Risk assessment in haematopoietic stem cell transplantation: Conditioning

Best Practice & Research Clinical Haematology Vol. 20, No. 2, pp. 295e310, 2007 doi:10.1016/j.beha.2006.09.004 available online at http://www.sciencedirect.com

11 Risk assessment in haematopoietic stem cell transplantation: Conditioning Johan Aschan*

MD, PhD

Associate Professor Centre for Allogeneic Stem Cell Transplantation and Division of Haematology, Department of Medicine, M54, Karolinska Institutet, Karolinska University Hospital Huddinge, SE-141 86 Stockholm, Sweden

After the introduction of cyclophosphamide and total body irradiation in the 1970s, a variety of conditioning regimens has been developed. However, none has proven to be superior. Fractionation of the irradiation results in less toxic side-effects, but the total dose has to be increased to obtain similar immunosuppressive effects. Data from randomized trials indicate that among patients with myeloid leukaemia, busulfan in combination with cyclophosphamide results in similar outcome, while a regimen containing total body irradiation is probably still the best for patients with acute lymphoblastic leukaemia. Busulfan treatment can be optimized by targeted steadystate concentration or with the use of intravenous preparations. Intensified regimens decrease the relapse incidence, but because of a higher mortality from transplant-related causes survival is unchanged. Reduced-intensity conditioning can reduce transplant-related mortality and offer otherwise ineligible patients a potentially curative treatment. Long-term results are unknown. Key words: conditioning; total body irradiation; cyclophosphamide; busulfan; reduced intensity conditioning.

The current era of allogeneic haematopoietic stem-cell transplantation (allo-HSCT) started with studies during the end of World War II following the atomic bomb explosions. It became clear that the marrow is the organ most sensitive to irradiation and that mice could be protected from marrow-lethal effects of irradiation by shielding of their spleens.1 Further animal studies showed that this protection was effected by transplanted haematopoietic stem cells (HSCs) and could induce tolerance to skin grafts.2 From these studies, a treatment schema evolved for patients with diseases in the marrow, such as leukaemia. Patients would receive maximum doses of irradiation therapy to eradicate the underlying diseases, and were then rescued from lethal marrow ablation by infused HSCs which could restore haematopoiesis. It soon * Tel.: þ46 8 585 800 00; Fax: þ46 8 774 87 25. E-mail address: [email protected] 1521-6926/$ - see front matter ª 2006 Elsevier Ltd. All rights reserved.

296 J. Aschan

became evident that leukaemia relapse occurred frequently, and this motivated research into modifying the irradiation and combining irradiation with chemotherapy.3 In allo-HSCT the purpose of the conditioning is to eradicate the disease or reduce it to a minimal residual disease state, and to suppress the patient’s immune system in order to abrogate the immunological resistance to engraftment. Although initially it was believed that it was necessary to ‘create space’ within the marrow, this has recently been questioned since animal trials have shown engraftment in non-irradiated limbs. It seems that the infused HSCs create their own space. Since medullary toxicity can be ignored, maximally tolerated doses are limited by non-haematopoietic toxicity. Although the goal of the conditioning ideally should be obtained with low morbidity and minimal mortality, trials have shown an association between the intensity of the conditioning and toxicity. Today a wide range of conditioning regimens exist and every regimen has its advantages and disadvantages. For example, intensified protocols decrease the relapse incidence but at the cost of increased transplantation-related mortality (TRM). Reduced-intensity regimens, on the other hand, decrease toxicity but might increase the rejection incidence. Furthermore, highly immunosuppressive regimens decrease the incidence of rejection but give a higher incidence of infections. TOTAL BODY IRRADIATION Because of its immunosuppressive properties, activity against a wide range of malignant disorders, even in chemoresistant diseases, and penetration of sanctuary sites such as the central nervous system and testicles, total body irradiation (TBI) has been an important part of the conditioning for malignant disorders for the last 35 years.4 However, there are concerns about late adverse effects such as secondary malignancies. Both radiation from dual opposing 60Co sources and linear accelerators has been used.5,6 An advantage with dual opposing 60Co sources is the highly homogenous radiation exposure which allows the patient some freedom of movement. Disadvantages include cost, difficulties in organ shielding, and the problem of delivering higher dose rates. With a linear accelerator a higher dose rate as well as organ shielding can easily be administered. When TBI is applied several components have to been considered: the dose rate, the fractioning and the total dose. The dose is usually calculated as midline tissue dose, but other strategies exist, such as maximum lung dose. Dose rate For most of the clinically used TBI regimens the radiation is given at low dose rates (5e8 cGy/min). In preclinical canine models higher dose rates (60e80 cGy/min) were found to give more gastrointestinal and marrow toxicity together with a more intense immunosuppressive effect. If the TBI was fractionated the toxicity of the higher dose rate was reduced. Lower dose rates permitted higher total doses and vice versa.5 According to both animal and human data, a high dose rate increases the risk for interstitial pneumonitis and perhaps also cataract. These side-effects can be reduced by organ-shielding or a reduced total dose. However, this might increase the relapse risk. In most centres a low dose rate is considered to have the best effect/side-effect ratio.

