Abstract Book Vol. 1 [International Conference on AIDS (16th: 2006: Toronto, Canada)]

MOAAO206 MOAB0102
Loop deletions in gpl20 expose the CD4 binding site Characteristics of people living with HIV-1 (PLWH)
for improved binding of 1b12 and F105 antibodies screened for isoniazid preventive therapy (IPT) -
Botswana, 2004-2005

I. Berkower, Y. Ni, C. Patel, A. Spadaccini. Center for Biologics, FDA, Division
of Viral Products, Office of Vaccine Research, Bethesda, MD, United States
Background: HIV-infected humans make broadly crossreactive neutralizing
antibodies specific for the CD4 binding site on gpl20. Vaccines based on native
gpl20 fail to elicit similar antibodies. Native gpl20 may cover up this site to
prevent antibody induction.
Methods: Based on the 3D structure of gpl20, we have identified four
conserved loops that project into the CD4 binding site and may partially block
antibody binding or may interfere with induction of antibodies to this site. Each
loop was deleted by quick change PCR, expressed as virus-like particles in a
baculovirus system, and partially purified by sedimentation through sucrose.
The amount of antigen was normalized by 2G12 binding, and exposure of the
CD4 binding site was determined with a panel of monoclonals and CD4-Ig.
Results: Three phenotypes were observed: one mutant abrogated binding of
both 1b12 and CD4-Ig, one removed 1b12 completely but had no effect on
CD4-Ig, and one enhanced 1b12 binding, with minimal effect on CD4-Ig. F105
binding was enhanced even more.
Conclusions: These results suggest that naturally occurring features of the
gpl20 structure may inhibit antibody binding and reduce the induction of
antibodies to the CD4 binding site. These structures can be removed without
upsetting the overall conformation. Exposure of the CD4 binding site could
occur by reducing steric hindrance or through an allosteric effect on the
excursion between open and closed forms of the protein, as occurs during CD4
binding. Open forms of gpl20 bearing an exposed CD4 binding site may favor
the induction of broadly cross-reactive neutralizing antibodies.
Track B
MOAB0101
ELISPOTs in the detection of Mycobacterium
tuberculosis infection in a population with high
prevalence of HIV and high exposure to BCG and
environmental mycobacteria
3. Mutsvangwal, E.L. Corbett2, K. Chaka-Boyd3, R. Vundla4, J. Muzangwa4,
T. Mavhudzi4, Y. Cheung5, P.R. Mason6, K. Millington', K. Ewer', A. Lalvani7,
A.E. Butterworth'. 'Biomedical Research and Training Institute, Harare,
Zimbabwe, 2London School of Hygiene and Tropical Medicine & Biomedical
Research and Training Institute, Department of Infectious Diseases, Harare,
Zimbabwe, 3Biomedical Research and Training Institute, Laboratories,
Harare, Zimbabwe, 4Biomedical Research and Training Institute, DetecTB,
Harare, Zimbabwe, 5London School of Hygiene and Tropical Medicine,
London, United Kingdom, 'Biomedical Research and Training Institute &
University of Zimbabwe, Harare, Zimbabwe, 'Nuffield Department of Clinical
Medicine, University of Oxford, Clinical Medicine, Oxford, United Kingdom,
8Biomedical Research and Training Institute & London School of Hygiene and
Tropical Medicine, Department of Infectious Diseases, Harare, Zimbabwe
Background: The tuberculin skin test (TST) remains the gold standard for the
detection of new or latent infections with Mycobacterium tuberculosis (MTB),
but has low sensitivity in HIV-infected subjects and lacks specificity in individuals vaccinated with BCG or exposed to environmental mycobacteria. The
interferon-gamma ELISPOT response to peptides of defined MTB antigens has
shown superior sensitivity and specificity in a number of settings. In this study
we have compared TSTs and ELISPOTs among factory workers and their household contacts.
Methods: Index cases (IX, n=75) and their household contacts (IXC, n=114)
were recruited through a site-randomised study of VCT and health care delivery
in factories in Harare. Index controls (CT, n=71) and their household contacts
(CTC, n=85) were randomly selected from the same factories. TSTs were compared with ELISPOT responses to peptides and recombinant antigens of ESAT-6
and CFP10 (RD1 responses) and to PPD.
Results: Positive TSTs and PPD responses were significantly more frequent than
positive RD1 responses, both overall (TST 71%, PPD 83%, RD1 59%, p<0.001)
and by case status. HIV prevalence was 79%, 32%, 18% and 9% among IX,
IXC, CT and CTC respectively. TST and PPD responses were significantly lower
among HIV+ than HIV- subjects, both overall (TST, 46% vs 79%, p<0.001:
PPD, 61% vs 94%) and by case status. In contrast, RD1 responses were not
affected by HIV status (overall, 59% positive for both HIV+ and HIV-).
Conclusions: A proportion of positive TSTs and PPD responses may be attributable to exposure to organisms other than MTB. Both TSTs and PPD ELISPOTs
are substantially reduced in HIV-infected individuals, whereas RD1 ELISPOTs
are unaffected. Thus, this study supports that the RD1 ELISPOT is a useful
marker of MTB infection in individuals from areas with a high prevalence of
HIV infection and high exposure to BCG or cross-reactive environmental mycobacteria.

