Impact of maternal HIV-1 viremia on lymphocyte subsets among HIV-exposed uninfected infants: protective mechanism or immunodeficiency

Disturbances in the IgG Antibody Profile in HIV-Exposed Uninfected Infants Associated with Maternal Factors

Over the last 20 years, the incidence of vertical HIV transmission has decreased from 25%-42% to less than 1%. Although there are no signs of infection, the health of HIV-exposed uninfected (HEU) infants is notoriously affected during the first months of life, with opportunistic infections being the most common disease. Some studies have reported effects on the vertical transfer of antibodies, but little is known about the subclass distribution of these antibodies. We proposed to evaluate the total IgG concentration and its subclasses in HIV+ mothers and HEU pairs and to determine which maternal factors condition their levels. In this study, plasma from 69 HEU newborns, their mothers, and 71 control pairs was quantified via immunoassays for each IgG isotype. Furthermore, we followed the antibody profile of HEUs throughout the first year of life. We showed that mothers present an antibody profile characterized by high concentrations of IgG1 and IgG3 but reduced IgG2, and HEU infants are born with an IgG subclass profile similar to that of their maternal pair. Interestingly, this passively transferred profile could remain influenced even during their own antibody production in HEU infants, depending on maternal conditions such as CD4+ T-cell counts and maternal antiretroviral treatment. Our findings indicate that HEU infants exhibit an altered IgG subclass profile influenced by maternal factors, potentially contributing to their increased susceptibility to infections.

Haematopoietic stem-cell transplantation in an HIV endemic area: time to consider donors exposed to or living with HIV

South Africa has more than 8 million people living with HIV. However, the number of patients undergoing haematopoietic stem-cell transplantation (HSCT) in South Africa is far below the target number. Donor numbers are insufficient to meet demand. Both HSCT and solid organ transplantation have proved successful in people living with HIV. Solid organ transplantation also has good outcomes when both donors and recipients have HIV. This Personal View explores the possible inclusion of people living with HIV and umbilical cord blood from HIV-negative infants exposed to HIV as donor sources for HSCT. Beyond the risk of HIV transmission, additional complications must be considered, such as delayed or inadequate immune reconstitution and an increased risk of haematological abnormalities and malignancies. Interactions between antiretroviral drugs and drugs used in the conditioning regimen, as well as the need to maintain virological suppression when gastrointestinal absorption deteriorates, are additional complicating factors. The process also requires more stringent ethical processes to be in place to minimise physical and emotional harm. However, in an HIV endemic country, people living with HIV or donors exposed to HIV must be considered as part of a multidisciplinary collaborative effort to provide more patients with the opportunity to have a life-saving HSCT.

Human immunodeficiency virus and antiretroviral therapy-mediated immune cell metabolic dysregulation in children born to HIV-infected women: potential clinical implications

Commencing lifelong antiretroviral therapy (ART) immediately following HIV diagnosis (Option B+) has dramatically improved the health of HIV-infected women and their children, with the majority being of HIV-exposed children born uninfected (HEU). This success has led to an increasing population of HIV-infected women receiving ART during pregnancy and children exposed to ART in utero. Nonetheless, a small proportion of children are still infected with HIV (HEI) each year. HEI children suffer from reduced immunocompetence and host-defence, due to CD4+ T lymphocyte depletion, but also dysregulation of other immune cells including CD8+ T lymphocytes, natural killer (NK) cells, macrophages including B lymphocytes. Furthermore, although HEU children are uninfected, altered immune responses are observed and associated with increased vulnerability to infections. The mechanisms underlying immune dysregulation in HEU children remain poorly described. Building on early studies, emerging data suggests that HIV/ART exposure early in life affects cell metabolic function of HEU children. Prenatal HIV/ART exposure has been associated with dysregulation of mitochondria, including impaired DNA polymerase activity. Furthermore, dysregulation of oxidative phosphorylation (OXPHOS) causes a decreased generation of adenosine triphosphate (ATP) and increased production of reactive oxygen species (ROS), resulting in oxidative stress. These altered metabolic processes can affect immune cell viability and immune responses. Recent studies have indicated that immune-metabolic dysregulation may contribute to HIV-associated pathogenesis and clinical observations associated with HIV and ART exposure in HEU/HEI children. Given the critical role metabolic processes in immune cell functioning, immune-metabolic dysregulation in HEU and HEI children may have implications in effective host-defence responses against pathogens, as well as efficacy of standard ART regimens and future novel HIV cure approaches in HEI children. At the same time, targeting metabolic pathways of immune cells may provide safer and novel approaches for HIV cure strategies. Here, we review the current literature investigating immune-metabolic dysregulation in paediatric HIV pathogenesis.

Immune and Metabolic Alterations in Children with Perinatal HIV Exposure

With the global rollout of mother-to-child prevention programs for women living with HIV, vertical transmission has been all but eliminated in many countries. However, the number of children who are exposed in utero to HIV and antiretroviral therapy (ART) is ever-increasing. These children who are HIV-exposed-but-uninfected (CHEU) are now well recognized as having persistent health disparities compared to children who are HIV-unexposed-and-uninfected (CHUU). Differences reported between these two groups include immune dysfunction and higher levels of inflammation, cognitive and metabolic abnormalities, as well as increased morbidity and mortality in CHEU. The reasons for these disparities remain largely unknown. The present review focuses on a proposed link between immunometabolic aberrations and clinical pathologies observed in the rapidly expanding CHEU population. By drawing attention, firstly, to the significance of the immune and metabolic alterations observed in these children, and secondly, the impact of their healthcare requirements, particularly in low- and middle-income countries, this review aims to sensitize healthcare workers and policymakers about the long-term risks of in utero exposure to HIV and ART.