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Fractionating In order to reduced the relapse incidence attempts were made to increase the irradiation dose by the use of dose fractionation. The rationale is that haematopoietic cells are less capable of DNA repair than other tissue cells. Administration of multiple fractions of TBI would then lead to profound marrow toxicity whereas other tissues would be much less affected. Dogs were given up to 23 Gy in fractions of 4.5e9 Gy, and 12e21 Gy were given in fractions of 1.5e2 Gy.7 At each total dose level the acute toxicity of single versus fractionated dose was comparable. However, at the same total dose, fractionated TBI is less immunosuppressive and results in a higher rate of graft failure. Therefore, the total dose of fractionated TBI needs to be increased to have a similar immunosuppressive effect as single-dose TBI. An important difference is the reduced risk for late organ toxicity and improved long-term survival in dogs given fractionated TBI.7 In a clinical randomized trial Thomas and co-workers compared 12 Gy fractionated TBI given in six fractions of 2 Gy with 10 Gy single-dose TBI.8,9 Patients given fractionated TBI had less toxic side-effects, a similar relapse incidence and a better survival. Similar findings were made by Girinsky et al who randomized patients to either 14.85 Gy (11 fractions over 5 days) or 10 Gy single-dose TBI.10 Fractionated TBI resulted in less veno-occlusive disease (VOD) of the liver, a trend for fewer relapses and improved survival. Today most centres use fractionated TBI. Total dose Two randomized trials evaluated 12 Gy given in 2-Gy fractions versus 15.75 Gy in 2.25-Gy fractions in patients with acute myeloid leukaemia (AML) in first remission and chronic myeloid leukaemia (CML) in chronic phase.11,12 Results were similar in both trials. With the more intense irradiation, the relapse incidence was decreased, but at the cost of more toxicity increasing the TRM. Therefore, the relapse-free survival was similar with both irradiation schedules in both studies (Table 1). CYCLOPHOSPHAMIDE The alkylating agent cyclophosphamide (CY) is strongly immunosuppressive and also an effective anti-neoplastic agent, but is not marrow-ablative. Dose-limiting toxicity Table 1. Randomized trials with different irradiation regimens in combination with cyclophosphamide 120 mg/kg. Diagnosis

TBI dose

Probability of relapse (%)

Probability of TRM (%)

Probability of RFS (%)

Reference

AML 1st CR

12 Gy (2 Gy  6) 15.75 Gy (2.25 Gy  7)

35 12

12 32

58 59

11

CML CP

12 Gy (2 Gy  6) 15.75 Gy (2.25 Gy  7)

25 0

24 34

58 66

12

TBI, total body irradiation; Gy, gray; TRM, transplant-related mortality; RFS, relapse-free survival; AML, acute myeloid leukaemia; CR, complete remission; CML, chronic myeloid leukaemia; CP, chronic phase.

