In haploidentical (haplo)-cord blood (CB)
transplantations, early haplo donor engraftment serves as a myeloid bridge to sustainable CB engraftment and is associated with early neutrophil recovery. The conditioning regimens as published for haplo-cord protocols usually contain serotherapy, such as
rabbit antithymocyte globulin (ATG) (
Thymoglobulin, Genzyme, Cambridge, MA). However, reducing or omitting serotherapy is an important strategy to improve early immune reconstitution after
transplantation. The need for serotherapy in successful haplo-cord
transplantation, defined as having a haplo-derived myeloid bridge to CB engraftment, has not been investigated before. Two consecutive cohorts of patients underwent
transplantation with haplo-CB. The first group underwent
transplantation with haplo-CB for active
infection and/or an underlying condition with expected difficult engraftment without a conventional donor available. They received a single unit (s) CB and haplo donor cells (CD34(+) selected, 5 × 10(6) CD34(+)/kg). The second cohort included patients with poor-risk
malignancies, not eligible for other treatment protocols. They received a sCB and haplo donor cells (CD19/αβTCR-depleted; 5 × 10(6) CD34(+)/kg). Retrospectively in both cohorts, active ATG (
Thymoglobulin) levels were measured and post-hematopoietic
cell transplantation area under the curve (AUC) was calculated. The influence of ATG exposure for having a successful haplo-myeloid bridge (early haplo donor engraftment before CB engraftment and no secondary
neutropenia) and
transplantation-related mortality (TRM) were analyzed as primary endpoints. Twenty patients were included (16 in the first cohort and 4 in the second cohort). In 58% of evaluable patients, there was no successful haplo-derived myeloid bridge to CB engraftment, for which a low post-
transplantation ATG exposure appeared to be a predictor (P <.001). TRM in the unsuccessful haplo-bridge group was 70% ± 16% versus 12% ± 12% in the successful haplo-bridge group (P = .012). In conclusion, sufficient in vivo T depletion with ATG is required for a successful haplo-myeloid bridge to CB engraftment.