FGF receptor inhibitor BGJ398 partially rescues osteoarthritis-like phenotype in older high molecular weight FGF2 transgenic mice via multiple mechanisms.

We have used Basic Fibroblast Growth Factor (FGF2) transgenic mice as experimental models for human X-linked hypophosphatemia (XLH)-related degenerative osteoarthritis (OA) to investigate the pathogenesis of the disease and to test potential pharmacotherapies for treatment. This study tested the efficacy of BJG398, a small molecule fibroblast growth factor receptor tyrosine kinase (FGFRTK) inhibitor, to rescue the knee joint osteoarthritis phenotype in High Molecular Weight fibroblast growth factor 2 transgenic (HMWTgFGF2) mice. BJG398 was administered in vivo to 8-month-old female HMWTgFGF2 mice for six weeks. Histomorphometry, immunohistochemistry and micro-CT were used to examine the knee joints in BGJ398-treated and control mice. We assessed: Fibroblast Growth Factor 23 (FGF23) expression and FGFR1 activity; Matrix metalloproteinase 13 (MMP13) and Aggrecanase2 (ADAMTS5) expression; then signaling by SMAD1/5/8-pSMAD6, pERK1/2 and Runt-related transcription factor 2 (RUNX2). Using PrimePCR arrays, we identified a contributing role for major target genes in the TGFB/BMP2 signaling pathway that were regulated by BGJ398. BGJ398 inhibited HMWFGF2/FGF23-induced increase in bone morphogenic protein receptor-1, bone morphogenic protein-2 and 4 and Serine peptidase inhibitor, clade E, member 1. The results from Micro-CT and histology show BGJ398 treatment rescued the OA changes in subchondral bone and knee articular cartilage of HMWTgFGF2 mice. The gene expression and signal transduction results provide convincing evidence that HMWFGF2 generates OA through FGFRTK with characteristic downstream signaling that defines OA, namely: increased FGF23-FGFR1 activity with BMP-BMPR, activation of pSMAD1/5/8-RUNX2 and pERK signaling pathways, then upregulation of MMP13 and ADAMTS5 to degrade matrix. BGJ398 treatment effectively reversed these OA molecular phenotypes, providing further evidence that the OA generated by HMWFGF2 in the transgenic mice is FGFR-mediated and phenocopies the OA found in the Hyp mouse homolog of XLH with a spontaneous mutation in the Phex (phosphate regulating endopeptidase on the X chromosome) gene and human XLH-OA. Overall, the results obtained here explain how the pleotropic effects of FGF2 emanate from the different functions of HMW protein isoforms for cartilage and bone homeostasis, and the pathogenesis of XLH-degenerative osteoarthropathy. BGJ398 inhibits HMWFGF2-induced osteoarthritis via multiple mechanisms. These results provided important scientific evidence for the potential application of BGJ398 as a therapeutic agent for osteoarthritis in XLH.

Western Australian adolescent emotional wellbeing during the COVID-19 pandemic in 2020.

BACKGROUND: The impacts of the COVID-19 pandemic have been vast and are not limited to physical health. Many adolescents have experienced disruptions to daily life, including changes in their school routine and family's financial or emotional security, potentially impacting their emotional wellbeing. In low COVID-19 prevalence settings, the impact of isolation has been mitigated for most young people through continued face-to-face schooling, yet there may still be significant impacts on their wellbeing that could be attributed to the pandemic. METHODS: We report on data from 32,849 surveys from Year 7-12 students in 40 schools over two 2020 survey cycles (June/July: 19,240; October: 13,609), drawn from a study of 79 primary and secondary schools across Western Australia, Australia. The Child Health Utility Index (CHU9D) was used to measure difficulties and distress in responding secondary school students only. Using comparable Australian data collected six years prior to the pandemic, the CHU9D was calibrated against the Kessler-10 to establish a reliable threshold for CHU9D-rated distress. RESULTS: Compared to 14% of responding 12-18-year-olds in 2013/2014, in both 2020 survey cycles almost 40% of secondary students returned a CHU9D score above a threshold indicative of elevated difficulties and distress. Student distress increased significantly between June and October 2020. Female students, those in older Grades, those with few friendships or perceived poor quality friendships, and those with poor connectedness to school were more likely to score above the threshold. CONCLUSIONS: In a large dataset collected during the first year of the COVID-19 pandemic, the proportion of secondary school students with scores indicative of difficulties and distress was substantially higher than a 2013/2014 benchmark, and distress increased as the pandemic progressed, despite the low local prevalence of COVID-19. This may indicate a general decline in social and emotional wellbeing exacerbated by the events of the pandemic. TRIAL REGISTRATION: ANZCTRN (ACTRN12620000922976). Retrospectively registered 17/08/2020. https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=380429&isReview=true .

