I
`
`Seminar
`
`Lancet 2009; 373: 1550–61
`Published Online
`March 12, 2009
`DOI:10.1016/S0140-
`6736(09)60237-3
`University of Michigan,
`Pediatrics and Internal
`Medicine, Blood and Marrow
`Transplantation Program,
`Ann Arbor, MI, USA
`(Prof J L M Ferrara MD,
`Prof J E Levine MD, P Reddy MD);
`and Internal Medicine and
`Department of Haematology/
`Oncology, University Hospital,
`Regensburg, Germany
`(Prof E Holler MD)
`Correspondence to:
`Prof James L M Ferrara,
`University of Michigan,
`1500 East Medical Center Drive,
`6303 CCC, Ann Arbor,
`MI 48109-5942, USA
`ferrara@umich.edu
`
`Graft-versus-host disease
`
`James L M Ferrara, John E Levine, Pavan Reddy, Ernst Holler
`
`Haemopoietic-cell transplantation (HCT) is an intensive therapy used to treat high-risk haematological malignant
`disorders and other life-threatening haematological and genetic diseases. The main complication of HCT is graft-
`versus-host disease (GVHD), an immunological disorder that aff ects many organ systems, including the
`gastrointestinal tract, liver, skin, and lungs. The number of patients with this complication continues to grow, and
`many return home from transplant centres after HCT requiring continued treatment with immunosuppressive drugs
`that increases their risks for serious infections and other complications. In this Seminar, we review our understanding
`of the risk factors and causes of GHVD, the cellular and cytokine networks implicated in its pathophysiology, and
`current strategies to prevent and treat the disease. We also summarise supportive-care measures that are essential for
`management of this medically fragile population.
`
`Introduction
`The number of allogeneic haemopoietic-cell trans-
`plantations (HCTs) continues to rise, with more than
`25 000 procedures undertaken annually. The graft-versus-
`leukaemia or graft-versus-tumour eff ect during this
`procedure eff ectively eradicates many haema tological
`malignant diseases.1 Development of novel strategies
`that use donor leucocyte infusions, non-myeloablative
`conditioning, and umbilical-cord blood transplantation
`has helped expand the indications for allogeneic HCT
`over the past few years, especially for older patients.2
`Improvements
`in
`infectious prophylaxis,
`immuno-
`suppressive treatments, suppor tive care, and DNA-based
`tissue typing have also contributed to enhanced outcomes
`after the technique.1 Yet, the major complication of
`allogeneic HCT—graft-versus-host disease (GVHD)—
`remains lethal and limits use of this important procedure.2
`In view of current trends, the number of transplants
`from unrelated donors is expected to double within the
`next 5 years, substantially increasing the population of
`patients with GVHD. In this Seminar, we review advances
`made in identifi cation of genetic risk factors and
`pathophysiology of this major HCT complication and its
`prevention, diagnosis, and treatment.
`
`Cause and clinical features
`50 years ago, Billingham formulated three requirements
`for development of GVHD: (1) the graft must contain
`immunologically competent cells; (2) the recipient must
`express tissue antigens that are not present in the
`transplant donor; and (3) the patient must be incapable
`
`Search strategy and selection criteria
`
`We searched PubMed and Medline with the term ‘‘GVHD’’
`and cross-referenced it with the following words: ‘‘clinical’’,
`‘‘cytokines’’, ‘‘MHC’’, ‘‘HLA antigens’’, ‘‘biology’’, and
`‘‘immunology’’. We included mostly peer-reviewed original
`and review journal articles published within the past
`decade, except for seminal articles that initially described
`the clinical features. All non-peer-reviewed manuscripts,
`supplements, and textbooks were excluded.
`
`of mounting an eff ective response to eliminate the
`transplanted cells.3 We know now that the immuno-
`logically competent cells are T cells and that GVHD can
`develop
`in various clinical settings when tissues
`containing T cells (blood products, bone marrow, and
`solid organs) are transferred from one person to another
`who is not able to eliminate those cells.4,5 Patients whose
`immune systems are suppressed and who receive white
`blood cells from another individual are at especially high
`risk for the disease.
