Efficacy of low-dose rituximab as preemptive treatment of EBV-DNA-emia after allogeneic hematopoietic stem cell transplantation

Abstract Introduction: Epstein-Barr virus (EBV) reactivation is a common complication following allogeneic hematopoietic stem cell transplantation, with potential progression to PTLD. To prevent EBV-related diseases, the European Conference on Infections in Leukemia recommends regular post-transplant EBV-DNA-emia monitoring and early intervention with preemptive therapy, including rituximab (RTX) and reduction of immunosuppression. RTX is typically administered with 375mg/m² until EBV clearance, while no robust clinical trails confirmed the necessity of this high-dose regimen. Given that RTX may impair post-transplant immune reconstitution and increase infection risk, and considering that EBV-DNA emia primarily occurs within the first four months after allo-HSCT, with high EBV viral load being a risk factor for the development and increasing RTX administration frequency. We hereby report the efficacy and safety of fixed low-dose RTX (100 or 200 mg per dose) in high-risk patients with low-load EBV-DNA-emia who received ATG-containing conditioning regimens. Methods: Among 1755 consecutive patients who received ATG-containing regimens for allo-HSCT at the First Affiliated Hospital of Soochow University between January 2019 and March 2022, we included 77 patients who received fixed low-dose preemptive RTX for EBV-DNA-emia within four months post-transplant in this retrospective study. Patients with a high viral load (10,000 copies/mL), probable PTLD or late-onset EBV reactivation were excluded. EBV-DNA was monitored with quantitative PCR in whole peripheral blood begins one week after stem cell infusion and was performed weekly for the first four months post-transplantation. EBV-DNA-emia is defined as detectable viremia exceeding 100 copies/mL in two consecutive measurements. Preemptive therapy with a fixed low dose of RTX (100 or 200 mg per dose). Treatment success was defined as achieving negative EBV-DNA results without subsequent development of PTLD. Results: Of 77 patients, 51 cases received 100mg of RTX, while 26 patients received 200mg. 66 patients received haplo-HSCT, 11 patients received URD-HSCT. The median time from transplantation to the first dose of RTX was 51 days (range, 18-113) and median EBV load at RTX initiation was 2260 copies/mL (range,212-9210). Of the 76 evaluable patients, 70 achieved viral clearance (92.1%, 95%CI, 85.9%-98.3%). The clearance rate was similar between the two cohort: 92% (84.2% to 99.8%) in the 100mg RTX cohort, 92.3% (81.3% to 100%) in the 200mg cohort. In the 100mg group, 28 patients tested negative after 1 dose, and 15 patients after 2 doses, while the corresponding numbers in the 200mg group were 8 and 12, respectively. Patients tolerated RTX treatment well, with no treatment discontinuations due to adverse events. Among the 77 patients, 43 underwent peripheral blood B-cell quantification by flow cytometry before and approximately two weeks after initiating RTX therapy. Of these, 41 achieved near-complete CD19+ B-cell depletion. Two (2.6%) patients developed PTLD. The median follow-up time was 44.2 (range,1.5 - 71.4) months. The 3-year OS, NRM and CIR were 70.7% (95%CI, 61.1% - 81.8%), 15.3% (95%CI, 6.0%- 23.6%), and 24.3% (95% CI, 13.5%- 33.8%). Three-year overall survival (100mg: 67.4%; 200mg: 76.9%, P=0.47), non-relapse mortality (100mg: 18.4%; 200mg: 8.9%, P=0.24), and cumulative relapse incidence (CIR) (100mg: 22.2%; 200mg: 28.2%, P=0.35) were statistically similar between two cohorts. In univariate and multivariate analyses, patients with an EBV load ≥2260 copies/ml demonstrated a tendency towards a poorer CIR (HR=0.43, 95%CI =0.16-1.15; P= 0.094). Clinically significant grade II-IV aGVHD occurred in 10 patients (13%) at day 100 after transplantation, with median onset of 44.5 (range 23-98) days. 5 patients developed EBV-viremia in the setting of grade II-IV aGVHD. Among 74 patients who survived for at least 100 days, chronic GVHD was diagnosed in 20 (27 %) patients, with the median onset of 5.8 (3.3-32.2) months. The cumulative incidence of chronic GVHD at third year was 29.1%. No statistically significant difference was observed in the incidence of cGVHD between the two dosage groups. (P=0.55). Conclusions: Low-dose RTX achieved a high EBV clearance rate (92%) with minimal toxicity, supporting its potential as an effective and safer alternative to the conventional high-dose regimen (375 mg/m²). prospective randomized multicentric trial with larger number of patient is needed.