is responsible for the decreased CCR5 binding affinity, while impaired binding to CD4 is due to sequence changes outside V3. Molecular dynamics simulations of gp120 binding to CCR5 further emphasize that the Ala insertion alters the structure of the V3 tip and weakens interaction with CCR5 ECL2. Paradoxically, infection experiments on cells expressing high levels of CCR5 also showed that Ala allows MVC-Res to use CCR5 efficiently, thereby improving viral fusion and replication efficiencies. Actually, although we found that the V3 loop of MVC-Res is required for high levels of MVC resistance, other regions outside V3 are sufficient to confer a moderate level of resistance. These sequence changes outside V3, however, come with a replication cost, which is compensated for by the Ala insertion in V3.

Conclusion

These results indicate that changes in the V3 loop of MVC-resistant viruses can augment the efficiency of CCR5-dependent steps of viral entry other than gp120 binding, thereby compensating for their decreased affinity for entry receptors and improving their fusion and replication efficiencies. This study thus sheds light on unsuspected mechanisms whereby MVC-resistant HIV-1 could emerge and grow in treated patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-015-0177-1) contains supplementary material, which is available to authorized users.

Infection of ectocervical tissue and universal targeting of T-cells mediated by primary non-macrophage-tropic and highly macrophage-tropic HIV-1 R5 envelopes

Background

HIV-1 variants carrying non-macrophage-tropic HIV-1 R5 envelopes (Envs) are predominantly transmitted and persist in immune tissue even in AIDS patients who have highly macrophage-tropic variants in the brain. Non-macrophage-tropic R5 Envs require high levels of CD4 for infection contrasting with macrophage-tropic Envs, which can efficiently mediate infection of cells via low CD4. Here, we investigated whether non-macrophage-tropic R5 Envs from the acute stage of infection (including transmitted/founder Env) mediated more efficient infection of ectocervical explant cultures compared to non-macrophage-tropic and highly macrophage-tropic R5 Envs from late disease.

Results

We used Env+ pseudovirions that carried a GFP reporter gene to measure infection of the first cells targeted in ectocervical explant cultures. In straight titrations of Env+ pseudovirus supernatants, mac-tropic R5 Envs from late disease mediated slightly higher infectivities for ectocervical explants although this was not significant. Surprisingly, explant infection by several T/F/acute Envs was lower than for Envs from late disease. However, when infectivity for explants was corrected to account for differences in the overall infectivity of each Env+ pseudovirus (measured on highly permissive HeLa TZM-bl cells), non-mac-tropic early and late disease Env+ pseudoviruses mediated significantly higher infection. This observation suggests that cervical tissue preferentially supports non-mac-tropic Env+ viruses compared to mac-tropic viruses. Finally, we show that T-cells were the main targets for infection regardless of whether explants were stimulated with T-cell or monocyte/macrophage cytokines. There was no evidence of macrophage infection even for pseudovirions carrying highly mac-tropic Envs from brain tissue or for the highly mac-tropic, laboratory strain, BaL, which targeted T-cells in the explant tissue.

Conclusions

Our data support ectocervical tissue as a favorable environment for non-mac-tropic HIV-1 R5 variants and emphasize the role of T-cells as initial targets for infection even for highly mac-tropic variants.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-015-0176-2) contains supplementary material, which is available to authorized users.

HIV-1 target cells in the CNS

HIV-1 replication in the central nervous system (CNS) is typically limited by the availability of target cells. HIV-1 variants that are transmitted and dominate the early stages of infection almost exclusively use the CCR5 coreceptor and are well adapted to entering, and thus infecting, cells expressing high CD4 densities similar to those found on CD4+ T cells. While the "immune privileged" CNS is largely devoid of CD4+ T cells, macrophage and microglia are abundant throughout the CNS. These cells likely express CD4 densities that are too low to facilitate efficient entry or allow sustained replication by most HIV-1 isolates. Examination of CNS viral populations reveals that late in disease the CNS of some individuals contains HIV-1 lineages that have evolved the ability to enter cells expressing low levels of CD4 and are well-adapted to entering macrophages. These macrophage-tropic (M-tropic) viruses are able to maintain sustained replication in the CNS for many generations, and their presence is associated with severe neurocognitive impairment. Whether conditions such as pleocytosis are necessary for macrophage-tropic viruses to emerge in the CNS is unknown, and extensive examinations of macrophage-tropic variants have not revealed a genetic signature of this phenotype. It is clear, however, that macrophage tropism is rare among HIV-1 isolates and is not transmitted, but is important due to its pathogenic effects on hosts. Prior to the evolution of macrophage-tropic variants, the viruses that are predominately infecting T cells (R5 T cell-tropic) may infect macrophages at a low level and inefficiently, but this could contribute to the reservoir.

Compartmentalized replication of R5 T cell-tropic HIV-1 in the central nervous system early in the course of infection

Compartmentalized HIV-1 replication within the central nervous system (CNS) likely provides a foundation for neurocognitive impairment and a potentially important tissue reservoir. The timing of emergence and character of this local CNS replication has not been defined in a population of subjects. We examined the frequency of elevated cerebrospinal fluid (CSF) HIV-1 RNA concentration, the nature of CSF viral populations compared to the blood, and the presence of a cellular inflammatory response (with the potential to bring infected cells into the CNS) using paired CSF and blood samples obtained over the first two years of infection from 72 ART-naïve subjects. Using single genome amplification (SGA) and phylodynamics analysis of full-length env sequences, we compared CSF and blood viral populations in 33 of the 72 subjects. Independent HIV-1 replication in the CNS (compartmentalization) was detected in 20% of sample pairs analyzed by SGA, or 7% of all sample pairs, and was exclusively observed after four months of infection. In subjects with longitudinal sampling, 30% showed evidence of CNS viral replication or pleocytosis/inflammation in at least one time point, and in approximately 16% of subjects we observed evolving CSF/CNS compartmentalized viral replication and/or a marked CSF inflammatory response at multiple time points suggesting an ongoing or recurrent impact of the infection in the CNS. Two subjects had one of two transmitted lineages (or their recombinant) largely sequestered within the CNS shortly after transmission, indicating an additional mechanism for establishing early CNS replication. Transmitted variants were R5 T cell-tropic. Overall, examination of the relationships between CSF viral populations, blood and CSF HIV-1 RNA concentrations, and inflammatory responses suggested four distinct states of viral population dynamics, with associated mechanisms of local viral replication and the early influx of virus into the CNS. This study considerably enhances the generalizability of our results and greatly expands our knowledge of the early interactions of HIV-1 in the CNS.

Bioinformatic analysis of neurotropic HIV envelope sequences identifies polymorphisms in the gp120 bridging sheet that increase macrophage-tropism through enhanced interactions with CCR5

Macrophages express low levels of the CD4 receptor compared to T-cells. Macrophage-tropic HIV strains replicating in brain of untreated patients with HIV-associated dementia (HAD) express Envs that are adapted to overcome this restriction through mechanisms that are poorly understood. Here, bioinformatic analysis of env sequence datasets together with functional studies identified polymorphisms in the β3 strand of the HIV gp120 bridging sheet that increase M-tropism. D197, which results in loss of an N-glycan located near the HIV Env trimer apex, was detected in brain in some HAD patients, while position 200 was estimated to be under positive selection. D197 and T/V200 increased fusion and infection of cells expressing low CD4 by enhancing gp120 binding to CCR5. These results identify polymorphisms in the HIV gp120 bridging sheet that overcome the restriction to macrophage infection imposed by low CD4 through enhanced gp120-CCR5 interactions, thereby promoting infection of brain and other macrophage-rich tissues.

HIV-1 non-macrophage-tropic R5 envelope glycoproteins are not more tropic for entry into primary CD4+ T-cells than envelopes highly adapted for macrophages

BACKGROUND

Non-mac-tropic HIV-1 R5 viruses are predominantly transmitted and persist in immune tissue even in AIDS patients who carry highly mac-tropic variants in the brain. Non-mac-tropic R5 envelopes (Envs) require high CD4 levels for infection contrasting with highly mac-tropic Envs, which interact more efficiently with CD4 and mediate infection of macrophages that express low CD4. Non-mac-tropic R5 Envs predominantly target T-cells during transmission and in immune tissue where they must outcompete mac-tropic variants. Here, we investigated whether Env+ pseudoviruses bearing transmitted/founder (T/F), early and late disease non-mac-tropic R5 envelopes mediated more efficient infection of CD4+ T-cells compared to those with highly mac-tropic Envs.

RESULTS

Highly mac-tropic Envs mediated highest infectivity for primary T-cells, Jurkat/CCR5 cells, myeloid dendritic cells, macrophages, and HeLa TZM-bl cells, although this was most dramatic on macrophages. Infection of primary T-cells mediated by all Envs was low. However, infection of T-cells was greatly enhanced by increasing virus attachment with DEAE dextran and spinoculation, which enhanced the three Env+ virus groups to similar extents. Dendritic cell capture of viruses and trans-infection also greatly enhanced infection of primary T-cells. In trans-infection assays, non-mac-tropic R5 Envs were preferentially enhanced and those from late disease mediated levels of T-cell infection that were equivalent to those mediated by mac-tropic Envs.

