[The variables affecting the time of B-cell reconstruction in children with steroid-sensitive nephrotic syndrome treated with rituximab].

<b>Objective:</b> To investigate the factors affecting the time taken for B cell reconstitution after rituximab (RTX) treatment in children with steroid-sensitive nephrotic syndrome. <b>Methods:</b> This was a retrospective cohort study. The clinical data of 42 children with SSNS who received treatment with RTX in Department of Nephrology, Rheumatology and Immunology, Children's Hospital Affiliated to Zhengzhou University between December 2019 and May 2023 were analyzed retrospectively. The data of demographics, immunosuppressant treatment and laboratory tests such as CD19⁺B cell count, urinary protein quantification were collected. The patients were divided into 2 groups, the early B cell reconstruction group and the late reconstruction group based on the average time of B cell reconstruction. A multivariate logistic regression model was used to analyze the factors impacting the timing of B cell reconstruction, and the predictive value of these factors was assessed by plotting the receiver operating characteristic (ROC) curve. <b>Results:</b> There were 42 children, with 35 males and 7 females. They were aged 3.5 (2.2, 5.9) years at the onset of PNS and (8.4±3.3) years at their first RTX treatment. The time for B cell reconstitution was (152±53) d. There were 20 children in the early reconstruction group and 22 children in the late reconstruction group. There were no statistically significant differences (all <i>P</i>>0.05) between the 2 groups in terms of the cumulative dose of steroids within 1 year before receiving RTX infusion (0.29 (0.16, 0.50) <i>vs.</i> 0.29 (0.19, 0.46) mg/(kg·d)), the percentage of children using tacrolimus before RTX (65%(13/20) <i>vs.</i> 45%(10/22)) and cumulative doses (0.04 (0.03, 0.05) <i>vs.</i> 0.03 (0.03, 0.06) mg/(kg·d)), the steroid doses at the time of RTX infusion (0.73 (0.49, 0.90) <i>vs.</i> 0.71 (0.58, 0.89) mg/(kg·d)), the percentage of children using tacrolimus at the initial RTX infusion (50% (10/20)<i>vs.</i> 41% (9/22)) and the doses (0.03 (0.02, 0.04) <i>vs.</i> 0.02 (0.01, 0.04) mg/(kg·d)), the discontinuation time of tacrolimus post-RTX infusion (71 (42, 91) <i>vs.</i> 64 (42, 91) d). A multivariate analysis revealed a correlation (<i>OR</i>=0.26, 95%<i>CI</i> 0.10-0.68, <i>P</i>=0.006) between B cell count following the second RTX infusion and the time taken for B cell reconstruction. The area under the ROC curve for B cell count after the RTX infusion in predicting the time to B cell reconstruction was 0.89 (95%<i>CI</i> 0.78-0.99, <i>P</i><0.001) and the cut-off value was 0.925×10⁶/L. <b>Conclusions:</b> The time of B cell reconstruction is not influenced by the previous or concurrent use of tacrolimus, regardless of its duration and the dosage of steroid and tacrolimus prior to the RTX infusion. Insteadly, the peripheral blood B cell count (0.925×10⁶/L) following the second RTX infusion for SSNS is identified as an independent predictor of reconstruction time, allowing for a more precise prediction and early intervention to maintain disease remission.