Reduced antiretroviral drug efficacy and concentration in HIV-infected microglia contributes to viral persistence in brain
© The Author(s) 2017
Received: 15 August 2017
Accepted: 1 October 2017
Published: 16 October 2017
In patients with HIV/AIDS receiving antiretroviral therapy (ART), HIV-1 persistence in brain tissue is a vital and unanswered question. HIV-1 infects and replicates in resident microglia and trafficking macrophages within the brain although the impact of individual ART drugs on viral infection within these brain myeloid cells is unknown. Herein, the effects of contemporary ART drugs were investigated using in vitro and in vivo models of HIV-1 brain infection.
The EC50 values for specific ART drugs in HIV-infected human microglia were significantly higher compared to bone marrow-derived macrophages and peripheral blood mononuclear cells. Intracellular ART drug concentrations in microglia were significantly lower than in human lymphocytes. In vivo brain concentrations of ART drugs in mice were 10 to 100-fold less in brain tissues compared with plasma and liver levels. In brain tissues from untreated HIV-infected BLT mice, HIV-encoded RNA, DNA and p24 were present in human leukocytes while ART eradicated viral RNA and DNA in both brain and plasma. Interruption of ART resulted in detectable viral RNA and DNA and increased human CD68 expression in brains of HIV-infected BLT mice. In aviremic HIV/AIDS patients receiving effective ART, brain tissues that were collected within hours of last ART dosing showed HIV-encoded RNA and DNA with associated neuroinflammatory responses.
ART drugs show variable concentrations and efficacies in brain myeloid cells and tissues in drug-specific manner. Despite low drug concentrations in brain, experimental ART suppressed HIV-1 infection in brain although HIV/AIDS patients receiving effective ART had detectable HIV-1 in brain. These findings suggest that viral suppression in brain is feasible but new approaches to enhancing ART efficacy and concentrations in brain are required for sustained HIV-1 eradication from brain.
From the outset of the HIV/AIDS epidemic, early entry and expression of HIV-1 in the brain and cerebrospinal fluid (CSF) has been consistently observed [1, 2]. With the availability of increasingly efficacious antiretroviral therapy (ART), plasma and CSF viral burden is usually undetectable by conventional assays . The impact of ART on viral burden in brain tissue has been less certain because of the relative inaccessibility of tissue for measurements except at autopsy; indeed, patients with HIV/AIDS rarely die while receiving effective ART. Nonetheless, with ART-associated improvement in immune status, the severity of degenerative brain disease associated with HIV/AIDS, termed HIV-associated neurocognitive disorders (HAND), has declined although it remains a serious challenge in ~ 25% of treated patients that often precludes employment and reduces overall survival [4–7]. All immunosuppressive lentiviruses (e.g., Human, Simian, Feline and Bovine Immunodeficiency Viruses) infect the brain and display a preference for macrophage tropism as well as infection and depletion of T lymphocyte populations. In the human brain, productive HIV-1 infection is evident in trafficking macrophages (bone marrow-derived macrophages) and resident microglia, but few if any infected T cells are observed [8–11]. These myeloid cell populations in the brain constitute a unique reservoir in which HIV-1 replicates because of the paucity of resident lymphoid cells within the brain and the blood–brain barrier’s impervious structure, which limits drug penetration. Of note, microglia and macrophages are less permissive to HIV-1 than CD4+ T-cells, possibly due to reduced CD4 expression and variable expression of specific host restriction factors [12–14]. Furthermore, macrophage-lineage cells are long lived (half-life of months–years) and comparatively resistant to cell death upon HIV-1 infection compared to CD4+ T-cells, although some groups have reported very short half-lives in HIV-infected macrophage-lineage cells [15, 16]. Likewise, recent studies of cerebrospinal fluid (CSF) show higher than expected rates of viral escape in CSF that were associated with brain injury in the setting of undetectable virus in plasma .
The impact of contemporaneous ART drugs on viral expression and replication in the brain remains unclear despite their potent viral suppressive properties in blood. Likewise, the actual ART drug concentrations in brain tissue are also uncertain. Studies of brain tissues from HIV-infected humans or SIV-infected nonhuman primates show that both viral RNA and DNA are detected in brain tissues despite receiving ART [15, 18, 19]. Of note, a very recent study reported that in a macrophage-only mouse model of HIV-1 infection, HIV-infected monocyte-derived macrophages were highly responsive to ART although the brain myeloid cells and tissues were not examined . In these patients and animal studies, the efficacy of ART was assessed in combination but not as individual drugs. These circumstances raise several questions regarding the efficacy of ART in HIV-infected brain myeloid cells, ART’s capacity to modulate HIV-1 entry of the brain and the impact of ART on established HIV-1 infection of the brain. It is important to evaluate the efficacy of individual ART ex vivo and in animal studies to select ART drugs with a high propensity to inhibit replication in the brain.
Given the questions concerning the impact of ART on HIV-1 brain infection, we investigated ART drugs’ efficacies and concentrations in different experimental platforms. The in vitro and in vivo efficacies and concentrations of different ART drugs were examined in a primary cell culture model. HIV-1 DNA and RNA quantities in brain and plasma from HIV-infected immunosuppressed mice reconstituted with human leukocytes (BLT) mice and human actively receiving ART was also quantified. These studies showed that several ART drugs exhibit reduced concentrations and efficacies in the brain myeloid cells (and in brain tissues) compared to PBMCs, but nonetheless inhibited in vivo HIV-1 brain infection in BLT mice. Investigation of brain tissues from HIV/AIDS patients indicated there was persistent viral detection in the setting of longstanding aviremia with concurrent ART.
