- Top of page
- Materials and methods
- Authors contributions
- Conflict of interest
There is little information published comparing peripheral blood stem cells (PBSC) with bone marrow (BM) as the stem cell source in the long-term outcome in recipients of T-cell depleted (TCD) unrelated donor (UD) transplants. We present retrospective outcome data on 306 recipients of myeloablative, human leucocyte antigen-matched UD allografts using pre-transplant in-vivo Alemtuzumab. Transplants were performed between 2000 and 2007 for chronic myeloid leukaemia in first chronic phase and acute leukaemia in first or second complete remission; 184 patients received BM and 122 PBSC. The median age was 28·9 years (<1–58) and the median follow-up was 48 months. Overall survival at 8 years was 53%. The incidence of acute graft-versus-host disease (GvHD) was significantly higher in PBSC (65%) than BM recipients (49%; P = 0·012). This represented only grade 1 GvHD with no difference in grade II–IV aGvHD (BM 23% PBSC 24%). The incidence of chronic GvHD, either overall (BM 47%, PBSC 49%) or extensive (BM 15%, PBSC 13%) was not increased with PBSC. The incidence of relapse, non-relapse mortality and survival were not significantly different. Whilst accepting the limitations of retrospective analyses, we suggest the increased risk of GvHD in recipients of PBSC in T-replete transplants is offset by in-vivo Alemtuzumab, and that either stem cell source can be used with good outcomes in this setting.
The use of unrelated donors (UDs) for allogeneic transplantation has extended the availability of this potentially life-saving therapy to those who lack a sibling donor. In view of the increased genetic disparity between recipient and donor the incidence of some complications, such as graft-versus-host disease (GvHD), are increased. Recent advances in technology, including those related to human leucocyte antigen (HLA)-typing, have resulted in the outcome of UD transplants reaching that of transplants using sibling donors (Goldstone & Rowe, 2009; Lee et al, 2009), in part due to a reduction in the incidence of severe GvHD. One highly successful strategy to reduce GvHD is the use of T cell depletion (TCD) – either in vivo or ex vivo (Kottaridis et al, 2000; Marks et al, 2000).
A commonly used method of in-vivo TCD is Alemtuzumab, given for several days pre-transplant. Alemtuzumab is an antibody against CD52 and as such depletes not only T cells, but also other cell subsets, such as B cells and dendritic cells (Hale et al, 1998). Alemtuzumab has been shown to persist in the patient’s circulation for up to 30 d post-infusion, allowing for depletion of CD52-positive cells from the patient as well as from the donor cells on infusion (Rebello et al, 2001).
Historically, all donors provided stem cells via a bone marrow (BM) harvest. Since the 1990s we have had the ability to collect granulocyte colony-stimulating factor (GCSF)-mobilized peripheral blood stem cells (PBSC) and their use in UD has increased considerably since 2000 (Ljungman et al, 2009). In view of the low incidence of significant short-term side effects and the ease of donation, c. 70–80% of UDs opt to donate via this method in preference to BM harvesting (Miller et al, 2008; Pulsipher et al, 2009). It was clear from early experience that the number of cells (CD34+ and CD3+ cells) harvested via PBSC was greater than obtained by BM harvesting (Pavletic et al, 1998). While this was associated with significantly shorter engraftment times, there were concerns that the incidence of GvHD would be increased with the use of PBSC. Indeed, a number of studies, predominantly in sibling transplants, showed an increased incidence of both acute and/or chronic GvHD in PBSC recipients (Storek et al, 1997; Schmitz et al, 2005, 2006) without, however, an impact on patient outcome (Ringden et al, 2002; Schmitz et al, 2005; Gallardo et al, 2009; Friedrichs et al, 2010). More recent studies have considered UD transplants (Blau et al, 2001; Remberger et al, 2001, 2005; Garderet et al, 2003; Eapen et al, 2007), again confirming an increase in GvHD with PBSC, but not consistently showing any difference in outcome. However, most of these studies included recipients of both HLA-matched and -mismatched grafts and all report series where transplants were predominantly T cell replete.
