Genetic evaluation of suspected cases of transient HIV-1 infection of infants

Development and Validation of a Genotypic Assay to Quantify CXCR4- and CCR5-Tropic Human Immunodeficiency Virus Type-1 (HIV-1) Populations and a Comparison to Trofile®

HIV-1 typically infects cells via the CD4 receptor and CCR5 or CXCR4 co-receptors. Maraviroc is a CCR5-specific viral entry inhibitor; knowledge of viral co-receptor specificity is important prior to usage. We developed and validated an economical V3-env Illumina-based assay to detect and quantify the frequency of viruses utilizing each co-receptor. Plasma from 54 HIV+ participants (subtype B) was tested. The viral template cDNA was generated from plasma RNA with unique molecular identifiers (UMIs). The sequences were aligned and collapsed by the UMIs with a custom bioinformatics pipeline. Co-receptor usage, determined by codon analysis and online phenotype predictors PSSM and Geno2pheno, were compared to existing Trofile® data. The cost of V3-UMI was tallied. The sequences interpreted by Geno2pheno using the most conservative cut-off, a 2% false-positive-rate (FPR), predicted CXCR4 usage with the greatest sensitivity (76%) and specificity (100%); PSSM and codon analysis had similar sensitivity and lower specificity. Discordant Trofile® and genotypic results were more common when participants had specimens from different dates analyzed by either assay. V3-UMI reagents cost USD$62/specimen. A batch of ≤20 specimens required 5 h of technical time across 1.5 days. V3-UMI predicts HIV tropism at a sensitivity and specificity similar to those of Trofile®, is relatively inexpensive, and could be performed by most central laboratories. The adoption of V3-UMI could expand HIV drug therapeutic options in lower-resource settings that currently do not have access to phenotypic HIV tropism testing.

Patterns and rates of viral evolution in HIV-1 subtype B infected females and males

Biological sex differences affect the course of HIV infection, with untreated women having lower viral loads compared to their male counterparts but, for a given viral load, women have a higher rate of progression to AIDS. However, the vast majority of data on viral evolution, a process that is clearly impacted by host immunity and could be impacted by sex differences, has been derived from men. We conducted an intensive analysis of HIV-1 gag and env-gp120 evolution taken over the first 6–11 years of infection from 8 Women’s Interagency HIV Study (WIHS) participants who had not received combination antiretroviral therapy (ART). This was compared to similar data previously collected from men, with both groups infected with HIV-1 subtype B. Early virus populations in men and women were generally homogenous with no differences in diversity between sexes. No differences in ensuing nucleotide substitution rates were found between the female and male cohorts studied herein. As previously reported for men, time to peak diversity in env-gp120 in women was positively associated with time to CD4+ cell count below 200 (P = 0.017), and the number of predicted N-linked glycosylation sites generally increased over time, followed by a plateau or decline, with the majority of changes localized to the V1-V2 region. These findings strongly suggest that the sex differences in HIV-1 disease progression attributed to immune system composition and sensitivities are not revealed by, nor do they impact, global patterns of viral evolution, the latter of which proceeds similarly in women and men.

Effective Cytotoxic T Lymphocyte Targeting of Persistent HIV-1 during Antiretroviral Therapy Requires Priming of Naive CD8+ T Cells

Curing HIV-1 infection will require elimination of persistent cellular reservoirs that harbor latent virus in the face of combination antiretroviral therapy (cART). Proposed immunotherapeutic strategies to cure HIV-1 infection include enhancing lysis of these infected cells by cytotoxic T lymphocytes (CTL). A major challenge in this strategy is overcoming viral immune escape variants that have evaded host immune control. Here we report that naive CD8⁺ T cells from chronic HIV-1-infected participants on long-term cART can be primed by dendritic cells (DC). These DC must be mature, produce high levels of interleukin 12p70 (IL-12p70), be responsive to CD40 ligand (CD40L), and be loaded with inactivated, autologous HIV-1. These DC-primed CD8⁺ T cell responders produced high levels of gamma interferon (IFN-γ) in response to a broad range of both conserved and variable regions of Gag and effectively killed CD4⁺ T cell targets that were either infected with the autologous latent reservoir-associated virus or loaded with autologous Gag peptides. In contrast, HIV-1-specific memory CD8⁺ T cells stimulated with autologous HIV-1-loaded DC produced IFN-γ in response to a narrow range of conserved and variable Gag peptides compared to the primed T cells and most notably, displayed significantly lower cytolytic function. Our findings highlight the need to selectively induce new HIV-1-specific CTL from naive precursors while avoiding activation of existing, dysfunctional memory T cells in potential curative immunotherapeutic strategies for HIV-1 infection.

Current immunotherapeutic approaches aim to enhance antiviral immunity against the HIV-1 reservoir; however, it has yet to be shown whether T cells from persons on cART can recognize and eliminate virus-infected cells. We show that in persons on cART a personalized medicine approach using their dendritic cells to stimulate their naive T cells induces potent effector CTL in vitro that recognize and eradicate HIV-1-infected CD4⁺ T cells. Additionally, we show that the same stimulation of existing memory T cells results in cytokine secretion but limited effector function. Our study demonstrates that the naive T cell repertoire can recognize persistent HIV-1 during cART and supports immunotherapy strategies for an HIV-1 cure that targets naive T cells, rather than existing, dysfunctional, memory T cells.

Reevaluation of possible outcomes of infections with human immunodeficiency virus

Several lines of evidence indicate that HIV infection can result in several possible incomes, including a very small proportion of individuals whose HIV replication is controlled after treatment interruption (known as HIV posttreatment controllers) or spontaneously without any treatment (known as HIV elite controllers). Both types of individuals are HIV RNA negative but HIV DNA positive, with living virus which can be stimulated ex vivo. A review was conducted to assess the literature on yet rarer cases with detectable integrated HIV DNA without HIV infectious virus in HIV-seropositive or -negative individuals. Three categories of patients were identified: (a) HIV-seropositive individuals with apparent spontaneous cure from their HIV infection, (b) HIV-seronegative children born to HIV-infected mothers and (c) highly exposed seronegative adults. Validity criteria were proposed to assess the presence of integrated HIV DNA as possible or unquestionable in these three categories. Only three articles among the 22 ultimately selected fulfilled these criteria. Among the highly exposed seronegative subjects, some individuals were described as being without integrated HIV DNA, probably because these subjects were not investigated using relevant, highly sensitive methods. Finally, we propose a definition of spontaneous cure of HIV infection based on clinical, immunologic and virologic criteria.

Are infants unique in their ability to be "functionally cured" of HIV-1?

