Transplantation potential of hematopoietic cells released into the circulation during routine chemotherapy for non-Hodgkin's lymphoma

Primitive hematopoietic cells released into the peripheral blood (PB) were studied in 50 patients with high-grade non-Hodgkin's lymphoma enrolled in a phase III trial of intensive weekly chemotherapy (VAPEC-B) alone or with granulocyte colony-stimulating factor (G-CSF). Mononuclear cells numbers were monitored and their in vitro growth potential assessed in clonogenic progenitor cell assays and in long-term culture. Total colony-forming cells (granulocyte-macrophage [GM], burst-forming unit, erythroid [BFU-E], Mix-CFC) were increased 40-fold (median) over baseline with chemotherapy alone and 106-fold with chemotherapy and G-CSF after the final dose. CD34+ cells were increased to a median of 4%, equivalent to that in normal bone marrow (BM) controls. Circulating colony-forming cell levels were maximal when the recovering total white blood cell (WBC) count reached 5 to 10 x 10(9)/L. The timing of the maximum was reproducible in individual patients. Therefore the WBC count can be used as a guide to the timing of leukapheresis. PB cells from normal controls' and patients' prechemotherapy were unable to sustain hemopoiesis in two-stage long-term cultures. In contrast, PB cells collected from patients primed with chemotherapy alone or chemotherapy with G-CSF at the time of predicted maximal colony-forming cell release were able to generate and sustain hematopoiesis in long-term cultures at a level comparable or superior to normal BM. These findings indicate that the use of G-CSF after routine outpatient chemotherapy stimulates maximal release of primitive hemopoietic cells into the circulation, including colony-forming cells and long-term culture-initiating cells. Their numbers are comparable with those in normal BM and are such that a single leukapheresis will usually yield enough cells for hemopoietic reconstitution after myeloablative chemotherapy.     

Allogeneic cell therapy with donor peripheral blood cells and recombinant human interleukin-2 to treat leukemia relapse after allogeneic bone marrow transplantation

Allogeneic bone marrow transplantation (BMT) is the only effective treatment for hematologic malignancies resistant to conventional chemotherapy. Until recently, no cure existed for patients who relapsed post-BMT. We present our long-term observations on remission induction, after relapse post-BMT, by allogeneic cell therapy (allo-CT) and the feasibility of remission induction in allo-CT-resistant patients by activation of antileukemia effector cells with recombinant human interleukin-2 (rhIL-2) in vitro and in vivo. The longest observation of successful allo-CT (event-free survival, greater than 8 years) was made in a patient with resistant pre-B lymphoblastic leukemia who received infusions with graded increments of donor (female) peripheral blood lymphocytes (PBL) as soon as bulky hematologic and extramedullary relapse was noticed early post-BMT. The patient is currently without evidence of residual host (male) cells as determined by polymerase chain reaction (PCR). Of 17 patients with acute and chronic leukemia in relapse after BMT, 10 were reinduced into complete remission. Four patients with cytogenetic relapse responded to allo-CT alone, while five of six patients with overt hematologic relapse responded only after additional activation of donor with rhIL-2. Allo-CT can, therefore, successfully reverse chemoradiotherapy-resistant relapse of both acute and chronic leukemia. Moreover, in patients resistant to donor lymphocyte infusion, remission can be accomplished by additionally activating donor PBL in vitro and/or in vivo with rhIL-2. Based on our observations, after BMT, allo-CT should be considered the treatment of choice for patients with hematologic malignancies resistant to conventional anticancer modalities. Allogeneic activated cell therapy (allo ACT) should be considered for patients with tumor cells resistant to allo-CT. Although allo-CT, followed if indicated by allo-ACT, can be effective for patients with overt hematologic relapse, reversal of persistent minimal residual disease or documented molecular/cytogenetic relapse early after BMT may also be considered as a possible indication for allo-CT.     

