The advantage of this in vivo technique is that it offers a meansof rapidly screening entire genomes, with the results of the searchdisplaying desired immunogenic traits. The mode of entry ofvaccines designed in this way closely resembles the naturalinfection process of host cells - an improvement over liveattenuated vaccines. This promising approach has been used effectively to engineer avaccine against hepatitis and may provide a new avenue for the development of protectiveagents against pathogens that have thus far eluded traditionalvaccine efforts, including HIV and ebola. "We had developed a method for screening for protective subunitsagainst a specific disease," Sykes says. "However this type ofsafer vaccine design is notoriously less potent than the wholepathogen designs. |
What we needed was a method to find generallyuseful vaccine components that would serve to enhance and controlimmunity." The group chose the pathogen parapoxvirus ovis (known as the Orfvirus) for the current set of experiments, in which expressionlibrary immunization techniques were used to screen for animmunogenic factor buried in the pathogen's genome. Parapoxvirus ovis causes a highly infectious disease known as Orf,which is prevalent in sheep and goats and may be transmittedcutaneously to humans handling these animals, causing pustularlesions and scabs. Once the group had sequenced the full genome of parapoxvirus, PCRwas used to amplify all the viral open reading frames, which codefor all of the viruse's proteins. Each ORF, comprising a library ofgenomic components, was compiled into a unique high throughputexpression construct, and these were randomly distributed intosub-library pools. These pools were directly delivered into sets ofmice for in vivo expression.
Functional testing for the activitydesired identified B2 as the immune cell accumulator. In further experiments, the team co-delivered B2L as an additive oradjuvant for an influenza gene vaccine, to see if it could improvesurvival rates in mice challenged with the influenza virus. Theco-immunized mice indeed displayed full protection againstinfluenza compared with 50 percent protection of the control group,immunized with influenza vaccine alone. In addition to infectious agents like Orf, non-infectious diseasesincluding cancer may be amenable to vaccine defense. Thus far however, thediscovery of tumor-specific antigens has been frustrating.
Oneapproach may lie in using non-specific immunogenic factors like B2. In the current study, two forms of cancer were investigated in amouse model, following the administering of B2 alone, in theabsence of a disease antigen. The experiments evaluated B2'sability to enhance survival and shrink tumor size. In the case ofan aggressive melanoma , tumor size was significantly reduced and survival rate improved.Administration of B2 to an infection induced by a breast cancer cell line also showed a modest but measureable reduction in tumorsize. With the growing popularity of sub-unit vaccines, the need arisesfor more effective adjuvants, which may be used to compensate forthe reduced immunogenicity of such vaccines compared with theirwhole-pathogen counterparts.
Techniques similar to those appliedhere to isolate and evaluate B2 could potentially permit thescreening of virtually any genome for any gene-encoded activitytestable in an organism. Additional References Citations.
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