Immunopathogenesis in HIV-associated pediatric tuberculosis

Tuberculosis (TB) is an increasing global emergency in human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS) patients, in which host immunity is dysregulated and compromised. However, the pathogenesis and efficacy of therapeutic strategies in HIV-associated TB in developing infants are essentially lacking. Bacillus Calmette-Guerin vaccine, an attenuated live strain of Mycobacterium bovis, is not adequately effective, which confers partial protection against Mycobacterium tuberculosis (Mtb) in infants when administered at birth. However, pediatric HIV infection is most devastating in the disease progression of TB. It remains challenging whether early antiretroviral therapy (ART) could maintain immune development and function, and restore Mtb-specific immune function in HIV-associated TB in children. A better understanding of the immunopathogenesis in HIV-associated pediatric Mtb infection is essential to provide more effective interventions, reducing the risk of morbidity and mortality in HIV-associated Mtb infection in infants. IMPACT: Children living with HIV are more likely prone to opportunistic infection, predisposing high risk of TB diseases. HIV and Mtb coinfection in infants may synergistically accelerate disease progression. Early ART may probably induce immune reconstitution inflammatory syndrome and TB pathology in HIV/Mtb coinfected infants.

Impaired T helper cell responses in human immunodeficiency virus-exposed uninfected newborns

Introduction

HIV‐exposed uninfected (HEU) newborns suffer from higher risks of opportunistic infections during the first months of life compared to HIV‐unexposed uninfected (HUU) newborns. Alterations in thymic mass, amounts of T helper (Th) cells, T‐cell receptor diversity, and activation markers have been found in HEU newborns, suggesting alterations in T cell ontogeny and differentiation. However, little is known about the ability of these cells to produce specialized Th responses from CD4⁺ T cells.

Method

To characterize the Th cell profile, we evaluated the frequency of Th₁ (CD183⁺CD194⁻CD196⁻/CXCR3⁺CCR4⁻CCR6⁻), Th₂ (CD183⁻CD194⁺CD196⁻/CXCR3⁻CCR4⁺CCR6⁻), Th₁₇ (CD183⁻CD194⁺CD196⁺/CXCR3⁻CCR4⁺CCR6⁺), and CD4⁺CD25⁺⁺ blood T‐cell phenotypes in 50 HEU and 25 HUU newborns. Early activation markers on CD4⁺ T cells and the Th cytokine profile produced from mononuclear cells under polyclonal T cell stimulation were also studied. Additionally, we probed the ability of CD4⁺ T cells to differentiate into interferon (IFN)‐γ‐producing Th₁ CD4⁺ T cells in vitro.

Results

Lower percentages of differentiated Th₁, Th₂, Th_17, and CD4⁺CD25⁺⁺ T cells were found in blood from HEU newborns than in blood from HUU newborns. However, polyclonally stimulated Th cells showed a similar ability to express CD69 and CD279 but produced less secreted interleukin (IL)‐2 and IL‐4. Interestingly, under Th₁ differentiation conditions, the percentages of CD4⁺IFN‐γ⁺ T cells and soluble IFN‐γ were higher in HEU newborns than in HUU newborns.

Conclusion

HEU neonates are born with reduced proportions of differentiated Th₁/Th₂/Th₁₇ and CD4⁺CD25⁺⁺ T cells, but the intrinsic abilities of CD4⁺ T cells to acquire a Th₁ profile are not affected by the adverse maternal milieu during development.

T cell Homeostatic Imbalance in Placentae from Women with HIV in the absence of Vertical Transmission

BACKGROUND

Implementation of universal antiretroviral therapy (ART) has significantly lowered vertical transmission rates but has also increased numbers of HIV-exposed uninfected children (HEU), who remain vulnerable to morbidities. Here, we investigated whether T cell alterations in the placenta contribute to altered immune status in HEU.

METHODS

We analyzed T cells from term placentae decidua and villous tissue and paired cord blood from pregnant women with HIV (PWH) who initiated ART late in pregnancy (n=21) with pregnant women not living with HIV (PWNH) (n=9).

RESULTS

Placentae from PWH showed inverted CD4:CD8 ratios and higher proportions of tissue resident CD8+ T cells in villous tissue relative to control placentae. CD8+ T cells in the fetal capillaries, which were of fetal origin, positively correlated with maternal plasma viraemia prior to ART initiation, implying that imbalanced T cells persisted throughout pregnancy. Additionally, the expanded memory differentiation of CD8+ T cells was confined to the fetal placental compartment and cord blood but was not observed in the maternal decidua.

CONCLUSIONS

T cell homeostatic imbalance in the blood circulation of PWH is reflected in the placenta. The placenta may be a causal link between HIV-induced maternal immune changes during gestation and altered immunity in newborn infants in the absence of vertical transmission.

