Summary Little is known about the maintenance of intestinal stem cells (ISCs) and progenitors during immune-mediated tissue damage or about the susceptibility of transplant recipients to tissue damage mediated by the donor immune system during graft vs. host disease (GVHD). We demonstrate here that deficiency of recipient-derived IL-22 increased acute GVHD tissue damage and mortality, that ISCs were eliminated during GVHD, and that ISCs as well as their downstream progenitors expressed the IL-22 receptor. Intestinal IL-22 was produced after bone marrow transplant by IL-23-responsive innate lymphoid cells (ILCs) from the transplant recipients, and intestinal IL-22 increased in response to pre-transplant conditioning. However, ILC frequency and IL-22 amounts were decreased by GVHD. Recipient IL-22 deficiency led to increased crypt apoptosis, depletion of ISCs, and loss of epithelial integrity. Our findings reveal IL-22 as a critical regulator of tissue sensitivity to GVHD and a protective factor for ISC during inflammatory intestinal damage.

After allogeneic hematopoietic stem cell transplantation (allo-HSCT), intestinal bacteria modulate risks of infection and graft-versus-host disease (GVHD). Neutropenic fever is common and treated with a choice of clinically equivalent antibiotics that target obligately anaerobic bacteria (anaerobes) to varying degrees. We retrospectively examined 857 allo-HSCT recipients and found that treatment of neutropenic fever with imipenem-cilastatin and piperacillin-tazobactam was associated with increased GVHD-related mortality at 5 years (21.5% in imipenem-cilastatin-treated patients vs. 13.1% in untreated patients, p=0.025, and 19.8% in piperacillin-tazobactam-treated patients vs. 11.9% in untreated patients, p=0.007). However, two other antibiotics also used to treat neutropenic fever, aztreonam and cefepime, were not associated with GVHD-related mortality (p=0.78 and p=0.98, respectively). Analysis of stool microbiota composition showed that piperacillin-tazobactam administration was associated with increased compositional perturbation. Studies in mouse models demonstrated similar effects of these antibiotics, as well as aggravated GVHD mortality with imipenem-cilastatin or piperacillin-tazobactm compared to aztreonam (p<0.01 and p<0.05, respectively). We found pathological evidence for increased GVHD in the colon of imipenem-cilastatin-treated mice (p<0.05), but no differences in short-chain fatty acid concentrations or regulatory T cells numbers. Notably, imipenem-cilastatin treatment of mice with GVHD led to loss of the protective lining of mucus in the colon (p<0.01) and intestinal barrier function was compromised (p<0.05). Sequencing of mouse stool specimens showed expansion of Akkermansia muciniphila (p<0.001), a commensal bacterium with mucus-degrading capabilities, raising the possibility that mucus degradation can contribute to murine GVHD. We demonstrate an underappreciated risk for antibiotics with activity against anaerobes to exacerbate colonic GVHD after transplant.

Endogenous thymic regeneration is a crucial function that allows for renewal of immune competence after stress, infection or immunodepletion. The mechanisms governing this regeneration, however, remain poorly understood. Here we detail a framework of thymic regeneration centred on IL-22 and triggered by depletion of CD4+CD8+ double positive (DP) thymocytes. Intrathymic levels of IL-22 were increased following thymic insult, and thymic recovery was impaired in IL-22-deficient mice. IL-22, which signalled through thymic epithelial cells (TECs) and promoted their proliferation and survival, was upregulated by radio-resistant RORγ(t)+CCR6+NKp46− lymphoid tissue-inducer cells (LTi) after thymic injury in an IL-23 dependent manner. Importantly, administration of IL-22 enhanced thymic recovery following total body irradiation (TBI). These studies reveal mechanisms of endogenous thymic repair and offer innovative regenerative strategies for improving immune competence.

Summary Somatic mutations in IDH1/2 and TET2 result in impaired TET2 mediated conversion of 5-methylcytosine (5-mC) to 5-hydroxymethylcytosine (5-hmC). The observation that WT1 inactivating mutations anti-correlate with TET2/IDH1/2 mutations in AML led us to hypothesize that WT1 mutations may impact TET2 function. WT1 mutant acute myeloid leukemia (AML) patients have reduced 5-hmC levels similar to TET2/IDH1/2-mutant AML. These mutations are characterized by convergent, site-specific alterations in DNA hydroxymethylation, which drive differential gene expression more than alterations in DNA promoter methylation. WT1 overexpression increases global levels of 5-hmC, and WT1 silencing reduced 5-hmC levels. WT1 physically interacts with TET2 and TET3, and WT1 loss of function results in a similar hematopoietic differentiation phenotype as observed with TET2 deficiency. These data provide a novel role for WT1 in regulating DNA hydroxymethylation and suggest that TET2 IDH1/2, and WT1 mutations define a novel AML subtype defined by dysregulated DNA hydroxymethylation.