298 J. Aschan

is haemorrhagic myocarditis. When used as a single agent, the maximum tolerated dose is approximately 200 mg/kg, and infusion of HSCs has no impact on survival.13 Following animal studies it was shown that CY can be substituted for TBI in the conditioning.14 CY 50 mg/kg/day for 4 successive days is one of the most common conditioning regimens for patients with severe aplastic anaemia (SAA).15 To decrease the risk of rejection in heavily transfused patients, anti-thymocyte globulin (ATG) was added. This combination resulted in a low incidence of graft rejection and an excellent survival, and is considered the standard conditioning regimen in HLA-identical sibling transplants for SAA.16 The mechanism of graft rejection was believed to be sensitization to minor histocompatibility antigens expressed on HSCs of the donor via transfusion of random blood products. However, it is not known whether the leukocyte filtered blood products used today decreases the incidence of sensitisation, making ATG unnecessary.

CY with TBI The combination of CY 60 mg/kg/day for 2 successive days and TBI was introduced to a patient undergoing syngeneic transplantation in 1971.17 CY was given to avoid the tumour lysis and acute renal failure that had been observed with TBI. The patient became a long-term survivor, and thereafter CY was commonly administered prior to TBI for patients with haematological malignancies receiving HSCT without any obvious additional toxicity compared to TBI alone. With few overlapping non-haematopoietic toxicities and a maximized anti-neoplastic and immunosuppressive effect. This has become the gold standard for 35 years. It must be pointed out, however, that while CYTBI is often referred to as a uniform regimen, this is in fact not the case. CY is usually given for 2 days at 60 mg/kg/day before TBI, but has been given at other doses and both before and after TBI. TBI has been given even more variably with different sources, dose rates, dose fractions, total doses and different lung and other organ shielding. It is unlikely that any two institutions use CYTBI in exactly the same manner. TBI with one drug other than CY TBI has been combined with drugs other than CY. Etoposide, melphalan and cytosine arabinoside are examples of such drugs (Table 2).18e21 A recent retrospective study in patients with acute lymphoblastic leukaemia (ALL) found etoposide plus TBI to be superior to CYTBI (<13 Gy) among patients in second remission.22 For patients in

Table 2. Preparative regimens with total body irradiation (TBI) and a single drug. Drug

Total dose

Total TBI dose

Reference

Cyclophosphamide Etoposide Cytosine arabinoside Melphalan

120 mg/kg 60 mg/kg 36 g/m2 110e140 mg/m2

8e16 Gy 12e13.2 Gy 10e12 Gy 9.5e14.85 Gy

8,72 18 19 20,21

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Table 3. Preparative regimens with total body irradiation (TBI), cyclophosphamide (CY) and a second drug. Drug

Total dose

CY dose

TBI dose

Reference

Etoposide Busulfan Cytosine arabinoside

25e60 mg/kg 7 mg/kg 6e36 g/m2

60e120 mg/kg 50 mg/kg 60e120 mg/kg

12e13.2 Gy 12 Gy 5e12 Gy

23,24 25 26

first remission results were similar. However, there is no prospective randomized trial comparing standard CYTBI versus TBI plus any other drug. CY with TBI and additional drugs Etoposide, busulfan (BU), and cytosine arabinoside have been given with CY plus TBI in the conditioning (Table 3).23e26 Although promising in phase II trials, none of these combinations has been evaluated in a randomized fashion. CHEMOTHERAPY-BASED HIGH-DOSE REGIMENS A wide range of high-dose chemotherapy regimens has been developed. Different mechanisms have driven this research. To decrease the incidence of relapse, disease-specific chemotherapy regimens were developed. In small children, attempts have been made to avoid detrimental effects from irradiation on growth and central nervous system development.27 Furthermore, chemotherapy regimens may avoid or diminish late complications from irradiation such as second malignancies, cataract, and sterility.28,29 Many patients have received prior dose-limiting irradiation, making further irradiation treatment too toxic. From a practical point of view, some institutions may have limited access to irradiation facilities. Chemotherapy-based regimens have used BU, carmustine, melphalan, thiotepa or etoposide and combined with each other or with other drugs in a variety of combinations and doses. Other agents used are CY, idarubicin, cytosine arabinoside, mitoxantrone, lomustine, cisplatin, amsacrine, carboplatin, paclitaxel, hydroxyurea, ifosfamide, and treosulfan. Except for CY 200 mg/kg and the combination of BU and CY, the largest experience with chemotherapy-based conditioning regimens is from autologous HSCT, and some examples are given in Table 4. BU and CY BU is an alkylating agent with myeloablative effects, and the maximum tolerated dose, when given as a single agent over 4 days with HSC support, is approximately 20 mg/kg.30 BU was introduced into the conditioning regimen by Santos and co-workers.31 They used 4 mg/kg/day for 4 days of BU in combination with CY 50 mg/kg/day for 4 days (BUCY4). Subsequent studies reduced the CY dose to 120 mg/kg in combination with BU 16 mg/kg (BUCY2). Uncontrolled comparisons between BUCY4 and BUCY2 showed a reduced toxicity without apparent increase in relapse incidence with the lower dose of CY.32 Potential advantages with BUCY versus CYTBI are easier administration, fewer secondary malignancies, reduced incidence of interstitial pneumonitis, cataract, and

