The EPIICAL project: an emerging global collaboration to investigate immunotherapeutic strategies in HIV-infected children

The EPIICAL (Early-treated Perinatally HIV-infected Individuals: Improving Children's Actual Life with Novel Immunotherapeutic Strategies) project arises from the firm belief that perinatally infected children treated with suppressive antiretroviral therapy (ART) from early infancy represent the optimal population model in which to study novel immunotherapeutic strategies aimed at achieving ART-free remission. This is because HIV-infected infants treated within 2-3 months of life have a much reduced viral reservoir size, and rarely show HIV-specific immunity but preserve normal immune development. The goal of EPIICAL is the establishment of an international collaboration to develop a predictive platform using this model to select promising HIV therapeutic vaccine candidates, leading to prioritisation or deprioritisation of novel immunotherapeutic strategies. To establish this platform, the EPIICAL Consortium aims to: develop predictive models of virological and immunological dynamics associated with response to early ART and to treatment interruption using available data from existing cohorts/studies of early-treated perinatally HIV-infected children; optimise methodologies to better characterise immunological, virological and genomic correlates/profiles associated with viral control; test novel immunotherapeutic strategies using in vivo proof-of-concept (PoC) studies with the aim of inducing virological, immunological and transcriptomic correlates/profiles equivalent to those defined by the predictive model. This approach will strengthen the capacity for discovery, development and initial testing of new therapeutic vaccine strategies through the integrated efforts of leading international scientific groups, with the aim of improving the health of HIV-infected individuals.

Lack of alternative coreceptor use by pediatric HIV-1 R5 isolates for infection of primary cord or adult peripheral blood mononuclear cells

HIV-1 infection of neonates results in an extended acute period of virus replication, frequent neurological problems and reduced survival compared to adults. In adults, R5 viruses mainly infect CCR5(+) CD4(+) memory T-cells. In neonates, CCR5(+) memory T-cells form a substantially smaller fraction of total lymphocytes. We therefore tested whether alternative coreceptors confer infection of lymphocytes by pediatric isolates. Pediatric HIV-1 R5 isolates failed to replicate in Delta32/Delta32 CCR5 PBMCs or in cord PBMCs treated with a CCR5 inhibitor. These results do not indicate a role for alternative coreceptors and provide support for CCR5 inhibitors in the therapy of HIV-1(+) neonates.

Immunogenicity and efficacy of childhood vaccines in HIV-1-infected children

Children infected by HIV-1 are particularly vulnerable to severe, recurrent, or unusual infections by vaccine-preventable pathogens. Routine immunisations seem to be generally safe for HIV-1-infected children, but responses may be suboptimal. Early HIV-1-induced immune attrition associated with viral replication may particularly interfere with the development of memory responses. In high HIV-1 prevalence regions, the accumulation of susceptible hosts may compromise disease-control efforts. Although early control of viral replication through treatment with highly active therapy may preserve immune function and responses to routine childhood vaccines, availability is limited in the areas most affected. In this review, we provide an overview of the immunogenicity and efficacy of childhood vaccines in HIV-1-infected children. The possible immunological bases for defective responses are discussed; unanswered questions and the need for further research are delineated.

Infrequent detection of HIV-1-specific, but not cytomegalovirus-specific, CD8(+) T cell responses in young HIV-1-infected infants

Early potent combination antiretroviral therapies (ART) for HIV-1 infection can preserve or restore immune function, but control of viral replication early in infection may interfere with the development of HIV-1-specific immune responses. Using an IFN-gamma ELISPOT assay, we evaluated the breadth and intensity of HIV-1-specific CD8(+) T cell responses in 17 vertically infected infants who began ART at 1-23 mo of age. CMV-specific responses were also characterized in three infants coinfected with HIV-1 and CMV. Before ART, HIV-1-specific CD8(+) T cell responses were detected in two of 13 (15%) infants <6 mo of age. HIV-1-specific CD8(+) T cells became undetectable in these two infants after the control of viral replication. Intermittent HIV-1-specific responses were noted in six infants who did not experience durable control of viral replication. In contrast, HIV-1-specific responses were detected before ART in four of four infants >6 mo of age and became persistently undetectable in only one child. CMV-specific CD8(+) T cell responses were persistently detected in all HIV-1 and CMV coinfected infants. In conclusion, HIV-1-specific CD8(+) T cell responses were less commonly detected before therapy in young infants than in older infants. Suppression of viral replication appeared to interfere with the development and maintenance of HIV-1-specific CD8(+) T cell responses. The detection of CMV-specific responses in HIV-1 and CMV coinfected infants suggests a selective defect in the generation or maintenance of HIV-1-specific CD8(+) T cell responses. Therapeutic HIV-1 vaccine strategies in young infants may prolong the clinical benefit of ART by expanding the HIV-1-specific CD8(+) T cell pool.