HIV-1 infection of microglia and macrophages
ART efficacy in HIV-infected myeloid cells and PBMCs
ART EC50 (ng/ml) values in different myeloid cells and PBMCs compared to published CSF concentrations
2.1 ± 0.24
14.7 ± 1.2
27.0 ± 3.1
44.0 ± 6.0
1.1 ± 0.1
1.8 ± 0.2
3.3 ± 0.6
21.3 ± 5.0
0.64 ± 0.08
1.1 ± 0.25
3.6 ± 0.2
8.4 ± 1.1
1.2 ± 0.15
1.9 ± 0.3
8.1 ± 0.78
47.0 ± 8.8
2.67 ± 0.2
0.1 ± 0.02
1.0 ± 0.15
2.87 ± 0.4
0.77 ± 0.04
0.3 ± 0.13
0.59 ± 0.05
In vivo tissue ART drug concentrations
In vivo efficacy of ART in HIV-infected humanized mice
Viral burden was examined next, disclosing that plasma mean HIV-1 RNA copy number in HIV-infected BLT mice ranged widely and was detected in the HIV[+] group (520,000 copy numbers/ml) and in the HIV[+]/ART-interrupt group (1,150,000 copy numbers/ml) (Fig. 6d) but was not detected in the HIV[+]/ART or HIV[-] groups. In brains from BLT mice, mean viral RNA levels ranged from 500 to 700,000 copies/g (tissue) in the HIV[+]/PBS group but HIV-1 RNA was not detectable in the HIV[−] or the HIV[+]/ART groups (Fig. 6e). In contrast, mean HIV-1 RNA copy numbers in the HIV[+]/ART-interrupt group were detectable in all animals but at low copy numbers (100–500 copies/g) (Fig. 6e). Total mean HIV-1 DNA copies were also measured in all groups, revealing that the HIV[+] group showed 50–40,000 copies/g but HIV-1 DNA was not detected in the HIV[−] or the HIV[+]/ART groups (Fig. 6f). As with HIV-1 RNA brain burden, mean HIV-1 DNA copy numbers in the HIV[+]/ART-interrupt group were detectable in all animals at 100–20,000 copies/g (Fig. 6f) although integrated proviral DNA in brain was not detected in all groups. Of note, RAL was not detected in the brains of the ART-treated animals. These findings highlighted the capacity for HIV-1 to infect brain myeloid cells but also emphasized that in HIV[+]/ART group viral RNA was undetectable in the brain.
HIV-1 detection and neuroimmune responses in human brain tissue during effective ART
The present study addresses several fundamental questions regarding the impact of ART on HIV-1 infection of the brain. To the best of our knowledge, this is the first report showing that contemporary ART drugs exert differential actions in HIV-infected brain myeloid cells depending on the infected cell type and individual drug, with overall higher EC50 values in HIV-infected microglia compared to macrophages and activated PBMCs. Additionally, this is the initial report comparing ART drug concentrations in human brain myeloid and activated PBMCs as well as in brain; the intracellular drug levels were substantially lower in microglia than in activated PBMCs and very low (and transient) in brain tissues from mice and humans. These studies also indicate that in ART-treated BLT mice, HIV-1 infection was undetectable within the brain (and plasma) but ART interruption resulted in a viral rebound. Our clinical observations supported the experimental findings of reduced efficacy in brain myeloid cells by disclosing that HIV-1 RNA and DNA were detected in brain tissues from stable aviremic HIV/AIDS patients receiving ART within hours of tissue collection. These findings underline the limited ART drug efficacies and concentrations in the brain together with the precarious vulnerability of the brain to HIV-1 infection derived from blood.
The human brain is a unique HIV-1 reservoir because it is established early in infection, harbors CCR5-dependent HIV-1 viruses, and the cell populations supporting HIV-1 replication are comprised solely of myeloid cells including trafficking macrophages and resident microglia . Although in vitro data show that HIV-1 infects and replicates in both macrophages and microglia [21, 38, 39], data reporting replication of HIV-1 in human brain myeloid cells in the setting of ART-mediated viral suppression in blood are limited and usually complicated by interruption of ART before tissue collection [40, 41]. In SIV-infected macaques, infected macrophages and perhaps microglia contribute to viral persistence in the brain [18, 42]. Effective ART resulted in complete suppression of plasma SIV levels associated with undetectable SIV RNA in brain while viral DNA levels remain unchanged [18, 42]. A quantitative outgrowth assay was reported that assessed the contribution of productively infected microglia/macrophages in ART-suppressed SIV-infected macaques and found productively infected macrophage-lineage cells in different tissues including the brain .
Although integrated proviruses might exhibit defective replication , their capacity to exert pathogenic effects could be maintained through expression of subgenomic mRNAs encoding pathogenic viral proteins including Vpr, Tat and Nef. To date, there are few studies quantifying integrated proviral (HIV-1) DNA in human brain in the presence or absence of ART; the ratio of integrated:total HIV-1 DNA in brain ranged from 1:6 to 1–81  in an early study, similar to that reported (1:86) for infected lymphocytes . Another study reported matched integrated and unintegrated HIV-1 LTR sequences from the same brain were similar, but LTR activity was not assessed ; nonetheless, LTRs from replication-competent brain-derived HIV-1 exhibit substantial variation in transcriptional activity [46, 47]. Herein, the ratio of integrated:total viral DNA in ART-treated HIV/AIDS patients was 1:147 for Pt-1 but integrated provirus was not detected in brain samples from Pt-2 (Fig. 7e). While brain tissue from Pt-1 was collected from frontal cortex and proximal white matter, Pt-2’s brain samples were from temporal lobe, an anatomic site that typically shows less viral burden , which may have contributed to the relative paucity of virus in Pt-2. Another differentiating aspect between the two patients that could explain high viral burden in Pt-1 compared to Pt-2 is the composition of the ART regimen at the time of tissue collection. Pt-1 was receiving abacavir, lamivudine and raltegravir while Pt-2 was on abacavir, lavimudine and dolutegravir. We observed increased antiviral efficacy of dolutegravir in brain myeloid cells compared to activated PBMCs, implying a potentially higher intracellular concentration and perhaps greater antiviral activity for longer periods, as suggested by others . As our in vitro data showed comparable efficacy in HFM and BMDMs with dolutegravir, its use in Pt-2 might explain the reduced viral burden and the absence of integrated virus.
