Antibody-basedtherapyofleukaemia
`
`http://www.expertreviews.org/
`
`expert reviews
`
`in molecular medicine
`
`Antibody-based therapy of leukaemia
`
`John C. Morris* and Thomas A. Waldmann
`Over the past decade, monoclonal antibodies have dramatically impacted the
`treatment of haematological malignancies, as evidenced by the effect of
`rituximab on the response rate and survival of patients with follicular and
`diffuse large B cell non-Hodgkin’s lymphoma. Currently, only two monoclonal
`antibodies – the anti-CD33 immunotoxin gemtuzumab ozogamicin and the
`CD52-directed antibody alemtuzumab – are approved for
`treatment of
`relapsed acute myeloid leukaemia in older patients and B cell chronic
`lymphocytic leukaemia,
`respectively. Although not approved for such
`treatment, alemtuzumab is also active against T cell prolymphocytic
`leukaemia, cutaneous T cell lymphoma and Se´ zary syndrome, and adult T cell
`leukaemia and lymphoma. In addition, rituximab has demonstrated activity
`against B cell chronic lymphocytic and hairy cell
`leukaemia. Monoclonal
`antibodies targeting CD4, CD19, CD20, CD22, CD23, CD25, CD45, CD66 and
`CD122 are now being studied in the clinic for the treatment of leukaemia.
`Here, we discuss how these new antibodies have been engineered to reduce
`immunogenicity and improve antibody targeting and binding.
`Improved
`interactions with Fc receptors on immune effector cells can enhance
`destruction of target cells through antibody-dependent cellular cytotoxicity
`and complement-mediated cell
`lysis. The antibodies can also be armed
`with cellular toxins or radionuclides to enhance the destruction of leukaemia cells.
`
`In his Croonian Lecture in 1900, the renowned
`immunologist Paul Ehrlich proposed that
`‘immunisations such as these which are of
`great
`theoretic
`interest may come
`to be
`available
`for
`clinical
`application attacking
`epithelium new formations,
`particularly
`carcinoma by means of specific anti-epithelial
`sera’ (Ref. 1). Unfortunately, Erlich’s dream of
`the ‘magic bullet’ of antibodies as a cancer
`treatment
`remained
`elusive
`until
`the
`groundbreaking work of Ko¨ hler and Milestein
`
`in the mid-1970s in which they developed
`techniques for generating specific monoclonal
`antibodies (Ref. 2). Despite the enthusiasm for
`antibodies as an anticancer
`therapy, early
`clinical results were discouraging. A number
`of
`improvements
`in
`understanding
`and
`biotechnology were
`required
`before
`the
`promise could be kept. Only now at
`the
`beginning of
`the twenty-first century have
`monoclonal antibodies come into their own as
`a treatment for cancer.
`
`Metabolism Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD USA.
`
`*Corresponding author: John C. Morris, Co-Director Clinical Trials, Metabolism Branch, Center for
`Cancer Research National Cancer Institute, Mark O. Hatfield Clinical Research Center, Room 4-5330,
`10 Center Drive, Bethesda, Maryland 20892-1457, USA. Tel: +1 301 402 2912; Fax: +1 301 402 1001;
`E-mail: jmorris@mail.nih.gov
`
`Accession information: doi:10.1017/S1462399409001215; Vol. 11; e29; September 2009
`& Cambridge University Press 2009
`
`1
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`Antibody-basedtherapyofleukaemia
`
`expert reviews
`
`in molecular medicine
`
`(1) its expression should be restricted to the
`leukaemic cells. If the antigen is expressed on
`normal cells,
`the loss of
`these cells should
`not result
`in serious complications such as
`life-threatening
`cytopaenias
`or
`prolonged
`immunosuppression; (2) the target should be
`expressed at high density on the leukaemic cells
`to provide an adequate number of antibody
`binding sites. Studies suggest
`that
`tumour
`responses correlate with target density. The
`lower responsiveness of CD20-expressing CLL
`to rituximab compared with follicular B cell
`NHL appears to be due to the lower level of
`CD20 expressed in CLL (Ref. 10). Escape
`mutants
`that
`lose
`antigen expression are
`unaffected because there is no target for the
`antibody to bind; (3) for unmodified or unarmed
`monoclonal antibodies, target antigens should
`not undergo internalisation (downmodulation).
`Internalisation
`of
`the
`antigen – antibody
`complex
`reduces
`the number
`of
`targets
`available
`for
`binding; however,
`antigen –
`antibody internalisation can be an advantage
`with immunotoxins. In addition, enhancement
`of antitumour activity is often seen when
`monoclonal antibodies are used in combination
`with cytotoxic chemotherapy (Refs 11, 12, 13).
