Low incidence of agvhd with ptcy, tacrolimus and post-engraftment low dose ATG-based GvHD prophylaxis in haplo-identical donor transplantation and establish of new predict score for grade II-iv agvhd

Abstract Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative therapy for hematological malignancies while acute graft-versus-host disease (aGvHD)-associated mortality and morbidity remain major concerns. Excessive GvHD prophylaxis decreases the incidence of GvHD while increases the risk of infection and relapse, underscoring the need for risk-stratified approach. So far, strategies based on biomarkers or clinical features mostly focus on response to systemic steroid or prediction of aGvHD-associated mortality. Reliable models for prediction of aGvHD occurrence remain lacking. Post-transplantation cyclophosphamide (PTCy) and anti-thymocyte globulin (ATG) have both exerted effective protection against GvHD in haplo-identical HSCT. We previously reported a low incidence of aGvHD with a prophylaxis regimen, named “Ruijin protocol”, combining PTCy, tacrolimus and post-engraftment low dose ATG. In the present study, we aim to validate this observation and figure out clinical risk factors for aGvHD under this specific prophylactic regimen in an expanded cohort. At first, a total of 210 subjects undergoing their first allogeneic HSCT for hematological malignancies with haplo-identical related donors from September 2019 to December 2023 at our center were included. All the subjects received Ruijin protocol consisting of PTCy at a cumulative dose of 100 mg/kg or 80 mg/kg on days 3 and 4, tacrolimus at a dose of 0.05 mg/kg/day from day 5 onward, and a single dose of 2.5 mg/kg ATG after neutrophil engraftment. The incidence of 100-day grade II-IV and III-IV aGvHD were 14.0±2.5% and 3.2%±1.3% respectively. To identify risk factors for aGvHD, variables reported to be risk factor for aGvHD in literature or considered critical to Ruijin protocol, such as transplant conditioning intensity, sequential transplantation, dose of PTCy, recipient age (<55 versus ≥55 years old), donor age (<37 versus ≥37 years old), disease status before transplant, female donor for male recipient, second-degree donor, CD34+ cell dose, CD3+ cell dose, were included in univariate and multivariate analysis. In univariate analysis, donor age (≥37) and CD34+ cell dose (<9.2x106/kg) were correlated with higher incidence of grade II-IV aGvHD. These two variables were then identified as independent predictors for grade II-IV aGvHD in multivariate analysis. Based on these 2 parameters, we developed the Ruijin score, which stratified patients into three risk groups: score 0 with 7.8%±3.1% grade II-IV aGvHD, score 1 with 18.3%±4.8% and score 2 with 34.8%±9.2% (p=0.003). To examine the discrimination performance of Ruijin score, we used 1000-fold bootstrap as internal validation and the AUC and bias-corrected 95% CI of AUC under competing risk model with Fine-Gray method was 0.714 (0.678-0.750). We then confirmed both the low incidence of aGvHD and the performance of Ruijin score in an independent multicentric validation cohort with 127 subjects receiving Ruijin protocol for haplo-identical HSCT. In the validation cohort, the cumulative 100-day incidence of grade II-IV and grade III-IV aGvHD was 15.6%±3.3% and 5.1%±2.1%, respectively. The incidence of grade II-IV aGvHD was 2.6%±2.6% for score 0, 22.2%±6.1% for score 1, and 44.1%±2.6% for score 2 (p=0.002). In conclusion, the Ruijin protocol achieves potent GvHD prophylactic efficacy, and the simple two-variable Ruijin score, derived from this platform, accurately stratifies HSCT recipients into low-, intermediate-, and high-risk groups for grade II-IV aGvHD. Prospective evaluation of Ruijin score is warranted within other PTCy-based prophylactic protocols and would further pave the way to future development of individualized GvHD prophylaxis based on risk stratification.