Indications, technique and risks in bone marrow transplantation in adulthood

The option of bone marrow transplantation (BMT) significantly improved prognosis of adult patients with hematologic malignancies aged less than 50 years. Allogeneic BMT using the marrow of an HLA-identical family member still provides the most effective method of BMT. Conventional indications for this form of BMT are chronic myeloid leukemia (CML), acute leukemias presenting with adverse risk factors, myelodysplastic syndromes and severe aplastic anemia. If performed early in the disease course (e.g. during the chronic phase of CML or first remission of acute leukemia and MDS) allogeneic BMT cures 50 to 60% of patients. About 20% die of therapy related complications, e.g. graft versus host disease (GvHD), fatal infections or venoocclusive disease of the liver (VOD) and about 20% of patients succumb to relapse of their hematologic disorder. 80% presenting with severe aplastic anemia can be cured, if allogeneic BMT is performed soon after diagnosis without previous immunosuppressive therapy and blood transfusions. BMT with the marrow of a matched unrelated donor or autologous BMT are increasingly used as alternative procedures. A rate of lethal complications as high as 50% hinders rapid extension of BMT with unrelated donors. Therefore, this form of BMT should be restricted to young patients with leukemias, who cannot achieve long-term remission with conventional chemotherapy (in case of acute leukemias) or alpha-interferon (in case of CML). Reconstitution of hematopoiesis is more rapid after peripheral blood stem cell transplantation (PBSCT) compared with autologous BMT. Therefore, PBSCT will replace autologous BMT in most cases. Most favourable results of PBSCT have been reported in patients with malignant lymphomas after relapse or inferior response to primary induction therapy. Due to the higher relapse rate autologous BMT is inferior to allogeneic BMT in leukemia patients. Trials are required to clarify the potential role of myeloablative therapy with stem cell support in the treatment of patients with solid tumors. Many of the preliminary results already published are unsatisfactory and data of larger trials are still lacking. Therefore, BMT or PBSCT cannot be recommended generally for the therapy of patients with solid tumors.     

Allogenic bone marrow transplantation in the treatment of malignant hematologic disease

We have treated 28 patients (pts) with malignant hematological diseases with allogeneic bone marrow transplantation (BMT). 18 pts had acute lymphoblastic (ALL) and non lymphoblastic leukemia (ANLL), 5 chronic myeloid leukemia (CML), 2 severe aplastic anemia (SAA), 1 myelodisplasia, 1 Fanconi's anemia and 1 advanced Non Hodgkin's lymphoma. All but three received the graft from HLA identical sibling donors. We used conditioning with total body irradiation and chemotherapy (cyclophosphamide, cytarabine and etoposide) in 17 pts and chemotherapy alone in 11. 24 pts had full hematological recovery 18 to 25 days post BMT. 15 pts died after BMT as a consequence of toxicity or early infection (4), graft failure (2), graft versus host disease (4) or relapse (5). Actuarial event free survival for the group with favorable prognosis (SAA, ALL and ANLL in first or second remission and CML in chronic phase) is 57% at 36 months. Allogeneic BMT is an effective and feasible therapeutic procedure for selected patients with hematological malignancies.     

A novel antithrombin gene mutation: slippage and mispairing as a mechanism of genetic disease

Treatment options for acute leukemia relapsing after allogeneic BMT include conventional chemotherapy or a second transplant; however, results are rather discouraging, the first option being associated with poor survival and the second with a high mortality rate. More recently, donor leukocyte infusion (DLI) from the original donor has been used for relapsed patients in an attempt to induce a graft-versus-leukemia (GVL) effect. This procedure is partially devoid of the toxicity inherent to a second BMT. At our Institution, a 36-year-old patient with biphenotypic AML in second complete remission after relapse following allogeneic BMT was treated with peripheral blood stem cell (PBSC)-enriched donor leukocytes, obtained after in vivo priming with rhG-CSF. The patient experienced extensive cGVHD but developed a testicular relapse while in full hematologic remission. After irradiation of the sanctuary site he remains free of disease, still with chronic GVHD, 21 months after bone marrow relapse. This case suggests that immunologically privileged sites are inaccessible to GVHD/GVL effect. This should be considered when planning salvage transplants procedures in patients at risk for extramedullary involvement.     