`
`Monoclonal antibodies targeting myeloid
`leukaemia
`Acute myeloid leukaemia (AML) is the most
`common acute leukaemia of adults and it
`accounts for about 15% of childhood leukaemias
`(Ref. 14). At diagnosis, 55% of AML patients are
`age 65 or older. Between 50% and 80% of
`previously untreated patients achieve a complete
`remission with combinations of cytarabine and
`an anthracycline. For patients achieving a
`remission, up to 40% will survive for 5 years;
`however, these outcomes are worse for older
`patients. Therapeutic options are limited in
`relapsed patients over the age of 60 because of
`lower
`response rates,
`increased toxicity of
`treatment, and the frequent comorbidities present
`in this population. For older patients who failed
`to respond or relapsed after first-line therapy,
`the prognosis is often limited. The introduction of
`the CD33-targeted immunotoxin, gemtuzumab
`ozogamicin, as well as a number of novel
`monoclonal antibodies directed against other
`myeloid
`antigens
`currently
`in
`clinical
`development, offer new promise to these patients
`(Table 1).
`
`http://www.expertreviews.org/
`
`and Drug
`Food
`the US
`Currently,
`Administration (FDA) has
`approved nine
`monoclonal antibodies for
`the treatment of
`cancer. Of these, only two, alemtuzumab and
`gemtuzumab ozogamicin, have indications in
`leukaemia. Rituximab
`approved
`for
`the
`treatment of B cell non-Hodgkin’s lymphoma
`(NHL), has demonstrated activity in B cell
`chronic lymphocytic leukaemia (CLL) and hairy
`cell leukaemia (HCL) (Refs 3, 4). In addition, a
`number of antibodies directed against novel
`antigens, or
`that have been engineered to
`improve effector function, or armed with toxins
`or radioisotopes to increase killing ability are
`currently being studied in various leukaemias.
`The vast majority of
`early
`therapeutic
`monoclonal antibodies were of rodent origin, and
`therefore exhibited a number of unfavorable
`characteristics. Most notably,
`the nonhuman
`framework was immunogenic and frequently
`induced human antirodent antibody responses
`after very few treatments. This resulted in the
`loss of therapeutic effect, and increased the risk
`of infusional reactions and toxicity. In addition,
`nonhuman
`antibodies
`exhibit
`unfavorable
`pharmacokinetics with
`shorter
`half-lives
`and reduced Fc
`receptor binding that
`is
`required
`for
`antibody-dependent
`cellular
`cytotoxicity (ADCC) (Refs 5, 6). To overcome
`these problems, most approved therapeutic
`monoclonal antibodies have been modified
`using
`recombinant DNA technology
`to
`express human framework sequences to reduce
`immunogenicity and improve pharmacokinetics
`(Ref. 7). ‘Chimeric’ antibodies have undergone
`substitution of up to 70% of the nonhuman
`framework sequences. In ‘humanised’ antibodies,
`up to 90% of nonhuman sequences have been
`replaced,
`leaving only the original nonhuman
`complementary determining regions,
`further
`reducing immunogenicity. Advancements
`in
`transgenic
`technology
`have
`allowed
`the
`generation of monoclonal
`antibodies with
`fully ‘human’ sequences, high antigen affinities
`and little or no immunogenicity (Ref. 8). Further
`efforts have focused on engineering the effector
`function of antibodies by Fc subtype switching
`to improve the antibody’s ability to activate
`complement to lyse target cells, and to enhance
`antibody–Fc-receptor binding on macrophages
`and other effector cells to increase ADCC (Ref. 9).
`The ideal
`leukaemia antigen for antibody
`therapy should exhibit certain characteristics:
`
`Accession information: doi:10.1017/S1462399409001215; Vol. 11; e29; September 2009
`& Cambridge University Press 2009
`
`2
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`Antibody-basedtherapyofleukaemia
`
`http://www.expertreviews.org/
`
`expert reviews
`
`in molecular medicine
`
`CD33-targeted antibodies
`CD33 is a 67 kDa glycoprotein sialoadhesin
`receptor (Ref. 15). Its intracytoplasmic domain
`expresses two immunoreceptor tyrosine-based
`inhibitory motifs (ITIMs). CD33 is believed to
`have an important role in modulating leuko-
`cyte function, inhibiting cellular activation and
`proliferation,
`inducing
`apoptosis,
`and
`modulating cytokine secretion (Ref. 16). It is
`expressed on normal and maturing myeloid
`progenitor cells, but not on early normal
`haematopoietic stem cells. Over 90% of acute
`myeloid leukaemia blast cells express CD33, but
`it is not found on nonhaematopoietic tissues
`(Ref. 17).