`GVHD arises when donor T cells respond to
`genetically defi ned proteins on host cells. The most
`important proteins are human leucocyte antigens
`(HLAs),2,6,7 which are highly polymorphic and are
`encoded by the major histocompatibility complex
`(MHC). Class I HLA (A, B, and C) proteins are expressed
`on almost all nucleated cells of the body at various
`densities. Class II proteins (DR, DQ, and DP) are mainly
`expressed on haemopoietic cells (B cells, dendritic cells,
`and monocytes), but their expression can be induced on
`many other cell types after infl ammation or injury.
`High-resolution DNA typing of HLA genes with
`PCR-based techniques has now largely replaced earlier
`methods. The frequency of acute GVHD is directly
`related to the degree of mismatch between HLA
`proteins,8,9 and thus ideally, donors and recipients are
`matched at HLA A, B, C, and DRB1 (referred to as
`8/8 matches), but mismatches can be tolerated for
`umbilical-cord blood grafts (see Clinical features of
`acute GVHD).10–12
`Despite HLA identity between a patient and donor,
`about 40% of recipients of HLA-identical grafts develop
`systemic acute GVHD that needs treatment with
`high-dose steroids. This disorder is due to genetic
`diff erences that lie outside the HLA loci and that encode
`proteins referred to as minor histocompatibility antigens.
`Some minor histocompatibility antigens, such as HY
`and HA-3, are expressed on all tissues and are targets for
`both GVHD and graft-versus-leukaemia.13 Others, such
`as HA-1 and HA-2, are expressed most abundantly on
`haemopoietic cells (including leukaemic cells) and could,
`therefore, induce an enhanced graft-versus-leukaemia
`eff ect with diminished GVHD.13,14
`
`1550
`
`www.thelancet.com Vol 373 May 2, 2009
`
`

`

`I
`
`Seminar
`
`Panel 1: Acute GVHD symptoms
`
`Skin
`• Maculopapular skin rash
`
`Upper gastrointestinal tract
`• Nausea, anorexia, or both, and positive histological fi ndings
`
`Lower gastrointestinal tract
`• Watery diarrhoea (≥500 mL)
`• Severe abdominal pain
`• Bloody diarrhoea or ileus (after exclusion of infectious
`causes)
`
`Liver
`• Cholestatic hyperbilirubinaemia
`
`Polymorphisms in both donors and recipients of
`cytokines that have a role in the classic cytokine storm of
`GVHD (see Pathophysiology of acute GVHD) have been
`implicated as risk factors for the disorder.15 Tumour
`necrosis factor (TNF) α, interleukin 10, and interferon γ
`variants have correlated with GVHD in some, but not all,
`studies.16–18 Genetic polymorphisms of proteins connected
`with innate immunity, such as nucleotide oligomerisation
`domain 2 and keratin 18 receptors, have also been
`associated with the disorder.19–22 Future strategies to
`identify the best possible transplant donor will probably
`incorporate both HLA and non-HLA genetic factors.
`
`Clinical features of acute GVHD
`On the basis of early work, acute GVHD was defi ned as
`arising before day 100 post-transplant, whereas chronic
`disease happened after that time.23–25 This defi nition is
`far from satisfactory, and a National Institutes of Health
`classifi cation includes late-onset acute GVHD (after
`day 100) and an overlap syndrome with features of both
`acute and chronic disorder.26,27 Late-onset acute GVHD
`and the overlap syndrome arise with greater frequency
`after reduced-intensity conditioning, an increasingly
`widespread technique (see Prevention of GVHD). Panel 1
`shows the clinical manifestations of acute GVHD. In a
`comprehensive review, Martin and colleagues noted that
`at onset of acute GVHD, aff ected regions included skin
`(81% of patients), gastrointestinal tract (54%), and
`liver (50%).23
`Skin is most frequently aff ected and is usually the fi rst
`organ involved, generally coinciding with engraftment of
`donor cells. The characteristic maculopapular rash is
`pruritic and can spread throughout the body, sparing the
`scalp (fi gure 1). In severe cases the skin can blister and
`ulcerate.28 Apoptosis at the base of epidermal rete pegs is
`a characteristic pathological fi nding. Other features
`include dyskeratosis, exocytosis of lymphocytes, satellite
`lymphocytes
`adjacent
`to dyskeratotic
`epidermal
`keratinocytes, and perivascular lymphocytic infi ltration
`in the dermis.29,30
`
`Figure 1: Acute GVHD of the skin (grade I)
`Photograph courtesy of J Levine.
