Synthetic Peptides Identify Promiscuous Human Th1 Cell Epitopes of the Secreted Mycobacterial Antigen MPB70

Abstract

MPB70 is a secreted protein ofTuberculosis (TB) is a chronic infectious disease of worldwide importance. In 1993 the World Health Organization declared TB a global emergency, and according to the latest survey conducted by this organization TB still exists at an alarming level, with about one-third of the world population infected with Mycobacterium tuberculosis, 8 million people developing the disease, and 2 million to 3 million people dying of TB each year (6). Control and eventual eradication of TB require protective vaccines. However, the protection induced by the currently available Mycobacterium bovis BCG vaccine against pulmonary TB varies tremendously in different parts of the world, and the efficacy ranges from 0 to 80% (7). In addition, BCG vaccination induces a positive response to the purified protein derivative (PPD) of M. tuberculosis, thereby compromising the diagnostic value of PPD. Moreover, use of the BCG vaccine, which consists of attenuated live organisms, is contraindicated in AIDS patients, who are at high risk of developing TB. The present situation calls for identification and characterization of M. tuberculosis antigens and peptides that might be used to develop universally efficacious and safer vaccines against TB.Although infection with M. tuberculosis induces both humoral immunity and cell-mediated immunity, only cell-mediated immunity responses mediated primarily by gamma interferon (IFN-␥)-producing Th1 cells are relevant to protection (4, 16). Thus, identification of antigens and peptides that induce Th1 cell responses could be useful for designing new vaccines to protect against TB. Secreted proteins of M. tuberculosis have been the focus of extensive research on the development of subunit vaccines because these proteins are considered to be important targets of recognition by the immune system (1, 31).MPB70 is a major secreted protein of M. bovis, and small quantities of this protein are expressed by M. tuberculosis. M. bovis BCG strains can be divided into strains that produce high levels of MPB70 and strains that produce low levels of MPB70 (9,18,34,58). There are no differences between M. bovis and M. tuberculosis (H37Rv and CDC1551) in terms of the sequences of the expressed proteins encoded by the mpb70 and mpt70 genes, respectively (17; http://www.ncbi.nlm.nih.gov /BLAST). MPB70 is an M. tuberculosis complex-specific nonglycosylated protein with a signal peptide consisting of 30 amino acids (aa) and a mature protein sequence consisting of 163 aa with a deduced molecular mass of 16.3 kDa (53). The mature MPB70 protein stimulates both cellular and humoral immune responses during infection with bovine and human tubercle bacilli (4,10,16, 28,47,49,36).The present work was carried out to identify dominant and natural Th1 cell epitopes of MPB70 which can be recognized by humans in the context of multiple HLA molecules. Peripheral blood mononuclear cells (PBMC) from healthy donors

Three-Dimensional Structure Determines the Pattern of CD4+T-Cell Epitope Dominance in Influenza Virus Hemagglutinin

“…The responses of 14 BCG-vaccinated subjects reported by Al-Attiyah et al (2) were based on lymphocyte proliferation stimulated by 25-mer peptides spanning Mpb70 with 10-residue overlaps. The authors scored the response for a given subject as positive if the SI was greater than 3.…”

Comparative Evaluation of MPT83 (Rv2873) for T Helper-1 Cell Reactivity and Identification of HLA-Promiscuous Peptides in Mycobacterium bovis BCG-Vaccinated Healthy Subjects

“…The overall results suggest that infection with M. tuberculosis did not affect the level of Th1 cell reactivity to BCG and most antigens of M. tuberculosis used in this study. Furthermore, the study confirms strong to moderate (10,50). Although the gene for PPE68 is present in the M. tuberculosis-specific RD1 segment (13,36), statistically similar responses in the ESAT-6/CFP10 responders and nonresponders could be due to the presence of an immunodominant epitope (aa 124 to 137), which is conserved in several PPE proteins of M. tuberculosis, BCG, and environmental mycobacteria (48,57).…”

“…Although several computational methods are available for HLA-DR binding and the prediction of T cell epitopes, including ProPred, NetMHCII 2.2, Petrochemitric, and IEDB Consensus, etc. (24,56,62,67), ProPred was evaluated first because comparative evaluations have previously been shown the usefulness of this method in predicting mycobacterial T-cell epitopes (5,10,44,53). The overall results of computational analysis suggest that MPT83 was highly promiscuous for binding to HLA-DR molecules, as all of the HLA-DR specificities included in the computational methods were predicted to bind the MPT83 sequence (see Fig.…”

“…However, none of the single peptides qualified to replace MPT83 as the best Th1 cell-stimulating peptide, i.e., P14 (aa 196 to 220), although a promiscuous HLA-DR binder with strong Th1 cell responses showed negative responses for 22% of MPT83-responding donors in Th1 cell assays. Thus, this protein behaves like other major antigenic proteins of M. tuberculosis, e.g., Ag85B, PPE68, MPT70, ESAT-6, and CFP10, etc., in which no single peptide could replace the complete protein sequences for Th1 cell reactivity (5,10,44,47,53). However, being a major Th1 cell antigen capable of stimulating Th1 cells from HLA-DR heterogeneous subjects, this protein may be considered in formulations to develop a new vaccine candidate against TB.…”

“…Therefore, to determine if latent infection with M. tuberculosis could have an effect on the Th1 cell responses to various antigens used in this study, the donors were divided into ESAT-6/CFP10 responders and nonresponders to indicate M. tuberculosis infection and noninfection, respectively (10,34). PBMCs from both donor groups had strong responses to all complex mycobacterial antigens without significant differences between the two donor groups (Table 1), which suggested the suitability of the donors to test for reactivity to single antigens.…”