Stem-cell transplantation in chronic lympocytic leukaemia

Best Practice & Research Clinical Haematology Vol. 20, No. 3, pp. 513–527, 2007 doi:10.1016/j.beha.2007.03.003 available online at http://www.sciencedirect.com

12 Stem-cell transplantation in chronic lympocytic leukaemia John G. Gribben *

MD, DSc

Professor of Experimental Cancer Medicine, Institute of Cancer St Bartholomew’s Hospital, CRUK Medical Oncology Unit, Barts and The London School of Medicine, Charterhouse Square, London EC1M 6BQ, UK

Excellent response rates are now achieved with modern chemoimmunotherapeutic approaches in chronic lymphocytic leukaemia (CLL), but the disease remains incurable. Younger patients and those with adverse prognostic factors will die from their disease, and are therefore candidates for clinical trials investigating the potential role of haematopoietic stem-cell transplantation (SCT) in the management of their disease. Autologous SCT is feasible and safe, but there is a high incidence of subsequent relapse. Myeloablative allogeneic SCT is associated with high treatment-related morbidity and mortality but few late relapses. Attempts to exploit the graft-versus-leukaemia effect of allogeneic donor cells but to reduce the toxicity are being explored in studies of reduced-intensity conditioning allogeneic SCT in CLL. With many potential treatments available, appropriate patient selection and the timing of SCT in the management of CLL remain controversial and the focus of ongoing clinical trials. Key words: chronic lymphocytic leukemia; stem-cell transplantation; graft-versus-host disease; graft-versus-leukemia; donor lymphocyte infusions.

STEM-CELL TRANSPLANTATION FOR CHRONIC LYMPHOCYTIC LEUKAEMIA (CLL) Haematopoietic stem-cell transplantation (SCT) is not a suitable treatment option for most patients with CLL. The disease often follows an extremely indolent course, and many patients are too elderly to undergo this procedure. However, 40% of CLL patients are younger than 60 years of age, and younger patients will die of their disease.1 High-risk patients can be identified using a number of clinical and biological features2, and such younger patients are suitable candidates for enrolment in clinical trials evaluating the role of SCT in CLL. Encouraging results have been achieved in phase-II * Tel./Fax: þ44 20 7882 6126. E-mail address: [email protected] 1521-6926/$ - see front matter ª 2007 Elsevier Ltd. All rights reserved.

514 J. G. Gribben

clinical trials, but unlike other haematological malignancies, where the role of SCT for specific risk groups has been established in prospective studies3–9, in CLL there have been no studies that have compared the outcome after standard chemotherapy with either autologous or allogeneic SCT. The biggest challenges remain the identification of patients with CLL who are at sufficiently high risk to merit this approach, as well as the timing of transplantation in the course of their disease. PATIENT SELECTION FOR SCT CLL is an extremely heterogeneous disease, the clinical course varying such that some patients can live with CLL for decades and never require therapy, while others have a rapidly progressive and fatal malignancy. Considerable work has been performed to identify the clinical and biological characteristics of this disease that would allow identification of patients who might merit transplant. Most phase-II studies have enrolled younger patients with ‘high-risk’ disease, but this term is rather loosely defined, and it is difficult to determine precisely the risk factors used in each of the reported studies. In addition, the risk factors identified have changed over time as newer risk factors – such as cytogenetics10, variable region of the immunoglobulin heavy chain (IgVH) mutational status11,12, and zeta-associated protein 70 (ZAP-70) expression13–15 – have been identified. European Group for Blood and Marrow Transplantation (EBMT) guidelines have now been established, outlining indications for SCT in CLL.16 The guidelines conclude that there is an evidence base for the efficacy of allogeneic SCT in CLL and that this is indicated in high-risk CLL patents. Precisely what factors are defined as high-risk remains unclear, but patients with p53 deletions or mutations are considered candidates in first remission, and ongoing studies are assessing the impact of biomarkers – including IgVH mutational status and cytogenetic abnormalities – to identify patients at sufficiently high risk to merit consideration for transplant in first remission. The consensus of the EBMT working group was that allogeneic transplant was recommended early in the disease course for young patients with CLL who fail to achieve complete remission (CR) or who progress within 12 months after purine analogues, and those who relapse within 24 months after having achieved a response with purine-analogue-based combination therapy or autologous transplantation. It is clear that neither of these categories requires assessment of biological risk factors, and ongoing prospective clinical studies will be required to determine the specific risk factors that identify patients at sufficiently high risk to merit the use of allogeneic SCT in first CR. However, there is a consensus that patients requiring treatment who have p53 abnormalities have a sufficiently poor prognosis to merit transplantation in first response. The role of autologous SCT in the management of CLL remains unclear. AUTOLOGOUS SCT The antitumour activity of autologous SCT is dependent upon a dose–response effect in CLL. It is clear that such a dose effect does occur in CLL, based on the increased response rates and longer duration of responses when more intensive chemotherapy regimens are used.17–19 Although no studies have prospectively compared the role of standard chemotherapy with transplantation in CLL, a retrospective matched-pair analysis suggested a survival advantage for autologous SCT over conventional therapy.20 In this study a risk-matched comparison was made between 66 patients who had undergone a uniform high-dose therapy plus autologous SCT and a database of