`
`Gemtuzumab ozogamicin
`Gemtuzumab ozogamicin (MylotargTM, Wyeth,
`Madison, NJ)
`is an immunotoxin composed
`of a humanised IgG4k monoclonal antibody
`(hP67.6) that recognises CD33 conjugated to the
`antitumour antibiotic g1-calicheamicin, which is
`active against a broad spectrum of leukaemic
`
`lines. Gemtuzumab is
`and solid tumour cell
`derived from the murine anti-CD33 antibody
`p67.6 (Ref. 18) and it is linked to N-acetyl-g1-
`calicheamicin (Ref. 19). It is approved for the
`treatment of CD33-positive AML in patients 60
`years of age or older in first relapse.
`Upon binding to CD33, the antibody–receptor
`complex is internalised and g1-calicheamicin is
`released through hydrolysis of the N-acetyl linker
`(Ref. 20). Calicheamicin binds to the minor
`groove of DNA and results in site-specific
`double-stranded DNA breaks. Given that CD33
`stimulation is normally inhibitory, gentuzumab
`may also exert effects through receptor binding.
`In vitro, gemtuzumab ozogamicin is almost 105
`times more toxic to CD33-expressing cells than to
`cells lacking CD33 (Ref. 21).
`At least 85% saturation of CD33 on leukaemic
`blasts is achieved with an initial dose of 9 mg/m2.
`Saturating levels of the antibody are believed
`to enhance efficacy. After a 9 mg/m2 dose,
`gentuzumab achieves a mean peak plasma
`concentration (Cmax) of 2.86 1.35 mg/ml and has
`
`Table 1. Monoclonal antibodies for the treatment of myeloid leukaemia
`
`Monoclonal
`antibody
`
`Gemtuzumab
`ozogamicin
`(MyelotargTM,
`hP67.6)
`
`Lintuzumab
`(HuM195, SGN-33)
`
`Anti-CD44 (A3D8)
`
`Anti-CD45 (BC8,
`YTH 24.5,
`YAMEL568)
`
`Anti-CD66
`(BW250/183)
`
`Anti-CD123
`(26292(Fv)-PE38-
`KDEL)
`
`Target
`antigen
`
`CD33
`
`Isotype
`
`Humanised IgG4-
`g1-calicheamicin
`immunotoxin
`
`Approval and
`indication
`
`Refs
`
`FDA approved; AML
`
`18, 24
`
`CD33
`
`Humanised IgG1
`
`Phase III; AML
`
`Adhesion
`glycoprotein
`
`Leukocyte
`protein tyrosine
`phosphatase
`
`CEA family
`granulocyte
`antigen
`
`CD123 (IL-3Ra)
`
`Murine IgG1
`
`Radiolabelled 131I
`murine IgG1; 99mTc
`murine IgG2b; 111In rat
`IgG2a-imaging/
`biodistribution
`
`Radiolabelled 188Re 90Y
`murine IgG1
`
`Murine anti-CD123-Fv-
`Pseudomonas exotoxin A
`immunotoxin
`
`Preclinical
`development; AML
`
`Phase I–II; AML,
`allogeneic stem cell
`transplantation,
`imaging
`
`Phase I–II; AML,
`allogeneic stem cell
`transplantation
`
`Preclinical
`development; AML
`
`35
`
`46
`
`39, 40
`
`42,
`43, 44
`
`49
`
`Abbreviations: AML, acute myeloid leukaemia; CEA, carcinoembryonic antigen; FDA, Food and Drug
`Administration; I, iodine; IL-3Ra, interleukin-3 receptor-a; In, indium; Re, rhenium; Tc, technetium; Y, yttrium.
`
`Accession information: doi:10.1017/S1462399409001215; Vol. 11; e29; September 2009
`& Cambridge University Press 2009
`
`3
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`Antibody-basedtherapyofleukaemia
`
`expert reviews
`
`in molecular medicine
`
`lintuzumab
`CMC. Similarly to gentuzumab,
`undergoes internalisation. In a Phase III trial in
`191 adults with refractory AML or AML at
`first
`relapse,
`lintuzumab
`in
`combination
`with mitoxantrone,
`etoposide
`and cytosine
`arabinoside was compared with chemotherapy
`alone (Ref. 35). A response rate of 36% was
`observed in the
`combined antibody and
`chemotherapy group compared with 28% in
`those undergoing chemotherapy alone, with no
`difference in overall survival noted between the
`two groups. Both M195
`and lintuzumab
`conjugated to a- or b-particle-emitting isotopes
`have been used to purge bone marrow of
`leukaemic blasts in patients undergoing stem cell
`transplantation (Refs 36, 37).
