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BackgroundThe PD-1/PD-L1 axis represents a key mechanism of tumor immune evasion. However, its expression across different immune compartments and clinical implications in DLBCL patients remain unclear.MethodsThis study included 67 newly diagnosed DLBCL patients and 59 healthy controls. The levels of PD-1-positive T cells in the peripheral blood (PB) and bone marrow (BM) were assessed via flow cytometry. Furthermore, this study analyzed the correlation between PD-1 expression on PB and BM T-cell subsets and the clinicopathological features of DLBCL patients to elucidate their clinical implications.ResultsCompared with healthy controls, DLBCL patients presented significantly elevated PD-1 expression on T cells in both the PB and BM. Elevated PD-1 expression is significantly correlated with adverse clinical outcomes and poor prognostic factors, including advanced Ann Arbor stage (III-IV), a high International Prognostic Index (IPI 3-5), elevated lactate dehydrogenase (LDH>250 U/L) and the presence of B symptoms. A strong concordance in PD-1 levels was observed between paired PB and BM samples.ConclusionIncreased PD-1 expression in the peripheral blood of DLBCL patients is correlated with PD-1 expression in the bone marrow. Our results demonstrate that elevated circulating PD-1+T cells are associated with high-risk, aggressive disease features. Importantly, our data support the potential utility of peripheral blood PD-1+T cells as a minimally invasive surrogate biomarker to reflect intramedullary T cell exhaustion. DLBCL patients with abundant circulating PD-1+T cells may have greater potential to respond to PD-1/PD-L1 blockade immunotherapy, although this hypothesis requires prospective validation. These findings warrant further clinical investigation.