`Gastrointestinal-tract involvement of acute GVHD
`usually presents as diarrhoea but can also include
`vomiting, anorexia, abdominal pain, or a combination
`when severe.29 Diarrhoea in GVHD is secretory and
`usually voluminous (>2 L per day). Bleeding, which has
`poor prognosis, happens as a result of mucosal
`ulceration,31 but patchy involvement of mucosa generally
`leads to a normal appearance on endoscopy.32 Radiological
`fi ndings of the gastrointestinal tract include luminal
`dilatation with thickening of the wall of the small bowel
`(ribbon sign on CT) and air or fl uid levels suggestive of
`an ileus.28 Histological features include patchy ulcerations,
`apoptotic bodies in the base of crypts, crypt abscesses,
`and loss and fl attening of surface epithelium.33
`Liver disease caused by GVHD can be diffi cult to
`distinguish from other causes of liver dysfunction after
`bone-marrow transplantation, such as veno-occlusive
`disease, toxic drug eff ects, viral infection, sepsis, or iron
`overload. The histological features of hepatic GVHD are
`endothelialitis, lymphocytic infi ltration of the portal
`areas, pericholangitis, and bile-duct destruction.34,35
`However, biopsy specimens of liver are taken rarely
`because thrombocytopenia early after transplantation
`greatly increases the risks of the biopsy procedure,
`making the diagnosis of GVHD one of exclusion.
`Severity of acute GVHD is ascertained by the extent of
`involvement of the three main target organs. Overall
`grades are I (mild), II (moderate), III (severe), and
`IV (very severe). Severe GVHD has poor prognosis, with
`25% long-term survival (5 years) for grade III disease and
`5% for grade IV.36
`
`www.thelancet.com Vol 373 May 2, 2009
`
`1551
`
`

`

`I
`
`Seminar
`
`Panel 2: Chronic GVHD symptoms
`
`Skin
`Dyspigmentation, new-onset alopecia, poikiloderma, lichen
`planus-like eruptions, or sclerotic features
`
`Nails
`Nail dystrophy or loss
`
`Mouth
`Xerostomia, ulcers, lichen-type features, restrictions of
`mouth opening from sclerosis
`
`Eyes
`Dry eyes, sicca syndrome, cicatricial conjunctivitis
`
`Muscles, fascia, joints
`Fasciitis, myositis, or joint stiff ness from contractures
`
`Female genitalia
`Vaginal sclerosis, ulcerations
`
`Gastrointestinal tract
`Anorexia, weight loss, oesophageal web or strictures
`
`Liver
`Jaundice, transaminitis
`
`Lungs
`Restrictive or obstructive defects on pulmonary function
`tests, bronchiolitis obliterans, pleural eff usions
`
`Kidneys
`Nephrotic syndrome (rare)
`
`Heart
`Pericarditis
`
`Marrow
`Thrombocytopenia, anaemia, neutropenia
`
`Prevalence of acute GVHD is directly related to the
`degree of mismatch between HLA proteins. It ranges
`from 35–45% in recipients of full-matched sibling donor
`grafts8,9 to 60–80% in people receiving one-antigen
`HLA-mismatched unrelated-donor grafts.6,37–39 The same
`amount of mismatch causes diminished GVHD with
`umbilical-cord blood grafts, and frequency of acute
`GVHD is low after transplantation of partly matched
`umbilical-cord blood units (35–65%).12
`
`Clinical features of chronic GVHD
`Chronic GVHD is the major cause of late non-relapse
`death after HCT.40 Its presentation can be progressive
`(active or acute GVHD merging into chronic), quiescent
`(acute disease that resolves completely but is followed
`later by chronic), or de novo. Older recipient age and a
`history of acute GVHD are the greatest risk factors for
`chronic disease.41 Therefore, strategies for acute GVHD
`prevention could help to prevent chronic disease. Panel 2
`shows that manifestations of chronic GVHD are
`
`somewhat protean and typically of an autoimmune
`nature. Clinical signs are generally seen fi rst in the buccal
`mucosa (fi gure 2). New consensus criteria for diagnosis
`and staging of chronic GVHD have been developed.26
`
`Pathophysiology of acute GVHD
`Two important principles should be considered with
`respect to the pathophysiology of acute GVHD. First,
`the disease is indicative of exaggerated but typical
`infl ammatory mechanisms mediated by donor
`lymphocytes infused into the recipient, in whom they
`function appropriately
`in view of
`the
`foreign