The recent report of an infant that appears to have achieved a "functional cure" of HIV-1 following receipt of antiretroviral therapy (ART) within 30 hours of birth raises many questions: was the child infected? Was this result due to unique features of this particular infant's immune system, the immune system of infants or the very early initiation of effective ART? In this manuscript, we discuss the pathogenesis of HIV-1 in infants, highlighting the unique features of infant immune development and how these may inform efforts to cure HIV infection. We will also compare the path to infant "cure" to cures in adults.

Dendritic cells restore CD8+ T cell reactivity to autologous HIV-1

Recall T cell responses to HIV-1 antigens are used as a surrogate for endogenous cellular immune responses generated during infection. Current methods of identifying antigen-specific T cell reactivity in HIV-1 infection use bulk peripheral blood mononuclear cells (PBMC) yet ignore professional antigen-presenting cells (APC) that could reveal otherwise hidden responses. In the present study, peptides representing autologous variants of major histocompatibility complex (MHC) class I-restricted epitopes from HIV-1 Gag and Env were used as antigens in gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) and polyfunctional cytokine assays. Here we show that dendritic cells (DC) enhanced T cell reactivity at all stages of disease progression but specifically restored T cell reactivity after combination antiretroviral therapy (cART) to early infection levels. Type 1 cytokine secretion was also enhanced by DC and was most apparent late post-cART. We additionally show that DC reveal polyfunctional T cell responses after many years of treatment, when potential immunotherapies would be implemented. These data underscore the potential efficacy of DC immunotherapy that aims to awaken a dormant, autologous, HIV-1-specific CD8+ T cell response.

IMPORTANCE

Assessment of endogenous HIV-1-specific T cell responses is critical for generating immunotherapies for subjects on cART. Current assays ignore the ability of dendritic cells to reveal these responses and may therefore underestimate the breadth and magnitude of T cell reactivity. As DC do not prime new responses in these assays, it can be assumed that the observed responses are not detected without appropriate stimulation. This is important because dogma states that HIV-1 mutates to evade host recognition and that CD8+ cytotoxic T lymphocyte (CTL) failure is due to the inability of T cells to recognize the autologous virus. The results presented here indicate that responses to autologous virus are generated during infection but may need additional stimulation to be effective. Detecting the breadth and magnitude of HIV-1-specific T cell reactivity generated in vivo is of the utmost importance for generating effective DC immunotherapies.

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.

Absence of detectable HIV-1 viremia after treatment cessation in an infant

An infant born to a woman with human immunodeficiency virus type 1 (HIV-1) infection began receiving antiretroviral therapy (ART) 30 hours after birth owing to high-risk exposure. ART was continued when detection of HIV-1 DNA and RNA on repeat testing met the standard diagnostic criteria for infection. After therapy was discontinued (when the child was 18 months of age), levels of plasma HIV-1 RNA, proviral DNA in peripheral-blood mononuclear cells, and HIV-1 antibodies, as assessed by means of clinical assays, remained undetectable in the child through 30 months of age. This case suggests that very early ART in infants may alter the establishment and long-term persistence of HIV-1 infection.

A time lag insensitive approach for estimating HIV-1 transmission direction

OBJECTIVES

Identifying the direction of transmission in transmission pairs is important both for forensic investigations and for the monitoring of HIV epidemics, however, reliable methods are not yet available due to the long time lag between infection and sampling in most real cases.

DESIGNS

Based on bottleneck effect and coreceptor switching, we aimed at identifying an estimator from sequences of viral gp120 proteins to determine transmission direction between transmission pairs. The estimator should be changed with HIV transmission but was independent of disease progression in an individual.

METHODS

Here, we present a novel and reliable approach for identifying transmission direction. We derived a set of conserved patterns, called common patterns, from the sequences of viruses, which differed in their coreceptor usage. The number of unique common patterns in viral sequences decreased with transmission but remained almost constant with the progress of disease in an individual. We used this number as an estimator to determine transmission direction in 73 transmission pairs for which the transmission direction was already known.

RESULTS

Our method predicted transmission direction with an accuracy of up to 94.5%. Of greater importance, our approach was not influenced by time lags between infection and sampling, and even transmission direction for transmission pairs with long time lags ranging from 2 years to more than 18 years were correctly determined.

CONCLUSION

Our approach for accurately determining transmission direction between transmission pairs is irrespective of the time lag between infection and sampling, which means a promising applications prospect.

Absence of reproducibly detectable low-level HIV viremia in highly exposed seronegative men and women

OBJECTIVE

Transient HIV infections have been invoked to account for the cellular immune responses detected in highly virus-exposed individuals who have remained HIV-seronegative. We tested for very low levels of HIV RNA in 524 seronegative plasma samples from 311 highly exposed women and men from three longitudinal HIV cohorts.

DESIGN

Two thousand and seventy-three transcription-mediated amplification (TMA) HIV RNA tests were performed for an average of 3.95 TMA assays per plasma sample. Quadruplicate TMA assays, analyzing a total of 2 ml of plasma, provided an estimated sensitivity of 3.5 HIV RNA copies/ml.

RESULTS

Four samples from individuals who did not seroconvert within the following 6 months were positive for HIV RNA. For one sample, human polymorphism DNA analysis indicated a sample mix-up. Borderline HIV RNA detection signals were detected for the other three positive samples but further replicate TMA testing yielded no positive results. Nested PCR assays (n = 254) for HIV proviral DNA in peripheral blood mononuclear cells (PBMCs) from these three individuals were negative.

CONCLUSION

Transient viremia was not reproducibly detected in highly HIV-exposed seronegative men and women. If transient infections do occur, plasma HIV RNA levels may remain below the detection limits of the sensitive assay used here, be of very short duration, or viral replication may be restricted to mucosal surfaces or their draining lymphoid tissues.

Comment on "The origins of sexually transmitted HIV among men who have sex with men"

Whether HIV from seminal cells or free HIV in semen is the origin of transmitted virus has important implications for the design of transmission prevention strategies. We found that a recent claim that HIV originates from seminal plasma and not from seminal cells was erroneous, because it was based on biological specimens that had been mislabeled, mixed-up, or contaminated. The origin of transmitted virus from semen therefore remains an open question.

Response to Comment on "The Origins of Sexually Transmitted HIV Among Men Who Have Sex with Men"

In this investigation, we evaluated explanations for the unusual degree of genetic diversity in HIV populations within the sampled seminal cell and plasma compartments observed in our previous study. These analyses included clonal sequencing of HIV DNA in peripheral blood mononuclear cells, ultradeep sequencing of HIV RNA in blood plasma, human leukocyte antigen (HLA) haplotyping of previously used samples, and a BLAST screen against both a local and public repository of HIV-1 sequences, and the investigations to determine whether these observations were secondary to contamination or artifact were unsuccessful. As there are very few HIV sequences from seminal cell tissues and transmission pairs described in the literature, future studies that evaluate more transmission pairs with sampling from multiple anatomic compartments and at multiple time points will most likely be required to resolve this controversy.