Mortality and Loss to Follow-Up Among HIV-Exposed Infants After Option B+ Guideline Implementation in Amhara Regional State Referral Hospitals, Ethiopia

Background: Prevention of mother-to-child transmission of HIV program (PMTCT) is a comprehensive approach that aimed for the wellbeing of all HIV-infected women, to prevent new HIV infection among infants born to HIV-positive mothers, and providing management for HIV-positive women and infants. Nevertheless, there was considerably high attrition within the prevention of mother-to-child transmission programs that was merely because of loss to follow-up (LTFU) followed by mortality. In resource-limited countries, one-third of infected children die before 1 year, and more than half of them die before 2 years. The aim of this study was to assess the prevalence or incidence of mortality and LTFU among infants born from HIV-positive mothers in the Amhara regional state referral hospitals, Ethiopia. Methods: This study was conducted in five Amhara regional state referral hospitals' prevention of mother-to-child transmission departments. A simple random sampling technique with proportional allocation was used to assess the outcomes of 221 exposed infants. A retrospective cohort design was used in selecting the 221 exposed infants' document from the referral hospitals of the region, Amhara. The exposed infants' profiles were documented between January 1, 2014 and May 30, 2017. Results: This study described attritions (death and loss-to-follow-up) of exposed babies in PMTCT departments of Amhara regional state referral hospitals in Ethiopia. In this study, low LTFU with zero death was reported. Residence, immunization status of babies, and place of delivery were independent factors of LTFU. Conclusions: The cumulative incidence of mortality in this study was zero. This assured that the recommended option is substantial for the elimination of HIV-caused death in 2030 as per WHO plan. However, the cumulative incidence of LTFU was not zero.

The University of Zimbabwe College of Health Sciences (UZ-CHS) BIRTH COHORT study: rationale, design and methods

BACKGROUND

Commencing lifelong antiretroviral therapy (ART) immediately following HIV diagnosis (Option B+), has greatly improved maternal-infant health. Thus, large and increasing numbers of HIV-infected women are on ART during pregnancy, a situation concurrently increasing numbers of HIV-exposed-uninfected (HEU) infants. Compared to their HIV-unexposed-uninfected (HUU) counterparts, HEU infants show higher rates of adverse birth outcomes, mortality, infectious/non-communicable diseases including impaired growth and neurocognitive development. There is an urgent need to understand the impact of HIV and early life ART exposures, immune-metabolic dysregulation, comorbidities and environmental confounders on adverse paediatric outcomes.

METHODS

Six hundred (600) HIV-infected and 600 HIV-uninfected pregnant women ≥20 weeks of gestation will be enrolled from four primary health centres in high density residential areas of Harare. Participants will be followed up as mother-infant-pairs at delivery, week(s) 1, 6, 10, 14, 24, 36, 48, 72 and 96 after birth. Clinical, socio-economic, nutritional and environmental data will be assessed for adverse birth outcomes, impaired growth, immune/neurodevelopment, vertical transmission of HIV, hepatitis-B/C viruses, cytomegalovirus and syphilis. Maternal urine, stool, plasma, cord blood, amniotic fluid, placenta and milk including infant plasma, dried blood spot and stool will be collected at enrolment and follow-up visits. The composite primary endpoint is stillbirth and infant mortality within the first two years of life in HEU versus HUU infants. Maternal mortality in HIV-infected versus -uninfected women is another primary outcome. Secondary endpoints include a range of maternal and infant outcomes. Sub-studies will address maternal stress and malnutrition, maternal-infant latent tuberculosis, Helicobacter pylori infections, immune-metabolomic dysregulation including gut, breast milk and amniotic fluid dysbiosis.

DISCUSSION

The University of Zimbabwe-College of Health-Sciences-Birth-Cohort study will provide a comprehensive assessment of risk factors and biomarkers for HEU infants' adverse outcomes. This will ultimately help developing strategies to mitigate effects of maternal HIV, early-life ART exposures and comorbidities on infants' mortality and morbidity.

TRIAL REGISTRATION

ClinicalTrial.gov Identifier: NCT04087239 . Registered 12 September 2019.

Influence of maternal HIV infection on fetal thymus size

Objective To reveal the effect of a maternal human immunodeficiency virus (HIV) infection on the fetal thymus size. Methods The sonographic fetal thymus size was measured retrospectively in 105 pregnancies with maternal HIV infection and in 615 uncomplicated singleton pregnancies. The anteroposterior thymic and the intrathoracic mediastinal diameter were determined in the three-vessel view and their quotient, the thymic-thoracic ratio (TT ratio), was calculated. The study group was subdivided into three groups by the maternal viral load on the date of ultrasound (<50 cop./mL, 50-1000 cop./mL, >1000 cop./mL). Furthermore, an association between prognostic factors of the HIV infection such as the lymphocyte count, CD4/CD8 ratio, HIV medication and the thymus size, was investigated using correlation analyses. Results Fetal thymus size in pregnancies of HIV-positive mothers showed to be noticeably larger than in uncomplicated pregnancies. The mean TT ratio in the HIV-positive group was 0.389 and in the control group 0.345 (P < 0.001). There was no association between any maternal HIV parameter or medication and the size of the thymus gland. Conclusion Maternal HIV infection was associated with an increased fetal thymus size. Further consequences of intrauterine HIV exposure for fetal outcome and the development of the immune system of HIV-exposed uninfected (HEU) infants must be discussed.

Immune Activation and Microbial Translocation Markers in HIV-Exposed Uninfected Malawian Infants in the First Year of Life

BACKGROUND

HIV-exposed uninfected (HEU) infants show a high rate of morbidity. We aimed to investigate on biomarkers of immune activation/microbial translocation in HEU infants, evaluating the impact that infections/malnutrition can have on biomarker levels during the first year of life.

METHODS

Clinical data of 72 Malawian infants were recorded monthly and correlated with levels of soluble CD14 (sCD14), lipopolysaccharide-binding protein (LBP) and intestinal fatty acid-binding protein (I-FABP), analyzed longitudinally.

RESULTS

Levels of sCD14 and LBP showed a significant age-related increase. Higher levels of LBP (19.4 vs. 15.2 μg/ml) were associated with stunting, affecting 30% of the infants. The association remained statistically significant after adjusting for cytomegalovirus acquisition, malaria and respiratory infections (p = 0.031). I-FABP levels were significantly increased in infants experiencing gastrointestinal infections (1442.8 vs. 860.0 pg/ml, p = 0.018).