`environment they encounter. Second, the recipient’s
`tissues that stimulate donor lymphocytes have usually
`been damaged by underlying disease, previous
`infections, and the transplant conditioning regimen.29
`As a result, these tissues produce molecules such as
`proinfl ammatory cytokines and chemokines, which
`increase
`expression
`of
`key
`receptors
`on
`antigen-presenting cells (APCs), thereby enhancing
`cross-presentation of polypeptide proteins (eg, minor
`histocompatibility antigens) to the donor immune cells
`that mediate GVHD.42–45
`Mouse models have been central to identifi cation and
`understanding of pathophysiological mechanisms of
`GVHD, and work undertaken in dogs has been vital for
`development of clinically useful strategies for GVHD
`prophylaxis and treatment advances in donor leucocyte
`infusions.36,46,47 Largely on the basis of these experimental
`data, progression of acute GVHD can be summarised in
`three sequential steps or phases: (1) activation of APCs;
`(2) donor T-cell activation, proliferation, diff erentiation,
`and migration; and
`(3)
`target
`tissue destruction
`(fi gure 3).
`The fi rst step entails activation of APCs by the
`underlying disease and the HCT conditioning regimen.
`Damaged host tissues respond by producing so-called
`danger signals, including proinfl ammatory cytokines (eg,
`TNFα and interleukins 1 and 6), chemokines, and
`amplifi ed expression of adhesion molecules, MHC
`antigens, and costimulatory molecules on host APCs.42,48–50
`Findings of a report showed that 1 week after HCT,
`increased amounts of TNFα receptor 1—a surrogate
`marker
`for TNFα—correlated strongly with
`later
`development of GVHD.51 Injury to the gastrointestinal
`tract from conditioning is especially important because it
`allows
`for
`systemic
`translocation of
`additional
`infl ammatory stimuli, such as microbial products
`including lipopolysaccharide or other pathogen-associated
`molecular patterns, that further enhance activation of
`host APCs.49
`The secondary lymphoid tissue in the gastrointestinal
`tract is probably the initial site of interaction between
`activated APCs and donor T cells.52 These observations
`have led to an important clinical strategy to diminish
`acute GVHD by reducing the intensity of the conditioning
`regimen.53,54 Experimental GVHD can also be decreased
`
`1552
`
`www.thelancet.com Vol 373 May 2, 2009
`
`

`

`I
`
`Seminar
`
`by manipulation of distinct subsets of APCs.55,56
`Furthermore, non-haemopoietic stem cells, such as
`mesenchymal stromal cells, can reduce allogeneic T-cell
`responses and ameliorate GVHD, although
`the
`mechanism for such inhibition remains unclear.57
`The idea that amplifi ed activation of host APCs
`increases the risk for acute GVHD unifi es several
`seemingly disparate clinical associations with that risk,
`such as advanced stages of malignant disease, more
`intense transplant conditioning regimens, and history of
`viral infection. APCs detect infections with receptors on
`their cell surfaces, such as Toll-like receptors, which
`recognise conserved molecular patterns of microbes.27,58
`Toll-like receptors specifi c for viral DNA or RNA activate
`APCs and could boost GVHD, providing a potential
`mechanistic basis for enhanced disease associated with
`viral infections such as cytomegalovirus.59
`The core of the graft-versus-host reaction is the second
`step, in which donor T cells proliferate and diff erentiate
`in response to host APCs (fi gure 3). The danger signals
`generated in the fi rst phase augment this activation, at
`least in part, by increasing expression of costimulatory
`molecules.60 Blockade of costimulatory pathways to
`prevent GVHD is successful in animal models, but this
`approach has not yet been tested in large clinical trials.2
`In mouse models, in which genetic diff erences between
`donor and recipient strains can be tightly controlled,
`CD4+ cells induce acute GVHD to MHC class II
`diff erences and CD8+ cells induce acute disease to class I
`diff erences.61,62 In most HLA-identical HCTs, both CD4+
`and CD8+ subsets respond to minor histocompatibility
`antigens and can cause GVHD
`in HLA-identical
`procedures.
