Quantitative lymphocyte subset reconstitution after allogeneic hematopoietic transplantation from matched related donors with CD34+ selected PBPC grafts unselected PBPC grafts or BM grafts

Comparison of reduced-toxicity conditioning protocols using fludarabine, melphalan combined with thiotepa or carmustine in allogeneic hematopoietic cell transplantation

The age of patients undergoing allogeneic hematopoietic cell transplantation (allo-HCT) has increased during the last decades, mainly due to improved reduced-intensity/toxicity conditioning protocols. A reduced-intensity conditioning based on fludarabin, carmustin/BCNU and melphalan (FBM) has been previously developed at our institution. Since we observed detrimental effects in individual patients with compromised lung function, efforts have been made in order to replace BCNU by thiotepa (FTM) to reduce toxicity. In this study, we retrospectively analyzed the outcome, GvHD incidence, lung function and organ toxicity of patients with a median age of 62 years (range 21–79) transplanted for malignant disease (96.7%, 62.3% in intermediate/advanced disease stage) at our institution after conditioning with FBM (n = 136) or FTM (n = 105) between 2013 and 2017. Median follow-up was 868 days (range 0–2615). In multivariate analysis for overall survival, no difference was detected between both conditioning protocols in the presence of impaired lung function, age, lower performance, and liver disease previous allo-HCT. In the subgroup analysis, FTM was not inferior to FBM in patients with pulmonary disease prior allo-HCT, lymphoid malignancies, and higher comorbidity index. In conclusion, the reduced-intensity FBM and FTM conditioning protocols show adequate antineoplastic efficacy and are suitable for patients with impaired lung function.

Conditioning protocol based on fludarabin, melphalan combined with thiotepa (FTM) showed sufficient anti-neoplastic effect and is suitable for patients with impaired lung function prior allo-HCT.

Joint Modeling of Immune Reconstitution Post Haploidentical Stem Cell Transplantation in Pediatric Patients With Acute Leukemia Comparing CD34+-Selected to CD3/CD19-Depleted Grafts in a Retrospective Multicenter Study

Rapid immune reconstitution (IR) following stem cell transplantation (SCT) is essential for a favorable outcome. The optimization of graft composition should not only enable a sufficient IR but also improve graft vs. leukemia/tumor effects, overcome infectious complications and, finally, improve patient survival. Especially in haploidentical SCT, the optimization of graft composition is controversial. Therefore, we analyzed the influence of graft manipulation on IR in 40 patients with acute leukemia in remission. We examined the cell recovery post haploidentical SCT in patients receiving a CD34⁺-selected or CD3/CD19-depleted graft, considering the applied conditioning regimen. We used joint model analysis for overall survival (OS) and analyzed the dynamics of age-adjusted leukocytes; lymphocytes; monocytes; CD3⁺, CD3⁺CD4⁺, and CD3⁺CD8⁺ T cells; natural killer (NK) cells; and B cells over the course of time after SCT. Lymphocytes, NK cells, and B cells expanded more rapidly after SCT with CD34⁺-selected grafts (P = 0.036, P = 0.002, and P < 0.001, respectively). Contrarily, CD3⁺CD4⁺ helper T cells recovered delayer in the CD34 selected group (P = 0.026). Furthermore, reduced intensity conditioning facilitated faster immune recovery of lymphocytes and T cells and their subsets (P < 0.001). However, the immune recovery for NK cells and B cells was comparable for patients who received reduced-intensity or full preparative regimens. Dynamics of all cell types had a significant influence on OS, which did not differ between patients receiving CD34⁺-selected and those receiving CD3/CD19-depleted grafts. In conclusion, cell reconstitution dynamics showed complex diversity with regard to the graft manufacturing procedure and conditioning regimen.

Immunological effects of nilotinib prophylaxis after allogeneic stem cell transplantation in patients with advanced chronic myeloid leukemia or philadelphia chromosome-positive acute lymphoblastic leukemia

Allogeneic stem cell transplantation remains the standard treatment for resistant advanced chronic myeloid leukemia and Philadelphia chromosome–positive acute lymphoblastic leukemia. Relapse is the major cause of treatment failure in both diseases. Post-allo-SCT administration of TKIs could potentially reduce relapse rates, but concerns regarding their effect on immune reconstitution have been raised. We aimed to assess immune functions of 12 advanced CML and Ph+ ALL patients who received post-allo-SCT nilotinib. Lymphocyte subpopulations and their functional activities including T-cell response to mitogens, NK cytotoxic activity and thymic function, determined by quantification of the T cell receptor (TCR) excision circles (TREC) and TCR repertoire, were evaluated at several time points, including pre-nilotib-post-allo-SCT, and up to 365 days on nilotinib treatment. NK cells were the first to recover post allo-SCT. Concomitant to nilotinib administration, total lymphocyte counts and subpopulations gradually increased. CD8 T cells were rapidly reconstituted and continued to increase until day 180 post SCT, while CD4 T cells counts were low until 180−270 days post nilotinib treatment. T-cell response to mitogenic stimulation was not inhibited by nilotinib administration. Thymic activity, measured by TREC copies and surface membrane expression of 24 different TCR Vβ families, was evident in all patients at the end of follow-up after allo-SCT and nilotinib treatment. Finally, nilotinib did not inhibit NK cytotoxic activity. In conclusion, administration of nilotinib post allo-SCT, in attempt to reduce relapse rates or progression of Ph+ ALL and CML, did not jeopardize immune reconstitution or function following transplantation.

Evolution of peripheral blood T lymphocyte subsets after allogenic or autologous hematopoietic stem cell transplantation

With the aim to search for differences in T cell reconstitution after allogenic or autologous hematopoietic stem cell transplantation (HSCT), we characterized peripheral blood T-cell subsets by means of flow cytometry, in adult patients who had undergone either allogenic (n=23) or autologous (n=29) HSCT for the treatment of hematological malignancies. The patients were followed every 3 months for 21 months after HSCT. Compared to healthy controls (n=20 blood donors), the two transplanted groups displayed (i) a CD4 lymphopenia, (ii) a low percentage of naive T cells, (iii) high percentages of memory T cells and of activated T cells (HLA-DR+, CD25+) and high percentages of CD4 T cells with a high expression of CD25. The levels of TRECs (TCR rearrangement excision circles) were not significantly different between the two groups. In total, the differences of the nature and the speed of T lymphocyte reconstitution observed between the two patient groups were minor. This leads us to conclude that in allografted patients, lymphocyte activation as well as many other disturbances of subpopulations of peripheral blood lymphocytes are probably not related to the allogenicity of the graft, but are due to the expansion of T cells transfused with HSC and slow differentiation of T lymphocytes in the thymus progressively colonized by bone marrow-derived T-cell precursors.