Stem-cell transplantation in CLL 515

291 patients treated conventionally. Four variables were matched –age, Binet stage, IgVH gene mutational status, and lymphocyte count – and 44 pairs fully matched for all four variables were identified; these patient groups were well balanced for additional risk factors, including adverse genomic abnormalities and CD38 expression. With an overall median follow-up time of 70 and 86 months, respectively, survival was significantly longer for the patients who had undergone autologous SCT compared with conventionally treated patients when calculated from diagnosis (P ¼ 0.03) or from study entry (P ¼ 0.006). Phase-II studies have been reported which examined the outcome following autologous SCT for CLL/small lymphocytic lymphoma (SLL).21–28 This approach is feasible in CLL with a transplant-related mortality (TRM) of 1–10%, with most toxicity occurring late (Table 1). Encouraging early results were reported in a pilot study in patients with chemosensitive relapsed disease.21 Eligibility criteria for entry into this study included documented chemosensitivity, and patients had to achieve a protocol-eligible minimal disease status before proceeding to autologous SCT. Following this pilot study, a total of 137 patients with chemosensitive disease underwent autologous SCT in a phase-II study.22 Patients transplanted in relapse or with chemoresistant disease have poor outcome with autologous SCT.23 These patients were heavily pre-treated and underwent autologous SCT not at a time of minimal tumour burden but after subsequent relapse. Seven patients received stem cells purged by immunomagnetic depletion, but residual clonal B cells remained detectable in five patients. The outcome of these patients was poor. Three underwent a Richter’s transformation, two died in CR, and two relapsed. Only two patients achieved CR, and one achieved a partial remission (PR). Poor results with a high relapse rate after autologous SCT were also observed in a study of 16 CLL patients in whom eight had relapsed and six had died (three from progressive malignancy) at a median follow-up of 41 months.25 Eight heavily pretreated patients received autologous SCT with partially purged CD34þ peripheralblood stem cells, and although four patients remained in complete remission, the median follow-up was very short at only 9 months.29 When autologous SCT is performed early in the course of the disease, outcome appears better. Among 18 such

Table 1. Autologous transplantation for chronic lymphocytic leukaemia (CLL). Number of patients 137

77 65

TRM 5 early 13 MDS/AML 15 other cancer 0 1 early 5 MDS/AML 2 0 1 0

16 13 11 8 20 enrolled 12 stem cells collected 5 0

Ongoing CR Median FU (months)

Reference

67

78

Gribben et al, 200522

50 45

28 36

Jantunen et al, 200627 Milligan et al, 200526

5 12 2 5

37 19 10 36

Pavletic et al, 199825 Dreger et al, 199824 Khouri et al, 199423 Sutton et al, 199828

4

9

Itala et al, 199729

TRM, transplant-related mortality; CR, complete remission; FU, fluorouracil; MDS, myelodysplasia; AML, acute myeloid leukaemia.