Erratum: Azimuthal Anisotropy of K_{S}

This corrects the article DOI: 10.1103/PhysRevLett.89.132301.

Erratum: Azimuthal Anisotropy at the Relativistic Heavy Ion Collider: The First and Fourth Harmonics [Phys. Rev. Lett. 92, 062301 (2004)].

This corrects the article DOI: 10.1103/PhysRevLett.92.062301.

Qualitative study of psychosocial factors impacting on Aboriginal women's management of chronic disease.

BACKGROUND: Aboriginal women are frequently called upon to support their families and other community members. At times, such supporting roles can be burdensome for these women. Many Aboriginal women live with chronic conditions. We explored the ways in which the women's caring roles impacted on how they maintained their own health. METHODS: The aim of this manuscript is to explore the psychosocial factors associated with the management of health and chronic disease in Aboriginal women. An interpretive phenomenological approach was used for the analysis of 72 in-depth semi-structured interviews. These interviews were conducted in four community controlled Aboriginal health services, in urban, rural and remote settings, across two states and a territory in Australia. RESULTS: Women living with chronic disease experience multiple challenges while caring for family, such as intergenerational trauma, mental health issues relating to addiction, domestic and family violence and incarceration. When these women become ill, they also have to take care of themselves. These women provided informal and unfunded care in response to a range of complex family and community problems. This continuous caring for family affected the women's ability to maintain their health and manage their own chronic conditions. CONCLUSION: The caring roles and responsibilities Aboriginal women have in their community impact on their health. Aboriginal women provide much needed refuge and support to family and the wider community. Underfunded and over-burdened formal support services are not meeting the needs of many Aboriginal women. Improved culturally secure resources and social services are required within communities to support Aboriginal women to successfully manage their own health.

Fibroblast Growth Factor 2 and Its Receptors in Bone Biology and Disease.

The fibroblast growth factor (FGF) regulatory axis is phylogenetically ancient, evolving into a large mammalian/human gene family of 22 ligands that bind to four receptor tyrosine kinases for a complex physiologic system controlling cell growth, differentiation, and metabolism. The tissue targets for the primary FGF function are mainly in cartilage and in bone for morphogenesis, mineralization, and metabolism. A multitude of complexities in the FGF ligand-receptor signaling pathways have made translation into therapies for FGF-related bone disorders such as osteomalacia, osteoarthritis, and osteoporosis difficult but not impossible.

Missing voices: Profile and extent of acquired communication disorders in Aboriginal and non-Aboriginal adult stroke survivors in Western Australia using linked administrative records.