CONCLUSIONS

Our results demonstrate that T/F, early or late disease non-mac-tropic R5 Envs do not preferentially mediate infection of primary CD4+ T-cells compared to highly mac-tropic Envs from brain tissue. We conclude that non-macrophage-tropism of HIV-1 R5 Envs in vitro is determined predominantly by a reduced capacity to target myeloid cells via low CD4 rather than a specific adaptation for T-cells entry that precludes macrophage infection.

Longitudinal Analysis of Cerebrospinal Fluid and Plasma HIV-1 Envelope Sequences Isolated From a Single Donor with HIV Asymptomatic Neurocognitive Impairment

OBJECTIVE

Combined antiretroviral treatment (cART) has changed the clinical presentation of HIV-associated neurocognitive disorders (HAND) to that of the milder forms of the disease. Asymptomatic neurocognitive impairment (ANI) is now more prevalent and is associated with increased morbidity and mortality risk in HIV-1-infected people. HIV-1 envelope (env) genetic heterogeneity has been detected within the central nervous system (CNS) of individuals with ANI. Changes within env determine co-receptor use, cellular tropism, and neuropathogenesis. We hypothesize that compartmental changes are associated with HIV-1 env C2V4 during ANI and sought to analyze paired HIV-1 env sequences from plasma and cerebrospinal fluid (CSF) of a female subject undergoing long-term cART.

METHODS

Paired plasma and CSF samples were collected at 12-month intervals and HIV-1 env C2V4 was cloned and sequenced.

RESULTS

Phylogenetic analysis of paired samples consistently showed genetic variants unique to the CSF. Phenotypic prediction showed CCR5 (R5) variants for all CSF-derived sequences and showed minor X4 variants (or dual-tropic) in the plasma at later time points. Viral compartmentalization was evident throughout the study, suggesting that the occurrence of distinctive env strains may contribute to the neuropathogenesis of HAND.

CONCLUSIONS

Our study provides new insights about the genetic characteristics within the C2V4 of HIV-1 env that persist after long-term cART and during the course of persistent ANI.

Macrophages and the Viral Dissemination Super Highway

Monocytes and macrophages are key components of the innate immune system yet they are often the victims of attack by infectious agents. This review examines the significance of viral infection of macrophages. The central hypothesis is that macrophage tropism enhances viral dissemination and persistence, but these changes may come at the cost of reduced replication in cells other than macrophages.

HIV gp120 sequence variability associated with HAND in Hispanic Women

OBJECTIVE

HIV-1 variants with different tropisms are associated with various neuropathologies. This study intends to determine if this correlation is determined by unique viral env sequences. We hypothesize that HIV-1 envelope gene sequence changes are associated with cognition status.

METHODS

Viral RNA was extracted from peripheral blood mononuclear cells (PBMCs) co-cultures derived from HIV-1 infected Hispanic women that had been characterized for HIV associated neurocognitive disorders (HAND).

RESULTS

Analyses of the C2V4 region of HIV gp120 demonstrated that increased sequence diversity correlates with cognition status as sequences derived from subjects with normal cognition exhibited less diversity than sequences derived from subjects with cognitive impairment. In addition, differences in V3 and V4 loop charges were also noted as well as differences in the N-glycosylation of the V4 region.

CONCLUSIONS

Our data suggest that the genetic signature within the C2V4 region may contribute to the pathogenesis of HAND. HIV env sequence characteristics for the isolates grouped in milder forms of HAND can provide insightful information of prognostic value to assess neurocognitive status in HIV⁺ subjects, particularly during the era of highly prevalent milder forms of HAND.

Eradication of human immunodeficiency virus from brain reservoirs

Isolated cases in which human immunodeficiency virus (HIV) infection was claimed to have been eradicated generated renewed interest in HIV reservoirs in the brain particularly since attempts to reproduce the findings using genetically engineered stem cells and immune- or myeloablation have failed. A clear understanding of the cell types in which the virus resides in the brain, the mechanism of viral persistence, restricted replication and latency, and the turnover rate of the infected cells is critical for us to develop ways to control or get rid of the virus in the brain. The brain has several unique features compared to other reservoirs. There are no resident T cells in the brain; the virus resides in macrophages and astrocytes where the viral infection is non-cytopathic. The virus evolves in the brain and since the turnover rate of these cells is low, the virus has the potential to reside in these cells for several decades and possibly for the life of the individual. This review discusses the HIV reservoirs in the brain, issues related to eradication of the virus from sanctuaries in the brain, and current challenges faced by neuroscientists in finding a cure.

Single genome analysis reveals genetic characteristics of Neuroadaptation across HIV-1 envelope

Background

The widespread use of highly effective, combination antiretroviral therapy (cART) has led to a significant reduction in the incidence of HIV-associated dementia (HAD). Despite these advances, the prevalence of HIV-1 associated neurocognitive disorders (HANDs) has been estimated at approximately 40%-50%. In the cART era, the majority of this disease burden is represented by asymptomatic neurocognitive impairment and mild neurocognitive disorder (ANI and MND respectively). Although less severe than HAD, these diagnoses carry with them substantial morbidity.

Results

In this cross-sectional study, single genome amplification (SGA) was used to sequence 717 full-length HIV-1 envelope (env) clade B variants from the paired cerebrospinal fluid (CSF) and blood plasma samples of fifteen chronically infected HIV-positive individuals with normal neurocognitive performance (NCN), ANI and MND. Various degrees of compartmentalization were found across disease states and history of cART utilization. In individuals with compartmentalized virus, mean HIV-1 env population diversity was lower in the CSF than plasma-derived variants. Overall, mean V1V2 loop length was shorter in CSF-derived quasispecies when compared to contemporaneous plasma populations, and this was found to correlate with a lower mean number of N-linked glycosylation sites in this region. A number of discrete amino acid positions that correlate strongly with compartmentalization in the CSF were identified in both variable and constant regions of gp120 as well as in gp41. Correlated mutation analyses further identified that a subset of amino acid residues in these compartmentalization “hot spot” positions were strongly correlated with one another, suggesting they may play an important, definable role in the adaptation of viral variants to the CSF. Analysis of these hot spots in the context of a well-supported crystal structure of HIV-1 gp120 suggests mechanisms through which amino acid differences at the identified residues might contribute to viral compartmentalization in the CSF.

Conclusions

The detailed analyses of SGA-derived full length HIV-1 env from subjects with both normal neurocognitive performance and the most common HAND diagnoses in the cART era allow us to identify novel and confirm previously described HIV-1 env genetic determinants of neuroadaptation and relate potential motifs to HIV-1 env structure and function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-014-0065-0) contains supplementary material, which is available to authorized users.

Discordant patterns of tissue-specific genetic characteristics in the HIV-1 env gene from HIV-associated neurocognitive disorder (HAND) and non-HAND patients

The genetic evolution of HIV-1 in the central nervous system (CNS) is different from that in peripheral tissues. We analyzed 121 clonal sequences of the V3-V5 regions of the env gene generated from paired cerebrospinal fluid (CSF) and plasma samples from nine chronically infected patients (four with HIV-associated neurocognitive disorder (HAND) and five without HAND). The sequence analysis indicated the significant differences between CSF and plasma was only observed in the C4 region (P = 0.043) in HAND patients. Significant increases in synonymous substitutions (dS) within the V4 region (P = 0.020) and in nonsynonymous substitutions (dN) within the C4 region (P = 0.029) were observed in the CSF-derived sequences. By contrast, CSF-derived sequences from non-HAND patients showed similar levels of diversity; dS and dN as the plasma-derived sequences. Signature differences between the CSF- and plasma-derived sequences were found at 12 amino acid positions for HAND patients and nine positions for non-HAND patients. Interestingly, five sites (positions 388, 396, 397, 404, and 406) that all belong to signature patterns exhibited positive selection pressure in CSF samples, but only site 406 was positively selected in the plasma samples from the HAND patients. Conversely, in the non-HAND patients, there were four sites (positions 397, 404, 432, and 446) showed positive selection pressure in the plasma samples, but only site 446 in the CSF samples. These results suggest that discordant patterns of genetic evolution occur between the tissue-specific HIV-1 quasispecies in the HAND and non-HAND patients. Viral molecular heterogeneity between specific tissues is greater in patients with HAND compared to non-HAND patients.

Vpx complementation of 'non-macrophage tropic' R5 viruses reveals robust entry of infectious HIV-1 cores into macrophages

BACKGROUND

It is now known that clinically derived viruses are most commonly R5 tropic with very low infectivity in macrophages. As these viruses utilize CD4 inefficiently, defective entry has been assumed to be the dominant restriction. The implication is that macrophages are not an important reservoir for the majority of circulating viruses.

