Monoclonal antibody combinations in CLL: evolving strategies

Best Practice & Research Clinical Haematology Vol. 19, No. 4, pp. 781e793, 2006 doi:10.1016/j.beha.2006.06.005 available online at http://www.sciencedirect.com

10 Monoclonal antibody combinations in CLL: evolving strategies Stefan Faderl*

MD

Associate Professor

Susan O’Brien

MD

Professor

Michael J. Keating

MBBS

Professor Department of Leukemia, Unit 428, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA

Monoclonal antibodies have led to a profound shift in the therapeutic landscape of chronic lymphocytic leukemia (CLL). Alemtuzumab and rituximab remain the most active antibodies, and their single-agent activity has been established in previously untreated and relapsed patients with CLL. Higher response rates and a better quality of response through eradication of minimal residual disease have been reported with monoclonal antibody combinations. Chemoimmunotherapy regimens are being actively explored in frontline CLL therapy, and numerous combination regimens have been investigated in relapse. New and more effective therapies are shifting the focus from palliation to treatment algorithms with curative attempt. Challenges for monoclonal antibody combinations in the future include: (1) defining appropriate patient populations for combination therapies; (2) assessing the impact of pretreatment biologic prognostic factors; (3) enhancing eradication of minimal residual disease; and (4) reassessing response criteria in CLL. Key words: CLL; monoclonal antibodies; alemtuzumab; rituximab.

Chronic lymphocytic leukemia (CLL) has the highest prevalence of any adult leukemia in the Western world and is a heterogeneous disease. Although summarily defined as an indolent lymphoproliferative disorder, outcomes in individual patients vary widely, and the disease course is frequently unpredictable.1,2 The last few years have seen an evolution in our knowledge of the biology of CLL and new prognostic markers, * Corresponding author. Tel.: þ1 713 745 4613; Fax: þ1 713 794 4297. E-mail address: [email protected] (S. Faderl). 1521-6926/$ - see front matter ª 2006 Elsevier Ltd. All rights reserved.

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as well as the development of new therapeutic modalities.3e7 Whereas therapy of CLL has historically revolved around chemotherapeutics such as alkylating agents (e.g. chlorambucil) and nucleoside analogs (e.g. fludarabine), complete clinical response rates remain low and even responding patients eventually relapse and progress. The introduction of monoclonal antibodies (moabs) has substantially expanded the therapeutic options for patients with hematologic malignancies, including Non-Hodgkin’s lymphoma and CLL.8,9 Moabs act through unique mechanisms distinct from traditional cytotoxic chemotherapy: (1) engagement of restricted cell-surface antigens; (2) activation of intracellular proapoptotic signaling pathways in some instances; and (3) activation of human effector functions, including components of the complement system and antibody-dependent cellular cytotoxicity (ADCC). Whereas multiple moabs are under investigation for the treatment of CLL (Table 1), the two most widely used and active moabs in CLL remain alemtuzumab and rituximab. Early experience with single-agent use of these moabs confirmed good tolerability and safety and a favorable activity profile.10e14 To build upon potential synergy with other active agents in CLL (chemotherapeutic drugs and moabs), combination studies of moabs were designed and executed early on and are now expanding at a rapid pace. As experience with these combinations is growing, new data are accumulating about the value of these combinations in various clinical stages of CLL. In addition, measurements of minimal residual disease reveal a new quality of responses hitherto not observed with traditional chemotherapy combinations, paving the way to novel concepts of consolidation and maintenance therapies in CLL as well. This chapter will review the evolution of moab combinations in CLL and attempt to put these combinations into the perspective of new therapeutic paradigms that have developed concurrently in recent years. CHEMOIMMUNOTHERAPY OF CLL Chemoimmunotherapy experience in frontline CLL Rationale The rationale of CLL therapy has traditionally been focused on chemotherapy. The introduction of purine nucleoside analogs (e.g. fludarabine) has increased complete Table 1. Monoclonal antibodies in use or under investigation in chronic lymphocytic leukemia (CLL). Antibody

Other designation

Target

Alemtuzumab Rituximab Epratuzumab Lumiliximab Apolizumab Anti-HLA-DR Bevacizumab Denileukin Diftitox Anti-CD40

Campath-1H Ritxuxan (Mab Thera) Lymphocide (hLL2, E-mab) IDEC-152 Remitogen (Hu1D10) 1D09C3 Avastin Ontak CHIR-12.12

