Rational combination of peptides derived from different M. leprae proteins improves sensitivity for immunodiagnosis of M. leprae infection

From the Dept. of Infectious Diseases/Immunohematology & Blood Transfusion, Leiden University Medical Center, The Netherlands & the Leprosy Laboratory, Dept. of Immunology, Oswaldo Cruz Institute, FIOCRUZ, Rio de Janeiro, Brazil

^* To whom correspondence should be addressed. Email: a.geluk{at}lumc.nl.

	Abstract

The stable incidence of new leprosy cases suggests that transmission of infection is continuing despite worldwide implementation of MDT programs. Highly specific tools are required to accurately diagnose asymptomatic and early stage Mycobacterium leprae infection, which are the likely sources of transmission and can not be identified using detection of antibodies against phenolic glycolipid-1 (PGL-I). One of the hurdles hampering T cell based diagnostic tests is that M. leprae antigens cross-react at the T cell level with antigens present in other mycobacteria, like M. tuberculosis or BCG. Using comparative genomics, we previously identified five candidate proteins highly restricted to M. leprae which showed promising features with respect to application in leprosy diagnostics. However, despite the lack of overall sequence homology, the use of recombinant proteins includes the risk of detecting T cell responses cross-reactive with other antigens. To improve the diagnostic potential of these M. leprae sequences, we used 50 synthetic peptides spanning the sequences of all five proteins for induction of T cell responses (IFN-) in leprosy patients, healthy contacts of leprosy patients (HHC) and healthy controls in Brazil, as well as in non-endemic TB patients, BCG vaccinees and healthy subjects. Using the combined T cell responses towards four of these peptides, all PB patients and 13 out of 14 HHC were detected, without compromising specificity. The peptides contain HLA binding motifs for various HLA class I and II alleles, thereby meeting an important requirement for applicability of diagnostic tools in genetically diverse populations. Thus, this study provides the first evidence for the possibility of immunodiagnostics for leprosy based on mixtures of peptides recognized in the context of different HLA alleles.