Bystander effects: children who escape infection but not harm

Maternal HIV infection and the milk microbiome

BACKGROUND

Children born to women with HIV but who do not become HIV infected experience increased morbidity and mortality compared with children born to women without HIV. The basis of this increased vulnerability is unknown. The microbiome, specifically the infant gut microbiome, likely plays an important role in infant immune development. The human milk microbiome is thought to have an important role in the development of the infant gut and therefore, if perturbed, may contribute to this increased vulnerability. We investigated the effects of HIV and its therapies on the milk microbiome and possible changes in the milk microbiome before or after infant HIV infection.

RESULTS

Seven-hundred fifty-six human milk samples were selected from three separate studies conducted over a 15-year period to investigate the role of HIV and its therapies on the human milk microbiome. Our data reveal that the milk microbiome is modulated by parity (R2 = 0.006, p = 0.041), region/country (R2 = 0.014, p = 0.007), and duration of lactation (R2 = 0.027-0.038, all p < 0.001). There is no evidence, however, using 16S rRNA V4 amplicon sequencing, that the human milk microbiome is altered by HIV infection (R2 = 0.003, p = 0.896), by combination antiretroviral therapy (R2 = 0.0009, p = 0.909), by advanced maternal disease (R2 = 0.003, p = 0.263), or in cases of infant infection either through isolated early mucosal (R2 = 0.003, p = 0.197) or early mucosal and breast milk transmission (R2 = 0.002, p = 0.587).

CONCLUSIONS

The milk microbiome varies by stage of lactation, by parity, and by region; however, we found no evidence that the human milk microbiome is altered by maternal HIV infection, disease severity, or antiretroviral therapy. Additionally, we found no association between the milk microbiome and transmission of HIV to the infant. Investigations including higher resolution microbiome approaches or into other potential mechanisms to understand why the approximately one million children born annually to women with HIV escape infection, but do not escape harm, are urgently needed. Video Abstract.

Maternal immunity shapes biomarkers of germinal center development in HIV-exposed uninfected infants

Introduction

HIV-exposed uninfected (HEU) infants exhibit elevated pro-inflammatory biomarkers that persist after birth. However, comprehensive assessments of bioprofiles associated with immune regulation and development in pregnant women with HIV (PWH) and HEU infants has not been performed. Maternal immunity in PWH may be imprinted on their HEU newborns, altering immune bioprofiles during early immune development.

Methods

Cryopreserved paired plasma samples from 46 HEU infants and their mothers enrolled in PACTG 316, a clinical trial to prevent perinatal HIV-1 transmission were analyzed. PWH received antiretrovirals (ARV) and had either fully suppressed or unsuppressed viral replication. Maternal blood samples obtained during labor and infant samples at birth and 6 months were measured for 21 biomarkers associated with germinal centers (GC), macrophage activation, T-cell activation, interferon gamma (IFN-γ)-inducible chemokines, and immune regulatory cytokines using Mesoscale assays. Pregnant women without HIV (PWOH) and their HIV unexposed uninfected (HUU) newborns and non-pregnant women without HIV (NPWOH) served as reference groups. Linear regression analysis fitted for comparison among groups and adjusted for covariant(s) along with principal component analysis performed to assess differences among groups.

Results

Compared with NPWOH, PWOH displayed higher levels of GC, macrophage, and regulatory biomarkers. PWH compared to PWOH displayed elevated GC, T cell activation, and IFN-γ-inducible chemokines biomarkers at delivery. Similar to their mothers, HEU infants had elevated GC, macrophage, and IFN-γ-inducible chemokines, as well as elevated anti-inflammatory cytokines, IL-10 and IL-1RA. Across all mother/newborn dyads, multiple biomarkers positively correlated, providing further evidence that maternal inflammation imprints on newborn bioprofiles. By 6 months, many HEU biomarkers normalized to levels similar to HUU infants, but some GC and inflammatory biomarkers remained perturbed. Bioprofiles in PWH and HEU infants were similar regardless of the extent of maternal viral suppression by ARV.

