Introduction: Graft-versus-host disease (GVHD) is a relatively common and highly morbid complication after intestinal transplantation. Its pathophysiology remains poorly understood. Resident memory T cells (TRM) are a newly described T cell subset with memory phenotype localizing to peripheral tissue. We hypothesized that the pathophysiology of GVHD might be related to increased donor TRM in the graft that subsequently migrate into host blood and tissue.

Methods: Intestinal transplantation from deceased donors was performed using our standard method. Graft and blood lymphocytes from 10 patients with GVHD and 34 without were longitudinally analyzed using flow cytometry.

Results: Levels of CD4 and CD8 TRM were approximately 20% higher in the grafts of GVHD vs. stable patients prior to implantation and significantly higher at the time of GVHD (p = 0.02 and 0.04). There was also a mean 60.3% higher level of CD8 TRM in the native bowels of GVHD patients compared to controls and 20-30% higher levels of IFN-γ and TNF-α expression in both the grafts and native bowels of GVHD patients. The percentage of CD4 and CD8 TRM in the blood of GVHD vs. stable patients significantly increased during GVHD (p = 0.005), and expression of HLA-DR, CD57, and PD-1 was significantly higher. There were also significant increases in CD8 effector memory cells (p = 0.0056) and decreases in naïve cells (p = 0.0034). Notably, CD8/PD-1 was also significantly elevated prior to transplantation in patients who later had GVHD (p = 0.025), and a pre-transplant CD8/PD1 level >45% was an absolute predictor of later GVHD. Moreover, we found significantly higher percentages of HLA-DR, CD57, and PD-1 in patients with GVHD who died vs. those who survived, and values that always correlated with mortality were CD8/CD57 > 35%, CD4/HLA-DR > 15%, CD8/HLA-DR > 45%, and CD4/PD1 > 35%.

Conclusion: In the largest longitudinal analysis to date, we demonstrate that increased TRM percentage and inflammatory cytokine expression in graft bowel correspond with increased TRM in blood and native bowel as well as increased cytokine expression in native bowel at time of GVHD. Thus GVHD pathogenesis may depend on donor TRM in graft bowel migrating to the blood and native tissue of recipients. Recipients with higher PD-1 expression, indicating T cell exhaustion, might be more vulnerable, providing a possible biomarker for GVHD risk, while increased expression of maturity and activation markers correlate with prognosis.