Early infant human immunodeficiency virus type 1 detection suitable for resource-limited settings with multiple circulating subtypes by use of nested three-monoplex DNA PCR and dried blood spots

The early detection of human immunodeficiency virus type 1 (HIV-1) infection in infants is complicated by the persistence of maternal antibodies and by diverse HIV-1 subtypes. We developed a nested, three-monoplex HIV-1 DNA PCR (N3M-PCR) assay to detect diverse HIV-1 subtypes in infants born to infected mothers. We optimized the test for use with dried blood spot (DBS) samples for ease of storage and transport from rural China to central laboratories. Six pairs of primers were designed that targeted env, gag, and pol genes, and the test was run in three reactions with an analytical sensitivity of 10 copies DNA per reaction to cover nine HIV-1 subtypes, A, B, C, D, F, G, CRF01-AE, CRF08-BC, and CRF07-BC. The assay performance was evaluated on 347 DBS specimens from 151 exposed infants in four diverse provinces of China in which multiple subtypes were circulating. The results of this test were compared to those of HIV antibody enzyme immunoassay and Western blotting confirmation for the infants at > or =18 months of age or to convincing clinical and epidemiologic data for deceased infants. The sensitivity of the N3M-PCR assay was 30.0% (3/10) for infants at 48 h after birth, 91.7% (11/12) at 1 to 2 months of age, and 93.7% (15/16) at 3 to 6 months of age. The specificity was 100% (94/94) at all three time points. The PCR reproducibility in the three DNA regions was 100% for samples at 48 h after birth, 96.7% at 1 to 2 months, and 100% at 3 to 6 months of age. The HIV-1 DNA N3M-PCR assay on DBSs offers a simple and affordable approach for early infant HIV-1 diagnosis in regions with diverse HIV-1 circulating subtypes.

HIV Type 1 Superinfection with a Dual-Tropic Virus and Rapid Progression to AIDS: A Case Report

BACKGROUND

The occurrence of human immunodeficiency virus type 1 (HIV-1) superinfection has implications for vaccine development and our understanding of HIV pathogenesis and transmission.

METHODS AND RESULTS

We describe a subject from the Multicenter AIDS Cohort Study who was superinfected with a dual-tropic (CXCR4/CCR5-utilizing) HIV-1 subtype B strain between 0.8 and 1.3 years after seroconversion who had rapid progression to AIDS; the subject developed Pneumocystis pneumonia 3.4 years after seroconversion, as well as multiple other opportunistic infections. The superinfecting strain rapidly became the predominant population virus, suggesting that the initial and superinfecting viruses in this individual differed in virulence. However, we found no molecular epidemiological evidence in the HIV database to suggest that this strain had been found in other individuals. In addition, this subject's HIV-1 viral load and pattern of human leukocyte antigen and coreceptor polymorphisms only partially explained his rapid disease progression.

CONCLUSIONS

Additional studies are needed to determine whether superinfection itself and/or infection with a dual-tropic virus causes rapid disease progression, or whether certain individuals who are innately more susceptible to rapid disease progression also lack the ability to resist the challenge of a second infection. This case appears to support the latter hypothesis.

Strong HIV-1-specific T cell responses in HIV-1-exposed uninfected infants and neonates revealed after regulatory T cell removal

BACKGROUND

In utero transmission of HIV-1 occurs on average in only 3%-15% of HIV-1-exposed neonates born to mothers not on antiretroviral drug therapy. Thus, despite potential exposure, the majority of infants remain uninfected. Weak HIV-1-specific T-cell responses have been detected in children exposed to HIV-1, and potentially contribute to protection against infection. We, and others, have recently shown that the removal of CD4(+) CD25(+) T-regulatory (Treg) cells can reveal strong HIV-1 specific T-cell responses in some HIV-1 infected adults. Here, we hypothesized that Treg cells could suppress HIV-1-specific immune responses in young children.

METHODOLOGY/PRINCIPAL FINDINGS

We studied two cohorts of children. The first group included HIV-1-exposed-uninfected (EU) as well as unexposed (UNEX) neonates. The second group comprised HIV-1-infected and HIV-1-EU children. We quantified the frequency of Treg cells, T-cell activation, and cell-mediated immune responses. We detected high levels of CD4(+) CD25(+) CD127(-) Treg cells and low levels of CD4(+) and CD8(+) T cell activation in the cord blood of the EU neonates. We observed HIV-1-specific T cell immune responses in all of the children exposed to the virus. These T-cell responses were not seen in the cord blood of control HIV-1 unexposed neonates. Moreover, the depletion of CD4(+) CD25(+) Treg cells from the cord blood of EU newborns strikingly augmented both CD4(+) and CD8(+) HIV-1-specific immune responses.

CONCLUSIONS/SIGNIFICANCE

This study provides new evidence that EU infants can mount strong HIV-1-specific T cell responses, and that in utero CD4(+) CD25(+) T-regulatory cells may be contributing to the lack of vertical transmission by reducing T cell activation.

Evidence for persistent, occult infection in neonatal macaques following perinatal transmission of simian-human immunodeficiency virus SF162P3

To model human immunodeficiency virus (HIV) perinatal transmission, we studied infection of simian-human immunodeficiency virus (SHIV) SF162P3 in 10 pregnant Macaca nemestrina females and their offspring. Four of nine infants born to and suckled by these dams had evidence of infection, a transmission rate of 44.4% (95% confidence interval, 13.7% to 78.8%). We quantified transplacentally acquired and de novo Env-specific immunoglobulin G (IgG), IgM, and neutralizing antibodies in newborns. Transmission of escape variants was confirmed. In utero infection (n = 1) resulted in high viremia, depletion of peripheral CD4+ T cells, and rapid evolution of env in blood and tissues. Peripartum or postpartum SHIV infection (n = 3) resulted in postacute viral control that was undetectable by very sensitive multiplex PCR, despite increasing antibodies. Seropositive infants with highly controlled viremia had homogeneous peripheral blood env sequences, and their tissues had <3 copies per million cells. A high incidence of seropositive virus-low or -negative SHIV infection in infant macaques has implications for HIV type 1 perinatal transmission and detection.

Human Immunodeficiency Virus type 1 in seronegative infants born to HIV-1-infected mothers

Background

Some individuals repeatedly exposed to Human Immunodeficiency Virus do not seroconvert and are resistant to HIV infection. Here, in a pediatric cohort of HIV seronegative infants born of HIV-infected mothers, we have studied eight non-breastfed children in whom viral DNA was detected in their PBMC. Our objective was to assess whether silent infection in these children can be explained by the presence of integrated viral DNA.

Methods

The presence of viral DNA was corroborated by nested PCR with primers for gag and the nef/LTR regions of HIV-1. Integration of HIV DNA into the host genome was assessed by an Alu-LTR PCR. Amplicons were sequenced and phylogenetic analyzes were done.