516 J. G. Gribben

patients enrolled, autologous SCT was performed in 13, only one of whom had relapsed at the time of publication.24 In the Medical Research Council (MRC) study, only one TRM was seen among 65 patients who underwent autologous SCT, and the CR rate after transplantation was 74% (48/65).26 The 5-year estimated overall survival (OS) was 77.5%, and progression-free survival (PFS) was 51.5%. None of the variables examined at study entry were predictive for OS or disease-free survival (DFS), but detectable minimal residual disease (MRD) after transplant was highly predictive of disease recurrence. There was no TRM among 72 patients who underwent autologous SCT in five Finnish centres; median age was 57 years (range 38–69 years), and transplantation was performed at a median of 32 months (range 6–181 months) from diagnosis.27 At median follow-up of 28 months, 37% had progressed, with median OS of 95 months and median PFS of 48 months. Feasibility of autologous SCT In many of the phase-II studies it is not possible to determine the denominator of patients, since patients were often referred to the transplant centre having achieved protocol-eligible response to therapy, and patients who failed to achieve this level of response may not have been referred or may have been referred for allogeneic SCT. However, single-centre studies have suggested that less than 50% of patients enrolled on an intent-to-treat basis will proceed to autologous SCT.28 Among 20 patients with relapsed CLL enrolled in this study, 13 patients responded to salvage chemotherapy, stem cells were collected from eight patients, but only eight patients proceed to autologous SCT. It is difficult to collect sufficient CD34þ cells in CLL, especially in heavily pre-treated CLL patients, and at least 3 months should be allowed between the last dose of fludarabine and leukapheresis.30 Among 115 previously untreated CLL patients prospectively enrolled in a multicentre pilot study to assess the feasibility of performing autologous SCT, only 65 (56%) proceeded to transplant.26 Ex-vivo and in-vivo purging of stem cells Various methods – including multiparameter flow cytometry analysis31 and polymerase chain reaction (PCR)32 – are being used to investigate whether persistence of MRD will predict which patients will relapse following transplant in CLL. Molecular remissions can be achieved in more than two thirds of patients, but these are not durable26,32–34, and most patients who achieve CR after autologous SCT will eventually relapse. Detectable molecular disease post-transplant is, however, highly predictive of clinical recurrence.26,32 One approach to increase the likelihood of elimination of MRD after autologous SCT is to attempt to eradicate any residual lymphoma cells ex vivo using monoclonal antibodies.22 Ex-vivo purging of stem cells results in stemcell loss that might be overcome by in-vivo treatment with alemtuzumab or rituximab. When alemtuzumab was used in the conditioning regimen for autologous SCT in one arm of the German CLL Study Group CLL3 trial, 12 of 16 patients (87%) developed a skin rash between 43 and 601 days post-SCT, and in seven of these patients a biopsy confirmed graft-versus-host disease (GVHD) which persisted for a median duration of 517 days (range 60–867 days).35 The trial was discontinued because of the TRM, but addition of alemtuzumab led to improved disease control. The concept of using alemtuzumab for in-vivo purging should perhaps not yet be discarded. When used at a modification from the standard doses (10 mg

