hiv induced aging of the immune system dr. tammy rickabaugh february 4, 2013

HIV Induced Aging of the Immune System

Dr. Tammy Rickabaugh

February 4, 2013

Overview

I. Immunological Aging in Seronegative Individuals

II. Premature Aging of the Immune System in HIV-1+ Individuals: Is this the cause of AIDS?

III. Implications of Premature Immunological Aging of HIV-1+ Individuals

Immunological Aging in Seronegative Individuals

Kovaiou, Grubeck-Loebenstien, 2006

General Concepts of Aging

Age-Associated Changes in the Immune System

• Elderly people are more susceptible to infections• Less protected by vaccines• Infections in the elderly are characterized by

more severe symptoms, longer duration, and poorer prognosis

• Reactivation of Varicella-Zoster, risks for pneumonia, urinary tract infections, meningitis, TB and viral gastroenteritis

• Related to age-related changes in the immune system

Jamieson, BD, et al, Immunity, 1999

Adult ThymusFetal Thymus

The Human Thymus Involutes With Age

• Significant decrease in naïve T cell number and increase in memory T cells

-hinders ability to respond to new infections

• Diversity of the naïve CD4+ T cell compartment is maintained until about 70 years of age

-a dramatic and sudden collapse of diversity occurs

-less diversity in T cell receptor, hinders ability to respond to new antigens

Age-Associated Changes in CD4+ T Cells

• Using cell surface markers normally used to identify naïve T cells is difficult

- “naïve” cells in the elderly express receptors and functional abilities more like memory cells

• Signaling and cytokine secretion in naïve CD4+ T cells is altered and the activation potential of memory cells is also decreased

-hinders ability to mount effective immune responses to antigens

Age-Associated Changes in CD4+ T Cells


Model for CD4+ T Cell Differentiation During Healthy Aging


Summary of Age-Related Changes Within the CD4+ T Cells

Summary of Age-related Changes Within the CD8+ T Cells

• Increase in terminally differentiated cells• Decrease in naïve CD8+ T cells• See an increase in Type 1 (IL-2, IFN-g,TNF-a) and

Type 2 (IL-4, IL-6, IL-10) cells- associated with chronic pro-inflammatory status

• Increase in clonal expansions• Decrease in T cell receptor diversity• Shortening of telomere length

What are the implications of increased numbers of senescent T-cells???

Why Do Senescent Cells Accumulate With Age?

• One main reason is an age-related decrease in apoptosis

• Apoptosis is necessary to create “immunological space” for naïve cells to inhabit

• This is more prominent in CD8+ T-cells• Senescent cells are not susceptible to

normal death signals

Mountz, JD, et al. Immunological Reviews, 2005

T-cells Become Resistant to Activation-Induced Cell Death (AICD)

-Happens at a stage prior to complete senescence-AICD is a mechanism to prevent the expansion of unwanted T-cells

Increase in Senescent Cells Occupying “Immunological Space” Results in a Decrease

in the Virus-Specific CTL Response

Mountz, JD, et al. Immunological Reviews, 2005

-This can also contribute to “inflammaging”

Consequences of “Inflammaging”

• In aging there is a profound modification in the cytokine network

• General increase in the levels of pro-inflammatory cytokines

• Chronic low grade pro-inflammatory condition is called “inflammaging”

Inflammaging can trigger the following conditions:

Franceschi, C., et al., Neuroimmunomodulation, 2008

Some of our data…….

The Proportion of Naïve T-cells Decreases Only Moderately Throughout Adulthood

PERCENT OF CELLS EXPRESSING CD45RA DECREASES SLIGHTLY WITH AGE

PARTICIPANT AGE

25 35 45 5520 30 40 50 60

% O

F C

D4

+ T

-CE

LL

S E

XP

RE

SS

ING

CD

45

RA

10

30

50

70

90

0

20

40

60

80

100

% o

f C

D4+

T-c

ells

Exp

ress

ing

CD

45R

A

Participant Age

100

90

80

70

60

50

40

30

20

10

020 25 30 35 40 45 50 55 60

CD4+ CD45RA+

8% 48%

14%CD

31

CD45RA

Four CD4+ T-cell Subsets Defined by CD45RA and CD31

Naive

RA+31+

RA+31-

TREC High

TREC Low

Least Differentiated

Differentiated

Maintenance of Naïve CD4+ T-cells During Aging Is Due To Stability of CD45RA+CD31- Subset

p=0.38

Participant Age (Years)