`Regulatory T cells can suppress proliferation of
`conventional T cells and prevent GVHD in animal
`models when added to donor grafts containing con-
`ventional T cells,63 but use of regulatory T cells in clinical
`acute GVHD will need enhanced techniques to identify
`and expand them. Natural killer T-cell 1.1+ subsets from
`the host and donors have also been shown to modulate
`acute GVHD.64 In a clinical trial of total lymphoid
`irradiation (as conditioning), GVHD was reduced
`signifi cantly and host natural killer T-cell function was
`amplifi ed.65
`Activation of immune cells results in rapid intracellular
`biochemical cascades that induce transcription of genes
`for many proteins,
`including cytokines and their
`receptors. T-helper 1 cytokines (interferon γ, interleukin 2,
`and TNFα) are released in large amounts during acute
`GVHD. Production of interleukin 2 by donor T cells
`remains the main target of many current clinical
`therapeutic and prophylactic approaches to GVHD, such
`as cyclosporine, tacrolimus, and monoclonal antibodies
`directed against this cytokine and its receptor.9 However,
`emerging data indicate an important role for interleukin 2
`in the generation and maintenance of CD4+CD25+
`regulatory T cells, suggesting that prolonged interference
`
`Figure 2: Lichenoid changes of buccal mucosa in chronic GVHD
`Photograph courtesy of J Ferrara and J Levine.
`
`with this cytokine could unintentionally stop development
`of long-term tolerance after allogeneic HCT.66
`Interferon γ has many functions and can either amplify
`or reduce GVHD.67,68 It could boost disease by increasing
`expression of molecules such as chemokine receptors,
`MHC proteins, and adhesion molecules; it also raises
`the sensitivity of monocytes and macrophages to stimuli
`such as lipopolysaccharide and accelerates intracellular
`cascades in response to these stimuli.69 Early polarisation
`of donor T cells so that they secrete less interferon γ and
`more interleukin 4 can also attenuate experimental acute
`GVHD.70 Interferon γ might amplify GVHD by direct
`damage to epithelium in the gastrointestinal tract and
`skin and by induction of immunosuppression by
`generation of nitric oxide.71 By contrast, this cytokine
`could suppress GVHD by hastening apoptosis of
`activated donor T cells.68,72 This complexity means
`manipulation of interferon γ could have diverse eff ects
`in vivo, making the cytokine a challenging target with
`respect to therapeutic intervention.
`Interleukin 10 has a key role in suppression of immune
`responses, and clinical data suggest it might regulate
`acute GVHD.17 Transforming growth factor β, another
`suppressive cytokine, can subdue acute GVHD but
`exacerbate chronic disease.73 Thus, timing and duration
`of secretion of any given cytokine could establish the
`specifi c eff ects of that molecule on GVHD severity.
`
`www.thelancet.com Vol 373 May 2, 2009
`
`1553
`
`

`

`I
`
`Seminar
`
`Conditioning: tissue damage
`
`(1) Host APC
`(1) HostAPC
`activation
`activation
`
`Host
`tissues
`
`TNFα
`IL1
`LPS
`
`Small
`intestine
`
`LPS
`
`--- --►
`.. .... -..
`..
`..
`..
`..
`
`IFNγ
`
`;
`
`;
`
`;
`
`;
`
`;
`
`;
`I
`
`Mφ
`
`TNFα
`IL1
`
`CD4
`CTL
`
`TNFα
`IL1
`
`CD8
`CTL
`
`Target cell
`apoptosis
`
`CD8
`CTL
`
`(3) Cellular and
`inflammatory
`effectors
`
`Treg
`
`T cell
`
`Treg
`
`(2) Donor T-cell
`activation
`
`Th1
`
`Figure 3: Pathophysiology of acute GVHD
`IL 1=interleukin 1. IFN γ=interferon γ. LPS=lipopolysaccharide. Treg=regulatory T cell. Th1=T-helper 1 cell. CTL=cytotoxic T lymphocyte.
