Low maternal viral loads and reduced granulocyte-macrophage colony-stimulating factor levels characterize exposed, uninfected infants who develop protective human immunodeficiency virus type 1-specific responses

Human immunodeficiency virus type 1 (HIV-1)-specific cellular immune responses are elicited in a proportion of infants born to HIV-1-infected mothers and are associated with protection against vertical transmission. To investigate correlates of these HIV-1-specific responses, we examined levels of the immune activation markers neopterin, beta(2)-microglobulin (beta(2)-m), and soluble l-selectin (sl-selectin); the immunomodulatory and hematopoietic factors interleukin-7 (IL-7), stromal-cell-derived factor 1 alpha (CXCL12), and granulocyte-macrophage colony-stimulating factor (GM-CSF); and the immunoregulatory cytokine IL-10 among a group of newborns born to HIV-1-positive mothers who did not receive any antiretroviral drugs for prevention of perinatal HIV-1 transmission. Cellular immune responses to HIV-1 envelope (Env) peptides were also measured. We aimed to determine whether newborns who elicit HIV-1-specific cellular immune responses (Env(+)) and those who lack these responses (Env(-)) exhibit unique immune features. Our data confirmed that no Env(+) infants acquired HIV-1 infection. Among exposed, uninfected infants, Env(+) infants had reduced immune activation (as measured by beta(2)-m and sl-selectin levels in cord blood plasma) compared to Env(-) infants as well as reduced GM-CSF levels in cord blood plasma. There was also a reduced ability of cord blood mononuclear cells to be induced to produce GM-CSF among Env(+) infants. Maternal viral load was lower in Env(+) infants, suggesting that exposure to low levels of antigen may be responsible for priming the protective responses. These findings suggest that infants who are able to develop apparently protective HIV-1-specific cellular immune responses have immunological features and viral exposure histories that distinguish them from their nonresponder counterparts, providing new insights into the development of HIV-1 protective immunity.     

Comparison of mother-to-child transmission rates in Ugandan women with subtype A versus D HIV-1 who received single-dose nevirapine prophylaxis: HIV Network For Prevention Trials 012

OBJECTIVE: To compare the rate of mother-to-child transmission (MTCT) in women with subtype A versus D HIV-1 who received single-dose nevirapine (NVP). METHODS: The MTCT rates were compared in women with subtype A versus D at birth and at 8 weeks and 18 months of age of the infants. The rate of late MTCT (after 8 weeks of age) was also analyzed. RESULTS: HIV-1 subtypes were determined for 300 of 306 women who received NVP in the HIV Network for Prevention Trials 012 study (158 women with subtype A and 105 women with subtype D). Infant infection status was known for 297 women. The cumulative rate of MTCT at 18 months was 13.2% for subtype A and 18.3% for subtype D (P=0.34). The rate of late transmission was 3.8% for subtype A and 7.6% for subtype D (P=0.28). Maternal baseline viral load was a significant predictor of MTCT, but maternal baseline CD4 cell count and subtype were not. CONCLUSIONS: No significant difference was observed in the rate of MTCT in women with subtype A versus D. There was a trend toward a higher rate of MTCT among women with subtype D, however, which was also apparent among women whose infants were infected after 8 weeks of age.     

Activation of Toll-like receptor 2 increases macrophage resistance to HIV-1 infection

Patients infected with HIV-1, the etiological agent of AIDS, have increased intestinal permeability, which allows for the passage of microbial products, including Toll-like receptor (TLR) ligands, into circulation. The exposure of HIV-1-infected cells to certain TLR agonists affects viral replication, but studies associating viral production with the activation of TLR2 in HIV-1-infected cells are rare and controversial. Here, we report that the TLR2 ligands Zymosan and Pam3CSK4 potently inhibit HIV-1 replication in acutely infected monocyte-derived macrophages and the exposure to TLR2 ligands prior to infection renders macrophages refractory to HIV-1 production. Macrophage treatment with Pam3CSK4 did not change the cellular expression of the HIV-1 entry receptors CD4 and CCR5. Both TLR2 ligands increased the macrophage production of β-chemokines and IL-10, and the blockage of these soluble factors prevented the inhibitory effect of TLR2 activation on HIV-1 replication. Our findings show that the direct engagement of TLR2 in HIV-1-infected macrophages increase cellular resistance to HIV-1 infection, and that controlling HIV-1 replication with agonists for TLR2 might have implications for the development of antiretroviral therapies.     

