Sjögren's disease (SjD), a common systemic autoimmune disease characterized by severe oral and ocular
dryness and multi-organ involvement, has no disease modifying treatment available. Clinical trials to date have
failed due to the clinical and biologic heterogeneity of SjD. As a result, it is important to subset SjD patients into
pathobiologically similar groups, called endotypes. SjD patients who have a high number of lymphocytes in their
salivary gland (SG) represent one endotype. This biopsy positive (Bx+) endotype has high cytokines that signal
via Janus kinases (JAKs) and higher levels of autoantibodies. Another approach to generate biologically unique
endotypes is to stratify by hallmark symptoms of dryness, pain, and fatigue. Mesenchymal stromal cells (MSCs)
are enriched in SjD compared to control SGs and have divergent signaling pathways preclinically, suggesting
that SG-MSCs might drive pathogenesis. The long-term goal is to mechanistically explain and generate therapies
that target SG-MSCs in SjD. The overall objective of this application is to define how SjD endotypes modify MSC
immunobiology, comparing mouse to human SG-MSCs. The central hypothesis is that MSCs are drivers of SjD
pathogenesis through their maladaptive response to the cytokines unique to certain endotypes. The rationale for
this project is based on new data that SG-MSCs treated with IFN become maladaptive and promote
CD4+CXCR3+ T-cell and B-cell chemotaxis. These new data identify targetable maladaptive MSC behavior;
however, the response to other inflammatory cytokines in endotype-specific SjD SG microenvironments is
unknown. This knowledge is critical to define and target the pathogenic contributions of SG-MSCs in SjD. The
central hypothesis will be tested by pursuing two specific aims: 1) determine the signaling pathways driving
maladaptive mouse MSCs and SjD using multiple JAK inhibitors as translational immunopharmacological probes
in Bx+ endotype; and 2) define pathologic responses and heterogeneity of human MSCs in SjD by endotype. In
aim 1, Bx+ phenotype SjD mice will be treated with JAK inhibitors as immunopharmacological probes. SG-MSC
transcript and protein profile, localization, and neighbors in situ will be determined using sequential FISH with
hybridization chain reaction (seqFISH-HCR) by each treatment. SG-MSC maladaptive phenotype and function
will be verified in vitro and SjD-like disease in mice will be measured. In aim 2, human MSC transcript and protein
profiles, localization, and neighbors will be determined, comparing endotypes. Maladaptive MSC behavior will
be mechanistically tested in vitro with aim 1 JAK inhibitors, identifying parallels between mice and humans. The
proposed research is innovative, because it focuses on SjD endotypes, critical to guiding future pharmacologic
MSC targeting and to deconvoluting SjD heterogeneity. Furthermore, it uses seqFISH-HCR technology for high
resolution insight into the MSC phenotype in situ. The proposal is significant because it clarifies the pathobiology
of a novel immunomodulatory cell, the SG-MSC, by SjD endotype, opening new horizons for MSC- and SjD
endotype-targeted therapies. It also performs highly translatable comparisons in vivo between JAK inhibitors.
