From Mosfet to MOSFET

Our system can convert externally-fluctuating signals into simple 0 and 1 signals to realize the function of an analog-to-digital converter. At the same time, because of the introduction of recombinases, our system will theoretically be more accurate as a biological switch, with lower leakage and less signal expression affected by the concentration of external inducers.

Due to the characteristics of the recombinases we used, the engineered cells of our subject can change different concentrations of signals from the outside into two kinds of simple outputs, and the threshold can be changed by changing the types of the promoter and the recombinase.

Based on these considerations above, our engineered cells can be used in the following situations:

Precision-targeted therapy for solid tumors

EGFR (epidermal growth factor receptor) is a very important protein for cell growth and differentiation that exists on the surface of both normal cells and cancer cells. When a ligand binds to EGFR, EGFR will be activated and send a signal to the inside of the cell to control cell growth through the cell pathway.

However, compared with normal cells, many cancer cells have mutations resulting in overexpression of EGFR. When the ligand is attached to the mutated EGFR, this signal will remain in "sent" mode all the time, resulting in uncontrolled cell response and growth and. Different EGFR mutations lead to different kinds of cancers^[1], such as non-small cell lung cancer, pancreatic cancer, breast cancer, medullary thyroid cancer, head and neck squamous cell cancer, colorectal cancer, chordoma, and malignant glioma.

Since the traditional cancer treatment methods, such as radiotherapy and chemotherapy, can kill all rapidly growing cells in addition to the actual cancer cells, there will be many side effects. Even targeted therapy may also have certain side effects because the target also exists in normal cells^[2]. Immunotherapy may also damage normal cells due to the strong immune response of the modified T cells^[3], so it is necessary to use an immune checkpoint inhibitor to adjust the intensity of the immune response. However, the use of immunosuppressive agents can also do some harm to the human body.

If we replace the upstream extracellular domain of our subject with EGFR antibodies, our design can accurately identify EGFR with different densities on the cell membrane surface, and judge whether the cells change according to the density of EGFR, thus enabling recognition of cancer cells. Moreover, we can adjust the immune strength of the engineered immune cells and the threshold value of EGFR recognition by adjusting the promoter strength and the type of recombinase, to accurately distinguish normal cells with low density EGFR from cancerous cells with high density EGFR, protecting normal cells to the maximum extent, while recognizing and killing cancerous cells. We have devised two strategies to achieve this.

1. Make the final secretion for the whole set of switches PD-1 and PD-L1 antibodies such as MPDL3280A, MEDI4736 BMS-936559, Nivolumab and Pembrolizumab^[4], to make the T cells identify and kill cancer cells through other surface molecules. Compared with the direct use of antibodies by injection therapy, our method of modifying T cells makes the antibody therapy more targeted and minimizes the damage to other immune cells in the body.

2. Make the whole set of switches finally secrete some molecules such as IL-12, CCL21 and so on^[5]. These molecules have the function of stimulating the growth and function of T cells, thus strengthening their ability to kill cancer cells.

More future application prospects

In addition, by replacing the identification object of the upstream system, the measurement of a certain substance can be realized. By adjusting the types of downstream promoters and recombinases, the system threshold can be adjusted. The system may then be used not only to detect the presence or absence of substances but also to dynamically detect the concentration of the detected substances.

If we install our system in two kinds of cells so that they can recognize each other and inhibit each other’s activity and growth, then we can realize the function of group sensing, which can keep the number of two kinds of cells fluctuating within a certain range. This will play an important role in industrial production, material detection and other fields. If the cells are made to emit fluorescence, periodic brightness changes of fluorescence will reflect periodic fluctuations in the number of cells, thus realizing the function of repressilator.

Reference

[1] Sigismund, S., Avanzato, D. & Lanzetti, L. Emerging functions of the EGFR in cancer. Mol. Oncol. 12, 3–20 (2018).

[2] Kalos, M. & June, C. H. Review Adoptive T Cell Transfer for Cancer Immunotherapy in the Era of Synthetic Biology. Immunity 39, 49–60 (2013).

[3] Rubens, J. R., Selvaggio, G. & Lu, T. K. Synthetic mixed-signal computation in living cells. Nat. Commun. 7, 1–10 (2016).

[4] Lote, H., Cafferkey, C. & Chau, I. PD-1 and PD-L1 blockade in gastrointestinal malignancies. Cancer Treat. Rev. 41, 893–903 (2015).

[5] Nissim, L. et al. Synthetic RNA-Based Immunomodulatory Gene Circuits for Cancer Immunotherapy. Cell 171, 1138–1150.e15 (2017).