Background information
Cancer is being called as the emperor of all maladies by Siddhartha Mukherjee, who is an Indian American physician and biologist. Indeed, there are estimated 10 million people died due to cancer annually[1]. The fatality rate of cancer in well-developed countries is 17% and 70% in low- or middle-income countries [2], according to the statistics provided by WebMD Cancer Center. However, due to unhealthy diet and unbalanced lifestyle in nowadays modern society, there’s an overall cancer prevalence increase of 26.9% every year, and it is estimated that there will be 16 million people die because of cancer by the year 2040 [3]. According to the data provided by WHO, it is said that 30%-50% of cancers can be prevented not only by correcting and improving lifestyles and habit, but also through medical approaches, such as cancer prevention vaccine [4]. The mechanism of such vaccines is like normal vaccines, training the immune cells to recognize cancer cells and eliminate those cells. However, using injected vaccine lacks efficiency, due to the limited subcutaneous distribution of antigen presenting cells in muscle tissue.
Why orally?
Considering about all the drawbacks and infeasibility of injection cancer vaccine, a new form of cancer vaccine is highly demanded as the increasing cancer incidence worldwide. To maximum the efficiency of cancer vaccine, the location of vaccine deployment is essential. The small and large intestine will be an ideal location . While there are over 70% immune cells within the system, the vaccine can target the immune system directly, instead of only in the draining lymph node. But it is crucial to deliver drugs to the site without drugs being damaged or ingested before reaching the small and large intestine.
Our Design
E coli is a common strain of bacteria found in the intestines of mammals, it is able to survive transit through the stomach to reach the intestines where it may multiply. We suggest that the natural resilience of this organism makes it an ideal candidate to carry antigens to the intestines. In our project, we constructed a genetically modified E. Coli top10 strain producing outer membrane vesicles(OMV) carrying antigen from the tumor. Which can successfully cross the intestinal epithelial barrier and be recognized by immune cells in lamina propria. In this way, the tumor-antigen-specific immune response can be triggered effectively and have a significant effect in preventing the development of tumors and limiting the tumor metastasis, which can result a long-term protection and prevention of cancer[5].
Immune tolerance caused by long-term antigenic stimulation can be a problem with cancer vaccines. To overcome this we plan to use the SulAp promoter(BBa_K518010), an optogenetic regulatory element that has been used by our team in 2020. However, based on our experiment result from iGEM 2020, the SulAp promoter has the problem of high leaking expression and relative low promoting strength (therefore, we are unable to complete the UV control lysis function at last due to high leaking expression in 2020）. Therefore, we also plan to use the technology of direct revolution to improve this part(and join the iDEC 2022 competition, team SZ-SHD) . We also designed an improved new part as a backup plan which contains two LexA binding sites(dLex).
How to control the engineering bacterica in the intestine? The inspiration of using optogenetic regulatory element first come to our mind when we look for the project from team SMS_Shenzhen in 2020. However, their wiki did not give clear information on how to achieve this. After have close discussion with their members(more information on page: Human practice), we found they did not know how to allow the light to touch the intestine. Hence, through the discussion of our own team, we decided to develop a micro- swellable auto-positioning capsule UVC light source hardware was developed to activate gene expression in the human intestine(detailed information on page: Hardware). To allow the capsule to navigate, we also designed a built-in camera and trained a convolutions neural network exposed to a large dataset of endoscopic video footage(detailed information on page: modeling; software tool).
To remove the engineer bacteria from the body after treatment, we designed a self-lysis system based on arabinose induction, after the patients intake arabinose, T4 lysozyme will be expressed and eliminate the bacteria.
References
- [1] Cancer Statistics - NCI; How Many People Die of Cancer a Year? (webmd.com)
- [2] Cancer Treatment Vaccines - Immunotherapy - NCI; Cancer Vaccines: Preventive and Therapeutic – Cancer Research Institute (CRI)
- [3] McBroom AJ, Kuehn MJ. Outer Membrane Vesicles. EcoSal Plus. 2005 Nov;1(2). doi: 10.1128/ecosal.2.2.4. PMID: 26443511.
- [4] Furuyama, N., Sircili, MP., Outer Membrane Vesicles (OMVs) Produced by Gram-Negative Bacteria: Structure, Functions, Biogenesis, and Vaccine Application. BioMed Research International, vol. 2021, Article ID 1490732, 16 pages, 2021.
- [4] Yue, Y., Xu, J., Li, Y. et al. Antigen-bearing outer membrane vesicles as tumour vaccines produced in situ by ingested genetically engineered bacteria. Nat. Biomed. Eng 6, 898–909 (2022).