Human immunodeficiency virus type 1 (HIV-1) gp120-specific antibodies in neonates receiving an HIV-1 recombinant gp120 vaccine

Infants born to human immunodeficiency virus type 1 (HIV-1)-infected mothers were immunized at birth and at ages 4, 12, and 20 weeks with low-, medium-, or high-dose recombinant gp120 vaccine with MF59 adjuvant (HIV-1(SF-2); n=52) or with MF59 alone as a placebo (n=9). An accelerated schedule (birth and ages 2, 8, and 20 weeks) was used for an additional 10 infants receiving the defined optimal dose and for 3 infants receiving placebo. At 24 weeks, anti-gp120 ELISA titers were greater for vaccine-immunized than for placebo-immunized infants on both schedules, and 87% of vaccinees had a vaccine-induced antibody response. At 12 weeks, antibody titers of infants on the accelerated vaccine schedule exceeded those of infants receiving placebo (4949 vs. 551; P=.01), and 63% of the vaccinees met the response criteria. Thus, an accelerated schedule of gp120 vaccinations generated an antibody response to HIV-1 envelope distinct from transplacental maternal antibody by age 12 weeks. These results provide support for further studies of vaccine strategies to prevent mother-to-infant HIV-1 transmission.

Differential evolution and stability of epitope-specific CD8(+) T cell responses in EBV infection

Murine models of lymphocytic choriomeningitis virus infection suggest that the memory CD8(+) T cell repertoire is reflective of the CD8(+) T cell repertoire generated during acute infection. Less is known regarding the evolution of CD8(+) T cell repertoires during human viral infections. We therefore examined epitope-specific CD8(+) T cell responses in a large cohort of individuals with acute through latent Epstein-Barr virus infection. Using 16 of 20 published EBV epitopes restricted by HLA-A2, HLA-A3 or HLA-B7, we showed that lytic cycle-specific CD8(+) T cell responses predominated during acute EBV infection. However, whereas HLA-A2(+)-restricted BMLF-1-specific CD8(+) T cell responses were maintained through latency, HLA-A2(+)- and HLA-B7(+)-restricted BZLF-1, as well as HLA-A3(+)-restricted BRLF-1 CD8(+) T cell responses, were generated but not readily maintained. Analyses of CD8(+) T cell responses to EBV latent cycle Ags showed delayed detection and lower frequencies of latent epitope-specific CD8(+) T cell responses during acute EBV infection, with maintenance of these responses 1 yr post-EBV infection. Early BMLF-1 and EBNA-3A epitope-specific CD8(+) T cell frequencies did not correlate with their frequencies at 1 yr postinfection. Interestingly, populations of EBV-specific CD8(+) T cells were stable during 20 mo in our long term EBV-seropositive populations, suggesting homeostasis between virus and the host immune system. This study demonstrates that CD8(+) T cell repertoires generated during persistent viral infections are not simply reflective of the initial pool of CD8(+) T cells and provides evidence that the generation of CD8(+) T cell responses to a persistent infection is a dynamic process.

Pharmacokinetics of nelfinavir in human immunodeficiency virus-infected infants

BACKGROUND

Nelfinavir dosed at approximately 20 to 30 mg/kg three times a day (TID) in older children provides exposure similar to 750 mg TID in adults. However, the pharmacokinetics (PK) of nelfinavir in infants who are < 2 years of age is not well-described. The objective of this study was to determine the pharmacokinetics of nelfinavir in infants < 2 years of age.

METHODS

Nelfinavir concentrations were evaluated in 22 HIV-infected infants between 15 days and 2 years of age receiving nelfinavir as part of Pediatric ACTG Study 356. Nelfinavir therapy was initiated at approximately 25 mg/kg TID (n = 18) or approximately 55 mg/kg twice a day (n = 4) and given in combination with nevirapine, stavudine and lamivudine. PK samples were obtained predose and 1.5 and 4 h postdose at approximately 6-month intervals. Eight infants (all < or = 3 months of age) also had intensive PK samples collected at Week 1.

RESULTS

The median apparent clearance in the infants with intensive pharmacokinetic sampling was 2.7 liters/h/kg (range, 1.8 to > or = 10) and was similar between twice a day and TID dosing cohorts. Overall nelfinavir concentrations at all collection times were lower in these infants than previously reported in older pediatric patients.

CONCLUSIONS

Nelfinavir concentrations in infants are highly variable and lower than those seen in adult or older pediatric populations receiving labeled dosing. Therefore it is necessary to further evaluate nelfinavir safety, effectiveness and pharmacokinetics at higher doses than used among other pediatric populations.