BACKGROUND: Limited data exist on the extent of specific functional sequelae, including acquired communication disorder, among Aboriginal stroke survivors, making planning of multidisciplinary services difficult. AIMS: To obtain estimates of the extent and profile of acquired communication disorder in Aboriginal and non-Aboriginal adult stroke survivors in Western Australia and investigate potential disparities in receiving in-hospital speech pathology services among survivors with acquired communication disorder. METHODS: Stroke cases surviving their first stroke episode during 2002-2011 were identified using Western Australia-wide person-based linked hospital and mortality data, and their five-year comorbidity profiles determined. The mid-year prevalence of stroke cases with acquired communication disorder was estimated for 2011. Regression methods were used to investigate determinants of receiving speech pathology services among acquired communication disorder cases. RESULTS: Of 14,757 stroke survivors aged 15-79 years admitted in 2002-2011, 33% had acquired communication disorder (22% aphasia/dysphasia) and 777 (5.3%) were Aboriginal. Aboriginal patients were more likely to be younger, live remotely, and have comorbidities. A diagnosis of aphasia was more common in Aboriginal than non-Aboriginal patients 15-44 years (p = 0.003). A minimum of 107 Aboriginal and 2324 non-Aboriginal stroke patients with acquired communication disorder lived in Western Australia in 2011. Aboriginal status was not associated with receiving in-hospital speech services among acquired communication disorder patients in unadjusted or adjusted models. CONCLUSIONS: The relative youth, geographical distribution, high comorbidity prevalence, and cultural needs of Aboriginal stroke patients with acquired communication disorder should inform appropriate service design for speech pathology and rehabilitation. Innovative models are required to address workforce issues, given low patient volumes.

HIV latency. Specific HIV integration sites are linked to clonal expansion and persistence of infected cells.

The persistence of HIV-infected cells in individuals on suppressive combination antiretroviral therapy (cART) presents a major barrier for curing HIV infections. HIV integrates its DNA into many sites in the host genome; we identified 2410 integration sites in peripheral blood lymphocytes of five infected individuals on cART. About 40% of the integrations were in clonally expanded cells. Approximately 50% of the infected cells in one patient were from a single clone, and some clones persisted for many years. There were multiple independent integrations in several genes, including MKL2 and BACH2; many of these integrations were in clonally expanded cells. Our findings show that HIV integration sites can play a critical role in expansion and persistence of HIV-infected cells.

BMP-2 differentially modulates FGF-2 isoform effects in osteoblasts from newborn transgenic mice.

We previously generated separate lines of transgenic mice that specifically overexpress either the Fibroblast growth factor (FGF)-2 low-molecular-mass isoform (Tg(LMW)) or the high-mass isoforms (Tg(HMW)) in the osteoblast lineage. Vector/control (Tg(Vector)) mice were also made. Here we report the use of isolated calvarial osteoblasts (COBs) from those mice to investigate whether the FGF-2 protein isoforms differentially modulate bone formation in vitro. Our hypothesis states that FGF-2 isoforms specifically modulate bone morphogenetic protein 2 (BMP-2) function and subsequently bone differentiation genes and their related signaling pathways. We found a significant increase in alkaline phosphatase-positive colonies in Tg(LMW) COBs compared with Tg(Vector) controls. BMP-2 treatment significantly increased mineralized colonies in Tg(Vector) and Tg(LMW) COBs. BMP-2 caused a further significant increase in mineralized colonies in Tg(LMW) COBs compared with Tg(Vector) COBs but did not increase alkaline phosphatase-positive colonies in Tg(HMW) COBs. Time-course studies showed that BMP-2 caused a sustained increase in phosphorylated mothers against decapentaplegic-1/5/8 (Smad/1/5/8), runt-related transcription factor-2 (Runx-2), and osterix protein in Tg(LMW) COBs. BMP-2 caused a sustained increase in phospho-p38 MAPK in Tg(Vector) but only a transient increase in Tg(LMW) and Tg(HMW) COBs. BMP-2 caused a transient increase in phospho-p44/42 MAPK in Tg(Vector) COBs and no increase in Tg(LMW) COBs, but a sustained increase was found in Tg(HMW) COBs. Basal expression of FGF receptor 1 protein was significantly increased in Tg(LMW) COBs relative to Tg(Vector) COBs, and although BMP-2 caused a transient increase in FGF receptor 1 expression in Tg(Vector) COBs and Tg(HMW) COBs, there was no further increase Tg(LMW) COBs. Interestingly, although basal expression of FGF receptor 2 was similar in COBs from all genotypes, BMP-2 treatment caused a sustained increase in Tg(LMW) COBs but decreased FGF receptor 2 in Tg(Vector) COBs and Tg(HMW) COBs.

