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Background T cell–mediated rejection (TCMR) is a major cause of graft dysfunction after liver transplantation. However, the spatial organization of immune responses within the portal area (PA), the primary site of rejection injury, remains incompletely understood. We applied high-resolution spatial transcriptomics and spatial proteomics to characterize the cellular and molecular landscape of TCMR in liver allograft biopsies.Methods Subcellular-resolution Xenium spatial transcriptomics was performed on liver biopsy specimens from 18 patients with TCMR(group R) and 5 non-rejection controls(group NR). Spatial transcriptomic (ST) profiles were analyzed using STAMP (Spatial Topic Analysis via Mixed-membership Probabilistic modeling), which deconvolutes gene expression into spatial gene topics. In addition, Digital Spatial Profiling (DSP) proteomics was conducted on 39 regions of interest (ROIs) derived from 10 rejection and 10 non-rejection liver tissues to validate spatial protein signatures.Results Cellular composition differed markedly between rejection and non-rejection samples ( IDDF2026-ABS-0180 Figure 1(A,B)). STAMP analysis identified 10 spatial gene topics representing distinct transcriptional programs across the tissue landscape (IDDF2026-ABS-0180 Figure 1(C)). Among them, Topic5 and Topic7 were significantly enriched in the portal area of rejected samples (IDDF2026-ABS-0180 Figure 1(D,E)). Topic5 was characterized by cytotoxic T-cell markers including CD8A, GZMA, and GZMK, indicating activation of T-cell–mediated cytotoxicity and cell-killing pathways. In contrast, Topic7 represented a myeloid cell–associated module, marked by MARCO, CD68, and FCGR3A, and was associated with biological functions such as monocyte chemotaxis, myeloid leukocyte activation, and tumor necrosis factor (TNF) production (IDDF2026-ABS-0180 Figure 1(F)). Consistent with these findings, gene-signature scores for both topics were significantly elevated in independent rejection samples from the GSE145780 dataset (IDDF2026-ABS-0180 Figure 1(G)). Spatial proteomic profiling further supported these results. DSP analysis revealed region-specific protein expression patterns (IDDF2026-ABS-0180 Figure 1(H,I)), with the portal regions of rejection tissues enriched for immune activation pathways, including T-cell activation, cytokine production, TNF signaling, and NF-κB signaling (IDDF2026-ABS-0180 Figure 1(J)).Conclusions Integrative spatial transcriptomic and proteomic analyses reveal that TCMR in liver allografts is characterized by coordinated cytotoxic T-cell and myeloid inflammatory programs localized to the portal microenvironment. These spatially resolved immune signatures provide mechanistic insights into rejection pathology and may facilitate the development of spatial biomarkers for improved diagnosis and therapeutic targeting of liver allograft rejection.Abstract IDDF2026-ABS-0180 Figure 1