Engraftment effects after intra-bone marrow versus Intravenous allogeneic stem cell transplantation in a reduced-intensity conditioning Dog leukocyte antigen-identical canine model

Following conventional i.v. hematopoietic stem cell transplantation (IV-HSCT), most of the hematopoietic stem cells get trapped in peripheral organs and do not reach the bone marrow niche. A promising approach to overcome this cell loss during the homing process seems to be the infusion of hematopoietic stem cells directly into the bone marrow cavity (intra-bone marrow [IBM]-HSCT). This study aimed to investigate the engraftment efficiency of IBM-HSCT compared with IV-HSCT following reduced-intensity conditioning in a canine HSCT model. Furthermore, the impact of 2 different graft infusion rates during IBM-HSCT on the engraftment was evaluated. Dogs received 4.5 Gy total body irradiation for conditioning at day -1 and 15 mg/kg cyclosporin A twice daily at days -1 to +35 as immunosuppression. The IV-HSCT group (n = 7) received unmodified bone marrow. The IBM-HSCT cohorts received buffy coat-enriched bone marrow that was applied into the humerus and femur simultaneously with an infusion time of either 10 minutes (IBM10; n = 8) or 60 minutes (IBM60; n = 7). Statistical analyses were performed using the Kruskal-Wallis test followed by the Mann-Whitney U test with Bonferroni correction for multiple comparisons. Statistical significance was declared at Bonferroni-adjusted P < .017. All dogs initially engrafted. One dog of the IBM10 cohort died at day +15 from infection. All 21 evaluable dogs developed a durable mixed donor chimerism over the course of 112 days. Engraftment kinetics did not differ significantly across the 3 groups. Leukocyte and platelet nadirs, as well as the durations of leukopenia and thrombocytopenia, were comparable in the 3 groups. Signs of toxicity for ingestion, body temperature, activity, and defecation did not show statistically significant differences among the 3 groups; only weight loss was greater in the IBM60 group compared with the IV group. IBM-HSCT following reduced-intensity conditioning resulted in an engraftment efficiency and hematopoietic recovery comparable to that seen with conventional IV-HSCT. In addition, modification of the graft infusion rate had no impact on engraftment and hematopoietic recovery in the canine IBM-HSCT model.