Human immunodeficiency virus (HIV)-specific cellular immune responses in newborns exposed to HIV in utero

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.

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.

Immune pathogenesis of pediatric HIV-1 infection

Vertical exposure to HIV occurs at a time when functional capacity of the infant's immune system is attenuated through immaturity. Immune response capability is rooted in host genetic makeup, and the broad and fine specificity of innate and adaptive immune responses, respectively, shape the outcomes of HIV encounter in some instances and imprint viral changes through selective immune pressure in others. Findings from recent studies have profound implications for understanding immune pathogenesis of pediatric HIV infection and, in particular, highlight the importance of host genetics of both mother and child in determining whether an exposed child acquires HIV infection or not and, if infected, the rate of disease progression. This review focuses on the key host molecules, the CC chemokine CCL3 and HLA, which have taken center stage in these new developments.

Gamma interferon production in response to Mycobacterium bovis BCG and Mycobacterium tuberculosis antigens in infants born to human immunodeficiency virus-infected mothers

In utero sensitization to infectious pathogens can establish immunological memory and may influence the immune response to unrelated antigens. Little is known about the influence of intrauterine human immunodeficiency virus (HIV) exposure on the cellular immune response to mycobacterial antigens. Whole-blood culture gamma interferon (IFN-gamma) production in response to mycobacterial antigens was measured at birth and 6 weeks of age to determine the characteristics of the IFN-gamma response in HIV-exposed infants to Mycobacterium bovis BCG and mycobacterial antigens. At birth, we observed an increased immune activation in response to phytohemagglutinin among HIV-exposed, uninfected infants. In a proportion of these infants, we also observed an increased immune activation in response to purified protein derivative, BCG, and early secreted antigen target 6. Increases in the IFN-gamma response to the four antigens between birth and 6 weeks of age, observed in all HIV-unexposed infants, was absent in a substantial proportion of HIV-exposed, uninfected infants. The immunological differences persisted at 6 weeks of age, suggesting a sustained impact of in utero immune priming by HIV. Intrauterine exposure to HIV affects the infants' cellular immune response to mycobacterial antigens, either specifically or as a consequence of nonspecific, broadly reactive immune activation. Further studies will be important to help determine optimal vaccination and disease prevention strategies for this vulnerable population group.

Maternal HIV type 1 infection suppresses MMP-1 expression in endothelial cells of uninfected newborns: nonviral vertical transmission of HIV type 1-related effects

HIV-1 infection is associated with vascular alterations. This is accompanied by an increased risk of cardiovascular diseases and Kaposi's sarcoma, an endothelial cell-derived tumor. We investigated the impact of maternal HIV-1 infection on phenotype and gene expression of endothelial cells in newborns. For this reason endothelial precursor cells and differentiated endothelial cells were isolated from cord blood as well as from umbilical veins and arteries of noninfected infants born to HIV-1-infected (H-group) and noninfected (Ngroup) mothers. No apparent differences in proliferation, capillary formation, and expression of endothelial cell markers were detected in these cells. Interestingly, the expression of matrix metalloproteinase was repressed significantly (X2 analysis, p < 0.002) and consistently at the RNA, the protein, and the secretory levels in the H-group as compared to the N-group. Neither treatment with zidovudine (AZT), mutations in the matrix metalloproteinase-1 (MMP-1) promoter, nor epigenetic changes in the promoter methylation pattern were responsible for the repression of MMP-1 expression in H-group endothelial cells. The reduced MMP-1 expression may contribute to the impaired cardiac function that has been observed in children of HIV-1-infected women. Most interestingly, our findings indicate that HIV-1-related effects can be transferred from mother to child in the absence of HIV-1 transmission.

Cognitive and motor deficits associated with HIV-2(287) infection in infant pigtailed macaques: a nonhuman primate model of pediatric neuro-AIDS

Lentivirus-infected nonhuman primates exhibit behavioral and neurological pathology similar to human immunodeficiency virus (HIV)-infected humans and offer a means to examine the effects of lentivirus infection while controlling for confounding factors inherent in human populations. The purpose of this study was to examine cognitive and motor development in infant macaques vertically infected with HIV-2287. Subjects were 20 infant pigtail macaques (Macaca nemestrina); 8 controls born to uninfected dams, and 12 infants whose dams had been inoculated and infected with HIV-2287 in the third trimester of pregnancy. Eight of these pregnancies had undergone surgical procedures in the form of maternal amniotic catheters or maternal amniotic and fetal carotid artery and jugular vein catheters. Data indicated that catheterization had little or no impact on behavioral development. Seven infants were vertically infected (as measured by polymerase chain reaction (PCR) at birth) and five were not infected (as measured by PCR and coculture on repeated testing). Infected infants attained cognitive and motor milestones at significantly later ages than controls. Uninfected infants, born to infected dams, attained developmental milestones at later ages than controls on all tasks, but this reached statistical significance only for the Fine Motor Task. Attainment of milestones was not correlated with viral dose, maternal CD4+ levels at parturition or infant viral RNA levels at birth. Attainment of milestones was negatively correlated with infants' proportions of CD4+ lymphocytes at birth and significantly correlated with proportions of CD4+ lymphocytes 2 weeks after birth, indicating poorer performance in those infants with a more rapid CD4+ depletion. These cognitive and motor deficits closely resemble those observed in human infants and children infected with HIV and indicate that HIV-2287-infected infant macaques represent an excellent model of pediatric neuro-acquired immunodeficiency syndrome (neuroAIDS).

Covert vertical transmission of feline immunodeficiency virus

Covert vertical transmission of feline immunodeficiency virus (FIV), the feline counterpart of human immunodeficiency virus type 1 (HIV-1), was identified in kittens born to FIV-infected cats. DNA PCR detected FIV gag and env sequences in tissues from kittens nonviable at birth, and in viable kittens monitored postnatally and necropsied at either 11 weeks or 1 year of age. Although FIV DNA was detected in initial blood samples from all 16 viable kittens, viral DNA became increasingly difficult to detect over time and infectious virus could rarely be demonstrated. Only maternal FIV antibody was detected in kitten plasma during the entire postnatal observation period, and kittens remained healthy, with normal CD4:CD8 T cell ratios at >14 months of age. Thus, mother-to-offspring FIV exposure, occurring in utero and postnatally, can result in covert infection in kittens with virus sequestered and contained in tissue sites. These findings appear directly relevant to suspected transient HIV infections and reports of HIV-specific cellular immune responses in highly exposed seronegative adults and uninfected infants born to HIV-positive women.

Salivary secretory leukocyte protease inhibitor is associated with reduced transmission of human immunodeficiency virus type 1 through breast milk

Secretory leukocyte protease inhibitor (SLPI), a protein found in saliva, breast milk, and genital secretions, is capable of inhibiting human immunodeficiency virus (HIV) type 1 in vitro. The aim of this study was to determine whether SLPI in infant saliva provides protection against mother-to-child HIV-1 transmission. In total, 602 saliva specimens were collected from 188 infants at birth and at ages 1, 3, and 6 months. Infants' median salivary SLPI concentrations were higher at birth than at 6 months (341 vs. 219 ng/mL; P=.001). There was no association between SLPI concentration and HIV-1 transmission overall. However, among 122 breast-fed infants who were HIV-1 uninfected at 1 month, higher salivary SLPI levels were associated with a decreased risk of HIV-1 transmission through breast milk (hazard ratio, 0.5; 95% confidence interval, 0.3-0.9; P=.03). These results suggest that SLPI plays an important role in reducing HIV-1 transmission through breast milk.