Hematopoietic Stem Cell Transplantation

Invasive mould infections (IMIs), predominately invasive aspergillosis (IA), remain a leading cause of death among patients following hematopoietic stem cell transplantation (HSCT).  Recent evidence suggests that the epidemiology of invasive fungal infections (IFIs) post HSCT may be changing in addition to emerging evidence that points to host risk for infection as determined by an individual’s genetic and transplant-related factors.  Here, we review the most recent data regarding the epidemiology of IA, risk factors for infection, the clinical spectrum of disease, and therapeutic approaches.

Epidemiology-Risk Factors

Epidemiology:Current estimates from the Transplant-Associated Infection Surveillance Network (TRASNET) Database, which prospectively enrolled HSCT recipients with proven or probable invasive fungal infections between 2001-2006 suggest that IA remains the most common of all IFIs following HSCT, accounting for upwards of 43% of all cases of IFIs [ Kontoyiannis et al, 2010].  The incidence of IA among allogeneic HSCT recipients has increased from an estimated 5% in the late 1980s to more than 10% in the 1990-2000’s [Marr et al [a], 2002, Marr et al [b], 2002, Wald et al, 1997].  This may, in part, be related to more aggressive HSCT practices being used leading to sicker patients susceptible to infections with Aspergillus species, higher clinical suspicion, and better diagnostics for IA.  The rates of IA among allogeneic HSCT recipients differ based on the relationship of the donor and the recipient (lower in related -family members vs. unrelated donors), the compatibility of their human leukocyte antigens (HLA; lower in matched vs. unmatched or mismatched donors), and manipulation of the grafts (lower in unmanipulated vs. T-cell depleted grafts) [Marr et al [a], 2002, Marr et al [b], 2002, Grow et al 2002, Cornet et al 2002, Mihu et al, 2008, van Burik et al, 2007].

Historically, A. fumigatus has been the most commonly isolated Aspergillus spp. among HSCT recipients with IA, followed by A. flavus, A. terreus, and A. niger [Marr et al [a], 2002, Marr et al [b], 2002, Wald et al 1997, Martino et al 2002, Pagano et al 2007, Jantunen et al 1997].  Isolation of A. fumigatus appears to have decreased from >50% in the late 1990s-early 2000s to 22.1-36.9% more recently [Pagano et al 2007, Neofytos et al 2009].  Until recently rarely encountered in clinical practice Aspergillus spp. , such as  A.ustus, A. lentulus, and Neosartorya udagawe, have been increasingly identified [Vinh et al 2009, Balajee et al 2005].  In addition, various resistance patterns to azoles, amphotericin B, and caspofungin amongst different Aspergillus species and A. fumigatus azole resistance have been recently reported [Snelders et al, 2008].  The above suggest that identifying the Aspergillus species may be pertinent for the successful management of these infections.  However, recent data suggest that in more than 50% of IA cases among HSCT recipients the Aspergillus spp. may not be identified [Pagano et al, 2007, Neofytos et al 2009]. 

Risk Factors: Infection tends to follow a bimodal pattern, with early and late infection peaks.  The median time for the development of invasive aspergillosis after alloSCT has varied from 25 days [Morrison et al, 1994] to 67 days [McWhinney et al, 1993], 100 days [Saugier-Veber et al, 1993] or 136 days [Jantunen et al, 1997]. Early infections, as defined by infection occurring prior to engraftment, is associated with host-factors such as older age at time of transplant, use of cord blood as a stem cell source, and unrelated T-cell depleted graphs [Marr et al [a], 2002, van Burik et al, 2007, Martino et al, 2002, Garcia-Vidal et al, 2008].  Traditional myeloablative conditioning, in contrast to reduced intensity conditioning, may provide additional risk for IA.  In contrast, infections that occur after engraftment tend to be associated with transplant complications such as graft-versus-host disease (GVHD) and treatment administered for GVHD, co-infections with cytomegalovirus (CMV) and other respiratory viruses. Biologic factors such as multiple cytopenias and iron overload appear to provide a risk for development of disease in both time periods [Garcia-Vidal et al, 2008].  
Furthermore, on a molecular level, an individual’s risk for IA may be enhanced by certain polymorphisms among donor Toll-like receptors (TLRs), which are key players in the immune response to fungal pathogens [Bochud et al, 2008]. Detection of Aspergillus DNA by PCR in BAL samples collected at the time of transplantation was highly predictive of subsequent invasive aspergillosis in one small study [Einsele et al, 1998]. A case of IA occurring 10 years after allogeneic HSCT, after discontinuation of immunosuppression but with a high home exposure, highlights the duration of the risk [Rashid, 2009].