`
`CD45-targeted antibodies
`CD45, also known as common leukocyte antigen,
`is a 200 kDa protein tyrosine phosphatase
`expressed at high levels on leukocytes and
`leukocyte precursors,
`including AML blasts
`(Ref. 38). CD45 functions as a regulator of T-
`and B-cell-receptor signalling. CD45 does not
`undergo internalisation. Anti-CD45
`labeled
`with 131I has been studied in Phase I and Phase
`II trials in AML patients as part of an allogeneic
`bone marrow transplant conditioning regimen
`in combination with cyclophosphamide and
`total body irradiation, or with busulfan and
`cyclophosphamide (Refs 39, 40). The 3 year
`disease-free survival rate was 61% in 46 treated
`patients. After adjusting for differences in risk,
`the hazard of mortality of the treatment group
`was 0.65 (95% CI, 0.39 – 1.08) compared with 509
`similar patients from the International Bone
`Marrow Transplant Registry, suggesting benefit
`from this approach (Ref. 40).
`
`CD66-targeted antibodies
`CD66 is a heavily glycosylated carcinoembryonic
`antigen (CEA)-related glycoprotein that
`is
`involved in adhesion to E-selectin surface
`glycoprotein. CD66 is expressed at high levels on
`granulocytes and it does not appear to be shed or
`internalised (Ref. 41). Radiolabeled anti-CD66
`with stem cell transplantation has been studied in
`AML (Refs 42, 43, 44). One trial compared the
`biodistribution of 99mTc-anti-CD66 versus 99mTc-
`anti-CD45 monoclonal antibodies in 12 AML
`patients undergoing stem cell transplantation and
`found that the anti-CD66 antibody (BW250/183)
`showed
`a
`favorable
`biodistribution
`and
`
`http://www.expertreviews.org/
`
`a plasma half-life of 72.4 42.0 hours (Ref. 22).
`Higher concentrations are observed with second
`doses. This is thought to be due to reduced
`tumour burden and lower availability of CD33 to
`bind gemtuzumab following the initial dose. The
`area under the curve (AUC) for g1-calicheamicin
`tracks with that of gemtuzumab, indicating that
`g1-calicheamicin remains
`conjugated to the
`antibody in the plasma.
`A Phase I trial defined the maximum tolerated
`dose of gemtuzumab ozogamicin administered as
`a 2 hour infusion as 9 mg/m2 (Ref. 23). The
`recommended treatment course is a total of two
`doses with at
`least 14 days between doses.
`A combined analysis of three open-label Phase II
`studies in 277 adults with recurrent CD33-
`positive AML reported an overall response rate of
`26% (Ref. 24). The response rate for patients 60
`years of age was 24% compared with 28% for
`those less than 60 years old. Gemtuzumab
`ozogamicin has also demonstrated activity as
`first-line single-agent therapy, as well as when
`used as consolidation therapy after remission-
`induction with chemotherapy, or used in
`combination with chemotherapy in CD33-postive
`AML (Refs 25, 26, 27, 28). Improved results were
`achieved when
`it was
`combined with
`chemotherapy at relapse over treatment with
`salvage
`chemotherapy alone
`(Refs 29, 30).
`Gemtuzumab ozogamicin combined with arsenic
`trioxide and all-trans-retinoic acid has also shown
`promise
`in
`recurrent
`acute promyelocytic
`leukaemia (Ref. 31).
`Toxicity includes chills, fever, nausea, vomiting,
`tachycardia, headaches,
`labile blood pressure,
`myelosuppression, stomatitis, elevation of liver
`transaminases and bilirubin, and rarely, hepatic
`veno-occlusive disease. Tumour lysis syndrome
`and acute adult respiratory distress syndrome
`have
`also
`been
`reported. Resistance
`to
`gemtuzumab ozogamicin has been correlated
`with expression of
`the multidrug resistance
`(MDR-1) p-glycoprotein and increased serum
`soluble CD33 antigen levels (Refs 32, 33, 34).
