Cytomegalovirus (CMV) infection remains a critical cause of mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT), despite improvement by pre-emptive antivirus treatment. CMV-specific cytotoxic T lymphocytes (CMV-CTL) are universally used and proven well-tolerance after allo-HSCT in adult clinical trials. However, it is not comprehensively evaluated in children’s patients. Herein, we conducted a retrospective study to determine the risk factors of CMV infection and evaluation of CMV-CTL in children patients who underwent allo-HSCT. As result, a significantly poor 5-year overall survival was found in the CMV infection group (87.3 vs. 94.6%, p=0.01). Haploidentical HSCT (haplo-HSCT) was identified as an independent risk factor for CMV infection through both univariate and multivariate analyses (p<0.001, p=0.027, respectively). Furthermore, the cumulative incidence of CMV infection was statistically higher in the haplo-HSCT group compared to the HLA-matched donor group (44.2% vs. 21.6%, p<0.001). Finally, the overall response rate of CMV-CTL was 89.7% (26/29 patients) in CMV infection after allo-HSCT. We concluded that CMV infection following allo-HSCT correlated with increased mortality in children’s patients, and haplo-HSCT was an independent risk factor for CMV infection. Adoptive CMV-CTL cell therapy was safe and effective in pediatric patients with CMV infection.

Background: For patients without HLA matched donor, Haploid stem cell transplantation with PTCY method has relatively higher risk of relapse and graft-versus-host disease (GVHD). Umbilical cord blood (UCB) is readily available and has helped expand the donor pool to almost all patients requiring a transplant. Meanwhile UCB transplant improves EFS in leukaemia with lower risk of relapse and GVHD. However, the clinical application of UCB is limited due to lower implantation rate because of its low dose of stem cells than other sources of hematopoietic stem cells (HSC). Aims: This study is to explore the feasibility and efficacy of post-transplantation fludarabine and cyclophosphamide to select and promote the unrelated UCB to engraft in combined transplantation of haploid and UCB stem cells for the treatment of childhood and adolescent leukemia. Methods: Total 40 children and adolescent patients with leukemia in Nanfang Hospital and Shenzhen Children's Hospital enrolled this study from Sept.2019 to Jun.2021. These patients were diagnosed as AML (20 HR, 5 IR, 2 relapsed AML), ALL (5 HR, 2 IR, 2 relapsed ALL), AL (1), JMML (2), MDS (1) and BPDCN (1) with a median age of 80 months (range 7 months -17 years). The biggest body weight reached to 77kg. The haploid stem cell was 5/10-9/10 mismatched and UCB was selected as 6/10-10/10 HLA matched or mismatched. The condition regimen was busulfan+fludarabine+CY+Ara-C. Haploid PBSC was infused in day0. All received PTCy 50 mg/kg and post-transplantation fludarabine 40mg/m 2 on days 3 and 4 along with tacrolimus or cyclosporine and mycophenolate mofetil for prophylaxis of acute GVHD. UCB was infused in day6. A median of haploid stem cells of 20.00×10 8/kg (13.00-32.10) of mononuclear cells was infused while a median of UCB cells of 4.32×10 7/kg (1.48-22.78) of total nucleated cells was infused. A median of CD34+ cells of haploid stem cells 13.00×10 6/kg (1.51-32.00) was infused while a median of CD34+ cells of UCB cells 1.74×10 5/kg (0.26-4.80) was infused. The survival rate, umbilical cord blood implantation rate, hematopoietic recovery and the rate of transplant-related complications were analyzed. Results: At a median follow-up of 8 months (range 1-21 months), there were 2/40（5%）cases of transplant-related death. All surviving patients were leukemia free, with one-year overall survival rate 92.8±5.0%. Among these patients, 37/40(92.5%, 95%CI: 84.0%~100.0%) of patients achieved complete chimerism of unrelated UCB cells and 3/40(7.5%, 95%CI: -1.0%~16.0%) of patients achieved mixed chimerism of unrelated UCB cells and haploid cells. In these transpltantation, the CD34+ cell dose of UCB less than 1.0×10 5/kg accounted for 10/40 (25.0%), and less than 2.0×10 5/kg accounted for 23/40 (57.5%).Two patients had primary poor graft function. Neutrophil reconstitution was achieved in 39/40 patients with a median time of 29 days (range 17 - 44 days) without G-CSF after transplantation. Platelet recovery was achieved in 37/40 patients with a median time of 37 days (range 8-92 days). There was a significant linear relationship between platelet recovery time and the dose of total nucleated cells and CD34+ cells in UCB（r=-0.368, P=0.025; r=-0.355, P=0.031）.The incidence of gradeⅠand gradeⅡGVHD was 32.5%（95%CI:17.3%-47.7%）and 42.5%（95%CI:26.5%-58.5%）, respectively. There was no grade Ⅲ-Ⅳ aGVHD and only 1/40(2.5%) case of extensive chronic GVHD. The incidence of chronic limited GVHD was 22.5% (95%CI: 9.0%-36.0%). Twenty-four of 40(60.0%, 95%CI:44.1%-75.9%) patients experienced clinically significant CMV reactivations or infections. One of 40（2.5%, 95%CI: -2.6%-7.6%）patients experienced EB virus reactivation. Two of 40（5.0%, 95%CI: -2.1%-12.1%）patients experienced human herpesvirus 6 infection. Thirteen of 40（32.5%, 95%CI: 17.3%-47.7%）patients presented with hemorrhagic cystitis. Conclusion: In our primary clinical study, post-transplantation fludarabine and cyclophosphamide could effectively select and promote the unrelated UCB to implant rather than haploid cells in combined transplantation of haploid and UCB stem cells even if the CD34+ cells of UCB less than 1.0×10 5/kg. Although acute GVHD was common but just milder degree and with lower incidence of EB virus reactivation. This new strategy has the potential to promote the wilder clinical use of unrelated UCB in the treatment of leukemia. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Purpose:Splenectomy can improve the quality of life of patients with β-thalassaemia major to some extent, but also increase some unpredictable risk.In order to understand the effects of splenectomy before transplantation on hematopoietic stem cell transplantation reconstruction time, infection, graft versus host disease and hepatic veno-occlusive disease of matched sibling and unrelated hematopoietic stem cell transplantation, the following studies were conducted. Methods:A retrospective analysis of 80 β-thalassaemia major patients in the southern hospital between January 2012 and December 2017 for matched hematopoietic stem cell transplantation, and 35 of them had a splenectomy before the transplant. Cox model adjustment, t test and χ2 test were used to compare the incidence of neutrophil implantation time, hemoglobin implantation time, platelet implantation time, infection, graft versus host disease and hepatic vein occlusion. Results:Neutrophilic granulocytes and platelets were implanted more rapidly in patients who underwent splenectomy than those who did not (P < 0.05).There was no significant difference in the incidence of infection, graft versus host disease and hepatic vein occlusion. Conclusion: For level of Ⅱ-Ⅲ β-thalassaemia major patients, hypersplenism can cause delayed reconstruction of hematopoietic stem cell transplantation, while before transplantation splenectomy to speed up the implantation of hematopoietic stem cell transplantation, and does not increase the incidence of complications after transplantation. Disclosures No relevant conflicts of interest to declare.