CONCLUSION

We provide evidence that stunting is associated with an enhanced inflammatory response to microbial products in HEU children, suggesting that malnutrition status should be taken into consideration to better understand the alteration of the immune profile of HEU infants living in poor socioeconomic settings.

A Meta-analysis Assessing Diarrhea and Pneumonia in HIV-Exposed Uninfected Compared With HIV-Unexposed Uninfected Infants and Children

OBJECTIVE

Previous studies have demonstrated that HIV-exposed uninfected (HEU) infants and children experience morbidity and mortality at rates exceeding those of their HIV-unexposed uninfected (HUU) counterparts. We sought to summarize the association between HEU vs. HUU infants and children for the outcomes of diarrhea and pneumonia.

DESIGN

Meta-analysis.

METHODS

We reviewed studies comparing infants and children in the 2 groups for these infectious disease outcomes, in any setting, from 1993 to 2018 from 6 databases.

RESULTS

We included 12 studies, and 17,955 subjects total [n = 5074 (28.3%) HEU and n = 12,881 (71.7%) HUU]. Random-effects models showed HEU infants and children had a 20% increase in the relative risk of acute diarrhea and a 30% increase in the relative risk of pneumonia when compared with their HUU counterparts. When stratifying by time since birth, we showed that HEU vs. HUU children had a 50% and 70% increased risk of diarrhea and pneumonia, respectively, in the first 6 months of life.

CONCLUSIONS

We show an increased risk of diarrhea and pneumonia for HEU vs. HUU infants and children. Although we acknowledge, and commend, the immense public health success of prevention of mother-to-child transmission, we now have an enlarging population of children that seem to be vulnerable to not only death, but increased morbidity. We need to turn our attention to understanding the underlying mechanism and designing effective public health solutions. Further longitudinal research is needed to elucidate possible underlying immunological and/or sociological mechanisms that explain these differences in morbidity.

Analysis of the TCR Repertoire in HIV-Exposed but Uninfected Infants

Maternal human immunodeficiency virus (HIV) infection has been shown to leave profound and lasting impacts on the HIV-exposed uninfected (HEU) infant, including increased mortality and morbidity, immunological changes, and developmental delays compared to their HIV-unexposed (HU) counterparts. Exposure to HIV or antiretroviral therapy may influence immune development, which could increase morbidity and mortality. However, a direct link between the increased mortality and morbidity and the infant's immune system has not been identified. To provide a global picture of the neonatal T cell repertoire in HEU versus HU infants, the diversity of the T cell receptor beta chain (TRB) expressed in cord blood samples from HEU infants was determined using next-generation sequencing and compared to healthy (HU) infants collected from the same community. While the TRB repertoire of HU infants was broadly diverse, in line with the expected idea of a naïve T cell repertoire, samples of HEU infants showed a significantly reduced TRB diversity. This study is the first to demonstrate differences in TRB diversity between HEU and HU cord blood samples and provides evidence that maternal HIV, in the absence of transmission, influences the adaptive immune system of the unborn child.

HIV in pregnancy: Identification of intrapartum and perinatal HIV exposures

The benefits of human immunodeficiency virus (HIV) testing in pregnancy, when combined with appropriate maternal antiretroviral therapy and intrapartum and postnatal prophylaxis, are well established. The vertical rate of transmission of HIV in North America is now well below 2%. Efforts must continue to ensure that these benefits are sustained. Women who have received little or no prenatal care and those who present for delivery with unknown HIV status need immediate testing. As more infants are exposed to antiretroviral agents, strategies need to be implemented to ensure adequate follow-up of these infants. Issues relating to the identification of HIV-exposed infants are highlighted.

Social conditions and immune response in human immunodeficiency virus-seropositive pregnant women: a cross-sectional study in Brazil

INTRODUCTION

The functioning of the immune system during pregnancy is altered in both human immunodeficiency virus (HIV)-infected and uninfected women. Unfavorable socioeconomic conditions have been indicative of higher morbidity and mortality and worsening of the immune system. The aim of this study was to correlate social status with levels of interleukin (IL)-10 (non-inflammatory) and interferon-gamma (IFN-γ; inflammatory) cytokines.

METHODS

A cross-sectional study was conducted with three groups of women: 33 pregnant HIV-infected (G1); 40 non-pregnant, HIV-infected (G2); and 35 pregnant, HIV-uninfected. To measure the social status, a compound indicator called the social status index (SSI), was established using sociodemographic variables (i.e., education level, housing conditions, per capita income, and habitation and sanitary conditions).

RESULTS

The HIV-infected women had a higher proportion of unfavorable SSI (73% and 75% of G1 and G2, respectively). There were significantly lower IL-10 levels in the G1 group with both unfavorable and favorable SSI than in the other groups. No significant difference in IFN-γ levels was observed among groups. However, the G1 group had higher IFN-γ values among both favorable and unfavorable SSI groups.

CONCLUSIONS

Higher rates of unfavorable conditions, including lower education levels, IL-10 levels, and a trend for higher IFN-γ levels, were identified among HIV-infected women, pregnant and non-pregnant. These factors may interfere in health care and lead to poor outcomes during pregnancy. Therefore, we suggest that health policies could be created to specifically address these factors in this population.