`
`Lintuzumab
`Lintuzumab (SGN-33, HuM195, Seattle Genetics,
`Bothell, WA) is a humanised IgG1 anti-CD33
`monoclonal antibody derived from the murine
`M195 antibody that exhibits a high affinity for
`CD33. Since it is humanised, lintuzumab is less
`immunogenic than M195. Unlike the IgG4-based
`gentuzumab,
`lintuzumab exhibits ADCC and
`
`Accession information: doi:10.1017/S1462399409001215; Vol. 11; e29; September 2009
`& Cambridge University Press 2009
`
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`Antibody-basedtherapyofleukaemia
`
`expert reviews
`
`in molecular medicine
`
`underlying disease; it is greatest in follicular and
`diffuse large B cell lymphoma and lower in CLL
`and HCL. CD20 is nonmodulating and it is not
`shed, making it an ideal target for antibody
`therapy (Ref. 52).
`
`Rituximab
`Rituximab (RituxanTM, MabTheraTM, Genentech,
`South San Francisco, CA) is a chimeric anti-CD20
`monoclonal antibody. It was generated from the
`murine anti-human CD20 antibody 2B8 by
`cloning the light- and heavy-chain comple-
`mentary determining regions (CDR) on to a
`human IgG1 heavy-chain and kappa light-chain
`constant region (Ref. 53).
`In 1997, Rituximab
`became the first monoclonal antibody to be
`licensed for the treatment of cancer. Since then, it
`has
`revolutionised the treatment of B cell
`malignancies. Rituximab is approved by the FDA
`for: (1) the treatment of relapsed or refractory,
`low-grade or follicular, CD20-positive, B cell
`NHL as a single agent; (2) previously untreated
`follicular, CD20-positive, B cell NHL in
`combination
`with
`chemotherapy;
`(3)
`nonprogressing low-grade, CD20-positive B cell
`NHL,
`as
`a
`single
`agent,
`after first-line
`chemotherapy, and (4) previously untreated
`diffuse large B cell, CD20-positive NHL in
`combination with CHOP (cyclophosphamide,
`doxorubicin, vincristine, prednisone) or other
`anthracycline-based chemotherapy regimens.
`Rituximab exhibits powerful B-cell-depleting
`properties. The mechanism of action is complex
`and may vary by disease
`(Ref.
`54).
`Its
`mechanism includes
`induction of apoptosis,
`inhibition of cell growth, complement-mediated
`cytotoxicity
`(CMC),
`sensitisation
`to
`both
`chemotherapy
`and radiation,
`and ADCC.
`Rituximab enhances sensitivity to chemotherapy
`by downregulating expression of Bcl-2 (Ref. 55).
`Some preclinical work suggested that
`full
`cytotoxic activity could only be achieved in
`mice expressing the stimulatory g-chain of the
`FcgRIII receptor (Ref. 56). Activation of allelic
`variants of the FcgRIIIa gene correlates with an
`improved response to rituximab in patients
`with follicular NHL, but not in patients with
`CLL (Refs 57, 58). Rituximab enhances caspase-
`9, caspase-3 and poly(ADP-ribose) polymerase
`(PARP) cleavage in CLL cells, suggesting that
`induction of
`apoptosis
`is
`the dominant
`mechanism of action in CLL, whereas CMC and
`ADCC appear to be the dominant effects in
`
`http://www.expertreviews.org/
`
`pharmacokinetics compared with the anti-CD45
`antibody (Ref. 45). Zenz and colleagues treated 20
`adults with allogeneic stem cell transplantation
`(188Re)-labeled anti-CD66
`and Rhenium-188
`for
`Philadelphia-chromosome-positive
`acute
`lymphoblastic leukaemia or advanced chronic
`myeloid leukaemia with acceptable toxicity;
`however, no reduction in the incidence of
`leukaemic relapse was observed (Ref. 44).
`
`Antibodies targeted against myeloid
`leukaemia stem cell antigen (CD44 and
`CD123)
`CD44 (phagocytic glycoprotein I) and CD123
`(interleukin-3 receptor a) represent potential
`targets for antibody-based therapy of myeloid
`leukaemia (Refs 46, 47). Cancer stem cells are
`increasingly
`recognised
`as
`a
`specialised
`population
`of
`selfrenewing
`tumour
`cells
`(Ref. 48). Ultimate success might
`lie in our
`ability to effectively target leukaemia stem cells.
`the a-subunit of
`CD123,
`the interleukin-3
`receptor (IL-3Ra) is highly expressed on various
`blasts and leukaemic stem cells. Du and co-
`workers studied the activity of a series of
`single-chain Fv antibody fragments fused to a
`38 kDa fragment of Pseudomonas exotoxin A
`(Ref. 49). One of these, 26292(Fv)-PE38-KDEL
`was cytotoxic to several CD123-expressing cell
`lines in vitro.