While the ART drugs we tested (DRV, RAL, ETR, AZT, MVC, DTG) are highly effective in controlling HIV-1 replication in blood, the extent to which they regulate viral replication in HIV-infected brain myeloid cells is largely unknown. Indeed, their levels in tissues are also uncertain although they are known to enter CSF which has prompted assignment of individual CPE values. Previous studies have reported that several ART drugs are efficacious in HIV-infected monocyte-derived macrophages  and some also inhibit HIV-transduced astrocytes . However, the current data indicate that, at matched input viral titers and drug concentrations, most of the ART drugs were significantly less efficient in controlling viral replication in HIV-infected microglia compared to BMDMs or activated PBMCs (Fig. 2a–d), although both MVC and DTG were highly efficacious. The increased efficacy of MVC is supported by studies indicating that intensification of ART in both HIV-1 and SIV infections with MVC improves neurocognition and further reduces latent viral reservoir in the brain [52–55]. It is probable that this feature of MVC likely stems from its capacity to block CCR5 as well as induce PPAR-gamma expression . It has previously been shown that PPAR-gamma up regulation can inhibit HIV-1 replication . Notably, activated PBMCs also appeared to concentrate RAL and DRV at higher intracellular levels compared to intracellular concentrations in microglia (Fig. 3a, b). Increased intracellular concentrations would enhance antiretroviral drug efficacy over time, leading to restricted viral integration and production. Our results also suggest that brain tissue is less accessible to intraperitoneally delivered drugs; ART drug concentrations were similar in different brain regions but substantially lower than in liver or blood (Fig. 4a–d), with minimal drug detection by 4 h post-delivery. Two independent studies have shown in lymphoid tissues of HIV/AIDS patients receiving ART with undetectable plasma viremia that there is continuous evolution and trafficking of HIV-1 persistent virus as well as lower tissue ART drug concentrations than in the peripheral blood [58, 59]. These findings also illustrate that viral persistence is associated with lower ART drug concentrations in lymphoid tissues. Collectively, the present data underline the limited efficacy of present-day ART drugs in the brain and perhaps other tissues/organs harboring HIV-infected tissue macrophages. The use of sub-optimal ART regimens might lead to low drug concentrations in infected brain cells, resulting in a viral reservoir in these long-lived cells together with the potential emergence of drug resistance.
We used a BLT murine model of HIV-1 infection  to examine the brain viral burden in animals infected with high titer HIV-1 and their responses to an established ART regimen. The present data are similar to a recent study  indicating that viral RNA (Fig. 6c) and total DNA (Fig. 6d) were detected in brains from BLT mice, although our data show higher viral levels, perhaps due to a higher input viral titer or efficiency of human cell engraftment. Nonetheless, viral RNA was undetectable in brain by the ART regimen implemented in this study in all animals treated until sacrifice while in animals in which ART was interrupted before termination of the study, both viral RNA and DNA were detected in brain, which was associated with an increase in human CD68 expression. Remarkably, other than CD68 expression, human (and mouse) host cell abundance and immune responses in BLT brains (Fig. 4) were minimally affected despite variable infectious input titers and durations of infection, unlike in human brains (Fig. 5).
These findings highlight the complex circumstances involved in HIV-1 infection of the brain while also emphasizing the challenges in establishing brain-specific contemporary ART regimens. Our in vitro data are supported by data from human brain tissue showing that the efficacy of contemporary ART drugs is less in the brain compared to peripheral blood. This reduced efficacy might contribute to HIV-1 viral persistence in the brain. The higher in vitro efficacies of MVC and DTG in brain myeloid cells suggest that inclusion of these drugs in first line ART regimens might prevent or diminish the development of HIV-associated neurological impairments as well as viral persistence in the brain.
Brain tissue from two HIV-1 seropositive patients receiving ART without detectable viremia (Patients 1 and 2) and uninfected (n = 6) seronegative patients were obtained by autopsy or biopsy. HIV-infected patients were receiving ART as part of the active care program at Southern Alberta Clinic, Calgary, Alberta, Canada [4–7] while uninfected patients died of other causes. Brain tissue was collected from HIV-infected patients (Patient 1: autopsy following death from a myocardial infarction; Patient 2; surgical resection of left temporal lobe for chronic complex partial epilepsy and from adult uninfected Other Disease Control patients (n = 6; causes of death included sepsis [n = 1], cancer [n = 2], Parkinson’s Disease [n = 1], pneumonia [n = 2]) at autopsy after receipt of consent. Patient 1 (Pt-1, Caucasian male, 57 yr, HIV-1 B clade seropositive for 27 yr, lifetime CD4 T cell nadir = 78 cells/μl, disease course complicated by distal sensory neuropathy and HIV-associated neurocognitive disorders [HAND, MND subtype for 10 years]) at the time of death was receiving RAL, abacavir (ABA) and lamivudine (3TC) while Patient 2 (Pt-2, Caucasian male, 38 yr, HIV-1 B clade seropositive for 12 yr, lifetime CD4 T cell nadir = 386 cells/μl, complicated by complex partial epilepsy since childhood with normal cognition and no HIV-associated complications) at the time of surgery was receiving ABA, 3TC and DTG.
CNS penetration effectiveness values of ART drugs
We used the updated CNS penetration effectiveness (CPE) values as reported previously . The CPE value for DTG has not been established. However, based on a study on the ratio CSF to plasma concentration of DTG and as well as the CSF and plasma HIV-1 RNA viral load , we assumed a CPE value of 3 for this study.
Generation of BLT mice, infection, ART and collection of brain tissue
BLT mice were generated and infected using sub-lethally irradiated NOD/SCID/IL2Rγ−/− mice [obtained from Jackson Laboratory (Bal Harbor ME), 6-10 weeks old], by implantation of human fetal thymus under the kidney capsule and IV injection of fetal liver CD34+ cells . After transplantation mice were monitored for engraftment of human cells by flow cytometry. The HIV-1 NL4-3 env ADA-IRES-GFP construct was used for virus production. Brain tissue (forebrain) and plasma were harvested from four groups of animals including uninfected (HIV[–]; n = 5), HIV-infected with PBS treatment (HIV[+]; n = 9), HIV-infected with ART treatment (HIV[+]/ART; n = 9) and HIV-infected that were treated with ART but interrupted before sacrifice (HIV[+]/ART-interrupt; n = 5). This latter group of mice was infected and treated for 2 weeks post-infection (between 4 and 6 or 8 and 10) and after 2 weeks of treatment, ART was stopped and the virus allowed to rebound and mice were sacrificed at week 13 post-infection. Animals in the (HIV[+]; n = 9) were infected for different durations or at different input titers (two mice that did not show infection after 8 weeks and were re-infected at a TCID50 50,000/animal for another 4 weeks, another two mice were infected at a TCID50 50,000/animal for 13 weeks and the other five mice were infected at a TCID50 100,000/animal for 7 weeks, by intraperitoneal infection. HIV-infected animals were treated with ART (RAL, emtricitabine and tenofovir) or PBS for 3 weeks and sacrificed at week 7 post infection. In another group, mice were infected for 8 weeks, treated with the same ART regimen or PBS for weeks and sacrificed at 12 weeks post infection. Brains were harvested at the time of necropsy and a half hemisphere was fixed in 4% paraformadehyde (PFA) and the other half stored at − 80 °C. Plasma HIV RNA was quantified in 25 μl of plasma. In brief, 50 μl of plasma was diluted to 2 ml with normal human plasma; 1 ml of diluted plasma was used to quantify RNA copy numbers using the Abbott real time HIV-1 assay (sensitivity, < 40 copies/ml).
