Serum indoleamine 2,3-dioxygenase activity is associated with reduced immunogenicity following vaccination with MVA85A.

BACKGROUND: There is an urgent need for improved vaccines to protect against tuberculosis. The currently available vaccine Bacille Calmette-Guerin (BCG) has varying immunogenicity and efficacy across different populations for reasons not clearly understood. MVA85A is a modified vaccinia virus expressing antigen 85A from Mycobacterium tuberculosis which has been in clinical development since 2002 as a candidate vaccine to boost BCG-induced protection. A recent efficacy trial in South African infants failed to demonstrate enhancement of protection over BCG alone. The immunogenicity was lower than that seen in UK trials. The enzyme Indoleamine 2,3-dioxygenase (IDO) catalyses the first and rate-limiting step in the breakdown of the essential amino acid tryptophan. T cells are dependent on tryptophan and IDO activity suppresses T-cell proliferation and function. METHODS: Using samples collected during phase I trials with MVA85A across the UK and South Africa we have investigated the relationship between vaccine immunogenicity and IDO using IFN-γ ELISPOT, qPCR and liquid chromatography mass spectrometry. RESULTS: We demonstrate an IFN-γ dependent increase in IDO mRNA expression in peripheral blood mononuclear cells (PBMC) following MVA85A vaccination in UK subjects. IDO mRNA correlates positively with the IFN-γ ELISPOT response indicating that vaccine specific induction of IDO in PBMC is unlikely to limit the development of vaccine specific immunity. IDO activity in the serum of volunteers from the UK and South Africa was also assessed. There was no change in serum IDO activity following MVA85A vaccination. However, we observed higher baseline IDO activity in South African volunteers when compared to UK volunteers. In both UK and South African serum samples, baseline IDO activity negatively correlated with vaccine-specific IFN-γ responses, suggesting that IDO activity may impair the generation of a CD4+ T cell memory response. CONCLUSIONS: Baseline IDO activity was higher in South African volunteers when compared to UK volunteers, which may represent a potential mechanism for the observed variation in vaccine immunogenicity in South African and UK populations and may have important implications for future vaccination strategies. TRIAL REGISTRATION: Trials are registered at ClinicalTrials.gov; UK cohort NCT00427830, UK LTBI cohort NCT00456183, South African cohort NCT00460590, South African LTBI cohort NCT00480558.

Transcriptional profiling of mycobacterial antigen-induced responses in infants vaccinated with BCG at birth.

BACKGROUND: Novel tuberculosis (TB) vaccines recently tested in humans have been designed to boost immunity induced by the current vaccine, Mycobacterium bovis Bacille Calmette-Guérin (BCG). Because BCG vaccination is used extensively in infants, this population group is likely to be the first in which efficacy trials of new vaccines will be conducted. However, our understanding of the complexity of immunity to BCG in infants is inadequate, making interpretation of vaccine-induced immune responses difficult. METHODS: To better understand BCG-induced immunity, we performed gene expression profiling in five 10-week old infants routinely vaccinated with BCG at birth. RNA was extracted from 12 hour BCG-stimulated or purified protein derivative of tuberculin (PPD)-stimulated PBMC, isolated from neonatal blood collected 10 weeks after vaccination. RNA was hybridised to the Sentrix(R) HumanRef-8 Expression BeadChip (Illumina) to measure expression of >16,000 genes. RESULTS: We found that ex vivo stimulation of PBMC with PPD and BCG induced largely similar gene expression profiles, except that BCG induced greater macrophage activation. The peroxisome proliferator-activated receptor (PPAR) signaling pathway, including PPAR-gamma, involved in activation of the alternative, anti-inflammatory macrophage response was down-regulated following stimulation with both antigens. In contrast, up-regulation of genes associated with the classic, pro-inflammatory macrophage response was noted. Further analysis revealed a decrease in the expression of cell adhesion molecules (CAMs), including integrin alpha M (ITGAM), which is known to be important for entry of mycobacteria into the macrophage. Interestingly, more leukocyte genes were down-regulated than up-regulated. CONCLUSION: Our results suggest that a combination of suppressed and up-regulated genes may be key in determining development of protective immunity to TB induced by vaccination with BCG.

