4. CD8+ T cell responses: memory and exhaustion Flashcards
1
Q
What are CD8 T cells?
A
- Cytotoxic effector cells
- They kill virally infected cells and cells with other intracellular pathogens.
2
Q
Why do we need to understand CD8 T cell differentiation?
A
- Once they are differentiated they are easy to activate
- This presents a threat to the body
- Their activation needs to be carefully controlled.
- The phenotype of CD8 changes as an infection progresses.
3
Q
How is LCMV used to detect CD8 T cell responses?
A
- LCMV Viral proteins are presented to the TCR which expands the T cell repertoire.
- Tetramers of MHC1 for these TCR can detect the new populations of T cells.
- The tetrameter stick to the cells that would be activated by that MHC1 molecules.
- We can then quantify the response to the LCMV and look at the phenotype of the CD8 cells over the course of the infection.
4
Q
What are the 2 main functions of CD8 cells?
A
- Cytotoxic killing
- Memory
5
Q
What are the 2 main types of Cd8 memory cells?
A
- Central memory cells that live in circulation.
- Tissue resident memory cells that live in the tissue the infection effected.
6
Q
How can we characterise a CD8 memory cell?
A
By what is expressed on its surface using flow cytometry.
7
Q
Phenotypic CD8 markers: Naive cells
A
Upregulation: CD62L and CD127
Downregulation: KRLG1
8
Q
Phenotypic CD8 markers: Short-lived effecter cells
A
Upregulation: KRLG1
Downregulation: CD62L and CD127
9
Q
Phenotypic CD8 markers: Effecter memory cells
A
upregulation: CD127
Downregulation: CD62L and KRLG1
10
Q
Phenotypic CD8 markers: central memory cells
A
Upregulation: CD62L and CD127
Downregulation: KRLG1
11
Q
What does CD62L do?
A
High endothelial venules access which helps lymph node circulation
12
Q
What does CD127 do?
A
It is the IL-7 receptor alpha that is involved in cell homeostasis.
13
Q
What does KLRG1 do?
A
E&N cadherin binding
14
Q
What is the process of naive cell to memory cell?
A
- The naive cell is activated and becomes a short lived effector cell.
- These cells are mostly destined to die but a small pool change their pattern of gene expression to become memory cells.
- These cells divide into 2 populations of memory cells: Tissue resident and Central.
15
Q
Why are memory cells important?
A
- they provide important protection against reinfection
- They allow vaccination to be effective.
16
Q
When is memory established during infection?
A
- After about 5 days
- Some CD8 show characteristics of pre cursor memory cells which will become memory cells.
17
Q
What are the characteristics of pre cursor CD8 memory cells?
A
CD25lo
CD62L hi
18
Q
Why are CD8 memory cells hard to study?
A
They are hard to isolate.
19
Q
What method allowed the study of CD8 memory cells?
A
Parabiosis
20
Q
What is parabiosis?
A
The anatomical and physiological union of 2 organisms. eg sewing 2 mice together
21
Q
How was parabiosis used to studying CD8 memory cells?
A
- 1 mouse was infected with LCMV and 1 was left uninfected.
- They were sewn together to form a parabiont with 1 common circulatory system.
- The memory cells found in the secondary lymphoid tissue were mixing in circulation of both mice these are central memory cells.
- When dissecting the mouse tissues, memory cells were only found in the tissues of the infected mouse. This shows there are populations of tissue-resident memory cells that stay in the tissues.
22
Q
What are CD8 central memory cells?
A
Memory cells that exist in circulation and secondary lymphoid tissue.
23
Q
What are CD8 tissue resident memory cells?
A
- Memory cells that stay in the site of infection
- They adapt to the tissue
- They almost never leave the tissue
- They prevent future infection
24
Q
What are the important characteristics of CD8 tissue resident memory cells?
A
- They adapt to local tissue
- They show epigenetic changes in chromatin accessibility to change the gene expression to adapt to the tissue.
- Mediate rapid responses to reinfection
- Express markers that overlap with those of exhaustion.
25
Transcription factors upregulated in CD8 tissue resident memory cells
1. Runx3
2. Notch
3. Hobit
4. Blimp1
5. AhR
26
Transcription factors downregulated in CD8 tissue-resident memory cells: KLF2
This is involved with movement through tissues and with circulation through the secondary lymphoid tissue so it not needed for tissue residence
27
Transcription factors downregulated in CD8 tissue resident memory cells: T-bet and Eomes
In CD4 cells these are associated with TH1 cells but they are down regulated here
28
Markers upregulated in CD8 tissue resident memory cells: CD103 and CD69
Expressed on the cell surface often together but they don't have to be.
29
Markers factors upregulated in CD8 tissue resident memory cells: CLTA4 and PD1
These inhibitory T cell signals and markers of exhaustion
30
How was different gene expression shown in tissue resident memory cells?
