EBV-Associated Lymphoma Consortium Annual Meeting (Abstract): Submission #7

Abstract Summary EBV is associated with the development of post-transplant lymphoproliferative disease (PTLD), a serious complication of solid organ and bone marrow transplantation. To understand the immune response to EBV in transplant recipients we analyzed the T cell response in EBV seropositive transplant recipients with no evidence of EBV disease and in transplant recipients with chronic (3-6 months) EBV DNAemia (CED). We detected a significantly reduced proportion of IL-2/IFN-g polyfunctional CD4+ T effector memory (TEM) cells in the CED group compared to the controls. CED CD8+ T cells had a higher proportion of TEMRA cells but significantly fewer of these were IL-2+TEMRA cells. Similarly, there were fewer IL-2+, TNF-a+, and IL-2/TNF-a+ polyfunctional TEM CD8+ T cells in the CED group compared to controls. Moreover, the CED group had fewer clonally expanded TEMRA compared to the control group. To investigate the molecular underpinnings of these differences we performed scRNAseq on PBMC after stimulation with EBV latent cycle peptides. Using UMAP we identified 19 clusters that include naïve, transitional, TEM, TEMRA, and central memory CD8+ T cells. CED CD8+ TEMRA and TEM cells express higher levels of exhaustion genes (LAG3, TIGIT, TOX, HAVCR2) compared to the control group. In contrast, CD8+ T cells from controls showed upregulation of T cell activation and co-stimulation genes (ICOS, CD2, CD28, CD27). KEGG and Gene Ontology Term Biological Processes analysis reveals enrichment of pathways for ribosomal activity, cell proliferation, and negative regulation of T cell apoptosis in CD8+ T cells from controls, while CD8+ T cells from the CED group were enriched for pathways related to apoptotic signaling, negative regulation of T cell activation, and EBV infection. These data pinpoint specific functional immune alterations in the T cell compartment of individuals that are unable to mount effective responses to EBV.