B and T Cell Phenotypic Profiles of African HIV-Infected and HIV-Exposed Uninfected Infants: Associations with Antibody Responses to the Pentavalent Rotavirus Vaccine

We examined associations between B and T cell phenotypic profiles and antibody responses to the pentavalent rotavirus vaccine (RV5) in perinatally HIV-infected (PHIV) infants on antiretroviral therapy and in HIV-exposed uninfected (PHEU) infants enrolled in International Maternal Pediatric Adolescent AIDS Clinical Trials P1072 study (NCT00880698). Of 17 B and T cell subsets analyzed, PHIV and PHEU differed only in the number of CD4+ T cells and frequency of naive B cells, which were higher in PHEU than in PHIV. In contrast, the B and T cell phenotypic profiles of PHIV and PHEU markedly differed from those of geographically matched contemporary HIV-unexposed infants. The frequency of regulatory T and B cells (Treg, Breg) of PHIV and PHEU displayed two patterns of associations: FOXP3+ CD25+ Treg positively correlated with CD4+ T cell numbers; while TGFβ+ Treg and IL10+ Treg and Breg positively correlated with the frequencies of inflammatory and activated T cells. Moreover, the frequencies of activated and inflammatory T cells of PHIV and PHEU positively correlated with the frequency of immature B cells. Correlations were not affected by HIV status and persisted over time. PHIV and PHEU antibody responses to RV5 positively correlated with CD4+ T cell counts and negatively with the proportion of immature B cells, similarly to what has been previously described in chronic HIV infection. Unique to PHIV and PHEU, anti-RV5 antibodies positively correlated with CD4+/CD8+FOXP3+CD25+% and negatively with CD4+IL10+% Tregs. In conclusion, PHEU shared with PHIV abnormal B and T cell phenotypic profiles. PHIV and PHEU antibody responses to RV5 were modulated by typical HIV-associated immune response modifiers except for the association between CD4+/CD8+FOXP3+CD25+Treg and increased antibody production.

Maternal HIV infection is an important health determinant in non-HIV-infected infants

OBJECTIVE

To assess morbidity and mortality in HIV-exposed uninfected (HEU) children to help guiding appropriate clinical care and effective preventive interventions.

DESIGN

This is a longitudinal study comparing two cohorts of children; one born to HIV-infected women and the other born to HIV-uninfected women.

METHODS

We have analyzed prospectively obtained information on nutritional status, morbidity and mortality from 966 HEU and 909 HIV-unexposed infants followed up until their first 18 months of life at a referral health facility in southern Mozambique. Determinants for adverse health outcomes in HEU children were also assessed using multivariate logistic regression.

RESULTS

Increased incidence of hospital admissions (P = 0.0015), shorter survival in the first 18 months of life (P = 0.0510) and moderate and severe malnutrition (P = 0.0006 and 0.0014, respectively) were observed among HEU children compared with HIV-unexposed children. Incidence of outpatient attendance in HEU children was associated with being men, older age and the mother being on antiretroviral treatment. Among HEU children, those who were never breastfed, or who were weaned or were partially breastfed, had an increased incidence of hospital admissions compared with children who were exclusively breastfed.

CONCLUSION

Maternal HIV infection has important health consequences in non-HIV-infected children. As the prevalence of HIV-infected pregnant women is maintained and the proportion of HIV-infected children declines because of the scale-up of antiretroviral treatment during pregnancy and breastfeeding, more focus should be given to the health needs of HEU children to ensure that the post-2015 sustainable development goals are met.

Excess respiratory viral infections and low antibody responses among HIV-exposed, uninfected infants

OBJECTIVE

HIV-exposed uninfected (HEUs) infants have frequent severe infection, hospitalization, and death. We performed a serologic investigation to determine the role of common childhood respiratory pathogens in the excess incidence of infections in HEUs.

DESIGN

Prospective cohort study of mother-infant pairs.

METHODS

Among 247 HEUs and 88 HIV-unexposed uninfected (HUU) infant-mother pairs, we measured maternal antibodies to respiratory syncytial virus (RSV) and pneumococcus (PNC 1, 5, 6B, 14); infant antibodies to RSV, influenza A (flu), parainfluenza viruses (1, 2, 3), and PNC 1, 5, 6B, and 14 were measured at 0 and 6 months, and antitetanus antibodies at 6 months.

RESULTS

HIV-infected mothers had higher RSV and lower PNC antibody concentrations at delivery than uninfected mothers. Transplacental transfer of maternal antibodies, particularly for RSV, was lower in HEUs compared with HUUs. At birth, HEUs had higher concentrations of anti-RSV antibodies than HUUs, but lower antibodies to the other respiratory agents. At 6 months, HEUs had significantly higher proportions of seroconversions and higher antibody concentrations against parainfluenza viruses 1, 2, and 3. There were no significant differences in seroconversions to flu and RSV, but antibody concentrations to RSV were six-fold lower in HEUs versus HUUs at 6 months. Antibody responses to at least two doses of tetanus vaccine were also six-fold lower in HEUs compared with HUUs.

CONCLUSION

Six-month-old HEUs had a higher incidence of respiratory viral infections than HUUs. In addition to the low passive protection from maternal antibodies, low antibody responses of HEUs may contribute to increased morbidity and mortality.