Results

HIV-1 DNA was detected in the earliest available PBMC sample from all eight infants, and two of them tested positive for HIV DNA at 2 years of age. Nested PCR resulted in the amplification of gag, nef/LTR and Alu-LTR fragments, which demostrated that HIV-1 DNA was integrated in the host cell genome. Each individual has a characteristic sequence pattern and is different from the LTR sequence of HXB2 prototype virus and other Mexican isolates.

Conclusion

HIV-1 DNA was observed in PBMC from HIV exposed seronegative children in this pediatric cohort.

Transient or occult HIV infections may occur more frequently than progressive infections: changing the paradigm about HIV persistence

Evidence of transient HIV infections was found in 8 subjects at high-risk for HIV infection among 47 longitudinally studied over 2-5 (average approximately 3.5) years, whereas only two subjects developed progressive infection. All of these subjects developed serum antibodies (Ab) to conformational epitopes of HIV gp41 (termed "early HIV Ab"), but the 8 transiently infected subjects lost this Ab within 4-18 months, and did not seroconvert to positivity in denatured antigen EIA or Western Blot (WB). However, the two progressively infected subjects eventually seroconverted in the EIA and WB tests within one to two months after the appearance of "early HIV Ab". HIV env and nef sequences were directly PCR amplified from the peripheral blood mononuclear cells (PBMCs) of two of the eight transiently infected subjects during the time of "early HIV Ab"-postivity, and these showed significant sequence divergence from the HIV strains in the laboratory, indicating that they were not laboratory contaminants. Genome identity typing ("paternity-typing") of PBMC samples obtained at the time of "early HIV Ab"-positivity, and later when Ab was absent from each of the 8 subjects, showed that blood samples were not mixed-up. This provides further evidence that transient or occult infection with HIV does occur, and perhaps at a greater frequency than do progressive infections.

Insights into the role of host genetic and T-cell factors in resistance to HIV transmission from studies of highly HIV-exposed Thais

Studies of resistance to HIV-1 transmission are likely to be valuable for the design of vaccines and other efforts to prevent HIV. Here, we review the T-cell and genetic factors associated with resistance to HIV-1 transmission in studies of highly exposed but persistently seronegative (HEPS) women from northern Thailand. Women were enrolled in two sex-worker studies and in a discordant couple study. We performed Cr51 cytotoxic T lymphocyte (CTL), interferon-gamma (IFN-gamma) ELISPOT, and proliferation assays as well as genetic studies, including HLA-class I typing. CTL and ELISPOT studies showed a skewing of T-cell responses to conserved HIV-1 proteins in HEPS, but not in HIV-1-seropositive women. T-cell responses were extremely long-lived in some HEPS women. In the two sex-worker studies, HLA-A11 was associated with resistance to HIV-1 transmission. These data provide promise for the ability of CTL to control HIV and emphasize the importance of developing HIV vaccines that stimulate strong, long-lasting Tcell responses.

Persistence of low levels of simian immunodeficiency virus in macaques that were transiently viremic by conventional testing

Transient SIV viremia after experimental SIV challenge has been documented. Whether SIV persists in these transiently viremic macaques remains unclear. In the present study, we applied a sensitive PCR and found persistent low levels of SIVmne infection (LLSI) (range: 0.1-5.3 SIV DNA copies/10(6) PBMC) in seven macaques that were transiently positive by conventional assays, which was 10(2)- to 10(6)-fold less than those of SIVmne infected monkeys with typical disease progression. SIV envelope V1 sequences remained homogeneous in these macaques for the 6-year study period, with a mean evolution rate of 0.005% per site per year, which was not different from zero (P = 0.612) and significantly lower than that (0.56-1.18%) in macaques with progressive infection of SIVmne. LLSI macaques have remained free from SIV-associated illness, and are still alive 10 years after virus inoculation. Understanding the mechanisms underlying this outcome may provide valuable insight into therapy and vaccine development.

Influence of Mother and Infant Zidovudine Treatment Duration on the Age at Which HIV Infection Can be Detected by Polymerase Chain Reaction in Infants

Objective

To investigate the influence of zidovudine (ZDV) prophylaxis duration in mothers and infants on the age at which infection becomes detectable by DNA polymerase chain reaction (PCR) in non-breastfed infants.

Methods

Blood samples were collected sequentially from birth to 6 months in a Thailand perinatal HIV prevention trial in which 98 transmissions occurred. The proportions of infections detectable at birth and the Turnbull distributions of age at which infection became detectable after birth were compared according to actual ZDV treatment duration (mothers: no more than 7.5 weeks versus more; infants: 3 days versus at least 4 weeks), provided an adherence greater than 75%.

Results

Detectable infection at birth was less frequent in children whose mothers received a long treatment as compared to a short treatment (27 vs 50%, P=0.04). When mothers received a long treatment, infant ZDV treatment duration did not influence the distribution of age at which infection became detectable after birth (median 24 days). However, when mothers received a short treatment, this distribution was shifted to the right when infants received a long treatment (median 43 days, P<0.0001), and to the left when infants received a short treatment (median 11 days, P<0.0001).

Conclusions

When mothers receive a short treatment, the proportion of infections detectable at birth is higher and the time at which infection becomes detectable after birth depends on the infant treatment duration. In the study conditions, a PCR result after 2 months could be used to define infection status.

Molecular investigation of two possible cases of accidental HIV-1 transmission in South Africa

HIV-1 sequences from two possible transmission cases in South Africa were examined for evidence of genetic linkage. HIV-1-seropositive blood samples were obtained from a donor and recipient within 8 months following a blood transfusion and from a healthcare worker and her patient within 10 months following a needle-stick injury. A 700-bp region in env and 550-bp region in gag were analyzed. All sequences were phylogenetically associated with HIV-1 subtype C, the predominant HIV-1 subtype in South Africa. The nucleotide sequences from the blood transfusion case grouped together significantly with a bootstrap value of 100%. These samples were 98% and 100% identical in the predicted amino acid sequences of env and gag, respectively. In contrast, sequences from the needle-stick case showed only 67% and 80% amino acid identity in env and gag, respectively, and were separated on a phylogenetic tree. Molecular analysis suggested that HIV transmission occurred in the blood transfusion case but not in the case of the needle-stick injury. These data emphasize the need for molecular investigation of epidemiologically linked cases of HIV transmission.

