Here, we show that, in mice and humans, a population of interleukin-9 (IL-9)-producing T cells activated via the ST2-IL-33 pathway (T9<sub>IL-33</sub> cells) increases GVL while decreasing GVHD through two opposing mechanisms: protection from fatal immunity by amphiregulin expression and augmentation of antileukemic activity compared with T9, T1, and unmanipulated T cells through CD8α expression.
EGFR, IL-6, IL-9, and NAMPT have the greatest potential as diagnostic biomarkers, with excellent sensitivity, specificity, and clinical relevance to the ocular surface status of GvHD.