Immune reconstitution kinetics as an early predictor for mortality using various hematopoietic stem cell sources in children

The severity of complications of allogeneic hematopoietic stem cell transplantation (HSCT) is governed mainly by the status of immune reconstitution. In this study, we investigated differences in immune reconstitution with different cell sources and the association between the kinetics of immune reconstitution and mortality. Immunophenotyping was performed every 2 weeks in children who had undergone HSCT between 2004 and 2008 at University Medical Center Utrecht. Lymphocyte reconstitution in the first 90 days after HSCT was studied in relation to mortality in 3 HSCT groups: matched sibling bone marrow (BM) recipients (35 patients), unrelated BM recipients (32 patients), and unrelated cord blood recipients (36 patients). The median age of recipients was 5.9 years (range, 0.1-21 years). The nature and speed of T cell, B cell, and natural killer (NK) cell reconstitution were highly dependent on the cell source. In the first 90 days after HSCT, faster B cell and NK cell reconstitution and delayed T cell reconstitution were shown in unrelated cord blood recipients compared with matched sibling BM and unrelated BM recipients. Of the lymphocyte subsets investigated, a large number of NK cells and a more rapid CD4(+) immune reconstitution over time, resulting in sustained higher CD4(+) counts, were the only predictors of a lower mortality risk in all cell sources. The final model showed that during the first 90 days, patients with an area under the CD4(+) cell receiver- operating curve of >4,300 cells/day and no peak in CD4(+) cell counts had the highest likelihood of survival (hazard ratio for mortality, 0.2; 95% confidence interval, 0.06-0.5). Our data indicate that CD4(+) kinetics may be used to identify patients at greatest risk for mortality early after HSCT.

Immune reconstitution after anti-thymocyte globulin-conditioned hematopoietic cell transplantation

BACKGROUND AIMS

Anti-thymocyte globulin (ATG) is being used increasingly to prevent graft-versus-host disease (GvHD); however, its impact on immune reconstitution is relatively unknown. We (i) studied immune reconstitution after ATG-conditioned hematopoietic cell transplantation (HCT), (ii) determined the factors influencing the reconstitution, and (iii) compared it with non-ATG-conditioned HCT.

METHODS

Immune cell subset counts were determined at 1-24 months post-transplant in 125 HCT recipients who received ATG during conditioning. Subset counts were also determined in 46 non-ATG-conditioned patients (similarly treated).

RESULTS

(i) Reconstitution after ATG-conditioned HCT was fast for innate immune cells, intermediate for B cells and CD8 T cells, and very slow for CD4 T cells and invariant natural killer T (iNKT) (iNKT) cells. (ii) Faster reconstitution after ATG-conditioned HCT was associated with a higher number of cells of the same subset transferred with the graft in the case of memory B cells, naive CD4 T cells, naive CD8 T cells, iNKT cells and myeloid dendritic cells; lower recipient age in the case of naive CD4 T cells and naive CD8 T cells; cytomegalovirus recipient seropositivity in the case of memory/effector T cells; an absence of GvHD in the case of naive B cells; lower ATG serum levels in the case of most T-cell subsets, including iNKT cells; and higher ATG levels in the case of NK cells and B cells. (iii) Compared with non-ATG-conditioned HCT, reconstitution after ATG-conditioned HCT was slower for CD4 T cells, and faster for NK cells and B cells.

CONCLUSIONS

ATG worsens the reconstitution of CD4 T cells but improves the reconstitution of NK and B cells.

Reconstitution rate of absolute CD8+ T lymphocyte counts affects overall survival after pediatric allogeneic hematopoietic stem cell transplantation

Immune reconstitution after allogeneic stem cell transplantation protects against opportunistic infections and disease relapse. Identifying the most protective lymphocyte subset would have implications of adoptive immunotherapy. We followed up a case series of 34 allogeneic transplantations for pediatric leukemias, aplastic anemias, or solid tumors. Regardless of baseline hematologic disorder, the speed of reconstitution of cytotoxic CD8 T lymphocytes and the achieving of the 10th percentile of normal CD4 T lymphocytes (but not B lymphocytes or natural killer cells) conditioned overall survival. The source of hematopoietic stem cells (peripheral blood vs bone marrow) and the occurrence of graft-versus-host disease (either acute or chronic) did not impact on immune reconstitution. Larger case series are needed to confirm the pivotal role of cytotoxic CD8 T lymphocytes in overall survival.

High incidence of secondary failure of platelet recovery after autologous and syngeneic peripheral blood stem cell transplantation in acute promyelocytic leukemia

Secondary failure of platelet recovery (SFPR), which is a delayed decline in platelet count after primary recovery following myeloablative hematopoietic SCT, is a significant problem in allogeneic SCT. However, its clinical characteristics have not been well described in autologous SCT for acute myeloid leukemia. We reviewed 11 consecutive patients who had received autologous or syngeneic SCT for acute promyelocytic leukemia. Seven of 11 patients (64%) had SFPR, which is defined as a decline in the platelet count to less than 30,000/microl for more than 7 days. The median onset of SFPR was day 36 (range, 25-51 days) and the median duration of thrombocytopenia was 13 days (range, 4-25 days). Of nine patients who received busulfan-containing preparative regimens, seven (78%) had SFPR and one had delayed primary platelet count recovery. Neither patient who received cyclophosphamide and total body irradiation as preparative regimens had SFPR. The clinical courses of SFPR were transient and self-limited. SFPR was not associated with relapse of underlying diseases, graft failure or other fatal morbidities. The unexpectedly high prevalence and the characteristics of SFPR may provide additional information on management following autologous SCT for acute myeloid leukemia.