300 J. Aschan

Table 4. Examples of chemotherapy-based regimens. Regimen

Drugs

Total dose

Reference

CY

Cyclophosphamide

200 mg/kg

13

BU/CY

Busulfan Cyclophosphamide

16 mg/kg 120e200 mg/kg

31,32

BU/CY/E

Busulfan Cyclophosphamide Etoposide

16 mg/kg 120 mg/kg 30e60 mg/kg

73

Mel

Melphalan

200 mg/m2

74

BU/Mel/TT

Busulfan Melphalan Thiotepa

12 mg/kg 100 mg/m2 500 mg/m2

75

BEAM

Carmustine (BCNU) Etoposide Cytosine arabinoside Melphalan

300e600 mg/m2 400e800 mg/m2 800e1600 mg/m2 140 mg/m2

76

CTCb (STAMP-V)

Cyclophosphamide Thiotepa Carboplatin

6 g/m2 500 mg/m2 800 mg/m2

77

ICE

Ifosfamide Carboplatin Etoposide

16e20 g/m2 1.8 g/m2 1.2e3.0 g/m2

78

growth and other endocrinological disturbances. Potential disadvantages are less potent anti-tumour effect in sanctuary sites, unpredictable drug absorption and metabolism, increased risks for VOD of the liver, haemorrhagic cystitis, and permanent alopecia. Trials with BUCY versus TBI-based regimens Four randomized prospective trials have compared BUCY2 to CYTBI (Table 5).33e36 Two studies in patients with CML in chronic phase given an HLA-identical sibling graft showed similar outcomes with BUCY2 and CYTBI.34,35 Furthermore, a trial in patients with AML, ALL and CML showed similar relapse-free survival in patients with early leukaemia. In the small subgroup of patients with advanced leukaemia, survival was inferior with BUCY2 due to a higher incidence of TRM.36 Only one trial in AML patients in first remission demonstrated superior survival in patients given CYTBI due to lower relapse and TRM rates.33 A long-term follow-up of those four studies included 316 patients with CML and 172 with AML (Table 5).37 No difference in outcome was found either for patients with CML or for those with AML, although patients with AML conditioned with CYTBI had a non-significant 10% better survival. With a mean follow-up of more than 7 years, CYTBI increased the risk of cataract, while BUCY2 gave a higher incidence of irreversible alopecia. The equivalence of CYTBI and BUCY was confirmed in two large retrospective analyses from the European Group for Blood and Marrow Transplantation (EBMT)

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Table 5. Randomized trials with BUCY versus CYTBI. Disease

Conditioning

n

TRM (%)

AML

BUCY2 CYTBI

51 50

27 8

CML

BUCY2 CYTBI

65 55

CML

BUCY2 CYTBI

AML, CML and ALL

BUCY2 CYTBI

REL (%)

DFS (%)

OS (%)

Reference

34 14

47 72

51 75

33

38 29

4 11/31a

59 55

61 63

34

73 69

18 24

13 13

71 68

80 80

35

88 79

28 9

22 26

56 67

62 76

36

37

Long-term follow-up of these four studies: AML BUCY2 92 CYTBI 80

NR NR

NR NR

47 57

51 63

168 148

NR NR

NR NR

52 46

65 63

CML

BUCY2 CYTBI

BU, busulfan; CY, cyclophosphamide; TRM, transplant-related mortality; REL, relapse; DFS, disease-free survival; OS, overall survival; AML, acute myeloid leukaemia; CML, chronic myeloid leukaemia; ALL, acute lymphoblastic leukaemia. a 11% with single-dose total body irradiation (TBI) and 31% with fractionated TBI.