20 30 40 50 60

60

40

50

30

20

10

0

60

50

40

30

20

10

0

20 30 40 50 60

Cross Sectional Study

31+

31-

Kilpatrick, R, Rickabaugh, T, et. al, J. Immunology, 2008

Participant Age (Years)

% C

D45

RA

+C

D31

- ce

lls

% C

D45

RA

+C

D31

+ c

ells

Telomeres• Hallmark of cellular aging• Region of repetitive DNA at the ends of

chromosomes• Protects the end of chromosome from damage

-similar to tips on shoelaces that keep it from unraveling-shortens with each replication of the cell

• Telomere shortening in humans can result in senescence (cells lose the ability to divide) and block cell division

• Cells have a limited capacity to replicate and this appears to be partly determined by telomere length

Telomeres

Human chromosome is gray and telomeres are the white dots

Kilpatrick, R, Rickabaugh, T, et. al, J. Immunology, 2008

Evidence of Telomere Shortening in Naïve CD4+ T cells with Age

HomeostaticProliferation

CD45RA+CD31+ CD45RA+CD31-

Antigen

CD45RA-

Memory

Model of CD4+ T-cell Differentiation

DifferentiatedNaive

Least DifferentiatedNaïve

• We observe telomere shortening in both subsets with age

WITH AGE

Thymus

Premature Aging of the Immune System in HIV-1+ Individuals:Is This the Cause of AIDS?

Some Causes of Clinical Immunodeficiency

• Not completely clear why the immune system initially controls HIV-1 infection and then ultimately fails to control viral replication

– Viral escape with mutations in epitopes recognized by cytotoxic T lymphocytes (CTLs)

– Functional impairment of HIV-specific CTLs

– High levels of immune activation

HIV-specific CD8+ T cell response: Impaired or Fully Functional?

• In primary HIV-1 infection there is a rapid expansion of HIV-specific effector CD8+ T cells-phenotypically the cells appear to be at an intermediate stage of differentiation-but they are fully functional

• Why is the virus not cleared??-the combination of CD4+ T cell depletion and immune escape may lead to an inability of the CD8+ T cells to respond to low levels of viral replication (around the set point)

- fully functional but unable to mount an effective response

HIV-1 Strategies to Evade Host Immunity

Appay, V and Rowland-Jones, SL, Trends in Immunology, 2002


The Adaptive Immune System in Aging and HIV-1 Infection

Parallels Between HIV-1 Pathogenesis and Human Aging

• Lifespan of both CD4+ and CD8+ T cells is shortened to about a third of normal

-increase of CD8+ T cells but CD4+ cannot keep up with the pace of destruction

• Increase in the amount of terminally differentiated T cells- consequence of immune activation

-leads to immunosenescence, also occurs with CMV

-get an accumulation of immune cells that cannot function or replicate normally, but are more resistant to apoptosis

• AIDS is much more severe immune senescence than what is seen in normal aging


Post-Thymic Development of CD8+ and CD4+ T cells

Appay, V, et al. Experimental Gerontology, 2007

Accumulation of Terminally Differentiated T cells in HIV infection

Exhaustion of Immune Resources by HIV-1 Leads to AIDS

• Chronic Immune Activation:-In primary infection there is massive immune activation-In chronic infection still have chronic immune activation due to viral rebounds-Indirect immune activation as depletion of CD4+ T cells results in more common infections and opportunistic infections

• This can result in premature aging of the immune system and exhaustion of immune resources

Appay, V, et al. Experimental Gerontology, 2007

Exhaustion of HIV-specific CD8+ T cell Clonal Populations

Some of our own data regarding naïve CD4+ T cells…….

Individuals Early in HIV Infection Have Significantly Fewer Naïve CD4+ T-cells

Rickabaugh, TM, et al., PLoS ONE 2011

HIV Infection Results in a Greater Loss of

CD31- T-cells


Naïve CD4+ T-cells of HIV Infected Men Have Shorter Telomere Lengths


CD

31 M

FI

0

1000

2000

3000

4000

5000

Progressed to AIDS within 1 year

Progressed to AIDS within > 5 years

* p=0.038

CD31 Expression on CD4+ T-cells is Associated with Progression to AIDS

Cao, WW et al., J Acquir Immune Defic Syndr 2008

What is the Effect of HAART on Naïve CD4+ T-cells?

