Team:McGill/Description
Project Description
Standardized cell-cell interactions
Cell-cell interactions are the ensemble of interactions occurring on the surfaces of cells that allow them to communicate with each other. Cell-cell interactions play a vital role in multicellular biological systems and manifest in many different forms.
For example, cell-cell interactions allow cell adhesion for tissue development, muscle fibers to contract in response to a neural signal, immune cells to detect potential pathogens or cancer cells, bacteria to form biofilms and regulate their growth.
We are attempting to create a form of standardized cell-cell interaction that is universal, modular, easy to control, and orthogonal.
Universal:
Most cell-cell interactions are highly specific. One that would be ideal for synthetic biology purposes would theoretically be able to interact with almost anything, eliminating the need for many different interaction systems to deal with different situations.
Modular:
This system should be able to be easily modified to suit other purposes as needed. It should also allow us to integrate it into a more complex biological system with relative ease.
Easy to control, reliable:
Cells can be difficult to work with. We want to have as much control over the interaction process as possible, in order to have a system that is responsive to inputs and can be trusted to work in a consistent manner.
Orthogonal:
This cell-cell interaction should ideally be isolated from the rest of the cell, so that it is easy to manipulate without unintended side effects.
What is synNotch?
Notch receptors are a class of transmembrane proteins that play a role in cell differentiation. Recently, it was discovered that both the extracellular domain and the intracellular domain could be “swapped”, allowing them to be replaced by another receptor domain and another transcription factor domain, respectively (Sica et al., 2016).
Diagram depicting wild-type Notch, Notch with a modified intracellular domain and synNotch with a modified intracellular and extracellular domain. Source: Morsut et al. 2016
This effectively allows for the engineering of cells that are able to interact with any antigen or ligand of interest – simply genetically modify the cells to express a synthetic Notch receptor with the appropriate receptor domain!
In the same vein, it is also possible to make the receptor regulate the expression of any gene: simply change the transcription factor by changing it to one that regulates the promoter of interest.
What is BiTE?
Bispecific T-Cell Engagers, or BiTEs for short, are bi-specific single chain fragment variable (scFV) antibodies, connected with a small linker segment. Their simplicity makes them relatively easy to synthesize.
BiTE antibodies are composed of the variable regions of 2 distinct antibodies, allowing them to bind to 2 different ligands. The removal of the other structural features makes them fairly unstable, with a half-life of around 2 hours. Source: Baeuerle and Reinhardt, 2009.
Our Project
Our idea is to combine these two technologies to create a universal, standardized system for mammalian cell-cell interactions.
Example of Notch-BiTE in action. In this case, a BiTE antibody allows the macrophage to detect the presence of a cancer cell, by binding to the Her2 antigen.
This technique would have several advantages. By having one side of the interaction be mediated by an antibody, we can use the same synNotch receptor for multiple interactions: simply change the antibody being used! The synNotch side would remain the same but the other scFv would be swapped.
This removes the need to constantly create new stable cell lines expressing a relevant synNotch receptor. It would be possible to create “libraries” of antibodies that could be used to interact with any ligand, and they would all work with the same cell! This removes a lot of the work needed to establish a system of cell-cell interactions.
Additionally, since BiTE has a short half-life, we can stop the interaction by not adding BiTE: within a few hours the BiTE concentration will be back down to near-basal levels.
This system could be used independently for tightly controlled cell-cell interactions or as a “building block” for more complex biological systems that require a cell-cell interaction component.
References
Baeuerle, P.A., and Reinhardt, C. (2009). Bispecific T-Cell Engaging Antibodies for Cancer Therapy. Cancer Res. 69, 4941–4944.
Morsut, L., Roybal, K.T., Xiong, X., Gordley, R.M., Coyle, S.M., Thomson, M., and Lim, W.A. (2016). Engineering Customized Cell Sensing and Response Behaviors Using Synthetic Notch Receptors. Cell 164, 780–791.