Early therapy of vertical human immunodeficiency virus type 1 (HIV-1) infection: control of viral replication and absence of persistent HIV-1-specific immune responses

Studies of potent antiretroviral combination regimens were undertaken in young infants to evaluate the potential for long-term suppression of viral replication and to evaluate the immune consequences of such therapies. Early combination antiretroviral therapy led to a loss of plasma viremia, cultivable virus, and labile extrachromosomal replication intermediates. Despite preservation of immune function, persistent human immunodeficiency type 1 (HIV-1)-specific immune responses were not detected in most infants. The absence of detectable, persisting immune responses in most HIV-1-infected infants treated early contrasts with what is typically seen in adults who are treated early. These results are consistent with the notion that early combination antiretroviral therapy of HIV-1-infected infants allows the long-term suppression of viral replication.

Effect of HIV on thymic function before and after antiretroviral therapy in children

Studies were undertaken to investigate the role of the thymus in T cell reconstitution in human immunodeficiency virus (HIV)-infected children treated with antiretroviral therapy. Nine pediatric patients who acquired HIV perinatally were treated with multidrug combinations of antiretroviral agents. Plasma virus load and CD4+ and CD8+ T cell subsets were measured, and thymus function was measured by quantifying T cell receptor rearrangement excision circles in peripheral blood. Patients with virus loads remaining >400 RNA copies/mL plasma were classified as virologic nonresponders. Thymus function was initially decreased in all subjects. After antiretrovirus therapy, peripheral CD4+ T cells increased in all subjects. Thymus function was restored in 4 of 5 virologic responders but in only 1 of 4 virologic nonresponders. This suggests that HIV has an adverse effect upon thymic function in pediatric HIV infection. Potent antiretroviral therapy restores thymic function but is affected by the degree to which virus suppression is achieved.

Viral and immunopathogenesis of vertical HIV-1 infection

High-level viral replication is the primary determinant of CD4 depletion or disease development in HIV-1--infected children. The developing immune system of infants might allow for more efficient viral replication and less efficient immune containment of viral replication. Advances in the understanding of the pathogenesis of vertical HIV-1 infection suggest that the use of potent combination regimens to control HIV-1 replication offers the best opportunity to prevent or reverse the sequelae of HIV-1 infection.

Persistence of episomal HIV-1 infection intermediates in patients on highly active anti-retroviral therapy

Treatment of HIV-1-infected individuals with a combination of anti-retroviral agents results in sustained suppression of HIV-1 replication, as evidenced by a reduction in plasma viral RNA to levels below the limit of detection of available assays. However, even in patients whose plasma viral RNA levels have been suppressed to below detectable levels for up to 30 months, replication-competent virus can routinely be recovered from patient peripheral blood mononuclear cells and from semen. A reservoir of latently infected cells established early in infection may be involved in the maintenance of viral persistence despite highly active anti-retroviral therapy. However, whether virus replication persists in such patients is unknown. HIV-1 cDNA episomes are labile products of virus infection and indicative of recent infection events. Using episome-specific PCR, we demonstrate here ongoing virus replication in a large percentage of infected individuals on highly active anti-retroviral therapy, despite sustained undetectable levels of plasma viral RNA. The presence of a reservoir of 'covert' virus replication in patients on highly active anti-retroviral therapy has important implications for the clinical management of HIV-1-infected individuals and for the development of virus eradication strategies.

Long-term nonprogressive infection with human immunodeficiency virus type 1 in a hemophilia cohort

Seven long-term nonprogressors (LTNPs) have been identified in a cohort of 128 human immunodeficiency virus (HIV)-1 infected individuals with hemophilia. Studies included quantitation of virus by polymerase chain reaction, characterization of primary virus isolates in vitro, analysis of lymphocyte surface markers, and measurement of virus-specific cytotoxic T lymphocytes (CTLs). Viruses of LTNPs exhibited slow growth in vivo and in vitro. LTNPs had expansion of CD8 T cells with increased expression of HLA-DR. Intermittent HIV-1-specific CTL effector activity was detected in freshly isolated peripheral blood mononuclear cells of most LTNPs. CTL precursor frequencies were higher in LTNPs than in patients with progressive disease. Virus antigen-specific lymphoproliferation was vigorous in some LTNPs. Thus, LTNPs in this cohort have maintained remarkably low virus burdens and vigorous HIV-1-specific cell-mediated immunity over a 15-year period. The presence of expanded, activated CD8 T cells with cytotoxic effector function in the peripheral blood suggests ongoing viral replication.