Effects of adenosine, ATP, and UTP on chloride secretion by epithelia explanted from fetal rat lung

To determine the role of intensive chemotherapy and allogeneic bone marrow transplantation (BMT) in treatment of refractory anemia with excess of blasts (RAEB) or RAEB-t (in transformation), the outcome of 37 consecutive children, 12 with RAEB and 25 with RAEB-t, diagnosed between 1985 and 1995 was analyzed. Fourteen patients received intensive chemotherapy according to the AML-BFM protocols 83, 87, or 93 (group 1). Seven patients were treated less intensively with the 6-week consolidation phase as induction (group 2). Allogeneic BMT was performed in 10 children of group 1 and 2 after, and in eight (group 3) without prior chemotherapy. Eight children received minimal or no chemotherapy (group 4). Of 21 children (groups 1 and 2) 17 (81%) achieved complete or partial remission after chemotherapy, 12 of them (10 of group 1) remained in remission, eight after BMT. Five-year survival in 29 children treated intensively (groups 1-3) was 46%, SE 12%. Two of the other eight children (group 4) remained alive, one after spontaneous remission. Outcome after BMT was related to the blast count in the bone marrow prior to BMT. None of 10 children (including two with minimal or no chemotherapy) with < or = 12% blasts before BMT relapsed, in contrast to five of eight patients with a higher blast count (P log rank 0.02). We conclude that a substantial number of children with RAEB or RAEB-t can achieve remission with intensive AML-specific chemotherapy. In patients responding to intensive chemotherapy an increase in long-term survival after allogeneic BMT can be expected.     

Philadelphia chromosome-positive (Ph+) childhood acute lymphoblastic leukemia: good initial steroid response allows early prediction of a favorable treatment outcome

Among 4,760 acute lymphoblastic leukemia (ALL) patients enrolled from 1986 to 1995 in two subsequent trials of the BFM and AIEOP study group, 61 patients were found to have Philadelphia chromosome-positive (Ph+) ALL. These patients were analyzed for presenting features and treatment outcome to identify specific prognostic factors. Treatment stratification was based on initial cell mass and early response as determined by blast count in peripheral blood after a 7-day induction prephase with prednisone and one dose of intrathecal methotrexate on day 1. All patients were treated by similar intensive Berlin-Frankfurt-Münster (BFM) protocols. The median age of Ph+ patients was 7.5 years, the median white blood cell count (WBC) was 75 x 10(9)/L, 77% of patients had common ALL, and 29% coexpressed myeloid markers. After a median observation time of 4.2 years, 29 of 61 patients are alive (survival probability [pSUR] at 4 years, 0.49; standard error [SE], 0.06), and 24 of 61 are in first complete remission (CR1; probability of event-free survival [pEFS] at 4 years, 0.38; SE, 0.06). Twenty (35%) of 57 evaluable patients had >/=1,000 leukemic blasts per microliter of blood on day 8 of induction (defined as prednisone-poor-response [PPR]). These patients were older (10.0 v 6.88 years; P = .02) and had a higher WBC (144 v 29 x 10(9)/L; P = .0016) as compared with patients with prednisone good response (PGR; <1,000 blasts/microL at day 8). Only 2 of 20 patients (10%) with PPR remained in CR1 and alive: 6 patients with PPR did not survive after allogeneic bone marrow transplantation (BMT) due to recurring disease (n = 3) and toxicity (n = 3), and 12 nontransplanted patients died due to progression (n = 5) or relapse (n = 7). In contrast, 26 (70%) of the 37 patients with PGR are alive. Of 18 patients transplanted by allo-BMT, 1 relapsed (now in CR2) and 4 died after BMT. Among the 19 patients with PGR treated by chemotherapy alone, 8 remained in CR1 and 11 relapsed, of which 4 are in CR2 or CR3. The prednisone response emerged as the only independent prognostic factor for survival in Cox regression analysis. Thus, two thirds of Ph+ childhood ALL cases can be identified early by PGR, which, when treated with intensive BFM chemotherapy, with or without BMT, have a significantly lower risk of treatment failure. With a median continuous complete remission (CCR) time of 4.1 years, pEFS for PGR is 0.55 (SE, 0.08) compared with 0.10 (SE, 0.07) in patients with PPR (P = .0001). PGR is also an indicator for treatment responsiveness and durable second remission after relapse, which in turn may provide a second chance for BMT.     

Treatment of chronic myeloid leukemia in relapse after umbilical cord blood transplantation

Umbilical cord blood (UCB) is increasingly used as a source of hematopoietic progenitor cells for allotransplantation. Donor-derived buffy coat cells are considered optimal treatment for leukemia relapses after transplantation of allogeneic bone marrow. Experience with relapses after UCB transplants are sparse. Here we report a girl who received an UCB transplant for chronic myeloid leukemia, relapsed after three years, failed to respond to donor buffy coat cells, but achieved a complete hematologic, cytogenetic, and molecular remission on interferon-alpha.     

