DEfective HUman SAlivary gland stem cells: the cause of Primary Sjögren*s syndrome?
-DEHUSAPS study-

Salivary glands (SGs) of patients with primary Sjögren*s Syndrome (pSS) harbor
lymphocytic infiltrations, and demonstrate gradual and permanent deterioration
in saliva production. Although extensively studied, no definitive cause of pSS
pathology has been reported. However, available evidence indicates that the
glandular epithelium plays an important role in the process. These cells are
targeted by the autoinflammation processes and also demonstrate immunological
functions. Possibly, intrinsic defects of the gland-specific parenchyma
contributes significantly to pSS development. This project will address this
issue.

To assess whether salivary gland stem cell (SGCS) defects are key to salivary
gland pathogenesis in pSS.

1) Establish the differentiation/proliferation/apoptosis tendencies of salivary
gland stem cells in pSS. This will be achieved using parotid gland biopsies
from patients grouped in 4 categories: 1) *healthy control patients* (=n=20);
2) non-pSS sicca patients (n=20); 3) incomplete pSS patients, i.e. patients
that do not full fill all the criteria for pSS (yet; n=20), and 4) pSS patients
(n=20). Parotid biopsies will be obtained during the diagnostic work-up for pSS
(patients may qualify as non-pSS sicca, incomplete pSS or pSS). Parotid
biopsies from *healthy* subjects will be obtained from patients subjective to
an elective neck dissection as part the treatment for head and neck cancer
(parotid salivary gland not affected by the underlying disease).
2) Elucidate mediators of SGSC defects in pSS using transcriptome and proteome
screens. Total RNA will be extracted from both salisphere cultures (SGSCs), and
organoids (mini SGs) from patients and RNA sequencing (RNASeq) performed
comparatively between each category.
3) Validate putative mediators of pSS using pSS tissue and saliva samples. We
will validate mediators/processes initially by returning to our stocks of
saliva and samples from patient categories 1-4 and examining activity of
identified pathways/mediators.
4) Interfere with pSS disease by genetically/chemically disrupting putative
pSS-mediator signals. Proof of principle that these molecules/processes are
salient to pSS will be obtained by chemical and/or genetic manipulation of
their expression/activity. Genetic manipulation will be achieved using
CRISPR-Cas9 gene editing technology. Function-blocking antibodies or chemical
inhibitors will be used to modulate activity of proteins implicated in pSS.
Concurrent monitoring of the SGSC and organoid culture dynamics following these
manipulations will allow us to determine if we can *rescue* the phenotype of
SGSCs and organoids from pSS biopsies.
5) Establish the immunological (response) capabilities of the organoids derived
from SCGCs.
In order to establish a full in vitro model for pSS as an autoimmune disease,
we will explore the immune modulating capabilities of pSS SGSCs.

This is a minimal risk study. The saliva collection is a non-invasive procedure
and the biopsy, as is the saliva collection, will be part of the subject*s
routine clinical care for diagnostic purposes. The parotid gland tissue needed
for the experiments will be collected simultaneously with the diagnostic biopsy
via the same surgical approach. It is presumed that taking this extra amount of
tissue, similar to the amount of tissue needed for the diagnostic work-up, will
not increase the morbidity of the diagnostic procedure as our intervention
studies with biologicals (rituximab, abatacept) has learned us that taking
repeated biopsies from the same parotid gland is not accompanied by increased
morbidity of the surgical procedure.