Stem-cell transplantation in CLL 517

subcutaneously three times per week for 6 weeks) in 34 patients who had had a clinical response to a fludarabine-based regimen, the CR rate improved from 35% to 79.5%, with 56% achieving eradication of MRD.36 Peripheral-blood stem cell (PBSC) collection was subsequently successfully performed in 92%. Eighteen patients underwent autoSCT, with 17 remaining in CR at a median follow-up of 14.5 months post-SCT. Late complications Studies reported with short follow-up focus only on the early post-transplant TRM. Of particular concern are the late consequences of high-dose therapy and autologous SCT. Notable among these is the development of secondary myelodysplasia and acute myeloid leukaemia (MDS/AML) after autologous SCT. Among 65 newly diagnosed patients treated with fludarabine followed by autologous SCT, eight developed MDS/ AML26, with a 5-year actuarial risk of developing MDS/AML of 12.4% (95% CI 2.5–24%) after autologous SCT. No potential risk factor analysed was predictive. The group postulate that potential causative factors may be exposure to fludarabine, the low stem-cell dose infused, and use of total body irradiation (TBI) in the conditioning regimen. The study with the longest reported follow-up is from the Dana Farber Cancer Institute22, which reports not only a high incidence of secondary MDS/AML, but also a high incidence of other tumours with longer follow-up. Second (nonCLL) malignancies developed after SCT in 31 (19%) patients. The median time from transplantation to the diagnosis of a haematological second malignancy was 35 months (range 1–138 months). Thirteen patients (9%) have developed MDS at a median of 36 months (range 11–87 months) after autologous SCT. Eight (62%) of the 13 patients diagnosed with MDS developed MDS during remission, whereas five patients developed MDS after progression of their CLL. At 8 years after transplantation the incidence of MDS was 12% (95% CI, 5–19%) and no patients have developed MDS at a later time point than this. The risk of MDS was not associated with the type of prior therapy (P ¼ 0.99). One patient developed diffuse large B-cell lymphoma at 13 months, and another a T-cell lymphoma at 138 months after autologous SCT. The B-cell lymphoma was not related to the underlying CLL clone, as assessed by IgH gene rearrangement sequencing from both malignancies. Fifteen patients have developed other cancers at a median time of 41 months (range 23–114 months) after SCT; four non-melanomatous skin cancers at 26–109 months and one melanoma at 25 months after autologous SCT. Nine patients have developed carcinomas at a median of 81 months (range 28–114 months) after autologous SCT (two colorectal, two breast, three lung, one head and neck, and one prostate cancer). Only two of these patients also had CLL progression. It is well recognized that patients with CLL are at greater risk for development of other cancers, but there is concern that the incidence of second malignancies after autologous SCT is higher than might be expected. This finding is not specific for autologous SCT for CLL, and second cancers are the most common cause of late TRM after autologous SCT.37 Conclusion Patients have better outcome after autologous SCT when they are treated early in the course of the disease and at a time with low tumour burden, suggesting that high-risk patients should be transplanted early in their disease course.24 However, high-risk patients may also have an adverse outcome after SCT, and IgVH mutation status

518 J. G. Gribben 1.0 0.9 0.8

Probability

0.7 0.6 0.5 0.4

Autologous

0.3 0.2 0.1

Allogeneic

P = 0.04

0.0 0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15

Years Figure 1. Progression-free survival after autologous and T-cell-depleted allogeneic stem-cell transplantation (SCT). Adapted from Gribben et al (2005, Blood 106: 4389–4396) with permission.

maintains its poor prognostic significance after autologous SCT20,38, although more than 90% of the patients undergoing autologous SCT in one series had unmutated IgVH genes.22 The major problem after autologous SCT remains relapse of disease, late complications, and no evidence of a plateau on DFS (Figure 1).22 Based upon the results obtained to date, autologous SCT is not recommended in routine clinical practice and should be offered only in the setting of well-designed clinical trials. ALLOGENEIC SCT Allogeneic SCT has significant morbidity and mortality from regimen-related toxicity, GVHD and infection, but surviving patients have long-term disease control.22,39–42 In registry data, TRM following allogeneic SCT in CLL patients was 46%, with mortality from GVHD of 20%.39 Studies from MD Anderson Cancer Center demonstrate improved outcome after allogeneic compared to autologous SCT.23 Among 14 patients with chemorefractory CLL, 13 (87%) achieved CR post-transplant, and nine remained alive and in CR with median follow-up of 36 months43, suggesting that allogeneic SCT can induce durable remission even in patients with refractory disease. Of 25 patients with CLL who underwent allogeneic SCT at the Fred Hutchinson Cancer Center42, grade 2–4 acute GVHD was seen in 14 patients, ten developed clinical extensive chronic GVHD, and estimated OS at 5 years was 32%. Non-relapse mortality at day 100 was unacceptably high at 57% for patients conditioned with busulphan and cyclophosphamide compared to 17% for patients conditioned with TBI-containing regimens. Among 30 patients (20 related donors and ten unrelated donors) transplanted for CLL between 1989 and 2001 in Vancouver, with a median followup of 4.3 years, 47% were alive in CR. Estimated OS and DFS at 5 years was 39%, and a strong graft-versus-leukaemia (GVL) effect was noted, with those developing acute or chronic GVHD having near-complete protection from relapse.44 IgVH