A few studies have suggested a differential effect on survival due to stem cell source, both in sibling (Eapen et al, 2004; Stem Cell Trialists’ Collaborative Group., 2005) and UD transplants (Garderet et al, 2003; Eapen et al, 2007). The large meta-analysis including 1111 adult recipients of HLA-identical sibling grafts (Stem Cell Trialists’ Collaborative Group., 2005), showed that PBSC was associated with increased incidences of both acute and chronic GvHD. However, PBSC was also associated with a decrease in relapse in both early and late stage disease, with a significantly improved survival in recipients of PBSC with late stage disease. Conversely, in another study (Eapen et al, 2004) in children receiving HLA-identical sibling allografts, PBSC was associated with a higher incidence of chronic GvHD, as well as a worse overall survival (OS) and a higher transplant-related mortality (TRM). Furthermore in a Center for International Blood and Marrow Transplant Research study of UD transplant outcome, Eapen et al (2007) showed a significantly higher incidence of both grade II–IV acute GvHD and of chronic GVHD. Although there was no detrimental effect on OS in the whole group, the subgroup of patients with chronic myeloid leukaemia (CML) in first chronic phase (CP1) receiving PBSC did have a significantly worse OS, with a trend to an increase in TRM. Garderet et al (2003), reported a trend to an increase in acute (but not chronic) GvHD in patients with acute lymphoblastic leukaemia receiving PBSC, which was associated with an inferior survival compared to BM (without an impact on relapse).
We hypothesized that any negative impact caused by increased GvHD using PBSC compared to BM might be abrogated in recipients of UD transplants incorporating in-vivo Alemtuzumab conditioning for T cell depletion. Here we present data on the outcome in 306 UK transplant recipients with leukaemia regarding the impact of stem cell source on outcome.
- Top of page
- Materials and methods
- Authors contributions
- Conflict of interest
This study is the first to consider the impact of stem cell source in a cohort of in-vivo TCD HLA-matched UD allograft recipients. In contrast to previous studies of T cell-replete UD transplants, we found no increase in the risk of grade II–IV acute GVHD or of chronic GVHD in recipients of PBSC. The only significant difference between BM and PBSC recipients in this study was a higher incidence of grade I aGvHD in the PBSC group.
In 617 adult recipients of T cell-replete UD transplants, Eapen et al (2007) reported an increase in the incidence of overall, but not grade III/IV, aGvHD with PBSC. In addition, unlike our report, the incidence of cGvHD was also found to be significantly higher in the patients receiving PBSC. Two smaller studies (Garderet et al, 2003; n = 213; Blau et al, 2001; n = 74) reported significant increases in aGvHD (only in HLA-mismatched patients in the latter study), but no increase in cGvHD. Another group, reporting on both short (Remberger et al, 2001) and long term (Remberger et al, 2005) follow-up in 214 adult transplant recipients, found no increase in aGvHD while the incidence of chronic extensive GvHD was significantly higher when PBSC was used compared to BM.
There are a number of clear differences between these studies, the most important being the use or not of T-cell depletion, in particular, Alemtuzumab. A possible additional factor explaining the lack of impact of stem cell source on cGvHD is the differing length of follow-up in each study. The median follow-up reported by Remberger et al (2005) was over 4 years (which is the same as in our current study), while that in the other studies ranges between 1·5 and 3 years and, in some, differed between the PBSC and BM groups. The pattern of GvHD may also be of interest. All of the studies to date reported outcomes using the ‘old’ classification of GvHD i.e. using a simple time cut-off between acute and chronic GvHD. It may be that use of the reclassification of GvHD in future studies, would provide further insights (Filipovich, 2008). In our study we noticed that the time to onset of cGVHD was shorter in the PBSC than the BM group (data not shown), suggesting that a proportion of the ‘chronic’ GvHD would now be reclassified as late onset acute or persistent rather than de novo chronic GvHD. It is well recognized that chronic GvHD is more likely in patients who have suffered acute GvHD (especially of higher grades) which may explain the increase in cGvHD in the study reported by Eapen et al (2007) (where the incidence of acute GvHD was higher than in our study), while this may be less discernable in the studies by Blau et al (2001) and Garderet et al (2003), where the overall and grade II/IV aGvHD incidence was less.