Biological mechanisms of vertical human immunodeficiency virus (HIV-1) transmission

In the absence of interventions, 30-45% of exposed infants acquire human immunodeficiency virus type 1 (HIV-1) through mother-to-child transmission. It remains unclear why some infants become infected while others do not, despite significant exposure to HIV-1 in utero, during delivery and while breastfeeding. Here we discuss the correlates of vertical transmission with an emphasis on factors that increase maternal HIV-1 levels, either systemically or locally in genital secretions and breast milk. Immune responses may influence maternal viral load, and data suggest that maternal neutralising antibodies reduce infection rates. In addition, infants may be capable of mounting HIV-specific cellular immune responses. We propose that both humoral and cellular responses are necessary to reduce infection because cell-free as well as cell-associated virus appears to play a role in vertical transmission. These distinct forms of the virus may be targeted most effectively by different components of the immune system. We also discuss the use of antiretrovirals to reduce transmission, focusing on the mechanisms of action of regimens currently used in developing country settings. We conclude that prevention relies not only on reducing maternal HIV-1 levels within blood, genital tract and breast milk, but also on pre- and/or post-exposure prophylaxis to the infant. However, HIV-1 has the capacity to mutate under drug pressure and rapidly acquires mutations conferring antiretroviral resistance. This review concludes with data on persistence of low-level resistance after delivery as well as recent guidelines for maternal and infant regimens designed to limit resistance.     

Plasma levels of soluble CD27: a simple marker to monitor immune activation during potent antiretroviral therapy in HIV-1-infected subjects

Plasma levels of soluble CD27 (sCD27) are elevated in diseases characterized by T cell activation and are used as a marker of immune activation. We assessed the usefulness of determining plasma sCD27 as a marker for monitoring immune activation in HIV-1-infected patients treated with highly active antiretroviral therapy (HAART). A first cross-sectional examination of 68 HIV-1-infected and 18 normal subjects showed high levels of sCD27 in HIV-1 infection; plasma sCD27 was correlated to HIV-1 viraemia and inversely correlated to CD4+ T cell count. Twenty-six HIV-1-infected patients undergoing HAART were studied at baseline and after 6, 12, 18 and 24 months of therapy. Seven additional patients under HAART were analysed at baseline, during and after interruption of therapy. In the total population, HAART induced a significant and progressive reduction, but not a normalization, of plasma levels of sCD27 after 24 months. A full normalization of plasma sCD27 was observed in the virological responders (undetectable HIV-1 RNA at months 18 and 24) and also in patients with moderate immunodeficiency at baseline (CD4+ T cell count >200 cells/mm3). Changes in plasma neopterin paralleled the changes in sCD27 but only baseline sCD27 levels were predictive of a greater increase in CD4+ T cell count during the follow-up. Discontinuation of therapy resulted in a rapid increase of sCD27 plasma levels associated with viraemia rebound and drop in CD4+ T cell count. Our findings suggest that plasma sCD27 may represent an alternative and simple marker to monitor immune activation during potent antiretroviral therapy. HIV-1-induced immune activation can be normalized by HAART in successfully treated patients where the disease is not advanced.     

Children born to HIV-1-infected women in Sweden in 1982-2003: trends in epidemiology and vertical transmission

To describe the HIV-1 epidemic among childbearing women and their children in Sweden, a population-based analysis of data on all known mother-child pairs in Sweden with perinatal exposure to HIV-1 1982-2003 was conducted. The mother-to-child transmission (MTCT) rate in children prospectively followed from birth decreased from 24.7% in 1985-1993 to 5.7% in 1994-1998 and 0.6% in 1999-2003. The use of antiretroviral treatment of the mother during pregnancy and/or prophylactic antiretroviral intervention increased from 2.3% to 91.6% during the same period, and the elective cesarean delivery rate increased from 8.0% to 80.3%. No MTCT of HIV-1 occurred in Sweden after 1999.Fifty-one vertically HIV-1-infected children aged 2.7 to 17.6 years were living in Sweden by 31 December 2003, 71% being treated with antiretroviral agents. No HIV-1-related child death has been reported in Sweden after 1996. The conclusion is that MTCT of HIV-1 can be almost eliminated when appropriate resources are available. A national pregnancy screening program for HIV-1 running since 1987 with a high acceptance rate and the implementation of measures to prevent MTCT since 1994 have resulted in a significant decrease in the number of infected children. Inasmuch as knowledge of the infection status of the mother is crucial for reduction in MTCT of HIV-1, continued antenatal screening is important even in a low-prevalence country such as Sweden.     