Phenotypically resembling myeloid derived suppressor cells are increased in children with HIV and exposed/infected with Mycobacterium tuberculosis

Increased disease susceptibility during early life has been linked to immune immaturity, regulatory T-cell/TH2 immune biasing and hyporesponsiveness. The contribution of myeloid derived suppressor cells (MDSCs) remains uninvestigated. Here, we assessed peripheral MDSC in HIV-infected and -uninfected children with tuberculosis (TB) disease before, during and after TB treatment, along with matched household contacts (HHCs), HIV-exposed, -infected and -uninfected children without recent TB exposure. Serum analytes and enzymes associated with MDSC accumulation/activation/function were measured by colorimetric- and fluorescence arrays. Peripheral frequencies of cells phenotypically resembling MDSCs were significantly increased in HIV-exposed uninfected (HEU) and M.tb-infected children, but peaked in children with TB disease and remained high following treatment. MDSC in HIV-infected (HI) children were similar to unexposed uninfected controls; however, HAART-mediated MDSC restoration to control levels could not be disregarded. Increased MDSC frequencies in HHC coincided with enhanced indoleamine-pyrrole-2,3-dioxygenase (IDO), whereas increased MDSC in TB cases were linked to heightened IDO and arginase-1. Increased MDSC were paralleled by reduced plasma IP-10 and thrombospondin-2 levels in HEU and significantly increased plasma IL-6 in HI HHC. Current investigations into MDSC-targeted treatment strategies, together with functional analyses of MDSCs, could endorse these cells as novel innate immune regulatory mechanism of infant HIV/TB susceptibility.

Maternal HIV infection alters the immune balance in the mother and fetus; implications for pregnancy outcome and infant health

PURPOSE OF REVIEW

With the rapid roll-out of combination antiretroviral therapy to prevent mother-to-child transmission of HIV, there is an annual increase in the number of uninfected infants born to HIV-infected women. Although the introduction of combination antiretroviral therapy has vastly improved pregnancy outcome and the health of infants born to HIV-infected women, concerns remain regarding the impact the maternal HIV infection on the pregnancy outcome and the health of HIV-exposed uninfected infants.

RECENT FINDINGS

Maternal HIV infection is associated with negative pregnancy outcomes such as low birth weight. In addition, an increased susceptibility to infections is reported in HIV-exposed uninfected infants compared with infants born to uninfected women. Studies have shown that HIV-exposure affects the maternal/fetal unit, with increase of proinflammatory cytokine produced by placental cells, as well as altered infant immune responses. These changes could provide the underlying conditions for negative pregnancy outcomes and facilitate mother-to-child transmission of HIV in the infant. Further studies are required to understand the underlying mechanisms and investigate whether these altered infant immune responses persist and have clinical consequences beyond childhood.

SUMMARY

HIV infection in pregnant women is associated with altered immune responses in HIV-infected women and their offspring with clinical consequences for pregnancy outcome and the HIV-exposed uninfected infant. Further studies are required to address the origin and long-term consequences of prenatal HIV-exposure and subsequent immune activation for infant health.

The Immune System of HIV-Exposed Uninfected Infants

Infants born to human immunodeficiency virus (HIV) infected women are HIV-exposed but the majority remains uninfected [i.e., HIV-exposed uninfected (HEU)]. HEU infants suffer greater morbidity and mortality from infections compared to HIV-unexposed (HU) peers. The reason(s) for these worse outcomes are uncertain, but could be related to an altered immune system state. This review comprehensively summarizes the current literature investigating the adaptive and innate immune system of HEU infants. HEU infants have altered cell-mediated immunity, including impaired T-cell maturation with documented hypo- as well as hyper-responsiveness to T-cell activation. And although prevaccination vaccine-specific antibody levels are often lower in HEU than HU, most HEU infants mount adequate humoral immune response following primary vaccination with diphtheria toxoid, haemophilus influenzae type b, whole cell pertussis, measles, hepatitis B, tetanus toxoid, and pneumococcal conjugate vaccines. However, HEU infants are often found to have lower absolute neutrophil counts as compared to HU infants. On the other hand, an increase of innate immune cytokine production and expression of co-stimulatory markers has been noted in HEU infants, but this increase appears to be restricted to the first few weeks of life. The immune system of HEU children beyond infancy remains largely unexplored.

Linking Susceptibility to Infectious Diseases to Immune System Abnormalities among HIV-Exposed Uninfected Infants

HIV-exposed uninfected (HEU) infants experience increased overall mortality from infectious causes when compared to HIV-unexposed uninfected (HU) infants. This is the case in both the resource-rich and resource-limited settings. Here, we explore the concept that specific types of infectious diseases that are more common among HEU infants could provide clues as to the potential underlying immunological abnormalities. The most commonly reported infections in HEU vs. HU infants are caused by encapsulated bacteria, suggesting the existence of a less effective humoral (antibody, complement) immune response. Decreased transplacental transfer of protective maternal antibodies has consistently been observed among HEU newborns, suggesting that this may indeed be one of the key drivers of their susceptibility to infections with encapsulated bacteria. Reassuringly, HEU humoral response to vaccination appears to be well conserved. While there appears to be an increase in overall incidence of acute viral infections, no specific pattern of acute viral infections has emerged; and although there is evidence of increased chronic viral infection from perinatal transmission of hepatitis C and cytomegalovirus, no data exist to suggest an increase in adverse outcomes. Thus, no firm conclusions about antiviral effector mechanisms can be drawn. However, the most unusual of reported infections among the HEU have been opportunistic infections, suggesting the possibility of underlying defects in CD4 helper T cells and overall immune regulatory function. This may relate to the observation that the immunological profile of HEUs indicates a more activated T cell profile as well as a more inflammatory innate immune response. However, both of these observations appear transient, marked in early infancy, but no longer evident later in life. The causes of these early-life changes in immune profiles are likely multifactorial and may be related to in utero exposure to HIV, but also to increased environmental exposure to pathogens from sicker household contacts, in utero and postnatal antiretroviral drug exposure, and, in certain circumstances, differences in mode of feeding. The relative importance of each of these factors will be important to delineate in an attempt to identify those HEU at highest risk of adverse outcomes for targeted interventions.