CD52 CD20 CD22 CD23 1D10a HLA-DR VEGF CD25b CD40

a

HLA-DR b-chain variant. Immunotoxin formed by the fusion of diphtheria toxin to interleukin 2 (IL-2); it binds to the IL-2 receptor (CD25). b

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remission (CR) and overall response (OR) rates, as well as progression-free survival (PFS) compared to single-agent alkylating-agent therapy such as with chlorambucil or cyclophosphamide.15 Although OR rates with fludarabine alone approach 80%, CR rates remain modest at around 20e30%.16 Based on in-vitro studies that suggested inhibition of alkylator-induced DNA repair in CLL lymphocytes when concurrently exposed to nucleoside analogs, combinations of fludarabine with cyclophosphamide have been developed and applied in clinical practice. Two randomized studies have recently confirmed higher CR and OR rates and prolonged PFS with the fludarabineplus-cyclophosphamide combination compared to fludarabine alone.17,18 Moabs have had a major impact on therapeutic considerations for patients with lymphoproliferative disorders, including CLL. The attraction of moabs is based on selective targeting of tumor-relevant and more or less specific surface markers, and a distinct mechanism of action involving elements of human effector functions such as the complement system and ADCC.9 Alemtuzumab (anti-CD52) and rituximab (anti-CD20) remain the most active moabs for CLL therapy (Table 1). Although response rates of relapsed CLL to standard-dose rituximab were disappointingly low, especially when compared to results in follicular Non-Hodgkin’s lymphoma (NHL), improved efficacy was demonstrated using higher doses or a more intense dose schedule.11,12,19 Higher responses have also been achieved in previously untreated symptomatic patients with CLL.10 In addition, in vitro studies demonstrated sensitization of lymphoma cell lines by rituximab to the cytotoxic effects of a number of chemotherapeutic drugs (including fludarabine and cyclophosphamide) and, vice versa, fludarabine exposure was shown to possibly enhance the rituximab effect by down-regulating complement defense proteins CD55 and CD59.20 Given the lack of CD20 expression on hematopoietic marrow progenitors and selectivity of rituximab for B lymphocytes (thereby avoiding myelosuppression and significant immunosuppression), plus the extensive experience with rituximab in NHL, it was not long before chemotherapy-plus-rituximab combinations were designed and evaluated in patients with CLL. The development of alemtuzumab in moab combinations has been lagging behind rituximab combinations for several reasons: (1) alemtuzumab has been available for a shorter period of time; (2) by binding to B and T lymphocytes through interaction with the CD52 antigen it is more immunosuppressive than rituximab; (3) infusionrelated adverse events, at least initially, tend to be more bothersome; and (4) alemtuzumab is predominantly active in CLL and does not have a track record of easy use and efficacy in the majority of NHLs as does rituximab. Nevertheless, over the last few years, the role of alemtuzumab in chemoimmunotherapy combinations has been increasing, a process that has been partly aided by the availability of the subcutaneous route of administration. Chemoimmunotherapy trials Several trials of chemoimmunotherapy combinations have been conducted in patients with untreated and symptomatic CLL (Table 2). The group at MD Anderson Cancer Center was among the first to combine rituximab with fludarabine and cyclophosphamide (FCR).21 Fludarabine was given at 25 mg/m2 intravenously daily for 3 days and cyclophosphamide at 250 mg/m2 intravenously daily for 3 days as well. Rituximab was administered on day 1 of each cycle at 375 mg/m2 intravenously during cycle 1, and then at 500 mg/m2 intravenously during subsequent cycles. Up to a total of six cycles were given. The median age of the patients was 58 years. Seventy-five patients

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Table 2. Chemoimmunotherapy regimens (frontline chronic lymphocytic leukemia, CLL).

Dose and schedule Fludarabine Pentostatin Cyclophosphamide Rituximab Total number of cycles N Median age, years (range) Rai stage
3 (%) b2M (mg/dL) Complete responses (CR) (%) Partial responses (PR) (%) Overall responses (OR) (%) Myelosuppression (%)
grade 3 Y ANC
grade 3 Y platelets a b c

FR22,a

FCR21

PCR23

25 mg/m2  5 days e e 375 mg/m2  1 dayb 6 51 63 (38e86) 39 4.01 47 43 90

25 mg/m2  3 days e 250 mg/m2  3 days 500 mg/m2  1 dayc 6 224 58 (24e86) 33 3.8 70 25 95

e 2 mg/m2  1 day 600 mg/m2  1 day 375 mg/m2  1 day NA 33 62 (40e79) 52 NA 33 60 90

76 20

82 18

NA NA

Concurrent regimen. Two doses of rituximab given during cycle 1. Dose of rituximab is 375 mg/m2 during cycle 1.