RNA and DNA preparation
Total RNA and DNA were extracted from brain of BLT mice and HIV-infected and non-infected patients using the RNeasy and DNeasy kits (Qiagen Germantown MD, USA), respectively, according to manufacturer’s instructions and as previously described [18, 63].
Quantitative real time PCR
List of primers used for quantitative real time PCR
Droplet digital PCR for viral RNA and DNA quantification
HIV-1 viral RNA was quantified using 5 μl of diluted cDNA as template. For genomic DNA (gDNA) quantification, 5 μl (200 ng) of DNA was incubated with the restriction enzyme Alu I for 5 min at room temperature together with the reaction mixture. The Bio-Rad QX200 droplet digital PCR system was used for quantification [57, 64]. For both RNA and DNA quantification the probe: 5′-/56-FAM/AAGCCAGGA/ZEN/ATGGATGGCC/3IABkFQ/-3′, primer 1: 5′-CAAATTTCTACTAATGCTTTTATTTTTTC-3′ and primer 2: 5′-GCACTTTAAATTTTCCCATTAGTCCTA-3′ were used. Human CD45 copy number in the brain of BLT mice was also quantified by droplet digital PCR. The probe: 5′-/5HEX/AGAATGTTC/ZEN/TGGCCCCTCAGTGC/3IABkFQ/-3′ and primer 1: 5′-GAAAAGCTCCCTGAAGCAAAG-3′, primer 2: 5′-GGTTTGGAGTTTCCTCATTTATGTC-3′. Droplets were generated from each reaction and consisted of 10 μl droplet digital PCR probe Supermix, 900 nM primers, 250 nM probe and template cDNA or gDNA in a final volume of 20 μl using a droplet generator. PCR was performed using an S1000 thermal cycler (Bio-Rad). The cycling conditions were as follows: 10 min at 95 °C, 30 s denaturation at 94 °C, 58 °C extension for 60 s, and 10 min at 98 °C for a total of 40 cycles. After the cycling, droplets were analyzed immediately or stored at 4 °C overnight and until analysis. Raw data were analyzed with the specific software (QX200) by setting a common fixed fluorescence threshold intensity based on non-template control (NTC). The number of template copies was then estimated based on the number of positives detected in a corresponding channel and the number of total accepted droplets. Samples were quantified in duplicate and the analysis repeated two or three times. Template copies per sample were calculated averaging the overall replicate wells per sample. We estimated the total number of cells from the concentration of gDNA input as described previously .
Quantification of HIV-1 integration by real time PCR
A two step PCR amplification was performed using DNA extracted from tissues as template. The primers, probes and cycling conditions described in a previous study were used . A serial dilution of U1 cells with a known concentration of DNA was also included and used to generate standard curve for quantification.
Cell cultures, virus infections and ART drugs
For in vitro ART studies, HFM, BMDMs or adult PBMCs were infected and allowed to replicate in the presence or absence of ART drugs [38, 57]. Primary HFM were isolated from 16 to 20 week fetal brain tissues, as previously described . Briefly, fetal brain tissues were dissected, meninges were removed, and a single cell suspension was prepared through enzymatic digestion with 0.25% trypsin and 0.2 mg/ml DNase I for 60 min at 37 °C in a water bath. This was followed by passage through a 70-μm cell strainer. The cells were washed twice and plated in vented Cell+ T-75 tissue culture flasks (Sarstedt) and cultures were incubated at 5% CO2 for two weeks. Cultures were maintained in MEM supplemented with 10% FBS, 2 mM l-glutamine, 1 mM sodium pyruvate, 1 × MEM nonessential amino acids, 0.1% dextrose, 100 U/ml Penicillin, 100 μg/ml streptomycin. After 2 weeks, cultures were gently rocked for 10 min to suspend the weakly adhering microglia in medium, which were then decanted, washed and plated. Purity of cultures was verified by immunofluorescence . BMDMs were isolated from 16 to 20 week fetal femurs. Briefly, using a 5 ml syringe each femur was drilled and flushed with DMEM into a tube. The cell suspension was then incubated with ACK lysis buffer to remove red blood cells, washed and centrifuged twice. The cell pellets were re-suspended in DMEM (10% FBS) containing 25 ng/ml of macrophage colony stimulating factor (M-CSF), transferred into a six well culture plate and incubated at 37 °C and 10% CO2. Cell culture medium was replaced every 3 days and macrophages were harvested on Day 7. Human THP-1 cells were cultured in RPMI (10% FBS) and differentiated for 72 h with PMA (50 nM) . After exposure to PMA, cells were washed with PBS and fresh medium without PMA was added and incubation continued for another 48 h before use. PBMCs were isolated from healthy donors using the Ficoll-Paque (Sigma) density gradient separation, stimulated with phytohemagglutinin-P (Sigma) for 3 days at 5 μg/ml and re-suspended at 3.5 × 106 cells/ml in RPMI 1640 supplemented with 10% heat-inactivated FBS, 1% penicillin/streptomycin, 1% glutamine and 1% recombinant human IL-2 at which time cells were infected. Viruses were produced by transfection of 16 μg of HIV-1 YU-2 plasmid into HEK293T cells using Lipofectamine 2000 (Invitrogen, Carlsbad, CA). Two days after transfection, supernatants from transfected cells were harvested and centrifuged at 1500 rpm for 10 min to remove cellular debris, filtered through a 0.22-μm-pore-size filter, and stored in aliquots at − 80 °C. Virus production was confirmed by HIV-1 p24 ELISA . For in vitro ART studies, HFM or BMDMs (5 × 104) were seeded into 96-well plates. Plates were incubated at 37 °C and 5% CO2 overnight to allow cells to adhere to the bottom of the plate and infected the following day for 4 h at 37° C and 5% CO2 at a multiplicity of infection (MOI) of 0.1 for 4 h and washed (×3). For HIV-1 replication, supernatant was collected at pre-defined time points post-infection. A total of 250 μl of diluted drug at different concentrations was added to each well post-infection and incubated for 5 days. On Day 5 post-infection, supernatants were collected for HIV-1 p24 quantification by ELISA. For PBMCs infections, cells were infected with HIV-1 YU-2 for 2 h (MOI 0.05), washed and re-suspended with fresh medium and 125 μl of cell suspension containing 250,000 cells were seeded into each well of a 96-well plate. Diluted drugs (125 μl) at different concentrations were added to each well post-infection. On day 4 post-infection supernatant was collected for HIV-1 p24 quantification.