Conclusions

GC immune pathways are perturbed in HEU newborns, but immune regulatory responses down regulate inflammation during early infancy, indicating a transient inflammatory effect. However, several GC biomarkers that may alter immune development remain perturbed.

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.

Maternal HIV status skews transcriptomic response in infant cord blood monocytes exposed to Bacillus Calmette--Guerín

OBJECTIVES

HIV-exposed uninfected (HEU) infants exhibit altered vaccine responses and an increased mortality compared with HIV-unexposed infants. Here, vaccine responses in HEU and HIV-unexposed cord blood monocytes (CBMs) were assessed following Bacillus Calmette--Guerín (BCG) treatment.

DESIGN

Innate responses to in-vitro BCG treatment were assessed through transcriptional profiling using CBMs obtained from a Nigerian cohort of HIV-infected and uninfected women.

METHODS

HIV-unexposed (n = 9) and HEU (n = 10) infant CBMs were treated with BCG and transcriptionally profiled with the Nanostring nCounter platform. Differential expression and pathway enrichment analyses were performed, and transcripts were identified with enhanced or dampened BCG responses.

RESULTS

Following BCG stimulation, several pathways associated with inflammatory gene expression were upregulated irrespective of HIV exposure status. Both HIV-unexposed and HEU monocytes increased expression of several cytokines characteristic of innate BCG responses, including IL1β, TNFα, and IL-6. Using differential expression analysis, we identified genes significantly upregulated in HEU compared with HIV-unexposed monocytes including monocyte chemokine CCL7 and anti-inflammatory cytokine TNFAIP6. In contrast, genes significantly upregulated in HIV-unexposed compared with HEU monocytes include chemokine CCL3 and cytokine IL23A, both of which influence anti-mycobacterial T-cell responses. Finally, two genes, which regulate prostaglandin production, CSF2 and PTGS2, were also more significantly upregulated in the HIV-unexposed cord blood indicating that inflammatory mediators are suppressed in the HEU infants.

CONCLUSION

HEU monocytes exhibit altered induction of several key innate immune responses, providing mechanistic insights into dysregulated innate response pathways that can be therapeutically targeted to improve vaccine responses in HEU infants.

Altered Toll-Like Receptor-4 Response to Lipopolysaccharides in Infants Exposed to HIV-1 and Its Preventive Therapy

Pathogen sensing and recognition through pattern recognition receptors, and subsequent production of pro-inflammatory cytokines, is the cornerstone of the innate immune system. Despite the fact that HIV-exposed uninfected (HEU) infants are prone to serious bacterial infections, no study has focused on the functionality of their bacteria recognition system. This is the first study to investigate baseline levels of three critically important immune response molecules in this population: complement component (C)-3, toll-like receptor (TLR)-4, and C-reactive protein (CRP). We enrolled 16 HEU and 6 HIV-unexposed (HU) infants. TLR4 function was investigated by stimulating whole blood with increasing concentrations of TLR4-agonist ultrapure lipopolysaccharides. TLR4/TLR4-agonist dose response were assessed by measuring IL-6 secretion. Complement C3 and CRP were measured by photo spectrometry. Data showed no significant differences in baseline concentration of CRP between HEU and HU infants. Complement C3 was significantly higher in HEU infants than HU infants. TLR4 anergy was observed in 7 of 12 HEU infants, whereas the rest of HEU infants (n = 4) and the control HU infants tested (n = 3) showed responsive TLR4. None of the HEU infants investigated in this study had severe infections in the year after their birth. In conclusion, TLR4 anergy can occur in HEU infants without necessarily translating to increased vulnerability to infectious diseases.

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.

Clinical outcomes of HIV-exposed, HIV-uninfected children in sub-Saharan Africa

OBJECTIVE

HIV-exposed but HIV-uninfected (HEU) children are widely considered at increased risk of mortality and morbidity. Recent advances in prevention of mother-to-child HIV transmission (PMTCT) strategies, incorporating life-long universal maternal antiretroviral therapy (ART, "Option B+") with extended breastfeeding, may improve HEU child health substantially. We critically reviewed reports of mortality/morbidity among HEU and HIV-unexposed (HU) children in sub-Saharan Africa.