A polymorphism in the regulatory region of the CC-chemokine receptor 5 gene influences perinatal transmission of human immunodeficiency virus type 1 to African-American infants

There are natural mutations in the coding and noncoding regions of the human immunodeficiency virus type 1 (HIV-1) CC-chemokine coreceptor 5 (CCR5) and in the related CCR2 protein (the CCR2-64I mutation). Individuals homozygous for the CCR5-Delta32 allele, which prevents CCR5 expression, strongly resist HIV-1 infection. Several genetic polymorphisms have been identified within the CCR5 5' regulatory region, some of which influence the rate of disease progression in adult AIDS study cohorts. We genotyped 1,442 infants (1,235 uninfected and 207 HIV-1 infected) for five CCR5 and CCR2 polymorphisms: CCR5-59353-T/C, CCR5-59356-C/T CCR5-59402-A/G, CCR5-Delta32, and CCR2-64I. The clinical significance of each genotype was assessed by measuring whether it influenced the rate of perinatal HIV-1 transmission among 667 AZT-untreated mother-infant pairs (554 uninfected and 113 HIV-1 infected). We found that the mutant CCR5-59356-T allele is relatively common in African-Americans (20.6% allele frequency among 552 infants) and rare in Caucasians and Hispanics (3.4 and 5.6% of 174 and 458 infants, respectively; P < 0.001). There were 38 infants homozygous for CCR5-59356-T, of whom 35 were African-Americans. Among the African-American infants in the AZT-untreated group, there was a highly significant increase in HIV-1 transmission to infants with two mutant CCR5-59356-T alleles (47.6% of 21), compared to those with no or one mutant allele (13.4 to 14.1% of 187 and 71, respectively; P < 0.001). The increased relative risk was 5.9 (95% confidence interval, 2.3 to 15.3; P < 0.001). The frequency of the CCR5-59356-T mutation varies between population groups in the United States, a low frequency occurring in Caucasians and a higher frequency occurring in African-Americans. Homozygosity for CCR5-59356-T is strongly associated with an increased rate of perinatal HIV-1 transmission.

Frequent detection of escape from cytotoxic T-lymphocyte recognition in perinatal human immunodeficiency virus (HIV) type 1 transmission: the ariel project for the prevention of transmission of HIV from mother to infant

Host immunologic factors, including human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL), are thought to contribute to the control of HIV type 1 (HIV-1) replication and thus delay disease progression in infected individuals. Host immunologic factors are also likely to influence perinatal transmission of HIV-1 from infected mother to infant. In this study, the potential role of CTL in modulating HIV-1 transmission from mother to infant was examined in 11 HIV-1-infected mothers, 3 of whom transmitted virus to their offspring. Frequencies of HIV-1-specific human leukocyte antigen class I-restricted CTL responses and viral epitope amino acid sequence variation were determined in the mothers and their infected infants. Maternal HIV-1-specific CTL clones were derived from each of the HIV-1-infected pregnant women. Amino acid substitutions within the targeted CTL epitopes were more frequently identified in transmitting mothers than in nontransmitting mothers, and immune escape from CTL recognition was detected in all three transmitting mothers but in only one of eight nontransmitting mothers. The majority of viral sequences obtained from the HIV-1-infected infant blood samples were susceptible to maternal CTL. These findings demonstrate that epitope amino acid sequence variation and escape from CTL recognition occur more frequently in mothers that transmit HIV-1 to their infants than in those who do not. However, the transmitted virus can be a CTL susceptible form, suggesting inadequate in vivo immune control.

Treatment of human immunodeficiency virus 1-infected infants and children with the protease inhibitor nelfinavir mesylate

An open-label study was conducted of nelfinavir mesylate, given with reverse transcriptase inhibitors to human immunodeficiency virus 1 (HIV-1)-infected infants and children 3 months to 13 years of age. Doses of nelfinavir mesylate of 20-30 mg/kg yielded drug exposures comparable to those seen in adults. The drug was well tolerated; mild diarrhea was the primary toxic effect observed. Seventy-one percent (39) of the 55 evaluable subjects had an initial decrease in plasma HIV-1 RNA, of at least 0.7 log10 copies/mL; suppression of plasma HIV-1 RNA levels to < 400 copies/mL was observed in 15. Children who began taking at least one new reverse transcriptase inhibitor near the time when nelfinavir mesylate was started, and those with a > or = 24% proportion of CD4 lymphocytes, had a greater chance of achieving and maintaining a decline in plasma HIV-1 RNA to < 400 copies/mL. Suppression of viremia was achieved in children as young as 3 months of age.

Persistent HIV-1-specific CTL clonal expansion despite high viral burden post in utero HIV-1 infection

To address the issue of clonal exhaustion in humans, we monitored HLA class I-restricted, epitope-specific CTL responses in an in utero HIV-1-infected infant from 3 mo through 5 years of age. Serial functional CTL precursor assays demonstrated persistent, vigorous, and broadly directed HIV-1 specific CTL activity with a dominant response against an epitope in HIV-1 Gag-p17 (SLYNTVATL, aa 77-85). A clonal CTL response directed against the immunodominant, HLA-A*0201-restricted epitope was found to persist over the entire observation period, as shown by TCR analysis of cDNA libraries generated from PBMC. The analysis of autologous viral sequences did not reveal any escape mutations within the targeted epitope, and viral load measurement indicated ongoing viral replication. Furthermore, inhibition of viral replication assays indicated that the epitope was properly processed from autologous viral protein. These data demonstrate that persistent exposure to high levels of viral Ag does not necessarily lead to clonal exhaustion and that epitope-specific clonal CTL responses induced within the first weeks of life can persist for years without inducing detectable viral escape variants.

