While stem cell transplantation is a transformative therapy for many cancer patients, acute graft-versus-host-disease (GVHD) remains a major, life threatening complication experienced by many. Acute GVHD leads to inflammatory immune infiltrates in the gut, alloantigen presentation, and ultimately gastrointestinal (GI) tract disruption. Understanding the mechanisms of GVHD may help us reduce these harmful effects. Recently, it was discovered that granulocyte-macrophage colony-stimulating factor (GM-CSF) secreted from donor T cells plays a pathogenic role in the disease course. However, the specific T cells that are involved in initiation of the disease, as well as the cellular and molecular mechanisms, remained elusive. The Hill laboratory in the Clinical Research Division set out to understand these key events using a cell fate reporter system that could track lineage-specific T cells over time in a paper published in Blood Advances.
The authors used a system to track the fate of interleukin 17-producing cells, which are known to potentiate GVHD in the GI tract. CD4+ Th17 cells (and their CD8+ counterpart, Tc17 cells) are defined by their ability to produce IL-17, secreted as part of a suite of cytokines that includes GM-CSF. Tracking Th/Tc17 cells in real time is difficult because IL-17 is not a continuous, stable marker. However, by using a cell fate system that permanently marks any cell that produces IL-17 with the stable fluorescent protein YFP, the Hill lab could follow Th/Tc17 cells over time and determine their role in acute GVHD. The authors first wanted to understand if Th/Tc17 cells were the predominant source of GM-CSF in the colon following bone marrow transplantation. Following irradiation, BALB/c mice received bone marrow (BM) from transgenic IL-17-fate reporter B6 mice, to model allotransplantation and track Th/Tc17 cells. While Th/Tc17 cells were a significant minority of the GM-CSF-producing cells in the colon and draining lymph node, the majority of Th17 cells were producing GM-CSF one week after transplantation. Additionally, CD4+ T cells accumulated in the colon post allotransplantation, largely due to accumulation of the GM-CSF-producing Th17 cell subset. Together these data indicated that both Th17 and non-Th17 T cell lineages secrete GM-CSF after BM transplantation and accumulate in the colon.
GM-CSF is an important growth factor for bone marrow-derived antigen-presenting cells (APCs), including macrophages and dendritic cells (DCs). The researchers wanted to understand the role donor T cell-derived GM-CSF played on donor APCs in the colon, a common site of severe GVHD. They used an alloantigen-specific transgenic T cell receptor system developed by Dr. Motoko Koyama to track alloantigen presentation during transplantation using bioluminescence. Briefly, BALB/c mice were transplanted with defined ratios of T cell-depleted BM and purified T cells from B6 mice, then given transgenic, bioluminescent, alloantigen-specific B6 T cells after initial cell engraftment. This allowed the authors to track both antigen-specific T cells, as well as the APCs presenting the model alloantigen. When recipients were transplanted with bone marrow and T cells that could secrete GM-CSF, donor DC presenting alloantigen accumulated in the colon and the mesenteric (draining) lymph node, which was associated with severe acute GVHD in the colon. However, when the authors transplanted GM-CSF secreting T cells with BM deficient in the ability to signal through the common β-chain, a necessary component for GM-CSF signaling, donor DC did not expand or present alloantigen in the gut and acute GVHD was prevented. To confirm that GM-CSF secretion from the donor T cell was the key player, the authors transplanted T cells that lacked the ability to produce GM-CSF (with normal, T cell-depleted BM). Like the experiments where DCs lacked the ability to respond to GM-CSF, when T cells could not produce GM-CSF, DCs presenting alloantigen did not accumulate in the draining lymph nodes and alloantigen presentation in the colon was prevented. Together, these results indicate that GM-CSF produced from donor T cells contributes to the onset of acute GVHD through its ability to signal to DCs, allowing donor DC accumulation and alloantigen presentation in the gut that in turn drives lethal GVHD.
These results highlight a signaling axis from the donor T cell to donor DCs that contributes to acute, life-threatening GVHD. Importantly, it’s a signaling axis that can be interrupted. “GM-CSF neutralizing monoclonal antibodies are now available and undergoing clinical study. We envisage that these therapeutic agents can now be tested in allogeneic stem cell transplantation with a focus on preventing severe acute GVHD in the GI tract.” said Dr. Geoffrey Hill, the lead investigator on the paper. Clinical blockade of this pathway represents a rational strategy to reduce incidence of acute GVHD in patients who need stem cell transplantation.
Gartlan KH, Koyama M, Lineburg KE, Chang K, Ensbey KS, Kuns RD, Henden AS, Samson LD, Clouston AD, Lopez AF, MacDonald KPA, Hill GR. 2019. Donor T-cell-derived GM-CSF drives alloantigen presentation by dendritic cells in the gastrointestinal tract. Blood Adv. 8;3(19):2859-2865.
This work was supported by funding from the National Health and Medical Research Council (G.R.H.).
Fred Hutch/UW Cancer Consortium member Geoffrey Hill contributed to this work.