| Current strategies for cancer therapy include surgery, chemotherapy and radiotherapy. But they all have many defects such as the injury to normal tissue, the side effects, nonspecificity and low efficiency, which limit the foreground of their application. Nowadays cancer specific immunotherapy is arisen gradually, such as those methods utilizing tumor cells and tumor antigen specific epitope peptides. Though these methods are tumor specific, but they have many disadvantages including the deficiency of primed immune response and the relatively low immune response.Comparing with 1st and 2nd generation vaccines, gene vaccines can avoid these obstacles partly. Gene vaccines have many advantages, such as the simplicity of preparation, the long time of immune stimulation and no considering the MHC restriction. Many achievements have been obtained using gene vaccines. In spite of these advantages of gene vaccine, the current gene vaccines also have many limitations, for instance, the immune-stimulation is not strong enough and the efficiency of immune response in human and big animals is very low. Thus it is essential to research novel strategy for gene vaccine. The ubiquitous obstacle of current gene vaccines is the deficiency of the expression of target protein and the deficiency of transforming in vivo. To overcome these key limits needs modificating gene carrier. At present, much research of gene vaccines have applied modified virus as gene vector in view of the efficiency of expression and infection of virus, and various high efficient virus-type gene vaccines have been used in various research field. Alphavirus, one of virus vectors, has been recognized gradually as one of the mostpromising vectors in the DNA vaccine. As a kind of novel vector, a -virus has the characteristics including the simplicity of preparation and handling, abroad host, extensively expression of RNA and target protein. Study on the function of function of a -virus has revealed that a -virus replicase is the key element of alphavirus and can catalyse effectively the replication of the genes lying downstream of it at RNA level, which leds to the abundant target protein expression subsequently. Therefore, we utilize the characteristics of a -virus to prepare various recombinant plasmids and rSFV to study the new characteristic of this modified gene vaccines, and then compare the difference of immune response between recombinant plasmids and SFV. We also observe the effect of IL-12 expressing plasimids on gene vaccines.Tumor specific gene vaccines need tumor specific antigen gene. Many tumor specific antigens such as mouse PI A, human MAGE, BAGE and GAGE families had been isolated during recent decade. PI A is a tumor specific antigen expressed by mouse mastocytoma P815. It is one kind of cancer-testis antigens and expresses in various mouse tumor such as mastocytoma P815, plasmoma J558 and fibrosarcoma Meth A but hardly in normal tissue except testis and placenta. Therefore, it has become an ideal model target for designing and studying tumor vaccines, and thus we chose it as the target of our research to evaluate the immune effect of gene vaccines based on the new vector.We amplified PI A gene from P815 cells by RT-PCR and made recombinant plasmids pCI/PlA and replicase expressing recombinant plasmid pSMART2a/P1A. We also prepared recombinant alphavirus P1A/SFV and control recombinant virus LacZ/SFV. Following vaccines inoculation, the amount of Thl-type cytokine (IFN- Y ) secreted by spleen cells of the mouse of experimental group was much more than that of Th2-type cytokine (IL-4). For P1A/SFV group, the ratio of amount of the two cytokines reached 2700. PI Aspecific antibody could not be detected in all groups. Antigen specific CTL could be detected in mice of each experimental group, but the activity of CTL in PI A/SFV group was the strongest. IL-12 expressing plasmids could enhance the immune response of pCI/PlA when co-injected with the latter. In the challenge and therapeutic experiment, within 60 days of experiment,...
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