Nucleic acid vaccines

There are no adequate vaccines against some of the new or reemerged infectious scourges such as HIV and TB. They may require strong and enduring cell-mediated immunity to be elicited. This is quite a task, as the only known basis of protection by current commercial vaccines is antibody. As DNA or RNA vaccines may induce both cell-mediated and humoral immunity, great interest has been shown in them. However, doubt remains whether their efficacy will suffice for their clinical realization. We look at the various tactics to increase the potency of nucleic acid vaccines and divided them broadly under those affecting delivery and those affecting immune induction. For delivery, we have considered ways of improving uptake and the use of bacterial, replicon or viral vectors. For immune induction, we considered aspects of immunostimulatory CpG motifs, coinjection of cytokines or costimulators and alterations of the antigen, its cellular localization and its anatomical localization including the use of ligand-targeting to lymphoid tissue. We also thought that mucosal application of DNA deserved a separate section. In this review, we have taken the liberty to discuss these enhancement methods, whenever possible, in the context of the underlying mechanisms that might argue for or against these strategies.     

Nucleic acid vaccines.

The use of nucleic acid-based vaccines is a novel approach to immunization that elicits immune responses similar to those induced by live, attenuated vaccines. Administration of nucleic acid vaccines results in the endogenous generation of viral proteins with native conformation, glycosylation profiles, and other posttranslational modifications that mimic antigen produced during natural viral infection. Nucleic acid vaccines have been shown to elicit both antibody and cytotoxic T-lymphocyte responses to diverse protein antigens. Advantages of nucleic acid-based vaccines include the simplicity of the vector, the ease of delivery, the duration of expression, and, to date, the lack of evidence of integration. Further studies are needed to assess the feasibility, safety, and efficacy of this new and promising technology.     

Nucleic acid immunization: concepts and techniques associated with third generation vaccines

A radical change in vaccine methodology arrived nine years ago with the advent of nucleic acid immunization. Aspects such as plasmid design, gene selection, the use of immunostimulatory complexes and clinical trials are discussed in this review. Furthermore, concepts and protocols involved in the construction, evaluation and immunization of a DNA vaccine have been examined as new strategies to enhance this technology continues to grow.     

Solid matrix-antibody-antigen (SMAA) complexes for constructing multivalent subunit vaccines

For successful vaccination to many diseases, it is necessary to induce both humoral and cell-mediated immune responses to the infectious agent: this may require the incorporation of multiple antigens from the same microbe into the vaccine. In this article, Richard Randall proposes that one of the most practical and effective ways of producing multivalent vaccines may be through the construction of solid matrix-antibody-antigen (SMAA) complexes. The advantages of such vaccines and their future potential is discussed.     

核酸疫苗作为治疗性疫苗的前景

联系核酸疫苗的免疫机理和慢性病毒感染的发生机制,对将核酸疫苗用作慢性病毒感染的治疗疫苗的发展前景作一简要阐述。     

RNA: The new revolution in nucleic acid vaccines

Nucleic acid vaccines have the potential to address issues of safety and effectiveness sometimes associated with vaccines based on live attenuated viruses and recombinant viral vectors. In addition, methods to manufacture nucleic acid vaccines are suitable as generic platforms and for rapid response, both of which will be very important for addressing newly emerging pathogens in a timely fashion. Plasmid DNA is the more widely studied form of nucleic acid vaccine and proof of principle in humans has been demonstrated, although no licensed human products have yet emerged. The RNA vaccine approach, based on mRNA and engineered RNA replicons derived from certain RNA viruses, is gaining increased attention and several vaccines are under investigation for infectious diseases, cancer and allergy. Human clinical trials are underway and the prospects for success are bright.     

Impact of methoxymycolic acid production by Mycobacterium bovis BCG vaccines

BCG vaccines are a family of closely related daughter strains of an attenuated isolate of Mycobacterium bovis derived by in vitro passage from 1908 to 1921. During subsequent laboratory propagation of the vaccine strain until its lyophilization in 1961, BCG Pasteur underwent at least seven further genomic mutations. The impact of these mutations on the properties of the vaccine is currently unknown. One mutation, a glycine-to-aspartic acid substitution in the mmaA3 gene, occurred between 1927 and 1931 and impairs methoxymycolic acid synthesis in BCG strains obtained from the Pasteur Institute after this period. Mycolic acids of the cell wall are classified into three functional groups (alpha-, methoxy-, and ketomycolic acids), and together these lipids form a highly specialized permeability barrier around the bacterium. To explore the impact of methoxymycolic acid production by BCG strains, we complemented the functional gene of mmaA3 into BCG Denmark and tested a number of in vitro and in vivo phenotypes. Surprisingly, restoration of methoxymycolic acids alone had no effect on cell wall permeability, resistance to antibiotics, or growth in cultured macrophages and C57BL/6 mice. Our results demonstrate that the loss of methoxymycolic acid production did not apparently affect the virulence of BCG strains.     

Release of fibronectin-lipoteichoic acid complexes from group A streptococci with penicillin.

Fibronectin binds to Streptococcus pyogenes, and this binding is inhibited by lipoteichoic acid (LTA). Previous studies have shown that LTA can be released from S. pyogenes by treatment with penicillin. Penicillin released LTA from both S. pyogenes and Staphylococcus aureus; however, the binding of fibronectin correlated with the amount of LTA released only in the case of S. pyogenes. Contrarily, clindamycin decreased the ability of S. aureus to bind fibronectin without affecting the binding of fibronectin to S. pyogenes. Further studies indicated that LTA does not inhibit the binding of fibronectin to S. aureus. Fibronectin bound to S. pyogenes could be released from the cell surface by penicillin. Immunological analysis of the released fibronectin indicated that LTA was the only surface component which could be detected as a soluble complex with the released fibronectin. These studies suggest that LTA plays a central role in the binding of fibronectin to S. pyogenes and is not involved in the binding of fibronectin to S. aureus.     

