Model-Based Antithymocyte Globulin in αßhaplo-Hematopoietic Stem Cell Transplantation Facilitates Engraftment, Expedites T Cell Recovery, and Mitigates the Risk of Acute Graft-versus-Host Disease.

In αß T-cell/CD19 B-cell depleted hematopoietic stem cell transplantation (αßhaplo-HSCT) recipients, antithymocyte globulin (ATG; Thymoglobulin) is used for preventing graft rejection and graft-versus-host disease (GVHD). The optimal dosing remains to be established, however. Here we present the first comparative analysis of 3 different ATG dosing strategies and their impact on immune reconstitution and GVHD. Our study aimed to evaluate the effects of 3 distinct dosing strategies of ATG on engraftment success, αß+ and γδ+ T cell immune reconstitution, and the incidence and severity of acute GVHD in recipients of αßhaplo-HSCT. This comparative analysis included 3 cohorts of pediatric patients with malignant (n = 36) or nonmalignant (n = 8) disease. Cohorts 1 and 2 were given fixed ATG doses, whereas cohort 3 received doses via a new nomogram, based on absolute lymphocyte count (ALC) and body weight (BW). Cohort 3 showed a 0% incidence of day 100 grade II-IV acute GVHD, compared to 48% in cohort 1 and 27% in cohort 2. Furthermore, cohort 3 (the ALC/BW-based cohort) had a significant increase in CD4+ and CD8+ naïve T cells by day 90 (P = .04 and .03, respectively). Additionally, we found that the reconstitution and maturation of γδ+ T cells post-HSCT was not impacted across all 3 cohorts. Cumulative ATG exposure in all cohorts was lower than previously reported in T cell-replete settings, with a lower pre-HSCT exposure (<40 AU*day/mL) correlating with engraftment failure (P = .007). Conversely, a post-HSCT ATG exposure of 10 to 15 AU*day/mL was optimal for improving day 100 CD4+ (P = .058) and CD8+ (P = .03) immune reconstitution without increasing the risk of relapse or nonrelapse mortality. This study represents the first comparative analysis of ATG exposure in αßhaplo-HSCT recipients. Our findings indicate that (1) a 1- to 2-fold ATG to ATLG bioequivalence is more effective than previously established standards, and (2) ATG exposure post-HSCT does not adversely affect γδ+ T cell immune reconstitution. Furthermore, a model-based ATG dosing strategy effectively reduces graft rejection and day 100 acute GVHD while also promoting early CD4+/CD8+ immune reconstitution. These insights suggest that further optimization, including more distal administration of higher ATG doses within an ALC/BW-based strategy, will yield even greater improvements in outcomes.

Sequential Stem Cell-Kidney Transplantation in Schimke Immuno-osseous Dysplasia.

Lifelong immunosuppression is required for allograft survival after kidney transplantation but may not ultimately prevent allograft loss resulting from chronic rejection. We developed an approach that attempts to abrogate immune rejection and the need for post-transplantation immunosuppression in three patients with Schimke immuno-osseous dysplasia who had both T-cell immunodeficiency and renal failure. Each patient received sequential transplants of αß T-cell-depleted and CD19 B-cell-depleted haploidentical hematopoietic stem cells and a kidney from the same donor. Full donor hematopoietic chimerism and functional ex vivo T-cell tolerance was achieved, and the patients continued to have normal renal function without immunosuppression at 22 to 34 months after kidney transplantation. (Funded by the Kruzn for a Kure Foundation.).

Safety of hematopoietic stem cell transplantation in children less than three years of age.

Allogeneic hematopoietic stem cell transplantation (HSCT) is a standard treatment for a variety of hematologic conditions. However, very young children may experience different complications of HSCT compared to older patients. The authors retrospectively analyzed the results of 51 transplants performed on children less than 3 years of age between June 1987 and October 2005. Donors were matched-related (n = 21), partially mismatched related (n = 3), and unrelated (n = 27). The majority of patients had one or more grade III organ toxicities, but all nonrelapse deaths were attributable to infection. Perineal dermatitis was found in a large number (73%) of recipients of cyclophosphamide-based conditioning regimens. The 1-year transplant-related mortality (TRM) was 14%, but significantly declined in the more modern period. Grades II-IV acute graft-versus-host-disease (GvHD) was seen in 22% of patients, while chronic extensive GvHD developed in only 7% of patients. Relapse was seen in 40% of transplants performed for a malignant condition, most commonly in those patients not in remission at time of HSCT. The 5-year event-free survival (EFS) and overall survival (OS) were 53 and 64%, respectively. Recipients of fractionated total body irradiation (fTBI) were more likely to have at least one long-term sequelae than patients who received chemotherapy-based regimens (p = .014). These data demonstrate that HSCT can be performed safely in very young children, especially as supportive-care techniques improve. Cyclophosphamide-related perineal dermatitis is a unique complication in very young children. Finally, the incidence of acute and chronic GvHD in this population is low.