Persistence of extraordinarily low levels of genetically homogeneous human immunodeficiency virus type 1 in exposed seronegative individuals

Some individuals remain inexplicably seronegative and lack evidence for human immunodeficiency virus type 1 (HIV-1) infection by conventional serologic or virologic testing despite repeated high-risk virus exposures. Here, we examined 10 exposed seronegative (ES) individuals exhibiting HIV-1-specific cytotoxicity for the presence of HIV-1. We discovered HIV-1 DNA in resting CD4(+) T cells (mean, 0.05 +/- 0.01 copies per million cells) at multiple visits spanning 69 to 130 weeks in two ES individuals at levels that were on average 10(4)- to 10(6)-fold lower than those of other HIV-1-infected populations reported. Sequences of HIV-1 envelope and gag genes remained markedly homogeneous, indicating little to undetectable virus replication. These results provide the evidence for HIV-1 infection in ES individuals below the detection limit of standard assays, suggesting that extraordinary control of infection can occur. The two HIV-infected ES individuals remained healthy and were not superinfected with other HIV-1 strains despite continued high-risk sexual exposures to multiple HIV-infected partners. Understanding the mechanisms that confer diminished replicative capacity of HIV-1 in these hosts is paramount to developing strategies for protection against and control of HIV-1 infection.

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.

Multiple viral genetic analyses detect low-level human immunodeficiency virus type 1 replication during effective highly active antiretroviral therapy

To evaluate human immunodeficiency virus type 1 (HIV-1) replication and selection of drug-resistant viruses during seemingly effective highly active antiretroviral therapy (HAART), multiple HIV-1 env and pol sequences were analyzed and viral DNA levels were quantified from nucleoside analog-experienced children prior to and during a median of 5.1 (range, 1.8 to 6.4) years of HAART. Viral replication was detected at different rates, with apparently increasing sensitivity: 1 of 10 by phylogenetic analysis; 2 of 10 by viral evolution with increasing genetic distances from the most recent common ancestor (MRCA) of infection; 3 of 10 by selection of drug-resistant mutants; and 6 of 10 by maintenance of genetic distances from the MRCA. When four- or five-drug antiretroviral regimens were given to these children, persistent plasma viral rebound did not occur despite the accumulation of highly drug-resistant genotypes. Among the four children without genetic evidence of viral replication, a statistically significant decrease in the genetic distance to the MRCA was detected in three, indicating the persistence of a greater number of early compared to recent viruses, and their HIV-1 DNA decreased by > or =0.9 log(10), resulting in lower absolute DNA levels (P = 0.007). This study demonstrates the variable rates of viral replication when HAART has suppressed plasma HIV-1 RNA for years to a median of <50 copies/ml and that combinations of four or five antiretroviral drugs suppress viral replication even after short-term virologic failure of three-drug HAART and despite ongoing accumulation of drug-resistant mutants. Furthermore, the decrease of cellular HIV-1 DNA to low absolute levels in those without genetic evidence of viral replication suggests that monitoring viral DNA during HAART may gauge low-level replication.

Virologic risk factors for vertical transmission of HIV type 1 in Puerto Rico

HIV-1 vertical transmission in Puerto Rico has decreased significantly due to the implementation of antiviral therapy. Several studies have shown that the phenotype of the HIV-1 isolates initially recovered from infected infants has generally been one that replicates rapidly, infects macrophages, and preferentially use the CCR5 coreceptor. Our hypothesis is that viral genotypic and phenotypic differences exist between HIV-1 nontransmitter and transmitter mothers. Viral DNA samples and virus isolates were analyzed from a Puerto Rican perinatal population. Heteroduplex tracking assay (HTA) was performed on DNA samples to detect env V3 evolutionary variants and the extent of heterogeneity within each sample. HIV-1 C2-V3 variants were cloned from each patient to study sequence variation among the groups. Differences in replication kinetics of viral isolates in macrophage and GHOST CCR5 cells were analyzed by use of repeated measures linear regression analysis. HTA analysis showed that only two nontransmitter patient samples showed the presence of evolutionary variants. Phylogenetic analysis between maternal-infant pairs showed that transmission of a single maternal variant occurred, with the exception of one sample pair. When evaluating amino acid sequences from cloned PCR products, nontransmitting mothers appear to have a higher number of distinct sequences than both the transmitting mothers (p = 0.0410) and the infected infants (p = 0.0315). Analysis of replication kinetics indicated that transmitters showed faster replication kinetics in GHOST CCR5 cell cultures at 12 days postinfection (p = 0.0434) and 15 days postinfection (p = 0.0181). In conclusion, viral homogeneity and rapid replication kinetics were correlated with vertical transmission.

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

Significant immunological changes are associated with intrauterine human immunodeficiency virus (HIV) encounter among uninfected infants of HIV-infected mothers. Peripheral blood cells of more than one-third of these exposed-uninfected infants proliferate and produce IL-2 after stimulation with HIV, and HIV-specific CD4+ T helper cell responses can be quantified in nearly all when sensitive intracellular cytokine assays are used. HIV-specific CD8+ cytotoxic T lymphocyte responses can be elicited in some, although less frequently. It is difficult to demonstrate that these responses are components of protective immunity and not simply epiphenomena of exposure. However, HIV-specific responses are associated with lack of infection, even with prolonged reexposure through breast-feeding. Elevations in nonspecific markers of immune activation provide further corroboration, as do similar findings in adults, consistent across all known routes of HIV transmission. Many questions remain, but much can be learned from this special population that may be informative for development of effective immunity in response to HIV vaccines.

Molecular epidemiology of human immunodeficiency virus type 1 transmission in a heterosexual cohort of discordant couples in Zambia

Most human immunodeficiency virus type 1 (HIV-1) transmissions in sub-Saharan Africa are believed to occur between married adults who are discordant for their HIV-1 infection status; however, no studies to date have investigated the molecular epidemiology of such transmission events. Here we report the genetic characterization of HIV-1 strains from 149 transmission pairs that were identified prospectively in a cohort of discordant couples in Lusaka, Zambia. Subgenomic gag, gp120, gp41, and/or long terminal repeat regions were amplified by PCR analysis of uncultured blood samples from both partners and sequenced without interim cloning. Pairwise genetic distances were calculated for the regions analyzed and compared to those of subtype-specific reference sequences as well as local controls. Sequence relationships were also examined by phylogenetic tree analysis. By these approaches, epidemiological linkage was established for the majority of transmission pairs. Viruses from 129 of the 149 couples (87%) were very closely related and clustered together in phylogenetic trees in a statistically highly significant manner. In contrast, viruses from 20 of the 149 couples (13%) were only distantly related in two independent genomic regions, thus ruling out transmission between the two partners. The great majority (95%) of transmitted viruses were of subtype C origin, although representatives of subtypes A, D, G, and J were also identified. There was no evidence for extensive transmission networks within the cohort, although two phylogenetic subclusters of viruses infecting two couples each were identified. Taken together, these data indicate that molecular epidemiological analyses of presumed transmission pairs are both feasible and required to determine behavioral, virological, and immunological correlates of heterosexual transmission in sub-Saharan Africa with a high level of accuracy.