Immune reconstitution after autologous hematopoietic transplantation with Lin-, CD34+, Thy-1lo selected or intact stem cell products

In sequential studies, we compared immune reconstitution following high-dose chemotherapy (HDT) and stem cell transplantation (SCT) using intact mobilized peripheral blood stem cell (PSC) in intermediate grade non-Hodgkin's lymphoma (NHL) patients and CD34(+), lineage-negative (Lin(-)), Thy-1(lo) (CD34(+)Lin(-)Thy-1(lo)) stem cells in low-grade NHL patients. Cytokine expression and cellular phenotype and function were used as the basis of comparison. Despite differences in cellular composition of the stem cell grafts, immune reconstitution in both groups was similar. Significantly higher levels of type 1- and 2-associated cytokine messenger ribonucleic acid (mRNA) were observed both prior to and following transplant in the peripheral blood (PB) of both cohorts as compared to normal individuals. Similar levels of interleukin (IL)-4, IL-10, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) messenger ribonucleic acid (mRNA) were seen in PB mononuclear cells following transplant with either product. In contrast, patients receiving isolated CD34(+)Lin(-)Thy-1(lo) cells expressed significantly higher IL-2 levels at all times examined post-transplant. Despite the high levels of cytokine gene expression and rapid restoration to pretransplant levels of CD3 cell number by day 30, T cell function and CD4:CD8 and CD4(+)CD45RA:CD4(+)CD45RO(+) ratios were significantly depressed in both cohorts compared to normal donors, and significantly lower in patients transplanted with CD34(+)Lin(-)Thy-1(lo) compared to patients receiving an intact PSC product. These data suggest that the peripheral tolerance in patients receiving HDT and an autologous SCT occurs independent of graft composition, although immune function and CD4 recovery are better facilitated by transplantation of an intact product.

Lymphocyte reconstitution following allogeneic hematopoietic stem cell transplantation: a retrospective study including 148 patients

Here we investigated the influence of parameters known before hematopoietic stem cell transplantation (HSCT) as well as the relevance of graft-versus-host disease (GvHD) and cytomegalovirus (CMV) reactivation on post transplant lymphocyte reconstitution in 148 patients treated in our institution between 1996 and 2003. Median patient age was 42 (19-68) years, HSCT followed standard high dose (n=91) or reduced-intensity conditioning regimens (n=57) with bone marrow (BM, n=67) or peripheral blood stem cells (PBSC, n=81) from related (n=71) or unrelated (n=77) donors. In the first months, we observed a partially faster reconstitution of CD3+4+, CD3+8+ and CD4+45RA+ T cells in patients following peripheral blood stem cell transplantation when compared to bone marrow transplantation. Prolonged CD3+4+ and CD4+45RA+ lymphopenia was noted after unrelated donor HSCT and GvHD prophylaxis containing anti-T-lymphocyte globulin. Lymphocyte subset counts in patients older than the median age were comparable to those in patients transplanted at a younger age and not influenced by the conditioning regimen. CD3+8+ T cell reconstitution was strongly correlated with CMV reactivation, but not significantly affected by CMV serostatus before HSCT. Incidence or extent of GvHD did not significantly influence lymphocyte reconstitution. Therefore, the source of graft is the most predictive parameter in early lymphocyte reconstitution, but the differences in lymphocyte recovery completely resolved within the first year after HSCT.

Immune recovery in children undergoing allogeneic stem cell transplantation: absolute CD8+CD3+ count reconstitution is associated with survival

To evaluate the correlation between kinetics of immune reconstitution and survival, we prospectively evaluated lymphocyte subsets in 32 paediatric patients undergoing allogeneic stem cell transplantation (SCT) for haematological malignancies. Four-colour flow cytometric analysis was performed at short intervals with a median follow-up of 4 years post SCT. A total of 50% of patients reached age-matched 5th percentile of natural killer, cytotoxic T, B and helper T cells 4, 9, 20 and 28 weeks after SCT, respectively, which increased to more than 80% within 1 year after SCT. Transplantation of peripheral blood stem cells (PBSC) seemed to elicit the fastest reconstitution of CD3+, CD4+ CD3+, CD8+ CD3+ and naïve T cells compared to bone marrow (BM) or CD34-selected PBSC, which did not differ. Most importantly, we observed a significantly higher number of survivors among patients whose CD8+ CD3+ absolute counts rose above the 5th percentile of age-matched normal levels during the first year post SCT compared to patients who never reached these levels (19/25 vs 0/7, P<0.001). This was still present in both subgroups, BM- and CD34-selected grafts (P=0.03, 0.02). These results from a small patient sample underline the importance of particular lymphocyte subsets for the outcome of children undergoing SCT. A larger study with detailed subset analysis is underway.

Survival Benefit of Asymptomatic Cytomegalovirus Reactivation after HLA-Identical Allogeneic Peripheral Blood Stem Cell Transplantation

BACKGROUND

Cytomegalovirus (CMV) reactivation (CMV-R) is associated with increased morbidity after allogeneic stem cell transplantation (SCT). However, after the introduction of ganciclovir preemptive therapy, CMV-R can be successfully controlled if the recipient's immunity recovers. Although many investigations have already focused on CMV-R as a risk factor, data related to the impact of asymptomatic CMV-R on transplant outcomes is scarce. Accordingly, the present study analyzed the differences in the transplant outcomes the immune reconstitution according to the CMV-R after allogeneic PBSCT.

METHODS

A total of 76 patients undergoing allogeneic peripheral blood stem cell transplantation (PBSCT) were included in the current study. The transplant outcomes and immune reconstitution after 3, 6, and 12 months were analyzed according to the occurrence of CMV-R in 33 patients.

RESULTS

The analysis revealed a favorable prognosis for the group with CMV-R compared to those without CMV-R: P = 0.0037 for OS, P = 0.0204 for NRM, and P = 0.05 for the risk of relapse. CMV-R was also found to correlate to the lymphoid reconstitution (P = 0.024). In multivariate analyses, CMV-R was found to be a favorable prognostic factor in terms of OS (P = 0.010, hazard ratio [HR] 2.948) and NRM (P = 0.05, HR 2.665), along with a higher transplant CD34 cell dose (P = 0.003 for OS, P = 0.002 for NRM), standard risk (P = 0.023 for OS), and acute GVHD grades 0-2 (P = 0.007 for NRM).

CONCLUSION

In a PBSCT setting, CMV-R did not seem to be a poor prognostic factor in terms of OS and NRM, possibly due to the accelerated lymphoid immune reconstitution associated with CMV-R.