and the International Bone Marrow Transplant Registry (IBMTR).38,39 In the EBMT analysis, patients with AML had similar outcome after BUCY2 versus BUCY4 conditioning, and were therefore analysed together. Among patients with AML in first remission, TRM, relapse, and leukaemia-free survival (LFS) were 16%, 23% and 64%, respectively, after BUCY. Corresponding figures for the CYTBI group were 19%, 19% and 66%. This study also analysed results after transplantation for AML in more advanced stages as well as results after transplantation for ALL in both early and later stages. All analyses showed similar results with BUCY and CYTBI. The IBMTR study included only patients with AML in first remission. The relapse risk was higher with BUCY, 19% versus 12% (P ¼ 0.042), but TRM (27 versus 30%), survival (55 versus 60%) and LFS (54 versus 58%) were comparable with BUCY and CYTBI. Both database analyses showed a higher incidence of hepatic VOD with BUCY. A randomized trial in patients with advanced acute leukaemia and CML (beyond first complete remission and first chronic phase, respectively) compared conditioning with TBI 13.2 Gy plus etoposide 60 mg/kg versus BUCY2.40 Neither survival nor disease-free survival differed significantly between the two treatment groups. In children with ALL, a small randomized trial demonstrated inferior results with BUCY2 plus etoposide 40 mg/kg compared to CYTBI þ etoposide 40 mg/kg.41 Furthermore, this finding was confirmed in a retrospective IBMTR study in children with ALL given either CYTBI or BUCY. Survival and LFS were better with CYTBI due to a lower TRM.42 On the basis of these data, most institutions consider TBI to be an important part of the conditioning for patients with ALL. However, it should be emphasized that except for 38 patients, and not all of them adults, included in the Nordic study by Ringde´n and co-workers, no data exist on adult patients included in randomized trials comparing BUCY and CYTBI.36

302 J. Aschan

A significant problem with oral BU is wide inter-patient variability of pharmacokinetics depending on unpredictable intestinal absorption and metabolism.43 By examining BU plasma concentrations, a large area under the curve (AUC) correlated with increased toxicity, mainly VOD and seizures, and a low AUC resulted in a higher risk of graft rejection and relapses.44e46 It is also well known that young children have a lower systemic exposure compared to adults given identical doses based on body weight.47 Therefore, monitoring blood BU levels using limited sampling models followed by dose adjustment to achieve a targeted steady-state concentration seems important.48 This strategy was not used in any of the randomized trials. Recently, intravenous preparations of BU have become available and result in a more predictable steady-state concentration.49,50 A retrospective multicentre study with intravenous BU versus fixed-dose oral BU reported a lower incidence of hepatic VOD and a better 100-day survival with intravenous BU.51 However, it is not known whether intravenous BU is superior to oral BU with targeted levels. RADIOIMMUNOTHERAPY Replacing, or augmenting, the external-beam TBI with more selective irradiation of the bone marrow might reduce the risk of relapse while causing only limited toxicity to non-target organs. A variety of antibodies (anti-CD20, anti-CD33, anti-CD45, and anti-CD66) have been labelled with different b-emitters (131I, 90Y and 188Re).52 Dose-escalation and distribution studies have been performed, and clinical trials with radioimmunotherapy in combination with both conventional myeloablative conditioning and reduced intensity conditioning (RIC) have demonstrated the feasibility of this technique. In high-risk AML patients transplanted with <15% blasts in the marrow, the relapse rate was 20e30%.52 For patients with refractory leukaemia, studies with the use of a-emitting radioimmunoconjugates or cocktails of antibodies with both a- and b-emitting conjugates are ongoing.53 REDUCED INTENSITY CONDITIONING The curative effect of allo-HSCT is partly mediated by the graft-versus-tumour (GVT) effect from immunocompetent cells originating from the graft. Evidence of this GVT effect was first seen in animal studies and later in clinical trials.54,55 Patients with graft-versus-host disease (GVHD) have a reduced incidence of relapse, whereas recipients of syngeneic, or T-cell-depleted grafts, have a higher risk of relapse.56 The ultimate proof of the potent GVT effect is the reinduction of remission obtained with infusions of donor lymphocytes in patients relapsing after an allo-HSCT.57 Unlike traditional myeloablative conditioning, RIC is primarily immunosuppressive, enabling donor-cell engraftment, and depends on the graft to eradicate the underlying disease. After transplantation, donor lymphocyte infusions can further enhance the antitumour effect. This less toxic approach allows transplantation in elderly patients and in those with co-morbidity, patients that are considered contraindicated for conventional myeloablative conditioning. With limited non-haematological side-effects the purine analogues fludarabine, 2chlorodeoxyadenosine, and pentostatin are immunosuppressive and potentiate the anti-tumour effect of alkylating agents by inhibiting the mechanisms of DNA repair. Consequently, the majority of RIC regimens include a purine analogue, although many different RIC regimens have been used (Table 6).

