Immunosenescence And AntiImunosenescence Strategies

1
Immunosenescence And Anti-Imunosenescence
Strategies

• Arne N. Akbar
• UCL Immunity Consortium

2
Old Individuals Are Susceptible To Infection

• Increased incidence of many infections including
• 1) Pneumonia
• 2) Urinary tract infections
• 3) Gastroenteritis
• 4) Influenza (severe complications and severity)
• 5) Tuberculosis re-activation
• 6) Shingles (adult chickenpox)
• 7) EBV reactivation (lymphoma)

3
We Now Live Twice As Long As We Did 150 Years Ago
90
80
70
60
50
Life expectancy (years)
40
30
20
10
0
1200
1300
1400
1500
1600
1900
1700
2000
1800
Year (AD)
Akbar A et. al. (2004) Nature Reviews
Immunology
4
Lymphocytes Cannot Proliferate Forever

• Proliferating cells - a finite number of cell
  divisions (Hayflick Limit)
• Telomere erosion a functional definition of
  end-stage differentiation
• Defective immunity during ageing - due in part to
  terminal differentiation of lymphocytes ?

5
What Are Telomeres?
Telomere (DNA Protein)

• Protect coding-DNA from degradation and confer
  stability to the chromosome
• Loss of telomeres beyond a critical point leads
  to growth arrest
• Telomerase Reverse transcriptase that
  synthesises telomeric repeats

6
Association between telomere length in blood and
mortality in people aged 60 years or older
Cawthorn RM et al (2003) The Lancet 361 393-395
Subjects with shorter telomeres have greater
mortality due to -3.18 fold higher fatal heart
disease -8.54 fold higher mortality rate from
infectious disease
Will telomere erosion lead to a loss of T cell
memory?
Akbar A et. al. (2004) Nature Reviews
Immunology
7
Flow FISH - Standard Curve
200
2
r
0.75
MFI
Telomere Length (kb)
8
Human T Cell Differentiation
CD8 T Cells
CD27
CD28
CD4 T cells
CD27
CD28
9
Is Telomere Erosion a Constraint on Human
Virus-Specific T Cells During Chronic Infection?

• Models for human in vivo progressive T cell
  differentiation are required
• Ageing healthy individuals (75 years)
• X-linked lymphoproliferative syndrome A model
  for accelerated human ageing in T cells
• Dyskeratosis congenita, dyskerin defect, no
  telomerase

10
Expression of CD28 and CD27 on CD8 T cells
Young
Old
XLP
DKC
31
60
1
8
CD27
CD28
11
Restricted Capacity For Expansion In CD8 T Cells
In Old Individuals
CD8
EBV lytic
EBV latent
45
45
45
40
40
40
35
35
young
young
35
young
30
30
30
25
25
Population Doublings
Population Doublings
25
Population Doublings
20
20
XLP
20


XLP

15
15


15
old
old
old
10
10
10
5
5
5
0
0
0
160
160
160
Days
Days
12
Telomerase Activity In Human T Cells

• Resting T cells no telomerase activity
• After activation- telomerase peaks at 5 days then
  returns to baseline
• Peak and duration of telomerase activity
  decreases after repeated T cell activation
• Telomerase regulation during T cell
  differentiation?

Telomerase activity
13
Telomerase Induction After Repeated
Re-Stimulation Of CD8 T Cells
Peak Telomerase Activity
1
2
3
4
5
Stimulation
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The Effect Of hTERT Transduction On Replicative
Capacity
45
35
30
25
15
5
0
0
50
100
150
CD8 Telomere (MFI)
Fresh
Clone 1
Clone 2
Clone 3
15
The Lasker Prize 2006
For the discovery of telomerase
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Telomere Regulation In T Lymphocytes

• Telomere erosion results from chronic stimulation
  during ageing
• Due to telomerase downregulation
• Leads to loss of proliferative capacity during
  ageing
• How is telomerase regulated in T cells?
• Does telomere erosion lead to loss of immunity?