AZT, ETR, RAL and DRV were obtained from the NIH AIDS Research and Reference Reagent Program. Additional RAL and DRV used for animal studies were purchased (Cedarlane or Sigma respectively).
Immunofluorescence and immunocytochemistry studies
Cultured fetal HFM, BMDMs and fixed brains were immunolabeled with specific antibodies as described previously [57, 67]. Briefly, fetal HFM and BMDMs were seeded into an 8-well chamber µ-slide (Ibidi, DE). Cells were fixed (4% PFA) for 20 min. and immunolabeled with antibodies to Iba-1 (rabbit pAb 1:250, Wako) or MHC II (Mouse mAb, 1:300, Dako) over night. After washes with PBS, cells were incubated with anti-rabbit (AlexaFluor 647 nm, red) and anti-mouse (AlexaFluor 488 nm, green) (1:250, Life Technologies) antibodies. Cell nuclei were stained with DAPI (1:100, ImmunoChemistry Technologies) for 15 min. An Olympus IX-81 confocal microscope (Quorum Technologies) was used to capture the images. Fixed brains from uninfected [–] and HIV-infected [+] BLT mice were paraffin-embedded followed by sectioning and mounting. Slides were rehydrated and subjected to antigen retrieval by boiling in 10 mM sodium citrate, pH6 before immunostaining. Tissues were labeled with primary antibodies [anti-hCD68 (Abcam), −hCD3ε (Millipore), anti-HIV-1 p24 (NIH AIDS reagents #530) and GFAP (Dako)] followed by application of appropriate secondary antibodies .
ART concentration measurements
RAL and DRV were injected intraperitoneally into adult mice (8–12 months old) at a concentration of 1.2 mg per animal in a total of 4 animals per group and the subsequent drug concentrations were measured in blood, liver and brain. Animals were sacrificed at 1, 4, 8 or 24 h post-drug administration and whole blood, liver and brain (cortex, striatum, cerebellum, medulla and hypothalamus) were harvested and the concentrations of RAL and DRV were measured using HPLC–MS after homogenizing in 80% methanol, centrifuging, and running the supernatants through Oasis HLB Prime uelution plates followed by elution of the drugs. A similar procedure was used for analysis of RAL concentrations in human brain.
One-way ANOVA (Kruskal–Wallis test) with multiple comparisons was used to analyze in vitro and in vivo experiments. Statistical tests were applied using GraphPad Prism version 5 (GraphPad Software, San Diego California USA, www.graphpad.com). Results are expressed as mean ± SEM. p values < 0.05 were considered significant.
ELA and CP designed the experiments and wrote the paper; ELA, OM, MKM, WFC, WGB, and GBB performed all experiments and analyzed results; LR provided and analysed brain tissues from Pt-1 and Pt-2; MAW provided Dolutegravir; MJG and CP administered ART and clinical follow up of patients; EH and JVG generated the BLT mice; EAC supervised the BLT mice experiments. All authors read and approved the final manuscript.
The expert technical assistance of Ms. Gail Rauw is gratefully acknowledged. The authors also thank Dr. Walter Hader for providing surgical brain samples as well as the patients and their families for their willingness to participate in the present studies. The authors thank Merck and Gilead for supplying antiretroviral drugs for the in vivo animal studies. The authors dedicate this paper to our colleague and co-author, Dr. Mark Wainberg, who died unexpectedly while this manuscript was being prepared.
The following co-authors have no conflict of interest; Eugene L. Asahchop, Oussama Meziane, Manmeet K. Mamik, Wing F. Chan, William G. Branton, Lothar Resch, Jean V. Guimond, Mark A. Wainberg, Glen B Baker, Eric A. Cohen, Christopher Power. However, Dr. Elie Haddad is a consultant for SigmaTau, and has received investigator initiated grants from CSL-Behring. Dr. M John Gill has served as an ad hoc member of National HIV advisory boards to Merck, Gilead and ViiV in last 3 years.
Availability of data and materials
All data generated or analysed during this study are included in this published article (and its additional files).
Consent for publication
The use of autopsied brain tissues for research has been approved (Pro00002291) by the University of Alberta Human Research Ethics Board. The University of Alberta Ethics Board has also approved the use of animals in research.
Ethics approval and consent to participate
Brain tissue from two HIV-1 seropositive patients and uninfected (n = 6) seronegative patients were obtained by autopsy or biopsy with informed consent. Fetal tissue used to generate BLT mice was obtained after written informed consent (ethical committee of CHU Sainte-Justine, CER#2126). Human fetal tissues were obtained from 15 to 20 week aborted fetuses with the written informed consent of the patient (Pro00027660) approved by the University of Alberta Human Research Ethics Board. All animal experiments were performed according to the Canadian Council on Animal Care and local animal care and use committee guidelines.
Sources of funding
The Canadian Institutes of Health Research (CIHR), Canada Foundation for Innovation (CFI), Alberta Innovates-Health Solution (AIHS), University of Alberta Hospital Foundation, University of Alberta Vice President of Research Office.