Low incidence of infectious complications after nonmyeloablative compared with myeloablative allogeneic stem cell transplantation

Allogeneic stem cell transplantation (SCT) using a myeloablative (MA) conditioning regimen is limited to relatively young patients because of increased transplant-related mortality in elderly patients. Nonmyeloablative (NMA) conditioning regimens have been developed aiming to reduce transplant mortality. In this study, we set out to evaluate the post-transplant occurrence of infectious complications in recipients of grafts from human leukocyte antigen (HLA)-identical sibling donors treated with either NMA or MA conditioning regimens. Data of 78 consecutively treated patients were analyzed. An NMA conditioning regimen was used in 40 patients and an MA regimen in 38 patients. A significantly lower rate of episodes of febrile neutropenia (0% vs. 34%, P<0.01) and post-transplant Epstein-Barr virus reactivations (0% vs. 18%, P<0.05) was found in SCT recipients treated with an NMA conditioning regimen compared with an MA conditioning regimen. Furthermore, fewer invasive fungal infections (2% vs. 12%, not significant) were diagnosed in the NMA group. The incidence of cytomegalovirus (CMV) reactivations and bacterial infections was low in both groups (CMV reactivations: 13% in both groups; bacterial infections: 10% in the NMA group vs. 8% in the MA group), while CMV disease developed in only 1 patient. Overall, compared to our MA regimen, we found a very low rate of infectious complications after NMA SCT.

Transplantation of allogeneic CD34+-selected cells followed by early T-cell add-backs: favorable results in acute and chronic myeloid leukemia

BACKGROUND

The aim of this study was to investigate preservation of anti-leukemic activity and protection from opportunistic infections after transplantation of allogeneic + cells in patients with hematologic malignancies and bad prognosis. Methods Thirty-three patients [median age 42 years, range 23-55 years, diagnosis AML/myelodysplastic syndrome (MDS) 14, ALL nine, CML seven and multiple myeloma (MM) three] received myeloablative conditioning followed by infusion of selected CD34+ cells from matched unrelated donors (31) or HLA-identical siblings (two). Early donor lymphocyte infusions (DLI; 0.5 and 1.0 x 10(6) CD3+ cells/kg) were given while patients were on immunosuppressive therapy.

RESULTS

Ninety-seven per cent of patients engrafted and 24 of 29 patients surviving more than 30 days received at least one pre-emptive DLI. Three patients (10%) developed acute (a)GvHD (two grade I-II, one grade III-IV) spontaneously, and 16 patients (67%) developed aGvHD after DLI (12 grade I-II, four grade III-IV). Eight of 24 evaluable patients developed chronic (c)GvHD (33%, six limited, two extensive). After a median follow-up of 590 days (range 138-1610 days) 18 patients were alive (55%), 16 in complete remission (CR), one in hematologic and one in molecular relapse. Seven patients died after relapse (21%) and eight died from transplantation-related causes (24%). Patients with myeloid malignancies had a significantly better survival than patients with ALL or MM (74%+/-10 vs. 30%+/-13, P<0.05).

DISCUSSION

Early pre-emptive low-dose DLI following transplantation of selected CD34+ cells from unrelated donors after myeloablative conditioning is feasible and effective without undue toxicity, especially in patients with myeloid malignancies.

Clinical impact of early absolute lymphocyte count after allogeneic stem cell transplantation

The role of repopulating lymphocytes after allogeneic stem cell transplantation (SCT) includes the prevention of serious infections and attacking residual tumour cells in the early post-transplant phase. Therefore, the current study analysed the role of the absolute lymphocyte count (ALC) on day 21 after SCT in predicting transplant outcomes of 82 patients in terms of the risk of opportunistic infections and recurrence of original disease. The median dose of CD34+, CD3+ and mononuclear cells (MNC) infused was 6.41 x 10(6)/kg, 1.96 x 10(8)/kg and 6.81 x 10(8)/kg respectively. The high ALC group (high ALC on day 21; > or =0.35 x 10(9)/l) was associated with the use of peripheral blood stem cells, matched sibling donors and higher cell doses of MNC, CD3+ and CD4+ cells. The high ALC group also exhibited a better overall survival (56.3% vs. 17.7%) and disease-free survival (50.1% vs. 15.9%) after 3 years and lower incidences of relapse (33.6% vs. 67.1%) and fungal infections (3.0% vs. 19.5%) after 1 year. The incidence of cytomegalovirus antigenaemia was lower in the high ALC group (47.7% vs. 73.7%). Accordingly, identifying the ALC on day 21 would appear to be a useful and simple measurement to predict those patients with a high risk of opportunistic infections and relapse after allogeneic SCT.

Immune reconstitution following reduced-intensity transplantation with cladribine, busulfan, and antithymocyte globulin: serial comparison with conventional myeloablative transplantation

The primary object of the conditioning regimen for allogeneic reduced-intensity stem cell transplantation (RIST) is immunosuppression to achieve stable engraftment of donor cells, rather than bone marrow ablation. Therefore, immune reconstitution after RIST might be different from that after conventional stem cell transplantation (CST). In this study, 22 patients underwent RIST and 28 underwent CST. The RIST regimen consisted of cladribine (2-CdA; 0.11 mg/kg/day for 6 days), BU (4 mg/kg/day for 2 days), and rabbit anti-thymocyte globulin (ATG; 2.5 mg/kg/day for 2-4 days). The CST group received either the BU (4 mg/kg/day x 4 days)/CY (60 mg/kg/day x 2 days) (n=13) or CY (60 mg/kg/day x 2 days)/TBI (4 Gy/day x 3 days) regimen (n=15). All patients underwent transplantation with G-CSF-mobilized blood stem cells. Engraftment speed after RIST was fast and seven of 22 patients did not require platelet transfusion. We noted that the numbers of CD4+, CD4+CD45RA+, and CD4+CD45RO+ T cells after transplant in the RIST group were significantly lower than those in the CST group (P=0.0001 for both the comparisons). However, the reconstitution of CD20+ B cells was faster in the RIST group (P=0.0001). The response of T cells to PHA stimulation was lower in the RIST group (P=0.0001 on day 30 and P=0.02 on day 90). Nevertheless, there were no significant differences in the incidence of bacterial, fungal, or viral infections between the two groups. We concluded that our RIST regimen might delay laboratory-evaluated T-cell immune reconstitution compared to CST; however, the observed setbacks did not directly translate into clinically significant increases in infectious episodes.