RESULTS

Macrophage infection by clinical transmitted/founder isolates was 10-100 and 30-450 fold less efficient as compared to YU-2 and BaL respectively. Vpx complementation augmented macrophage infection by non-macrophage tropic viruses to the level of infectivity observed for YU-2 in the absence of Vpx. Augmentation was evident even when Vpx was provided 24 hours post-infection. The entry defect was measured as 2.5-5 fold, with a further 3.5-10 fold block at strong stop and subsequent stages of reverse transcription as compared to YU-2. The overall block to infection was critically dependent on the mechanism of entry as demonstrated by rescue of infection after pseudotyping with VSV-G envelope. Reverse transcription in macrophages could not be enhanced using a panel of cytokines or lipopolysaccharide (LPS).

CONCLUSIONS

Although the predominant block to clinical transmitted/founder viruses is post-entry, infectivity is determined by Env-CD4 interactions and can be rescued with VSV-G pseudotyping. This suggests a functional link between the optimal entry pathway taken by macrophage tropic viruses and downstream events required for reverse transcription. Consistent with a predominantly post-entry block, replication of R5 using viruses can be greatly enhanced by Vpx. We conclude therefore that entry is not the limiting step and that macrophages represent clinically relevant reservoirs for 'non-macrophage tropic' viruses.

Loss of a conserved N-linked glycosylation site in the simian immunodeficiency virus envelope glycoprotein V2 region enhances macrophage tropism by increasing CD4-independent cell-to-cell transmission

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) strains differ in their capacity to replicate in macrophages, but mechanisms underlying these differences are not fully understood. Here, we identify a highly conserved N-linked glycosylation site (N173 in SIV, corresponding to N160 in HIV) in the V2 region of the SIV envelope glycoprotein (Env) as a novel determinant of macrophage tropism and characterize mechanisms underlying this phenotype. Loss of the N173 glycosylation site in the non-macrophage-tropic SIVmac239 by introducing an N173Q mutation enhanced viral replication and multinucleated giant cell formation upon infection of rhesus macrophages, while the addition of N173 to SIVmac251 had the opposite effect. The removal of N173 in SIVmac239 enhanced CD4-independent cell-to-cell transmission to CCR5-expressing cells. SIVmac239 with N173Q mediated CD4-independent cell-cell fusion but could not infect CD4-negative cells in single-round infections. Thus, CD4-independent phenotypes were detected only in the context of cell-to-cell contact. Similar results were obtained in SIVmac251 with and without N173. N173 decreased the neutralization sensitivity of SIVmac251 but had no effect on the neutralization sensitivity of SIVmac239. The N173Q mutation had no effect on SIVmac239 binding to CD4 in Biacore assays, coimmunoprecipitation assays, and enzyme-linked immunosorbent assays (ELISAs). These findings suggest that the loss of the N173 N-linked glycosylation site increases SIVmac239 replication in macrophages by enhancing CD4-independent cell-to-cell virus transmission through CCR5-mediated fusion. This mechanism may facilitate the escape of macrophage-tropic viruses from neutralizing antibodies while promoting spreading infection by these viruses in vivo.

IMPORTANCE

In this study, we identify a genetic determinant in the viral envelope (N173) that increases replication and spreading infection of SIV strains in macrophages by enhancing cell-to-cell virus transmission. This effect is explained by a novel mechanism involving increased cell-to-cell fusion in the absence of CD4, the primary receptor that normally mediates virus entry. The same genetic determinant also affects the sensitivity of these viruses to inhibition by neutralizing antibodies. Most macrophage-tropic HIV/SIV strains are known to be neutralization sensitive. Together, these findings suggest that this efficient mode of virus transmission may facilitate the escape of macrophage-tropic viruses from neutralizing antibodies while promoting spreading infection by these viruses to cells expressing little or no CD4 in vivo.

HIV-associated neurocognitive disorder

Neurological involvement in HIV is often associated with cognitive impairment. Although severe and progressive neurocognitive impairment has become rare in HIV clinics in the era of potent antiretroviral therapy, most patients with HIV worldwide have poor outcomes on formal neurocognitive tests. In this Review, we describe the manifestations of HIV-associated neurocognitive disorder in the era of effective HIV therapy, outline diagnosis and treatment recommendations, and explore the research questions that remain. Although comorbid disorders, such as hepatitis C infection or epilepsy, might cause some impairment, their prevalence is insufficient to explain the frequency with which it is encountered. HIV disease markers, such as viral load and CD4 cell counts, are not strongly associated with ongoing impairment on treatment, whereas cardiovascular disease markers and inflammatory markers are. New cerebrospinal fluid and neuroimaging biomarkers are needed to detect and follow impairment. Ongoing research efforts to optimise HIV therapy within the CNS, and potentially to intervene in downstream mechanisms of neurotoxicity, remain important avenues for future investigation. Ultimately, the full control of virus in the brain is a necessary step in the goal of HIV eradication.

HIV-1 envelope-receptor interactions required for macrophage infection and implications for current HIV-1 cure strategies

Myeloid cells residing in the CNS and lymphoid tissues are targets for productive HIV-1 replication, and their infection contributes to the pathological manifestations of HIV-1 infection. The Envs can adopt altered configurations to overcome entry restrictions in macrophages via a more efficient and/or altered mechanism of engagement with cellular receptors. This review highlights evidence supporting an important role for macrophages in HIV-1 pathogenesis and persistence, which need to be considered for strategies aimed at achieving a functional or sterilizing cure. We also highlight that the molecular mechanisms underlying HIV-1 tropism for macrophages are complex, involving enhanced and/or altered interactions with CD4, CCR5, and/or CXCR4, and that the nature of these interactions may depend on the anatomical location of the virus.

Affinofile Assay for Identifying Macrophage-Tropic HIV-1

The ability to enter monocyte-derived macrophage (MDM) in vitro is commonly used to define macrophage-tropic HIV-1 despite the fact that viruses vary continuously in their ability to enter MDMs in vitro, and MDMs vary in their ability to support HIV-1 entry (Joseph et al., 2014; Peters et al., 2006). This makes it difficult to distinguish viruses that are adapted to replicating in macrophage from those that are adapted to replicating in T cells. We use the Affinofile cell line (Johnston et al., 2009) to assay for macrophage tropism by capitalizing on the fact that macrophage-tropic HIV-1 has an enhanced ability to enter cells expressing low levels of CD4 (Joseph et al., 2014; Peters et al., 2006; Duenas-Decamp et al., 2009; Dunfee et al., 2006; Gorry et al., 2002; Martin-Garcia et al., 2006; Peters et al., 2004) and Affinofile cells can be induced to express a wide range of CD4 densities (Johnston et al., 2009). We induce Affinofile cells to express either high or low CD4, infect those cells with pseudotyped reporter virus, and quantify percent infectivity at low CD4 relative to infectivity at high CD4. Macrophage-tropic viruses have an enhanced ability to infect at low CD4. Using this approach we have found that macrophage-tropic strains of HIV-1 are relatively rare and that most HIV-1 variants require high levels of CD4 to enter cells, a phenotype we have referred to as R5 T cell-tropic.

Human immunodeficiency virus-associated dementia: a link between accumulation of viral proteins and neuronal degeneration

In the late stage of human immunodeficiency virus-1 (HIV) infection, a subset of individuals develops HIV associated neurocognitive disorders (HAND), which in its severe form, is characterized by motor and cognitive dysfunction. Dendritic pruning, synaptic abnormalities and neuronal apoptosis are observed in these patients. There are numerous advances in our understanding of HIV interactions with cells of the central nervous system. However, the underlying causes of neurological symptoms and pathological alterations observed in HIV positive subjects are poorly understood. Moreover, little is still known about the molecular mechanisms by which HIV induces synaptic dysfunction and degeneration. HAND resembles other common neurological diseases such as Alzheimer's and Huntington's diseases. These neurodegenerative disorders are characterized by accumulation of toxic proteins such as tau and huntingtin, respectively, which promote axonal degeneration by impairing axonal transport. Axonal degeneration precedes neuronal death. Therefore, a better understanding of the mechanisms whereby HIV triggers axonal degeneration has potential implications for developing therapeutic compounds to prevent synaptic failure in HAND. This article highlights and reviews evidence showing that neuronal accumulation of viral proteins promotes axonal damage.

Genetic variation and HIV-associated neurologic disease

HIV-associated neurologic disease continues to be a significant complication in the era of highly active antiretroviral therapy. A substantial subset of the HIV-infected population shows impaired neuropsychological performance as a result of HIV-mediated neuroinflammation and eventual central nervous system (CNS) injury. CNS compartmentalization of HIV, coupled with the evolution of genetically isolated populations in the CNS, is responsible for poor prognosis in patients with AIDS, warranting further investigation and possible additions to the current therapeutic strategy. This chapter reviews key advances in the field of neuropathogenesis and studies that have highlighted how molecular diversity within the HIV genome may impact HIV-associated neurologic disease. We also discuss the possible functional implications of genetic variation within the viral promoter and possibly other regions of the viral genome, especially in the cells of monocyte-macrophage lineage, which are arguably key cellular players in HIV-associated CNS disease.

