Advanced imaging techniques for imaging cell therapies in vivo Flashcards
Where are cell and gene therapy techniques predominanty used?
In therapeutic areas like oncology, ophthlmology and neurology
What are the predominant cell types used in vivo?
T cells
Mesenchymal cells
How are cell and gene therapies being translated into cancer treatment?
- Genes are integrated into the cell genome which makes them identify the cancer
- The engineered cell is now expressing the gene of interest
- The modified cells are stimulated and expanded in vitro
- The cells are inserted into the patient
- The patient undergoes imaging techniques to check the therapeutic response of the stem cell therapy
Why is there so much interest in imaging stem cell therapy in cancer?
Highly variable response of the cancer cells to the genetically modified cells
Are the cells not going to the area of interest?
Are we not using the right antigen?
What is hindering the use of cell-based therapies?
The lack of efficacy data
Their distribution in a patient over time is unknown
This is due to the lack of suitable imaging techniques
Questions remaining regarding cell strategies
What are the safety concerns of cell therapies?
What are the optimal injection routes for the cancer being treated?
What are the two ways to label cells with imaging tracers?
Direct labelling - add label to cell prior to injecting the cell into the body
Reporter gene - modify the cell to express a non-native gene of interest.
What do tracers have to be specific of?
The cell type you are expandin
T cells - expand quickly, so the direct labels are not as useful since they reduce with every division
Mesenchymal stem cells - doubling time of days, direct tracer can label for months
Describe fluorescence imaging
- Excitation wavelength excites an electron
2. The electron gives off light as it goes back down to ground state
What wavelength is preferrebly used in fluorescence imaging?
Red wavelength
Bigger penetration
Which wavelengths are not used in fluorescence imaging?
Green or blue
Since autofluorescence is green
How can we modify a fluorescent image?
Using quantum dots
Semiconductor nanoparticles
Why is it disadvantageous to dye cells?
Highly toxic properties
What is tissue attenuation?
Absorption of light emitted
What is tissue refraction?
Scattering of light emitted
Explain the use of luciferase
Luciferin is taken up across the cell membrane and catalysed by oxygen and ATP to emit light
Emission requires AT{ and oxygen, so used to identify cell viability
When is luciferase used in investigations?
The gene is inserted into cancer cells in order to visualise them
As the cell divides, it transmits its genes to the daughter cells
As the tumour expands, so does the emission of light or photons from the tumour cell
Modified the gene (FLuc enzyme) to a more red pigment so it penetrates more tissues
Describe photoacoustic imaging
NIR laser pulses are delivered to biological tissues
Leads to a ultrasonic wave emission
The US waves are detected by a transducer
Benefits of photoacoutic imaging
Highest resolution from all imaging techniques
Non-invasive
Non-ionising
Do MRIs provide detail on cell resolution?
No
How can we track cells in an MRI?
Contrast agents
Why do we not use contrast agents that increase the signals?
The amount of gallidinium you would need to have a high contrast would be toxic
Use iron oxide instead, which decreases the signals
What is russian blue?
Labels iron
To identify whether cells have been labelled with the contrast agent
Why isPET not useful for cell tracking?
Positron emitter half-lives are too short
What allows SPECT to be used for cell tracking?
Gamma emitters have a long half-life
What is the gold standard for white blood cell imaging?
SPECT imaging
Which cell labelling techniques are toxic?
All at high doses
Fluorescent dye
Nanoparticles
Nuclear tracers
Reporter genes
