Background: Diffuse large B-cell Lymphoma (DLBCL) is an aggressive malignancy where the tumor immune microenvironment (TME) plays a crucial role in lymphomagenesis and immune evasion. However, there is a lack of analyses about the comprehensive immunophenotypic profiling of peripheral blood lymphocyte subsets in newly diagnosed patients to their clinical features including symptom burden, IPI, and infections, as well as outcomes such as treatment response and infection risk. This study analyses associations with clinical features, prognosis, and infection risk, providing a composite biomarker for prognosis and risk-adapted prophylaxis.Methods: Sixty-six newly diagnosed DLBCL patients were retrospectively enrolled in this study. The immune status of lymphocyte subset distribution and maturation profiles was comprehensively evaluated using flow cytometry. Expression levels were compared across groups stratified by the following criteria: B-symptoms (fever >38°C, night sweats, and weight loss >10%) vs. A-symptoms (absence); IPI score (0-2 vs 3-5), and infection status during treatment (infected vs. uninfected). Correlations between clinical features and differentiation subsets of T and B cells were analyzed. Logistic regression was used to identify indicators of infection risk, and ROC analysis was applied to assess prognostic value.Results: Compared with A-symptomatic patients, patients with B-symptoms had significantly lower percentages of effector memory (EM) CD4+ T cells (p=0.043), EM CD8+ T cells (p=0.048), and Th1 cells (p=0.016), along with significantly higher percentages of naive CD8+ T cells (p=0.030) and activated/helper-induced T cells (p=0.015). In comparison to patients with an IPI score of 0-2, those with an IPI score of 3-5 patients showed lower naive CD4+ T cells (p=0.024), naive CD8+ T cells (p=0.004), helper/suppressor T cell ratio (p=0.01), double-negative B cells (p=0.043), and EM CD4+ T cells (p=0.011). Compared to uninfected patients, infected patients demonstrated significantly higher EM CD8+ T cells (p<0.001), peripheral helper T cells (p=0.019), CD4+PD-1+ cells (p=0.022), and Th1 cells (p=0.002). Conversely, the percentage of transitional B cells was notably lower in the infected group. Besides, infection was strongly associated with poorer 2-year progression-free survival (PFS) (p=0.002). .Logistic regression identified EM CD8+ T cells (OR=1.07, 95% CI 1.03-1.12, p<0.01), Th1 cells (OR=1.06, 95% CI 1.01-1.12, p=0.028), and CD4+PD-1+ cells (OR=1.03, 95% CI 1.01-1.14, p=0.022) as infection risk factors, while transitional B cells (OR=0.93, 95% CI 0.87-0.99, p=0.02) were protective. Receiver operating characteristic (ROC) analysis yielded AUC=0.686 for EM CD8+ T cells and AUC=0.698 for Th17 TFH cells in predict prognosis The logistic combination of both markers significantly improved predictive power (AUC=0.753).Conclusion: Beyond tumor burden, this study identifies B-symptoms as direct indicators of impaired T-cell differentiation characterized by reduced effector memory (EM) T cells alongside compensatory naive expansion. Decreased Th1 cells likely underpin weakened cellular immunity. High-risk IPI patients exhibit a “triple immune collapse”, initial T cell depletion weakens the antigen response, immune regulatory imbalance (reduced helper/suppressor ratio) disrupts homeostasis, and memory response deficits (decreased EM CD4+T) hinder recall immunity. Infection risk was found to stem from specific immune dysregulation rather than neutropenia alone. Expansion of EM CD8+ T-cells indicates terminal differentiation or mitochondrial dysfunction, which reduces anti-pathogen capacity; loss of transitional B-cells (regulatory precursors) diminishes IL-10-mediated immune control; and PD-1+CD4+ T cells signify T-cell exhaustion. Reduced EM T cells, impaired Th1 polarization, and PD-1+ T cells converge to create a high-risk infection-prone DLBCL microenvironment, further exacerbated by transitional B-cell loss. Moreover, EM CD8+ T cells and Th17 TFH cells their logistic combination significantly improved predictive power (AUC=0.753), establishing a potential composite biomarker. In addition, this work defines a novel “Effector CD8+ T - Transitional B Cell” immune axis. It offers a paradigm for personalized DLBCL management with implications for risk-adapted prophylaxis.

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2025
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