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Table 6. Examples of reduced-intensity conditioning regimens. Regimen

Drugs/irradiation

Total dose

Reference

Flu/TBI

Fludarabine TBI

90 mg/m 2 Gy

59

Flu/BU  ATG

Fludarabine Busulfan ATGa

180 mg/m2 8 mg/kg 40 mg/kg

79

Flu/Mel  Campath

Fludarabine Melphalan Campath-1H

150 mg/m2 140e180 mg/m2 100 mg

63

Flu/CY

Fludarabine Cyclophosphamide

125 mg/m2 120 mg/kg

67

a

2

ATG (anti-thymocyte globulin) dose depends on specific brand of ATG.

After studies in a canine model, Storb and colleagues introduced a clinical protocol of low-dose TBI (2 Gy) and post-grafting immunosuppression with cyclosporine A and mycophenolate mofetil to permit engraftment and prevent GVHD.58,59 By adding fludarabine 30 mg/m2/d for 3 days before TBI the rejection rate was reduced from 20% to 3%.60 With this protocol regimen-related toxicity and myelosuppression was mild, allowing outpatient transplantation. Analysis of 451 patients transplanted for a variety of haematological malignancies in different stages showed a 2-year probability of TRM and survival of 22% and 51%, respectively.61 GVHD and infections were main causes of mortality. Thus, GVHD is still a problem despite speculations that the lower levels of inflammatory cytokines during conditioning and the mixed recipient and donor chimerism status early after transplant should result in a lower incidence of GVHD after RIC.62 Kottaridis et al added Campath-1H, a CD52 antibody, to an RIC protocol consisting of fludarabine and melphalan.63 Only two patients developed acute GVHD grade II. However, Campath-1H can also reduce the risk of acute GVHD after HSCT with conventional conditioning. Chimerism analyses after RIC are important to guide further immunotherapy. High levels of donor chimerism among T cells but not natural killer (NK) cells were associated with increased risk of acute GVHD, while high levels of donor chimerism among T cells and NK cells were associated with decreased risk of relapse. Graft rejection was increased among patients with low levels of donor chimerism in T cells and NK cells.64 With few exceptions, most experience with RIC is from transplants in patients not eligible for conventional myeloablative conditioning. Early experiences suggest that TRM is reduced, and the safety and effectiveness of RIC have led to their wider application. However, for patients with advanced malignancy, the low TRM may be offset by high relapse rates. Allo-HSCTwith RIC is probably most effective in treating slow-growing malignancies such as CML, chronic lymphocytic leukaemia and low-grade lymphoma. Furthermore, patients that have failed autologous HSCT can also be offered an allo-HSCT after RIC. For patients with acute leukaemia in remission and early stages of myelodysplastic syndrome, studies are ongoing and preliminary results are encouraging.65,66 Immunotherapy with allo-HSCT has been used in patients with metastatic solid tumours. A GVTeffect has been shown for renal carcinoma, adenocarcinoma of the colon, metastatic carcinoma of the breast, ovary, prostate and pancreas. The largest experience is from metastatic renal cancer. Patients received RIC in order to have