Impact of HIV-1 infection on the feto-maternal crosstalk and consequences for pregnancy outcome and infant health

Adaptation of the maternal immune system to establish maternal/fetal equilibrium is required for a successful pregnancy. Viral infections, including HIV-1 infection, can alter this maternal/fetal equilibrium, with significant consequences for pregnancy outcome, including miscarriages, impaired fetal growth, and premature delivery. Furthermore, maternal HIV-1 infection has been shown to have a long-term impact on the developing fetal immune system also when the infant is not infected with the virus. In this review, we discuss the consequences of maternal HIV-1 infection and antiretroviral therapy on pregnancy outcome and the health of the uninfected HIV-1-exposed infant.

HIV-Exposed Uninfected Infants Show Robust Memory B-Cell Responses in Spite of a Delayed Accumulation of Memory B Cells: an Observational Study in the First 2 Years of Life

Improved HIV care has led to an increase in the number of HIV-exposed uninfected (HEU) infants born to HIV-infected women. Although they are uninfected, these infants experience increased morbidity and mortality. One explanation may be that their developing immune system is altered by HIV exposure, predisposing them to increased postnatal infections. We explored the impact of HIV exposure on the B-cell compartment by determining the B-cell subset distribution, the frequency of common vaccine antigen-specific memory B cells (MBCs), and the levels of antibodies to the respective antigens in HEU and HIV-unexposed uninfected (HUU) infants born to uninfected mothers, using flow cytometry, a B-cell enzyme-linked immunosorbent spot assay, and an enzyme-linked immunosorbent assay, respectively, during the first 2 years of life. For the majority of the B-cell subsets, there were no differences between HEU and HUU infants. However, HIV exposure was associated with a lower proportion of B cells in general and MBCs in particular, largely due to a lower proportion of unswitched memory B cells. This reduction was maintained even after correcting for age. These phenotypic differences in the MBC compartment did not affect the ability of HEU infants to generate recall responses to previously encountered antigens or reduce the antigen-specific antibody levels at 18 months of life. Although HIV exposure was associated with a transient reduction in the proportion of MBCs, we found that the ability of HEU infants to mount robust MBC and serological responses was unaffected.

Delayed acquisition of Plasmodium falciparum antigen-specific CD4(+) T cell responses in HIV-exposed uninfected Malawian children receiving daily cotrimoxazole prophylaxis

Background

Cotrimoxazole (CTX) prophylaxis, recommended in HIV-exposed uninfected (HEU) children primarily against HIV-related opportunistic infections, has been shown to have some efficacy against Plasmodium falciparum malaria. The effects of CTX prophylaxis on the acquisition of P. falciparum antigen specific CD4⁺ T cells-mediated immunity in HEU children is still not fully understood.

Methods

Peripheral blood was collected from HEU and HIV-unexposed uninfected (HUU) children at 6, 12 and 18 months of age. Proportion of CD4⁺ T cells subsets were determined by immunophenotyping. P. falciparum antigen-specific CD4⁺ T cells responses were measured by intracellular cytokine staining assay.

Results

There were no differences in the proportions of naïve, effector and memory CD4⁺ T cell subsets between HEU and HUU children at all ages. There was a trend showing acquisition of P. falciparum-specific IFN-γ and TNF-producing CD4⁺ T cells with age in both HUU and HEU children. There was, however, lower frequency of P. falciparum-specific IFN-γ-producing CD4⁺ T cells in HEU compared to HUU at 6 and 12 months, which normalized 6 months after stopping CTX prophylaxis.

Conclusion

The results demonstrate that there is delayed acquisition of P. falciparum-specific IFN-γ-producing CD4⁺ T cells in HEU children on daily cotrimoxazole prophylaxis, which is evident at 6 and 12 months of age in comparison to HUU age-matched controls. However, whether this delayed acquisition of P. falciparum-specific IFN-γ-producing CD4⁺ T cells leads to higher risk to malaria disease remains unknown and warrants further investigation.

HIV-exposed, uninfected infants: new global challenges in the era of paediatric HIV elimination

The number of infants infected with HIV is declining with the rise in interventions for the elimination of paediatric HIV infection, but the number of uninfected infants exposed to HIV through their HIV-infected mothers is increasing. Interest in the health outcomes of HIV-exposed, uninfected infants has grown in the past decade, with several studies suggesting that these infants have increased mortality rates, increased infectious morbidity, and impaired growth compared with HIV-unexposed infants. However, heterogeneous results might reflect the inherent challenges in studies of HIV-exposed, uninfected infants, which need large populations with appropriate, contemporaneous comparison groups and repeated HIV testing throughout the period of breastfeeding. We review the effects of HIV exposure on mortality, morbidity, and growth, discuss the immunological abnormalities identified so far, and provide an overview of interventions that could be effective in this susceptible population. As the number of infants infected with HIV declines, the health needs of HIV-exposed, uninfected infants should be prioritised further, to ensure that post-2015 Sustainable Development Goals are achieved.