(33%) had disease
Rai stage 3. Among 224 previously untreated patients, the OR rate was 95% (70% CR, 10% nodular PR, and 15% PR). Older age (particularly >70 years) and elevated b2-microglobulin indicated a lower probability of achieving CR. In addition to evaluating clinical response as defined by the NCI Working Group Criteria, persistence of minimal residual disease was assessed by two-color flow cytometry (CD5/CD19) and polymerase chain reaction (PCR) assay for IgH gene rearrangements. When evaluated by flow cytometry, two thirds of the patients had less than 1% CD5/CD19-positive marrow lymphocytes, and a strong correlation existed between flow cytometry response and probability of relapse. PCR negativity reflecting molecular responses was demonstrated in almost half of the patients tested, and a positive association with molecular responses and remission duration could be shown as well. Time-to-treatment-failure analysis projected 69% of the patients to be failurefree at 4 years. Toxicities associated with the FCR combination were similar to the experience with fludarabine and cyclophosphamide in preceding treatment programs. Nausea and vomiting occurred during 23% of courses and were manageable. Grade
3 neutropenia and thrombocytopenia occurred in 52% and <5% of assessable courses, respectively. Even though severe neutropenia was common, only 2.6% of the courses were associated with major infections. Autoimmune hemolytic anemia developed in ten patients (three Coombs-positive, seven Coombs-negative). The Cancer and Leukemia Group B (CALGB) conducted a randomized phase-2 study to determine the optimal schedule and efficacy of rituximab in combination with fludarabine (CALGB 9712).22 The study included 104 patients who received either six monthly courses of fludarabine concurrently with rituximab followed 2 months later by four weekly doses of rituximab consolidation (n ¼ 51), or fludarabine alone followed 2 months later by the same consolidation schedule (sequential therapy, n ¼ 53). The median age of the patients was 64 years (range 36e86 years); 40% of the patients had disease of
Rai stage 3 at the start of treatment. The median

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b2-microglobulin level was 4.01 mg/dL. The OR rate was 90% (47% CR and 43% PR) for the concurrent regimen and 77% (28% CR and 49% PR) for the sequential therapy. At a median follow-up of almost 2 years, median response duration and survival have not been reached for either regimen. Toxicities were similar in both schedules with the exception of more frequent neutropenia grade
3 (74% versus 41%) and infusionrelated toxicities (20% versus 0%) in the concurrent regimen during the induction sequence. The combination of pentostatin together with cyclophosphamide and rituximab has been used in the ‘PCR’ regimen.23 In this combination pentostatin is administered at 2 mg/m2 intravenously, cyclophosphamide at 600 mg/m2 intravenously, and rituximab at 375 mg/m2 intravenously per course every 4 weeks for a total of six cycles. Thirty-three patients have been enrolled. Their median age was 62 years (range 40e79 years). About half of the patient had
Rai stage 3 disease. The OR was 93% (33% CR, 21% nodular PR, 39% PR). Three-color flow cytometry (CD5/CD19/ CD79b) was used to identify minimal residual disease. In all three response groups there was >90% reduction of B CLL cells. In addition, abnormalities detectable by fluorescence-in-situ hybridization (FISH) disappeared in 25 of 27 patients after therapy. Twenty-two patients experienced
grade 3, mainly non-hematological, toxicities, most commonly nausea and vomiting. Comparative analyses Comparisons to historical data using fludarabine alone, or fludarabine plus cyclophosphamide, have been conducted by both the CALGB (FR) and the MD Anderson Cancer Center (FCR), respectively (Table 3).21,24 Thirty-four patients have received fludarabine plus cyclophosphamide as their initial treatment, and 224 patients were treated with FCR at MD Anderson Cancer Center; the chemoimmunotherapy combination achieved significantly higher (P < 0.05) CR rates (70% versus 35%), median levels of cells co-expressing CD5/CD19 by two-color flow cytometry (0.45 versus 12.8), longer time-to-treatment failure (not reached versus 40 months), and time to progression (not reached versus 47 months), as well as longer median overall survival (not reached versus 73þ months).21 There was no significant difference in the number of infections per treatment course, nor in the frequency of severe neutropenia or thrombocytopenia. The CALGB retrospectively compared treatment outcome of 178 patients who received single-agent fludarabine as part of the US Intergroup trial comparing fludarabine with chlorambucil with the 104 patients in the CALGB 9712 trial of concurrent versus sequential fludarabine plus rituximab.24 The findings were similar to those of the MD Anderson Cancer Center experience: the chemoimmunotherapy combination achieved significantly higher CR rates (38% versus 20%, P ¼ 0.002) and OR rates (84% versus 63%, P ¼ 0.0003). Furthermore, patients treated with fludarabine plus rituximab had significantly better PFS (67% versus 45% at 2 years, P < 0.0001) and overall survival (93% versus 81%, P ¼ 0.003) compared to patients who were treated with fludarabine alone. Toxicities such as neutropenia, hypotension, and dyspnea were more commonly observed in the chemoimmunotherapy group, but there was no significant difference with regard to
grade 3 anemia and thrombocytopenia, or infections. It should be emphasized that both analyses rely on comparative data that are retrospective and that to date no prospective randomized trial of chemoimmunotherapy versus chemotherapy alone has been conducted and concluded. Problems inherent to

