Introduction: Approximately 50% of heart transplant recipients receive induction therapy. According to the guidelines of the International Society for Heart and Lung Transplantation (ISHLT), the target CD3 count ranges from 25 to 50 cells/mm³ when rabbit antithymocyte globulin (rATG) is used as induction therapy. This study aimed to assess the association between CD3 count levels and biopsy-proven acute rejection (BPAR) at 3 months post-heart transplant in patients receiving rATG induction therapy.
Method: This retrospective study was conducted at a medical center from January 2016 to December 2022. Patients over 20 years old who underwent their first heart transplant and received rATG induction therapy were included. Postoperatively, rATG was administered at a dose of 0.75-1 mg/kg/day for 3-5 days, with CD3 counts monitored after each dose. Patients achieving CD3 counts < 50 cells/mm³ were categorized into the high-intensity (HI) group, while those with counts between 50-150 cells/mm³ were classified into the low-intensity (LI) group. BPAR at 3 months post-transplant and cytopenia (WBC < 3,000 cells/mm³ or platelet < 70,000 cells/mm³) were compared between groups. Multivariate logistic regression models were used to assess the association between BPAR and the intensity of rATG induction. Receiver operating characteristic (ROC) curve analysis was conducted to determine a cut-off point for cytopenia.
Results: A total of 104 heart transplant recipients were included, with 77 patients (74.0%) in the HI group, 22 patients (21.2%) in the LI group, and 5 patients (4.8%) with CD3 counts >150 cells/mm³. Baseline characteristics did not significantly differ between the two groups. The mean cumulative rATG dosage was significantly higher in the HI group compared to the LI group (1.57±0.53 mg/kg vs 1.32±0.51 mg/kg, P=0.02). The overall rate of any grade BPAR at 3 months post-transplant was 17.2%, with 16 patients (20.8%) in the HI group and 2 patients (9.1%) in the LI group (P=0.35). The proportions of ≥ grade 2 BPAR were comparable between the HI and LI groups (1.3% vs 4.6%, P=0.40). In the multivariate logistic regression model, the intensity of rATG induction was not associated with any grade BPAR at 3 months post-transplant. A trend of a higher proportion of cytopenia was observed in the HI group compared to the LI group (42.9% vs 27.3%, P=0.22). The ROC analysis suggested that a cumulative rATG dosage exceeding 0.91 mg/kg was likely to increase the risk of cytopenia (71.3% sensitivity and 46.8% specificity, P=0.04).
Conclusion: There was no significant difference in BPAR at 3 months post-heart transplant between patients with CD3 counts < 50 cells/mm³ and those with counts between 50 and 150 cells/mm³ when using rATG induction therapy.