Definition of a critical T cell threshold for prevention of GVHD after HLA non-identical PBPC transplantation in children

Abstract

Summary:The aim of this study was to reduce the rate of graft failure after HLA non-identical stem cell transplantation by using G-CSF mobilized CD34 ؉ peripheral blood progenitor cells (PBPC), either in combination with bone marrow or as single grafts. To prevent GVHD, PBPC were highly purified, resulting in a 5 to 6 log T cell depletion. In additon to T cell depletion no further GVHD prophylaxis was used. We transplanted 23 pediatric patients with life-threatening malignant or non-malignant hematological disorders, who had no available matched donor. Engraftment was obtained in 18 of 21 evaluable patients. Five patients developed acute GVHD of grade II and III, which became chronic in four cases and was fatal in four. The use of highly purified PBPC allowed the exact quantification of residual T cells in the grafts and a strict correlation between the residual T cell load and the development of GVHD was observed: patients with GVHD had received numbers of T cells between 8 and 20 ؋ 10 4 /kg, whereas patients without GVHD were grafted with T cell numbers ranging from 0.7 to 6.0 ؋ 10 4 /kg. We therefore clearly demonstrate that a residual T cell content of Ͻ5 ؋ 10 4 /kg is safe for prevention of GVHD after HLA non-identical PBPC transplantation in children. Keywords: HLA non-identical transplantation; peripheral blood progenitor cells; grafted T cell number; GVHD HLA haplo-identical BMT with T cell depletion (TCD) has been used successfully to treat children with primary immunodeficiency disorders. [1][2][3] In patients with other diseases, this transplant approach has frequently failed because of graft rejection. [4][5][6] Graft failure may result from the profound T cell depletion required to prevent GVHD, with the ensuing loss of the graft-enhancing effect mediated by T cells. 7,8 More intensive immunosuppressive conditioning to counterbalance this disadvantage has usually had limited success because of significant complications from toxicity. Less vigorously T cell-depleted grafts carry the risk of severe GVHD. From animal models it is clear that engraftment may also be improved by increasing the number of grafted cells, either using unmanipulated bone marrow, taking advantage of the effect of alloreactive T cells or, as shown in recent studies, by using high numbers of highly purified T cell-depleted stem cells. 9 The latter approach was used by Aversa et al to transplant patients with leukemia from HLA non-identical family donors using either a combination of purified peripheral blood progenitor cells (PBPC) and T cell-depleted marrow or, in more recent patients, PBPC alone. 10-12 A remarkably high engraftment rate of more than 90% was observed.Here we report results of a pilot study in pediatric patients, where we explored a comparable transplant approach. Like the findings of Aversa et al, we observed a high engraftment rate of 86%. In contrast, GVHD developed in the initial patients, but was completely preventable in patients receiving grafts containing fewer T cells than 5 ϫ 10 4 /kg. Patients and meth...

Outcome of alloanergized haploidentical bone marrow transplantation after ex vivo costimulatory blockade: results of 2 phase 1 studies

“…Steroid-refractory aGVHD only occurred in 2 patients (9%), despite a median T-cell dose 2 logs greater than the dose (8-20 ϫ 10 4 /kg) at which 30% of children undergoing nsTCD haploidentical HSCT were observed to develop steroid-refractory GVHD and 3 logs above a published threshold dose below which severe aGVHD was reliably prevented in the haploidentical setting. 34,35 AGVHD did not occur more often in those patients receiving CD3 ϩ , CD4 ϩ , or CD8 ϩ T cell doses above median levels, and although alloreactive precursor frequency data were available on a relatively small proportion of patients, we also did not see an association between residual in vitro CD4 ϩ alloresponses and aGVHD occurrence. A potential explanation for this observation might be that residual alloresponses after alloanergization are mediated in vivo by CD28 Ϫ donor T cells (which are predominantly CD8 ϩ ), ␥␦ T cells, or successfully alloanergized CD4 ϩ donor T cells that had their anergic state temporarily reversed by high levels of cytokines in vivo.…”

Combined positive and negative cell selection from allogeneic peripheral blood progenitor cells (PBPC) by use of immunomagnetic methods

“…[10][11][12][13] However, in recipients of HLAmismatched or haploidentical donor grafts, a higher TCD of the graft may be required to avoid aGVHD. 2,3 Methods that allow additional T cell removal from the purified CD34 + cell product combining both CD34 positive and T negative cell selections (positive/negative selection, +/− selection) are of clinical relevance. In this sense, CD34 + cell-enriched components obtained with the Isolex 300i device leave cell surface antigens intact and free of surfacebound reagent and allow additional rounds of negative cell selection.…”

“…Nevertheless, these approaches result in T cell numbers in the graft that may still trigger GVHD, particularly in transplants across HLA barriers. 2,3 A new approach to reduce the high numbers of T cells present in the allo-PBPC grafts is CD34 + cell selection. Various methods have been developed for CD34 + cell purification in the clinical setting.…”

“…Bone Marrow Transplantation ( The development of HLA-mismatched or haploidentical donor stem cell transplantation requires a high degree of T cell depletion (TCD) while preserving an adequate number of CD34 + cells in the graft in order effectively to prevent acute graft-versus-host disease (aGVHD) and ensure engraftment. [1][2][3] Several reasons make CD34 positive cell selection methods (positive selection, + selection) particularly attractive to deplete T cells especially in peripheral blood progenitor cell (PBPC) grafts: they can be applied to the large numbers of cells present in PB, they are able to preserve adequate numbers of progenitors after selection, thus maintaining the potential benefits of a PBPC transplant in this setting and they passively deplete the elevated numbers of T cells present in the PB grafts.Several methods are available for positive selection. 4-7 The immunomagnetic technique, which is now exploited by the Isolex 300i cell selection technology (Nexell Therapeutics, Irvine, CA, USA), involves specific binding of target cells by a mouse anti-CD34 MoAb, 9C5.…”

“…[1][2][3] Several reasons make CD34 positive cell selection methods (positive selection, + selection) particularly attractive to deplete T cells especially in peripheral blood progenitor cell (PBPC) grafts: they can be applied to the large numbers of cells present in PB, they are able to preserve adequate numbers of progenitors after selection, thus maintaining the potential benefits of a PBPC transplant in this setting and they passively deplete the elevated numbers of T cells present in the PB grafts.…”