Efficacy of percutaneous versus intradermal BCG in the prevention of tuberculosis in South African infants: randomised trial.

OBJECTIVE: To compare the incidence of tuberculosis over two years in infants vaccinated at birth with intradermal BCG or with percutaneous BCG. DESIGN: Randomised trial. SETTING: South Africa. PARTICIPANTS: 11,680 newborn infants. INTERVENTIONS: Infants were randomised by week of birth to receive Tokyo 172 BCG vaccine through the percutaneous route (n=5775) or intradermal route (n=5905) within 24 hours of birth and followed up for two years. MAIN OUTCOME MEASURES: The primary outcome measure was documented Mycobacterium tuberculosis infection or radiological and clinical evidence of tuberculosis disease. Secondary outcome measures were rates of adverse events, all cause and tuberculosis specific admissions to hospital, and mortality. RESULTS: The difference in the cumulative incidence of definite, probable, and possible tuberculosis between the intradermal group and the percutaneous group, as defined using study definitions based on microbiological, radiological, and clinical findings was -0.36% (95.5% confidence interval -1.27% to 0.54%). No significant differences were found between the routes in the cumulative incidence of tuberculosis using a range of equivalence of "within 25%." Additionally, no significant differences were found between the routes in the cumulative incidence of adverse events (risk ratio 0.98, 95% confidence interval 0.91 to 1.06), including deaths (1.19, 0.89 to 1.58). CONCLUSION: Equivalence was found between intradermal BCG vaccine and percutaneous BCG in the incidence of tuberculosis in South African infants vaccinated at birth and followed up for two years. The World Health Organization should consider revising its policy of preferential intradermal vaccination to allow national immunisation programmes to choose percutaneous vaccination if that is more practical. Trial registration ClinicalTrials.gov NCT00242047.

Evaluation of the quality of informed consent in a vaccine field trial in a developing country setting.

BACKGROUND: Informed consent is an ethical and legal requirement for research involving human participants. However, few studies have evaluated the process, particularly in Africa. Participants in a case control study designed to identify correlates of immune protection against tuberculosis (TB) in South Africa. This study was in turn nested in a large TB vaccine efficacy trial. The aim of the study was to evaluate the quality of consent in the case control study, and to identify factors that may influence the quality of consent. Cross-sectional study conducted over a 4 month period. METHODS: Consent was obtained from parents of trial participants. These parents were asked to complete a questionnaire that contained questions about the key elements of informed consent (voluntary participation, confidentiality, the main risks and benefits, etc.). The recall (success in selecting the correct answers) and understanding (correctness of interpretation of statements presented) were measured. RESULTS: The majority of the 192 subjects interviewed obtained scores greater than 75% for both the recall and understanding sections. The median score for recall was 66%; interquartile range (IQR) = 55%-77% and for understanding 75% (IQR = 50%-87%). Most (79%) were aware of the risks and 64% knew that they participated voluntarily. Participants who had completed Grade 7 at school and higher were more likely (OR = 4.94; 95% CI = 1.57 - 15.55) to obtain scores greater than 75% for recall than those who did not. Participants who were consented by professional nurses who had worked for more than two years in research were also more likely (OR = 2.62; 95% CI = 1.35-5.07) to obtain such scores for recall than those who were not. CONCLUSION: Notwithstanding the constraints in a developing country, in a population with low levels of literacy and education, the quality of informed consent found in this study could be considered as building blocks for establishing acceptable standards for public health research. Education level of respondents and experience of research staff taking the consent were associated with good quality informed consent.

The impact of HIV infection and trimethoprim-sulphamethoxazole prophylaxis on bacterial isolates from children with community-acquired pneumonia in South Africa.