1. Use P14 T cells which have had forced TCR expression to LCMV.
2. Isolate the different populations and aks about their gene expression.
3. Cells found in the spleen and blood have similar gene expression
4. Cells in other tissues showed massively different patterns of gene expression depending on the tissue they were found in
5. This shows that CD8 memory cells adapt to the tissue they are in and change gene expression accordingly.
31
what causes the variation in gene expression in CD8 tissue resident memory cells?
chromatin modification
32
What is an example of CD8 tissue resident memory cells adapting to their environment?
1. Skin specific memory cells
2. A group of genes are gradually turned on as the differentiation progresses
3. 2 of these genes are Fabp4 and Fabp5, transporter proteins that aid fatty acid entry into the mitochondria.
4. Compare to central memory cells the skin memory cells had a much higher oxygen consumption rate and therefore respiration rate when using fatty acids as the source of carbon.
5. This shows the skin memory cells have adapted to the lack of glucose at the skin and given themselves a survival advantage to help protect the body from infection.
33
Why is LCMV a useful tool for studying immune response?
It is a group of different virus strains that all induce different immune responses.
34
Why is LCMV good for studying exhaustion?
Exhausted T cells often present with LCMV infection
35
How were exhausted T cell first desrcibed?
The T cells had run out of energy and stopped being effective.
36
What do exhausted T cells unregulate?
coinhibitory molecules and exhaustion markers
37
Phenotypic markers in exhausted CD8 cells: Antigen experienced cells
Upregulation: TCF1
Downregulation: PD1, LAG3 and TOX
38
Phenotypic markers in exhausted CD8 cells: Early dysfunction cells
Upregulation: PD1, LAG3, TCF1 and TOX
downregulation: TIM3 CD38 and CD39
39
Phenotypic markers in exhausted CD8 cells: LAte dysfunction cells
Upregulation: PD1, LAG3, TIM3, CD38, CD39 and TOX
Downregulation: TCF1
40
Transcription factors involved in exhaustion
TCF1 and TOX
41
Coinhibitory markers involved in exhaustion
PD1, LAG3 and TIM3
42
Enzymes involved in exhaustion
CD38 and CD39
43
How can coinhibitory receptors be used in cancer therapy?
1. A tumour drives T cell exhaustion so it can escape immunity
2. If we target coinhibitory receptors we can override T cell exhaustion and release the immune system in responsive patients
3. This increases survival of cancer patients
44
CD8 cells in autimmunity
This is an underrepresented area of research but still important
45
CD8 cells in autoimmune uveitis
1. As the disease progresses there is expansion of CD8 cells
2. The CD8 cells express coinhibitory receptors and other exhaustion markers like PD1, CD44 and CD69.
46
What are NOD mice?
Non obese diabetic mice. They are used to study autoimmune diabetes.
47
What is TCF1?
A transcription factor that controls the expression of TCF7 in the Wnt pathway
48
How were CD8 exhaustion phenotypes studied in diabetes in NOD mice?
1. Tetramer MHC with specific peptides for pancreatic autoantigen TCRs.
2. Pancreatic lymph nodes (pLN) had high amounts of tetramer-positive cells.
3. The tetramer positive T cells recognise an autoantigen and destroy ß cells.
4. These T cells also expressed exhaustion markers like CD44 and PD1
5. These T cells expressed the transcription factors TOX and TCF1.
49
What is TOX?
A transcription factor thought to drive exhaustion
50
How does TCF1 expression vary in different NOD T cell populations?
1. In non activated cells TCF1 expression is high. This is the control.
2. In T cells from the pancreas TCF1 expression is low.
3. In T cells from the pLN there is a bi-morphic expression where some t cells have high TCF1 expression and others have low.
4. These populations of T cells have different gene expression.
51
What is the population of autoreactive T cells like in the pLN of NOD mice?
1. There are TCF1hi and TCF1lo populations but much higher levels of TCF1hi.
2. This is a diverse pool of memory cells.
3. Most of the T cells in the pancreas originated from the lymph node.
4. The TCF1hi population can be selected and expanded when they come into contact with the antigen.
52
What do the NOD mice experiments tell us about autoimmune CD8 memory cells?
1. There are 2 pools of autoreactive memory cells.
2. A precursor pool and an effector pool
53
What are the properties of a precursor autoimmune CD8 memory cell?
1. Lives in the lymph node
2. can self renew like stem cells
3. has high TCF1 gene expression
4. Can reliably transfer diabetes during experiments
54
What are the properties of an effector autoimmune CD8 memory cell?
1. Short lived
2. Does the damage in the tissue
55
How are the autoimmune CD8 memory cells stem cell like?
1. They live in a niche
2. they self renew
3. They provide an endless supply of effector cells
4. They retain the property of destructiveness
