Improved immune recovery after transplantation of TCRαß/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 αß 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-TCRαß 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.

Favorable NK cell activity after haploidentical hematopoietic stem cell transplantation in stage IV relapsed Ewing's sarcoma patients.

Natural killer (NK) cell activity has been shown to have potential activity against Ewing's sarcoma (EWS) especially in tumors with low HLA I expression and high NKG2D expression. Two patients with metastatic relapsed and primary metastatic stage IV EWS who had received two courses of high dose chemotherapy with autologous stem cell rescue were transplanted from a haploidentical parental stem cell donor. Patients are alive in ongoing CR for 10.2 and 3.4 years now. Post transplant local second and first relapses were treated successfully in both patients. In vivo IL-2 stimulation not only increased the number and activity of effector cells in one patient but was also associated with severe GvHD. In vitro studies demonstrated high NK cell activity against K562 and relevant activity against EWS cell line A673 post transplant. NK activity was enhanced by cytokine prestimulation as well as by EWS targeting anti-GD2 Ab. Haploidentical hematopoietic stem cell transplantation (HSCT) might contribute to long-term survival by NK cell-mediated effect exerted by donor-derived NK cells. Local tumor recurrence was manageable in both high-risk patients indicating systemic immune control preventing subsequent metastasizing. The efficacy of haploidentical HSCT, cytokine application and tumor targeting antibodies for the use of Ab-dependent cellular cytotoxicity needs evaluation in clinical trials.

Cytolytic activity of NK cell clones against acute childhood precursor-B-cell leukaemia is influenced by HLA class I expression on blasts and the differential KIR phenotype of NK clones.

Relapse after allo-SCT in patients with acute leukaemia remains a major problem. A beneficial impact of alloreactive natural killer (NK) cells has been reported for myeloid malignancies, but has been questionable for B-lineage ALL. We analysed lysis of primary paediatric precursor-B-ALL blasts by 285 NK cell clones to investigate whether HLA class I expression on the blasts and phenotypic killer cell Ig-like receptor (KIR) expression on NK cells affect the lytic activity against ALL blasts. Precursor-B-ALL blasts with low HLA-I expression were lysed by a majority (79%) of NK cell clones, whereas those with high HLA-I expression showed low susceptibility to NK clones independent of their KIR expression patterns. NK cell activity against susceptible blasts was regulated by differential surface expression of the three major KIRs (CD158a, CD158b, CD158e). NK clones with none of these three KIRs or a single KIR that recognized no ligand, were not inhibited by the targets and exerted higher lysis (P = <0.0005) in comparison to NK clones expressing KIRs with a ligand on the ALL blasts. In conclusion, the quantity of HLA-I expression on precursor-B-ALL blast regulates overall NK cell susceptibility; in case of reduced HLA expression, differential surface expression of KIRs affects NK cell alloreactivity against those blasts.