Update on HIV-associated neurocognitive disorders

Neurocognitive disorders are a feared complication of HIV infection, especially in the post-antiretroviral era as patients are living longer. These disorders are challenging in terms of diagnosis and treatment. The clinical syndrome has evolved, driven in part by comorbidities such as aging, drug abuse, psychiatric illnesses, and a metabolic syndrome associated with the use of antiretroviral drugs. Additionally some individuals may develop a fulminant immune reconstitution syndrome. Hence, treatment of these patients needs to be individualized. The focus of research in the HIV field has recently switched towards elimination of the HIV reservoir as a means of combating long-term HIV complications. However, these approaches may be suitable for limited populations and might not be applicable once the HIV reservoir has been established in the brain. Further, all clinical trials using neuroprotective or anti-inflammatory drugs for treatment of HIV-associated neurocognitive disorders have been unsuccessful. Hence, neurological complications of HIV infection are the biggest challenge facing HIV researchers, and there is a critical need to develop new diagnostics and approaches for treatment of these disorders.

Where does HIV hide? A focus on the central nervous system

PURPOSE OF REVIEW

To review the literature on infection and evolution of HIV within the brain in the context for understanding the nature of the brain reservoir and its consequences.

RECENT FINDINGS

HIV-1 in the brain can evolve in separate compartments within macrophage/microglia and astrocytes. The virus adapts to the brain environment to infect these cells and brain-specific mutations can be found in nearly all genes of the virus. The virus evolves to become more neurovirulent.

SUMMARY

The brain is an ideal reservoir for the HIV. The brain is a relatively immune privileged site and the blood-brain barrier prevents easy access to antiretroviral drugs. Further, the virus infects resident macrophages and astrocytes which are long-lived cells and causes minimal cytopathology in these cells. Hence as we move towards developing strategies for eradication of the virus from the peripheral reservoirs, it is critical that we pay close attention to the virus in the brain and develop strategies for maintaining it in a latent state failure of which could result in dire consequences.

CD4+ T cells support production of simian immunodeficiency virus Env antibodies that enforce CD4-dependent entry and shape tropism in vivo

CD4(+) T cells rather than macrophages are the principal cells infected by human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) in vivo. Macrophage tropism has been linked to the ability to enter cells through CCR5 in conjunction with limiting CD4 levels, which are much lower on macrophages than on T cells. We recently reported that rhesus macaques (RM) experimentally depleted of CD4(+) T cells before SIV infection exhibit extensive macrophage infection as well as high chronic viral loads and rapid progression to AIDS. Here we show that early-time-point and control Envs were strictly CD4 dependent but that, by day 42 postinfection, plasma virus of CD4(+) T cell-depleted RM was dominated by Envs that mediate efficient infection using RM CCR5 independently of CD4. Early-time-point and control RM Envs were resistant to neutralization by SIV-positive (SIV(+)) plasma but became sensitive if preincubated with sCD4. In contrast, CD4-independent Envs were highly sensitive to SIV(+) plasma neutralization. However, plasma from SIV-infected CD4(+) T cell-depleted animals lacked this CD4-inducible neutralizing activity and failed to neutralize any Envs regardless of sCD4 pre-exposure status. Enhanced sensitivity of CD4-independent Envs from day 42 CD4(+) T cell-depleted RM was also seen with monoclonal antibodies that target both known CD4-inducible and other Env epitopes. CD4 independence and neutralization sensitivity were both conferred by Env amino acid changes E84K and D470N that arose independently in multiple animals, with the latter introducing a potential N-linked glycosylation site within a predicted CD4-binding pocket of gp120. Thus, the absence of CD4 T cells results in failure to produce antibodies that neutralize CD4-independent Envs and CD4-pretriggered control Envs. In the absence of this constraint and with a relative paucity of CD4(+) target cells, widespread macrophage infection occurs in vivo accompanied by emergence of variants carrying structural changes that enable entry independently of CD4.

Differential type 1 interferon-regulated gene expression in the brain during AIDS: interactions with viral diversity and neurovirulence

The lentiviruses, human and feline immunodeficiency viruses (HIV-1 and FIV, respectively), infect the brain and cause neurovirulence, evident as neuronal injury, inflammation, and neurobehavioral abnormalities with diminished survival. Herein, different lentivirus infections in conjunction with neural cell viability were investigated, concentrating on type 1 interferon-regulated pathways. Transcriptomic network analyses showed a preponderance of genes involved in type 1 interferon signaling, which was verified by increased expression of the type 1 interferon-associated genes, Mx1 and CD317, in brains from HIV-infected persons (P<0.05). Leukocytes infected with different strains of FIV or HIV-1 showed differential Mx1 and CD317 expression (P<0.05). In vivo studies of animals infected with the FIV strains, FIV(ch) or FIV(ncsu), revealed that FIV(ch)-infected animals displayed deficits in memory and motor speed compared with the FIV(ncsu)- and mock-infected groups (P<0.05). TNF-α, IL-1β, and CD40 expression was increased in the brains of FIV(ch)-infected animals; conversely, Mx1 and CD317 transcript levels were increased in the brains of FIV(ncsu)-infected animals, principally in microglia (P<0.05). Gliosis and neuronal loss were evident among FIV(ch)-infected animals compared with mock- and FIV(ncsu)-infected animals (P<0.05). Lentiviral infections induce type 1 interferon-regulated gene expression in microglia in a viral diversity-dependent manner, representing a mechanism by which immune responses might be exploited to limit neurovirulence.

When human immunodeficiency virus meets chemokines and microglia: neuroprotection or neurodegeneration?

Chemokines are chemotactic cytokines that were originally discovered as promoters of leukocyte proliferation and mobility. In recent years, however, evidence has demonstrated constitutive expression of chemokines and chemokine receptors in a variety of cells in the central and peripheral nervous system and has proposed a role for chemokines in neurodegenerative diseases characterized by inflammation and microglia proliferation. In addition, chemokine receptors, and in particular CXCR4 and CCR5, mediate human immunodeficiency virus type 1 (HIV) infection of immunocompetent cells as well as microglia. Subsequently, HIV, through a variety of mechanisms, promotes synapto-dendritic alterations and neuronal loss that ultimately lead to motor and cognitive impairments. These events are accompanied by microglia activation. Nevertheless, a microglia-mediated mechanism of neuronal degeneration alone cannot fully explain some of the pathological features of HIV infected brain such as synaptic simplification. In this article, we present evidence that some of the microglia responses to HIV are beneficial and neuroprotective. These include the ability of microglia to release anti-inflammatory cytokines, to remove dying cells and to promote axonal sprouting.

Efficiency of bridging-sheet recruitment explains HIV-1 R5 envelope glycoprotein sensitivity to soluble CD4 and macrophage tropism

HIV-1 R5 viruses vary extensively in their capacity to infect macrophages. R5 viruses that confer efficient infection of macrophages are able to exploit low levels of CD4 for infection and predominate in brain tissue, where macrophages are a major target for infection. HIV-1 R5 founder viruses that are transmitted were reported to be non-macrophage-tropic. Here, we investigated the sensitivities of macrophage-tropic and non-macrophage-tropic R5 envelopes to neutralizing antibodies. We observed striking differences in the sensitivities of Env(+) pseudovirions to soluble CD4 (sCD4) and to neutralizing monoclonal antibodies (MAbs) that target the CD4 binding site. Macrophage-tropic R5 Envs were sensitive to sCD4, while non-macrophage-tropic Envs were significantly more resistant. In contrast, all Envs were sensitive to VRC01 regardless of tropism, while MAb b12 conferred an intermediate neutralization pattern where all the macrophage-tropic and about half of the non-macrophage-tropic Envs were sensitive. CD4, b12, and VRC01 share binding specificities on the outer domain of gp120. However, these antibodies differ in their ability to induce conformational changes on the trimeric envelope and in specificity for residues on the V1V2 loop stem and β20-21 junction that are targets for CD4 in recruiting the bridging sheet. These distinct specificities of CD4, b12, and VRC01 likely explain the observed differences in Env sensitivity to inhibition by these reagents and provide an insight into the envelope mechanisms that control macrophage tropism. We present a model where the efficiency of bridging-sheet recruitment by CD4 is a major determinant of HIV-1 R5 envelope sensitivity to soluble CD4 and macrophage tropism.

