الفهرس 
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Abstract
Among human parasitic diseases, schistosomiasis ranks second to malaria in terms of socio-economic and public health importance in tropical and subtropical areas. The disease is endemic in many developing countries in the Middle East, Africa, and South America, infecting more than 207 million people in rural and peri-urban areas. Close to 800 million people worldwide, especially under-14 children, are at risk of infection. A vaccine for schistosomiasis would complement drug treatment and other control strategies in terms of reducing levels of disease transmission.
The laboratory of Dr Amr Karim, University of Ain Shams, has been engaged in schistosomiasis vaccine research for many years during which many candidate vaccine antigens have been identified, cloned and characterized, including most of the internationally recognized candidate antigens. However, protection studies in mice with our antigens and many others have led to limited protection. In order to enhance vaccine efficiency, DNA vaccination using pSec Tag2 vectors was employed. The pSec Tag2 vectors are designed for high level expression of proteins in mammalian cells under the control of the cytomegalovirus (CMV) promoter. Proteins expressed from the pSec Tag2 vectors are fused at their N-terminus to the murine Ig chain leader sequence to facilitate their secretion from the cell, which offers a unique approach to immune presentation. The selected cDNA inserts, encoding schistosome antigens were identified by immunoscreening bacteriophage λ cDNA libraries for tegument associated antigens and have been subcloned in plasmid vectors.
Four S. mansoni antigens were evaluated in this study. Four cDNA inserts encoding GST 28 (0.9 Kb), filamin (1.4 Kb), GAPDH (0.9Kb) and Sm 21.7 (0.8 Kb) were cloned into pSec Tag2 vectors.
We have conducted immunization studies in mice with these four constructs using two DNA delivery routes: intramuscular and intradermal, with or without a booster dose of corresponding recombinant protein antigens. Mice were challenged with 100 cercariae 2 weeks after the last booster dose. Adult worms were counted by liver perfusion 6 weeks later. Protection was calculated as the percent reduction in worm burden in comparison with a control group receiving the native pSec Tag2 C vector.
While no protection was observed in case of mice immunized intramuscularly with GST DNA construct alone, a statistically significant protection levels of 59% was observed in case of mice immunized with GST DNA construct and a booster dose of r-GST protein. In contrast, a significant level of protection (18%) was observed in mice injected intradermally with GST DNA construct.
No protection was observed when mice were injected intramuscularly with filamin DNA alone but boosting the DNA immunized mice with r-filamin induced a significant protection of 42%. On the other hand, a significant level of protection (37%) was observed for the intradermal immunization of mice with the filamin DNA construct.
Intradermal vaccination with DNA pSec-GAPDH resulted in a significant level of protection (38%).
In concurrent studies in our laboratory, intramuscular mice protection with the Sm 21.7 construct, yielded levels of protection exceeding 60% with and without booster protein injection. In line with the results of the intramuscular study, the Sm 21.7 construct injected intradermally in the current study induced a 50% protection level, the highest protection observed for all four antigens.
Humoral immune response to the Schistosome antigens (filamin, GST, GAPDH and Sm 21.7) following DNA immunization, was assessed using Western blot analysis against native soluble worm antigen preparation (SWAP) or their corresponding recombinant antigens.
Western blot analysis revealed that antisera from mice immunized intramuscularly with GST or filamin (DNA and DNA plus booster dose of r-protein) specifically recognized the GST or filamin bands, respectively, in SWAP and also recognized their corresponding recombinant antigens, both pre and post challenge.
Similar results were obtained for sera of mice immunized via the intradermal route with GST, filamin, GPDH or Sm 21.7 DNA constructs except for sera of filamin immunized mice which did not recognize r-filamin.
In conclusion, the results of the present investigation point to high levels of humoral immune response and protection following intramuscular immunization with antigen-encoding DNA constructs and boosting with r-protein antigens as observed for GST and filamin. The significant levels of protection observed in this study with DNA vaccination by the intradermal route for GST, filamin, GAPDH and Sm 21.7 demonstrates the promise of an effective intradermal vaccination approach. Of the antigens tested in our experiments Sm 21.7 shows the most promise with consistent protection exceeding 50% in intramuscular and intradermal protection experiments.