Identification of non-naïve CD4+CD45RA+ T cell subsets in adult allogeneic haematopoietic cell transplant recipients

The study of thymic-dependent pathways of T cell reconstitution in T cell replete haematopoietic cell transplant (HCT) recipients in previous studies was complicated by the transfer of naïve CD4(+)CD45RA(+) T cells with the stem cell graft. However, direct quantification of thymic output has been enabled by measurement of T cell receptor excision circles (TREC). We analysed T cell reconstitution using T cell phenotyping and TREC quantification in 12 T cell-replete HCT recipients 6-53 years of age during the first 12 months post transplant. We have identified a novel subpopulation of CD4(+)CD45RA(+) T cells in the peripheral blood of these HCT recipients with expansions of this subset being more pronounced in older recipients. The recovery of classical naïve CD4(+)CD45RA(+) T cells was dependent on thymic output whereas this novel CD4(+)CD45RA(+) subpopulation arose independently of thymic output and displayed effector function and phenotype. These results suggest that CD4(+)CD45RA(+) effector populations exist, similar to the CD8(+)CD45RA(+) effector subset, and that the CD45RA antigen should not be used alone to define naïve CD4(+) T cells when monitoring T cell reconstitution in T cell replete HCT recipients. Furthermore, these results raise important questions regarding the role of the thymus in regulating T cell homeostasis in older HCT recipients and normal individuals.

Interleukin-7 improves T-cell recovery after experimental T-cell-depleted bone marrow transplantation in T-cell-deficient mice by strong expansion of recent thymic emigrants

Interleukin-7 (IL-7) has been shown to enhance thymic output of newly developed T cells following bone marrow transplantation (BMT) in mice. In addition, IL-7 may affect peripheral expansion of T cells. In order to study the relative contribution of thymopoiesis versus peripheral T-cell expansion in the setting of compromised thymopoiesis, we have applied IL-7 in an experimental stem cell transplantation model using T cell-deficient RAG-1(-/-) mice. C57BL/6 RAG-1(-/-) mice received transplants of syngeneic T-cell-depleted (TCD) bone marrow (Ly5.1) with or without supplemented T cells (Ly5.2). IL-7 was administered until day 63 after BMT. Peripheral blood T- and B-cell recovery was quantified by flow cytometry and thymopoiesis was studied by quantification of T-cell receptor rearrangement excision circles (TRECs). In mice receiving a T-cell-replete BMT, IL-7 selectively expanded mature CD45.2+ T cells without affecting the recovery of new bone marrow-derived CD45.1+ T cells. In contrast, IL-7 significantly enhanced the recovery of bone marrow-derived T cells after TCD BMT. Quantification of TRECs in mice receiving a TCD BMT revealed that enhanced T-cell recovery following IL-7 treatment resulted from a strong expansion of newly developed naive T cells. These results suggest that peripheral expansion of recent thymic emigrants or mature T cells may be a preferential mechanism by which IL-7 enhances T-cell recovery after BMT.

Blood versus marrow hematopoietic allogeneic graft

Allogeneic G-CSF-mobilized blood cell transplantation (BCT), an alternative to allogeneic bone marrow transplantation (BMT), is associated with enhanced engraftment and accelerated hematopoietic recovery. In addition, immune reconstitution and overall alloreactivity after BCT versus BMT differ significantly. Indeed, despite an increased number of donor T cells infused, the incidence of acute graft-versus-host disease (GvHD) after BCT appears to remain identical or lesser than after BMT. On the other hand, a higher risk of chronic GvHD has been reported after BCT. In a SFGM phase III trial, 101 patients with early leukemia and an HLA-matched sibling donor randomly received a BCT or BMT. BCT was associated with a higher number of infused CD34+ cells, accelerated platelet and neutrophil reconstitution, fewer platelet transfusions and similar acute GvHD incidence. However, chronic GvHD occurred more frequently after BCT. With a median follow-up of 20 months, relapse, survival and leukemia-free survival were not different. In the course of this study, immune parameters related to the graft as well as to early reconstitution were prospectively examined. T cells subsets, B cells, NK cells and monocytes numbers were significantly higher in BC grafts (versus BM). T cells in BC grafts were less activated than in BM grafts. Frequency of IFN-gamma, IL-2- and TNF-alpha-secreting cells and single-cell IFN-gamma production potential was reduced in BC graft. One month after BCT, blood T-cell counts were 3-fold higher than after BMT. Moreover, post-BCT T cells were less activated and counts correlated with the number of T cells infused with the graft, which was not the case after BMT. Several acute hemolysis episodes, resulting from anti-A and/or -B donor-derived Ab directed at Ag present on recipient red blood cells (minor ABO mismatch), have been described after BCT. Recipients indeed exhibited significantly increased anti-A and/or -B Ab titers after BCT, particularly in the setting of a "minor" ABO mismatch. Furthermore, the frequency of anti-HLA Ab early after BCT was significantly increased (despite the reduction in platelet transfusion requirements). The higher number of activated B cells and/or CD4 T cells and monocytes in a BCT graft and/or the higher number of circulating CD4 T- and B-cells after BCT could be associated with the enhanced alloAb production. G-CSF-induced TH2 cytokine profile of the T cells present in the graft could also be contributive. Recent studies have determined that BC grafts contained a higher number of type 2 dendritic cells (DC2), themselves associated with high frequencies of TH2 CD4+ cells. Since chronic GvHD is associated with the occurrence of Ab-mediated auto-immune-like syndromes, it is tempting to speculate that a higher incidence of chronic GvHD may result from these findings. In conclusion, BCT results in clinically relevant distinct hematopoietic and immune reconstitution patterns.

T-Cell recovery in adults and children following umbilical cord blood transplantation

T-cell reconstitution following allogeneic stem cell transplantation may involve thymic education of donor-derived precursors or peripheral expansion of mature T cells transferred in the graft. T cell-receptor excision circles (sjTRECs) are generated within the thymus and identify new thymic emigrants and those that have not divided. We measured quantitative and qualitative immunologic reconstitution and sjTREC levels in adult and pediatric recipients of umbilical cord blood transplants (UCBTs). sjTRECs were detected at normal levels in all children, starting 12 months after transplantation. sjTRECs were not detected until 18 months after transplantation in adults, and then only at a 3-fold lower level than expected for age. We used complementarity-determining region 3 (CDR3) spectratyping to measure changes in T cell-receptor diversity occurring with restoration of thymic function. T-cell repertoires were skewed in adults and children at 12 to 18 months after transplantation but recovered to near-normal diversity at 2 to 3 years post-UCBT. T-cell repertoires appeared more diverse earlier in children (at 1 to 2 years post-UCBT) than in adults (at 3 to 4 years post-UCBT). We conclude that early T-cell recovery after UCBT occurs primarily through peripheral expansion of adoptively transferred donor T cells and results in skewing of the T-cell repertoire. The reappearance of sjTREC-containing cells after UCBT is associated with increasing numbers of phenotypicaly naive T cells, improved mitogen and recall antigen responses, and diversification of the T-cell repertoire. The delay in central T-cell recovery in adults relative to children may be due to differences in thymic function resulting from age-related atrophy, graft-versus-host disease, or the pharmacologic effects of prophylaxis and treatment of graft-versus-host disease.

