Turnover of Antigen Specific Lymphocytes After Immunization With the 17D Yellow Fever Vaccine

In general, T cell responses to viral infections occur in three distinct stages: expansion,
contraction and memory. During expansion, antigen-specific CD8+ T cells proliferate to
increase in numbers as well as acquire the ability to kill virus infected cells i.e become
'effectors'. Once the virus is cleared, 90-95% of the effectors die. The small pool of
remaining cells differentiates gradually to become memory cells and provide life-long
protection. The rate of cell division is distinct in the generation of effectors and memory
cell maintenance. These concepts have been primarily derived from mouse studies. Human CD8+ T
cell turnover is not completely understood because of the lack of appropriate tools and
techniques suitable for human studies.

In this protocol, we want to understand the lifespan and decay curve of effector CD8+ T cells
and the rate of homeostatic turnover of memory CD8+ (CD28+/- subsets) T cells after 17D YFV
immunization using an innovative method developed by Dr. Marc Hellerstein's group (at the
University of California, Berkeley) for measuring DNA replication and cell proliferation in
humans using a naturally occurring stable isotope called deuterium (2H). This technique has
been used to track the turnover of a number of human cell types in vivo. We plan to use 2H
labeling to track YFV specific CD8+ T cells in human vaccinees (HLA-A2 positive participants
only). The availability of a T cell epitope (A2-NS4B214), a major component of the human YFV
specific CD8+ T cell response, allows for the longitudinal analysis of virus specific CD8+ T
cells. The unique feature of this study is that it allows for tracking of differentiation of
YFV specific CD8+ T cells in humans. Thus, we can overcome the inherent limitations due to
heterogeneity in cross-sectional studies that involve bulk CD8+ T cells.

We plan to enroll 50 healthy, adult volunteers (18-45 of age) for Projects 1 and 2 to study
memory CD8 T cell responses. All subjects will receive the FDA approved YFV-17D vaccine (at
the FDA approved dose and route of administration). CD28 expression will be determined to see
if it is coupled to the generation and/or maintenance of YFV-specific memory CD8 T cells.
Phenotypic differences between CD28+ and CD28-_YFV-specific CD8 T cells will be studied to
determine differences in longevity. Gene expression profiles of CD28+ and CD28 YFV-specific
CD8 T cells will be determined. The influence of IL-7 and IL-15 on survival of YFV-specific
CD8 T cells will be studied. This information will be gained from YFV specific cells isolated
at Day 0, 14, 28 and 3 to 6 months, 1-2 years and >5 years after vaccination.

The study will be conducted at the Hope Clinic of Emory Vaccine Center. Individuals who are
planning to travel to yellow fever endemic areas and who require the vaccine for travel
purposes as well as non-travelers will be recruited into the study. Potential participants
may be recruited from the Emory Travel Well Clinic or the CDC employee health or the Emory
University campus or the general population of metro Atlanta using radio and print
advertisements, electronic mailings, Internet postings, flyers, and posters. IRB approval
from Emory University will be obtained prior to the initiation of the study.

There will be a screening visit to determine the eligibility for the study. Signed informed
consent forms will be obtained prior to the initiation of study procedures. The inclusion and
exclusion criteria and a brief history and physical examination will be performed. In
addition, participants will be asked to undergo phlebotomy to determine the HLA type.
Participants who are positive for the HLA A202 allele, will be asked to participate in this
study. It is estimated that 25% of the Caucasian US population will be positive for this
allele. Participants who test negative for this allele will be offered other vaccine trials
that are being conducted at the Emory Hope clinic and their participation in this protocol
will end.

Prior to the administration of the yellow fever vaccine, the risk-benefit ratio of the
vaccine-related adverse events versus the risk of contracting yellow fever is determined.
Healthy individuals who have not been previously vaccinated with YFV vaccine will be included
in the study. Both female and male volunteers will be recruited.

We plan to enroll 50 healthy volunteers between 18 to 45 years of age. In order to meet these
enrollment goals, we may need to screen 200 subjects. All subjects will receive the FDA
approved YFV-17D vaccine (at the FDA approved dose and route of administration) once on day 0
of the study visit. Blood specimens will be obtained from the volunteers on Day 0, and on
scheduled time points post-vaccination. The total volume of blood drawn will not exceed the
Red Cross limit of 473mls in 56 days.

The study volunteers will be maintained on a 100ml - 150ml daily intake of 2H2O, with a goal
of maintaining 1.5-2% body water enrichment (assuming total body water turnover of ~3.5
liters per day in healthy, ambulatory subjects). Plasma and saliva samples will be obtained
during the 2H2O administration protocol for measurement of body 2H2O enrichment.

Inclusion Criteria:

1. Able to understand and give informed consent

2. Age 18-45 years

3. Participants agree not to take any live vaccines 30 days before or after (14 days for
inactivated) yellow fever vaccination

4. Women of child bearing potential must agree to use effective birth control for at
least 2 months after yellow fever vaccination. A negative urine pregnancy test must be
documented prior to vaccination and prior to the initiation of drinking deuterium
labeled water.

5. Must be positive for the HLA A202 allele

6. Must agree not to receive any other vaccination during the labeling period with heavy
water and in the first 28 days after receipt of yellow fever vaccination.

Exclusion Criteria:

1. Travel to or having lived in a country/area which is endemic for yellow fever

2. History of previous yellow fever, West Nile, Dengue, St. Louis encephalitis, Japanese
encephalitis vaccination or infection

3. Any history of allergy to eggs, chicken or gelatin or to any previous vaccine

4. A history of a medical condition resulting in impaired immunity (such as HIV
infection, cancer, particularly leukemia, lymphoma, use of immunosuppressive or
antineoplastic drugs or X-ray treatment). Persons with previous skin cancers or cured
non-lymphatic tumors are not excluded from the study.

5. History of HIV infection, Hepatitis B or Hepatitis C infection

6. History of any chronic medical conditions that are considered progressive (ex,
diabetes, heart disease, lung disease, liver disease, kidney disease, gastrointestinal
diseases and uncontrolled hypertension). Use of systemic immunosuppressive medications
(ex, prednisone) for 2 weeks or more in the past 3 months

7. History of excessive alcohol consumption, drug abuse, psychiatric conditions, social
conditions or occupational conditions that in the opinion of the investigator would
preclude compliance with the trial

8. Thymus gland problems (such as myasthenia gravis, DiGeorge syndrome, thymoma) or
removal of thymus gland or history of autoimmune disorder.

9. Recipient of a blood products or immune globulin product within 42 days of the
vaccination visit

10. Pregnant women and nursing mothers or women who are planning to become pregnant within
2 months after receiving the yellow fever vaccination.

11. Any condition in the opinion of the investigator that would interfere with the proper
conduct of the trial