Identification of ICOS as a biomarker of acute GvHD. (A-B) Volcano plots summarizing the differential gene expression analysis performed on publicly available RNA-seq data comparing murine (A) and human (B) T cells recovered from murine models of acute GvHD with cells prior to adoptive transfer. Vertical dashed lines on volcano plots indicate a log₂ fold change of 1.5; horizontal dashed lines indicate an adjusted P value of .05. Genes encoding for selected activation markers previously employed as immunoPET targets are highlighted in red. (C) Representative FACS histograms (left panels) and summary of percentages (right panels) of ICOS expression on CD90.1⁺CD45.1⁺CD4⁺ (top panels) and CD8⁺ (bottom panels) T cells recovered from the spleen 4 and 7 days post–adoptive transfer of C57BL/6 T cells into allogeneic BALB/c recipients. Values are summarized as box plots, representing the range, first quartile, median, third quartile, and eventual outliers. Results are pooled from 2 independent experiments (n = 9-11 mice per group). Day 4 and 7 values were compared with day 0 values using a nonparametric Mann-Whitney U test. P values are indicated. (D) Representative FACS histograms (left panels) and summary of percentages (right panels) of ICOS expression on human-CD45⁺ murine-CD45⁻ CD3⁺ T cells recovered from spleen 14 days post–adoptive transfer of human PBMCs from healthy donors into sublethally irradiated NSG mice. Results are pooled for a total of 9 mice (n = 2-4 mice per group). Day 14 and 0 values were compared using a nonparametric Mann-Whitney U test. P values are indicated. (E-F) Uniform Manifold Approximation and Projection plots of FACS data obtained from the analysis of spleens recovered at day 7 after MHC-mismatch murine allogeneic HCT (E) or at day 14 upon induction of xenogeneic GvHD by adoptive transfer of PBMCs into NSG mice (F). ICOS-expressing cells are depicted in red.