To investigate the kinetics of T cell subsets absolute counts as a long-term monitoring tool during infections.

The clinical data of 26 kidney transplant recipients (KTRs), transplanted at Ruijin Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, with newly diagnosed infection from January 2017 to May 2021 were retrospectively analyzed (infection group, infections occurred between 1 month and 240 months post-transplant). A total of 129 healthy KTRs without infection from matching post-transplant periods were selected as a control group. T cell subsets CD3⁺ , CD4⁺ , and CD8⁺ absolute counts in peripheral blood were continuously or periodically measured in the infected group, and then compared with the data of the control group. Afterward, the infected and control groups were each further split into 6 subgroups according to the sampling time post-transplant. Then we analyzed the kinetics of T cell subsets absolute counts between each control subgroups, and the difference between each infected subgroup and their corresponding control subgroup. Normally distributed data were compared using two independent samples t-test and one-way ANOVA. Non-normally distributed data were compared using Mann-Whitney U test. Nominal data were compared using χ² test. Receiver operating characteristic (ROC) curves were used to analyze the optimal cut-off value of absolute T cell subset counts in determining patients at risk of infectious diseases following renal transplantation. P<0.05 was considered statistically significant.

No difference was found between the CD4⁺ /CD8⁺ ratio of the infected group (1.2±0.5) and that of the control group (1.3±0.6) (t=0.610, P>0.05). The CD3⁺ , CD4⁺ , and CD8⁺ T cells absolute counts of the infected group were significantly lower than those of the control group [(367±212), (189±117), and (161±92) cells/μL vs (1, 374±663), (695±334), and (626±377) cells/μL, respectively] (t=14.036, 13.541 and 12.311, all P values<0.05). No significant difference was found in the CD3⁺ , CD4⁺ , and CD8⁺ T cells absolute counts across the 6 subgroups of the infected group (all P values >0.05). However, the CD3⁺ , CD4⁺ , and CD8⁺ T cells absolute counts of the control subgroup 1 were lower than those of the control subgroup 5 (all P values <0.05). The best cut-off values of CD4⁺ , CD8⁺ , and CD3⁺ determined from the ROC curves analysis in this patient population were 712, 362, and 255 cells/μL, with a sensitivity of 94.6%, 92.2%, and 96.1%, and specificity of 92.3%, 96.2%, and 88.5%, respectively.

Low T cell subsets absolute counts may be regarded as a potential risk factor for developing opportunistic infections and a biomarker with meaningful predictive value.