Allogeneic hematopoietic cell transplantation (Allo-HCT) is a curative therapy for patients with hematological
malignancies (i.e. leukemia and lymphoma), through graft versus leukemia/lymphoma (GVL) effect mediated
by alloreactive donor T cells. However, graft-versus-host disease (GVHD) caused by the same alloreactive T
cells remains a major obstacle. Chronic GVHD (cGVHD), a systemic autoimmune-like syndrome, remains a
major cause of morbidity and mortality in long-term survivors of Allo-HCT. During the past decade, we have
used murine and humanized murine models of cGVHD and biospecimens from cGVHD patients to
demonstrate that CD4+ T cells and B cells and their interactions in GVHD target tissues such as the liver, lung
and skin play a critical role in the pathogenesis and persistence of the disease. The premise of this new
proposal is that deeper mechanistic understanding of the interactions between non-circulating tissue-
resident CD4+ memory T (Trm) and tissue-resident B (Brm) cells in GVHD target tissues will identify
new therapeutic targets for prevention or treatment of cGVHD. In Aim 1, we will determine whether CD4+
Trm cells initiate formation of tertiary lymphoid structures (TLS) in GVHD target tissues, in which Ly108+ stem
cell-like progenitors maintain the pool of Trm and Brm to perpetuate cGVHD pathogenesis. We will also
develop novel cell-penetrating PS-Cas9-gRNA to target STAT3 in donor T cells to prevent development of
pathogenic CD4+ Trm and cGVHD while preserving GVL activity, because our recent studies indicate that
STAT3 is required for Trm development. In Aim 2, we will determine whether B cell helper PD-1hiPSGL1loCD4+
Trh cells interact with T-bet+ Brm cells to produce autoantibodies that augment systemic tissue damage. In
Aim 3, we will determine whether non-B cell helper PSGL1hiCD4+ Trm cells interact with dendritic cells,
macrophages, and fibroblasts in cGVHD target tissues to mediate damage and fibrosis in an IL-33/ST2
pathway-dependent manner. These studies have high biological and translational significance and may lead to
a paradigm shift in our understanding of cGVHD pathogenesis and to development of novel approaches for
preventing and treating cGVHD.