`
`The third eff ector phase of the graft-versus-host process
`(fi gure 3) is a complex cascade of cellular mediators (such
`as cytotoxic T lymphocytes and natural killer cells) and
`soluble infl ammatory agents (eg, TNFα, interferon γ,
`interleukin 1, and nitric oxide).2,29 These molecules work
`synergetically to amplify local tissue injury and further
`promote infl ammation and target tissue destruction.
`The cellular eff ectors of acute GVHD are mainly
`cytotoxic T lymphocytes and natural killer cells.49 Cytotoxic
`T lymphocytes that prefer to use the Fas and FasL pathway
`of target lysis seem to predominate in GVHD liver
`damage (hepatocytes express large amounts of Fas)
`whereas cells that use the perforin and granzyme
`pathways are more important in the gastrointestinal tract
`and skin.2,74 Chemokines direct migration of donor T cells
`from lymphoid tissues to the target organs in which they
`cause damage. Macrophage infl ammatory protein 1α and
`other chemokines (such as CCL2–CCL5, CXCL2, CXCL9,
`CXCL10, CXCL11, CCL17, and CCL27) are overexpressed
`and enhance homing of cellular eff ectors to target organs
`during experimental GVHD.75 Expression of integrins,
`such as α4β7 and its ligand MADCAM1, is also important
`
`for homing of donor T cells to Peyer’s patches during
`intestinal GVHD.52,76,77
`Microbial products such as lipopolysaccharide, which
`leak through damaged intestinal mucosa or skin, can
`stimulate secretion of infl ammatory cytokines through
`Toll-like receptors.49,78 The gastrointestinal
`tract
`is
`especially susceptible to damage from TNFα, and the
`gastrointestinal tract has a major role in amplifi cation
`and propagation of the cytokine storm characteristic of
`acute GVHD.49 TNFα can be produced by both donor and
`host cells and it acts in three diff erent ways: (1) it activates
`APCs and enhances alloantigen presentation; (2) it
`recruits eff ector cells to target organs via induction of
`infl ammatory chemokines; and (3) it directly causes
`tissue necrosis (as its name suggests).79–81
`
`Prevention of GVHD
`On the basis of evidence from animal models for the
`central role of T cells in initiation of GVHD, many clinical
`studies of T-cell depletion as prophylaxis for the disease
`were undertaken in the 1980s and 1990s. Three main
`depletion strategies were studied: (1) negative selection
`
`1554
`
`www.thelancet.com Vol 373 May 2, 2009
`
`

`

`I
`
`Seminar
`
`of T cells ex vivo; (2) positive selection of CD34+ stem
`cells ex vivo; and (3) antibodies against T cells in vivo.82
`Most approaches showed substantial limitation of both
`acute and chronic GVHD.83–85 Unfortunately, the lowest
`frequency of severe GVHD was off set by high rates of
`graft failure, relapse of malignant disease, infections,
`and Epstein-Barr virus-associated lymphoproliferative
`disorders. Negative-selection purging strategies with
`various antibodies against T cells achieved similar
`long-term results irrespective of the breadth of antibody
`specifi city.86–88 Findings of one large registry study showed
`that purging techniques that used antibodies with broad
`specifi cities produced inferior leukaemia-free survival
`than standard immunosuppression in patients receiving
`unrelated donor transplants.89
`Several research groups have investigated partial T-cell
`depletion, either by elimination of specifi c T-cell subsets
`(eg, CD8+) or by titration of the dose of T cells present in
`the inoculum.90–92 None of these approaches, however,
`has been shown convincingly to be the best strategy that
`enhances long-term survival.
`Alemtuzumab is a monoclonal antibody that binds
`CD52, a protein expressed on a broad range of leukocytes
`including lymphocytes, monocytes, and dendritic cells.