Immune reconstitution after haematopoietic cell transplantation in children: immunophenotype analysis with regard to factors affecting the speed of recovery

Immune reconstitution was studied prospectively in 66 children who underwent 77 haematopoietic cell transplantations (HCT): 46 autologous HCTs in 39 patients and 31 allogeneic HCTs in 27 patients. We studied the dynamic analysis of immune recovery with regard to potential factors affecting its speed, including age, type of HCT, diagnosis, graft-versus-host disease (GvHD) and cytomegalovirus (CMV) infection reactivation. Absolute counts of different lymphocyte subsets and immunoglobulin serum levels were determined in peripheral blood of patients on d -7 and +16, and then at various intervals up to 24 months post transplant. Common patterns of immune recovery after both allogeneic and autologous HCT were identified: (i) CD4+CD45RO+ peripheral T-cell expansion on d +16; (ii) inverted CD4+:CD8+ ratio from d +30 onwards; (iii) rapid natural killer (NK) cell (CD16+/-CD56+) count normalization. We observed prolonged T-cell lymphopenia (CD3+, CD3+CD4+, CD4+CD45RA+) until 24 months after autologous HCT, whereas in the allogeneic setting CD3+CD4+ cells, including naive CD45RA+ cells, returned to normal values at 9 months post transplant. Age > 10 years and coexistence of GvHD and CMV reactivation were associated with a substantial delay in T- (CD4+, including CD45RA+) and B-cell recovery after allogeneic HCT. Multidrug GvHD prophylaxis resulted in impaired T- (CD4+, CD4+CD45RA+) and B-cell reconstitution only in the early phase after allogeneic HCT (up to 4 months). Our results demonstrated that T-cell recovery was severely impaired in children after autologous HCT. It should be emphasized that specific approaches to enhance immune reconstitution are necessary to control minimal residual disease and avoid the risk of infectious complications in the autologous setting. Thymic involution after allogeneic HCT seems to be associated with age and coexistence of GvHD and CMV reactivation.

Effect of slow lymphocyte recovery and type of graft-versus-host disease prophylaxis on relapse after allogeneic bone marrow transplantation for acute myelogenous leukemia

Allogeneic BMT is potentially curative for patients with acute myelogenous leukemia (AML) in first remission. However, many patients relapse after transplantation. Various immunotherapeutic options have been attempted with variable success in preventing relapse. Early identification of patients at high risk for relapse could allow prompt intervention. We examined the effect of slow lymphocyte recovery after sibling-matched allogeneic BMT on the risk of relapse in patients with AML. We also examined the effect of prednisone-containing GVHD prophylaxis on the rate of lymphocyte recovery. Patients with absolute lymphocyte count (ALC) <150 x 10(6)/l by day +30 had a 3.5-fold higher risk of relapse (P = 0.0088) and a lower overall survival (P = 0.0079) than patients with a higher ALC. We did not find correlation between lymphocyte count determined earlier in the post-transplantation course (day +21) and the risk of relapse. Patients receiving prednisone had a significantly lower ALC at day +30 than those who did not receive prednisone (289 vs 549 x 10(6)/l, P = 0.002). We conclude that a slow lymphocyte recovery after allogeneic BMT for AML is strongly predictive of subsequent relapse and that the type of GVHD prophylaxis should be considered when analyzing lymphocyte recovery.

Excessive T cell depletion of peripheral blood stem cells has an adverse effect upon outcome following allogeneic stem cell transplantation

We evaluated the outcome of two modes of T cell depletion for HLA-identical sibling stem cell transplants in 34 consecutive adult patients: group A (n = 11) received PBSC post CliniMACs immuno-magnetic enrichment of CD34(+) cells and group B (n = 23) received bone marrow following in vitro incubation with CAMPATH-1M and complement. All patients received an identical conditioning regimen which consisted of in vivoCAMPATH-1H 20 mg over 5 days, thiotepa 10 mg/kg, cyclophosphamide 120 mg/kg and 14.4 Gy TBI. No additional graft-versus-host disease prophylaxis was given. The mean T cell dose administered was 0.02 +/- 0.05 x 10(6)/kg for group A and 2.8 +/- 2.8 10(6)/kg for group B (P < 0.001). With a median follow-up of 28 months overall survival was 36.4% for group A at 12 months compared to 78.3% for group B (P = 0.001). Transplant-related mortality in group A at 12 months was 63.6% as compared to 18.0% in group B (P = 0.003). Most of the procedure-related deaths in group A occurred secondary to infection. These results suggest that extensive in vitro T cell depletion of peripheral blood stem cells in combination with in vivo T cell depletion may have profound effects upon the incidence of infections following allogeneic stem cell transplantation and this may adversely effect transplant-related mortality.

Lymphocyte reconstitution following non-myeloablative hematopoietic stem cell transplantation follows two patterns depending on age and donor/recipient chimerism

The effect of mixed chimerism on the pace of post-transplant immune reconstitution is unknown. Using flow cytometry, recall and neo-antigen vaccine responses, and T cell receptor recombination excision circle (TREC) quantification, we evaluated phenotypic and functional characteristics of T and B cells in nine patients following non-myeloablative, HLA-identical peripheral blood stem cell transplantation for chronic granulomatous disease. Engraftment of T cell, B cell, and myeloid lineages proceeded at similar paces within each patient, but engraftment kinetics segregated patients into two groups: adults, who became full donor T cell chimeras before 6 months (rapid engrafters) and children, who became full donor T cell chimeras after 6 months or not at all (slow engrafters). Quantitative B cell recovery was achieved by 6 weeks after transplantation in children, but was delayed until 1 year in adults. Early quantitative B cell recovery was not accompanied by an early humoral immune response to tetanus toxoid (TT). Emergence of TT-specific T cell responses coincided with naive T cell reconstitution, as measured by CD4/CD45RA T cell recovery and TREC quantification. These data suggest that immune reconstitution occurs faster in pediatric patients who have prolonged mixed hematopoietic chimerism compared to adults, who have rapid donor stem cell engraftment.