Adoptive immunotherapy with donor mononuclear cell infusions to treat relapse of acute leukemia or myelodysplasia after allogeneic bone marrow transplantation

Relapse remains a significant problem after allogeneic bone marrow transplantation (BMT). For patients with relapsed chronic myelogenous leukemia (CML), infusions of donor mononuclear cells (MNC) provide a potent graft-versus-leukemia (GVL) reaction inducing complete remissions in the majority of patients. Little is known about the efficacy of donor MNC infusions for patients who relapse with other diseases. We have studied the GVL effects of donor MNC in eight patients with relapsed acute leukemia or myelodysplasia (MDS). One patient with relapsed MDS achieved complete remission and another patient had a transient response. Five of six non-responders died of progressive leukemia and one non-responder died of complications during second BMT. Three patients developed grade I-II acute GVHD responsive to immunosuppression. These data, and review of the literature, suggest that GVL induction with donor MNC infusions is less effective for patients with relapsed acute leukemia than for patients with relapsed CML; too few patients with relapsed MDS have been treated to draw definite conclusions. However, some patients respond, and given the high mortality associated with alternative procedures such as second BMT, donor MNC infusions are a reasonable approach for relapsed acute leukemia and MDS after allogeneic BMT.     

Adoptive immunotherapy for leukemia: donor lymphocytes transduced with the herpes simplex thymidine kinase gene for remission induction. HGTRI 0103

This study will evaluate the safety and efficacy of allogenic donor lymphocyte infusions in patients who have relapsed hematologic malignancies after allogeneic bone marrow transplantation (BMT). Donor lymphocyte transfusions have resulted in the cure of some patients with relapsed leukemia or lymphoproliferative disorder after allogeneic BMT, but has been complicated by the development of graft versus host disease (GvHD). We hypothesize that a retroviral vector containing the Herpes simplex thymidine kinase (HStk) gene will allow for retention of the anti-leukemia response of transfused donor lymphocytes while allowing for the adverse effects of GVHD to be mitigated. Patients with relapsed hematologic malignancies after allogeneic BMT will be infused with ex vivo gene modified donor lymphocytes. The Herpes Simplex thymidine kinase (HStk) gene will be transduced into the cells ex vivo using LTKOSN. 1 vector supernate. Insertion of the HStk gene into lymphocytes confers a sensitivity to the anti-herpes drug ganciclovir (GCV). This selective destruction of donor lymphocytes in situ will be used to abrogate the effect of graft versus host disease, if it develops.     

Allogeneic peripheral blood progenitor cells for treatment of relapse after bone marrow transplantation

Donor leukocyte infusions (DLI) are an effective therapy for patients who relapse with leukemia after bone marrow transplantation (BMT). Severe graft-versus-host disease and prolonged periods of pancytopenia compromise the success of this treatment in a substantial number of patients. We used filgrastim-mobilized peripheral blood progenitor cells (PBPCs), in some cases preceded by cytoreductive therapy, to circumvent some of the problems associated with DLI. Eleven patients (median age 41 years) received a total of 20 donor cell infusions. Their diagnosis was CML in hematological (two patients) or cytogenetic relapse (two patients), six patients suffered from acute myeloid leukemia (AM; n = 5) or Philadelphia chromosome-positive acute lymphoblastic leukemia (ALL Ph+). One patient had multiple myeloma (MM). All six patients with acute leukemias received cytoreductive therapy prior to PBPC infusions; three patients with CML were pretreated with IFN alpha. Four of four patients with CML responded to PBPC infusions and currently are in complete clinical and molecular remission for time periods between 1 and 12 months. Six of six patients with acute leukemias achieved a complete remission. All of them relapsed after a median remission duration of 24 weeks (range 11-49 weeks). Three patients relapsed at extramedullary sites (CNS, testes, skin). Four of six acute leukemia patients received further cytoreductive therapy. All patients responded again and are in complete remission for time periods between 14 and 615 days. Two patients with acute leukemias have died due to dissemination of the disease. The patient with MM did not respond and is alive with disease. Severe (grade III) acute GVHD developed in two of 11 patients, three patients developed grade II disease, six patients did not show any signs of GVHD. Extensive chronic GVHD has developed in two cases to date. Patients with chemotherapy prior to PBPC infusion developed neutropenia and thrombocytopenia with a maximum duration of 20 and 14 days, respectively; prolonged periods of neutropenia did not occur. Two patients developed long-lasting thrombocytopenia in spite of PBPC infusion, in one case followed by leukemic relapse. Repeated courses of chemotherapy and PBPC infusion were generally tolerated well; no early deaths due to treatment-related toxicity or GVHD were observed. We conclude that the use of allogeneic PBPC instead of DLI in patients with relapse after BMT is technically feasible and safe. The efficacy of PBPC infusions seems comparable to DLI in patients with CML. Patients with acute leukemias also achieved complete albeit transient remissions. Aggressive chemotherapy followed by PBPC infusions resulted in only limited duration of cytopenia. The usage of PBPC infusion instead of non G-CSF-mobilized donor cells for treatment of relapse after BMT may reduce pancytopenia-related complications and merits further investigation.     