786 S. Faderl et al

Table 3. Chemoimmunotherapy: comparative analysis. Characteristic

MDACC21

CALGB24

FC

FCR

P

F

FR

P

N Median age (years) Age range (years)
Rai stage 3 (%)

34 53 33e92 50

224 57 24e86 33

e NS

178 64 37e87 43

104 63 38e88 40

e NS

Response (%) CR OR

35 88

Survival: progression-free overall

47a 73þa

Myelosuppression (%):
grade 3 neutropenia
grade 3 Y platelets Major infections (%)

74 15 9

NS

NS

70 95

<0.05 <0.05

20 63

38 84

<0.05 <0.05

NR NR

<0.05 <0.05

45b 81b

67b 93b

<0.05 <0.05

NS NS NS

21 11 23

61 16 26

<0.05 NS NS

82 18 11

MDACC, MD Anderson Cancer Center; CALGB, Cancer and Leukemia Group B; F, fludarabine; C, cyclophosphamide; R, rituximab; NS, not significant; CR, complete remission; OR, overall response. a Median in months. b % at 2 years.

the use of historical controls include differences in patient subsets (e.g. based on their cytogenetic/molecular profile), differences in supportive care, or trial effects in general. Outlook Chemoimmunotherapy combinations are rapidly gaining ground as first-line treatment for many newly diagnosed, symptomatic patients with CLL. Other combinations rediscovering mitoxantrone in the context of chemoimmunotherapy (e.g. FCR plus M) are being actively explored and information from ongoing clinical trials in CLL will soon become available.25,26 Regardless of the improvement in response rates and superior quality of responses (such as molecular remissions) that are associated with chemoimmunotherapy, no data are available from randomized studies that have so far proven a survival benefit of chemoimmunotherapy over traditional chemotherapy regimens. Experience from the FCR trial at MD Anderson Cancer Center suggested decreased response rates and a higher likelihood of prolonged myelosuppression in patients
70 years of age with advanced-stage disease, indicating the need for alternative therapies in these patients. Furthermore, clinical trials are under way that prospectively look at the results of therapy in the context of newer biologic parameters such as ZAP-70 expression, mutation status of IgH-chain genes, and cytogenetic/molecular abnormalities (e.g. 17pe and p53 deletions and mutations). Although information about correlations between biologic predictors and therapy are currently lacking, the obvious goal is to use those prognostic markers to offer risk-adapted therapy to the appropriate group of patients.