Stem-cell transplantation in CLL 519

mutation status maintains its poor prognostic significance after autologous SCT20,38, but it would appear that this adverse event can be overcome with the use of allogeneic SCT.45 Among 50 patients who underwent SCT, 34 had unmutated IgVH genes (14 allogeneic SCT and 20 autologous SCT) and 16 had mutated IgVH genes (nine allogeneic SCT and seven autologous SCT). There was no difference in CR rate between type of transplantation and IgVH mutational status; however, after a median follow-up of 5 years, there was a significantly higher relapse rate following autologous compared with allogeneic SCT in both mutational groups. Therefore the GVL effect of allogeneic SCT may overcome the negative impact of unmutated IgVH gene mutation status on outcome. There are no randomized studies comparing the outcome of autologous versus allogeneic SCT. In a phase-II study at Dana-Farber Cancer Institute, 162 patients with high-risk CLL were enrolled in a ‘biologic randomization’ in which 25 patients with an HLA-matched sibling donor underwent T-cell-depleted myeloablative allogeneic SCT, while 137 with no sibling donor underwent B-cell-purged autologous SCT. The 100-day TRM was 4% after autologous or allogeneic SCT, but later TRM had a major impact on outcome. At the median follow-up of 6.5 years, PFS was significantly longer following autologous than T-cell-depleted allogeneic SCT, but no significant differences were observed in disease recurrence or deaths without recurrence related to type of transplant; there was no difference in OS between the two groups, with OS of 58% after autologous and 55% after allogeneic SCT (Figure 1). Registry data have suggested that although durable responses were being achieved after allogeneic SCT, survival was worse after allogeneic than after autologous SCT, with 3-year probability of survival reported as 45% for allogeneic SCT and 87% for autologous SCT.46 On the basis of these results, myeloablative allogeneic SCT is associated with high morbidity and mortality in CLL (Table 2), and its use should be restricted to young patients with chemorefractory disease. The use of TBI-containing regimens appears to be related to a lower TRM than chemotherapy-based regimens for this patient population and is the preferred preparative regimen. REDUCED-INTENSITY CONDITIONING SCT FOR CLL The major advantage of allogeneic SCT is the potential for a GVL effect. There is a decreased risk of relapse in patients with chronic GVHD44, increased risk of relapse with T-cell depletion22, and GVL can be generated by donor lymphocyte infusion (DLI) (Figure 2).22 Ongoing studies are attempting to exploit maximal GVL effect without concomitant GVHD and decrease the TRM of allogeneic SCT. A major

Table 2. Myeloablative allogeneic transplantation for chronic lymphocytic leukaemia (CLL). n

TRM

Severe GVHD

Ongoing CR

Median FU (months)

Reference

54 25

25 1 early 5 late 7 8 5

18 5

24 13 8 after DLI 9 14 8

27 78

Michellet et al, 199639 Gribben et al, 200522

60 24 35

Doney et al, 200242 Pavletic et al, 200041 Khouri et al, 199743

25 23 15

56 47 26

TRM, transplant-related mortality; GVHD, graft-versus-host disease; FU, fluorouracil.

520 J. G. Gribben CLINICAL RELAPS

SCT

DLI

1E+0 1E+0 1E+0 1E+0 1E+0 1E+0 1E+0 Limit of detection 2

4

6

Years Post

2

4

6

8

Years Post Figure 2. Response to donor lymphocyte infusion (DLI) in chronic lymphocytic leukaemia (CLL): quantitative real-time polymerase chain reaction (PCR) analysis of levels of disease following T-cell-depleted allogeneic SCT. DLI administered as sole therapy after clinical evidence of relapse induced subsequent achievement of complete remission (CR) and eradication of PCR-detectable disease. Adapted from Gribben et al (2005, Blood 106: 4389–4396) with permission.