T cell depletion using Alemtuzumab was universal in our study. This method of GvHD prophylaxis was either absent or used in a very small minority of patients in the other studies (Blau et al, 2001; Garderet et al, 2003; Eapen et al, 2007) except for one (Remberger et al, 2005), where one third of patients received antithymocyte globulin (ATG). Direct comparisons between ATG and Alemtuzumab cannot be made because Alemtuzumab depletes all CD52-positive cells and not just T cells. The use of ATG in only a proportion of patients and the likelihood of ‘hidden’ HLA mismatches in that study, especially for HLA-C (low resolution HLA-A and -B and high resolution -DRB1 matching criteria were used) may account for the high incidence of chronic GvHD that they observed. All of the recipients included in our study had high resolution typing performed.
The significant reduction in overall incidence of GvHD following TCD strategies (in particular grade III–IV acute and extensive chronic GvHD) compared to that following T cell-replete transplantation has been reported in both randomized (Bacigalupo et al, 2001, 2006; Wagner et al, 2005; Finke et al, 2009) as well as non-randomized studies (Kottaridis et al, 2000; Chakraverty et al, 2002; Mohty et al, 2003; Kennedy-Nasser et al, 2008; Malladi et al, 2009; Craddock et al, 2010). Conversely, both infection (Bacigalupo et al, 2001; Malladi et al, 2009) and relapse (Wagner et al, 2005) may be increased in the TCD setting, due to delayed immune reconstitution and a reduced graft-versus-leukaemia effect. In this study CMV seropositivity in the recipient was associated with an inferior survival. It is well recognized that CMV reactivation is common following TCD (Wagner et al, 2005; Finke et al, 2009). Although the direct impact of CMV reactivation on mortality is minimal due to pre-emptive strategies, it is known that CMV seropositivity is associated with a predisposition to other infections and may impact on survival in other less well defined ways (Craddock et al, 2001; Nichols et al, 2002). Although the relapse risk in the AL patients in this study was acceptable, the relapse risk in CML was disappointingly high (although not significantly different based on stem cell source). This may be due to the inclusion of TCD in the conditioning as previously reported (Wagner et al, 2005).
Neither our or other UD studies have reported any significant differences due to stem cell source in TRM, relapse or OS in the overall group studied. In the study reported by Eapen et al (2007) there was a trend to a higher TRM, with a significantly lower OS, in recipients with CML in CP1, although the reason for this is not clear. In the study reported by Garderet et al (2003) patients with ALL receiving PBSC had a significantly lower disease-free survival and OS. Besides the obvious differences with regards to TCD, other differences between the studies are noted, such as the inclusion of both paediatric and adult patients, the degree of HLA matching, the diseases and stage of disease included, medical GvHD prophylaxis and the year of transplantation. None of the studies in UDs are randomized and the results of the Blood and Marrow Transplant Clinical Trials Network 0201 randomized trial (Peripheral Blood versus Bone Marrow Grafts from UDs) (http://www.cibmtr.org/Studies/ClinicalTrials/BMT_CTN/Protocols/0201/index.html) are keenly awaited.
It is recognized that the current study has a number of limitations. In common with most retrospective studies there is some heterogeneity in the study group. Although TCD using Alemtuzumab was universal, the schedule and dosage varied between centres. Importantly, however, the dose of Alemtuzumab within an institution did not differ depending on whether the stem cell product was BM or PBSC. In addition the use of cyclosporin (with or without methotrexate) differed by centre. DLI were given for various reasons, but none as part of a planned immunotherapy program. Any impact of DLI on outcomes should be negligible, as most were given for relapse, and this was taken into account as a competing risk for chronic GvHD. Although the number of CD34+ cells is known, the data on CD3+ and other cell subset content of the graft were not available.
In conclusion, this study confirmed the low incidence of severe GvHD following TCD myeloablative transplantation from UD for patients with standard risk leukaemia, with excellent long-term survival rates. The use of either BM or PBSC was associated with equally good outcomes. The only significant difference between the groups was an increase in grade 1 acute GvHD in the PBSC recipients. The risk of extensive cGVHD was low and did not differ with stem cell source. These data suggest that either stem cell source can be used with equivalent results and that there is no deleterious effect from the use of PBSC in Alemtuzumab-containing UD transplants.