White Matter Microstructural Integrity and Neurobehavioral Outcome of HIV-Exposed Uninfected Neonates

The successful implementation of prevention programs for mother-to-child human immunodeficiency virus (HIV) transmission has dramatically reduced the prevalence of infants infected with HIV while increasing that of HIV-exposed uninfected (HEU) children. Neuropsychological assessments indicate that HEU children may exhibit differences in neurodevelopment compared to unexposed children (HUU). Pathological mechanisms leading to such neurodevelopmental delays are not clear. In this observational birth cohort study we explored the integrity of regional white matter microstructure in HEU infants, shortly after birth. Microstructural changes in white matter associated with prenatal HIV exposure were evaluated in HEU infants (n = 15) and matched controls (n = 22) using diffusion tensor imaging and tract-based spatial statistics. Additionally, diffusion values were extracted and compared for white matter tracts of interest, and associations with clinical outcomes from the Dubowitz neonatal neurobehavioral tool were investigated. Higher fractional anisotropy in the middle cerebellar peduncles of HEU compared to HUU neonates was found after correction for age and gender. Scores on the Dubowitz abnormal neurological signs subscale were positively correlated with FA (r = 0.58, P = 0.038) in the left uncinate fasciculus in HEU infants. This is the first study to present data suggesting that prenatal HIV exposure without infection is associated with altered white matter microstructural integrity in the neonatal period. Longitudinal studies of HEU infants as their brains mature are necessary to understand further the significance of prenatal HIV and antiretroviral treatment exposure on white matter integrity and neurodevelopmental outcomes.

Morbidity and mortality in HIV-exposed uninfected children

Approximately 1.5 million HIV-positive women become pregnant annually. Antiretroviral therapy (ART) is central to prevention of mother-to-child transmission and maternal ART continued postpartum allows breastfeeding for at least 1 year of life, with important benefits for the child. In the pre-ART era, it was suggested that HIV-exposed uninfected (HEU) children may be at higher morbidity and mortality risk than children of HIV-negative mothers, associated with maternal illness and death and the lack, or limited duration, of breastfeeding as recommended for preventing mother-to-child transmission at that time. This review summarizes the evidence on morbidity and mortality risk in HEU children compared with HIV-unexposed children, and assesses the likely impact of roll-out of ART, which prolongs maternal survival and allows breastfeeding.

Proportions of CD4+, CD8+ and B cell subsets are not affected by exposure to HIV or to Cotrimoxazole prophylaxis in Malawian HIV-uninfected but exposed children

BACKGROUND

As a result of successful PMTCT programs, children born from HIV-infected mothers are now effectively protected from contracting the infection. However, it is not well known whether in utero exposure to the virus and the subsequent exposure to Cotrimoxazole (CTX) prophylaxis affect the cell mediated immune system of the children. This observational prospective study was aimed at determining how CD4(+) T, CD8(+) T and B cell subsets varied in HIV-exposed but uninfected (HEU) children at different ages.

METHODS

We recruited HEU and HIV-unexposed and uninfected (HUU) children from 6 months of age and followed them up until they were 18 months old. HEU children received daily CTX prophylaxis beginning at 6 weeks of age until when 12 months of age. Venous blood samples were collected 6 monthly and analysed for different subsets of CD8(+) T, B cells and totalCD4(+) T cells.

RESULTS

At 6 months of age, HEU children had a lower percentage of total CD4(+) T cells compared to HUU children and a lower proportion of naïve CD8(+) T cells but higher percentage of effector memory CD8(+) T cells compared to HUU children. HEU and HUU children had similar proportions of all B cell subsets at all ages.

CONCLUSIONS

The study showed that the subtle variations in CD4(+) and CD8(+) T cell subsets observed at 6 months do not last beyond 12 months of age, suggesting that HEU children have a robust cell-mediated immune system during first year of life.

TRIAL REGISTRATION

This article report is not based on results of a controlled health-care intervention.

Impact of elevated maternal HIV viral load at delivery on T-cell populations in HIV exposed uninfected infants in Mozambique

Background

HIV-uninfected infants born to HIV-infected mothers (HIV-exposed uninfected, HEU) have been described to have immune alterations as compared to unexposed infants. This study sought to characterize T-cell populations after birth in HEU infants and unexposed infants living in a semirural area in southern Mozambique.

Methods

Between August 2008 and June 2009 mother-infant pairs were enrolled at the Manhiça District Hospital at delivery into a prospective observational analysis of immunological and health outcomes in HEU infants. Infants were invited to return at one month of age for a clinical examination, HIV DNA-PCR, and immunophenotypic analyses. The primary analysis sought to assess immunological differences between HEU and unexposed groups, whereas the secondary analysis assessed the impact of maternal HIV RNA viral load in the HEU group. Infants who had a positive HIV DNA-PCR test were not included in the analysis.

Results

At one month of age, the 74 HEU and the 56 unexposed infants had similar median levels of naïve, memory and activated CD8 and CD4 T-cells. Infant naïve and activated CD8 T-cells were found to be associated with maternal HIV-RNA load at delivery. HEU infants born to women with HIV-RNA loads above 5 log₁₀ copies/mL had lower median levels of naïve CD8 T-cells (p = 0.04), and higher median levels of memory CD8 T-cells, (p = 0.014).

Conclusions

This study suggests that exposure to elevated maternal HIV-RNA puts the infant at higher risk of having early T-cell abnormalities. Improving prophylaxis of mother to child HIV programs such that more women have undetectable viral load is crucial to decrease vertical transmission of HIV, but may also be important to reduce the consequences of HIV virus exposure in HEU infants.

The role of environmental factors in modulating immune responses in early life

The concept of immunological memory stipulates that past exposures shape present immune function. These exposures include not only specific antigens impacting adaptive immune memory but also conserved pathogen or danger associated molecular patterns that mold innate immune responses for prolonged periods of time. It should thus not come as a surprise that there is a vast range of external or environmental factors that impact immunity. The importance of environmental factors modulating immunity is most readily recognized in early life, a period of rapidly changing environments. We here summarize available data on the role of environment shaping immune development and from it derive an overarching hypothesis relating the underlying molecular mechanisms and evolutionary principles involved.