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- Koenig S, Gendelman HE, Orenstein JM, Dal Canto MC, Pezeshkpour GH, Yungbluth M, et al. Detection of AIDS virus in macrophages in brain tissue from AIDS patients with encephalopathy. Science. 1986;233:1089–93.View ArticlePubMedGoogle Scholar
- Elovaara I, Iivanainen M, Valle SL, Suni J, Tervo T, Lahdevirta J. CSF protein and cellular profiles in various stages of HIV infection related to neurological manifestations. J Neurol Sci. 1987;78:331–42.View ArticlePubMedGoogle Scholar
- Antinori A, Giancola ML, Grisetti S, Soldani F, Alba L, Liuzzi G, et al. Factors influencing virological response to antiretroviral drugs in cerebrospinal fluid of advanced HIV-1-infected patients. AIDS. 2002;16:1867–76.View ArticlePubMedGoogle Scholar
- Vivithanaporn P, Heo G, Gamble J, Krentz HB, Hoke A, Gill MJ, et al. Neurologic disease burden in treated HIV/AIDS predicts survival: a population-based study. Neurology. 2010;75:1150–8.View ArticlePubMedPubMed CentralGoogle Scholar
- Van Marle G, Rourke SB, Zhang K, Silva C, Ethier J, Gill MJ, et al. HIV dementia patients exhibit reduced viral neutralization and increased envelope sequence diversity in blood and brain. AIDS. 2002;16:1905–14.View ArticlePubMedGoogle Scholar
- McCombe JA, Vivithanaporn P, Gill MJ, Power C. Predictors of symptomatic HIV-associated neurocognitive disorders in universal health care. HIV Med. 2013;14:99–107.View ArticlePubMedGoogle Scholar
- Maingat F, Halloran B, Acharjee S, van Marle G, Church D, Gill MJ, et al. Inflammation and epithelial cell injury in AIDS enteropathy: involvement of endoplasmic reticulum stress. FASEB J. 2011;25:2211–20.View ArticlePubMedPubMed CentralGoogle Scholar
- Avalos CR, Price SL, Forsyth ER, Pin JN, Shirk EN, Bullock BT, et al. Quantitation of productively infected monocytes and macrophages of simian immunodeficiency virus-infected macaques. J Virol. 2016;90:5643–56.View ArticlePubMedPubMed CentralGoogle Scholar
- Honeycutt JB, Wahl A, Baker C, Spagnuolo RA, Foster J, Zakharova O, et al. Macrophages sustain HIV replication in vivo independently of T cells. J Clin Investig. 2016;126:1353–66.View ArticlePubMedPubMed CentralGoogle Scholar
- Koyanagi Y, Itoyama Y, Nakamura N, Takamatsu K, Kira J, Iwamasa T, et al. In vivo infection of human T-cell leukemia virus type I in non-T cells. Virology. 1993;196:25–33.View ArticlePubMedGoogle Scholar
- Pang S, Koyanagi Y, Miles S, Wiley C, Vinters HV, Chen IS. High levels of unintegrated HIV-1 DNA in brain tissue of AIDS dementia patients. Nature. 1990;343:85–9.View ArticlePubMedGoogle Scholar
- Cobos Jimenez V, Booiman T, de Taeye SW, van Dort KA, Rits MA, Hamann J, et al. Differential expression of HIV-1 interfering factors in monocyte-derived macrophages stimulated with polarizing cytokines or interferons. Sci Rep. 2012;2:763.View ArticlePubMedPubMed CentralGoogle Scholar
- Dimitrov DS, Norwood D, Stantchev TS, Feng Y, Xiao X, Broder CC. A mechanism of resistance to HIV-1 entry: inefficient interactions of CXCR4 with CD4 and gp120 in macrophages. Virology. 1999;259:1–6.View ArticlePubMedGoogle Scholar
- Pauls E, Jimenez E, Ruiz A, Permanyer M, Ballana E, Costa H, et al. Restriction of HIV-1 replication in primary macrophages by IL-12 and IL-18 through the upregulation of SAMHD1. J Immunol. 2013;190:4736–41.View ArticlePubMedGoogle Scholar
- Micci L, Alvarez X, Iriele RI, Ortiz AM, Ryan ES, McGary CS, et al. CD4 depletion in SIV-infected macaques results in macrophage and microglia infection with rapid turnover of infected cells. PLoS Pathog. 2014;10:e1004467.View ArticlePubMedPubMed CentralGoogle Scholar
- Askew K, Li K, Olmos-Alonso A, Garcia-Moreno F, Liang Y, Richardson P, et al. Coupled proliferation and apoptosis maintain the rapid turnover of microglia in the adult brain. Cell Rep. 2017;18:391–405.View ArticlePubMedPubMed CentralGoogle Scholar
- Kugathasan R, Collier DA, Haddow LJ, El Bouzidi K, Edwards SG, Cartledge JD, et al. Diffuse white matter signal abnormalities on magnetic resonance imaging are associated with human immunodeficiency virus type 1 viral escape in the central nervous system among patients with neurological symptoms. Clin Infect Dis. 2017;64:1059–65.View ArticlePubMedPubMed CentralGoogle Scholar
- Zink MC, Brice AK, Kelly KM, Queen SE, Gama L, Li M, et al. Simian immunodeficiency virus-infected macaques treated with highly active antiretroviral therapy have reduced central nervous system viral replication and inflammation but persistence of viral DNA. J Infect Dis. 2010;202:161–70.View ArticlePubMedPubMed CentralGoogle Scholar
- Lamers SL, Rose R, Maidji E, Agsalda-Garcia M, Nolan DJ, Fogel GB, et al. HIV DNA is frequently present within pathologic tissues evaluated at autopsy from combined antiretroviral therapy-treated patients with undetectable viral loads. J Virol. 2016;90:8968–83.View ArticlePubMedPubMed CentralGoogle Scholar
- Honeycutt JB, Thayer WO, Baker CE, Ribeiro RM, Lada SM, Cao Y, et al. HIV persistence in tissue macrophages of humanized myeloid-only mice during antiretroviral therapy. Nat Med. 2017;23:638–43.View ArticlePubMedGoogle Scholar
- Watkins BA, Dorn HH, Kelly WB, Armstrong RC, Potts BJ, Michaels F, et al. Specific tropism of HIV-1 for microglial cells in primary human brain cultures. Science. 1990;249:549–53.View ArticlePubMedGoogle Scholar
- Brinkmann R, Schwinn A, Narayan O, Zink C, Kreth HW, Roggendorf W, et al. Human immunodeficiency virus infection in microglia: correlation between cells infected in the brain and cells cultured from infectious brain tissue. Ann Neurol. 1992;31:361–5.View ArticlePubMedGoogle Scholar
