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Thermal Bioswitches for Non-Invasive Control of Cellular Therapies


Abedi, Mohamad (2021) Thermal Bioswitches for Non-Invasive Control of Cellular Therapies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/z7ac-2g66.


Temperature is a unique input signal that could be used by engineered therapeutic cells to sense and respond to host conditions or spatially targeted external triggers such as focused ultrasound. To enable these possibilities, I present here a new class of thermal bioswitches that enables thermal control over bacterial and mammalian cells. For bacterial applications, we developed two new families of tunable, orthogonal, temperature-dependent transcriptional repressors providing switch-like control of bacterial gene expression at thresholds spanning the biomedically relevant range of 32–46 °C. We integrated these molecular bioswitches into thermal logic circuits and demonstrated their utility in three in vivo microbial therapy scenarios, including spatially precise activation using focused ultrasound, modulation of activity in response to a host fever, and self-destruction after fecal elimination to prevent environmental escape. This technology provides a critical capability for coupling endogenous or applied thermal signals to cellular function in basic research, biomedical and industrial applications.

To apply this technology in a relevant clinical scenario, we sought to engineer microbial immunotherapies that can be thermally controlled with focused ultrasound. This technology was enabled by rapid advances in synthetic biology that are driving the development of genetically modified microbes as therapeutic agents for a multitude of human diseases, including cancer. In particular, the reduced immune surveillance within the core of some solid tumors creates an ideal environment for microbes to engraft and release therapeutic payloads. However, these therapeutic payloads could be harmful if released in healthy tissues where microbes tend to also engraft in smaller numbers. As described in Chapter 2, my colleagues and I introduced a temperature-actuated state switch that enables tight spatiotemporal control over the activity of therapeutic microbes when combined with focused ultrasound hyperthermia. Through a combination of rational design and high throughput screening, we optimized the behavior of this switch to minimize leakage and maximize inducibility. When tested in a clinically relevant in vivo model, engineered microbes, successfully switched states, and induced a marked suppression of tumor growth upon focal activation. This bioswitch provides a critical tool to attain selective and sustained activity of therapeutic microbes in vivo.

Encouraged by the successful development of thermally actuated circuits in microbes, we aimed to establish equivalent technologies for thermal control of human T cells. Genetically engineered T cells are actively being developed to perform a variety of therapeutic functions with great clinical promise. However, no robust mechanisms exist to externally control the activity of T cells at specific locations within the body. Such spatiotemporal control could help mitigate potential off-target toxicity due to incomplete molecular specificity in applications such as T-cell immunotherapy against solid tumors. In Chapter 4, my colleagues and I tested the ability of heat shock promoters to mediate thermal actuation of genetic circuits in primary human T cells in the well-tolerated temperature range of 37−42 °C, and we introduced genetic architectures enabling the tuning of the amplitude and duration of thermal activation. We demonstrated the use of these circuits to control the expression of chimeric antigen receptors and cytokines, and the killing of target tumor cells. Overall, the technologies developed here provide critical tools to direct control therapeutic cells after they have been deployed deep inside the body.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:T-cells; CAR; Thermal Control; Mammalian Synthetic Biology, Heat Shock Promoters; Synthetic Biology; and Immunotherapy
Degree Grantor:California Institute of Technology
Division:Biology and Biological Engineering
Major Option:Bioengineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Shapiro, Mikhail G.
Thesis Committee:
  • Rothenberg, Ellen V. (chair)
  • Baltimore, David L.
  • Murray, Richard M.
  • Shapiro, Mikhail G.
Defense Date:5 February 2021
Funding AgencyGrant Number
Paul and Daisy Soros Fellowship for New AmericansUNSPECIFIED
NSF Graduate Research Fellowship ProgramUNSPECIFIED
Defense Advanced Research Projects Agency (DARPA)D14AP00050
Sontag FoundationUNSPECIFIED
Record Number:CaltechTHESIS:03032021-224823348
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter IV (Thermal Control of Engineered T-cells). adapted for Chapter I (Biomolecular Ultrasound and Sonogenetics. Annual Review of Chemical and Biomolecular Engineering). adapted for Chapter II (Tunable Thermal Bioswitches for in vivo Control of Microbial Therapeutics).
Abedi, Mohamad0000-0001-9717-6288
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14098
Deposited By: Mohamad Abedi
Deposited On:24 Mar 2021 23:47
Last Modified:26 Oct 2021 20:35

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