Invariant NKT cells from HIV-1 or Mycobacterium tuberculosis-infected patients express an activated phenotype

The frequency, subsets and activation status of peripheral blood invariant NKT (iNKT) cells were evaluated in pulmonary tuberculosis (TB) patients and in chronically HIV-1-infected subjects. The absolute numbers of iNKT cells were significantly decreased in TB patients and in HIV-1+ individuals who were antiretroviral therapy naive or had detectable viremia despite receiving HAART. iNKT cell subset analysis demonstrated a decreased percentage of CD4(+) iNKT cells in HIV-1+ subjects, and a decreased percentage of double negative iNKT cells in TB patients. Peripheral blood iNKT cells from HIV-1+ and TB patients had significantly increased expression of CD69, CD38, HLA-DR, CD16, CD56, and CD62L. The expression of CD25 was significantly increased only on iNKT cells from TB patients. These findings indicate that peripheral blood iNKT cells in these two chronic infections show an up-regulated expression of activation markers, suggesting their role in the immune response to infection.     

HIV-1 reservoirs in breast milk and challenges to elimination of breast-feeding transmission of HIV-1

By compensating for the relative immaturity of the neonatal immune system, breast milk and breast-feeding prevent deaths in children. Nevertheless, transmission of HIV-1 through breast-feeding is responsible for more than half of new pediatric HIV infections. Recent studies of possible HIV-1 reservoirs in breast milk shed new light on features that influence HIV-1 transmission through breast-feeding. The particular characteristics of breast milk CD4(+) T cells that distinguish them from circulating blood lymphocytes (high frequency of cell activation and expression of memory and mucosal homing markers) facilitate the establishment of HIV-1 replication. Breast milk also contains a plethora of factors with anti-infectious, immunomodulatory, or anti-inflammatory properties that can regulate both viral replication and infant susceptibility. In addition, CD8(+) T lymphocytes, macrophages, and epithelial cells in breast milk can alter the dynamics of HIV-1 transmission. Even during efficient antiretroviral therapy, a residual stable, CD4(+) T cell-associated reservoir of HIV-1 is persistently present in breast milk, a likely source of infection. Only prophylactic treatment in infants--ideally with a long-acting drug, administered for the entire duration of breast-feeding--is likely to protect HIV-exposed babies against all forms of HIV transmission from breast milk, including cell-to-cell viral transfer.     

Combination antiretroviral strategies for the treatment of pregnant HIV-1-infected women and prevention of perinatal HIV-1 transmission

CONTEXT: The Women and Infants Transmission Study is a prospective natural history study that has been enrolling HIV-1-infected pregnant women and their infants since 1989. OBJECTIVE: To evaluate the impact of different antiretroviral regimens on perinatal HIV-1 transmission at the population level. DESIGN: Prospective cohort study. Plasma HIV-1 RNA levels were serially measured in 1542 HIV-1-infected women with singleton live births between January 1990 and June 2000. MAIN OUTCOME MEASURE: HIV-1 status of the infant. RESULTS: HIV-1 transmission was 20.0% (95% confidence interval [CI], 16.1%-23.9%) for 396 women who not receiving prenatal antiretroviral therapy; 10.4% (95% CI, 8.2%-12.6%) for 710 receiving zidovudine monotherapy; 3.8% (95% CI, 1.1%-6.5%) for 186 receiving dual antiretroviral therapy with no or one highly active drug (Multi-ART); and 1.2% (95% CI, 0-2.5%) for 250 receiving highly active antiretroviral therapy (HAART). Transmission also varied by maternal delivery HIV RNA level: 1.0% for <400; 5.3% for 400 to 3499; 9.3% for 3500 to 9999; 14.7% for 10,000 to 29,999; and 23.4% for >30,000 copies/mL (p =.0001 for trend). The odds of transmission increased 2.4-fold (95% CI, 1.7-3.5) for every log10 increase in delivery viral load. In multivariate analyses adjusting for maternal viral load, duration of therapy, and other factors, the odds ratio for transmission for women receiving Multi-ART and HAART compared with those receiving ZDV monotherapy was 0.30 (95% CI, 0.09-1.02) and 0.27 (95% CI, 0.08-0.94), respectively. CONCLUSION: Levels of HIV-1 RNA at delivery and prenatal antiretroviral therapy were independently associated with transmission. The protective effect of therapy increased with the complexity and duration of the regimen. HAART was associated with the lowest rates of transmission.     