Clinical Presentation

Infection with Aspergillus species is thought to occur when a susceptible individual inhales fungal spores which travel to the lungs and germinate to form hyphae.  Impairment in host macrophages and ciliary clearance due to cytotoxic chemotherapy may prevent the host from effectively containing the infection and hence lead to progression to invasive disease [Brummer et al, 2003, Grazziutti et al, 1997, Hebart et al, 2002].  Disease with Aspergillus most frequently affect the sinuses or the lungs, but may occasionally disseminate (often silently) to distant sites of infection, either contiguously or hematogenously.  Dissemination to the brain is particularly common and should be systematically looked for by brain imaging, especially MR [Hagansee et al, 1994, Miaux et al, 1995; Ribaud et al, 1999; Guermazi A et al, 2003; Liapis K et al, 2009]. Sinus infections are also relatively common [Drakos et al, 1993; Morrison et al, 1993; McWhinney et al, 1993; Verschraegen et al, 1997; Savage et al, 1997; Kennedy et al, 1997; Connolly JL et al, 2007]. A multitude of involved body sites have been described including skin, gastrointestinal tract, kidney, and the central nervous system [Lacerda et al, 2005; Kalokhe et al, 2010;] . Cutaneous aspergillosis is proportionately more common in this patient population [Wald et al, 1997; Cornely et al, 2001; Nakai et al 2002; Chen et al, 2009], probably because of the propensity for dissemination.  Aspergillus tracheobronchitis is a less common although an equally severe site of infection [Machida et al, 1999; van Assen et al, 2000; Chang et al, 2005].

Clinical features of invasive pulmonary disease include fever, cough, hemoptysis, dyspnea, and pleuritic chest pain.  Disseminated aspergillosis may present with fever.  Clinical characteristics of disseminated disease may vary, depending on the body site involved, and can range from nodular cutaneous lesions to sinus congestion or palatal necrosis to brain lesions.   

Diagnosis

Imaging:Historically,radiographic features of pulmonary IA have included nodular lesions and the traditional “halo sign”: a nodular infiltrate surrounded by a halo of ground glass infiltrates representing alveolar hemorrhage.  The halo sign may be seen in up to 93% of all patients with acute pulmonary IA [Greene et al, 2007, Horger et al, 2005, Caillot et al, 2001, Kuhlman et al, 1985].  However, this finding is not specific to the pathogen but may be suggestive of other IMIs or even bacterial infections (e.g. Pseudomonas) [Lee et al, 2005].   Notably, the halo sign is more commonly seen in cases of pulmonary IA during periods of profound neutropenia, such as the pre-engraftment period after an HCST.  The “air-crescent sign”, a crescentic lucency surrounding a nodular lesion, can be occasionally seen in advanced cases of pulmonary IA and it usually represents necrosis of the affected parenchyma.  However, we have recently appreciated that pulmonary IA after engraftment may present with non-specific radiologic findings, including nodular lesions, diffuse infiltrates, peribronchial infiltrates, and even ground-glass opacities [Kojima et al, 2005]. 

Pathology-Microbiology: Confirming a diagnosis of IA requires tissue biopsy where Aspergillus species may be identified by their narrow, septated, acute (45 degree) angle branching hyphae.  Although this presentation may help microscopically distinguish Aspergillus spp. from the Zygomycetes, other filamentous fungi (e.g. Fusarium spp., Penicillium spp.,Scedosporium spp.) may look similar under the microscope.  Colonies of Aspergillus fumigatus, the most commonly isolated Aspergillus species, grow gray-green on potato flakes agar.  Unfortunately, the sensitivity of sputum and bronchoalveolar lavage cultures for the diagnosis of pulmonary IA has not exceeded 70% in multiple series [Bodey et al, 1992, Albelda et al, 1984, Horvath et al, 1996, Kahn et al, 1986, Levy et al, 1992].   

Galactomannan:Galactomannan is a polysaccharide present in the cell wall of Aspergillus which is released when Aspergillus hyphae start growing.  A sandwich enzyme-linked immunosorbent assay is used and an optical density index (ODI), calculated by dividing the OD of each sample with that of the threshold control, of 0.5 and 1.5 has been used to define positivity.  An ODI of 0.5 using the Platelia ELISA (BioRad, Marnes-La-Coquette, France) has been approved by the United States Food and Drug Administration (FDA).  In a meta-analysis of 27 studies with a total of 4000 patients, the overall sensitivity and specificity of the GM EIA for the diagnosis of IA were 61% (95% CI 59-63%) and 93% (95% CI 92-94%), respectively [Pfeiffer et al, 2006].  Notably, the assay appears to perform better in patients with an underlying hematological malignancy or among HSCT recipients. 

