Previous research has established acute graft-versus-host disease (GVHD) in the gastrointestinal tract as the primary cause of both GVHD severity and mortality, and as a result, emphasis is placed on preventing acute gut GVHD while still preserving the graft-versus-leukemia effect of allogeneic hematopoietic stem cell transplantation.
A new study examining DC-mediated differentiation of alloreactive donor CD4+ T cells during exacerbation of acute gut graft-versus-host disease (GVHD) has led researchers to suggest that the findings could aid in examining T cell differentiation in patients undergoing allogeneic hematopoietic stem cell transplantation (alloSCT).
While alloSCT is a curative therapy for an array of acute leukemias through its graft-versus-leukemia (GVL) effect, the procedure can also cause GVHD when donor T cells damage noncancerous host tissue, including in the gastrointestinal (GI) tract. Previous research has established acute GVHD in the GI tract as the primary cause of both GVHD severity and mortality, and as a result, emphasis is placed on preventing acute gut GVHD while still preserving the GVL effect of alloSCT.
According to the researchers, the key to this is determining the spatial and temporal differences between GVL and GVHD.
Through droplet-based scRNA-Seq and computational modeling, the researchers observed an emergence of pathogenic and regulatory states along a single developmental trajectory in mesenteric lymph nodes (mLNs). Unexpectedly, the researchers also observed a second trajectory with little proliferation or cytokine expression, reduced glycolysis, and high tcf7 expression.
“We previously showed in preclinical models that donor CD4+ T cells are initially activated by recipient nonhematopoietic antigen-presenting cells (APCs) within the gut, including epithelial cells that upregulate class II MHC molecules,” explained the researchers. “Donor-derived colonic DCs also prime donor CD4+ cells in mesenteric lymph nodes (mLNs) and trigger Th cell differentiation, which serves to amplify and exacerbate GVHD.”
From the preclinical model, the researchers were able to determine that cytokines like IL-17A, IFN-γ, and granulocyte-macrophage colony-stimulating factor created by alloreactive Th1 and Th17 cells in the GI tract promote GVHD. On the other hand, IL-10 produced by Tr1 and iTreg cells offer protection from the disease.
In the current study, the researchers sampled transcriptomes from thousands of alloreactive CD4+ T cells of a single specificity from both lymphoid and nonlymphoid gut-associated tissue. In doing this, they found cellular states expressing canonical Th1/Th17 cytokine genes Ifng and Il17a, as well as the Foxp3 and Il10 regulatory genesat frequencies similar to that expressed by flow cytometry. Of note, there was significant similarity between the transcriptomes of the lymphoid tissue but also in the gut.
“Subtle differences became more evident among gut-trafficked TEa cells that had stopped proliferating, with Ifng expressed more uniformly that either Il17a or Foxp3,” explained the researchers. “Given that Tea cells can upregulate T-bet and IFN-γ but not IL-17A or Foxp3 in the complete absence of the class II MHC presentation, our data are broadly consistent with a Th1-like state being a default program in the gut, which may be countered by alloantigen presentation via class II MHC molecule toward iTreg or Th17-like states.”
According to the researchers, a main takeaway from the study was that proinflammatory states were not readily distinguished from immune-suppressive iTreg states.
They added: “One question, however, is whether our inability to separate proinflammatory and regulatory states was attributed to reliance on droplet-based scRNA-Seq, without supplementing this with high-dimensional protein assessment via flow or mass cytometry, single-cell epigenomic assessment via scATAC-Seq, or scRNA-Seq at higher sequencing depths.”
Engel J, Lee H, Williams C, et al. Single-cell transcriptomics of alloreactive CD4+ T cells over time reveals divergent fates during gut graft-versus-host disease. JCI Insight. 2020;5(13):e137990. doi: 10.1172/jci.insight.137990.