Independent effects of nevirapine prophylaxis and HIV-1 RNA suppression in breast milk on early perinatal HIV-1 transmission

BACKGROUND: The mechanism of action of single-dose nevirapine on reducing mother-to-child transmission of HIV-1 may involve reduction of maternal HIV-1 or prophylaxis of infants. METHODS: In a study that randomized pregnant mothers to HIVNET 012 nevirapine versus short-course antenatal zidovudine, we compared breast milk HIV-1 RNA viral shedding and administration of single-dose nevirapine between mothers who transmitted HIV-1 to their infants at 6 weeks postpartum and those who did not. RESULTS: In multivariate analyses, maximum breast milk HIV-1 RNA levels (hazard ratio [HR] = 2.50, 95% confidence interval [CI]: 1.25 to 4.99; P = 0.01) and nevirapine use (HR = 0.12, 95% CI: 0.02 to 0.97; P = 0.05) were each independently associated with perinatal transmission at 6 weeks postpartum. Mothers who transmitted HIV-1 to their infants had significantly higher HIV-1 RNA levels in their breast milk between the second day and sixth week postpartum. Among mothers with maximum breast milk virus levels less than a median of 3.5 log(10) copies/mL, the administration of nevirapine further decreased HIV-1 transmission risk from 22.2% to 0.0% (P = 0.04). CONCLUSIONS: Peripartum administration of single-dose nevirapine to mother and infant decreases early perinatal HIV-1 transmission by means of breast milk HIV-1 RNA suppression and, independently, by providing the infant with exposure prophylaxis.     

HIV-1-induced neuronal injury in the developing brain

HIV-1 infection of the nervous system causes neuronal injury and death, resulting in cognitive, motor, and behavioral dysfunction in both adults and children. In infants a characteristic feature of HIV-1 infection is impaired brain growth resulting in secondary microcephaly with onset between 2 and 4 months of age. This post-natal period of brain development is particularly vulnerable to excitotoxic neuronal injury due to the active synaptogenesis and pruning that takes place at this age associated with over-expression of excitatory amino acid (EAA) receptors. HIV-1 infection of brain microglia and perivascular macrophages results in chronic inflammation manifest pathologically as diffuse microglial activation and reactive astrogliosis. Several inflammatory products of activated microglia, including tumor necrosis factor alpha (TNF-alpha) and platelet-activating factor (PAF) have been shown to act as neuronal toxins. This toxic effect can be antagonized by blocking NMDA (or AMPA) glutamate receptors, suggesting that (weak) excitotoxicity leads to oxidative stress, neuronal injury, and apoptosis. HIV-1 infection and chronic inflammation may also contribute disruption of the blood-brain barrier and could result in further entry into the CNS of toxic viral or cellular products or additional HIV-1-infected cells. We hypothesize that prolonged microglial activation during HIV-1 infection underlies the neuronal injury and impaired brain growth in affected infants. Further investigation of the interaction between HIV-1-infected/activated microglia and developing neurons seems warranted. The current understanding of HIV neuropathogenesis implies that therapeutic strategies should target the sustained immune activation in microglia, attempt to repair the integrity of the blood-brain barrier, and provide "neuroprotection" from excitotoxic neuronal injury.     