`
`Monoclonal antibodies targeting lymphoid
`leukaemia: B cell leukaemia antigens
`A list of antibodies currently in development or
`clinical
`trial
`for
`the
`treatment of B cell
`leukaemia is provided in Table 2. The various
`antibodies are considered in detail within their
`respective groups below.
`
`CD20-targeted antibodies
`CD20 is a 31–37 kDa antigen expressed on almost
`all normal B cells and most B cell malignancies
`(Ref. 50). It is a nonglycosylated phosphoprotein
`member of the membrane-spanning 4A gene
`family.
`Its function is unclear, but CD20 is
`believed to have a role in B cell activation and
`regulation of B cell growth, as well as acting as a
`cell membrane calcium channel (Ref. 51). CD20 is
`expressed at almost all
`stages of B cell
`development,
`except
`in pro-B cells
`and
`terminally differentiated plasma cells. CD20 is
`expressed on the malignant B cells of NHL, CLL
`and HCL. The number of targets varies with the
`
`Accession information: doi:10.1017/S1462399409001215; Vol. 11; e29; September 2009
`& Cambridge University Press 2009
`
`5
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`http://www.expertreviews.org/
`
`expert reviews
`
`in molecular medicine
`
`Table 2. Monoclonal antibodies for the treatment of B cell leukaemia
`
`Monoclonal antibody
`
`XmAb 5574
`
`Rituximab (RituxanTM,
`MabTheraTM, C2B8)
`
`Ofatumumab
`(HuMax-CD20TM)
`
`Ocrelizumab
`
`Target
`antigen
`
`CD19
`
`Isotype
`
`Approval and
`indication
`
`Humanised and Fc
`enhanced mouse IgG1
`
`Preclinical
`development
`
`CD20
`
`Humanised mouse IgG1
`
`CD20
`
`Fully human IgG1
`
`CD20
`
`Humanised IgG1
`
`Veltuzumab
`(IMMUNO-106, hA20)
`
`CD20
`
`Humanised and
`enhanced IgG2a
`
`Epratuzumab (hLL2)
`
`CD22
`
`Humanised IgG1
`
`FDA approved;
`follicular and diffuse
`large B cell NHL
`
`Phase I–II; follicular
`B cell NHL
`
`Phase II; follicular B
`cell NHL
`
`Phase I; follicular B
`cell NHL and CLL
`
`Phase I–II; follicular
`B cell NHL
`
`Antibody-basedtherapyofleukaemia
`
`Refs
`
`92
`
`3, 63
`
`79, 80
`
`83, 84
`
`85, 86
`
`99, 103
`
`107
`
`CD22
`
`CD22
`
`CD23
`
`Inotuzumab ozogamicin
`(CMC-544, G5/44)
`
`BL22, HA22
`
`Lumiliximab
`
`Alemtuzumab
`(CampathTM,
`MabCampathTM,
`Campath-1H)
`
`Humanised IgG4–N-
`acetyl-g1-calicheamicin
`
`Preclinical
`development
`
`Murine IgG1 Fv(RFB4)-
`Pseudomonas exotoxin
`A immunotoxin
`
`Cynomolgus macaque–
`human IgG1
`
`Phase I–II; HCL and
`B cell CLL
`
`104, 106
`
`Phase I–II–III; CLL
`
`111, 113
`
`CD52
`
`Humanised rat IgG2b
`
`FDA approved; B cell
`CLL
`
`115, 119
`
`Abbreviations: CLL, chronic lymphocytic leukaemia; FDA, Food and Drug Administration; HCL, hairy cell
`leukaemia; NHL, non-Hodgkin’s lymphoma.
`
`NHL (Ref. 59). Mechanisms of resistance to
`rituximab are unclear, but might
`involve
`alterations
`in CD20
`expression,
`reduced
`antibody
`penetration
`of
`tumour masses,
`increased expression of complement inhibitors,
`enhanced prosurvival pathways and inhibition
`of ADCC.
`Phase I studies failed to identify a maximum
`tolerated dose
`and established rituximab
`375 mg/m2/week for 4 weeks as standard (Refs
`60, 61). Pharmacokinetic studies showed a
`plasma half-life of 76.3 hours achieved with the
`first infusion that increased to 205.8 hours after
`the fourth infusion (Ref. 62). The efficacy of
`rituximab was established in a pivotal Phase II
`trial
`in 166 patients with relapsed NHL
`
`In low-grade and follicular B cell
`(Ref. 63).