Central nervous system compartmentalization of HIV-1 subtype C variants early and late in infection in young children

HIV-1 subtype B replication in the CNS can occur in CD4+ T cells or macrophages/microglia in adults. However, little is known about CNS infection in children or the ability of subtype C HIV-1 to evolve macrophage-tropic variants. In this study, we examined HIV-1 variants in ART-naïve children aged three years or younger to determine viral genotypes and phenotypes associated with HIV-1 subtype C pediatric CNS infection. We examined HIV-1 subtype C populations in blood and CSF of 43 Malawian children with neurodevelopmental delay or acute neurological symptoms. Using single genome amplification (SGA) and phylogenetic analysis of the full-length env gene, we defined four states: equilibrated virus in blood and CSF (n = 20, 47%), intermediate compartmentalization (n = 11, 25%), and two distinct types of compartmentalized CSF virus (n = 12, 28%). Older age and a higher CSF/blood viral load ratio were associated with compartmentalization, consistent with independent replication in the CNS. Cell tropism was assessed using pseudotyped reporter viruses to enter a cell line on which CD4 and CCR5 receptor expression can be differentially induced. In a subset of compartmentalized cases (n = 2, 17%), the CNS virus was able to infect cells with low CD4 surface expression, a hallmark of macrophage-tropic viruses, and intermediate compartmentalization early was associated with an intermediate CD4 entry phenotype. Transmission of multiple variants was observed for 5 children; in several cases, one variant was sequestered within the CNS, consistent with early stochastic colonization of the CNS by virus. Thus we hypothesize two pathways to compartmentalization: early stochastic sequestration in the CNS of one of multiple variants transmitted from mother to child, and emergence of compartmentalized variants later in infection, on average at age 13.5 months, and becoming fully apparent in the CSF by age 18 months. Overall, compartmentalized viral replication in the CNS occurred in half of children by year three.

Genetically compartmentalized human immunodeficiency virus type 1 (HIV-1) subtype B populations can be variably detected in the cerebrospinal fluid (CSF) of adults. Compartmentalization is indicative of local CNS replication, and late in disease is linked to HIV-associated dementia (HAD). Compartmentalized viral populations can comprise either CCR5-using T cell-tropic or macrophage-tropic virus. Little is known about CNS infection in children or the ability of subtype C HIV-1 to evolve macrophage-tropic variants. We examined viral populations in the blood and CSF of HIV-1 subtype C-infected children. We found an intermediate level of compartmentalization in about half of the children under 18 months of age. About 50% of children older than 18 months had clearly compartmentalized virus in the CSF/CNS, and in some cases CSF virus evolved a low CD4 entry phenotype. In some of the children two variants were transmitted from the mother. In several of these cases one of the transmitted viruses was replicating in the CNS while the other was found predominantly in the blood/periphery. Our results suggest that compartmentalized CSF/CNS populations can be detected in up to 50% of children by year three, either established early in the infection or through sequestration of a transmitted variant within the CNS.

A machine learning approach for identifying amino acid signatures in the HIV env gene predictive of dementia

The identification of nucleotide sequence variations in viral pathogens linked to disease and clinical outcomes is important for developing vaccines and therapies. However, identifying these genetic variations in rapidly evolving pathogens adapting to selection pressures unique to each host presents several challenges. Machine learning tools provide new opportunities to address these challenges. In HIV infection, virus replicating within the brain causes HIV-associated dementia (HAD) and milder forms of neurocognitive impairment in 20-30% of patients with unsuppressed viremia. HIV neurotropism is primarily determined by the viral envelope (env) gene. To identify amino acid signatures in the HIV env gene predictive of HAD, we developed a machine learning pipeline using the PART rule-learning algorithm and C4.5 decision tree inducer to train a classifier on a meta-dataset (n = 860 env sequences from 78 patients: 40 HAD, 38 non-HAD). To increase the flexibility and biological relevance of our analysis, we included 4 numeric factors describing amino acid hydrophobicity, polarity, bulkiness, and charge, in addition to amino acid identities. The classifier had 75% predictive accuracy in leave-one-out cross-validation, and identified 5 signatures associated with HAD diagnosis (p<0.05, Fisher's exact test). These HAD signatures were found in the majority of brain sequences from 8 of 10 HAD patients from an independent cohort. Additionally, 2 HAD signatures were validated against env sequences from CSF of a second independent cohort. This analysis provides insight into viral genetic determinants associated with HAD, and develops novel methods for applying machine learning tools to analyze the genetics of rapidly evolving pathogens.

Programming of neurotoxic cofactor CXCL-10 in HIV-1-associated dementia: abrogation of CXCL-10-induced neuro-glial toxicity in vitro by PKC activator

Background

More than 50% of patients undergoing lifelong suppressive antiviral treatment for HIV-1 infection develop minor HIV-1-associated neurocognitive disorders. Neurological complications during HIV-1 infection are the result of direct neuronal damage by proinflammatory products released from HIV-1-infected or -uninfected activated lymphocytes, monocytes, macrophages, microglia and astrocytes. The specific pro-inflammatory products and their roles in neurotoxicity are far from clear. We investigated proinflammatory cytokines and chemokines in the cerebrospinal fluid (CSF) of HIV-demented (HIV-D) and HIV-nondemented (HIV-ND) patients and studied their affect on neuroglial toxicity.

Methods and results

Bioplex array showed elevated levels of signatory chemokines or cytokines (IL-6, IFN-γ, CXCL10, MCP-1 and PDGF) in the CSF of HIV-D patients (n = 7) but not in that of HIV-ND patients (n = 7). Among the signatory cytokines and chemokines, CXCL10 was distinctly upregulated in-vitro in HIV-1 (NLENG1)-activated human fetal astrocytes, HIV-1 (Ba-L)-infected macrophages, and HIV-1 (NLENG1)-infected lymphocytes. Virus-infected macrophages also had increased levels of TNF-α. Consistently, human fetal astrocytes treated with HIV-1 and TNF-α induced the signatory molecules. CXCL10 in combination with HIV-1 synergistically enhanced neuronal toxicity and showed chemotactic activity (~ 40 fold) for activated peripheral blood mononuclear cells (PBMC), suggesting the intersection of signaling events imparted by HIV-1 and CXCL10 after binding to their respective surface receptors, CXCR4 and CXCR3, on neurons. Blocking CXCR3 and its downstream MAP kinase (MAPK) signaling pathway suppressed combined CXCL10 and HIV-1-induced neurotoxicity. Bryostatin, a PKC modulator and suppressor of CXCR4, conferred neuroprotection against combined insult with HIV-1 and CXCL10. Bryostatin also suppressed HIV-1 and CXCL10-induced PBMC chemotaxis. Although, therapeutic targeting of chemokines in brain may have adverse consequences on the host, current findings and earlier evidence suggest that CXCL10 could strongly impede neuroinflammation.

Conclusion

We have demonstrated induction of CXCL10 and other chemokines/cytokines during HIV-1 infection in the brain, as well as synergism of CXCL10 with HIV-1 in neuronal toxicity, which was dampened by bryostatin.

Macrophage-tropic HIV-1 variants from brain demonstrate alterations in the way gp120 engages both CD4 and CCR5

BR-derived HIV-1 strains have an exceptional ability to enter macrophages via mechanisms involving their gp120 Env that remain incompletely understood. Here, we used cell-based affinity-profiling methods and mathematical modeling to generate quantitative VERSA metrics that simultaneously measure Env-CD4 and Env-CCR5 interactions. These metrics were analyzed to distinguish the phenotypes of M-tropic and non-M-tropic CCR5-using HIV-1 variants derived from autopsy BRs and LNs, respectively. We show that highly M-tropic Env variants derived from brain can be defined by two distinct and simultaneously occurring phenotypes. First, BR-derived Envs demonstrated an enhanced ability to interact with CD4 compared with LN-derived Envs, permitting entry into cells expressing scant levels of CD4. Second, BR-derived Envs displayed an altered mechanism of engagement between CD4-bound gp120 and CCR5 occurring in tandem. With the use of epitope mapping, mutagenesis, and structural studies, we show that this altered mechanism is characterized by increased exposure of CD4-induced epitopes in gp120 and by a more critical interaction between BR-derived Envs and the CCR5 N-terminus, which was associated with the predicted presence of additional atomic contacts formed at the gp120-CCR5 N-terminus interface. Our results suggest that BR-derived HIV-1 variants with highly efficient macrophage entry adopt conformations in gp120 that simultaneously alter the way in which the Env interacts with CD4 and CCR5.

A species-specific amino acid difference in the macaque CD4 receptor restricts replication by global circulating HIV-1 variants representing viruses from recent infection

HIV-1 replicates poorly in macaque cells, and this had hindered the advancement of relevant nonhuman primate model systems for HIV-1 infection and pathogenesis. Several host restriction factors have been identified that contribute to this species-specific restriction to HIV-1 replication, but these do not fully explain the poor replication of most strains of HIV-1 in macaque cells. Only select HIV-1 envelope variants, typically those derived from viruses that have been adapted in cell culture, result in infectious chimeric SIVs encoding HIV-1 envelope (SHIVs). Here we demonstrate that most circulating HIV-1 variants obtained directly from infected individuals soon after virus acquisition do not efficiently mediate entry using the macaque CD4 receptor. The infectivity of these viruses is ca. 20- to 50-fold lower with the rhesus and pig-tailed macaque versus the human CD4 receptor. In contrast, culture-derived HIV-1 envelope variants that facilitate efficient replication in macaques showed similar infectivity with macaque and human CD4 receptors (within ∼2-fold). The ability of an envelope to mediate entry using macaque CD4 correlated with its ability to mediate entry of cells expressing low levels of the human CD4 receptor and with soluble CD4 sensitivity. Species-specific differences in the functional capacity of the CD4 receptor to mediate entry mapped to a single amino acid difference at position 39 that is under strong positive selection, suggesting that the evolution of CD4 may have been influenced by its function as a viral receptor. These results also suggest that N39 in human CD4 may be a critical residue for interaction of transmitted HIV-1 variants. These studies provide important insights into virus-host cell interactions that have hindered the development of relevant nonhuman primate models for HIV-1 infection and provide possible markers, such as sCD4 sensitivity, to identify potential HIV-1 variants that could be exploited for development of better SHIV/macaque model systems.

