A comparison of IFNgamma detection methods used in tuberculosis vaccine trials

Interferon gamma (IFNgamma) is a critical component of the pro-inflammatory immune response that provides protection against Mycobacterium tuberculosis. In the absence of an immunological correlate of protection, antigen-specific production of IFNgamma is a commonly used marker of a protective immune response. To facilitate the evaluation of tuberculosis candidate vaccines three different IFNgamma detection methods were compared. The cultured whole blood ELISA, ex vivo IFNgamma ELISpot and whole blood ex vivo intracellular cytokine staining (ICS) assays were performed head-to-head during a Phase I clinical trial using the candidate vaccine MVA85A. Whilst all three assays detected significant increases in IFNgamma production immediately following vaccination, distinctions between the assays were apparent. Higher baseline IFNgamma responses were detected using the cultured whole blood ELISA, whereas the ex vivo ELISpot assay was the most sensitive in detecting long-term (52 weeks) post-vaccination responses. The whole blood ex vivo ICS assay provided novel information by dissecting the IFNgamma response into responding CD4, CD8 and gamma/delta T cell subsets. Future tuberculosis vaccine trials and immunology studies should ideally include a combination of ex vivo and cultured assays to ensure a thorough and multifaceted evaluation of the immune response is achieved.