advance in reducing the short-term morbidity and mortality of allogeneic SCT has been the introduction of non-myeloablative or reduced-intensity conditioning (RIC) regimens to allow engraftment of allogeneic stem cells. Although these procedures are commonly known as ‘mini-SCT’, this misnomer significantly underestimates the risks of such procedures, mainly due to the high incidence of GVHD. Several RIC regimens have been developed, and there is wide variation in the regimen components and intensity, GVHD prophylaxis, and timing of the application of DLI, which may contribute the subsequent morbidity of the procedure. In addition, there is a marked heterogeneity of patients’ specific disease characteristics, and many patients to date have been treated on experimental treatment protocols that allowed enrolment of many patients with chemorefractory end-stage disease. The truly non-myeloablative regimens are highly immunosuppressive and include the cyclophosphamide and fludarabine regimen, low-dose TBI with or without fludarabine, and total lymphoid radiation with thymoglobulin. Median intensity regimens include fludarabine in combination with busulfan. Others have used more intense regimens, such as fludarabine and melphelan or the BEAM (carmustine, etoposide, cytosine arabinoside and melphelan) combination, which allow cytoreduction and donor-cell engraftment. To date, there is little evidence that any one of these regimens is associated with any survival advantage over any other, but there is no evidence to support the use of the more toxic reduced-intensity regimens in patients with chemosensitive disease. RIC regimens allow transplantation in older patients, making this approach more applicable to increased numbers of CLL patients.47–52 In this setting most of the antilymphoma effect results from the graft-versus-lymphoma effect and not from the chemotherapy.47,53 Results from selected studies are shown in Table 3. The outcome from the Fred Hutchinson Cancer Research Center multi-institutional protocol after RIC allogeneic SCT was reported for 64 patients with advanced CLL using related (n ¼ 44) or unrelated (n ¼ 20) donors50, median age 56 years (range 44–69 years), and the majority of patients were fludarabine-refractory. TRM at 100 days was 11%,

Table 3. Reduced-intensity conditioning (RIC) allogeneic stem-cell transplantation (SCT) for chronic lymphocytic leukaemia (CLL). n

Age years (range)

Prior regimens (range)

Chemotherapy refractory

Donor (includes mismatch)

TRM

GVHD Acute grade 2e4

Survival

Reference

OS 72% 2 years PFS 67% OS 72% 2 years PFS 56%

Schetelig et al, 200220

OS 60% 2 years PFS 52% OS 48% 4 years PFS 44%

Sorror et al, 200522

Chronic extensive

30

50

3

47%

50% related

13% overall

56%

21%

77

(12e63) 54

(0e8) 3

33%

50% unrelated 81% related

18% 12 months

34%

58%

(30e66)

(0e8)

64

56

4

10 prior auto-SCT 53%

69% related

11% at 100 days

61%

50%

39

(44e69) 57

3

Not stated

31% unrelated 90% related

22% overall 2% at 100 days

45%

58%

(34e70)

(2e8)

53

5

87% ‘active’ diseasea 57%

17% overall

34%

43%

Brown et al, 200624

(35e67)

(1e10)

OS 54% 2 years PFS 34%

54

Delgado et al, 200625

(37e67)

OS 51 2 years PFS 45%

41

a

33% related

3

10 prior auto-SCT 27%

67% unrelated 58% related

5% at 100 days

10%

33%a

(1e8)

11 prior auto-SCT

42% unrelated

26% overall

(grade 3e4)

after DLIa

GVHD, graft-versus-host disease; OS, overall survival; PFS, progression-free survival; DLI, donor leukocyte infusion.

