Roadmap for the development of diagnostic test for bTB

What are we trying to achieve and why? What is the problem we are trying to solve?

To identify antigens which the host is responding to at different stages of infection. Individual antigens may only initiate responses at different stages of infection. PPD is the basis of most current tests, but it hasn’t been standardised.

What are the scientific and technological challenges
(knowledge gaps needing to be addressed)?

• Characterisation of PPD (Purified Protein Derivative)-proteomics, glycosylation, acylation patterns.
• Differentiation between exposure and infection.
• Identify productive infection, transmissibility?
• Differentiation between latent and active infections.
• Large-scale sample testing, including animals at different stages of infection, to establish the reliability and accuracy of the identified biomarkers.
• The immune response to bTB infection can vary among individuals, which can make it challenging to identify universal stage-specific antigen markers.
• Ensuring high sensitivity and specificity of stage-specific antigen markers to minimize false-positive and false-negative results.
• Factor in, or control for, host genetic background, i.e.,susceptibility.

What approaches could/should be taken to address the research question?

Molecular fractionation and characterisation of PPD, proteins, glycolipids etc.
Preparation (synthesis) of molecularly defined antigens.
Recombinant antigens may have a role but challenging to standardise.
Development of synthetic reagents/antigens.
Longitudinal studies of host serological and CMI responses during the course of infection.

What else needs to be done before we can solve this need?

The identity of the antigens being expressed by the organism in macrophages at different stages of infection in “immune” and “resistant” hosts (in vitro or in vivo experiments)

Existing knowledge including successes and failures