Identification of HLA-DR4-restricted T-cell epitope on MPT51 protein, a major secreted protein derived from Mycobacterium tuberculosis using MPT51 overlapping peptides screening and DNA vaccination

Identification of HLA-A*11:01-restricted Mycobacterium tuberculosis CD8(+) T cell epitopes

New vaccines are needed to combat Mycobacterium tuberculosis (MTB) infections. The currently employed Bacillus Calmette‐Guérin vaccine is becoming ineffective, due in part to the emergence of multidrug‐resistant tuberculosis (MDR‐TB) strains and the reduced immune capacity in cases of HIV coinfection. CD8⁺ T cells play an important role in the protective immunity against MTB infections, and the identification of immunogenic CD8⁺ T cell epitopes specific for MTB is essential for the design of peptide‐based vaccines. To identify CD8⁺ T cell epitopes of MTB proteins, we screened a set of 94 MTB antigens for HLA class I A*11:01‐binding motifs. HLA‐A*11:01 is one of the most prevalent HLA molecules in Southeast Asians, and definition of T cell epitopes it can restrict would provide significant coverage for the Asian population. Peptides that bound with high affinity to purified HLA molecules were subsequently evaluated in functional assays to detect interferon‐γ release and CD8⁺ T cell proliferation in active pulmonary TB patients. We identified six novel epitopes, each derived from a unique MTB antigen, which were recognized by CD8⁺ T cells from active pulmonary TB patients. In addition, a significant level of epitope‐specific T cells could be detected ex vivo in peripheral blood mononuclear cells from active TB patients by an HLA‐A*11:01 dextramer carrying the peptide Rv3130c_194‐204 (from the MTB triacylglycerol synthase Tgs1), which was the most frequently recognized epitope in our peptide library. In conclusion, this study identified six dominant CD8⁺ T cell epitopes that may be considered potential targets for subunit vaccines or diagnostic strategies against TB.

Alleles of HLA-DRB1*04 Associated with Pulmonary Tuberculosis in Amazon Brazilian Population

Immunogenetic host factors are associated with susceptibility or protection to tuberculosis (TB). Strong associations of HLA class II genes with TB are reported. We analyzed the HLA-DRB1*04 alleles to identify subtypes associated with pulmonary TB and their interaction with risk factors such as alcohol, smoking, and gender in 316 pulmonary TB patients and 306 healthy individuals from the Brazilian Amazon. The HLA-DRB1*04 was prevalent in patients with pulmonary TB (p<0.0001; OR = 2.94; 95% CI = 2.12 to 4.08). Direct nucleotide sequencing of DRB1 exon 2 identified nine subtypes of HLA-DRB1*04. The subtype HLA-DRB1*04:11:01 (p = 0.0019; OR = 2.23; 95% CI = 1.34 to 3.70) was associated with susceptibility to pulmonary TB while DRB1*04:07:01 (p<0.0001; OR = 0.02; 95% CI = 0.001 to 0.33) to protection. Notably, the interaction between alcohol and HLA-DRB1*04:11:01 increased the risk for developing pulmonary TB (p = 0.0001; OR = 51.3; 95% CI = 6.81 to 386). Multibacillary pulmonary TB, the clinical presentation of disease transmission, was strongly associated with interaction to alcohol (p = 0.0026; OR = 11.1; 95% CI = 3.99 to 30.9), HLA-DRB1*04:11:01 (p = 0.0442; OR = 2.01; 95% CI = 1.03 to 3.93) and DRB1*04:92 (p = 0.0112; OR = 8.62; 95% CI = 1.63 to 45.5). These results show that HLA-DRB1*04 are associated with pulmonary TB. Interestingly, three subtypes, DRB1*04:07:01, DRB1*04:11:01 and DRB1*04:92 of the HLA-DRB1*04 could be potential immunogenetic markers that may help to explain mechanisms involved in disease development.

