Uncovering the roles of B lymphocytes in the NOD mouse model of type 1 diabetes through genetic engineering and therapeutic targeting
Wang, Qiming.
2019
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β-cell
destruction in type 1 diabetes (T1D) is considered a T-cell mediated autoimmune
manifestation, but based on studies in the NOD mouse model, B-lymphocytes also play a
critical role in disease development. They do so by serving as a preferential subset of
pathogenic antigen resenting cells (APC) that expand diabetogenic T cells. Immunological
tolerance induction mechanisms that normally ... read moreeliminate or inactivate autoreactive
B-lymphocytes are defective in NOD mice and also in T1D patients. Our previous studies
mapped a faulty NOD B-lymphocyte tolerance phenotype to a 6.22Mb region on Chromosome 4.
With a combination of differential gene expression and ingenuity pathway analyses (IPA)
we identified a hypomorphic Ephb2 allelic variant as a potential candidate gene that
allowed the generation of pathogenic B-lymphocytes in NOD mice. We experimentally tested
the candidacy of Ephb2 by creating a NOD mouse model transgenically expressing the Ephb2
allele from B6 origin (NOD-Ephb2B6). Expression of the B6 derived Ephb2 allele afforded
significant T1D protection by attenuating the pathogenicity of B-lymphocytes. As a
result of their involvement in the pathogenicity of T1D, B-lymphocyte-targeted therapies
have received considerable interest as potential T1D interventions. However, in
new-onset human T1D patients, rituximab (anti-CD20) mediated B-lymphocyte depletion was
only partially effective as a possible disease intervention. Therefore, I tested whether
other possible B-lymphocyte-directed approaches that either independently or in
combination with anti-CD20 might provide an improved means for T1D inhibition. I found
that both continuous and transient blockade of the fundamental B-lymphocyte survival
factor BAFF protected NOD mice from T1D even when initiated at late disease stage
characterized by the presence of insulin autoantibodies (IAA). B-lymphocytes surviving
after BAFF blockade are functionally compromised in their ability to present
autoantigens to T cells. Surprisingly, addition of anti-CD20 abrogated the protective
effects of transient BAFF blockade. I found that this is due to B-lymphocytes that have
immunoregulatory functions (Bregs) becoming enriched after transient BAFF blockade were
sensitive to anti-CD20 mediated depletion. These Bregs are characterized by secretion of
anti-inflammatory cytokine IL-10 and expression of the ecto-enzyme CD73 that converts
inflammatory ATP to immunosuppressive adenosine. To dissect which one of these molecules
was employed by Bregs to suppress autoreactive T cells, we created NOD-CD73null mice
using CRISPR/Cas9 genome editing approach. NOD-CD73null mice developed T1D at similar
rate as standard NOD controls. However, BAFF blockade mediated T1D protection is
compromised in NOD.IL10null but not NOD-CD73null mice. Taken together, these data
highlight a B-lymphocyte centric model in the etiology of T1D in which genetic
approaches that restore faulty B-lymphocyte tolerance induction attenuates T1D
development. Our cellular and molecular dissection of pathogenic versus regulatory
B-lymphocyte subsets in NOD mice yields two important conclusions. First, the pattern of
B-lymphocyte depletion elicited by rituximab treatment may underlie why the agent failed
as a T1D intervention, whereas even when initiated at a late stage of disease
development BAFF blockade that preferentially depletes pathogenic B-lymphocytes and
enriches Bregs can provide an effective means to block progression to overt
hyperglycemia. Second, IL-10 secretion instead of CD73 expression is a necessary
component of BAFF blockade mediated T1D
protection.
Thesis (Ph.D.)--Tufts University, 2019.
Submitted to the Dept. of Genetics.
Advisors: David Serreze, and Henry Wortis.
Committee: Gareth Howell, Derry Roopenian, and Jennifer Trowbridge.
Keywords: Genetics, and Immunology.read less - ID:
- bz60d854x
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