HIV-specific cytotoxic T lymphocytes, HLA-A11, and chemokine-related factors may act synergistically to determine HIV resistance in CCR5 delta32-negative female sex workers in Chiang Rai, northern Thailand

Understanding how highly HIV-exposed individuals remain HIV uninfected may be useful for HIV vaccine design and development of new HIV prevention strategies. To elucidate mechanisms associated with resistance to HIV infection, immunologic and genetic factors were examined in 14 HIV-exposed but persistently seronegative (HEPS) female sex workers from Chiang Rai, northern Thailand and in ethnically matched, HIV-positive (n = 9) and HIV-negative women (n = 9). The HEPS women were identified in a study of commercial sex workers who had an HIV-1 incidence of 20.3 per 100 person-years. A high frequency of HLA-A11 was observed in HEPS women (86%) compared with northern Thai controls (56%). HIV-specific cytotoxic T lymphocyte (CTL) lytic responses were detected in cryopreserved peripheral blood mononuclear cells (PBMCs), using HLA-A-matched subtype E HIV-1 peptides in four of seven (57%) HEPS women, eight of eight HIV-positive women, and zero of nine HIV-negative unexposed controls (p = 0.019 HEPS women vs. HIV-negative controls). CTL lysis levels were low, but responses were detected to peptides from Nef, Pol, Gag, and Env. Nef responses predominated in HEPS women. Compared with controls, HEPS women tended to have higher frequencies of CCR5 promotor 59402GG and SDF-1 3'UTR 801A genotypes known to influence HIV transmission or course of disease. HEPS women also had higher levels of spontaneous RANTES production by PBMCs than other groups. Each of these factors could potentially contribute to HIV resistance. As most HEPS women had one or more of these factors, they may prevent HIV infection synergistically by blocking HIV cell entry, delaying its dissemination, or killing HIV-infected cells.

T-helper cell responses to HIV envelope peptides in cord blood: protection against intrapartum and breast-feeding transmission

BACKGROUND

Acquired HIV-specific cell-mediated immune responses have been observed in exposed-uninfected individuals, and it has been inferred, but not demonstrated, that these responses constitute a part of natural protective immunity to HIV. This inference was tested prospectively in the natural exposure setting of maternal-infant HIV transmission in a predominantly breast-fed population.

METHODS

Cord blood from infants of HIV-seropositive women in Durban, South Africa, were tested for in vitro reactivity to a cocktail of HIV envelope peptides (Env) using a bioassay measuring interleukin-2 production in a murine cell line. Infants were followed with repeat HIV RNA tests up to 18 months of age to establish which ones acquired HIV-infection.

RESULTS

T-helper cell responses to Env were detected in 33 out of 86 (38%) cord blood samples from infants of HIV-seropositive women and in none of nine samples from seronegative women (P = 0.02). Among infants of HIV-seropositive mothers, three out of 33 with T-helper responses to Env were already infected before delivery (HIV RNA positive on the day of birth), two were lost to follow-up, and none of the others (out of 28) were found to be HIV infected on subsequent tests. In comparison, six out of 53 infants unresponsive to Env were infected before delivery, and eight out of 47 (17%) of the others were found to have acquired HIV infection intrapartum or post-partum through breast-feeding (P = 0.02).

CONCLUSIONS

T-helper cell responses to HIV envelope peptides were detected in more than one-third of newborns of HIV-infected women; no new infections were acquired by these infants at the time of delivery or post-natally through breast-feeding if these T-helper cell responses were detected in cord blood.

Vertical human immunodeficiency virus type 1--HIV-1--transmission--a review

Several factors appear to affect vertical HIV-1 transmission, dependent mainly on characteristics of the mother (extent of immunodeficiency, co-infections, risk behaviour, nutritional status, immune response, genetical make-up), but also of the virus (phenotype, tropism) and, possibly, of the child (genetical make-up). This complex situation is compounded by the fact that the virus may have the whole gestation period, apart from variable periods between membrane rupture and birth and the breast-feeding period, to pass from the mother to the infant. It seems probable that an extensive interplay of all factors occurs, and that some factors may be more important during specific periods and other factors in other periods. Factors predominant in protection against in utero transmission may be less important for peri-natal transmission, and probably quite different from those that predominantly affect transmission by mothers milk. For instance, cytotoxic T lymphocytes will probably be unable to exert any effect during breast-feeding, while neutralizing antibodies will be unable to protect transmission by HIV transmitted through infected cells. Furthermore, some responses may be capable of controlling transmission of determined virus types, while being inadequate for controlling others. As occurrence of mixed infections and recombination of HIV-1 types is a known fact, it does not appear possible to prevent vertical HIV-1 transmission by reinforcing just one of the factors, and probably a general strategy including all known factors must be used. Recent reports have brought information on vertical HIV-1 transmission in a variety of research fields, which will have to be considered in conjunction as background for specific studies.

Simple, sensitive, and specific detection of human immunodeficiency virus type 1 subtype B DNA in dried blood samples for diagnosis in infants in the field

The detection of virus is used to diagnose human immunodeficiency virus type 1 (HIV-1) infection in infants due to the persistence of maternal antibodies for a year or more. An HIV-1 DNA PCR assay with simple specimen collection and processing was developed and evaluated. Whole blood was collected on filter paper that lysed cells and bound the DNA, eliminating specimen centrifugation and extraction procedures. The DNA remained bound to the filter paper during PCR amplification. Assays of copy number standards showed reproducible detection of 5 to 10 copies of HIV-1 in 5 microl of whole blood. The sensitivity of the assay did not decrease after storage of the standards on filter paper for 3 months at room temperature or after incubation at 37 or 45 degrees C for 20 h. The primers used for nested PCR of the HIV-1 pol gene amplified templates from a reference panel of multiple HIV-1 subtypes but did not amplify a subtype A or a subtype C virus from children living in Seattle. The assay had a sensitivity of 98.4% and a specificity of 98.3% for testing of 122 specimens from 35 HIV-1-infected and 16 uninfected children and 43 seronegative adults living in Washington. The assay had a sensitivity of 99% and a specificity of 100% for testing of 102 HIV-1-positive (as determined by enzyme immunoassay) Peruvian women and 6 seropositive and 34 seronegative infants. This assay, with adsorption of whole blood to filter paper and no specimen processing, provides a practical, economical, sensitive, and specific method for the diagnosis of HIV-1 subtype B infection in infants.