The Ariel Project: A prospective cohort study of maternal-child transmission of human immunodeficiency virus type 1 in the era of maternal antiretroviral therapy

In a prospective cohort study, clinical and biologic factors that contribute to maternal-child transmission of human immunodeficiency virus type 1 (HIV-1) were studied. HIV-infected pregnant women and their infants were evaluated prospectively according to a standardized protocol. Of 204 evaluable women, 81% received zidovudine during their pregnancy. The infection rate among the 209 evaluable infants was 9.1%. By univariate analysis, histologic chorioamnionitis, prolonged rupture of membranes, and a history of genital warts were significantly associated with transmission. Additional factors associated with transmission that approached significance included a higher maternal virus load at delivery and the presence of cocaine in the urine. In a logistic regression model, histologic chorioamnionitis was the only independent predictor of transmission. Despite a significantly higher transmission rate at one site, no unique viral genotype was found at any site. Thus, chorioamnionitis was found to be the major risk factor for transmission among women receiving zidovudine.

Dynamics of human immunodeficiency virus type 1 replication in vertically infected infants

Plasma human immunodeficiency virus type 1 (HIV-1) turnover and kinetics were studied in children aged 15 days to 2 years following the initiation of a triple antiretroviral drug regimen consisting of zidovudine, lamivudine, and nevirapine. HIV-1 turnover was at least as rapid as that previously described in adults; turnover rates were more rapid in infants and children aged 3 months to 2 years than in infants less than 3 months of age. These data confirm the central role of HIV-1 replication in the pathogenesis of vertical HIV-1 infection and reinforce the importance of early, potent combination therapies for the long-term control of HIV-1 replication.

Delayed generation of antibodies mediating human immunodeficiency virus type 1-specific antibody-dependent cellular cytotoxicity in vertically infected infants. WITS Study Group. Women and Infants Transmission Study

Human immunodeficiency virus type 1 (HIV-1)-specific antibody-dependent cellular cytotoxicity (ADCC) antibody titers were serially measured from birth to 24 months in the plasma of 14 intrapartum-infected and 10 uninfected infants born to HIV-1-infected women. The mean ADCC antibody titers measured at birth in infected and uninfected infants were similar (10(-3.9) and 10(-4.0), respectively), suggesting that ADCC antibodies did not protect infants from the intrapartum transmission of HIV-1. In infected infants, ADCC titers at birth did not predict subsequent clinical disease course. The active production of HIV-1-specific ADCC antibodies was detected in most infected infants only after 12 months of age, well after the loss of passively acquired maternal ADCC antibody. The delayed production of ADCC antibodies in infancy may account, in part, for the less efficient control of viral replication and more rapid disease progression following vertical infection compared with that in adults.

Combination treatment with zidovudine, didanosine, and nevirapine in infants with human immunodeficiency virus type 1 infection

BACKGROUND

In infants and children with maternally acquired human immunodeficiency virus type 1 (HIV-1) infection, treatment with a single antiretroviral agent has limited efficacy. We evaluated the safety and efficacy of a three-drug regimen in a small group of maternally infected infants.

METHODS

Zidovudine, didanosine, and nevirapine were administered in combination orally to eight infants 2 to 16 months of age. The efficacy of antiretroviral treatment was evaluated by serial measurements of plasma HIV-1 RNA, quantitative plasma cultures, and quantitative cultures of peripheral-blood mononuclear cells.

RESULTS

The three-drug regimen was well tolerated, without clinically important adverse events. Within four weeks, there were reductions in plasma levels of HIV-1 RNA of at least 96 percent (1.5 log) in seven of the eight study patients. Over the 6-month study period, replication of HIV-1 was controlled in two infants who began therapy at 2 1/2 months of age. Plasma RNA levels were reduced by 0.5 to 1.5 log in five of the other six infants.

CONCLUSIONS

Although further observations are needed, it appears that in infants with maternally acquired HIV-1 infection, combined treatment with zidovudine, didanosine, and nevirapine is well tolerated and has sustained efficacy against HIV-1.

Early HIV-1 envelope-specific cytotoxic T lymphocyte responses in vertically infected infants

High frequencies of cytotoxic T lymphocyte precursors (CTLp) recognizing HIV-1 laboratory strain gene products have been detected in adults within weeks of primary infection. In contrast, HIV-1-specific CTLp are uncommonly detected in infants younger than 6 mo. To address the hypothesis that the use of target cells expressing laboratory strain env gene products might limit the detection of HIV-1 env-specific CTLp in early infancy, recombinant vaccinia vectors (vv) expressing HIV-1 env genes from early isolates of four vertically infected infants were generated. The frequencies of CTLp recognizing target cells infected with vv-expressing env gene products from early isolates and HIV-1 IIIB were serially measured using limiting dilution followed by in vitro stimulation with mAb to CD3. In one infant, the detection of early isolate env-specific CTLp preceded the detection of IIIB-specific CTLp. CTLp recognizing HIV-1 IIIB and infant isolate env were detected by 6 mo of age in two infants. In a fourth infant, HIV-1 IIIB env and early isolate env-specific CTLp were simultaneously detected at 12 mo of age. These results provide evidence that young infants can generate HIV-1-specific CTL responses and provide support for the concept of neonatal vaccination to prevent HIV-1 transmission. However, the early predominance of type-specific CTL detected in some young infants suggests that the use of vaccines based on laboratory strains of HIV-1 may not protect against vertical infection.