- Ghorpade A, Nukuna A, Che M, Haggerty S, Persidsky Y, Carter E, et al. Human immunodeficiency virus neurotropism: an analysis of viral replication and cytopathicity for divergent strains in monocytes and microglia. J Virol. 1998;72:3340–50.PubMedPubMed CentralGoogle Scholar
- Calcagno A, Cusato J, Simiele M, Motta I, Audagnotto S, Bracchi M, et al. High interpatient variability of raltegravir CSF concentrations in HIV-positive patients: a pharmacogenetic analysis. J Antimicrob Chemother. 2014;69:241–5.View ArticlePubMedGoogle Scholar
- Calcagno A, Yilmaz A, Cusato J, Simiele M, Bertucci R, Siccardi M, et al. Determinants of darunavir cerebrospinal fluid concentrations: impact of once-daily dosing and pharmacogenetics. AIDS. 2012;26:1529–33.View ArticlePubMedGoogle Scholar
- Croteau D, Letendre S, Best BM, Ellis RJ, Breidinger S, Clifford D, et al. Total raltegravir concentrations in cerebrospinal fluid exceed the 50-percent inhibitory concentration for wild-type HIV-1. Antimicrob Agents Chemother. 2010;54:5156–60.View ArticlePubMedPubMed CentralGoogle Scholar
- Croteau D, Rossi SS, Best BM, Capparelli E, Ellis RJ, Clifford DB, et al. Darunavir is predominantly unbound to protein in cerebrospinal fluid and concentrations exceed the wild-type HIV-1 median 90% inhibitory concentration. J Antimicrob Chemother. 2013;68:684–9.View ArticlePubMedGoogle Scholar
- Yilmaz A, Watson V, Else L, Gisslen M. Cerebrospinal fluid maraviroc concentrations in HIV-1 infected patients. AIDS. 2009;23:2537–40.View ArticlePubMedGoogle Scholar
- Yilmaz A, Gisslen M, Spudich S, Lee E, Jayewardene A, Aweeka F, et al. Raltegravir cerebrospinal fluid concentrations in HIV-1 infection. PLoS ONE. 2009;4:e6877.View ArticlePubMedPubMed CentralGoogle Scholar
- van Praag RM, van Weert EC, van Heeswijk RP, Zhou XJ, Sommadossi JP, Jurriaans S, et al. Stable concentrations of zidovudine, stavudine, lamivudine, abacavir, and nevirapine in serum and cerebrospinal fluid during 2 years of therapy. Antimicrob Agents Chemother. 2002;46:896–9.View ArticlePubMedPubMed CentralGoogle Scholar
- Tiraboschi JM, Niubo J, Vila A, Perez-Pujol S, Podzamczer D. Etravirine concentrations in CSF in HIV-infected patients. J Antimicrob Chemother. 2012;67:1446–8.View ArticlePubMedGoogle Scholar
- Tiraboschi JM, Niubo J, Curto J, Podzamczer D. Maraviroc concentrations in cerebrospinal fluid in HIV-infected patients. J Acquir Immune Defic Syndr. 2010;55:606–9.View ArticlePubMedGoogle Scholar
- Foudraine NA, Hoetelmans RM, Lange JM, de Wolf F, van Benthem BH, Maas JJ, et al. Cerebrospinal-fluid HIV-1 RNA and drug concentrations after treatment with lamivudine plus zidovudine or stavudine. Lancet. 1998;351:1547–51.View ArticlePubMedGoogle Scholar
- Nguyen A, Rossi S, Croteau D, Best BM, Clifford D, Collier AC, et al. Etravirine in CSF is highly protein bound. J Antimicrob Chemother. 2013;68:1161–8.View ArticlePubMedPubMed CentralGoogle Scholar
- Croteau D, Best BM, Letendre S, Rossi SS, Ellis RJ, Clifford DB, et al. Lower than expected maraviroc concentrations in cerebrospinal fluid exceed the wild-type CC chemokine receptor 5-tropic HIV-1 50% inhibitory concentration. AIDS. 2012;26:890–3.View ArticlePubMedPubMed CentralGoogle Scholar
- Letendre SL, Mills AM, Tashima KT, Thomas DA, Min SS, Chen S, et al. ING116070: a study of the pharmacokinetics and antiviral activity of dolutegravir in cerebrospinal fluid in HIV-1-infected, antiretroviral therapy-naive subjects. Clin Infect Dis. 2014;59:1032–7.View ArticlePubMedPubMed CentralGoogle Scholar
- Sturdevant CB, Joseph SB, Schnell G, Price RW, Swanstrom R, Spudich S. Compartmentalized replication of R5 T cell-tropic HIV-1 in the central nervous system early in the course of infection. PLoS Pathog. 2015;11:e1004720.View ArticlePubMedPubMed CentralGoogle Scholar
- Walsh JG, Reinke SN, Mamik MK, McKenzie BA, Maingat F, Branton WG, et al. Rapid inflammasome activation in microglia contributes to brain disease in HIV/AIDS. Retrovirology. 2014;11:35.View ArticlePubMedPubMed CentralGoogle Scholar
- Cunyat F, Rainho JN, West B, Swainson L, McCune JM, Stevenson M. CSF-1R antagonists sensitize HIV-1-infected macrophages to TRAIL-mediated killing. J Virol. 2016;90(14):6255–62.View ArticleGoogle Scholar
- Lamers SL, Rose R, Maidji E, Agsalda-Garcia M, Nolan DJ, Fogel GB, et al. HIV DNA is frequently present within pathologic tissues evaluated at autopsy from cART-treated patients with undetectable viral load. J Virol. 2016;90(20):8968–83.View ArticlePubMedPubMed CentralGoogle Scholar
- Gelman BB, Lisinicchia JG, Morgello S, Masliah E, Commins D, Achim CL, et al. Neurovirological correlation with HIV-associated neurocognitive disorders and encephalitis in a HAART-era cohort. J Acquir Immune Defic Syndr. 2013;62(5):487–95.View ArticlePubMedPubMed CentralGoogle Scholar
- Damouche A, Lazure T, Avettand-Fenoel V, Huot N, Dejucq-Rainsford N, Satie AP, et al. Adipose tissue is a neglected viral reservoir and an inflammatory site during chronic HIV and SIV infection. PLoS Pathog. 2015;11:e1005153.View ArticlePubMedPubMed CentralGoogle Scholar
- Bruner KM, Murray AJ, Pollack RA, Soliman MG, Laskey SB, Capoferri AA, et al. Defective proviruses rapidly accumulate during acute HIV-1 infection. Nat Med. 2016;22:1043–9.View ArticlePubMedPubMed CentralGoogle Scholar
- Suspene R, Meyerhans A. Quantification of unintegrated HIV-1 DNA at the single cell level in vivo. PLoS ONE. 2012;7:e36246.View ArticlePubMedPubMed CentralGoogle Scholar
- Teo I, Veryard C, Barnes H, An SF, Jones M, Lantos PL, et al. Circular forms of unintegrated human immunodeficiency virus type 1 DNA and high levels of viral protein expression: association with dementia and multinucleated giant cells in the brains of patients with AIDS. J Virol. 1997;71:2928–33.PubMedPubMed CentralGoogle Scholar