304 J. Aschan

Table 7. Conditioning regimen by diseases. Disease

Regimen

Dose per day

Days

AML and CML

CYTBI: Cyclophosphamide 120 mg/kg Total body irradiation 12e14.4 Gy

60 mg/kg 4e4.8 Gy

5, 4 3, 2, 1

BYCY2: Busulfan Cyclophosphamide

4 mg/kg 60 mg/kg

7, 6, 5, 4 3, 2

CYTBI: Cyclophosphamide 120 mg/kg Total body irradiation 12e14.4 Gy

60 mg/kg 4e4.8 Gy

5, 4 3, 2, 1

CYVPTBI: Cyclophosphamide 120 mg/kg Etoposide 30e60 mg/kg Total body irradiation 12e13.2 Gy

60 mg/kg 30e60 mg/kg 4e4.4 Gy

6, 5 4 3, 2, 1

200 mg/kg 8e90 mg/kg

50 mg/kg 2e30 mg/kg

5, 4, 3, 2 3e4 daysa

BUCY: Busulfan Cyclophosphamide

14e16 mg/kg 200 mg/kg

3.5e4 mg/kgb 50 mg/kg

9, 8, 7, 6 5, 4, 3, 2

FluBUCY: Fludarabine Busulfan Cyclophosphamide ATGa

100 mg/m2 6 mg/kg 40 mg/kg 6 mg/kg

25 mg/m2 1.5 mg/kg 10 mg/kg 1.5 mg/kg

5, 9, 5, 4,

200 mg/m2

200 mg/m2

1

ALL

Severe aplastic anaemia CY: Cyclophosphamide ATGa Thalassaemia

Fanconi

Total dose

16 mg/kg 120 mg/kg

4, 8, 4, 3,

3, 7, 3, 2,

2 6 2 1

Myeloma

Mel: Melphalan

Lymphoma

BEAM: Carmustine (BCNU) Etoposide Cytosine arabinoside Melphalan

300e600 mg/m2 400e800 mg/m2 800e1600 mg/m2 140 mg/m2

300e600 mg/m2 150e200 mg/m2 200e400 mg/m2 140 mg/m2

6 5, 4, 3, 2 5, 4, 3, 2 1

CTCb (STAMPeV): Cyclophosphamide Thiotepa Carboplatin

6000 mg/m2 500 mg/m2 800 mg/m2

1500 mg/m2 125 mg/m2 200 mg/m2

7, 6, 5, 4 7, 6, 5, 4 7, 6, 5, 4

LACE: CCNU (Lomustine) Etoposide Cytosine arabinoside Cyclophosphamide

200 mg/m2 1000 mg/m2 4000 mg/m2 5400 mg/m2

200 mg/m2 1000 mg/m2 2000 mg/m2 1800 mg/m2

7 7 6, 5 4, 3, 2

Solid tumours

a b

ATG dose depends on specific brand of ATG. Oral dose, corresponding intravenous dose 2.8e3.2 mg/kg/day.