HIV-1 transmission in the male genital tract

HIV-1 is mainly a sexually transmitted infection, and epithelial surfaces covering genital mucosa are the primary site of HIV-1 transmission. Although male circumcision was reported to reduce male acquisition of HIV-1 by 60%, the initial mechanisms of HIV-1 transmission in the male genitals remain elusive. We established two novel models of the adult human foreskin epithelium that allowed for polarized infection via the mucosal pole with either HIV-1-infected cells that are present in all secretions vectorizing HIV-1 or cell-free HIV-1. Efficient HIV-1 transmission occurs following 1 hr of polarized exposure of the inner, but not outer, foreskin to mononuclear cells highly infected with HIV-1, but not to cell-free virus. HIV-1-infected cells form viral synapses with apical foreskin keratinocytes, leading to polarized budding of HIV-1, which is rapidly internalized by Langerhans cells (LCs) in the inner foreskin. In turn, LCs form conjugates with T-cells, thereby transferring HIV-1. Seminal plasma from HIV-negative men mixed with cervico-vaginal secretions from HIV-positive women, which mimics the in-vivo mixture of these genital fluids during woman-to-man HIV-1 sexual transmission, decreases HIV-1 infection at the foreskin. Our results rationalize at the cellular level the apparent protective outcome of circumcision against HIV-1 acquisition by men.     

Regulatory T cells and HIV-1 infection

Recently, it has been emphasized that chronic generalized immune activation is a leading event in the pathogenesis of HIV-1 infection. Supporting evidence comes from observations that in cases of lack of activation, infected subjects maintain a high number of T cells and do not develop AIDS-related events. Despite intensive studies, the exact mechanisms of T-cell activation are still not well understood and options for their control are limited. Very promising in this direction is a recently described T-cell subpopulation--regulatory T cells. Their functional activity and vitality are strongly dependent on the presence of IL-2. Better understanding of the mechanisms of T-cell activation, as well as the contribution of regulatory T cells to its control will increase therapeutic options for HIV-1-infected subjects. The application of immune-based therapy together with highly active antiretroviral therapy will lend a helping hand to the natural regulatory mechanisms in the control of infection.     

Hormonal contraception and HIV-1 transmission

Safe and effective contraceptive choices are essential for women with HIV-1 infection and at risk for HIV-1 infection. Epidemiological and laboratory-based studies suggest that hormonal contraception may influence HIV-1 transmission. Several large studies in high-risk populations indicate that hormonal contraceptive use may modestly increase the risk of HIV-1 acquisition. In addition, HIV-1-infected users of hormonal contraceptives may be more infectious to their uninfected partners, although no studies have directly measured HIV-1 transmission risk from women to men. However, several studies failed to demonstrate a link between contraceptive use and HIV-1 acquisition or transmission, and interpretation of many studies limited by methodological considerations, such as infrequent measurements of contraceptive exposure and HIV-1 status. As a result, many questions remain, and high-quality studies remain needed. It is clear that hormonal contraceptives are not protective against HIV-1 infection and that dual protection with condoms should be the goal for women using hormonal contraception.     

Effects of combined antiretroviral therapy on B- and T-cell release from production sites in long-term treated HIV-1+ patients

ABSTRACT: BACKGROUND: The immune system reconstitution in HIV-1- infected patients undergoing combined antiretroviral therapy is routinely evaluated by T-cell phenotyping, even though the infection also impairs the B-cell mediated immunity. To find new laboratory markers of therapy effectiveness, both B- and T- immune recovery were evaluated by means of a follow-up study of long-term treated HIV-1- infected patients, with a special focus on the measure of new B- and T-lymphocyte production. METHODS: A longitudinal analysis was performed in samples obtained from HIV-1-infected patients before therapy beginning and after 6, 12, and 72 months with a duplex real-time PCR allowing the detection of K-deleting recombination excision circles (KRECs) and T-cell receptor excision circles (TRECs), as measures of bone-marrow and thymic output, respectively. A cross sectional analysis was performed to detect B- and T-cell subsets by flow cytometry in samples obtained at the end of the follow-up, which were compared to those of untreated HIV-1-infected patients and uninfected controls. RESULTS: The kinetics and the timings of B- and T-cell release from the bone marrow and thymus during antiretroviral therapy were substantially different, with a decreased B-cell release and an increased thymic output after the prolonged therapy. The multivariable regression analysis showed that a longer pre-therapy infection duration predicts a minor TREC increase and a major KREC reduction. CONCLUSIONS: The quantification of KRECs and TRECs represent an improved method to monitor the effects of therapies capable of influencing the immune cell pool composition in HIV-1-infected patients.