Administration of vorinostat disrupts HIV-1 latency in patients on antiretroviral therapy.

Despite antiretroviral therapy, proviral latency of human immunodeficiency virus type 1 (HIV-1) remains a principal obstacle to curing the infection. Inducing the expression of latent genomes within resting CD4(+) T cells is the primary strategy to clear this reservoir. Although histone deacetylase inhibitors such as suberoylanilide hydroxamic acid (also known as vorinostat, VOR) can disrupt HIV-1 latency in vitro, the utility of this approach has never been directly proven in a translational clinical study of HIV-infected patients. Here we isolated the circulating resting CD4(+) T cells of patients in whom viraemia was fully suppressed by antiretroviral therapy, and directly studied the effect of VOR on this latent reservoir. In each of eight patients, a single dose of VOR increased both biomarkers of cellular acetylation, and simultaneously induced an increase in HIV RNA expression in resting CD4(+) cells (mean increase, 4.8-fold). This demonstrates that a molecular mechanism known to enforce HIV latency can be therapeutically targeted in humans, provides proof-of-concept for histone deacetylase inhibitors as a therapeutic class, and defines a precise approach to test novel strategies to attack and eradicate latent HIV infection directly.

'I am absolutely shattered': the impact of chronic low back pain on Australian Aboriginal people.

BACKGROUND: Aboriginal people in Australia have been uniquely identified as less susceptible to chronic low back pain (CLBP) disability when compared to non-Aboriginal populations, reportedly due to cultural beliefs about pain. A qualitative, culturally secure research approach was used to explore this assumption. METHODS: In-depth interviews were undertaken with 32 Aboriginal men and women with CLBP in regional and remote areas of Western Australia. Interviews were conducted collaboratively with male and female Aboriginal co-investigators, and with the support of local Aboriginal community organizations. A primary focus was to investigate the impact of CLBP from the perspective of Aboriginal people living with the condition. RESULTS: The experience of CLBP was found to be multidimensional, impacting on activities of daily life, employment, sport and family participation, emotional and cultural well-being. CONCLUSIONS: Contrary to previous assumptions, CLBP is profoundly disabling for some Aboriginal people and a priority health concern. Issues of gender, cultural obligations and the emotional consequences of CLBP are important consideration for health care. These findings, and the contextual approach used to gain an in-depth understanding of CLBP, may be relevant to populations elsewhere.

HIV reservoirs and the possibility of a cure for HIV infection.

Recent studies demonstrate that suppressive therapy can drive HIV-1 RNA levels to less than 50 copies mL(-1) in patient plasma. Yet, ultrasensitive assays show that most patients continue to harbour low-level persistent viremia. Treatment intensification studies indicate that low-level viremia could arise from several different sources. These sources include: (i) long-lived HIV-infected cells that replicate and produce virus; (ii) ongoing replication cycles in cells located in sanctuary sites where drug levels are suboptimal; and/or (iii) proliferation of latently infected cells with regeneration of a stable reservoir of slowly dividing infected cells. A well-defined latent reservoir of HIV is memory CD4+ T-cells where latency is established when an activated CD4+ T-cell becomes infected by HIV, but transitions to a terminally differentiated memory cell before it is eliminated. This review examines the dynamics and possible reservoirs of persistent HIV in patients on suppressive therapy, the mechanisms promoting viral latency and strategies to purge latent viral reservoirs. The promising research described here takes a number of steps forward to seriously address HIV remission and/or eradication.

Prevalence of XMRV nucleic acid and antibody in HIV-1-Infected men and in men at risk for HIV-1 Infection.