Overlapping epitopes in human immunodeficiency virus type 1 gp120 presented by HLA A, B, and C molecules: effects of viral variation on cytotoxic T-lymphocyte recognition

Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) are thought to exert immunologic selection pressure in infected persons, yet few data regarding the effects of this constraint on viral sequence variation in vivo, particularly in the highly variable Env protein, are available. In this study, CD8+ HIV type 1 (HIV-1) envelope-specific CTL clones specific for gp120 were isolated from peripheral blood mononuclear cells of four HIV-infected individuals, all of which recognized the same 25-amino-acid (aa) peptide (aa 371 to 395), which is partially contained in the CD4-binding domain of HIV-1 gp120. Fine mapping studies revealed that two of the clones optimally recognized the 9-aa sequence 375 to 383 (SFNCGGEFF), while the two other clones optimally recognized the epitope contained in the overlapping 9-aa sequence 376 to 384 (FNCGGEFFY). Lysis of target cells by the two clones recognizing aa 375 to 383 was restricted by HLA B15 and Cw4, respectively, whereas both clones recognizing aa 376 to 384 were restricted by HLA A29. Sequence variation, relative to the IIIB strain sequence used to identify CTL clones, was observed in autologous viruses in the epitope-containing region in all four subjects. However, poorly recognized autologous sequence variants were predominantly seen for the A29-restricted clones, whereas the clones specific for SFNCGGEFF continued to recognize the predominant autologous sequences. These results suggest that the HLA profile of an individual may not only be important in determining the specificity of CTL recognition but may also affect the ability to recognize virus variants and suppress escape from CTL recognition. These results also identify overlapping viral CTL epitopes which can be presented by HLA A, B, and C molecules.

Pharmacokinetics, safety, and activity of nevirapine in human immunodeficiency virus type 1-infected children

Phase I trials were conducted in human immunodeficiency virus type 1 (HIV-1)-infected children to examine the pharmacokinetics, safety, and antiretroviral activity of nevirapine, a nonnucleoside HIV-1 reverse transcriptase inhibitor. Nevirapine was rapidly absorbed, but the time to peak plasma concentrations increased with higher doses. Clearance was more rapid in chronic dosing studies than predicted by single-dose studies and was more rapid in younger children than in adolescent children. Rash, which occurred in 1 of the 21 study participants, was the single toxicity regarded as nevirapine-related. At doses > or = 240 mg/m2/day, 5 of 10 children experienced durable suppression of plasma p24 antigen to < 50% of baseline values through 8 weeks of nevirapine monotherapy. Viruses resistant to nevirapine were isolated from all children during therapy, but their isolation did not always predict loss of antiviral activity. The evaluation of nevirapine in combination therapy trials is underway in children.

Comparison of virus burden in blood and sequential lymph node biopsy specimens from children infected with human immunodeficiency virus

BACKGROUND

Lymph nodes serve as reservoirs for the replication of human immunodeficiency virus (HIV) type 1. Comparison of serial measurements of virus burden in lymph nodes and peripheral blood after a change in antiretroviral therapy may provide insights into pathogenic mechanisms and permit a more accurate assessment of a therapeutic response.

STUDY DESIGN

Nevirapine was added to the drug regiment of eight children with HIV infection treated with the combination of zidovudine and didanosine who had increasing levels of serum p24 antigen. Lymph node biopsies were performed at entry and after 12 weeks of therapy.

RESULTS

Neither CD4 counts nor p24 antigen level correlated with the degree of viremia as measured by ribonucleic acid copy numbers in plasma. Correlations were found between HIV DNA copy number in peripheral blood mononuclear cells and HIV DNA copy number in lymph nodes (p = 0.02), as well as between peripheral blood CD4 counts and lymph node architecture. The HIV signals in the lymph nodes conformed to the anatomic organization of apical light zones in the germinal centers; however, in more advanced disease stages, organized germinal centers disappeared as evidence by a decline in the extent of the follicular dendritic network.

CONCLUSIONS

Lymph node biopsies in this small number of HIV-infected children revealed a progressive loss of an organized architecture, especially of the follicular dendritic network. This correlated with a progressive loss of CD4+ cells but not with other measures of disease stage, including viral load, as measured by ribonucleic acid copy numbers.