Induction of IL-6 and CCL5 (RANTES) in human respiratory epithelial (A549) cells by clinical isolates of respiratory syncytial virus is strain specific

BACKGROUND

Respiratory syncytial virus (RSV) is the major respiratory pathogen of infants and young children. During each seasonal epidemic, multiple strains of both subgroup A and B viruses circulate in the community. Like other RNA viruses, RSV genome replication is prone to errors that results in a heterogeneous population of viral strains some of which may possess differences in virulence. We sought to determine whether clinical isolates of RSV differ in their capacity to induce inflammatory cytokines IL-6 and CCL5 (previously known as RANTES [regulated upon activation, normal T-cell expressed and secreted protein]), which are known to be induced in vitro and in vivo in response to RSV, during infection of A549 cells.

RESULTS

Screening of subgroup A and B isolates revealed heterogeneity among strains to induce IL-6 and CCL5. We chose two subgroup B strains, New Haven (NH)1067 and NH1125, for further analysis because of their marked differences in cytokine inducing properties and because subgroup B strains, in general, are less genetically heterogeneous as compared to subgroup A strains. At 12 and 24 hours post infection RSV strains, NH1067 and NH1125 differed in their capacity to induce IL-6 by an order of magnitude or more. The concentrations of IL-6 and CCL5 were dependent on the dose of infectious virus and the concentration of these cytokines induced by NH1125 was greater than that of those induced by NH1067 when the multiplicity of infection of NH1067 used was as much as 10-fold higher than that of NH1125. The induction of IL-6 was dependent on viable virus as infection with UV-inactivated virus did not induce IL-6. The difference in IL-6 induction most likely could not be explained by differences in viral replication kinetics. The intracellular level of RSV RNA, as determined by quantitative RT-PCR, was indistinguishable between the 2 strains though the titer of progeny virus produced by NH1125 was greater than that produced by NH1067 at 16, 24 and 36 hours but essentially equal at 48 and 72 hours. Full genome sequencing of the 2 strains revealed 193 polymorphisms and 4 insertions in NH1067 when compared to NH1125 (2 single base insertions in non-coding regions and 2 duplications of 3 and 60 bases in the RSV G gene). Of the polymorphisms, 147 occurred in coding regions and only 30 resulted in amino acid changes in 7 of the RSV genes.

CONCLUSIONS

These data suggest that RSV strains may not be homogeneous with regard to pathogenesis or virulence. Identification of the genetic polymorphisms associated with variations in cytokine induction may lead to insights into RSV disease and to the development of effective antiviral agents and vaccines.

Structural elements of primary CCR5-using HIV-1 gp120 proteins influencing sensitivity and resistance to the broadly neutralizing monoclonal antibody b12

Structure-guided approaches to HIV-1 vaccine design depend on knowledge of the presentation of neutralizing epitopes on gp120, such as the epitope for the broadly neutralizing mAb b12. Here, we characterized predicted three-dimensional structures of functionally diverse gp120 proteins in their b12-bound conformation, to better understand the gp120 determinants that expose or occlude the b12 epitope. Mapping the gp120-b12 binding interface identified amino acid polymorphisms within the C2, C3, C4 and V5 regions of gp120 associated with augmented b12 binding, and importantly, identified residues in the b12-exclusive binding domain of gp120 that are important for b12 neutralization resistance. Structural studies suggest that these b12 resistance variants promote reduced conformational flexibility in the b12 recognition site, which we show involves structural alterations within the gp120 CD4 binding loop and the V4 loop. Together, our studies provide new mechanistic insights into the gp120 determinants influencing sensitivity and resistance to HIV-1 neutralization by b12.

Lineage-specific differences between human and simian immunodeficiency virus regulation of gp120 trimer association and CD4 binding

Metastable conformations of the gp120 and gp41 envelope glycoproteins of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) must be maintained in the unliganded state of the envelope glycoprotein trimer. Binding of gp120 to the primary receptor, CD4, triggers the transition to an open conformation of the trimer, promoting interaction with the CCR5 chemokine receptor and ultimately leading to gp41-mediated virus-cell membrane fusion and entry. Topological layers in the gp120 inner domain contribute to gp120-trimer association in the unliganded state and to CD4 binding. Here we describe similarities and differences between HIV-1 and SIVmac gp120. In both viruses, the gp120 N/C termini and the inner domain β-sandwich and layer 2 support the noncovalent association of gp120 with the envelope glycoprotein trimer. Layer 1 of the SIVmac gp120 inner domain contributes more to trimer association than the corresponding region of HIV-1 gp120. On the other hand, layer 1 plays an important role in stabilizing the CD4-bound conformation of HIV-1 but not SIVmac gp120 and thus contributes to HIV-1 binding to CD4. In SIVmac, CD4 binding is instead enhanced by tryptophan 375, which fills the Phe 43 cavity of gp120. Activation of SIVmac by soluble CD4 is dependent on tryptophan 375 and on layer 1 residues that determine a tight association of gp120 with the trimer. Distinct biological requirements for CD4 usage have resulted in lineage-specific differences in the HIV-1 and SIV gp120 structures that modulate trimer association and CD4 binding.

Neurocognitive and motor deficits in HIV-infected Ugandan children with high CD4 cell counts

BACKGROUND

Human immunodeficiency virus (HIV) infection causes neurocognitive or motor function deficits in children with advanced disease, but it is unclear whether children with CD4 cell measures above the World Health Organization (WHO) thresholds for antiretroviral therapy (ART) initiation suffer significant impairment.

METHODS

The neurocognitive and motor functions of HIV-infected ART-naive Ugandan children aged 6-12 years with CD4 cell counts of >350 cells/μL and CD4 cell percentage of >15% were compared with those of HIV-uninfected children, using the Test of Variables of Attention (TOVA), the Kaufman Assessment Battery for Children, second edition (KABC-2), and the Bruininks-Oseretsky Test of Motor Proficiency, second edition (BOT-2).

RESULTS

Ninety-three HIV-infected children (median CD4 cell count, 655 cells/μL; plasma HIV RNA level, 4.7 log(10) copies/mL) were compared to 106 HIV-uninfected children. HIV-infected children performed worse on TOVA visual reaction times (multivariate analysis of covariance; P = .006); KABC-2 sequential processing (P = .005), simultaneous processing (P = .039), planning/reasoning (P = .023), and global performance (P = .024); and BOT-2 total motor proficiency (P = .003). High plasma HIV RNA level was associated with worse performance in 10 cognitive measures and 3 motor measures. In analysis of only WHO clinical stage 1 or 2 HIV-infected children (n = 68), significant differences between the HIV-infected and HIV-uninfected groups (P < .05) remained for KABC-2 sequential processing, KABC-2 planning/reasoning, and BOT-2 motor proficiency.

CONCLUSIONS

Significant motor and cognitive deficits were found in HIV-infected ART-naive Ugandan children with CD4 cell counts of ∼350 cells/μL and percentages of >15%. Study of whether early initiation of ART could prevent or reverse such deficits is needed.

The HIV-1 env protein: a coat of many colors

HIV-1 is completely dependent upon the Env protein to enter cells. The virus typically replicates in activated CD4+ T cells due to viral entry requirements for the CCR5 coreceptor and for high surface levels of the CD4 receptor. This is the case for the transmitted virus and for most of the virus sampled in the blood. Over the course of infection, the env gene can evolve to encode a protein with altered receptor and coreceptor usage allowing the virus to enter alternative host cells. In about 50% of HIV-1 infections, the viral population undergoes coreceptor switching, usually late in disease, allowing the virus to use CXCR4 to enter a different subset of CD4+ T cells. Neurocognitive disorders occur in about 10% of infections, also usually late in disease, but caused (ultimately) by viral replication in the brain either in CD4+ T cells or macrophage and/or microglia. Expanded host range is significantly intertwined with pathogenesis. Identification and characterization of such HIV-1 variants may be useful for early detection which would allow intervention to reduce viral pathogenesis in these alternative cell types.