Xenotropic MLV-Related Virus (XMRV) was recently reported to be associated with prostate cancer and chronic fatigue syndrome (CFS). Infection was also reported in 3.7% of healthy individuals. These highly reported frequencies of infection prompted concerns about the possibility of a new, widespread retroviral epidemic. The Multicenter AIDS Cohort Study (MACS) provides an opportunity to assess the prevalence of XMRV infection and its association with HIV-1 infection among men who have sex with men. Reliable detection of XMRV infection requires the application of multiple diagnostic methods, including detection of human antibodies to XMRV and detection of XMRV nucleic acid. We, therefore, tested 332 patient plasma and PBMC samples obtained from recent visits in a subset of patients in the MACS cohort for XMRV antibodies using Abbott prototype ARCHITECT chemiluminescent immunoassays (CMIAs) and for XMRV RNA and proviral DNA using a XMRV single-copy qPCR assay (X-SCA). Although 9 of 332 (2.7%) samples showed low positive reactivity against a single antigen in the CMIA, none of these samples or matched controls were positive for plasma XMRV RNA or PBMC XMRV DNA by X-SCA. Thus, we found no evidence of XMRV infection among men in the MACS regardless of HIV-1 serostatus.

Nucleic Acid, Antibody, and Virus Culture Methods to Detect Xenotropic MLV-Related Virus in Human Blood Samples.

The MLV-related retrovirus, XMRV, was recently identified and reported to be associated with both prostate cancer and chronic fatigue syndrome. At the National Cancer Institute-Frederick, MD (NCI-Frederick), we developed highly sensitive methods to detect XMRV nucleic acids, antibodies, and replication competent virus. Analysis of XMRV-spiked samples and/or specimens from two pigtail macaques experimentally inoculated with 22Rv1 cell-derived XMRV confirmed the ability of the assays used to detect XMRV RNA and DNA, and culture isolatable virus when present, along with XMRV reactive antibody responses. Using these assays, we did not detect evidence of XMRV in blood samples (N = 134) or prostate specimens (N = 19) from two independent cohorts of patients with prostate cancer. Previous studies detected XMRV in prostate tissues. In the present study, we primarily investigated the levels of XMRV in blood plasma samples collected from patients with prostate cancer. These results demonstrate that while XMRV-related assays developed at the NCI-Frederick can readily measure XMRV nucleic acids, antibodies, and replication competent virus, no evidence of XMRV was found in the blood of patients with prostate cancer.

Disruption of the Fgf2 gene activates the adipogenic and suppresses the osteogenic program in mesenchymal marrow stromal stem cells.

Here we determine the Fibroblast Growth Factor-2 (FGF2) dependency of the time course of changes in bone mass in female mice. This study extends our earlier reports that knockout of the FGF2 gene (Fgf2) caused low turnover bone loss in Fgf2(-/-) male mice by examining bone loss with age in Fgf2(-/-) female mice, and by assessing whether reduced bone formation is associated with differentiation of bone marrow stromal cells (BMSCs) towards the adipocyte lineage. Bone mineral density (BMD) was similar in 3-month-old female Fgf2(+/+) and Fgf2(-/-) mice but was significantly reduced as early as 5 months of age in Fgf2(-/-) mice. In vivo studies showed that there was a greater accumulation of marrow fat in long bones of 14 and 20 month old Fgf2(-/-) mice compared with Fgf2(+/+) littermates. To study the effect of disruption of FGF2 on osteoblastogenesis and adipogenesis, BMSCs from both genotypes were cultured in osteogenic or adipogenic media. Reduced alkaline phosphatase positive (ALP), mineralized colonies and a marked increase in adipocytes were observed in Fgf2(-/-) BMSC cultures. These cultures also showed an increase in the mRNA of the adipogenic transcription factor PPARgamma2 as well as the downstream target genes aP2 and adiponectin. Treatment with exogenous FGF2 blocked adipocyte formation and increased ALP colony formation and ALP activity in BMSC cultures of both genotypes. These results support an important role for endogenous FGF2 in osteoblast (OB) lineage determination. Alteration in FGF2 signaling may contribute to impaired OB bone formation capacity and to increased bone marrow fat accumulation both of which are characteristics of aged bone.