Prenatal transmission of subtype C HIV-1 in Zimbabwe: HIV-1 RNA and DNA in maternal and cord blood

Maternal and cord samples from HIV-seropositive women and their infants in Zimbabwe, where subtype C is the predominant strain of HIV, were analyzed to determine the frequency of detection of HIV RNA and DNA. HIV RNA was detected in 90% of maternal and in 38% of cord plasma at levels at least 25% of maternal plasma. Heteroduplex mobility assays and sequencing of virus envelope (C2-V5) demonstrated closely related, but unique, subtype C viruses in maternal and cord RNA, and a significantly greater frequency of cord viremia among women with homogenous, compared with heterogeneous viral envelope RNA. Quantification of RNA, measures of envelope viral diversity, and phylogenetic analysis of maternal and cord plasma RNA provide evidence for the frequent exposure and potential transmission of HIV from mother to infant before birth.

Will genome detection replace serology in blood screening for microbial agents?

The residual risk of transfusion-transmitted viral infection in developed countries is considered minimal or negligible. However, zero risk remains a strong political objective. Genomic screening for HCV, HIV and HBV represents a major advance, eliminating infectious blood donations collected during the pre-seroconversion window period, rare cases of immunosilent infections and, possibly, a large spectrum of viral variants. In Western countries, HCV RNA genomic screening started on pools of 16-400 plasma samples from individual donations. Pooling may produce false-positive and false-negative results. Individual donation testing is more suitable to blood screening but requires multiplexing, automation, and affordable cost. Because donations from individuals who are HBV DNA-negative/serologically positive, or those apparently recovered from HCV infection, may remain infectious, it is unlikely that HBsAg, anti-HCV, and anti-HIV will be discontinued when genomic screening is extended to all three viruses. HIV-1 p24 antigen may prove redundant with HIV RNA screening. Anti-HTLV-I and HTLV-II will remain more effective than genomic testing.

Interventions to prevent vertical transmission of HIV-1: effect on viral detection rate in early infant samples

OBJECTIVE

To determine whether mode of delivery or the use of maternal or neonatal antiretroviral prophylaxis influence the age when HIV-1 can first be detected in infected infants, particularly the probability of detection at birth.

METHODS

In a collaboration between four multicentre studies, data on 422 HIV-1 infected infants who were assessed by HIV-1 DNA PCR or cell culture before 14 days of age were analysed. Weibull mixture models were used to estimate the cumulative proportion of infants with detectable levels of HIV-1 according to use of maternal/neonatal antiretroviral therapy (mainly zidovudine monotherapy) and mode of delivery.

RESULTS

HIV-1 was detected in 162 infants (38%) when they were first tested, at a median age of 2 days. At birth, it was estimated that 36% [95% confidence interval (CI), 31-41%] of infants have levels of virus that can be detected by DNA PCR or cell culture. This percentage was not associated with either mode of delivery (35% for vaginal delivery versus 40% for cesarean section delivery; P = 0.4) or the use of maternal or neonatal antiretroviral prophylaxis. Among infants with undetectable levels of HIV-1 at birth, the median time to viral detectability was estimated to be 14.8 days (95% CI, 12.9-16.8 days). This time was increased by 15% (95% CI, -11 to 48%; P = 0.3) among infants who were exposed to antiretroviral therapy postnatally compared with infants who were not exposed. No effect was observed for mode of delivery.

CONCLUSIONS

The outcome of an early virological test for HIV-1 is thought to be related directly to the timing of transmission and cesarean section delivery primarily reduces the risk of intrapartum transmission. The absence of an association between mode of delivery and viral detectability at birth was therefore unexpected. There was no evidence that foetal or neonatal exposure to prophylactic zidovudine delays substantially the diagnosis of infection, although this cannot be inferred for combination antiretroviral therapy.

Identification of a new recipient in the Sydney Blood Bank Cohort: a long-term HIV type 1-infected seroindeterminate individual

We have reported previously a cohort of long-term survivors of HIV-1 infection, known as the Sydney Blood Bank Cohort, who received HIV-1-positive blood from a common infected donor. A new recipient, C135, has been identified. This recipient became infected after receiving blood donated during the presumed time of seroconversion of the donor in February 1981. C135 has been infected for more than 18 years without signs of disease progression. The virus load in this recipient has remained below the detectable level (<20 RNA copies/ml of plasma) and repeated Western blot analyses have given an indeterminate result. By booster PCR techniques we have demonstrated that this individual is infected with HIV-1 and have characterized the viral nef and nef/LTR region sequences present. The strain of HIV-1 identified contains deletions of 88 bp from the nef alone region and a total of 139 bp deleted from the nef/LTR overlap and LTR regions. The LTR contains three wild-type Sp1 transcription factor-binding sites, the 3' wildtype NF-kappaB site, and a duplicated Sp1 and NF-kappaB region. A truncated Nef protein of only 19 amino acids is encoded. The deletions and rearrangements in the nef gene and LTR sequences are characteristic of Sydney Blood Bank Cohort strains of virus. The identification of C135 increases the Sydney Blood Bank Cohort size to nine individuals and represents a rare example of a genuine, long-term HIV-1 infection accompanied by indeterminate anti-HIV-1 serology.

Nosocomial HIV-transmission in an outpatient clinic detected by epidemiological and phylogenetic analyses

OBJECTIVE

To determine if a case of HIV-infection in a patient (GP) with common variable immunodeficiency, and with no known risk factors for HIV-infection, could be due to horizontal nosocomial transmission.

METHODS

For determination of time of transmission stored serum-samples from GP were analysed for HIV RNA content. Patient records were used to identify patients, who had received intravenous therapy on the same day as GP. Samples from GP and these possible source patients were identified and phylogenetic analyses of the env, gag and RT-encoding region of pol were performed. Furthermore, routines in conjunction with intravenous therapy were examined.

RESULTS

We identified a patient (FDL) harbouring virus almost indistinguishable from the virus isolated from GP. The pairwise nucleotide distance between the C2-V3-C3 region of the env and gag sequences from the two patients were 1.9 and 0.9% respectively. In addition, GP harboured HIV RNA with a foscarnet resistance mutation further lending support to virus from the foscarnet-treated FDL being the source of the infection. Interestingly, GP experienced increases in immunoglobulin production after contracting the HIV-infection, and decreases after antiretroviral-induced viral suppression. A clinical procedure which, under stressful conditions, could lead to breaches in infection control measures was identified. The source of the infection was most likely a contaminated multidose vial.

CONCLUSION

Through epidemiological and phylogenetic analyses a case of horizontal nosocomial HIV-transmission was disclosed. Identification of multidose vials as possible vehicles for horizontal nosocomial transmission recently led to the recommendation of restriction of the use of multidose vials, a recommendation supported by the present study. The study underlies the importance of a constant survey of infection control precautions.

T lymphocyte responses in HIV-1 infection: implications for vaccine development

Substantial progress has been made over the past year in understanding the cellular immune response in HIV pathogenesis. Cytotoxic T lymphocytes play a critical role in establishing the level of viremia and virus-specific Th cell responses appear to affect the in vivo efficacy of cytotoxic T lymphocytes. Together, these new data provide important insights to refocus efforts aimed at immunotherapeutic interventions and vaccine development.

