Leprosy patients with lepromatous disease recognize cross-reactive T cell epitopes in the Mycobacterium leprae 10-kD antigen.

R. HUSSAIN, H. M. DOCKRELL†, F. SHAHID, S. ZAFAR* & T. J. CHIANG*Department of Microbiology,The Aga Khan University and *Marie Adelaide Leprosy Centre, Karachi, Pakistan, and † Department of Infectious andTropical Diseases, London School of Hygiene and Tropical Medicine, London, UK(Accepted for publication 21 July 1998)SUMMARYT cell responses play a critical role in determining protective responses to leprosy. Patients with self-limiting tuberculoid leprosy show high T cell reactivity, while patients with disseminated lepromatousform of the disease show absent to low levels of T cell reactivity. Since the T cell reactivity oflepromatous patients to purified protein derivative (PPD), a highly cross-reactive antigen, is similar tothat of tuberculoid patients, we queried if lepromatous patients could recognize cross-reactive epitopesin Mycobacterium leprae antigens as well. T cell responses were analysed to a recombinant antigen10-kD (a heat shock cognate protein) which is available from bothM.tuberculosis (MT) and M.leprae(ML) and displays 90% identity in its amino acid sequence. Lymphoproliferative responses wereassessed to ML and MT 10kD in newly diagnosed leprosy patients (lepromatous, n¼23; tuberculoid,n¼65). Lepromatous patients showed similar, but low, lymphoproliferative responses to ML and MT10kD, while tuberculoid patients showed much higher responses to ML 10kD. This suggests that thetuberculoid patients may be recognizing both species-specific and cross-reactive epitopes in ML 10kD,while lepromatous patients may be recognizing only cross-reactive epitopes. This was further supportedby linear regression analysis. Lepromatous patients showed a high concordance in T cell responsesbetween ML and MT 10kD (r¼0·658; P 0·1). Identification of cross-reactive T cell epitopes inM.leprae which could induce protectiveresponses should prove valuable in designing second generation peptide-based vaccines.Keywords leprosy 10-kD recombinant antigen T cell epitopes cross-reactiveINTRODUCTIONMycobacterium leprae remains one of the few bacterial pathogensof humans that has not been cultivated in vitro and thereforedevelopment of a successful vaccine depends on the identificationof antigens and epitopes that induce protective responses across theleprosy disease spectrum. Several biochemical, immunologicaland molecular approaches have been recently used for identifica-tion and characterization of protein antigens of the leprosy bacillus[1–4]. It has long been recognized that leprosy patients with self-limiting tuberculoid leprosy show high T cell reactivity, whilepatients with disseminated lepromatous form of the disease showabsent to low levels of T cell reactivity [5]. T cell hyporespon-siveness in patients with lepromatous disease is highly antigen-specific, since this group of patients show normal responses toT cell mitogens and unrelated recall antigens [6]. Among the 10or more dominant M.leprae T cell antigens which have beencharacterized and cloned [4], heat shock proteins (hsp) havebeen shown to induce strong T cell responses in leprosy patientswith tuberculoid or self-limiting disease [7]. Among the hsp,M.leprae 10kD has been shown to induce strong T cell responsesacross the leprosy spectrum [8,9] as well as in leprosy contacts[10]. We therefore queried if the lepromatous patients wererecognizing cross-reactive rather than M.leprae species-specificepitopes in M.leprae 10kD.Mycobacterium leprae 10kD is a homologue of the GroESgene product of Escherichia coli and the human chaperonin 10 [11]and participates in protein folding [12]. The structure of theM.leprae 10kD has already been elucidated [13] and the aminoacid composition and sequence determined [13]. A highly homo-logous hsp with 90% amino acid homology to M.leprae 10kD hasbeen characterized in M.tuberculosis [14]. Both M.leprae andM.tuberculosis 10kD preparations are available as recombinantantigens from the WHO/TDR antigen bank. We compared the two10-kD recombinant antigens in parallel across the leprosy spectrumand in controls to see if lepromatous patients were recognizing