Xiang et al. found a new approach in inhibiting tumour growth and metastasis by simultaneously attacking both the tumour and its vasculature by a cytotoxic T cell (CTL) response against the survivin protein, which will later result in the activation of apoptosis in tumour cells.
The idea and general principle behind his technique is described below. Mice were immunized with the oral vaccination and then subjected to tumour challenges by injecting them in the chest with a certain number of tumour cells and a Matrigel pre-formed extracellular matrix to hold the tumour cells together. The mice were sacrificed and the endothelium tissue was stained with a fluorescent dye that would aid in the quantification of tumour neovascularisation using a Matrigel assay. There was found to be a significant difference between the control and test groups, whereby mice given the vaccine had less angiogenesis from the tumour challenge than the control mice that were not given any of the vaccine prior to tumour challenge. In vitro assays and other tests were also performed to validate the idea of the occurrence of an actual immune response to support what they observed in the mice. For example, the spleen on the challenged mice were isolated and measured for the presence of any cytokines, and specifically activated immune cell groups that would indicative that a specific immune response did occur upon vaccination. The isolated CTLs specific for the survivin protein after vaccination of the mice were used in cytoxicity assays where mice tumour cells expressing survivin were shown to be killed upon incubation with the specific CTLs.
By using an oral DNA vaccine carried in an attenuated non-virulent form of Salmonella typhimurium, which co-encoded secretory chemokine CCL21 and survivin protein in C57BL/6J mice, Xiang et al. have been able to elicit an immune response carried out by dendritic cells (DCs) and CTLs to eliminate and suppress the pulmonary metastases of non-small cell lung carcinoma. The activation of the immune response is most likely taking place in the secondary lymphoid organ called the Peyer's Patch in the small intestine where DCs take up the survivin protein by phagocytosis and present them on their surface receptors to naive CD8+ T cells (uninactivated CTL) to achieve a specific immune response targeting survivin exclusively. Activated CTLs specific for a particular antigen kill their target cells by first recognizing parts of the survivin protein expressed on MHC I (immunohistocompatability) proteins presented on the surface of tumour cells and vasculature and then releasing granules that induce the tumour cells to undergo apoptosis. The DNA vaccine contained the CCL21 secretory chemokine as a way to enhance the likelihood of eliciting the immune response by better mediating the physical interaction of the antigen-presenting DCs and the naive CD8+ T cells, resulting in a greater likelihood of immune activation.