Independent evolution of macrophage-tropism and increased charge between HIV-1 R5 envelopes present in brain and immune tissue

Background

Transmitted HIV-1 clade B or C R5 viruses have been reported to infect macrophages inefficiently, while other studies have described R5 viruses in late disease with either an enhanced macrophage-tropism or carrying envelopes with an increased positive charge and fitness. In contrast, our previous data suggested that viruses carrying non-macrophage-tropic R5 envelopes were still predominant in immune tissue of AIDS patients. To further investigate the tropism and charge of HIV-1 viruses in late disease, we evaluated the properties of HIV-1 envelopes amplified from immune and brain tissues of AIDS patients with neurological complications.

Results

Almost all envelopes amplified were R5. There was clear compartmentalization of envelope sequences for four of the five subjects. However, strong compartmentalization of macrophage-tropism in brain was observed even when brain and immune tissue envelope sequences were not segregated. R5 envelopes from immune tissue of four subjects carried a higher positive charge compared to brain envelopes. We also confirm a significant correlation between macrophage tropism and sensitivity to soluble CD4, a weak association with sensitivity to the CD4 binding site antibody, b12, but no clear relationship with maraviroc sensitivity.

Conclusions

Our study shows that non-macrophage-tropic R5 envelopes carrying gp120s with an increased positive charge were predominant in immune tissue in late disease. However, highly macrophage-tropic variants with lower charged gp120s were nearly universal in the brain. These results are consistent with HIV-1 R5 envelopes evolving gp120s with an increased positive charge in immune tissue or sites outside the brain that likely reflect an adaptation for increased replication or fitness for CD4+ T-cells. Our data are consistent with the presence of powerful pressures in brain and in immune tissues selecting for R5 envelopes with very different properties; high macrophage-tropism, sCD4 sensitivity and low positive charge in brain and non-macrophage-tropism, sCD4 resistance and high positive charge in immune tissue.

Generation of transmitted/founder HIV-1 infectious molecular clones and characterization of their replication capacity in CD4 T lymphocytes and monocyte-derived macrophages

Genome sequences of transmitted/founder (T/F) HIV-1 have been inferred by analyzing single genome amplicons of acute infection plasma viral RNA in the context of a mathematical model of random virus evolution; however, few of these T/F sequences have been molecularly cloned and biologically characterized. Here, we describe the derivation and biological analysis of ten infectious molecular clones, each representing a T/F genome responsible for productive HIV-1 clade B clinical infection. Each of the T/F viruses primarily utilized the CCR5 coreceptor for entry and replicated efficiently in primary human CD4(+) T lymphocytes. This result supports the conclusion that single genome amplification-derived sequences from acute infection allow for the inference of T/F viral genomes that are consistently replication competent. Studies with monocyte-derived macrophages (MDM) demonstrated various levels of replication among the T/F viruses. Although all T/F viruses replicated in MDM, the overall replication efficiency was significantly lower compared to prototypic "highly macrophage-tropic" virus strains. This phenotype was transferable by expressing the env genes in an isogenic proviral DNA backbone, indicating that T/F virus macrophage tropism mapped to Env. Furthermore, significantly higher concentrations of soluble CD4 were required to inhibit T/F virus infection compared to prototypic macrophage-tropic virus strains. Our findings suggest that the acquisition of clinical HIV-1 subtype B infection occurs by mucosal exposure to virus that is not highly macrophage tropic and that the generation and initial biological characterization of 10 clade B T/F infectious molecular clones provides new opportunities to probe virus-host interactions involved in HIV-1 transmission.

Viral determinants of HIV-1 macrophage tropism

Macrophages are important target cells for HIV-1 infection that play significant roles in the maintenance of viral reservoirs and other aspects of pathogenesis. Understanding the determinants of HIV-1 tropism for macrophages will inform HIV-1 control and eradication strategies. Tropism for macrophages is both qualitative (infection or not) and quantitative (replication capacity). For example many R5 HIV-1 isolates cannot infect macrophages, but for those that can the macrophage replication capacity can vary by up to 1000-fold. Some X4 viruses are also capable of replication in macrophages, indicating that cellular tropism is partially independent of co-receptor preference. Preliminary data obtained with a small number of transmitted/founder viruses indicate inefficient macrophage infection, whereas isolates from later in disease are more frequently tropic for macrophages. Thus tropism may evolve over time, and more macrophage tropic viruses may be implicated in the pathogenesis of advanced HIV-1 infection. Compartmentalization of macrophage-tropic brain-derived envelope glycoproteins (Envs), and non-macrophage tropic non-neural tissue-derived Envs points to adaptation of HIV-1 quasi-species in distinct tissue microenvironments. Mutations within and adjacent to the Env-CD4 binding site have been identified that determine macrophage tropism at the entry level, but post-entry molecular determinants of macrophage replication capacity involving HIV-1 accessory proteins need further definition.

HIV-1 replication in the central nervous system occurs in two distinct cell types

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system (CNS) can lead to the development of HIV-1-associated dementia (HAD). We examined the virological characteristics of HIV-1 in the cerebrospinal fluid (CSF) of HAD subjects to explore the association between independent viral replication in the CNS and the development of overt dementia. We found that genetically compartmentalized CCR5-tropic (R5) T cell-tropic and macrophage-tropic HIV-1 populations were independently detected in the CSF of subjects diagnosed with HIV-1-associated dementia. Macrophage-tropic HIV-1 populations were genetically diverse, representing established CNS infections, while R5 T cell-tropic HIV-1 populations were clonally amplified and associated with pleocytosis. R5 T cell-tropic viruses required high levels of surface CD4 to enter cells, and their presence was correlated with rapid decay of virus in the CSF with therapy initiation (similar to virus in the blood that is replicating in activated T cells). Macrophage-tropic viruses could enter cells with low levels of CD4, and their presence was correlated with slow decay of virus in the CSF, demonstrating a separate long-lived cell as the source of the virus. These studies demonstrate two distinct virological states inferred from the CSF virus in subjects diagnosed with HAD. Finally, macrophage-tropic viruses were largely restricted to the CNS/CSF compartment and not the blood, and in one case we were able to identify the macrophage-tropic lineage as a minor variant nearly two years before its expansion in the CNS. These results suggest that HIV-1 variants in CSF can provide information about viral replication and evolution in the CNS, events that are likely to play an important role in HIV-associated neurocognitive disorders.

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system (CNS) can lead to the development of a severe neurological disease termed HIV-1-associated dementia (HAD). Individuals diagnosed with HAD commonly have genetically distinct HIV-1 variants in their cerebrospinal fluid (CSF) that are not detected in the blood virus population, suggesting that independent viral replication is occurring in the CNS of HIV-1-infected subjects with severe neurological disease. We examined HIV-1 variants in the blood plasma and CSF of HAD subjects to determine the viral characteristics associated with the development of dementia during HIV-1 infection. We found that genetically distinct HIV-1 variants in the CSF of HAD subjects were either R5 T cell-tropic or macrophage-tropic. The R5 T cell-tropic viruses required high levels of the cellular surface receptor CD4 to enter cells, while macrophage-tropic viruses could enter cells with low levels of CD4, suggesting that HIV-1 can replicate in at least two cell types within the CNS during the course of dementia. Finally, macrophage-tropic viruses were detected in the CSF but poorly represented in the blood virus population. Our results suggest that HIV-1 variants in the CSF can provide information about independent viral replication in the CNS during the course of HIV-1 infection.

HIV-1 clade B and C isolates exhibit differential replication: relevance to macrophage-mediated neurotoxicity

HIV-associated neurocognitive disorders (HAND) continue to be a consequence of HIV-1 infection among clade B-infected individuals. In contrast, the incidence of severe neurological impairment is lower among clade C-infected patients in regions of Sub-Saharan Africa and India. Biological aspects such as replication, cytopathicity, inflammatory response, and neurotoxicity unique to each clade influence neuropathogenicity and ultimately affect the clinical outcome of the disease. We hypothesize that productive infection by clade C isolates leads to macrophage-mediated neurotoxicity, although to a lesser extent than clade B isolates. Using a panel of primary isolates of clades B and C we demonstrated that clade B has higher replication efficiency in monocyte-derived macrophages (MDM) through reverse transcriptase activity assay and HIV-1 p24 antigen ELISA. To test the neurotoxicity of clades B and C, we used an in vitro neurotoxicity model. Conditioned medium from clade B-infected MDM was neurotoxic to rat and human neuron cultures. In contrast, clade C isolates mediated neurotoxicity when a higher initial viral titer was used for MDM infection. Furthermore, neurotoxicity mediated by isolates of both clades correlated with virus replication in MDM. Together, these results suggest that in comparison to clade B, primary isolates of clade C have slower replication kinetics in primary MDM, leading to lower levels of macrophage-mediated neurotoxicity. Elucidating the differences in replication and macrophage-mediated neurotoxicity between isolates of HIV-1 clades B and C will provide important insights needed to clarify the disparity seen in HAND incidence.