Potentiation of interferon-gamma-stimulated nitric oxide production by retinoic acid in RAW 264.7 cells.

Nitric oxide (NO) production is essential for normal immunity. We have examined the capacity of retinoic acid (RA), a pleiotropic hormone necessary for normal immunity, to modulate NO production in RAW 264.7 cells. NO production induced by suboptimal concentrations of interferon-gamma (IFN-gamma) was significantly greater in cells cultured in low-retinoid medium and treated with all-trans-RA (10(-10) - 10(-6) M, P <0.05), as well as with 9-cis-RA and several retinoids selective for the RA receptor subfamily of nuclear retinoid receptors. Similar results were obtained with lipopolysaccharide and monophosphoryl lipid A as stimuli. The RA-potentiated production of NO was positively correlated with inducible NO synthase (iNOS) protein (r =0.94, P <0.002), although the expression of iNOS mRNA was not altered. We hypothesize that modulation of the macrophage response to suboptimal immune stimuli by physiological concentrations of RA, as observed in these studies, may be important in establishing an optimal balance between T helper (Th) 1- and Th2-mediated immunity.     

Potentiation by glutamic acid dimethyl ester of GLP-1 insulinotropic action in fed anaesthetized rats

The dimethyl ester of L-glutamic acid (DMG) stimulates insulin release and was proposed as a possible insulinotropic tool in the treatment of non-insulin-dependent diabetes. In such a perspective, it was investigated whether DMG enhances the B-cell secretory response to GLP-1 in fed anaesthetized rats. The primed constant infusion of DMG (1.0 micromol and then 0.5 micromol/min, both per g body wt.) provoked a rapid and sustained increase in plasma insulin concentration and augmented the release of insulin caused by GLP-1. Thus, DMG indeed appears as a suitable tool to potentiate the insulinotropic action of GLP-1.     

Water soluble complexes of chitosan-g-MPEG and hyaluronic acid

Novel water soluble, biocompatible, and highly viscoelastic polyelectrolyte complexes were prepared by mixing of positively charged chitosan grafted with poly (ethylene glycol) monomethyl ether (CS-g-MPEG) and negatively charged hyaluronic acid (HA). CS-g-MPEGs having different degrees of substitution were synthesized by reacting chitosan with MPEG-aldehyde. The molecular structure, thermal and rheological properties, as well as biocompatibility of CS-g-MPEG/HA complexes were characterized. Rheological results showed that a small amount of HA could greatly enhance the viscosity of CS-g-MPEG solution. The highest viscosity was obtained when the charge ratio of CS-g-MPEG/HA was close to 1.0. Small-angle X-ray scattering measurements provided some insights into the lamellar structure of the CS-g-MPEG/HA complex. The CS-g-MPEG/HA complex system offers promising potentials in pharmaceutical, cosmetic, and biotechnology applications (e.g., cell scaffold, artificial synovial fluid, and drug/gene delivery medium).     

Cancer therapy with DNA-based vaccines

The development of DNA-based vaccines arises from the knowledge that weakly immunogenic, tumor-associated antigens (TAAs), the products of mutant or dysregulated genes in the malignant cells, are expressed in a highly immunogenic form by antigen presenting cells. We successfully prepared vaccines that were effective in the treatment of cancer in mice by transfection of DNA from breast cancer cells into a mouse fibroblast cell line (LM). Fibroblasts express MHC class I-determinants along with B7.1, a co stimulatory molecule. (Classic studies indicate that transfection of genomic DNA can stably alter both the genotype and the phenotype of the cells that take-up the exogenous DNA.) The fibroblasts were transfected with sheared, unfractionated genomic DNA from a breast adenocarcinoma that arose spontaneously in a C3H/He mouse (H-2(k)). To increase their non-specific immunogenic properties, the fibroblasts were modified before transfection to express allogeneic MHC-determinants (H-2K(b)) and to secrete IL-2. Afterward, the IL-2-secreting semi allogeneic cells were co transfected with DNA from the spontaneous breast neoplasm, along with a plasmid (pHyg) conferring resistance to hygromycin. Pooled colonies of hygromycin-resistant cells were then tested in C3H/He mice for their immunotherapeutic properties against the growth of the breast neoplasm. The results indicated that tumor-bearing mice immunized with the transfected cells survived significantly longer than mice in various control groups. Similar beneficial effects were seen in C57BL/6 mice injected with a syngeneic melanoma cells and semi allogeneic, IL-2-secreting fibroblasts transfected with DNA from the melanoma cells. The immunity was mediated by CD8(+) T cells and was specific for the type to tumor from which the DNA was obtained.     

Potentiation of the anticoccidial effect of salinomycin with dihydroquinoline-type antioxidants

The potentiating efficacy was determined on day 8 after infection with Eimeria tenella on the basis of oocyst counts and gross caecal lesions. The prototype of dihydroquinoline-type antioxidants (6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline) had no potentiating effect. When two molecules of the prototype were linked with an alkyl group (methylidene, ethylidene, or propylidene), the anticoccidial efficacy of salinomycin was increased such that a dose of 15 mg/kg was as effective as the standard 60 mg/kg given alone. The potentiating effect was lost if the molecule were acetylated or sulphonated. A similar potentiating effect was also demonstrable for monensin but was lacking for lasalocid.