METHODS

We searched Medline, EMBASE, CINAHL, PsycINFO, Academic Search Premier, Global Health & Psychosocial Instruments databases, conference abstracts, and reference lists for longitudinal studies from sub-Saharan Africa reporting mortality and clinical morbidity among HIV-uninfected children aged ≤10 years, by maternal HIV status. Studies were appraised by Newcastle-Ottawa Scale and ACROBAT-NRSI. Due to substantial heterogeneity of study designs, populations and results (I(2) = 75%), data were not synthesised.

RESULTS

We included 37 reports (28 studies, 11 164 HEU children); methodological and reporting quality were variable. Most reports came from settings without universal access to maternal ART (n = 35). Results were conflicting, with some studies indicating increased risk of mortality, hospitalisation and/or under-nutrition among HEU children, while others found no evidence of increased risk. In subanalyses, improved maternal health, ART use and breastfeeding were strongly protective for all outcomes. Only 39% (11/28) of studies adjusted for major confounders. Reports from settings using universal maternal ART with breastfeeding (n = 2) found no differences in growth or development but did not report mortality or infectious morbidity.

CONCLUSIONS

The existing literature provides little insight into HEU child health under recently adopted PMTCT strategies. There is a need for robust comparative data on HEU and HIV-unexposed child health outcomes under Option B+; optimising breastfeeding practices and increasing maternal use of ART should be urgent public health priorities.

Oligosaccharide composition of breast milk influences survival of uninfected children born to HIV-infected mothers in Lusaka, Zambia

BACKGROUND

Human milk oligosaccharides (HMOs) have multiple immunomodulatory functions that influence child health.

OBJECTIVE

In this study we investigated whether HMO composition influences survival to 2 y of age in HIV-infected and HIV-exposed, uninfected (HEU) children during and after breastfeeding.

METHODS

In the context of an early weaning trial in 958 HIV-infected women in Lusaka, Zambia, we conducted a nested case-cohort analysis of mortality to 2 y of age among 103 HIV-infected and 143 HEU children. Breast-milk samples collected at 1 mo postpartum were analyzed for HMO content. Samples were selected to include mothers of all HIV-infected children detected by 6 wk of age, of whom 63 died at <2 y of age; mothers of all HEU children who died at <2 y of age (n = 66); and a random sample of 77 HEU survivors. Associations before and after weaning in HIV-infected and HEU infants separately were investigated by using Cox models.

RESULTS

Among HEU children, higher maternal breast-milk concentrations of 2-linked fucosylated HMOs [2'-fucosyllactose and lacto-N-fucopentaose (LNFP) I] (HR: 0.33; 95% CI: 0.14, 0.74) as well as non-2-linked fucosylated HMOs (3-fucosyllactose and LNFP II/III; HR: 0.28; 95% CI: 0.13, 0.67) were significantly associated with reduced mortality during, but not after, breastfeeding after adjustment for confounders. Breastfeeding was protective against mortality only in HEU children with high concentrations of fucosylated HMOs. Among HIV-infected children, no consistent associations between HMOs and mortality were observed, but breastfeeding was protective against mortality.

CONCLUSIONS

The oligosaccharide composition of breast milk may explain some of the benefits of breastfeeding in HEU children. HIV infection may modulate some of the consequences of HMOs on child survival.

Immunology of pediatric HIV infection

Most infants born to human immunodeficiency virus (HIV)-infected women escape HIV infection. Infants evade infection despite an immature immune system and, in the case of breastfeeding, prolonged repetitive exposure. If infants become infected, the course of their infection and response to treatment differs dramatically depending upon the timing (in utero, intrapartum, or during breastfeeding) and potentially the route of their infection. Perinatally acquired HIV infection occurs during a critical window of immune development. HIV's perturbation of this dynamic process may account for the striking age-dependent differences in HIV disease progression. HIV infection also profoundly disrupts the maternal immune system upon which infants rely for protection and immune instruction. Therefore, it is not surprising that infants who escape HIV infection still suffer adverse effects. In this review, we highlight the unique aspects of pediatric HIV transmission and pathogenesis with a focus on mechanisms by which HIV infection during immune ontogeny may allow discovery of key elements for protection and control from HIV.

