In vivo generation of cytotoxic T cells from epitopes displayed on peptide-based delivery vehicles

Improving the endosomal escape of cell-penetrating peptides and their cargos: strategies and challenges

Cell penetrating peptides (CPPs) can deliver cell-impermeable therapeutic cargos into cells. In particular, CPP-cargo conjugates tend to accumulate inside cells by endocytosis. However, they often remain trapped inside endocytic organelles and fail to reach the cytosolic space of cells efficiently. In this review, the evidence for CPP-mediated endosomal escape is discussed. In addition, several strategies that have been utilized to enhance the endosomal escape of CPP-cargos are described. The recent development of branched systems that display multiple copies of a CPP is presented. The use of viral or synthetic peptides that can disrupt the endosomal membrane upon activation by the low pH of endosomes is also discussed. Finally, we survey how CPPs labeled with chromophores can be used in combination with light to stimulate endosomal lysis. The mechanisms and challenges associated with these intracellular delivery methodologies are discussed.

Synthesized OVA323-339MAP octamers mitigate OVA-induced airway inflammation by regulating Foxp3 T regulatory cells

Background

Antigen-specific immunotherapy (SIT) has been widely practiced in treating allergic diseases such as asthma. However, this therapy may induce a series of allergic adverse events during treatment. Peptide immunotherapy (PIT) was explored to overcome these disadvantages. We confirmed that multiple antigen peptides (MAPs) do not cause autoimmune responses, which led to the presumption that MAPs intervention could alleviate allergic airway inflammation without inducing adverse effects.

Results

In this study, synthesized OVA_323-339MAP octamers were subcutaneously injected into ovalbumin (OVA)-sensitized and -challenged Balb/c mice to observe its effect on allergic airway inflammation, Th2 immune response, and immune regulating function. It was confirmed that OVA sensitization and challenge led to significant peritracheal inflammatory, cell infiltration, and intensive Th2 response. Treatment of OVA_323-339MAP octomers in the airway inflammation mice model increased CD4⁺CD25⁺Foxp3⁺ T regulatory (Treg) cells and their regulatory function in peripheral blood, mediastinal draining lymph nodes, and the spleen. Furthermore, OVA_323-339MAP increased IL-10 levels in bronchial alveolar lavage fluid (BALF); up-regulated the expression of IL-10, membrane-bound TGF-β1, as well as Foxp3 in lung tissues; and up-regulated programmed death-1 (PD-1) and cytotoxic T lymphocyte associated antigen 4 (CTLA-4) on the surface of Treg cells. These results were further correlated with the decreased OVA specific immunoglobulin E (sIgE) level and the infiltration of inflammatory cells such as eosinophils and lymphocytes in BALF. However, OVA_323-339 peptide monomers did not show any of the mentioned effects in the same animal model.

Conclusions

Our study indicates that OVA_323-339MAP had significant therapeutic effects on mice allergic airway inflammation by regulating the balance of Th1/Th2 response through Treg cells in vivo.

The importance of valency in enhancing the import and cell routing potential of protein transduction domain-containing molecules

Protein transduction domains (PTDs) are peptides that afford the internalization of cargo macromolecules (including plasmid DNA, proteins, liposomes, and nanoparticles). In the case of polycationic peptides, the efficiency of PTDs to promote cellular uptake is directly related to their molecular mass or their polyvalent presentation. Similarly, the efficiency of routing to the nucleus increases with the number of nuclear localization signals (NLS) associated with a cargo. The quantitative enhancement, however, depends on the identity of the PTD sequence as well as the targeted cell type. Thus the choice and multivalent presentation of PTD and NLS sequences are important criteria guiding the design of macromolecules intended for specific intracellular localization. This review outlines synthetic and recombinant strategies whereby PTDs and signal sequences can be assembled into multivalent peptide dendrimers and promote the uptake and routing of their cargoes. In particular, the tetramerization domain of the tumour suppressor p53 (p53tet) is emerging as a useful scaffold to present multiple routing and targeting moieties. Short cationic peptides fused to the 31-residue long p53tet sequence resulted in tetramers displaying a significant enhancement (up to 1000 fold) in terms of their ability to be imported into cells and delivered to the cell nucleus in relation to their monomeric analogues. The design of future polycationic peptide dendrimers as effective delivering vehicles will need to incorporate selective cell targeting functions and provide solutions to the issue of endosomal entrapment.

Delivery of bioactive molecules into the cell: the Trojan horse approach

In recent years, vast amounts of data on the mechanisms of neural de- and regeneration have accumulated. However, only in disproportionally few cases has this led to efficient therapies for human patients. Part of the problem is to deliver cell death-averting genes or gene products across the blood-brain barrier (BBB) and cellular membranes. The discovery of Antennapedia (Antp)-mediated transduction of heterologous proteins into cells in 1992 and other "Trojan horse peptides" raised hopes that often-frustrating attempts to deliver proteins would now be history. The demonstration that proteins fused to the Tat protein transduction domain (PTD) are capable of crossing the BBB may revolutionize molecular research and neurobiological therapy. However, it was only recently that PTD-mediated delivery of proteins with therapeutic potential has been achieved in models of neural degeneration in nerve trauma and ischemia. Several groups have published the first positive results using protein transduction domains for the delivery of therapeutic proteins in relevant animal models of human neurological disorders. Here, we give an extensive review of peptide-mediated protein transduction from its early beginnings to new advances, discuss their application, with particular focus on a critical evaluation of the limitations of the method, as well as alternative approaches. Besides applications in neurobiology, a large number of reports using PTD in other systems are included as well. Because each protein requires an individual purification scheme that yields sufficient quantities of soluble, transducible material, the neurobiologist will benefit from the experiences of other researchers in the growing field of protein transduction.

Epitope-based vaccines: an update on epitope identification, vaccine design and delivery

The basic premise of the epitope-based approach to vaccine development is that, in certain cases, the responses induced by the natural immunogen are not optimal, and can be improved upon by isolation or optimization of specific components of the response. For example, immunodominance is a key factor limiting the type and breadth of adaptive immunity. Recent advances in understanding the mechanisms of immunodominance thus represent an opportunity to further develop the epitope-based approach.