Reconstitution by HAART Does Not Completely Restore the CD31- Naïve T-

Cell Compartment

Rickabaugh, TM, et al., PLoS ONE, 2011

CD31+/Hi T-cells Increase Significantly Post-HAART

Rickabaugh, TM, et al., PLoS ONE, 2011

Reconstitution of CD31+ T-cells appears to be better with more time on ART

050

10

015

020

0

20 30 40 50 60 70

Age at time of analysis

Seronegative

4-8 years

12-16 years

CD45RA+CD28+CD31+CD4+

Ab

solu

te C

ell C

ou

nts

Time on ART does not appear to increase CD31- naïve CD4+ T-cells

20

40

60

80

10

012

0

20 30 40 50 60 70

Seronegative

4-8 years

12-16 years

CD45RA+CD28+CD31-CD4+

Age at time of analysis

Ab

solu

te C

ell C

ou

nts

HomeostaticProliferation

CD45RA+CD31+ CD45RA+CD31-

Antigen

CD45RA-

Memory

Model of CD4+ T-cell Differentiation

DifferentiatedNaive

Least DifferentiatedNaïve

• We observe telomere shortening in both subsets with age and HIV

AGE HIVHIV AGE

Thymus


HIV-1 Infection Compared to Human Aging

Implications of Premature Immunological Aging of HIV-1+

Individuals

Deeks, SG, and Phillips, AN, BMJ, 2009

Evidence of Premature Aging Despite

Anti-Retroviral Treatment

Age-Related Diseases Diagnosed in HIV+ Individuals

• Cardiovascular Disease

-higher in untreated versus treated

-link between lower CD4+ T cells and CD

-some anti-retroviral drugs are associated with CD

• Cancer- Untreated HIV is associated with Kaposi’s Sarcoma and non-Hodgkin’s lymphoma- Even treated HIV individuals at increased risk

for lung cancer, skin cancer, colorectal cancer, prostate cancer, anal cancer- Higher risk is associated with less CD4+ T cells, similar to immune compromised transplant patients



Older HIV+ individuals are at even greater risk due to normal immunological aging coupled with aging caused by HIV-1 infection

Another problem….HIV infected people are getting older

CDC estimates that by 2015 over 50% of all HIV infected people will be over the age of 50 in the US

Two reasons for this:

• Higher percentage of new infections in people over 50

• Individuals with HIV infection are living longer on drug treatment

We also see an increase in new AIDS cases in >50 year olds

The Search for the Immunological Fountain of Youth

Possible Therapies to Improve Naïve T-cell Numbers and Function

• The first treatment in HIV patients was IL-2

-some evidence of efficacy

-results of the trials were not consistent and there are concerns with toxicity

• Human growth hormone (HGH) and Insulin Growth Factor-1 (IGF1)

- increased thymic volume in children with AIDS but did not affect T-cell function significantly

• IL-7 is a very promising treatment-cytokine that plays a key role in the thymus in lymphocyte development and survival-in the periphery it is important for T-cell homeostasis and is required for homeostatic proliferation of CD4+ and CD8+ T-cells

• When used in cancer patients it preferentially expanded naïve T-cells

• In a phase I/IIa clinical trial in HIV+ patients it was shown to increase naïve and central memory CD4+ and CD8+ T-cells

• The T-cells are functional and the patients had improved cell mediated immunity

• There also seem to be very little side effects

Possible Therapies to Improve Naïve T-cell Numbers and Function

What About Telomere Length??

• A screen of Chinese medicine plant extracts for telomerase inducing agents resulted in the discovery of TAT2

• TAT2 has been shown to transiently increase telomerase levels in vitro in cells from HIV-, HIV+, and individuals with AIDS (highest amounts)

• This increase was associated with longer telomere lengths, improved immune effector function, and increased ability for cellular proliferation

• In vitro it has also been shown to reduce viral load and this is correlated to telomerase induction

TAT2 Can Improve Cellular Proliferation and Telomere Length

Fauce, SR, et al., J Immunol, 2008

Summary• Immune resources decline with age leading to a

reduced ability to respond to new and old antigens• HIV-1 infection appears to prematurely age both

CD8+ and CD4+ T cells - this leads to immune exhaustion and senescence- may be a significant factor in the development of AIDS

• HIV-1+individuals, treated or untreated, are at a higher risk for non-AIDS related diseases seen in much older individuals

• There are some promising therapeutics but more work must be done to develop safe, effective, therapies to improve immune function

hiv induced aging of the immune system dr. tammy rickabaugh february 4, 2013

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