Early inflammatory complications after haploidentical hematopoietic stem cell transplantation with post transplant cyclophosphamide for acute leukemia: a pediatric multicenter experience.

Haploidentical hematopoietic cell transplantation (haplo-HCT) with post-transplant cyclophosphamide (PTCy) is a viable option for patients lacking a matched donor. In this setting, early inflammatory complications (EICs), such as cytokine release syndrome (CRS) and engraftment syndrome (ES), represent significant complications. Their risk factors and clinical impact, particularly in pediatric populations, remain poorly defined. This multicenter, retrospective study analyzed 102 consecutive pediatric haplo-HCT with PTCy for acute leukemia. It aimed to define EICs incidence, risk factors, and transplantation outcomes. The incidence of EICs was 21.6%, 95% CI (14.7-30.5). Use of peripheral blood stem cells (PBSC) was the sole independent risk factor, OR = 5.1, 95% CI (1.3-19.8), p = 0.017. Notably, all patients who developed CRS started CNI therapy (tacrolimus in all cases) on day 5. While not increasing initial acute GvHD (aGvHD) frequency, EICs predicted poorer response to first-line aGvHD therapy (45.5% vs. 6.9% complete response, p = 0.011) and a significantly higher risk of chronic GvHD (cGvHD) (55.6% vs. 20.6%; OR = 4.8, p = 0.008). No effect was seen on relapse, non-relapse mortality, or survival. EICs are common after haplo-HCT with PTCy and primarily associated with PBSC use. They identify a high-risk subgroup with refractory aGvHD and markedly increased cGvHD risk, supporting preferential bone marrow use, intensified monitoring and potentially novel strategies for GvHD prevention and management.