ELISPOTs in the detection of Mycobacterium tuberculosis infection in a population with high prevalen

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ELISPOTs in the detection of Mycobacterium
tuberculosis infection in a population with high
prevalence of HIV and high exposure to BCG and
environmental mycobacteria

• Junior Mutsvangwa
• Biomedical Research and Training Institute,
  Harare, Zimbabwe

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Rationale 1
The Conventional Tuberculin Skin Test

• Inherent reliability problems
• Poor intrinsic specificity PPD
• Susceptibility to HIV-induced cutaneous anergy
• Operational drawbacks
• Borock et al, Int J Tuberc Lung Dis 20015 (5)
  462-467
• Fine et al, Int J Tuberc Lung Dis 1999 3 962-75

Reproduced with permission from CDC Public
Inquiry inquiry_at_cdc.gov
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Rationale 2

• Rapid ex vivo enzyme linked immunospot assay
• Enumerates T cell responses to specific MTB
  antigens
• Antigens
• ESAT-6 CFP-10 derived from the Region of
  Difference (RD1) of MTB
• Synthetic peptide pools
• Lalvani et al, Am J Respir Crit Care Med 2001
  163 824-82
• Hill et al, Clin Infect Dis 2004 38966-295
• Shams et al, J Immunol 2004 173 1966-1977

ELISPOT responses to defined MTB antigens
Courtesy of Dr Clive Gray, Principal Specialist
Scientist, Johannesburg, S.Africa
cgray_at_niv.ac.za
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Objective

• To compare ELISPOT response to RD-1 antigens
  with the tuberculin skin test for the detection
  of latent TB infection in an area of
• high exposure to environmental mycobacteria
• high BCG coverage
• high prevalence of HIV infection

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Setting 1

• Household contact study of TB in factory workers
• 129 TB cases
• All met case-definitions for TB disease
• Include smearve, cultureve, and smear and
  culture-ve
• 149 Controls, randomly selected from the same
  factories
• No clinical, bacteriological or radiological
  evidence of TB disease

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Setting 2

• (0nly age 10 years)
• 226 household contacts of TB cases
• Share same environment as TB case patients
• 188 household contacts of Controls
• Share same environment as Controls
• Provided a comparable Control group
• A priori would expect with latent TB infection
• TB Cases gt TB contacts gt Controls gt Control
  contacts

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Definitions

• Positive TST
• Induration of 10 mm 48 72 hours after
  tuberculin placement
• Positive RD1- ELISPOT response
• Responses to any pool of ESAT-6 and CFP-10
  peptides
• 5 spots gt than background (negative control)
• and
• 2X background

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Baseline characteristics
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Comparison of TST and RD-1 ELISPOT responses by
Case Status
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TST vs RD-1 ELISPOT responses All groups
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HIV prevalence by Case Status
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Effect of HIV status on TST responses
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Effect of HIV status on RD-1 ELISPOT responses
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Effect of HIV status on TST and RD-1 ELISPOT
responses
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Effect of smear and culture status on responses
of HIV TB patients
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Effect of HIV status of Case/Control on TST and
RD-1 responses of contacts
Even with RD little evidence of transmission to
household contacts from patients with HIV-related
TB
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Conclusions

• HIV infection reduces the sensitivity of the TST
• RD -1 ELISPOT not significantly affected by HIV
• In patients HIV-related TB disease
• RD -1 ELISPOT more sensitive than the TST
• TST did not distinguish TB patients from control
  subjects in this population
• ve RD -1 ELISPOT TB patients gt than controls
• HIV effect on TSTs more marked in smear
  negative/culture negative patients with TB
• Profound immunosuppression or diagnostic
  uncertainty?
• RD-1 ELISPOT more appropriate test of MTB
  infection for HIV prevalent settings
• But, false-ves in most immunosuppressed?
• logistics and cost

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Collaborators

• Biomedical Research and Training Institute
• K. Chaka, E. Corbett, R. Vundla, J. Muzangwa, T.
  Mavhudzi, P. Mason, A. Butterworth
• London School of Hygiene and Tropical Medicine
• E. Corbett, Y-B. Cheung, A. Butterworth
• University of Oxford
• K. Millington, K. Ewer, A Lalvani
• (STUDY FUNDED BY WELLCOME TRUST)