`Its use in a phase II trial of GVHD prophylaxis lowered
`incidence of
`acute
`and
`chronic GVHD
`after
`reduced-intensity transplant.93 In two prospective studies,
`patients who received alemtuzumab rather
`than
`methotrexate showed signifi cantly lower rates of acute
`and chronic GVHD,94 but they had more infectious
`complications and higher rates of relapse, so no overall
`survival benefi t was recorded. Alemtuzumab might also
`contribute to graft failure when used with minimum-
`intensity conditioning regimens.95
`An alternative strategy to T-cell depletion attempted to
`induce anergy in donor T cells by ex-vivo antibody
`blockade of costimulatory pathways before transplantation.
`Findings of a small study of this approach in patients
`undergoing haploidentical HCT was quite encouraging,
`but they have not yet been replicated.96 Thus, the focus of
`most preventive strategies remains pharmacological
`manipulation of T cells after transplant.
`Administration of antibodies against T cells in vivo as
`GVHD prophylaxis has also been tested extensively. The
`best studied drugs are anti-thymocyte globulin or
`anti-lymphocyte globulin preparations. These serum
`samples, which have high titres of polyclonal antibodies,
`are made by immunisation of horses or rabbits to
`thymocytes or lymphocytes, respectively. A complicating
`factor in establishing the role of these polyclonal serum
`samples in transplantation is the observation that even
`diff erent brands of the same class exert diverse biological
`eff ects.97 However, the side-eff ects of anti-thymocyte
`globulin and anti-lymphocyte globulin infusions are
`similar across diff erent preparations and include fever,
`chills, headache, thrombocytopenia (from cross-reactivity
`to platelets), and, infrequently, anaphylaxis.
`
`In retrospective studies, rabbit anti-thymocyte globulin
`reduced the frequency of GVHD in related-donor
`haemopoietic stem-cell transplant recipients without
`seeming to enhance survival.98,99 In patients receiving
`unrelated-donor haemopoietic stem cells, addition of
`anti-lymphocyte globulin to standard GVHD prophylaxis
`prevented severe GVHD eff ectively but did not result in
`better survival because of increased infections.86 In a
`long-term
`follow-up study, however, pretransplant
`anti-thymocyte globulin provided signifi cant protection
`against extensive chronic GVHD and chronic lung
`dysfunction.100
`The primary pharmacological strategy to prevent GVHD
`is inhibition of the cytoplasmic enzyme calcineurin,
`which is important for activation of T cells. The calcineurin
`inhibitors cyclosporine and tacrolimus have similar
`mechanisms of action, clinical eff ectiveness, and toxic
`eff ects, including hypomagnesaemia, hyperkalaemia,
`hypertension, and nephrotoxicity.9,101 Serious side-eff ects
`include transplant-associated thrombotic microangio-
`pathy and neurotoxic eff ects that can lead to premature
`discontinuation. Although clinically similar to thrombotic
`thrombocytopenic
`purpura,
`transplant-associated
`thrombotic micro angio pathy does not respond reliably to
`therapeutic plasmapheresis, carries a high mortality rate,
`and removal of the off ending agent does not always result
`in improvement.102 Posterior reversible encephalopathy
`syndrome includes mental status changes, seizures,
`neurological defi cits, and characteristic fi ndings on MRI;
`this syndrome has been seen in 1–2% of patients
`undergoing HCT and taking calcineurin inhibitors.103
`Side-eff ects of these drugs fall as the dose is tapered,
`usually 2–4 months after transplantation.
`Calcineurin inhibitors are usually administered in
`combination with other immunosuppressants, such as
`methotrexate, which is given at low doses in the early
`post-transplant period.9,101 The toxic eff ects of methotrexate
`(neutropenia and mucositis) have led some investigators
`to replace it with mycophenolate mofetil. In a prospective
`randomised trial, patients who received mycophenolate
`mofetil as part of GVHD prophylaxis had signifi cantly less
`severe mucositis and more rapid neutrophil engraftment
`than did those who received methotrexate.104 Frequency
`and severity of acute GVHD was similar between the two
`groups, but the study closed early because of superiority of
`the mycophenolate mofetil arm with respect to reduced
`mucositis and speed of haemopoietic engraftment. A
`desire for faster neutrophil engraftment has led to use of
`mycophenolate mofetil in umbilical-cord blood transplants
`for which graft failure is a major concern.105 This drug is
`also sometimes used after reduced-intensity conditioning
`regimens for similar reasons.106,107
`Sirolimus is an immunosuppressant that is structurally
`similar to tacrolimus but does not inhibit calcineurin. In
`phase II trials, sirolimus was very eff ective in combination
`with tacrolimus;108,109 the drug damages endothelial cells,
`however, and it might enhance transplant-associated
`
`www.thelancet.com Vol 373 May 2, 2009
`
`1555
`
`

`

`I
`
`Seminar
`
`thrombotic microangiopathy, which is associated with
`calcineurin inhibitors.110 The combination of tacrolimus
`and sirolimus is currently being compared in a large
`randomised multicentre trial.
