Characterization of a Cross-Reactive, Immunodominant and HLA-Promiscuous Epitope of Mycobacterium tuberculosis-Specific Major Antigenic Protein PPE68

Abstract

PPE68 (Rv3873), a major antignic protein encoded by Mycobacteriun tuberculosis-specific genomic region of difference (RD)1, is a strong stimulator of peripheral blood mononuclear cells (PBMCs) obtained from tuberculosis patients and Mycobacterium bovis bacillus Calmette Guerin (BCG)-vaccianted healthy subjects in T helper (Th)1 cell assays, i.e. antigen-induced proliferation and interferon-gamma (IFN-γ) secretion. To confirm the antigen-specific recognition of PPE68 by T cells in IFN-γ assays, antigen-induced human T-cell lines were established from PBMCs of M. Bovis BCG-vaccinated and HLA-heterogeneous healthy subjects and tested with peptide pools of RD1 proteins. The results showed that PPE68 was recognized by antigen-specific T-cell lines from HLA-heteregeneous subjects. To further identify the immunodominant and HLA-promiscuous Th1-1 cell epitopes present in PPE68, 24 synthetic peptides covering the sequence of PPE68 were indivdually analyzed for HLA-DR binding prediction analysis and tested with PBMCs from M. bovis BCG-vaccinated and HLA-heterogeuous healthy subjects in IFN-γ assays. The results identified the peptide P9, i.e. aa 121-VLTATNFFGINTIPIALTEMDYFIR-145, as an immunodominant and HLA-DR promiscuous peptide of PPE68. Furthermore, by using deletion peptides, the immunodominant and HLA-DR promiscuous core sequence was mapped to aa 127-FFGINTIPIA-136. Interestingly, the core sequence is present in several PPE proteins of M. tuberculosis, and conserved in all sequenced strains/species of M. tuberculosis and M. tuberculosis complex, and several other pathogenic mycobacterial species, including M. leprae and M. avium-intracellulalae complex. These results suggest that the peptide aa 121–145 may be exploited as a peptide-based vaccine candidate against tuberculosis and other mycobacterial diseases.

Comparative Genomics and Proteomic Analysis of Four Non-tuberculous Mycobacterium Species and Mycobacterium tuberculosis Complex: Occurrence of Shared Immunogenic Proteins

“…Five of the 11 genomic pairs are contained in five loci: ESX-1 to ESX-5 encoding components of the type VII secretion system (Uplekar et al, 2011 ). Four of the five loci, except ESX-4, also harbor 11 proteins of the Proline Glutamate (PE), or Proline Proline Glutamate (PPE) family, several of which have been implicated in immune evasion (Akhter et al, 2012 ; Mustafa, 2014 ). The PE and PPE and Esx proteins whose genes are adjacent to each other in the genome of Mycobacterium tuberculosis interact to form pairs which appear to be essential for their secretion (Renshaw et al, 2005 ).…”

“…The PE and PPE and Esx proteins whose genes are adjacent to each other in the genome of Mycobacterium tuberculosis interact to form pairs which appear to be essential for their secretion (Renshaw et al, 2005 ). The secretory proteins have been the focus of research aimed at development of TB vaccines and immunodiagnostic assays, because they are thought to have a potential to induce protective immunity and immune responses of diagnostic value (Ize and Palmer, 2006 ; Ganguly et al, 2008 ; Marongui et al, 2013 ; Mustafa, 2014 ). Studies have shown however, that some genes encoding for proteins of the Esx family, as well as PE/PPE do occur in pathogenic NTM like Mycobacterium kansasii Mycobacterium marinum, Mycobacterium szulgai, Mycobacterium gordonae, Mycobacterium gastri, Mycobacterium ulcerans, Mycobacterium sp.…”

Insights from the predicted epitope similarity between Mycobacterium tuberculosis virulent factors and its human homologs

“…Promiscuous peptides for HLA class II were 24% (19/79) and none for HLA class I molecules. Interestingly, the presence of promiscuous peptides for HLA class II suggest that these peptides could have role in presentation of antigens for immune recognition and amplification of response against M.tb ( Table 3 and 4 ) [ 30 ]. Genetic studies on HLA class I and II alleles are associated with susceptibility to disease and the present study indicates their similarities/binding to M.tb virulent factors.…”

Molecular Basis Underlying Host Immunity Subversion by Mycobacterium tuberculosis PE/PPE Family Molecules

“…Therefore, we generally focus on enhancing the Th1/IFN-g response for novel TB vaccines (Stephen-Victor et al, 2016). PE27 (Kim et al, 2016) and PPE68 (Rv3873) (Mustafa, 2014) can induce Th1 cell response in host, suggesting their TB vaccine potential. Deletion peptides assay indicates that aa 127-FFGINTIPIA-136 of PPE68 is the immunodominant and HLA-DR promiscuous core sequence.…”

“…Deletion peptides assay indicates that aa 127-FFGINTIPIA-136 of PPE68 is the immunodominant and HLA-DR promiscuous core sequence. Intriguingly, the core sequence is conserved in all sequenced strains/species of MTB and MTB complex, and several other pathogenic mycobacterial species, including M. leprae and M. avium-intracellulare complex, indicating that the peptide aa 121-145 has potential to be a peptidebased vaccine candidate against TB and other mycobacterial infection (Mustafa, 2014).…”