HIV and malaria interactions: where do we stand?

Reversing the spread of HIV infection and the incidence of malaria constitute two of the Millenium Development Goals. However, despite recent achievements, both diseases still entail global heath problems. Furthermore, their overlapping geographical distribution raises concerns and challenges for potential immunological, clinical and therapeutic interactions. It has been reported that HIV infection increases malaria susceptibility and reduces the efficacy of antimalarial drugs. On the other hand, the effect of malaria on HIV-infected individuals has also been explored, with the parasitic infection increasing the risk of HIV disease progression and mother-to-child transmission of HIV. The spread of malaria and parasite resistance to antimalarials could also be accelerated by HIV-associated immunosuppresion. Current knowledge of the epidemiological, clinical, immunological and therapeutic interactions of the two diseases is reviewed in this article. We focus on the latest available data, pointing out key future research areas and challenges of the field.

Protective efficacy of co-trimoxazole prophylaxis against malaria in HIV exposed children in rural Uganda: a randomised clinical trial

OBJECTIVE

To evaluate the protective efficacy of co-trimoxazole prophylaxis against malaria in HIV exposed children (uninfected children born to HIV infected mothers) in Africa.

DESIGN

Non-blinded randomised control trial

SETTING

Tororo district, rural Uganda, an area of high malaria transmission intensity

PARTICIPANTS

203 breastfeeding HIV exposed infants enrolled between 6 weeks and 9 months of age

INTERVENTION

Co-trimoxazole prophylaxis from enrollment until cessation of breast feeding and confirmation of negative HIV status. All children who remained HIV uninfected (n = 185) were then randomised to stop co-trimoxazole prophylaxis immediately or continue co-trimoxazole until 2 years old.

MAIN OUTCOME MEASURE

Incidence of malaria, calculated as the number of antimalarial treatments per person year.

RESULTS

The incidence of malaria and prevalence of genotypic mutations associated with antifolate resistance were high throughout the study. Among the 98 infants randomised to continue co-trimoxazole, 299 malaria cases occurred in 92.28 person years (incidence 3.24 cases/person year). Among the 87 infants randomised to stop co-trimoxazole, 400 malaria cases occurred in 71.81 person years (5.57 cases/person year). Co-trimoxazole prophylaxis yielded a 39% reduction in malaria incidence, after adjustment for age at randomisation (incidence rate ratio 0.61 (95% CI 0.46 to 0.81), P = 0.001). There were no significant differences in the incidence of complicated malaria, diarrhoea, pneumonia, hospitalisations, or deaths between the two treatment arms.

CONCLUSIONS

Co-trimoxazole prophylaxis was moderately protective against malaria in HIV exposed infants when continued beyond the period of HIV exposure despite the high prevalence of Plasmodium genotypes associated with antifolate resistance. Trial registration Clinical Trials NCT00527800.

Breastfeeding, HIV status and weights in South African children: a comparison of HIV-exposed and unexposed children

OBJECTIVES

To examine growth of children by maternal and infant HIV status allowing for infant feeding mode.

DESIGN

Women enrolled into a nonrandomized intervention cohort.

METHODS

Children of HIV-infected and uninfected women weighed and assessed for HIV status, monthly: from birth to 9 months; quarterly: 10-24 months. Daily infant feeding practices recorded at weekly intervals. Weight-for-age z-scores of children born to HIV-infected mothers compared with the reference population of children of HIV-uninfected mothers. Changes in z-scores over age were examined by HIV infection status and infant feeding practice using linear mixed effects models.

RESULTS

The 1261 children of HIV-infected mothers grew as well as the reference group of 1061 children of HIV-uninfected mothers, irrespective of feeding mode. z-scores for HIV-infected children were consistently lower than those of HIV-exposed but uninfected children: a difference of 420 g for male children and 405 g for female children at 52 weeks of age. Breastfed HIV-infected infants had consistently higher z-scores for weight, especially during first 6 weeks (difference of 130 g for male children; 110 g for female children). In an adjusted regression analysis, maternal mid-upper arm circumference, CD4 cell count, infant birth weight and HIV status had the biggest impact on infant growth (z-score coefficient: 0.38 for mid-upper arm circumference > or =28.35 vs. <25.7 cm; P < 0.001; -0.32 for CD4 cell count <200 vs. > or =500; P = 0.001; -2.01 for birth weight <2500 vs. > or =2500 g; P < 0.001; -0.20 for infected vs. uninfected children; P < 0.001).

