Advanced imaging techniques for imaging cell therapies in vivo

Question 1

Where are cell and gene therapy techniques predominanty used?

Answer 1

In therapeutic areas like oncology, ophthlmology and neurology

Question 2

What are the predominant cell types used in vivo?

Answer 2

T cells

Mesenchymal cells

Question 3

How are cell and gene therapies being translated into cancer treatment?

Answer 3

1. Genes are integrated into the cell genome which makes them identify the cancer
2. The engineered cell is now expressing the gene of interest
3. The modified cells are stimulated and expanded in vitro
4. The cells are inserted into the patient
5. The patient undergoes imaging techniques to check the therapeutic response of the stem cell therapy

Question 4

Why is there so much interest in imaging stem cell therapy in cancer?

Answer 4

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?

Question 5

What is hindering the use of cell-based therapies?

Answer 5

The lack of efficacy data

Their distribution in a patient over time is unknown

This is due to the lack of suitable imaging techniques

Question 6

Questions remaining regarding cell strategies

Answer 6

What are the safety concerns of cell therapies?

What are the optimal injection routes for the cancer being treated?

Question 7

What are the two ways to label cells with imaging tracers?

Answer 7

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.

Question 8

What do tracers have to be specific of?

Answer 8

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

Question 9

Describe fluorescence imaging

Answer 9

1. Excitation wavelength excites an electron

2. The electron gives off light as it goes back down to ground state

Question 10

What wavelength is preferrebly used in fluorescence imaging?

Answer 10

Red wavelength

Bigger penetration

Question 11

Which wavelengths are not used in fluorescence imaging?

Answer 11

Green or blue

Since autofluorescence is green

Question 12

How can we modify a fluorescent image?

Answer 12

Using quantum dots

Semiconductor nanoparticles

Question 13

Why is it disadvantageous to dye cells?

Answer 13

Highly toxic properties

Question 14

What is tissue attenuation?

Answer 14

Absorption of light emitted

Question 15

What is tissue refraction?

Answer 15

Scattering of light emitted

Question 16

Explain the use of luciferase

Answer 16

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

Question 17

When is luciferase used in investigations?

Answer 17

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

Question 18

Describe photoacoustic imaging

Answer 18

NIR laser pulses are delivered to biological tissues

Leads to a ultrasonic wave emission

The US waves are detected by a transducer

Question 19

Benefits of photoacoutic imaging

Answer 19

Highest resolution from all imaging techniques

Non-invasive

Non-ionising

Question 20

Do MRIs provide detail on cell resolution?

Answer 20

No

Question 21

How can we track cells in an MRI?

Answer 21

Contrast agents

Question 22

Why do we not use contrast agents that increase the signals?

Answer 22

The amount of gallidinium you would need to have a high contrast would be toxic

Use iron oxide instead, which decreases the signals

Question 23

What is russian blue?

Answer 23

Labels iron

To identify whether cells have been labelled with the contrast agent

Question 24

Why isPET not useful for cell tracking?

Answer 24

Positron emitter half-lives are too short

Question 25

What allows SPECT to be used for cell tracking?

Answer 25

Gamma emitters have a long half-life

Question 26

What is the gold standard for white blood cell imaging?

Answer 26

SPECT imaging

Question 27

Which cell labelling techniques are toxic?

Answer 27

All at high doses

Fluorescent dye
Nanoparticles
Nuclear tracers
Reporter genes