Treatment of Ph1-positive chronic myelogenous leukemia in children: comparison between allogeneic bone marrow transplantation and conventional chemotherapy. Spanish Working Party for BMT in Children (GETMON)

BACKGROUND AND OBJECTIVE: To compare the estimated survival and disease-free survival between children with Ph1-positive chronic myeloid leukemia treated with allogeneic bone marrow transplantation or conventional chemotherapy. DESIGN AND METHODS: In this retrospective study we compared the results obtained in a group of 14 children who received allogeneic bone marrow transplantation (BMT) between 1983 and 1993, and another group of 27 children treated with busulfan, hydroxyurea or alpha-interferon during the same time period. Patients were transplanted at a median of 7 months from diagnosis and all except one were in their first chronic phase. Conditioning consisted in total body irradiation and cyclophosphamide in 12 cases, and busulfan was added in two. RESULTS: Of the 14 patients treated with BMT, two died of transplant-related complications and two relapsed 18 and 48 months after the BMT. Ten children remain alive and disease free at a median follow up of 60 months. The probability of DFS at 5 years is 70%. Of the 27 patients treated with chemotherapy, 22 have died at a median of 36 months from diagnosis. The probability of survival at 5 years is 5% versus 83% for the BMT group (p = 0.001). INTERPRETATION AND CONCLUSIONS: Allogeneic BMT is a safe and very effective treatment for Ph-positive CML in children. Patients who have an HLA-identical sibling donor must receive a transplant as soon as possible after being diagnosed.     

Dose-escalation trial of M195 labeled with iodine 131 for cytoreduction and marrow ablation in relapsed or refractory myeloid leukemias

PURPOSE: Mouse monoclonal antibody (mAb) M195 (anti-CD33) is reactive with most myeloid leukemia cells, monocytes, and hematopoietic progenitors, but not with other hematopoietic cells or stem cells nor with nonhematopoietic human tissues. A therapeutic dose-escalation study of M195 labeled with iodine 131 was conducted in patients with relapsed or refractory myeloid leukemias. METHODS: Twenty-four patients (16 relapsed or refractory acute myeloid leukemias, five blastic myelodysplastic syndromes [MDS], two chemotherapy-related secondary leukemias, and one blastic chronic myelogenous leukemia [CML]), including seven who had failed to respond to prior bone marrow transplantation (BMT), received from 50 mCi/m2 to 210 mCi/m2 of 131I-M195 in divided doses. RESULTS: In 22 patients, whole-body gamma-imaging demonstrated marked uptake of antibody into all areas of bone marrow. Twenty-three patients (96%) demonstrated decreases in peripheral-blood cell counts, with decreased percentage of bone marrow blasts seen in 83% of cases. Eighty-nine percent of bone marrow biopsies examined quantitatively demonstrated substantial decreases in the number of blasts, with greater than 99% of blasts killed in some patients. The two cases that failed to demonstrate leukemic cytoreduction occurred in the first two dose levels. For 131I doses of 135 mCi/m2 or greater, pancytopenia was profound and lasted for at least 12 days. Eight patients had sufficient marrow cytoreduction to proceed to BMT. Three of these achieved marrow remission, one of 6+, and one of 9 months' duration. Two patients in blastic phase temporarily reverted to their original myelodysplastic states. Thirty-seven percent of assessable patients developed human anti-mouse antibody (HAMA). In two patients with HAMA who were re-treated, plasma 131I-M195 levels could not be maintained and no therapeutic effect resulted. Significant nonhematologic toxicity (hepatic) was seen in one patient and the maximum-tolerated dose (MTD) was not reached. CONCLUSION: These data suggest that safe leukemic cytoreduction can be achieved with 131I-M195 even in multiply relapsed or chemotherapy-refractory leukemias. This agent may be useful as part of a preparative regimen for BMT.     