HIV-1-specific cytotoxic T lymphocyte responses in the first year of life

HIV-1-specific CTL responses were prospectively evaluated in infants born to HIV-1-seropositive women to assess the capability of the young infant to generate HIV-1-specific CTL and to examine the potential role of HIV-1-specific CTL in the pathogenesis of vertical infection. Our results indicate that some young infants, and even the fetus, seem to be capable of generating virus-specific CTL responses. The detection of HIV-1-specific CTL responses varied among infants, however, with respect to timing, HIV-1 gene product recognition, and the magnitude of detectable responses; HIV-1-specific CTL responses were uncommonly detected in the first few months of life. The less consistent detection of HIV-specific CTL in early infancy contrasts with reports of the detection of HIV-1-specific CTL soon after primary infection in adults. HIV-1-specific CTL were not detected in any uninfected infants born to HIV-1-seropositive women. This description of HIV-1-specific CTL in infants may have important implications for understanding the pathogenesis of vertical HIV-1 infection and for the development of a vaccine to interrupt vertical infection.

HIV-1-specific cytotoxic T lymphocyte responses in the first year of life

HIV-1-specific CTL responses were prospectively evaluated in infants born to HIV-1-seropositive women to assess the capability of the young infant to generate HIV-1-specific CTL and to examine the potential role of HIV-1-specific CTL in the pathogenesis of vertical infection. Our results indicate that some young infants, and even the fetus, seem to be capable of generating virus-specific CTL responses. The detection of HIV-1-specific CTL responses varied among infants, however, with respect to timing, HIV-1 gene product recognition, and the magnitude of detectable responses; HIV-1-specific CTL responses were uncommonly detected in the first few months of life. The less consistent detection of HIV-specific CTL in early infancy contrasts with reports of the detection of HIV-1-specific CTL soon after primary infection in adults. HIV-1-specific CTL were not detected in any uninfected infants born to HIV-1-seropositive women. This description of HIV-1-specific CTL in infants may have important implications for understanding the pathogenesis of vertical HIV-1 infection and for the development of a vaccine to interrupt vertical infection.

Pathogenesis of pediatric human immunodeficiency virus type 1 infection

This discussion of the pathogenesis of infant human immunodeficiency virus (HIV) type 1 infection emphasizes features unique to pediatric disease and provides general insights into HIV illness in all populations. Therapies designed to interrupt transmission of HIV can be most efficiently addressed through studies of maternal-infant transmission. The rapid progression of disease in children constantly emphasizes the urgent need for continued progress in treatment of HIV infection and presents a unique opportunity optimally to assess effects of early intervention.

Quantitation of HIV-1 in whole blood of infected children

OBJECTIVE

To validate the technique of HIV-1 culture from whole blood for the quantitation of viral load in infected children.

PATIENTS

Forty-three HIV-1-infected children were followed in two paediatric centres.

METHODS

Quantitative HIV-1 cultures from unfractionated whole blood using an end-point dilution technique were compared with simultaneous quantitative cultures of peripheral blood mononuclear cells (PBMC) and plasma.

RESULTS

Good sensitivity (93%) of the methods used was confirmed. A close correlation (r = 0.80) was observed between HIV-1 titres measured directly from whole blood and those expected from PBMC and plasma titres. The mean whole blood viral load was higher in patients with more severe signs of disease, but the difference did not reach statistical significance. The whole blood viral titres measured sequentially at monthly intervals remained within one dilution of each other in 16 of the 22 patients studied.

CONCLUSION

In this study, the quantitation of HIV-1 in unfractionated blood allowed for a reliable and sensitive measurement of the whole blood viral load in infected children.

Early viremia and immune responses in vertical human immunodeficiency virus type 1 infection

Thirty-three infants born to human immunodeficiency virus type 1 (HIV-1)-seropositive women were evaluated from birth using plasma and peripheral blood mononuclear cell (PBMC) cultures, polymerase chain reaction, and serum p24 antigen assays. Five children were identified as infected. Evidence of infection was found in cord blood and subsequent samples from 2 infected children, suggesting in utero infection. Virologic studies on cord blood and early neonatal specimens from the 3 other infected children were negative but became positive by 8 weeks of age, suggesting either intrapartum transmission or sequestration of virus with subsequent detection. An increase in blood (plasma and PBMC) virus titers consistent with primary viremia was observed in 4 infants between 3 and 16 weeks of age. Blood virus titers subsequently declined in the absence of antiretroviral therapy and in the absence of activated HIV-1-specific cytotoxic T lymphocyte responses or broadly neutralizing antibodies. Confirmation of these results in larger studies may be helpful in the design of clinical trials to interrupt vertical transmission or to modify the course of infection.