Factors affecting lymphocyte subset reconstitution after either related or unrelated cord blood transplantation in children -- a Eurocord analysis

Immune recovery after cord blood transplantation (CBT) is of concern owing to the low number of lymphocytes transferred with the graft and their immaturity. Risk factors influencing lymphocyte subset reconstitution related to disease, patient, donor and transplant were studied in 63 children (< 16 years), given either related (n = 14) or unrelated (n = 49) CBT for malignant (n = 33) or non-malignant diseases (n = 30). Only children with sustained myeloid engraftment were analysed. Absolute numbers of T (CD3(+), CD4(+), CD8(+)), B and natural killer (NK) cells were reported 2--3, 6, 9, 12 and 12--24 months after CBT. Median patient age was 4.0 years (0--15) and median follow-up was 23 months (1.7--61.0). Twenty-six patients received human leucocyte antigen (HLA)-matched CBT and 37 received HLA-mismatched CBT. The median number of nucleated cells (NCs) collected/recipient weight was 6.1 x 10(7)/kg. In this selected population, the estimate 2 year survival was 85%. Lymphocyte reconstitution (defined as the median time to reach the normal value of age-matched healthy children) was 3, 6 and 8 months for NK, B and CD8(+) cells, while it was 11.7 months for both CD3(+) and CD4(+) lymphocytes. In the multivariate analysis, factors favouring T-cell recovery were: related donor (P = 0.002); higher NCs/kg (P = 0.005) and recipient cytomegalovirus (CMV)-positive serology (P = 0.04). Presence of acute graft-versus-host disease (GVHD) delayed T-cell recovery (P = 0.04). To summarize, in children with sustained myeloid engraftment the concern that lymphocyte recovery after CBT could be delayed does not appear to be substantiated by our results.

Stem Cell Transplantation for Chronic Lymphocytic Leukaemia: Is this the Way Forward in the New Millennium?; Malignancy; Current Clinical Practice

The failure of conventional chemotherapy to eradicate chronic lymphocytic leukaemia cells and induce cure has led many clinicians to investigate the use of high dose chemotherapy and haemopoietic stem cell rescue in this disease. The selection of patients remains a major problem because this is a disease of elderly patients with a median overall survival of 7 years and will only therefore be applicable to a minority of patients. However transplantation is the most likely therapeutic option at this time to lead to cure in this condition. The best type of transplant is not known and not all patients will be able to mobilise adequate numbers of stem cells or have a suitable donor identified. Autologous transplantation relies on the ability of high doses of chemotherapy to eradicate disease whilst allogeneic transplantation attempts to harvest the graft versus leukaemia effect that has been identified in chronic granulocytic leukaemia. However, the high treatment related mortality and morbidity of allogeneic transplants has led to interest in the use of non-myeloablative allografts which hope to maximise the immunological effects of transplantation to achieve durable remissions. To date there have been no randomised clinical trials to compare the efficacy of combination chemotherapy, autologous or allogeneic transplants and this is unlikely to happen in the near future. Other issues that need to be addressed include the timing of transplantation, the source of stem cells, the optimal conditioning regimen and the role of immunomodulation post transplantation. This review attempts to answer some of these questions.

Blood stem cell transplantation: factors influencing cellular immunological reconstitution

Recovery of immune function following stem cell transplantation is necessary for a good outcome. Immune recovery is facilitated by transplanting higher numbers of cells than neutrophil or platelet reconstitution requires. Estimates from studies in the allogeneic setting suggest the minimum stem cell dose to achieve optimal lymphocyte recovery is about 10(7) CD34+ cells/kg. Increasing the number of autologous stem cells infused potentially increases the risk of reinfusing tumor cells. Transplanted mature immune cells apparently have very limited early contribution to cellular immune recovery. Mobilizing cytokines permit collection of greater numbers of stem cells, but they also can polarize T cells with potentially significant consequences, for example, granulocyte colony-stimulating factor (G-CSF) decreases the antitumor cytotoxic effector functions of cells. Although this could be a disadvantage in the autologous setting, it might decrease graft versus host disease in the allogeneic setting. Thus, identification of cytokines, which alone or in combination provide the most potent mobilizing effect to permit the collection of the highest number of stem cells without inadvertent detrimental polarization of the responses of immune cells, and employment of cytokines posttransplantation, which direct differentiation of the stem cells along the most desirable pathways, for example, to generate antitumor immune responses, might improve immunological outcome. A future emphasis should be to better define the cytokines and target cell populations that provide optimal immune reconstitution rather than focusing solely on rapid hematological recovery. More complete immunological reconstitution in a greater proportion of patients should be accompanied by improvements in outcomes of blood stem cell transplantation.

Different immune reconstitution in multiple myeloma, chronic myeloid leukemia and acute myeloid leukemia patients after allogeneic transplantation of peripheral blood stem cells

In this study we compared the lymphocyte reconstitution in 13 multiple myeloma (MM), nine acute myeloid leukemia (AML) and 10 chronic myeloid leukemia (CML) patients after allogeneic G-CSF-mobilized PBSC transplantation from HLA-identical siblings. Conditioning regimens included standard total body irradiation + cyclophosphamide (CY), or busulphan + CY, whereas VP-16 was added in patients with advanced disease. Overall comparable numbers of mononuclear cells, CD34+ cells and CD3+ T cells were infused in each group. A significantly higher CD3+ T cell number was observed in MM and AML than in CML patients 1 month after transplant. However, MM patients showed a faster and better recovery of CD4+ T cells than both AML and CML patients at 3 months (P = 0.01 and P = 0.01, respectively) and 12 months (P = 0.01 vs AML, while P = NS vs CML) after transplant, and had a CD4:CD8 ratio > 1 with a median CD4+ T cell value > 400/microl 1 year after transplant. Development of acute graft-versus-host disease (GVHD) did not affect CD4:CD8 ratios but patients who experienced acute GVHD > grade I had lower CD4+ and CD8+ T cell numbers at all time points. However, after excluding patients with GVHD > grade I, MM patients still showed a significantly higher CD4+ T cell value than patients with myeloproliferative diseases 1 year after transplant. These findings suggest that although allogeneic PBSC transplantation induces rapid immune reconstitution, different kinetics may occur among patients with hematological malignancies. In particular, the rapid reconstitution of CD4+ T cells in MM patients may contribute to the low transplant-related mortality achieved in this disease.

