D2.390 - Evaluation of CD4⁻ CD8⁻ T Cell Population According to Patient Diagnostic Groups: A Single-Center Study

In lymphocyte subset analysis performed by flow cytometry, elevated CD4⁻ CD8⁻ T cell levels are occasionally detected. However, it is often overlooked whether this increase reflects true double-negative T (DNT; αβTCR⁺) cells or γδTCR⁺ T cells. In this study, we aimed to evaluate the CD4⁻ CD8⁻ T cell (DNT) population in patients undergoing lymphocyte subset analysis at an immunology outpatient clinic and to investigate its distribution according to diagnostic categories and its association with other immunological parameters.

A total of 316 patients who attended the Immunology and Allergy outpatient clinic of Başkent University Ankara Hospital between 2020 and 2025 and underwent lymphocyte subset analysis were retrospectively included. Eight groups were defined: primary immunodeficiencies, secondary immunodeficiencies, autoimmune diseases, allergic diseases, autoinflammatory diseases, undefined immunological disorders, and healthy controls. Intergroup comparisons were performed using non-parametric tests; when statistical significance was detected, post-hoc multiple comparison analyses were conducted. The potential effect of age was evaluated using multivariable analyses. Statistical significance was defined as p < 0.05 within a 95% confidence interval.

The median age of the cohort was 40 years (range: 16–88), with a predominance of female patients; age distribution was similar between sexes. DNT cell percentages differed significantly among diagnostic groups (p < 0.01). Compared with healthy controls, significantly higher DNT cell proportions were observed in patients with primary immunodeficiencies, secondary immunodeficiencies, autoimmune diseases, autoinflammatory diseases, and undefined immunological disorders. In contrast, DNT levels in the allergic diseases group were comparable to controls. The association between elevated DNT proportions and disease groups remained independently significant after adjustment for age.

An increase in CD3⁺ CD4⁻ CD8⁻ T cells detected in lymphocyte subset analysis may serve as a warning biomarker in clinical practice, indicating the need for further immunological evaluation.