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a low TRM. Responses were shown, including a few complete ones.67 Good prognostic factors were less than three metastatic sites and a Karnofsky score 70. Patients who received donor leukocyte infusion (DLI) and developed chronic GVHD had a better survival: 70% at 3 years after allo-HSCT.68 Survival and tumour response will probably be better if allo-HSCT is done earlier in the course of the disease when the tumour load is lower. Future studies will show the place of allo-HSCT in patients with solid tumours. RIC versus conventional conditioning Two retrospective analyses e one with HLA-identical sibling donors and one with HLAmatched unrelated donors e compared outcome after RIC versus myeloablative conditioning.69,70 Both studies concluded that they had a lower 1-year TRM even though recipients of RIC were older, had higher co-morbidities, and had more extensive treatment before transplantation, including failed conventional allo-HSCT. Similar results were reported by Alyea and co-workers who compared outcomes among patients over the age of 50 with haematological malignancies undergoing allo-HSCT after conventional conditioning or RIC.71 However, currently no results from prospective randomized trials exist. Furthermore, with limited follow-up time no data regarding late effects after RIC have been reported. INDIVIDUALIZATION A common trend in recent years is the individualization of the transplant procedure. With a variety of conditioning regimens, stem-cell sources and methods of GVHD prevention, the complexity has increased substantially. Conditioning regimen depends on both the disease and the age and co-morbidity of the patient. Patients with high risks for TRM and a low risk for relapse should probably receive a different conditioning regimen from patients with low risk for TRM and a high relapse risk. Some examples of commonly used disease-specific regimens are given in Table 7. RIC may vary considerably in its cytotoxic and immunosuppressive effect. Depending on diagnosis and the risk of graft rejection, the RIC could be individualized. For example, a more intense RIC may give adequate disease control until the GVT effect is established. Stem-cell source also depends on the diagnosis and conditioning regimen. With non-malignant disorders, bone marrow is preferred since chronic GVHD should be avoided. With RIC, peripheral-blood stem cells are the first choice since it is important with a high stem-cell dose to overcome allograft resistance. Practice points  cyclophosphamide in combination with total body irradiation is still the gold standard  fractionation of the irradiation decreases side-effects  busulfan and cyclophosphamide result in similar outcome among patients with myeloid leukaemias  busulfan treatment can be optimized by targeted steady-state concentration or with the use of intravenous preparations  reduced-intensity conditioning can reduce transplantation-related mortality and offer otherwise ineligible patients a potential curative transplantation

306 J. Aschan

Research agenda  new myeloablative or intensified conditioning regimens should be compared in a prospective randomized fashion to cyclophosphamide plus irradiation or busulfan plus cyclophosphamide  reduced-intensity conditioning should be compared to conventional conditioning for eligible patients  transplantation after reduced-intensity conditioning should be compared to chemotherapy for patients not eligible for a conventional conditioning  long-term results after reduced-intensity conditioning are needed to evaluate late side-effects SUMMARY The conditioning given before allo-HSCT has evolved from a standard maximized radiochemotherapy into an individualized treatment. Depending on disease, age, co-morbidity, previous treatment, stem-cell source and type of donor, the composition of the conditioning may vary considerably. However, the number of prospective randomized trials comparing different conditioning regimens is low. A conventional myeloablative preparative regimen is still the gold standard for eligible patients. BUCY results in similar outcome to CYTBI for patients with myeloid leukaemias, while a TBI-containing regimen seems superior for patients with ALL. By monitoring blood BU levels followed by dose adjustment to achieve a targeted steady-state concentration, transplant outcome can be optimized. Intravenous preparations of BU can probably reduce sideeffects compared to oral BU given as a fixed dose, but this has not been shown in randomized trials. RIC can most likely reduce TRM and offer a curative allo-HSCT to patients not eligible for a conventional conditioning. RIC is probably most effective in treating slow-growing malignancies, but a longer follow-up is needed before we know if late side-effects are reduced. Few patients eligible for a myeloablative conditioning have received an RIC, and results from properly designed prospective randomized trials comparing RIC with myeloablative conditioning are needed. REFERENCES 1. Jacobson LO, Marks EK, Robson MJ et al. Effect of spleen protection on mortality following x-irradiation. The Journal of Laboratory and Clinical Medicine 1949; 34: 1538e1543. 2. Main JM & Prehn RT. Successful skin homografts after the administration of high dosage X radiation and homologous bone marrow. Journal of the National Cancer Institute 1955; 15: 1023e1029. 3. Thomas ED, Lochte Jr. HL, Cannon JH et al. Supralethal whole body irradiation and isologous marrow transplantation in man. The Journal of Clinical Investigation 1959; 38: 1709e1716. *4. Thomas ED, Storb R, Clift RA et al. Bone-marrow transplantation. Parts I and II. The New England Journal of Medicine 1975; 292: 832e843, 895e902. 5. Storb R. Preparative regimens for patients with leukemias and severe aplastic anemia (overview) e biological basis, experimental animal studies and clinical trials at the Fred Hutchinson Cancer Research Center. Bone Marrow Transplantation 1994; 14(supplement 4): S1eS3. 6. Brochstein JA, Kernan NA, Groshen S et al. Allogeneic bone marrow transplantation after hyperfractionated total-body irradiation and cyclophosphamide in children with acute leukemia. The New England Journal of Medicine 1987; 317: 1618e1624.

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