- Burdo TH, Gartner S, Mauger D, Wigdahl B. Region-specific distribution of human immunodeficiency virus type 1 long terminal repeats containing specific configurations of CCAAT/enhancer-binding protein site II in brains derived from demented and nondemented patients. J Neurovirol. 2004;10(Suppl 1):7–14.View ArticlePubMedGoogle Scholar
- Gray LR, Cowley D, Welsh C, Lu HK, Brew BJ, Lewin SR, et al. CNS-specific regulatory elements in brain-derived HIV-1 strains affect responses to latency-reversing agents with implications for cure strategies. Mol Psychiatry. 2016;21:574–84.View ArticlePubMedGoogle Scholar
- Kure K, Weidenheim KM, Lyman WD, Dickson DW. Morphology and distribution of HIV-1 gp41-positive microglia in subacute AIDS encephalitis. Pattern of involvement resembling a multisystem degeneration. Acta Neuropathol. 1990;80:393–400.View ArticlePubMedGoogle Scholar
- Osman N, Mesplede T, Quashie PK, Oliveira M, Zanichelli V, Wainberg MA. Dolutegravir maintains a durable effect against HIV replication in tissue culture even after drug washout. J Antimicrob Chemother. 2015;70:2810–5.View ArticlePubMedPubMed CentralGoogle Scholar
- Scopelliti F, Pollicita M, Ceccherini-Silberstein F, Di Santo F, Surdo M, Aquaro S, et al. Comparative antiviral activity of integrase inhibitors in human monocyte-derived macrophages and lymphocytes. Antivir Res. 2011;92:255–61.View ArticlePubMedGoogle Scholar
- Gray LR, Tachedjian G, Ellett AM, Roche MJ, Cheng WJ, Guillemin GJ, et al. The NRTIs lamivudine, stavudine and zidovudine have reduced HIV-1 inhibitory activity in astrocytes. PLoS ONE. 2013;8:e62196.View ArticlePubMedPubMed CentralGoogle Scholar
- Gates TM, Cysique LA, Siefried KJ, Chaganti J, Moffat KJ, Brew BJ. Maraviroc-intensified combined antiretroviral therapy improves cognition in virally suppressed HIV-associated neurocognitive disorder. AIDS. 2016;30:591–600.View ArticlePubMedGoogle Scholar
- Martin-Blondel G, Brassat D, Bauer J, Lassmann H, Liblau RS. CCR5 blockade for neuroinflammatory diseases—beyond control of HIV. Nat Rev Neurol. 2016;12:95–105.View ArticlePubMedGoogle Scholar
- Kelly KM, Beck SE, Pate KAM, Queen SE, Dorsey JL, Adams RJ, et al. Neuroprotective maraviroc monotherapy in simian immunodeficiency virus-infected macaques: reduced replicating and latent SIV in the brain. AIDS. 2013;27:F21–8.View ArticlePubMedPubMed CentralGoogle Scholar
- Tiraboschi JM, Munoz-Moreno JA, Puertas MC, Alonso-Villaverde C, Prats A, Ferrer E, et al. Viral and inflammatory markers in cerebrospinal fluid of patients with HIV-1-associated neurocognitive impairment during antiretroviral treatment switch. HIV Med. 2015;16:388–92.View ArticlePubMedGoogle Scholar
- Liu FC, Tsai YF, Yu HP. Maraviroc attenuates trauma-hemorrhage-induced hepatic injury through PPAR gamma-dependent pathway in rats. PLoS ONE. 2013;8:e78861.View ArticlePubMedPubMed CentralGoogle Scholar
- Mamik MK, Asahchop EL, Chan WF, Zhu Y, Branton WG, McKenzie BA, et al. Insulin treatment prevents neuroinflammation and neuronal injury with restored neurobehavioral function in models of HIV/AIDS neurodegeneration. J Neurosci. 2016;36:10683–95.View ArticlePubMedGoogle Scholar
- Fletcher CV, Staskus K, Wietgrefe SW, Rothenberger M, Reilly C, Chipman JG, et al. Persistent HIV-1 replication is associated with lower antiretroviral drug concentrations in lymphatic tissues. Proc Natl Acad Sci USA. 2014;111:2307–12.View ArticlePubMedPubMed CentralGoogle Scholar
- Lorenzo-Redondo R, Fryer HR, Bedford T, Kim EY, Archer J, Kosakovsky Pond SL, et al. Persistent HIV-1 replication maintains the tissue reservoir during therapy. Nature. 2016;530:51–6.View ArticlePubMedPubMed CentralGoogle Scholar
- Arainga M, Su H, Poluektova LY, Gorantla S, Gendelman HE. HIV-1 cellular and tissue replication patterns in infected humanized mice. Sci Rep. 2016;6:23513.View ArticlePubMedPubMed CentralGoogle Scholar
- Letendre SL, Ellis RJ, Ances BM, McCutchan JA. Neurologic complications of HIV disease and their treatment. Top HIV Med. 2010;18:45–55.PubMedPubMed CentralGoogle Scholar
- Dave VP, Hajjar F, Dieng MM, Haddad E, Cohen EA. Efficient BST2 antagonism by Vpu is critical for early HIV-1 dissemination in humanized mice. Retrovirology. 2013;10:128.View ArticlePubMedPubMed CentralGoogle Scholar
- Branton WG, Ellestad KK, Maingat F, Wheatley BM, Rud E, Warren RL, et al. Brain microbial populations in HIV/AIDS: alpha-proteobacteria predominate independent of host immune status. PLoS ONE. 2013;8:e54673.View ArticlePubMedPubMed CentralGoogle Scholar
- Bosman KJ, Nijhuis M, van Ham PM, Wensing AM, Vervisch K, Vandekerckhove L, et al. Comparison of digital PCR platforms and semi-nested qPCR as a tool to determine the size of the HIV reservoir. Sci Rep. 2015;5:13811.View ArticlePubMedPubMed CentralGoogle Scholar
- Yu JJ, Wu TL, Liszewski MK, Dai J, Swiggard WJ, Baytop C, et al. A more precise HIV integration assay designed to detect small differences finds lower levels of integrated DNA in HAART treated patients. Virology. 2008;379:78–86.View ArticlePubMedPubMed CentralGoogle Scholar
- Mamik MK, Hui E, Branton WG, McKenzie BA, Chisholm J, Cohen EA, et al. HIV-1 Viral Protein R Activates NLRP3 Inflammasome in Microglia: implications for HIV-1 Associated Neuroinflammation. J Neuroimmune Pharmacol. 2017;12(2):233–48.View ArticlePubMedGoogle Scholar
- Branton WG, Lu JQ, Surette MG, Holt RA, Lind J, Laman JD, et al. Brain microbiota disruption within inflammatory demyelinating lesions in multiple sclerosis. Sci Rep. 2016;6:37344.View ArticlePubMedPubMed CentralGoogle Scholar