Conventional cytogenetics and FISH evaluation of chimerism after sex-mismatched bone marrow transplantation (BMT) and donor leukocyte infusion (DLI)

BACKGROUND AND OBJECTIVES: Sensitive and quantitative cytogenetic methods to better assess the biological significance of post-BMT chimerism have been recently developed. In this study, we compared the results of chimerism analysis and evolution employing conventional cytogenetics and fluorescence in situ hybridization (FISH) in 16 patients after sex-mismatched BMT, and in 5 patients after donor lymphocyte infusion (DLI) to treat post-BMT relapse. DESIGN AND METHODS: FISH studies were performed using separate digoxigenin labeled centromeric DNA probes for the X (pDMX1) and Y (DYZ1/DYZ3) chromosomes. To this purpose, different types of samples were used: bone marrow (BM) and peripheral blood (PB) slides processed for conventional cytogenetics, and routine BM and PB smears. RESULTS: Results of chimerism studies performed on different types of samples showed no significant differences. No significant differences in the ability to identify the sex of each cell with both pDMX1 and DYZ1/DYZ3 probes were found and the results obtained from independent experiments showed a high linear correlation. Chimerism analysis by FISH showed initial mixed chimerism after BMT in 10 patients. Seven of these patients were also studied by conventional cytogenetics and 2 of these showed mixed chimerism. Seven of the former 10 patients evolved to complete donor chimera. 6 patients showed cytogenetic or hematologic bone marrow relapse, 3 of which were preceded by mixed chimaerism as revealed by FISH studies. FISH studies permitted an easy and accurate monitorization of the response to DLI in 5 relapsed patients, showing an increase in the proportion of donor cells in 4 patients as they reached a new complete remission. INTERPRETATION AND CONCLUSIONS: Both FISH and conventional cytogenetics are quantitative methods to assess chimerism. However, FISH is more sensitive, accurate and can even be applied on routine BM and PB smears. Furthermore, its combination with immunophenotyping approaches to quantify chimerism on cell subpopulations, will help to clarify post-BMT chimerism significance.     

Importance of mixed chimerism to predict relapse in persistently BCR/ABL positive long survivors after allogeneic bone marrow transplantation for chronic myeloid leukemia

Determination of hematological chimerism could be helpful in understanding the biology of leukemic relapse after allogeneic bone marrow transplant (BMT) for chronic myeloid leukemia (CML), because the detection of malignant residual cells carrying the bcr/abl message by qualitative RT-PCR is of limited value in predicting disease progression for individual patients. We have studied the chimerism pattern and the bcr/abl status by Southern-blot in 15 CML patients (M/F:6/9) transplanted with unmanipulated BM from HLA identical sibling donors, persistently bcr/abl positive by RT-PCR. The median age of the series was 31 years (18-49) and disease status at BMT was: chronic phase: 11, accelerated phase: 3 and blast crisis: 1 patient. Of the 15 patients, 9 are alive and in complete remission (CR), 4 have died in CR and 2 are alive but suffered relapse at + 19 and +26 months post-BMT. The median follow-up is 81 months (13,7-168). Rearrangement of the BCR gene was performed by Southern-blot using P32-labeled transprobe-1. PCR analysis of chimerism was assessed using primers for the following VNTR loci: D1S80, D1S111, 33.1, APO-B, YNZ-22, lambdag3 and DXS52. Seventy-nine samples were analyzed (median per patient 5 (range 2-9)). Thirteen patients showed complete chimerism and lacked BCR rearrangement over time by Southern-blot. The 2 patients who relapsed showed mixed chimera status from +9 and +5 months respectively until the end of the study. Persistent BCR rearrangement was observed in these 2 patients from +12 and +11 months respectively. Our data suggest that mixed chimerism may predict hematologic or cytogenetic relapse by several months in those patients who are persistently PCR-positive post-BMT.