Close contact interferon-gamma response to the new PstS1:CPF10: a preliminary 1-year follow-up study.

BACKGROUND

The available diagnostic tools for latent tuberculosis (TB) infection (LTBI) via interferon-gamma (IFN-g) release assays (IGRA) are based on ESAT6:CFP10 stimulation. However, the mycobacterial antigen PstS1 is also highly immunogenic and some of its fragments, such as PstS1, have shown higher immunoreactivity in LTBI than in active TB. PstS1, therefore, could increase the accuracy of the existing IGRA to detect LTBI. Thus, a new chimeric protein has recently been developed (PstS1:CFP10) showing potential for LTBI screening of recent close contacts (rCt) exposed to Mycobacterium tuberculosis. The aim of this study was to analyze the PstS1:CFP10 longitudinal IFN-g profile in comparison to ESAT6:CFP10 and full PstS1/CFP10 stimulation in a rCt cohort and correlate the responses to these in-house IGRA with any clinical changes/interventions that might occur.

METHODS

A free-of-cost, one-year follow up was offered to 120 rCt recruited in Rio de Janeiro, RJ, Brazil. Whole blood short-term (WBA), long-term stimulation (LSA) assays, and the tuberculin skin test (TST) were performed during follow up.

RESULTS

Among the enrolled rCt, 44.2% (53/120) returned for re-evaluation and the control group (TST negative, n = 17) showed low IFN-g reactivity to all antigen stimulations during the entire follow up, except for one participant who had shown radiological evidence of past TB/LTBI. Both incident cases were detected by IGRA-PstS1:CFP10 during LTBI and after disease progression. Moreover, subsequent to the prophylactic treatment for LTBI (tLTBI), a significant regression in the LSA response was predominantly observed through stimulation of the new chimeric protein (8/10, 80%) followed by ESAT6:CFP10 (5/10, 50%) and PstS1/CFP10 (4/10, 40%). No clinical or epidemiological characteristics were exclusively shared among IGRA convertors.

CONCLUSION

It was demonstrated that the TST negative rCt without radiological evidence of LTBI/TB did not develop an IGRA-PstS1:CFP10 response during the one-year follow up. Moreover, all incident cases were detected by our new IGRA; and a significant decrement of LSA-PstS1:CFP10 reactivity post-prophylactic tLTBI was found. To our knowledge, this is the first study to monitor changes in the immune response profile of IGRA-PstS1:CFP10 among rCt during a consecutive one-year period, thus providing additional evidence of its potential in the detection of LTBI.