Identifying the underlying mechanisms and consequences of the loss of nasal T cells in vital and frail older individuals

Individuals with advanced age are at a progressively increasing risk of
acquiring lower respiratory tract infections. Over the coming decades, as the
population ages, the incidence of respiratory infections and community-acquired
pneumonia is expected to substantially increase. The current outbreak of
SARS-CoV-2 demonstrates the global urgency of understanding the effect of age
on local mucosal immunity given the increased susceptibility of the elderly.
With advanced age, increased inflammation (*inflammaging*), immunosenescence
and reduced naïve and expanded memory lymphocyte pools have been described in
peripheral blood. In addition to calendar age, the degree of frailty also is
important for susceptibility to severe infections as this associates with
increased risk of hospital admission in elderly with community-acquired
pneumonia. Frailty has been shown to also be associated with alterations in the
immune system in peripheral blood, although this association and its role in
the susceptibility to infections remains poorly characterized. While many
studies have investigated how the immune system changes with age, most of these
have been conducted in peripheral blood, which poorly reflects the immune
system at mucosal surfaces. Indeed, whether and how alterations in the mucosal
immune system with age predispose to infections in the very old remains unclear
as access to relevant tissue samples is limited. Increased understanding of
local immunity could thus be critical in the development of new vaccines
against respiratory pathogens. Recent developments in minimally-invasive nasal
sampling techniques now allow us to address this knowledge gap. Recently, we
already observed that in healthy older adults, both CD4+ T cells and CD8+ T
cells are selectively lost from the nasal mucosa.

However, the exact phenotype, underlying mechanisms, key molecules and
consequences of this have not yet been investigated. We also do not currently
know whether specific mucosal T cell populations are associated with the
increased susceptibility to infection seen in advanced age. Nor do we know
whether these reduced T cells indicate a limited ability of older adults to
mount robust mucosal T cell responses. Addressing these knowledge gaps could be
beneficial to develop vaccines or interventions that increase mucosal
resident-memory T cells, which are crucial for protection against respiratory
viral infections. For example, if reduced migration to the nose underlies this
paucity, it is conceivable to add chemo-attractants to nasal vaccines that lead
to an increased efflux of T cells at time of vaccination. Alternatively, if
increased apoptosis is present in the nasal mucosa of older adults, because of
limited availability of specific metabolites or tissue factors, prophylactic
local administration could sustain good mucosal immunity.

Primary Objective:
To compare nasal CD8+ T cell frequency between young adults and frail older
adults.

Secondary Objective(s):
1. In depth profiling of T cells in nose and blood of young adults and older
adults with and without frailty.
2. Assess the stability of T cell populations and other immune populations over
time.
3. Compare blood and nasal T cells between older adults with and without
recurrent respiratory tract infections.
4. Compare other nasal and systemic immune populations and parameters between
young adults, vital older adults and frail older adults (with or without
recurrent infections).
5. Associate nasal and systemic factors (e.g. cytokines and metabolites) and
with T cells.
6. Associate respiratory tract microbiota with T cells and other immune
parameters.
7. Associate covariates, such as biological age, HLA type and sex with T cells
and other immune parameters.
8. Assess the impact of acute respiratory tract infection on (antigen-specific)
T cell populations and other immune parameters in nose and blood.
eters in nose and blood.

This is a prospective follow-up study.

Four patient groups (healthy young adults, vital older adults, older adults
with frailty without recurring respiratory tract infections and older adults
with frailty with recurring respiratory tract infections) will be included and
provide samples of nose and blood immunology (see figure 1). This will allow
for immunological cross-sectional comparisons. Up to 30 participants per group
will be asked to return after 2-4 months to provide the same set of samples to
be able to analyze stability of T cells.

Participants will be asked to contact the study team if they experience
symptoms of respiratory tract infection, such as a sore throat or runny nose,
OR fever, OR test positive for SARS-CoV-2, within the 3 months from start of
study. For these participants we will collect additional samples to identify
aetiological agents and perform immunological analysis at that time (within 7
days of onset). If a causative agent (Viral: RSV / influenza A or B, Human
Rhinovirus, Metapneumovirus, Parainfluenza virus 1-4, SARS-CoV-2, Human
Coronavirus 229E, NL63, HKU1, OC43, Bocavirus, Adenovirus and/or bacterial,
e.g. Staphylococcus aureus / Streptococcus pneumoniae, H. influenzae) is
identified they will be asked to return 3 more times to provide samples to
longitudinally monitor immunity.

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Healthy young adults and older adults will be recruited from LUMC*s vaccination
clinic. (Frail) elderly will be recruited from the geriatric outpatient clinic,
emergency department and acute admittance ward in the LUMC. Participants who
provide informed consent to participate in the study and meet all of the
inclusion criteria and none of the exclusion criteria are included in the study.

Participants will be asked to provide samples as indicated in figure 1. If they
are unable to come to LUMC for the visit, a member of the study team will
perform a home visit.

For participants who develop symptoms the maximum study duration is 8 months
(symptom at any point in first 3 months and then 5 months follow-up), for other
participants, the study duration is either single timepoint or 2-4 months.

The following samples will be collected: 80mL of peripheral blood, nasal
curettage, nasosorption, nasopharyngeal and oropharyngeal swab. Also a
questionnaire will be taken to collect relevant information. A subset of people
(up to 30/group) that do not develop symptoms during the study will be asked to
come back after 2-4 months to compare the stability of T cells over time.. If
people develop symptoms congruent with respiratory infection they will be asked
to contact the study team and give samples to identify the causative agent and
study nasal and systemic responses. If a common respiratory tract viral or
bacterial pathogen is identified as causative, blood and nasal samples will be
collected 3 more times at 1, 3 and 5 months. There are no direct benefits to
taking part, but this study can provide information that ultimately could lead
to improved vaccination or prophylaxis in the elderly against respiratory tract
infections. Risks associated with the study are minimal.