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Telomerase Activity Of Different CD8 T Cell
Subsets
CD8 T Cells
25
CD28CD27
CD28-CD27-
CD28-CD27
CD28CD27-
20
15
Telomerase activity
10
5
0
CD27CD28
CD27-CD28
CD27-CD28-
18
Mechanism For Defective Telomerase induction

• Decreased hTERT translation ?
• Post-translational modification (phosphorylation)
  ?
• Signalling pathway is required for telomerase
  activation ?
• Reversible ?

19
JAK1
PI3K
STAT pathway
Telomere maintenance
20
Expression of hTERT 48hrs following activation
Plunkett et al J. Immunol 2007
21
Defective Akt Phosphorylation In CD28-CD27- CD8
T Cells
22
Telomerase Downregulation During Memory CD8 T
Cell Differentiation

• CD8CD27-CD28- T cells are highly differentiated
  but not functionally exhausted
• Decreased hTERT and Akt phosphorylation
• Loss of telomerase activity in CD8CD27-CD28- T
  cells heralds proliferative end-stage of CD8 T
  cells
• Reversible?

23
How Does Replicative Senescence In a T Cell
Population Manifest Itself?

• Which Memory T Cells Are Closest To Senescence?

24
Relatively High Frequency Of CMV-Specific CD4 T
Cells in vivo
YOUNG
OLD
15
CD4 T cells
10
g
5
IFN
0
CMV
PPD
VZV
EBV
HSV
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Chronic Herpesvirus Re-activation Occurs In
Ageing
Stowe RP, Kozlova EV, Yetman DL, Walling DM,
Goodwin JS and Glaser R Experimental
Gerontology (2007), 42563-570
Old subjects vs young 1) Significantly greater
EBV and CMV antiviral antibody titres 2)
Significantly higher frequency of EBV and
CMV-specific CD8 T cells 3) EBV DNA copies in
plasma in old but not young (plt 0.001) 4) No CMV
in PBMC 5) However, CMV in urine of old but not
young (plt 0.001)
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CMV-Specific T Cells Have Short Telomeres
150
125
Relative telomere length
100
75
YOUNG
50
CMV
PPD
VZV
SEB
CD4
plt0.05
150
125
100
Relative telomere length
75
OLD
50
PPD
VZV
SEB
CD4
CMV
plt0.05
Fletcher et al J.Immunol 2005
27
Is there loss of anti-CMV immunity during ageing
? NO
Is there evidence that CMV infection is
detrimental during ageing? YES
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The Immune Risk Phenotype

• Significantly increased mortality in individuals
  over 80 years
• Reversed CD4/CD8 ratio
• Expansions of highly differentiated circulating
  CD8 T cells with reduced function
• High levels of pro-inflammatory cytokines (IL-6)
• Seropositivity for cytomegalovirus

Olsson J. et al Mech Ageing Dev 2000
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Ag
Ag
Ag
Expansion of activated cells
Expansion of activated cells
Expansion of activated cells
Replicative senescence
CMV specific T cells Decreasing efficiency
Ag
CMV
Contraction of other specificities
Large accumulation of less efficient
Ag-specific T cells
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Conclusion

• Telomere erosion drives exhaustion of the most
  efficient cells
• More inefficient cells required for protection
• Manifested as accumulations of cells that have
  decreased efficiency
• CMV infection drives exhaustion, accumulation of
  less functional cells and susceptibility to other
  infections/malignancy?

31
How Can We Treat Immunosenescence ?

• Thymic rejuvenation?
• Vaccination against CMV (when ?)
• Anti-CMV-drugs e.g. Valacyclovir
• Remove expanded clones of cells ?
• Diet ?
• Impact for vaccination against other infections ?

32
Acknowledgements

• UCL
• Fiona Plunkett
• Ornella Franzese
• Milica Vukmanovic-Stejic
• Jean Fletcher
• Jo Masters
• Diana Wallace
• Sian Henson
• Sarah Jackson
• Maria Soares
• Padraic Dunne
• David Webster
• Malcolm Rustin
• Arne Akbar

Jenner Institute Peter Beverley
Oxford Paul Klenerman

• Birmingham
• Mike Salmon
• Janet Lord
• Alan Rickinson

Institute Of Child Health Bobby
Gaspar Kimberley Gilmour
Imperial College Indejeet Dokal
UCB Celltech Helene Finney Alastair Lawson
Funded By BBSRC Research Into Ageing