The aim of this study was to compare the type and antimicrobial resistance patterns of bacteria cultured from blood or respiratory tract secretions by HIV status and the use of trimethoprim-sulphamethoxazole (TMP-SMX) prophylaxis in children hospitalized with community-acquired pneumonia. During a 1-year prospective study in Cape Town, South Africa, 250 children [median aged 6 (3-16) months] hospitalized with pneumonia were enrolled; 151 (60.4 per cent) were HIV-infected. The incidence of bacteremia [35 of 244 cultures (14.3 per cent)] did not differ by HIV status. Bacteria were cultured in 17 of 32 (53 per cent) bronchoalveolar lavage specimens (BAL), 128 of 210 (61 per cent) induced sputa and 166 of 231 (71 per cent) nasopharyngeal specimens (NPAs). The type and number of bacteria in respiratory secretions did not differ by HIV status, except for a higher rate of Staphylococcus aureus in sputum or BAL [22 of 146 (15 per cent) vs. 3 of 96 (3 per cent), p = 0.003] and NPAs [41 of 135 (30 per cent) vs. 9 of 96 (9 per cent), p < 0.001] of HIV-positive children. The use of TMP-SMX prophylaxis in HIV-infected children was associated with an increased nasopharyngeal carriage of S. aureus [22 of 51 (43 per cent) vs. 17 of 79 (22 per cent), p = 0.009]. The rising prevalence of HIV infection and the use of TMP-SMX prophylaxis may alter the spectrum of colonizing and pathogenic bacteria in children in developing countries.

The etiology and outcome of pneumonia in human immunodeficiency virus-infected children admitted to intensive care in a developing country.

In developing countries, many human immunodeficiency virus (HIV)-infected children require intensive care unit (ICU) resources for pneumonia, but there is little information on the etiology of pneumonia or the impact of ICU intervention. OBJECTIVE: To compare the etiology and outcome of pneumonia in HIV-positive and seronegative children admitted to ICU. DESIGN: Prospective study. SETTING: Two pediatric ICUs linked to the University of Cape Town, South Africa. PATIENTS: Consecutive children admitted for pneumonia during 1998. MEASUREMENTS AND MAIN RESULTS: Clinical, demographic, ventilatory, and laboratory data were collected. Blood for testing was obtained. Induced sputum or nondirected bronchoalveolar lavage was performed for culture and Pneumocystis carinii identification; gastric lavage (GL) provided specimens for mycobacterial culture. Seventy-six children (21 [27.6%, 95% confidence interval {CI} = 18-39.1] HIV-positive) were enrolled. At admission, HIV infection was diagnosed in 15 of the 21 (71.4% [47.8-88.7]) HIV-positive patients. P. carinii pneumonia occurred in eight HIV-positive children (38% of HIV-infected patients) and one HIV-negative child. It was the acquired immunodeficiency syndrome (AIDS)-defining illness in seven children (47%). The incidence of bacteremia (15.3%) was similar in HIV-positive (15.8%) and HIV-negative children (15.1%), p =.94; Streptococcus pneumoniae and Staphylococcus aureus were the predominant isolates. Bacterial and viral isolates from sputum or bronchoalveolar lavage, including Mycobacterium tuberculosis in six (8%) children, did not differ by HIV status. Intermittent positive pressure ventilation was used in 8 of 21 (38%) HIV-positive children and 28 of 55 (51%) HIV-negative children, p =.32. Median days of intermittent positive pressure ventilation (3 [2-6]), ICU (5 [3-9.5]), and hospital (11 [7.5-19]) did not vary by HIV status. The in-hospital mortality rate for HIV-positive children (6 of 21 [28.6%]) was double that for seronegative patients (8 of 55[14.5%], relative risk [RR] 1.96 [0.77-4.99], p =.16). CONCLUSION: More than a quarter of children admitted to ICU for pneumonia in this geographic area are HIV-positive; most are diagnosed with HIV at admission. P. carinii pneumonia is a common AIDS indicator disease. HIV-infected children admitted with pneumonia had a worse outcome than seronegative children, a difference that is rendered statistically insignificant by the small sample size.