Function and Potentials of M. tuberculosis Epitopes

Study of the function of epitopes of Mycobacterium tuberculosis antigens contributed significantly toward better understanding of the immunopathogenesis and to efforts for improving infection and disease control. Characterization of genetically permissively presented immunodominant epitopes has implications for the evolution of the host–parasite relationship, development of immunodiagnostic tests, and subunit prophylactic vaccines. Knowledge of the determinants of cross-sensitization, relevant to other pathogenic or environmental mycobacteria and to host constituents has advanced. Epitope-defined IFNγ assay kits became established for the specific detection of infection with tubercle bacilli both in humans and cattle. The CD4 T-cell epitope repertoire was found to be more narrow in patients with active disease than in latently infected subjects. However, differential diagnosis of active TB could not be made reliably merely on the basis of epitope recognition. The mechanisms by which HLA polymorphism can influence the development of multibacillary tuberculosis (TB) need further analysis of epitopes, recognized by Th2 helper cells for B-cell responses. Future vaccine development would benefit from better definition of protective epitopes and from improved construction and formulation of subunits with enhanced immunogenicity. Epitope-defined serology, due to its operational advantages is suitable for active case finding in selected high disease incidence populations, aiming for an early detection of infectious cases and hence for reducing the transmission of infection. The existing knowledge of HLA class I binding epitopes could be the basis for the construction of T-cell receptor-like ligands for immunotherapeutic application. Continued analysis of the functions of mycobacterial epitopes, recognized by T cells and antibodies, remains a fertile avenue in TB research.

Identification of T cell epitopes of Mycobacterium tuberculosis with biolistic DNA vaccination

Tuberculosis (TB) has been listed as one of the most prevalent and serious infectious diseases worldwide. The etiological pathogen of TB is Mycobacterium tuberculosis (Mtb), a facultative intracellular bacterium. Mycobacterium bovis bacillus Calmette-Guérin (BCG) is the only approved vaccine against TB to date. BCG has been widely used, but the efficacy is questionable, especially in adult pulmonary TB. Therefore, more effective, safe and reliable TB vaccines have been urgently needed. T cell-mediated cellular immune response is a key immune response for effective protective immunity against TB. DNA vaccines using Mtb antigens have been studied as promising future TB vaccines. Most TB DNA vaccine studies so far reported used intramuscular or intradermal injection with needles, as these methods tend to induce a type 1 helper T lymphocyte (Th1)-type immune response that is critical for the protective immunity. We have been using DNA vaccines with gene gun bombardment for T cell epitope identification of various Mtb antigens. We show here our strategy to identify precise Mtb T cell epitopes using DNA vaccines with gene gun bombardment.

An in silico DNA vaccine against Listeria monocytogenes

Listeria monocytogenes causes listeriosis with mortality rate >20%. Listeriolysin-O (LLO), a pore-forming hemolysin, belongs to the family of cholesterol-dependent toxins (CDTX) and plays roles in the pathogenicity. In this study bioinformatic analyses were carried out on LLO sequence as a major immunodominant listerial antigen toward designing a DNA vaccine stimulating cytotoxic T-lymphocytes (CTLs). Mouse and human constructs were designed based on predicted T cell epitopes and MHC class I binders, which were then tandemly fused together. LLO-derived construct codons and a variety of critical gene expression efficiency parameters were optimized. Post-translational modifications such as glycosylation, phosphorylation were analysed. The constructs corresponded to LLO sequences of L. monocytogenes in BLAST search. Neither human nor mouse construct was allergen. Secretory pathway was location of the human construct that enhances immune induction and contribute to the efficacy of the vaccine candidate. mRNAs from optimized DNA sequences of both human and mouse constructs are more stable than the native and are suitable for initiation of translation. The constructs contain several sites for phosphorylation that could improve its degradation and subsequent entry into the MHC class I pathway. Addition of GPI anchor, myristoylation and ubiquitin signals or proline (P), glutamic acid (E), serine (S), threonine (T) (PEST)-like motifs at the N-terminal of constructs increase efficacy of the DNA vaccine. Close physical contact between the favorable immunogen and the suitable CpG oligodeoxynucleotides (CpG ODN) promotes immune response. Vectors for checking the expression of constructs in mammalian cells and for harboring the foreign genes as DNA vaccine are suggested.