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Natural killer cell activity influences outcome after T cell depleted stem cell transplantation from matched unrelated and haploidentical donors

https://doi.org/10.1016/j.beha.2011.04.009Get rights and content

Lytic activity and recovery of natural killer (NK) cells was monitored in pediatric patients with leukemias (ALL, AML, CML, JMML) and myelodysplastic syndromes after transplantation of T cell depleted stem cells from matched unrelated (n = 18) and mismatched related (haploidentical, n = 29) donors. CD34 + selection with magnetic microbeads resulted in 8 × 103/kg residual T cells. No post-transplant immune suppression was given. NK cells recovered rapidly after transplantation (300 CD56+/μL at day 30, median), whereas T cell recovery was delayed (median: 12 CD3+/μL at day 90). NK activity was measured as specific lysis of K 562 targets several times (mean: 3 assays per patient). Four temporal patterns of lytic activity could be differentiated: consistently low, consistently high, decreasing and increasing activity. Patients with consistently high or increasing activity had significantly lower relapse probability than patients with consistently low or decreasing levels (0.18 vs 0.73 at 2 years, p < 0.05). The subgroup of patients with ALL showed similar results (0.75 vs 0.14 at 2 years, p < 0.05). Speed of T cell recovery had no influence. These data suggest that both achieving and maintaining a high level of NK activity may contribute to prevent relapse. Since NK activity could be markedly increased by in vitro stimulation with Interleukin 2 (IL-2), in vivo administration should be considered.

Introduction

Transplantation of T cell depleted peripheral stem cells from mismatched related donors as well as from matched or partially matched unrelated donors has become an option for the treatment of children with high risk and relapsed acute lymphoblastic leukemias (ALL) *[1], [2], *[3]. Graft versus host disease (GvHD) and GvHD-related mortality has been reduced significantly by positive selection of CD34+ progenitors and other T cell depletion techniques, but relapses still remain a major problem after successful transplantation *[4], [5]. Recovery of T cells has been reported to be delayed due to graft manipulation [6]. This was also observed in our patients transplanted with CD34+ selected stem cells from both haploidentical family donors and matched unrelated donors. Therefore, we investigated the role of the more rapidly regenerating donor derived NK cells for post-transplant anti-leukemic effects *[3], *[4].

Natural killer cells lyse several types of malignant cells, and the extent of lysis depends on several effector and target cell related factors. Two of the most important factors are the absolute levels of HLA class I molecules expressed by the target cells and the presence or absence of incompatibilities between inhibitory killer cell immunoglobulin-like receptors (KIRs) of NK cells and their HLA class I ligands. In particular, cells with reduced HLA class I expression, including solid tumors, lymphomas and leukemias, are valid targets for lysis by NK cells *[7], [8]. Those cells have clearly been shown in vivo to provide a first line defense against malignant transformation. Moreover, changes in NK cell activity appeared to be of significance in several malignant conditions and in particular reduced NK activity was reported to preceed relapse in acute leukemia [9], [10]

Consequently, we monitored the temporal development of NK cell mediated anti-leukemic activity in patients after transplantation of highly T cell depleted stem cells and investigated whether NK activity (measured over a longer time period) would influence the risk of relapse in leukemias and myelodysplastic syndromes.

Section snippets

Patients

Temporal development of NK cell activity was measured in 47 pediatric patients. The diagnoses were: ALL (n = 27), AML/MDS, CML/JMML (n = 17) and lymphomas (n = 3; Table 1). 18 patients had matched unrelated donors and 29 had full haplotype mismatched related donors. Median age was 8.6 years. All patients received T cell depleted grafts. The CLINIMACS device (Miltenyi Biotec, Bergisch Gladbach, Germany) was used for positive selection of CD34+ peripheral stem cells. The patients received a

Immune reconstitution of NK- and T-cells after transplantation

Reconstitution of CD3+ and CD56+CD16+ lymphocytes after transplantation with CD34+ selected cells was monitored by flow cytometry for all patients. Mean values of CD3+ remained below 100 cells/μl in the first three months after transplantation (median cell count: 12/μL at day 90) and returned to the normal range after approximately two years. By contrast, the recovery of CD56+ NK cells was rapid: a clear NK cell peak was observed as early as 1 month after transplantation (median cell count:

Discussion

Transplantation of positive selected hematopoietic stem cells has gained wide acceptance in the treatment of leukemias and several nonmalignant diseases *[4], [12], [13]. The method is a fundamental prerequisite for haploidentical transplantation from mismatched related donors, since profound depletion of T and B cells facilitates the prevention of GvHD and EBV LPD *[3], [5], [14], *[15] and it remains an interesting option also in matched donor transplantation. Our experience has shown CD34+

Conflict of interest

The authors of this paper have no conflicts of interest.

Acknowledgments

We thank Ulrike Krauter and Anni Babarin-Dorner for excellent technical assistance. We are thankful to Drs. Barbara Lang and David D. Martin for critical review of the manuscript.

This work was supported by grants (SFB 685 and TransarNet) from the Deutsche Forschungsgemeinschaft (DFG) and from the Bundesministerium fuer Bildung und Forschung (BMBF) and from the Reinhold Beitlich Stiftung to P.L.

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