`Reduced-intensity conditioning regimens attempt to
`suppress the host immune system suffi ciently so
`that donor T cells can engraft and then ablate the
`lymphohaemopoietic compartment of the recipient.
`The term non-myeloablative is therefore somewhat
`misleading. Reduced-intensity conditioning regimens
`diminish tissue damage and lead to decreased amounts
`of infl ammatory cytokines, which are important in the
`initiation of GVHD pathophysiology; this eff ect could
`account for the reduced frequency of severe GVHD after
`reduced-intensity conditioning versus
`full-intensity
`conditioning used in historical controls.53,54,93,111 Onset of
`acute GVHD can be delayed after reduced-intensity
`conditioning until after day 100, however, and acute
`disease could present simultaneously with elements of
`chronic GVHD (known as overlap syndrome).111–113
`
`Treatment of acute GVHD
`GVHD fi rst develops, generally, in the second month
`after HCT during calcineurin-based prophylaxis.114
`Steroids, with
`their potent anti-lymphocyte and
`anti-infl ammatory activity, are the gold standard for
`treatment of GVHD. Many centres treat mild GVHD of
`the skin (grade I) with topical steroids alone, but for more
`severe disease and any degree of visceral GVHD
`involvement high-dose systemic steroids are usually
`initiated. Administration of steroids results in complete
`remission in less than half of patients,115 and more severe
`GVHD is less likely to respond to treatment.116 In a
`prospective randomised study, addition of anti-thymocyte
`globulin to steroids as primary treatment did not increase
`the response rate.116 In a retrospective study, use of
`anti-thymocyte globulin in patients who showed early
`signs of steroid resistance was benefi cial,115 but not all
`study fi ndings show such benefi t, and this antibody
`preparation is not used as standard because of raised
`infection risks.100,117 Infusion of mesenchymal stromal
`cells—expanded in culture either from the original HCT
`donor or from a third party—is a promising approach,
`which produced 55% complete responses in a phase II
`study of patients with steroid-resistant GVHD.57
`An increasingly frequent treatment for GVHD is
`extracorporeal photopheresis. During this procedure, the
`patient’s white blood cells are gathered by apheresis,
`incubated
`with
`the DNA-intercalating
`agent
`8-methoxypsoralen, exposed to ultraviolet light, and
`returned to the patient. Extracorporeal photopheresis is
`known to induce cellular apoptosis, which has strong
`anti-infl ammatory eff ects in several systems, including
`prevention of rejection of solid organ grafts.118 Work done
`in animals shows that extracorporeal photopheresis
`reverses acute GVHD by increasing the number of
`regulatory T cells.119 Data from a phase II clinical study of
`
`steroid-dependent or steroid-refractory GVHD showed
`resolution of disease in most patients, with 50% long-term
`survival in this very-high-risk group.120 Randomised
`multicentre studies of this approach are needed to
`establish its place in management of acute GVHD.
`Another strategy to treat GVHD is blockade of the
`infl ammatory cytokine TNFα. TNFα can activate APCs,
`recruit eff ector cells, and cause direct tissue damage (see
`Pathophysiology of acute GVHD).121 Data from a phase II
`trial of etanercept (solubilised TNFα receptor 2) showed
`signifi cant eff ectiveness of the drug when added to
`systemic steroids as primary treatment for acute GVHD.
`70% of patients had complete resolution of all GVHD
`symptoms within 1 month, with 80% complete responses
`in the gastrointestinal tract and skin. The researchers also
`reported that concent