Improved immune recovery after transplantation of TCRαβ/CD19-depleted allografts from haploidentical donors in pediatric patients

Immune recovery was retrospectively analyzed in a cohort of 41 patients with acute leukemia, myelodysplastic syndrome and nonmalignant diseases, who received αβ T- and B-cell-depleted allografts from haploidentical family donors. Conditioning regimens consisted of fludarabine or clofarabine, thiotepa, melphalan and serotherapy with OKT3 or ATG-Fresenius. Graft manipulation was carried out with anti-TCRαβ and anti-CD19 Abs and immunomagnetic microbeads. The γδ T cells and natural killer cells remained in the grafts. Primary engraftment occurred in 88%, acute GvHD (aGvHD) grades II and III-IV occurred in 10% and 15%, respectively. Immune recovery data were available in 26 patients and comparable after OKT3 (n=7) or ATG-F (n=19). Median time to reach >100 CD3+ cells/μL, >200 CD19+ cells/μL and >200 CD56+ cells/μL for the whole group was 13, 127 and 12.5 days, respectively. Compared with a historical control group of patients with CD34+ selected grafts, significantly higher cell numbers were found for CD3+ at days +30 and +90 (267 vs 27 and 397 vs 163 cells/μL), for CD3+4+ at day +30 (58 vs 11 cells/μL) and for CD56+ at day +14 (622 vs 27 cells/μL). The clinical impact of this accelerated immune recovery will be evaluated in an ongoing prospective multicenter trial.