The effects of zidovudine in the subset of infants infected with human immunodeficiency virus type-1 (Pediatric AIDS Clinical Trials Group Protocol 076)

OBJECTIVE

To describe the effect of zidovudine on human immunodeficiency virus type 1 (HIV-1) and on the course of disease in infants who became infected while they and their mothers received zidovudine preventive therapy or placebo in Pediatric AIDS Clinical Trials Group Protocol 076.

STUDY DESIGN

Observational substudy of a multicenter, randomized, double-blind, placebo-controlled trial.

METHODS

We compared the progression of disease, timing of HIV-1 transmission, and the plasma HIV-1 RNA level in infected infants of mother-infant pairs who were randomly assigned to receive zidovudine (n = 14) or placebo (n = 43). The development of genotypic zidovudine resistance was assessed among infected infants in the zidovudine treatment group.

RESULTS

In this limited study, zidovudine therapy during pregnancy and labor and in the neonatal period for 6 weeks failed to have a major effect on rapid progression of disease, timing of transmission, and viral replication in HIV-infected infants. When the zidovudine treatment regimen failed to prevent maternal-infant transmission of HIV-1, resistance to zidovudine did not develop during study treatment.

CONCLUSIONS

Our study supports the safety of zidovudine use in pregnancy and in the newborn period but demonstrates the continued need for more potent antiretroviral treatment of the infected infant.

Protective Role of β-Chemokines Associated with HIV-Specific Th Responses Against Perinatal HIV Transmission

To examine the protective role of cellular immunity in the vertical transmission of HIV, we analyzed HIV-specific IL-2 and CTL responses, as well as β-chemokine expression in HIV-infected and uninfected infants of HIV+ mothers. Our results showed that HIV envelope (env) peptide-specific IL-2 responses associated with β-chemokine production were detectable at birth in the majority of uninfected infants of HIV+ mothers. The responses falling to background before the infants were 1 yr old were rarely associated with HIV-specific CTL activity. Conversely, HIV-specific Th and CTL cellular responses were absent at birth in HIV-infected infants. Infants with AIDS-related symptoms exhibited undetectable or very low levels of HIV-specific cellular immunity during the first year of life, whereas those with a slowly progressive disease showed evidence of such immunity between their second and ninth month. The latter group of infected infants tested negative for plasma HIV RNA levels shortly after birth, suggesting lack of intrauterine exposure to HIV. The presence of HIV-specific Th responses at birth in uninfected newborns of HIV+ mothers, but absence of such activities in HIV-infected infants without evidence of intrauterine HIV infection, suggests that in utero development of HIV-specific Th responses associated with β-chemokines could mediate nonlytic inhibition of infection during vertical transmission of HIV.

Occult systemic infection and persistent simian immunodeficiency virus (SIV)-specific CD4(+)-T-cell proliferative responses in rhesus macaques that were transiently viremic after intravaginal inoculation of SIV

The intact cervicovaginal mucosa is a relative barrier to the sexual transmission of human immunodeficiency virus type 1 (HIV-1). In the simian immunodeficiency virus (SIV) macaque model of HIV infection, seronegative transient viremia (STV; virus isolation positive followed by repeated negative cultures) occurs after intravaginal inoculation of a low dose of pathogenic SIVmac251 (C. J. Miller, M. Marthas, J. Torten, N. Alexander, J. Moore, G. Doncel, and A. Hendrickx, J. Virol. 68:6391-6400, 1994). Thirty-one adult female macaques that had been inoculated intravaginally with pathogenic SIVmac251 became transiently viremic. One monkey that had been culture negative for a year after SIV inoculation became persistently viremic and developed simian AIDS. No other STV monkey developed persistent viremia or disease. Results of very sensitive assays showed that 6 of 31 monkeys had weak SIV-specific antibody responses. SIV-specific antibodies were not detected in the cervicovaginal secretions of 10 STV monkeys examined. Twenty of 26 monkeys had lymphocyte proliferative responses to p55(gag) and/or gp130(env) antigens; 3 of 6 animals, including the monkey that became persistently viremic, had detectable cytotoxic T-lymphocyte (CTL) responses to SIV. At necropsy, lymphoid tissues and vaginal mucosa were virus culture negative, but in 10 of 10 animals, SIV provirus was detected by PCR using gag-specific primer pairs. Fifty percent of the PCR-positive tissue samples were also positive for SIV gag RNA by reverse transcriptase PCR. Thus, transient viremia following intravaginal inoculation of pathogenic SIV is associated with persistent, systemic infection, either latent or very low level productive. Atypical immune responses, characterized by lymphocyte proliferation and some CTL responses in the absence of conventionally detectable antibodies, develop in transiently viremic monkeys.

Sensitivity and specificity of a qualitative RNA detection assay to diagnose HIV infection in young infants. Perinatal AIDS Collaborative Transmission Study

OBJECTIVE

To evaluate the sensitivity and specificity of an RNA detection assay for diagnosing perinatal HIV infection.

METHODS

Plasma and serum specimens taken during the first 3 months of life from HIV-infected and uninfected children enrolled in a cohort study were assayed for HIV RNA using the qualitative nucleic acid sequence-based amplification (NASBA) kit. Sensitivity, specificity, and predictive values were calculated. NASBA results from infected children were compared with DNA PCR results from the same blood samples. Autoantibody patterns of suspected false-positive specimens were compared with those of subsequent specimens from the same child to exclude specimen labelling errors.

RESULTS

Amongst 131 specimens from 105 HIV-infected children, the sensitivity of the qualitative NASBA assay was 13 out of 34 [38%; 95% confidence interval (CI), 22-56] at < 7 days, 56 out of 58 (97%; 95% CI, 88-100) at 7-41 days, and 37 out of 39 (95%; 95% CI, 83-99) at 42-93 days of life. Of 252 specimens from 206 uninfected children, six tested positive and one tested indeterminate by NASBA. Four of these positive specimens had discordant autoantibody patterns suggesting mislabelling; excluding these, the test specificity was 245 out of 248 (99%; 95% CI, 97-100). Amongst 128 paired specimens from infected children, NASBA results were more often positive than those from DNA PCR (103 versus 92; P=0.01). Amongst infants with specimens drawn in the first week of life, the proportion born after > 4 h of membrane rupture was greater amongst those testing negative (81%) than those testing positive (46%; P=0.05).

CONCLUSIONS

The qualitative NASBA RNA assay is highly specific and more sensitive than DNA PCR. Qualitative RNA assays may be useful for diagnosing and excluding perinatal HIV infection in children after the first week of life for such purposes as initiating antiretroviral therapy and other treatment, resolving parental uncertainty, determining timing of transmission, and providing endpoints for intervention trials.