T. Samandari', B. Mosimaneotsile2, S. Nyirenda3, T. Agizew2, O. Motsamai4,
P.H. Kilmarxs, E.A. Talbot', C.D. Wells'. 'CDC/BOTUSA, Division of TB
Elimination, Gaborone, Botswana, 2BOTUSA, Gaborone, Botswana, 3BOTUSA,
Francistown, Botswana, 4Ministry of Health, National TB Programme,
Gaborone, Botswana, 5CDC, Division of HIV/AIDS Prevention, Atlanta, United
States, 6CDC, Division of TB Elimination, Atlanta, United States
Background: IPT aims to prevent active tuberculosis (TB) among PLWH in
TB-endemic countries. Because of high rates of both TB and HIV, Botswana
rolled out an IPT program nationwide by mid-2004. This analysis aims to better
inform national IPT programs about characteristics of PLWH seeking IPT from
data derived from an ongoing clinical trial that recruited at the same sites as
the Botswana National IPT Program.
Methods: PLWH were referred largely from local clinics and voluntary
counseling and testing centers, and were screened in two parts. First-round
screening followed guidelines set by Botswana's National IPT Program; exclusion
criteria included any current illness, terminal AIDS, or recent TB treatment. If
not excluded, candidates underwent second-round (trial-related) screening:
exclusion criteria included abnormal chest radiographs (CXRs), elevated hepatic
enzymes, significant neutropenia, or anemia.
Results: Between January-December 2005, 3,458 persons (65% female;
median age 33 years) underwent first-round screening. Of these, 987 (28%)
were excluded; the most frequent reasons were current illness (51%) and
recent TB treatment (8%). Of the PLWH who underwent first-round screening,
2,261 persons (65%) proceeded to second-round screening. Of these 511
(23% of second-round subjects) were excluded; the most frequent reasons
were abnormal CXRs (50%) and neutropenia (20%). Of the original 3,458
who underwent first-round screening, 1,499 (43%) were enrolled for the trial.
Among enrollees, 25% had tuberculin skin tests with >5 mm induration, median
CD4 lymphocyte count was 313 cells/mm3 and 18% were already receiving
highly active antiretroviral therapy.
Conclusions: Many PLWH seeking IPT in Botswana have advanced HIV disease,
and were ineligible for IPT due to current illness at first-round screening or
an abnormal CXR in second-round screening. As these exclusions were most
likely related to advanced HIV disease, national IPT programs may best target
candidates for IPT by targeting HIV screening to healthier individuals.
MOAB0103
Factors associated with multidrug-resistant
tuberculosis in HIV-infected patients, Peru
D. Vargas'1, A. Bernab&2, R.H. Gilman3, V. Kawail, G. Soto1, D.A. Moore',
L. Caviedes4, C.T. Bautistas, M. Tovar', V. Chavez', L. Huaroto6, E. Ticona6,
C.A. Evans'. 1NGO PRISMA, Research, Lima, Peru, 2Cayetano Heredia
University, Epidemiology, Sexually Transmitted Diseases and HIV Unit,
Lima, Peru, 3NGO PRISMA, Public Health School, Lima, Peru, 4NGO PRISMA,
Laboratory, Lima, Peru, sNGO PRISMA, Statisitics, Lima, Peru, 6Dos de Mayo
Hospital, Lima, Peru
Background: To evaluate factors associated with multidrug resistant
tuberculosis (MDR-TB) in patients with HIV infection.
Methods: A longitudinal observational study was undertaken at the Dos de
Mayo Hospital (Lima) between May 1999 and December 2004. All patients were
HIV positive adults and had tuberculosis cultured from sputum. Tuberculosis
susceptibility to isoniazid and rifampicin was determined by testing the
diagnostic, pre-treatment sample. The factors associated with MDR-TB at the
time of diagnosis were calculated using logistic regression analysis.
Results: A total of 209 subjects were enrolled, 165 (79%) were males and
the mean age was 32 years (standard deviation 8.0). CD4 was measured for
166 (79%) and the median was 44 cells/pl (inter-quartile range 15-118). The
MDR-TB prevalence in these patients was 34% and an additional 20 (9.6%) of
patients had tuberculosis resistant only to isoniazid. 180 (81%) were sputum
microscopy positive but this was not associated with MDR-TB (P=0.8). In the
multivariate analysis, the risk factors significantly associated with MDR-TB
were: previous anti-tuberculosis chemoprophylaxis, odds ratio (OR)= 4.8 (95%
confidence intervals (CI), 2.2 - 11), hospital admissions during the two years
prior to this episode, OR= 2.9 (95% CI, 1.2 - 6.9) and known close contact
with another tuberculosis patient, OR= 3.9 (95% CI, 1.6 - 9.9). MDR-TB was
not significantly associated with the presence of a BCG scar, OR= 0.65 (95% CI,
0.30 - 1.4), past tuberculosis therapy, OR= 1.8 (95% CI, 0.91 - 3.4) or CD4
count, OR= 1.9 (95% CI, 0.77 - 4.6).
Conclusions: Amongst this population of HIV-positive subjects, the risk factors
associated with MDR-TB were previous anti-tuberculosis chemoprophylaxis
with isoniazid, recent hospital admission and the close contact witn another
tuberculosis patient. These results emphasize the importance of ruling-out
active tuberculosis before administering isoniazid preventive therapy and
optimizing infection control practices to prevent nosocomial and domiciliary
dissemination of MDR-TB.

Monday
14 August
Oral

XVI INTERNATIONAL AIDS CONFERENCE * 13-18 AUGUST 2006 * TORONTO CANADA * ABSTRACT BOOK VOLUME 1