`NHL patients who relapsed or failed primary
`therapy, extending treatment to eight weekly
`doses appeared to increase the number of
`responses,
`improve complete response rate,
`time
`to progression and the duration of
`response (Ref. 64). The 8 week course is
`often used for
`the treatment of bulky or
`resistant disease, or for patients undergoing
`retreatment.
`Rituximab is not approved for the treatment of
`CLL or other B cell
`leukaemias; however, a
`substantial number of studies demonstrated its
`activity in previously treated and untreated
`CLL (Refs 3, 65, 66, 67). One early trial treated a
`variety of malignant B cell disorders including
`
`Accession information: doi:10.1017/S1462399409001215; Vol. 11; e29; September 2009
`& Cambridge University Press 2009
`
`6
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`

`Antibody-basedtherapyofleukaemia
`
`expert reviews
`
`in molecular medicine
`
`74). Rituximab has also demonstrated activity in
`a number of other B cell leukaemias including
`hairy cell leukaemia (HCL), where response rates
`of 25–80% have been reported (Refs 75, 76).
`Rituximab toxicities include acute infusional
`reactions,
`fever,
`chills,
`nausea,
`vomiting,
`bronchospasm and hypotension, most often
`with the initial infusion. Other serious adverse
`events include the potentially fatal cytokine
`release syndrome (Ref. 77). B cell
`counts
`nadir 24 –72 hours after the initial rituximab
`infusion and begin to return to normal values
`at an average of 9 months after
`therapy.
`The risk of serious infection is marginally
`increased in the months following rituximab
`treatment.
`
`Ofatumumab
`(ArzzeraTM, GlaxoSmithKline,
`Ofatumumab
`Philadelphia, PA; HuMax-CD20TM, Genmab,
`Copenhagen, Denmark) is a second-generation
`anti-CD20 monoclonal antibody (Ref. 78). The
`lower levels of CD20 expression in CLL and
`other B cell malignancies
`suggest
`that an
`antibody designed with enhanced Fc effector
`function may be required. Based on this, a
`number of CD20-targeted monoclonal antibodies
`have been generated with enhanced effector
`IgG1k immunoglobulin
`function using the
`framework. These enhanced antibodies strongly
`bind to CD20-positive cells, efficiently recruit
`mononuclear
`cells
`(ADCC) and lyse
`even
`rituximab-resistant targets (Ref. 79). Ofatumumab
`exhibits
`a higher
`affinity for CD20
`than
`rituximab; it attaches to a different epitope closer
`to the cell surface, which makes it easier for
`effector cells to kill the target cell and activate
`complement.
`Ofatumumab has shown activity in low-grade
`follicular B cell NHL and is currently in clinical
`trials for CLL (Refs 80, 81). One hundred and
`thirty-eight patients with fludarabine
`and
`alemtuzumab refractory (double refractory, DR)
`or bulky (.5 cm lymph nodes) fludarabine-
`refractory (BFR) CLL received eight weekly
`infusions of ofatumumab followed by four
`monthly infusions (Ref. 82). The overall response
`rate was 51% for the DR group and 44% for the
`BFR group, with one patient achieving a
`complete response. Serious toxicities included
`infections,
`granulocytopaenia
`and anaemia.
`An FDA Oncologic Drugs Advisory Committee
`has
`recommended accelerated approval of
`
`http://www.expertreviews.org/
`
`15 patients with small lymphocytic lymphoma or
`chronic lymphocytic leukaemia (SLL/CLL) and
`mantle cell
`lymphoma (MCL)
`in leukaemic
`phase with rituximab 375 mg/m2/week for 4
`weeks, and concluded that
`the efficacy of
`rituximab against SLL/CLL and MCL was
`limited (Ref.
`68). O’Brien and colleagues
`examined the efficacy of higher doses rituximab
`in CLL (Ref. 69). Forty patients with CLL and
`ten with other mature B cell leukaemias were
`treated with four weekly infusions of rituximab.