Alternative coreceptor requirements for efficient CCR5- and CXCR4-mediated HIV-1 entry into macrophages

Macrophage tropism of human immunodeficiency virus type 1 (HIV-1) is distinct from coreceptor specificity of the viral envelope glycoproteins (Env), but the virus-cell interactions that contribute to efficient HIV-1 entry into macrophages, particularly via CXCR4, are not well understood. Here, we characterized a panel of HIV-1 Envs that use CCR5 (n = 14) or CXCR4 (n = 6) to enter monocyte-derived macrophages (MDM) with various degrees of efficiency. Our results show that efficient CCR5-mediated MDM entry by Env-pseudotyped reporter viruses is associated with increased tolerance of several mutations within the CCR5 N terminus. In contrast, efficient CXCR4-mediated MDM entry was associated with reduced tolerance of a large deletion within the CXCR4 N terminus. Env sequence analysis and structural modeling identified amino acid variants at positions 261 and 263 within the gp41-interactive region of gp120 and a variant at position 326 within the gp120 V3 loop that were associated with efficient CXCR4-mediated MDM entry. Mutagenesis studies showed that the gp41 interaction domain variants exert a significant but strain-specific influence on CXCR4-mediated MDM entry, suggesting that the structural integrity of the gp120-gp41 interface is important for efficient CXCR4-mediated MDM entry of certain HIV-1 strains. However, the presence of Ile326 in the gp120 V3 loop stem, which we show by molecular modeling is located at the gp120-coreceptor interface and predicted to interact with the CXCR4 N terminus, was found to be critical for efficient CXCR4-mediated MDM entry of divergent CXCR4-using Envs. Together, the results of our study provide novel insights into alternative mechanisms of Env-coreceptor engagement that are associated with efficient CCR5- and CXCR4-mediated HIV-1 entry into macrophages.

Conformational alterations in the CD4 binding cavity of HIV-1 gp120 influencing gp120-CD4 interactions and fusogenicity of HIV-1 envelopes derived from brain and other tissues

Background

CD4-binding site (CD4bs) alterations in gp120 contribute to HIV-1 envelope (Env) mediated fusogenicity and the ability of gp120 to utilize low levels of cell-surface CD4. In a recent study, we constructed three-dimensional models of gp120 to illustrate CD4bs conformations associated with enhanced fusogenicity and enhanced CD4-usage of a modestly-sized panel of blood-derived HIV-1 Envs (n = 16). These conformations were characterized by a wider aperture of the CD4bs cavity, as constrained by the inner-most atoms at the gp120 V1V2 stem and the V5 loop. Here, we sought to provide further validation of the utility of these models for understanding mechanisms that influence Env function, by characterizing the structure-function relationships of a larger panel of Envs derived from brain and other tissues (n = 81).

Findings

Three-dimensional models of gp120 were generated by our recently validated homology modelling protocol. Analysis of predicted CD4bs structures showed correlations between the aperture width of the CD4bs cavity and ability of the Envs to mediate cell-cell fusion, scavenge low-levels of cell-surface CD4, bind directly to soluble CD4, and bind to the Env mAb IgG1b12 whose epitope overlaps the gp120 CD4bs. These structural alterations in the CD4bs cavity were associated with repositioning of the V5 loop.

Conclusions

Using a large, independent panel of Envs, we can confirm the utility of three-dimensional gp120 structural models for illustrating CD4bs alterations that can affect Env function. Furthermore, we now provide new evidence that these CD4bs alterations augment the ability of gp120 to interact with CD4 by increasing the exposure of the CD4bs.

Two closely related Env antigens from the same patient elicited different spectra of neutralizing antibodies against heterologous HIV-1 isolates

Identification of immunogens capable of eliciting broadly neutralizing antibody (NAb) responses against HIV-1 is a major goal toward the development of an AIDS vaccine. Despite significant progress in understanding the structural features of the HIV-1 envelope glycoprotein (Env) and the discovery of multiple broadly neutralizing monoclonal antibodies with defined antigenic structures, the design of optimal Env immunogens to elicit broad NAbs remains a major challenge. As the structural determinants of Env immunogenicity remain unclear, we assessed two closely related Env antigens isolated from the same HIV-1-infected patient with different phenotypic features to identify what may result in a favorable immunogenic profile. One Env, B33, isolated from brain, was highly macrophage tropic with a high CD4 affinity, while the other, LN40, isolated from the lymph nodes, was poorly macrophage tropic with a low CD4 affinity. Using a DNA prime-protein boost approach, rabbits primed with LN40 Env antigen had a NAb response against heterologous primary isolates, while B33 Env antigens were capable of eliciting NAbs against only homologous and sensitive viral isolates. Further analysis revealed that the specificity of NAbs elicited by the LN40 antigen mapped to limited residues within or flanking the CD4 binding site. Certain key structural determinants were identified that could differentiate primary Env immunogens based on their potential to elicit broader NAbs. This progress will facilitate the rational design of effective HIV-1 vaccine formulations with optimal Env antigens.

Intercompartmental recombination of HIV-1 contributes to env intrahost diversity and modulates viral tropism and sensitivity to entry inhibitors

HIV-1 circulates within an infected host as a genetically heterogeneous viral population. Viral intrahost diversity is shaped by substitutional evolution and recombination. Although many studies have speculated that recombination could have a significant impact on viral phenotype, this has never been definitively demonstrated. We report here phylogenetic and subsequent phenotypic analyses of envelope genes obtained from HIV-1 populations present in different anatomical compartments. Assessment of env compartmentalization from immunologically discrete tissues was assessed utilizing a single genome amplification approach, minimizing in vitro-generated artifacts. Genetic compartmentalization of variants was frequently observed. In addition, multiple incidences of intercompartment recombination, presumably facilitated by low-level migration of virus or infected cells between different anatomic sites and coinfection of susceptible cells by genetically divergent strains, were identified. These analyses demonstrate that intercompartment recombination is a fundamental evolutionary mechanism that helps to shape HIV-1 env intrahost diversity in natural infection. Analysis of the phenotypic consequences of these recombination events showed that genetic compartmentalization often correlates with phenotypic compartmentalization and that intercompartment recombination results in phenotype modulation. This represents definitive proof that recombination can generate novel combinations of phenotypic traits which differ subtly from those of parental strains, an important phenomenon that may have an impact on antiviral therapy and contribute to HIV-1 persistence in vivo.

HIV-1 infection and cognitive impairment in the cART era: a review

With the introduction of combination antiretroviral therapy AIDS dementia complex or HIV-associated dementia, as it was termed later, largely disappeared in clinical practice. However, in the past few years, patients, long-term infected and treated, including those with systemically well controlled infection, started to complain about milder memory problems and slowness, difficulties in concentration, planning, and multitasking. Neuropsychological studies have confirmed that cognitive impairment occurs in a substantial (15-50%) proportion of patients. Among HIV-1-infected patients cognitive impairment was and is one of the most feared complications of HIV-1 infection. In addition, neurocognitive impairment may affect adherence to treatment and ultimately result in increased morbidity for systemic disease. So what may be going on in the CNS after so many years of apparently controlled HIV-1 infection is an urgent and important challenge in the field of HIV medicine. In this review we summarize the key currently available data. We describe the clinical neurological and neuropsychological findings, the preferred diagnostic approach with new imaging techniques and cerebrospinal fluid analysis. We try to integrate data on pathogenesis and finally discuss possible therapeutic interventions.

HIV-1 escape from the CCR5 antagonist maraviroc associated with an altered and less-efficient mechanism of gp120-CCR5 engagement that attenuates macrophage tropism

Maraviroc (MVC) inhibits the entry of human immunodeficiency virus type 1 (HIV-1) by binding to and modifying the conformation of the CCR5 extracellular loops (ECLs). Resistance to MVC results from alterations in the HIV-1 gp120 envelope glycoproteins (Env) enabling recognition of the drug-bound conformation of CCR5. To better understand the mechanisms underlying MVC resistance, we characterized the virus-cell interactions of gp120 from in vitro-generated MVC-resistant HIV-1 (MVC-Res Env), comparing them with those of gp120 from the sensitive parental virus (MVC-Sens Env). In the absence of the drug, MVC-Res Env maintains a highly efficient interaction with CCR5, similar to that of MVC-Sens Env, and displays a relatively modest increase in dependence on the CCR5 N terminus. However, in the presence of the drug, MVC-Res Env interacts much less efficiently with CCR5 and becomes critically dependent on the CCR5 N terminus and on positively charged elements of the drug-modified CCR5 ECL1 and ECL2 regions (His88 and His181, respectively). Structural analysis suggests that the Val323 resistance mutation in the gp120 V3 loop alters the secondary structure of the V3 loop and the buried surface area of the V3 loop-CCR5 N terminus interface. This altered mechanism of gp120-CCR5 engagement dramatically attenuates the entry of HIV-1 into monocyte-derived macrophages (MDM), cell-cell fusion activity in MDM, and viral replication capacity in MDM. In addition to confirming that HIV-1 escapes MVC by becoming heavily dependent on the CCR5 N terminus, our results reveal novel interactions with the drug-modified ECLs that are critical for the utilization of CCR5 by MVC-Res Env and provide additional insights into virus-cell interactions that modulate macrophage tropism.