Developments in T-cell depletion of allogeneic stem cell grafts

The quantitative depletion of T-cells has long been established as a highly effective way to prevent graft-versus-host disease. The disadvantages associated with T-cell depletion (TCD), including loss of the graft-versus-leukemia effect and impaired immune recovery have been important drawbacks for application on a wider scale. Recently, however, new approaches such as the use of peripheral blood stem cells and the application of TCD, in conjunction with delayed donor lymphocyte infusion, have opened new possibilities. The first clinical studies addressing the merits of these approaches suggest that effective prevention of graft-versus-host disease may be achieved by TCD, whereas the graft-versus-leukemia effect may be maintained by delayed donor lymphocyte infusion. Also, immune recovery may be accelerated by the use of peripheral blood stem cells. New techniques to manipulate stem cell grafts in vitro are being developed with the purpose to either selectively delete alloantigen specific T cells or tolerize such T cells by blocking costimulatory pathways. As a result, the in vitro manipulation of T cells of allogeneic stem cell grafts currently enjoys renewed scientific interest.

Analysis of engraftment, graft-versus-host disease, and immune recovery following unrelated donor cord blood transplantation

Unrelated cord blood (UCB) is being used as a source of alternative hematopoietic stem cells for transplantation with increasing frequency. From November 1994 to February 1999, 30 UCB transplant procedures were performed for both malignant and nonmalignant diseases in 27 children, aged 0.4 to 17.1 years. Patients received either HLA-matched (n = 3) or 1- or 2-antigen–mismatched (n = 27) UCB following 1 of 2 standardized preparative and graft-versus-host disease regimens (hyperfractionated total body irradiation, cyclophosphamide, and antithymocyte globulin [ATG] with cyclosporine A and methotrexate; or busulfan, melphalan, and ATG with cyclosporine A and prednisone). The median time to neutrophil and platelet engraftment was 27 days (12-60 days) and 75 days (33-158 days) posttransplantation, respectively. No correlation was noted between neutrophil and platelet engraftment and nucleated cells per kilogram, CD34+ cells per kilogram infused, or cytomegalovirus status of recipient. The cumulative probability of acute grade 2 or greater graft-versus-host disease (GVHD) was 37.2%, and of grade 3 or greater GVHD was 8.8%. No patients developed chronic GVHD. CD4, CD19, and natural killer cell recovery was achieved at a median of 12, 6, and 2 months, respectively. CD8 recovery was delayed at a median of 9 months. Normal mitogen response was achieved at 6 to 9 months. The probability of survival, disease-free survival, and event-free survival at 1 year was 52.3% (34.1%-70.5%), 54.7% (34.5%-74.9%) and 49.6% (29.9%-69.4%), respectively. This series of 30 UCB transplants suggests that although CD8 cell recovery is delayed, the pattern of immune reconstitution with UCB is similar to that reported for other stem cell sources.

Analysis of engraftment, graft-versus-host disease, and immune recovery following unrelated donor cord blood transplantation

Unrelated cord blood (UCB) is being used as a source of alternative hematopoietic stem cells for transplantation with increasing frequency. From November 1994 to February 1999, 30 UCB transplant procedures were performed for both malignant and nonmalignant diseases in 27 children, aged 0.4 to 17.1 years. Patients received either HLA-matched (n = 3) or 1- or 2-antigen–mismatched (n = 27) UCB following 1 of 2 standardized preparative and graft-versus-host disease regimens (hyperfractionated total body irradiation, cyclophosphamide, and antithymocyte globulin [ATG] with cyclosporine A and methotrexate; or busulfan, melphalan, and ATG with cyclosporine A and prednisone). The median time to neutrophil and platelet engraftment was 27 days (12-60 days) and 75 days (33-158 days) posttransplantation, respectively. No correlation was noted between neutrophil and platelet engraftment and nucleated cells per kilogram, CD34+ cells per kilogram infused, or cytomegalovirus status of recipient. The cumulative probability of acute grade 2 or greater graft-versus-host disease (GVHD) was 37.2%, and of grade 3 or greater GVHD was 8.8%. No patients developed chronic GVHD. CD4, CD19, and natural killer cell recovery was achieved at a median of 12, 6, and 2 months, respectively. CD8 recovery was delayed at a median of 9 months. Normal mitogen response was achieved at 6 to 9 months. The probability of survival, disease-free survival, and event-free survival at 1 year was 52.3% (34.1%-70.5%), 54.7% (34.5%-74.9%) and 49.6% (29.9%-69.4%), respectively. This series of 30 UCB transplants suggests that although CD8 cell recovery is delayed, the pattern of immune reconstitution with UCB is similar to that reported for other stem cell sources.

Allogeneic bone marrow transplantation from unrelated donors using in vivo anti-T-cell globulin

Despite improvements in HLA typing, graft-versus-host disease (GVHD) continues to impair the results after volunteer unrelated donor bone marrow transplantation (VUD-BMT) in adult patients compared with matched sibling BMT. Here, the outcome after VUD-BMT using a specific regimen with high-dose anti-T-lymphocyte globulin (ATG) was analysed. Fifty-five adult patients, median age 34 years (range 17-55 years), with acute or chronic leukaemia or myelodysplastic syndrome (MDS) were transplanted in first complete remission (CR1)/first chronic phase (CP1) (early disease) (n = 21) or in advanced (CR2/CP2, no remission) disease (n = 34) from an unrelated marrow donor. GVHD prophylaxis consisted of ATG-S (Fresenius) 60-90 mg/kg b.w. prior to transplantation, in addition to cyclosporin A and short-course methotrexate. Graft failure did not occur and white blood cell count (WBC) > 1.0 x 10(9)/l was reached at median day +16. The cumulative incidence of acute (a)GVHD grade II-IV was 15% [95% CI (8%, 28%)] and of chronic GVHD was 51% [95% CI (38%, 68%)]. The cumulative incidence of relapse within 1 year was 0% [95% CI (0%, 19%)] and 21% [95% CI (11%, 40%)] for patients with early and advanced disease respectively. With a median follow-up of 28 months (range 16-45 months), 2-year disease-free and overall survival for patients transplanted in CR1/CP1 was 81% and 81% [95% CI (64%, 98%)], respectively, and for patients with advanced disease was 33% [95% CI (17%, 50%)] and 40% [95% CI (23%, 57%)] respectively. Complete and persistent donor chimaerism was seen in 77.5% of 40 patients evaluated. All 14 chronic myeloid leukaemia (CML)-CP1 patients became bcr-abl negative within 250 d. High-dose ATG pretransplant results in a low incidence of severe aGVHD without compromising donor chimaerism or elimination of minimal residual disease. Our results are similar to data obtained after matched sibling donor transplantation.