CONCLUSION

Optimal early feeding practices ameliorate the effect of being born to an HIV-infected mother and strengthen the recommendation of exclusive breastfeeding for HIV-infected women in terms of long-term child health.

HIV prevention is not enough: child survival in the context of prevention of mother to child HIV transmission

Clinical and epidemiologic research has identified increasingly effective interventions to reduce mother to child HIV transmission in resource-limited settings These scientific breakthroughs have been implemented in some programmes, although much remains to be done to improve coverage and quality of these programmes. But prevention of HIV transmission is not enough. It is necessary also to consider ways to improve maternal health and protect child survival.

A win-win approach is to ensure that all pregnant and lactating women with CD4 counts of <350 cells/mm³ have access to antiretroviral therapy. On its own, this approach will substantially improve maternal health and markedly reduce mother to child HIV transmission during pregnancy and delivery and through breastfeeding. This approach can be combined with additional interventions for women with higher CD4 counts, either extended prophylaxis to infants or extended regimens of antiretroviral drugs to women, to reduce transmission even further.

Attempts to encourage women to abstain from all breastfeeding or to shorten the optimal duration of breastfeeding have led to increases in mortality among both uninfected and infected children. A better approach is to support breastfeeding while strengthening programmes to provide antiretroviral therapy for pregnant and lactating women who need it and offering antiretroviral drug interventions through the duration of breastfeeding. This will lead to reduced HIV transmission and will protect the health of women without compromising the health and well-being of infants and young children.

Preventing mother-to-child transmission of HIV in resource-limited settings

Mother-to-child transmission (MTCT) before, during and after delivery may result in the acquisition of HIV for 30–35% of infants of HIV-infected mothers. Peripartum HIV transmission can be reduced to under 5% in resource-limited settings using a feasible prophylactic antiretroviral regimen. Reducing postnatal transmission through breastfeeding, whilst maintaining child survival, is an urgent priority, given that breastfeeding causes one-third to one-half of all infant HIV infections. Recent evidence highlights the impact of breastfeeding duration and pattern, and hazards associated with the avoidance of breastfeeding in different settings. New international guidelines on HIV and infant feeding have been published. Despite knowledge of how to reduce MTCT of HIV in resource-poor settings, an unacceptably low proportion of women access prevention of MTCT services (PMTCT); follow-up of women and children is poor. To improve survival of mothers and children, health services need to be strengthened, with the integration of PMTCT into existing maternal and child health services.

Role of breastfeeding cessation in mediating the relationship between maternal HIV disease stage and increased child mortality among HIV-exposed uninfected children

BACKGROUND

Maternal CD4 count predicts child mortality in HIV-uninfected children born to HIV-infected women.

METHODS

To explore the mediating role of breastfeeding cessation in this relationship, we compared marginal structural models of maternal CD4 count on child death with and without adjustment for breastfeeding.

RESULTS

In crude analyses, children of mothers with CD4<200 during pregnancy were 3.2 times more likely to die by 18 months (CI 1.3-8.1) as children whose mothers had CD4>500. Earlier breastfeeding cessation was also associated with low CD4 (HR 1.8; CI 1.2-2.7). After adjusting for breastfeeding and low birth weight using a marginal structural model, the low CD4 count-child mortality association through 18 months was reduced 17%. The change was overestimated using a traditional Cox proportional hazards model (35% reduction in HR from 3.4 to 2.5).

CONCLUSIONS

Our analysis suggests that only a small part of the effect of low vs high CD4 count on child mortality through 18 months is mediated through breastfeeding cessation. Our results must be taken into account when deciding whether or not to recommend breastfeeding for infants of HIV-infected mothers.