Khouri et al, 200623 Stem-cell transplantation in CLL 521

46

10% unrelated

Dreger et al, 200321

522 J. G. Gribben

and 22% by 2 years, with significant GVHD remaining a problem. At a median follow-up of 24 months, 39 patients were alive, 25 in CR; 2-year OS was 60%, and DFS was 52%. Although complications were higher in the patients with unrelated donors, there were higher CR and lower relapse rates, suggesting more effective GVL activity with unrelated donors. Excellent results have been obtained using RIC based on a combination of fludarabine, cyclophosphamide and rituximab at the MD Anderson Cancer Center, an approach designed to maximize GVL by early tapering of immune suppression with use of rituximab and DLI. Among 39 patients treated, median age was 57 years (range 34–70 years), median time from diagnosis to transplantation was 4.5 years.51 All patients had recurrent advanced disease, were heavily pre-treated with a median of three (range 2–8) chemotherapy regimens, and all had been previously treated with fludarabine–rituximab-based regimens. At transplant, 34 patients (87%) had active disease, including nine (23%) with evidence of Richter’s transformation. In this series only four of the donors were unrelated. Fourteen patients required immunomodulation with rituximab and DLI for persistent disease after SCT. Only one patient died early, and among the 38 evaluable patients, 27 (71%) achieved CR, with estimated OS at 4 years of 48%, with current PFS of 44%. Acute grade II–IV GVHD was observed in 45%, and chronic extensive GVHD was seen in 58%. Forty-six patients underwent RIC transplantation at Dana-Farber Cancer Institute, 67% using unrelated donors.52 These patients were heavily pre-treated, with a median of five prior therapies (range 1–10); ten (22%) had relapsed after prior autologous SCT. At the time of SCT, 26 (57%) had progressive chemoresistant disease, 50% had active progressive disease, 7% induction failures, and only 17% were in CR. Two-year OS was 54% and PFS 34% in this refractory patient population. The primary cause of treatment failure was relapse, with a 2-year cumulative incidence of 48%. Factors associated with increased risk of relapse include low levels of donor chimerism at day 30, chemorefractory disease, increased number of previous therapies, and adverse cytogenetics.52 At median follow-up of 2 years, 23 of 30 patients (77%) were alive, with 2-year estimated OS of 72%, PFS of 67% and non-relapse mortality of 15%.48 Acute GVHD grade 2–4 was seen in 17 patients (56%), with chronic GVHD in 21 patients (75%). Among 28 responding patients, 12 (40%) achieved CR, and late CR occurred up to 2 years after transplantation. MRD was monitored using clone-specific PCR. All CR patients analysed achieved a molecular CR. Most reported patients were heavily pretreated and refractory to therapy, but despite this the majority demonstrated donor engraftment and there was a high CR rate. The induction of molecular remissions in patients with advanced CLL and the observation of late remissions in patients treated with low doses of chemotherapy provide the strongest direct evidence for a powerful GVL effect that can be exploited in the management of CLL. When immune manipulation is planned, this should be performed early before the tumour becomes too bulky. It is clear from the results seen in Table 3 that GVHD remains a major concern. GVHD can be decreased using alemtuzumab in the conditioning regimen, but this delays post-SCT immune reconstitution, increases the risk of infective complications, and impairs the GVL effect. In 41 consecutive CLL patients treated (24 HLA-matched sibling donors and 17 unrelated volunteer donors, including four mismatched) the conditioning regimen alemtuzumab with fludarabine and melphelan had significant antitumour effects, with 100% of patients with chemosensitive disease and 86% with chemorefractory disease responding.54 The TRM rate was 26%, overall survival 51%, and relapse risk 29% at 2 years. GVHD rates were relatively low, with aGVHD occurring in 17 (41%) and cGVHD in 13 (33%). The unexpectedly high TRM rate was due to a high incidence of fungal and viral infections.