`The initial dose was 375 mg/m2 in all patients,
`with the subsequent doses escalated in groups
`of patients from 500 to 2250 mg/m2. Toxicity
`with the first dose was significantly more
`common in patients with non-CLL B cell
`leukaemias, occurring in 5 out of 10 patients,
`versus 1 out of 40 patients with CLL. The
`overall response rate was 36% in CLL and 60%
`in the other B cell
`leukaemias. The lower
`responsiveness
`of CLL to
`rituximab was
`attributed to the lower density of CD20 targets on
`CLL cells
`compared with
`other B cell
`malignancies (Ref. 70). Similarly to follicular
`and diffuse large B cell NHL, combinations
`of rituximab and chemotherapy demonstrated
`improved
`responses
`and
`progression-free
`survival compared with treatment with either
`chemotherapy or rituximab alone in CLL. The
`CALGB 9712 clinical trial randomised concurrent
`treatment with fludarabine and rituximab versus
`sequential
`treatment
`in 104 symptomatic CLL
`patients (Ref. 71). Patients receiving concurrent
`treatment experienced greater haematological
`toxicity and infusional reactions compared with
`the sequential
`treatment group; however,
`the
`response rate of the concurrent group was 90%
`compared with 77% in the sequential treatment
`group. In a retrospective analysis, these data were
`combined with that of a second multicenter
`clinical trial of fludarabine in CLL (CALGB 9011)
`(Ref. 72). In multivariate analyses controlling for
`pretreatment characteristics, patients receiving
`fludarabine and rituximab had a significantly
`better progression-free survival (P , 0.0001) and
`(P ¼ 0.0006)
`overall
`survival
`than patients
`receiving fludarabine alone. The number of
`infectious events was similar between the two
`treatments. A number of clinical trials in CLL of
`rituximab in combination with fludarabine and
`cyclophosphamide at varying drug doses, or
`sequential or concurrent treatment, demonstrated
`molecular responses in excess of 85% (Refs 73,
`
`Accession information: doi:10.1017/S1462399409001215; Vol. 11; e29; September 2009
`& Cambridge University Press 2009
`
`7
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`

`Antibody-basedtherapyofleukaemia
`
`expert reviews
`
`in molecular medicine
`
`XmAb 5574
`is a
`XmAb 5574 (Xencor, Monrovia, CA)
`humanised anti-CD19 monoclonal antibody that
`has an engineered Fc domain to increase
`binding to Fcg receptors and enhance Fc-
`mediated effector function. In vitro, XmAb 5574
`enhanced ADCC 1000-fold relative to an anti-
`CD19 IgG1 analogue against a broad range of
`B cell
`lymphoma and leukaemia cell
`lines
`including primary ALL and mantle
`cell
`lymphoma (Ref. 92). XmAb 5574 increased
`effector
`cell phagocytosis
`and target
`cell
`apoptosis.
`In vivo, XmAb 5574
`inhibited
`tumour growth in established lymphoma
`mouse xenograft models, and demonstrated
`more potent antitumour activity than its IgG1
`analogue. Comparison with a variant antibody
`incapable of Fcg-receptor binding showed that
`engagement of these receptors was critical for
`efficacy. In a nonhuman primate model, XmAb
`5574 depleted B cells from the peripheral blood,
`lymph nodes and spleen (Ref. 93). XmAb 5574
`has not yet entered clinical trials.
`Anti-CD19 antibodies and immunomagnetic
`separation have been used to deplete B cells
`from the bone marrow in CLL patients
`undergoing autologous transplants (Refs 94, 95,
`96). In one study, 20 patients with poor-risk
`CLL underwent stem-cell mobilisation with
`chemotherapy
`and
`granulocyte-colony
`stimulating factor (Ref. 96). B cell depletion was
`þ
`cells and
`performed using selection for CD34
`selection against B cells with anti-CD19, -CD20,
`-CD23 and -CD37 immuno- magnetic beads.
`With a median follow-up of 20 months, 17
`patients were in complete remission.
`
`Anti-CD19 immunotoxins
`The internalisation of CD19 after antibody
`binding suggests that an immunotoxin might be
`an effective strategy for treatment of CD19-
`expressing leukaemias. One study examined the
`use of an anti-CD19-based immunotoxin in
`acute
`lymphocytic
`leukaemia
`(ALL)
`for
`eradication of residual disease after treatment
`(Ref. 97). After initial chemotherapy, 46 adults
`with previously untreated CD19-positive ALL
`received an immunotoxin composed of
`the
`murine B4
`anti-CD19
`antibody linked to
`modified ricin. The most
`frequent
`toxicities
`were transient elevation of liver transaminases
`and lymphopaenia. Molecular studies, however,
`failed to show a consistent decrease in the
`
`http://www.expertreviews.org/
`
`ofatumumab for the treatment of fludarabine and
`alemtuzumab-refractory CLL.
`
`Ocrelizumab
`Ocrelizumab (rhumAb 2H7v.16, Biogen-IDEC,
`Cambridge, MA) is a recombinant humanised
`anti-human CD20 antibody (Ref. 83)