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Chemoimmunotherapy in relapsed and refractory CLL Various chemoimmunotherapy protocols have been investigated in CLL relapse and are outlined in more detail in the following sections (Table 4). Rituximab combinations Several rituximab-containing regimens have been developed and investigated in patients with relapsed and refractory CLL. For the most part, these closely resemble the chemoimmunotherapy combinations that have been described for previously untreated patients with CLL. Building upon the success of the FCR combination in frontline patients, an identical dose and schedule have been explored in the relapse setting.27 Wierda et al treated 177 patients with FCR. The median age of their patients was 59 years (range 36e81 years). The median number of prior therapies was two, with some patients receiving up to ten prior regimens. Thirty-seven patients (21%) were fludarabine-refractory. Median serum b2-microglobulin levels were 4.5 mg/dL. The OR rate was 73%, including 25% of patients achieving CR. The lowest response was seen in fludarabine-refractory patients where the OR rate was 58% with a CR rate of only 6%. In a multivariate analysis, CR rate was positively associated with higher pretreatment platelet counts, fewer numbers of prior therapies, and lower pretreatment b2-microglobulin. Of 37 patients in CR, 12 (32%) achieved molecular remission based on PCR testing for immunoglobulin heavychain gene rearrangements. Molecular remissions were also documented in two of 16 patients (13%) in nodular PR and two of 22 patients (9%) in PR. Myelosuppression was the most significant adverse event, preventing 26% of patients from completing the full six courses of therapy. Major infections requiring hospitalization, sepsis, and pneumonia were seen in 16% of all patients treated. One patient developed CMV pneumonitis. The frequency of infections was similar among fludarabine-sensitive and fludarabine-refractory patients. Schulz et al investigated the fludarabine and rituximab combination in relapsed patients with CLL.28 They included 11 previously treated patients among a total of 31 patients with B-CLL. Treatment consisted of fludarabine 25 mg/m2 intravenously Table 4. Monoclonal antibody combinations in chronic lymphocytic leukemia (CLL) relapse. Combination

27

FCR FR28 PCR29 FA30 FA31 CFAR33 AR35 AR36 AR37

N

177 11 28 6 34 21 48 12 20

Age (years, median)

59 (36e81) NA 62 (30e80) 46 (38e67) 61 (38e80) 58 (46e72) 62 (44e79) 70 (53e73) 57 (39e78)

Number of prior regimens (median)

Response (%) CR

PR

OR

2 (1e10) 1 (1e2) 2 (1e7) 8 (4e10) 2 (1e8) 4 (1e8) 4 (1e9) NA 3 (1e5)

25 27 29 17 29 14 8 e 30

48 63 50 67 56 38 44 8 25

73 90 79 84 85 52 52 8 55

FCR, fludarabine, cyclophosphamide, rituximab; FR, fludarabine, rituximab; FA, fludarabine, alemtuzumab; CFAR, fludarabine, cyclophosphamide, rituximab, alemtuzumab; AR, alemtuzumab, rituximab; NA, not available.

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daily for 5 days every 4 weeks for a total of four courses with rituximab 375 mg/m2 intravenously given on days 57, 85, 113, and 151 of the regimen. Among the relapsed group, ten patients (90%) responded, with three patients (27%) achieving CR and two (18%) CRu. Side-effects were generally mild. Hematologic toxicities of
grade 3 occurred in 42% (neutropenia) and 9% (thrombocytopenia), respectively. Pentostatin has also been used in combination with cyclophosphamide and rituximab in CLL relapse. Lamanna et al treated 46 patients with the PCR regimen.29 The median age was 62 years (range 30e80 years). Patients had failed a median of two prior regimens (range 1e7). Pentostatin was administered at 4 mg/m2 and cyclophosphamide at 600 mg/m2 intravenously every 3 weeks for a total of six courses. Rituximab was added at a dose of 375 mg/m2 starting with cycle 2. The overall response rate was 79% including 29% complete responders. As with other chemoimmunotherapy combinations, myelosuppression was the predominant toxicity. Alemtuzumab combinations One of the first indications of the activity of alemtuzumab in combination with fludarabine came from a small study of six patients with CLL refractory to either alemtuzumab or fludarabine as single agents.30 Five of the six patients responded, including one CR, and complete morphologic marrow responses were seen in another three patients with eradication of flow-cytometry-measurable disease in two of them. Elter et al pursued the fludarabine plus alemtuzumab combination further.31 Fludarabine was given at 30 mg/m2 intravenously daily on days 1e3, which was immediately followed by alemtuzumab at 30 mg intravenously given over 2 hours for 3 doses on days 1e3 as well. Courses were repeated every 4 weeks for a total of six rounds. In addition to evaluating clinical responses, minimal residual disease was measured using four-color flow cytometry. Of 37 patients, 34 were evaluable. Their median age was 61 years (range 38e80 years); 76% had high-risk disease (Binet stage C), and the median number of prior therapies was two (range 1e8). Ten patients (29%) achieved CR with an OR rate of 85%. MRD negativity was demonstrated in 15 of 34 patients (44%) based on peripheral-blood testing.32 Infectious complications were few. Seven patients with autoimmune hemolytic cytopenias prior to the start of therapy were successfully treated. The positive experience of the fludarabine and alemtuzumab combination has led to an ongoing randomized phase III trial of this combination versus fludarabine alone in CLL relapse. Future trials will also explore the combination in previously untreated CLL. Based on the positive FCR experience in CLL relapse, the group at MDACC has investigated the safety and efficacy of adding alemtuzumab to FCR (‘CFAR’).33 The CFAR regimen copied the FCR schedule with FþC given at identical doses on days 3e5 and rituximab on day 2. Alemtuzumab was administered at 30 mg intravenously on days 1, 3, and 5. Cycles were repeated every 4 weeks for a total of six cycles. All patients received tumor lysis prophylaxis with allopurinol (as established with the FCR regimen) and anti-infective prophylaxis consisting of trimethroprim/sulfamethoxazole and valacyclovir (or equivalent). More recently, oral valgancyclovir has been substituted for valacyclovir. The most recent update includes 21 evaluable patients with a median age of 58 years (range 46e72 years) and a median number of prior therapies of four (range 1e8); the patients were resistant to purine nucleoside analogs, and almost 40% had an unfavorable cytogenetic profile (17pe, 11qe, or complex). The OR rate was 52%, including 14% of patients who achieved CR. All CR patients were also negative for MRD when evaluated by two-color flow cytometry. Neutropenia

