Epigenetic Plasticity of Type II Innate Lymphoid Cells in the Lower Gastrointestinal Tract

Though hematopoietic stem cell transplantation (HSCT) is the preferred treatment for a variety of blood malignancies, its use is limited by the development of acute graft-versus-host disease (aGvHD). Type II innate lymphoid cells (ILC2s) are immune cells that play an important role in maintaining mucosal homeostasis, and our lab has previously shown that ILC2s in the gastrointestinal tract (GI) are sensitive to conditioning therapy prior to HSCT. Strikingly, we have demonstrated that the infusion of activated donor ILC2s markedly reduces aGvHD-associated mortality. We therefore wanted to investigate the mechanism of the loss of protective ILC2s from the GI tract. We hypothesized that ILC2s fail to repopulate the gut after HSCT due to inflammatory environmental cues that convert ILC2 precursors to an alternate, ILC1- or ILC3-like fate. Thus, we evaluated the impact of cytokines associated with commitment on murine ILC2s by exposing them to cytokines that may promote differentiation to an ILC1 or ILC3 fate (IL-1b/IL-12/IFN-γ and TGF-b/IL-6/IL-23, respectively). We found ILC2 cells acquired the ability to secrete TNF and IL-17 after in vitro skewing (with these lineage-defining cytokines. To test the ability of these "ex-ILC2" cells to home to other tissues in vivo, GFP-ILC2s were infused into recipients at the time of transplantation. We tracked GFP-ILC2s to the liver and spleen, where they made IFN-g and IL-17 and expressed transcription factors associated with the ILC1 and ILC3 lineages (Figure 1). Next we assessed the ability of cytokines alter ILC2 fate via epigenetic reprogramming by using ChIP-sequencing to evaluate the presence of histone marks that may underlie cellular plasticity. We show that these changes are associated with alterations in epigenetic marks around pioneer, lineage-determining factors. We therefore chose to test a screen of compounds known to modulate a variety of epigenetic targets to ask if they can maintain or convert ILC2s to alternate fates and identified a number of compounds that target bromodomains, methyltransferases, and histonedeacetylases, respectively, that alter the viability and differentiation of ILC2s into an "ex-ILC2"-like phenotype. Preliminary work suggests that maintenance ofG9a expression is able to rescue the loss of ILC2s, which is being tested in vivo. Taken together, these data provide new insights into mechanisms by which innate lymphoid cell precursors are epigenetically regulated, providing novel approaches to treating aGvHD following HSCT.

Figure 1

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Figure 1

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