Stem-cell transplantation in CLL 523

No formal assessment of RIC compared to myeloablative allogeneic SCT has been undertaken, but the outcome after RIC allogeneic SCT of 73 patients who had undergone RIC was compared with that of 82 matched patients who had undergone standard myeloablative conditioning for CLL from the EBMT registry database during the same time period. Patients undergoing RIC transplants had significantly reduced TRM but higher relapse incidence, and there was no significant difference in OS or PFS between these two groups.55 Risk factors for poor outcome after RIC allogeneic SCT RIC procedures are currently investigational in nature, and although the acute morbidity and mortality appears significantly lower compared to high-dose conditioning regimens with myeloablative allogeneic SCT, longer-term results with regard to morbidity of chronic GVHD and disease control are currently lacking. Further research is required to elucidate the mechanisms of treatment failure after non-myeloablative allogeneic SCT (NST). Whether chemotherapy-refractory disease and adverse cytogenetics predict intrinsic resistance to graft-versus-CLL activity is unclear; alternatively, they could be markers of aggressive disease that progresses too rapidly to be controlled even by an active immune response. High-dose therapy and myeloablative conditioning regimens do not appear to be necessary to overcome the poor prognostic impact of IgVH mutational status and cytogenetics. In 30 patients with poor-prognosis CLL – as defined by mutational status of VH genes and cytogenetic abnormalities (11q–, 17p–) – who had undergone RIC allogeneic SCT, OS and DFS for the poor-prognosis group were 90% and 92%, respectively, and were not significantly different from those in the good-prognosis group.56 The impact of ZAP-70 expression on outcome was retrospectively examined in 39 patients with CLL who had undergone RIC allogeneic SCT.57 Using immunohistochemical techniques on marrow biopsies, 25 patients were ZAP-70-positive, 13 were ZAP-70-negative, and one was of indeterminate status. Patients who were ZAP70-positive had a median age of 54 years. With a median follow-up time of 41 months (range 4–80 months), their OS and current PFS rates at 4 years were 56% and 53%, respectively. By multivariate analysis, chemorefractory disease at transplantation (P ¼ 0.01) and mixed T-cell chimerism at day 90 (P ¼ 0.02), but not ZAP-70 status, were correlated with the risk of progression after transplantation. In the Dana-Farber series52, 34% of heavily pre-treated patients with refractory disease achieved an objective response, suggesting some capacity of GVL reaction to control the disease, at least transiently. In multivariate analysis, chemotherapy-refractory disease at transplantation was associated with a 3.2-fold risk of progression (P ¼ 0.01) and a 4.6-fold risk of death (P ¼ 0.02). Increasing number of previous therapies and increasing marrow involvement were also associated with decreased PFS and OS. High haematopoietic donor chimerism on day 30 was also a significant predictor of 2-year PFS. It is not clear whether achieving high early donor chimerism is primarily a function of disease status prior to transplant or of GVL activity. In either case, research efforts to enhance early donor chimerism could include better cytoreduction and marrow debulking prior to NST, early taper of immunosuppression, or donor lymphocyte infusion. Maintaining this initial graft-versus-CLL response over time would then be the challenge. Relapses tend to reflect the original pattern of disease, suggesting a widespread loss of GVL activity. Consistent with this hypothesis, once relapse occurred in this study, less than 20% responded to DLI infusions alone.48,50,54 Co-culture of CLL cells with allogeneic T cells induces changes in gene expression of the donor

524 J. G. Gribben

T cells, suggesting that tumour bulk might have a direct effect to impair effector-T-cell function. Research efforts to promote and sustain the initial GVL reaction are therefore needed, and could include transplantation of patients earlier in their disease course while they are still chemoresponsive, planned prophylactic DLI, vaccination with or without cytokine stimulation, or maintenance antibody therapy.

Practice points  autologous SCT has no defined role, and should only be used in clinical trials  myeloablative allogeneic SCT can be used for chemorefractory disease in young patients  RIC allogeneic SCT can be appropriate when there is an incomplete response to first-line therapy; when the response to purine-analogue-containing regimens is of short duration; in Richter’s transformation p53 mutation at first treatment; and in other ‘high-risk’ cases in clinical trials

Research agenda  RIC allogeneic transplant is the treatment of choice for patients requiring transplantation  the impact of prognostic factors – including disease status, disease bulk, marrow involvement at SCT, cytogenetics, IgVH mutational status and ZAP-70 expression – still require further evaluation  further studies are required to evaluate steps to increase donor chimerism and predict which patients will require early DLI  further studies are also required to evaluate the use of monoclonal antibodies and other agents which can be used post-transplant to control disease without impacting GVL or worsening GVHD

CONCLUSIONS SCT has a role to play in selected CLL patients. Autologous SCT is feasible in younger patients with poor-risk CLL but is not curative, particularly in patients with high-risk disease. Autologous SCT may result in prolongation of OS compared to conventional therapy, but this must always be considered in the context of improved outcome using conventional chemoimmunotherapy. Myeloablative allogeneic SCT has high TRM and morbidity and should be restricted to patients with a very poor prognosis. Although no direct comparisons of myeloablative and RIC transplants have been performed, given the older age of patients with CLL it seems most reasonable to consider RICregimen transplants as the approach of choice for CLL patients in whom SCT is being considered. Although RIC SCT appears to result in high response rates and eradication of PCR-detectable MRD, the follow-up in most clinical trials is too short to assess whether SCT can cure CLL. Future approaches to the management of this disease must take into account the balance between the increased morbidity and mortality of SCT in CLL and the curative

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