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grade
3 occurred in 62% of all evaluable courses and thrombocytopenia grade
3 in 39%. Cytomegalovirus (CMV) reactivation was seen in five of 21 patients (23%, none receiving valganciclovir). All patients responded to therapy and no CMV-related fatalities occurred. The study is ongoing in CLL relapse. Given the high response rate in this patient group and the predictable and manageable toxicity profile, the combination is now being investigated in frontline patients with the unfavorable pretreatment characteristic of a b2-microglobulin level >4 mg/dL. MONOCLONAL ANTIBODIES IN COMBINATION Alemtuzumab plus Rituximab Rationale One of the main rationales for using moabs in combinations is to overcome some of the limitations of single-agent moab use.34 These include: (1) variable expression of CD20 and CD52 on CLL cells of individual patients; (2) synergistic activity in anatomic compartments such as lymph-node sites (where rituximab is expected to be more effective) versus marrow (better clearance of malignant lymphocytes with alemtuzumab); and (3) engagement of distinct intracellular signaling pathways resulting in apoptotic cell death. Establishing the feasibility and efficacy of the alemtuzumab/rituximab combination may provide more active schedules for consolidation and maintenance strategies, or the treatment and eradication of minimal residual disease. Early trials Faderl et al conducted an exploratory study of alemtuzumab plus rituximab in patients with relapsed and refractory chronic lymphoid malignancies.35 The schedule was empirically derived from established single-agent moab experience. Rituximab was given at 375 mg/m2 weekly for 4 weeks with alemtuzumab at 30 mg intravenously twice weekly during weeks 2e4, preceded by a dose escalation of 3, 10, and 30 mg on three consecutive days during week 1. Patients received standard premedication (antihistamine and acetaminophen) and anti-infectious prophylaxis (trimethoprim/sulfamethoxazole and valacyclovir or valganciclovir). Forty-eight patients were enrolled: 32 CLL, nine CLL/prolymphocytic leukemia (PLL), one PLL, four mantle-cell leukemia (MCL), two Richter transformation. Their median age was 62 years (range 44e79 years). Patients had received a median of four (range 1e9) prior therapies, 39 (79%) had
Rai stage 3 disease, and 26 (54%) were refractory to fludarabine. The OR rate after a 4-week course of therapy was 52%, including a CR rate of 8%. Among 32 patients with CLL, the OR rate was 63%. Treatment-related adverse events included expected infusion-related side-effects (fever, rigors, skin reactions, fatigue, nausea and vomiting), and infectious complications. About half the patients experienced at least one infectious episode, including seven patients (15%) with symptomatic CMV reactivation who responded to CMV-directed therapy. A different schedule was investigated by Nabhan et al.36 In their phase-1 study rituximab was given at the standard dose of 375 mg/m2 on weeks 1, 3, 4, and 5, and alemtuzumab at 3 mg (first cohort), 10 mg (second cohort), and eventually 30 mg (third cohort) three times weekly during weeks 2e5. Twelve patients were enrolled; all had failed prior purine-analog-based therapy. One patient achieved PR whereas all remaining patients had stable disease. Treatment was well tolerated, with

