Protection against most intracellular pathogens requires T cells that recognize pathogen-derived peptides in association with MHC class I molecules on the surface of infected cells. However, because exogenous proteins do not ordinarily enter the cytosol and access the MHC class I-processing pathway, protein-based vaccines that induce class I-restricted CTL responses have proved difficult to design. We have addressed this problem by conjugating proteins, such as OVA, to a short cationic peptide derived from HIV-1 tat (residues 49-57). When APC were exposed in vitro to such protein conjugates, they processed and presented the peptides in association with MHC class I molecules and stimulated CD8+ Ag-specific T cells. Moreover, Ag-specific CTLs were generated in vivo by immunizing mice with histocompatible dendritic cells that had been exposed to protein-tat conjugates.
"During acute infection, Tat is taken up by monocyte derived dendritic cells (MDDC) and promotes MDDC maturation and activation resulting in maximum antigen presentation, leading to increased T cell responses against heterologous antigens . CD8+ T cell-mediated responses (CTL) are also induced through major histocompatibility complex (MHC) class I pathway , . Mainly, Tat transactivates viral gene expression and replication within the cells and favours the transmission of macrophage-tropic and T lymphocyte-tropic HIV-1 strains through induction of CCR5 and CXCR4 co-receptors . "
[Show abstract][Hide abstract] ABSTRACT: Designing an ideal vaccine against HIV-1 has been difficult due to enormous genetic variability as a result of high replication rate and lack of proofreading activity of reverse transcriptase leading to emergence of genetic variants and recombinants. Tat transactivates HIV-1 LTR, resulting in a remarkable increase in viral gene expression, and plays a vital role in pathogenesis. The aim of this study was to characterize the genetic variations of Tat exon-1 from HIV-1 infected patients from North India.
Genomic DNA was isolated from PBMCs and Tat exon-1 was PCR amplified with specific primers followed by cloning, sequencing and sequence analyses using bioinformatic tools for predicting HIV-1 subtypes, recombination events, conservation of domains and phosphorylation sites, and LTR transactivation by luciferase assay.
Phylogenetic analysis of Tat exon-1 variants (n = 120) revealed sequence similarity with South African Tat C sequences and distinct geographical relationships were observed for B/C recombinants. Bootscan analysis of our variants showed 90% homology to Tat C and 10% to B/C recombinants with a precise breakpoint. Natural substitutions were observed with high allelic frequencies which may be beneficial for virus. High amino acid conservation was observed in Tat among Anti Retroviral Therapy (ART) recipients. Barring few changes, most of the functional domains, predicted motifs and phosphorylation sites were well conserved in most of Tat variants. dN/dS analysis revealed purifying selection, implying the importance of functional conservation of Tat exon-1. Our Indian Tat C variants and B/C recombinants showed differential LTR transactivation.
The possible role of Tat exon-1 variants in shaping the current HIV-1 epidemic in North India was highlighted. Natural substitutions across conserved functional domains were observed and provided evidence for the emergence of B/C recombinants within the ORF of Tat exon-1. These events are likely to have implications for viral pathogenesis and vaccine formulations.
PLoS ONE 01/2014; 9(1):e85452. DOI:10.1371/journal.pone.0085452 · 3.23 Impact Factor
"Fully exploiting this ability, CPPs are being utilized in vaccine studies for the delivery of antigens to APCs with the aim of antigen presentation and the induction of an immune response [61,62]. CPP-antigen conjugates enhance the cross-penetration of antigens into DCs [63,64]; however, CPPs function in all cell types, and a dual functionalized compound (CPP conjugation and DC targeting) that was designed in one study showed no synergistic enhancement of the immune response . "
[Show abstract][Hide abstract] ABSTRACT: ABSTRACT: Many studies are currently investigating the development of safe and effective vaccines to prevent various infectious diseases. Multiple antigen-presenting peptide vaccine systems have been developed to avoid the adverse effects associated with conventional vaccines (i.e., live-attenuated, killed or inactivated pathogens), carrier proteins and cytotoxic adjuvants. Recently, two main approaches have been used to develop multiple antigen-presenting peptide vaccine systems: (1) the addition of functional components, e.g., T-cell epitopes, cell-penetrating peptides, and lipophilic moieties; and (2) synthetic approaches using size-defined nanomaterials, e.g., self-assembling peptides, non-peptidic dendrimers, and gold nanoparticles, as antigen-displaying platforms. This review summarizes the recent experimental studies directed to the development of multiple antigen-presenting peptide vaccine systems.
Chemistry Central Journal 08/2011; 5(1):48. DOI:10.1186/1752-153X-5-48 · 2.19 Impact Factor
"In line with this approach, a number of other works also focused on the development of a reliable technique to deliver the antigens inside DCs using penetratin  or Tat peptide . In this study, we demonstrated the benefit of enhanced antigen delivery in improving cell therapy. "
[Show abstract][Hide abstract] ABSTRACT: To investigate the role of enhanced antigen presentation in dendritic cell (DC)-based immunotherapy. Here, we describe the development of a cell-penetrating mucin 1 (MUC1) antigen and its immunotherapeutic potential against tumors. After animal groups received two immunizations of MUC1-MPA(11)P-pulsed DCs, we observed a marked tumor regression compared with the mice treated with DCs alone or DCs pulsed with MUC1 peptide. We confirmed the migration and homing of DCs in the popliteal lymph node using magnetic resonance imaging during the study. In summary, enhanced antigen uptake using an MPA(11)P delivery molecule improves cell therapy.
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