Current schistosomiasis vaccine research is beginning to explore DNA vaccine as one of the alternatives. The latest development in DNA vaccine research shows great promises against parasitic helminthes albeit some challenges. (Akram et al.) Remarkable progress has been made in the past few years in terms of DNA vaccine research and it is undoubtedly one of the most novel ways that we can be used to develop vaccines against different kinds of infectious diseases. The ingenuity in the success of DNA vaccines arises from the fact that it entails a fairly simple procedure. A purified and modified DNA sequence encoding for the target antigen is inserted into a bacterial plasmid, which is done under the regulation of Eukaryotic promoter. The plasmid with the insert is then injected into specific host cells usually the muscle cells. The idea is that the host’s immune cells will recognize the foreign antigen but nonetheless treats the foreign antigen as harmless and thus regulates the expression of the newly introduced antigen. This is an incredible way of introducing new antigen (extracted from Schistosome) into the body of the human host so that antibody can safely be mounted against it. This technology is already in use to derive vaccines for cancer and other infectious diseases.
DNA vaccine can also be used to invoke all kinds of immune response including T-helper cells which are crucial for the schistosomiasis immune response mechanism. It is thought that there are complex adjuvants that play crucial roles involving Toll-like receptor pathways. Also DNA vaccine, unlike conventional vaccines can be used to develop multi-antigen vaccine. Furthermore, it is easy produce DNA vaccine on a lager scale since they don’t require specialized storage like temperature. What is even more interesting is the recent development in our ability to sequence the genomes of some parasites. With the help of proteomics and genomics, one can probe the genes of interest and its functionality fairly easily. Thus DNA vaccine represents a new beginning in terms of effectively developing a fast, but reliable vaccine product against many infectious diseases threatening humans worldwide. Some researchers are also making use of this new paradigm in vaccine research to find effective vaccines against schistosomes.
For instance, a number of studies have been conducted using the method of DNA vaccine. A DNA vaccine based on S.mansoni, as large sub-unit of caplain (Sm-p80) was tested in mice. When the test was done using plasmids that encode either IL-4,-2, -12 or GM-CSF, the result was more powerful than if the Sm-p80 was used alone (Akram, vaccine review). Other multi-antigen DNA vaccines have also been explored using different vaccine candidates including sm14. In addition, vaccine candidates like S.japonicum paramyosin (rSjc97) was also tested in mice and water buffalo showing the potential for DNA vaccine as an effective strategy to develop new vaccines. In addition, a study by E Nascimento et al. further shows the use of DNA vaccine. In this study the use of combinatorial plasmids were explored. They took three plasmids encoding tegumental, (Pecl and Psm14) and muscular (Pirv5) and immunized female BALB/c mice with the vaccine. The mice were later infected with circariae and studied for the worm load. Results from this study shows that the induction of protective immunity by triple schistosome antigen encoded-vaccine was higher than that of single vaccine with a higher efficacy in the lowering of worm burden. The study concluded that vaccine derived from the three DNA encoded S.mansoni antigens Sm14, IrV5, and ECL resulted in the induction of protective immunity in the range of 45-50%. Thus this and other studies show the prospect for further research in vaccine development is paramount to reduce the heavy burden of infectious diseases. Furthermore, DNA vaccine is perhaps one of the most interesting biological tools that we can exploit to understand the role of parasites and eventually to find interventions in the form of vaccine. Schistosomiasis is a complex disease and a better understanding of the immune modulation in humans is essential for effective vaccine development.