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most toxicities related to the infusion of alemtuzumab. No opportunistic infections e particularly no CMV reactivations e were observed. Continuous-infusion alemtuzumab plus rituximab: optimizing dose and schedule In an effort to (1) further optimize dose, schedule and route of administration; (2) obtain data about soluble CD52 serum levels and their association with prognosis; and (3) gain easy access to subcutaneous alemtuzumab, the group at MD Anderson Cancer Center is investigating a continuous intravenous infusion followed by subcutaneous injection of alemtuzumab plus rituximab.37 Rituximab is given at 375 mg/m2 intravenously on day 1 followed by 500 mg/m2 on days 8, 15, and 22, and alemtuzumab at 15 mg by continuous intravenous infusion daily for 6 days (days 2e7) followed by 30 mg subcutaneously twice weekly on days 3 and 5 of weeks 2e4. Premedications and anti-infectious prophylaxis remain identical to those in previous regimens. Twenty patients of a total of 28 (27 CLL and one marginal-zone lymphoma) with relapsed and refractory disease are evaluable for response. Their median age is 57 years (range 39e78 years) with a median number of prior therapies of three (range 1e5), a median b2-microglobulin of 3.5 mg/dL (range 2.1e13.6), 50% with Rai stage
3 disease, and 30% refractory to fludarabine and alkylating agents. The OR rate is 55%, including a CR rate of 30%, and all responders achieved their maximum response after 4 weeks of therapy. Correlative studies to measure soluble CD52 and antibody levels are planned. SUMMARY The use of moabs has dramatically changed the therapeutic options for patients with lymphoproliferative disorders. Alemtuzumab and rituximab remain among the most active moabs in CLL. Within only a few years, combination therapies have been developed and are becoming a mainstay of the therapeutic armamentarium in CLL. Chemoimmunotherapy combinations have demonstrated unprecedented clinical response rates in previously untreated and asymptomatic patients. Numerous new combinations are being tested in relapsed and refractory patients and are starting to move into groups of patients with a better prognosis. In effect, therapy has become so effective that more sensitive laboratory tools for assessment of response have become necessary, such as polymerase chain reaction (PCR) testing and multicolor flow cytometry that go far beyond traditional clinical response criteria. Higher response rates and better-quality responses (molecular responses) have verified the importance of moab use not only as part of debulking chemotherapy, but also within the context of consolidation and maintenance. Despite the significant progress that moab combinations have generated in the preceding years, several issues remain to be evaluated. Chemoimmunotherapy combinations in previously untreated CLL patients have uniformly produced higher CR and OR rates than would have been expected from chemotherapy or single-agent moab use alone. However, no randomized studies have been conducted between chemoimmunotherapy and traditional chemotherapy regimens or among the various chemoimmunotherapy regimens. Larger trials comparing the different approaches will be necessary. An open question remains as to which patients will benefit from chemoimmunotherapy and which will not. Risks related to myelosuppression and immunodeficiency will have to be carefully weighed against the prospect of a favorable outcome. Furthermore, the role of chemoimmunotherapy regimens vis-a`-vis novel

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pretreatment biological prognostic factors and how these impact on therapy outcome remains to be determined. Notwithstanding the questions that are being raised by moab combinations, their success has contributed to shifting the focus from purely palliative to therapy with a curative intent. New treatment algorithms have emerged and continue to be refined in the light of rapidly accumulating experience and data.

Research agenda  in phase-II studies chemoimmunotherapy combinations are achieving higher CR rates and better-quality responses than chemotherapy alone; randomized studies of chemoimmunotherapy versus chemotherapy alone are needed to further substantiate the superiority of chemoimmunotherapy  different chemoimmunotherapy combinations are being used (e.g. FCR, FR, PCR); although overall response rates are similar, no formalized comparison among these different approaches has been conducted and will be necessary to identify the merits of specific combinations  chemoimmunotherapy results in a high frequency of myelosuppression; the question of routine use of hematopoietic growth factors (e.g. G-CSF, GM-CSF) as part of these combinations needs to be further evaluated  factors predictive for response following chemoimmunotherapy need to be highlighted, and alternative strategies should be pursued in patients with a low likelihood of benefit (e.g. patients > 70 years)  monoclonal antibody combinations continue to play an increasing role in consolidation and maintenance programs; questions remain as to optimal combinations, timing and duration of maintenance, and impact on overall survival

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