Diagnosis of vertical human immunodeficiency virus type 1 infection by whole blood culture

The qualitative and quantitative performance of a human immunodeficiency virus type 1 (HIV-1) whole blood culture method was assessed for use in the diagnosis of vertical HIV-1 infection. This method requires < 1 mL of whole blood and allows for the quantification of blood virus load. HIV-1 was isolated from 36 (95%) of 38 whole blood specimens from 27 HIV-1-infected children compared with 0 of 16 whole blood specimens from 16 uninfected children. HIV-1 titers were significantly higher in severely symptomatic children (2450 TCID/mL) than in less symptomatic children (179 TCID/mL). This simple quantitative culture assay may be useful for the early diagnosis of vertical HIV-1 infection, the assessment of blood virus load, and the evaluation of antiretroviral therapies.

Limiting dilution analysis of cytotoxic T lymphocytes to human immunodeficiency virus gag antigens in infected persons: in vitro quantitation of effector cell populations with p17 and p24 specificities

The presence of cytotoxic T lymphocytes (CTL) to the gag antigens of human immunodeficiency virus (HIV) has been described in infected populations. We found that the majority of this immune response as measured in bulk CTL assays of unstimulated peripheral blood mononuclear cells (PBMC) is directed against the p24 component of the p55 gag precursor protein. Using limiting dilution analysis of this effector cell population we confirm that the majority of activated gag-specific CTL circulating in the PBMC of infected hemophilic patients are directed at p24 determinants and are present at frequencies of 1/36,000 to 1/86,000 lymphocytes. By performing in vitro stimulation after limiting dilution, the precursor population of gag-specific CTL are characterized and quantitated. HIV gag-specific CTL precursors are identified at frequencies of 1/1700 to 1/17,000 lymphocytes and are made up of cells with both p17 and p24 specificities. No HIV gag-specific CTL precursor cells are identified in the PBMC of HIV-uninfected individuals. These studies demonstrate that CTL directed at both p17 and p24 determinants make up the cellular immune repertoire in HIV-infected individuals but that only the p24-specific CTL are routinely found in an activated state in the circulation.

Deficient human immunodeficiency virus type 1-specific cytotoxic T cell responses in vertically infected children

Cytotoxic T lymphocyte (CTL) responses to human immunodeficiency virus type 1 (HIV-1) gag proteins were studied prospectively in 17 children (12 infected) born of mothers with HIV-1 seropositivity and in five pediatric patients with hemophilia infected by transfusion of HIV-1-contaminated factor VIII concentrate. B lymphoblastoid cells infected with vaccinia virus vectors expressing HIV-1 gag gene products were combined with autologous peripheral blood mononuclear cells to detect circulating CTLs. Effector cells were defined by monoclonal antibody-mediated, complement-dependent cytolysis. Circulating HIV-1 gag-specific cytotoxic responses were detectable in 4 of 5 HIV-1-infected pediatric hemophilic patients, and were similar in magnitude to those previously described in adults. In contrast, circulating HIV-1 gag-specific cytolysis was detectible in only 3 of 12 vertically infected children. Depletion data revealed that the majority of detectible gag-specific cytolysis was CD8 T cell-mediated. No apparent relationships between CD4 T cell counts, CD8 T cells counts, or serum p24 antigen levels and CTL responses were seen. Deficient CTL development may, in part, explain the more rapid onset of symptomatic disease following vertical HIV infection.

Quantitation of human immunodeficiency virus in vertically infected infants and children

We used a quantitative human immunodeficiency virus, type 1 (HIV-1) culture method to determine whether there is a relationship between the amount of replicating virus in the blood of vertically infected children and the relatively short latency period before development of symptomatic disease in these children. HIV-1 titers were determined by end point dilution in the peripheral blood mononuclear cells and the plasma of 30 infected (CDC class P1 and P2), 36 indeterminate (CDC class PO), and 19 uninfected (CDC class P3) infants and children born to HIV-1 seropositive mothers. HIV-1 was recovered from 35 (90%) of 39 PBMC cultures and 23 (60%) of 38 plasma cultures of infected patients not receiving antiretroviral therapy. The mean HIV-1 titers tended to be higher in patients with more advanced disease (P2, D, E, or F: 1760 TCID/10(6) PBMC, 460 TCID/ml plasma) than in asymptomatic or mildly symptomatic patients (P1; P2, A or C: 90 TCID/10(6) PBMC; 60 TCID/ml plasma). A poor correlation between HIV-1 titers and serum p24 antigen levels was found. No correlation was observed between viral titers and relative or absolute numbers of CD4 lymphocytes. Plasma virus titers were lower in 9 patients receiving zidovudine (ZDV) therapy (mean 2 TCID/ml) than in untreated patients of similar clinical status. The viral titers measured in the blood of vertically infected infants and children were on the same order of magnitude as the viral titers measured in HIV-infected adults. We conclude that the relatively rapid progression to symptomatic disease of the majority of vertically infected patients is not due to a higher load of replicating virus in blood.