The influence of FGF2 high molecular weight (HMW) isoforms in the development of cardiac ischemia-reperfusion injury.

Fibroblast growth factor 2 (FGF2) consists of multiple protein isoforms (low [LMW] and high molecular weight [HMW]), which are localized to different cellular compartments, indicating unique biological activity. We previously showed that the LMW isoform is important in protecting the heart from myocardial dysfunction associated with ischemia-reperfusion (I/R) injury, but the roles of the HMW isoforms remain unknown. To elucidate the role of HMW isoforms in I/R and cardioprotection, hearts from novel mouse models, in which the murine FGF2 HMWs are knocked out (HMWKO) or the human FGF2 24 kDa HMW isoform is overexpressed (HMW Tg) and their wildtype (Wt) or non-transgenic (NTg) cohorts were subjected to an ex vivo work-performing heart model of I/R. There was a significant improvement in post-ischemic recovery of cardiac function in HMWKO hearts (76+/-5%, p<0.05) compared to Wt hearts (55+/-5%), with a corresponding decrease in HMW Tg function (line 20: 38+/-6% and line 28: 33+/-4%, p<0.05) compared to non-transgenic hearts (68+/-9%). FGF2 LMW isoform was secreted from Wt and HMWKO hearts during I/R, and a FGF receptor (FGFR) inhibitor, PD173074 caused a decrease in cardiac function when administered in I/R in Wt and FGF2 HMWKO hearts (p<0.05), indicating that FGFR is involved in FGF2 LMW isoform's biological effect in ischemia-reperfusion injury. Moreover, overexpression of HMW isoform reduced FGFR1 phosphorylation/activation with no further decrease in the phosphorylation state in the presence of the FGFR inhibitor. Overall, our data indicate that HMW isoforms have a detrimental role in the development of post-ischemic myocardial dysfunction.

Short-course raltegravir intensification does not reduce persistent low-level viremia in patients with HIV-1 suppression during receipt of combination antiretroviral therapy.

BACKGROUND: Combination antiretroviral therapy suppresses but does not eradicate human immunodeficiency virus type 1 (HIV-1) in infected persons, and low-level viremia can be detected despite years of suppressive antiretroviral therapy. Short-course (28-day) intensification of standard antiretroviral combination therapy is a useful approach to determine whether complete rounds of HIV-1 replication in rapidly cycling cells contribute to persistent viremia. We investigated whether intensification with the integrase inhibitor raltegravir decreases plasma HIV-1 RNA levels in patients receiving suppressive antiretroviral therapy. METHODS: Subjects (n = 10) with long-term HIV-1 suppression receiving combination antiretroviral regimens had their regimens intensified for 4 weeks with raltegravir. Plasma HIV-1 RNA level was determined before, during, and after the 4-week intensification period, using a sensitive assay (limit of detection, 0.2 copies of HIV-1 RNA/mL of plasma). A 4-week intensification course was chosen to investigate potential HIV-1 replication in cells with relatively short (approximately 1-14-day) half-lives. RESULTS: There was no evidence in any subject of a decline in HIV-1 RNA level during the period of raltegravir intensification or of rebound after discontinuation. Median levels of HIV-1 RNA before (0.17 log10 copies/mL), during (0.04 log10 copies/mL), and after (0.04 log10 copies/mL) raltegravir intensification were not significantly different (P > .1 for all comparisons in parametric analyses). High-performance liquid chromatography and mass spectroscopy experiments confirmed that therapeutic levels of raltegravir were achieved in plasma during intensification. CONCLUSIONS: Intensification of antiretroviral therapy with a potent HIV-1 integrase inhibitor did not decrease persistent viremia in subjects receiving suppressive regimens, indicating that rapidly cycling cells infected with HIV-1 were not present. Eradication of HIV-1 from infected persons will require new therapeutic approaches. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT00618371.

Nuclear isoforms of fibroblast growth factor 2 are novel inducers of hypophosphatemia via modulation of FGF23 and KLOTHO.

FGF2 transgenic mice were developed in which type I collagen regulatory sequences drive the nuclear high molecular weight FGF2 isoforms in osteoblasts (TgHMW). The phenotype of TgHMW mice included dwarfism, decreased bone mineral density (BMD), osteomalacia, and decreased serum phosphate (P(i)). When TgHMW mice were fed a high P(i) diet, BMD was increased, and dwarfism was partially reversed. The TgHMW phenotype was similar to mice overexpressing FGF23. Serum FGF23 was increased in TgHMW mice. Fgf23 mRNA in bones and fibroblast growth factor receptors 1c and 3c and Klotho mRNAs in kidneys were increased in TgHMW mice, whereas the renal Na(+)/P(i) co-transporter Npt2a mRNA was decreased. Immunohistochemistry and Western blot analyses of TgHMW kidneys showed increased KLOTHO and decreased NPT2a protein. The results suggest that overexpression of HMW FGF2 increases FGF23/FGFR/KLOTHO signaling to down-regulate NPT2a, causing P(i) wasting, osteomalacia, and decreased BMD. We assessed whether HMW FGF2 expression was altered in the Hyp mouse, a mouse homolog of the human disease X-linked hypophosphatemic rickets/osteomalacia. Fgf2 mRNA was increased in bones, and Western blots showed increased FGF2 protein in nuclear fractions from osteoblasts of Hyp mice. In addition, immunohistochemistry demonstrated co-localization of FGF23 and HMW FGF2 protein in osteoblasts and osteocytes from Hyp mice. This study reveals a novel mechanism of regulation of the FGF23-P(i) homeostatic axis.

Interpreting the effect of vaccination on steady state infection in animals challenged with Simian immunodeficiency virus.

A representative vaccinated macaque challenged with SIVmac251 establishes a persistent infection with a lower virus load, higher CTL frequencies, and much higher helper cell frequencies, than a representative control animal. The reasons for the difference are not fully understood. Here we interpret this effect using a mathematical model we developed recently to explain results of various experiments on virus and CTL dynamics in SIV-infected macaques and HIV-infected humans. The model includes two types of cytotoxic lymphocytes (CTLs) regulated by antigen-activated helper cells and directly by infected cells, respectively, and predicts the existence of two steady states with different viremia, helper cell and CTL levels. Depending on the initial level of CTL memory cells and helper cells, a representative animal ends up in either the high-virus state or the low-virus state, which accounts for the observed differences between the two animal groups. Viremia in the low-virus state is proportional to the antigen sensitivity threshold of helper cells. Estimating the infectivity ratio of activated and resting CD4 T cells at 200-300, the correct range for the critical memory cell percentage and the viremia peak suppression is predicted. However, the model does not explain why viremia in the "low-virus state" is surprisingly high , relative to vaccinated animals infected with SHIV, and broadly distributed among challenged animals. We conclude that the model needs an update explaining extremely low sensitivity of uninfected helper cells to antigen in vaccinated animals.

Treatment intensification does not reduce residual HIV-1 viremia in patients on highly active antiretroviral therapy.

In HIV-1-infected individuals on currently recommended antiretroviral therapy (ART), viremia is reduced to <50 copies of HIV-1 RNA per milliliter, but low-level residual viremia appears to persist over the lifetimes of most infected individuals. There is controversy over whether the residual viremia results from ongoing cycles of viral replication. To address this question, we conducted 2 prospective studies to assess the effect of ART intensification with an additional potent drug on residual viremia in 9 HIV-1-infected individuals on successful ART. By using an HIV-1 RNA assay with single-copy sensitivity, we found that levels of viremia were not reduced by ART intensification with any of 3 different antiretroviral drugs (efavirenz, lopinavir/ritonavir, or atazanavir/ritonavir). The lack of response was not associated with the presence of drug-resistant virus or suboptimal drug concentrations. Our results suggest that residual viremia is not the product of ongoing, complete cycles of viral replication, but rather of virus output from stable reservoirs of infection.