PCR: PCR on blood and other body fluids (e.g. bronchoalveolar lavage -BAL, cerebrospinal fluid) has been used for the diagnosis of IA, with a sensitivity and specificity of blood PCR having ranged between 64-100% and 63.5-100%, respectively [Donnelly, 2006].  Unfortunately the use of PCR for the diagnosis of IA has been hindered due to lack of standardization and commercially available assays, in part as a result of the variability of specimens studied (e.g. whole blood, plasma, serum), molecular techniques used, patient populations, or number of samples tested.  The combined use of PCR and the GM EIA appears to increase the diagnostic yield for the diagnosis of IA in patients with hematologic malignancies, with a sensitivity and specificity of 82% and 96%, respectively [Musher et al, 2004]. 

Treatment

Historically, amphotericin B deoxycholate has been considered the mainstay of therapy for IMIs, including IA.  A prospective, randomized, unblinded, multi-center trial compared voriconazole to amphotericin B deoxycholate for the treatment of IA among immunocompromized patients, including 67 allogeneic HSCT recipients [Herbrecht et al, 2002].  Administration of voriconazole was associated with better clinical outcomes (as measured by complete and partial response rates) (32.4% versus 13.3%), overall survival, and fewer severe drug adverse events B.  Based on the results of this study, voriconazole has become the standard of care for patients with IA as suggested by the most recently published treatment guidelines, endorsed by the Infectious Disease Society of America [Walsh et al, 2008]. 

Voriconazole has not been compared to a lipid formulation of amphotericin B for the treatment of IA.  However, two doses of liposomal amphotericin B (3 mg/kg vs. 10 mg/kg) were compared for the treatment of IMIS (97% of those being IA)[35].  There were 35 allogeneic HSCT patients enrolled in this study.  This study failed to demonstrate any significant differences in clinical outcomes and overall survival with the higher dose, which was associated with more toxicities.  Notably, successful clinical outcomes were in the range of 50% and overall survival between 60-70%, comparable to 52.8% and 70.8%, respectively, as reported by Herbrecht et al in the sentinel voriconazole trial for the treatment of IA [Herbecht et al, 2002, Cornely et al, 2007], however possibly softer response criteria and changing practice in HSCT may have influenced headline response rates [Denning, 2007].  Clearly, more data are required before we can make any meaningful conclusions on the efficacy of lipid formulations of amphotericin B as primary therapy for IA.  Despite, often in clinical practice, we tend to use one of the lipid formulations of amhotericin B instead of the conventional amphotericin B for the treatment of IA and other IMIs.  This is mainly driven from the relatively better adverse event profile of the lipid formulations and the ability to administer and deliver high doses of amphotericin B to target tissues.  Posaconazole and caspofungin have been studied as salvage therapy for IA with clinical success rates in the range of 40% [Walsh et al, 2007].

In vitro and some animal data have suggested that combination antifungal therapy (echinocandin with either a mould-active triazole or amphotericin B) may be more effective than monotherapy [Kirkpatrick et al, 2002, Perea et al, 2002].  In a small retrospective study from the Fred Hutchinson Cancer Center, HSCT (mostly allogeneic) recipients with IA that had failed primary therapy, received salvage therapy with voriconazole or voriconazole and caspofungin [Marr et al [c], 2004].  The salvage combination therapy arm showed improved 3-month survival and in multivariate analyses combination therapy was associated with reduced mortality, compared with voriconazole alone (HR, 0.28; 95% CI, 0.28–0.92; p=0.01).  A prospective, randomized, multi-center, international study has been initiated to address the efficacy of combination therapy of voriconazole with anidulafungin among high risk hematologic malignancy patients HSCT recipients (Clinical Trials Gov: NCT00531479). 
There may be a role for lung or brain surgery to resect lesions as adjunct treatment; however, definite timing and modalities cannot be recommended yet [Salerno et al, 1998; Trigg et al 1993; Reichenberger et al, 1998; Lupinetti et al, 1992; Coleman et al, 1995; Camarata et al, 1992]. In any case, it is important to continue antifungal therapy, even though lesion resection was complete, if the patient continues to have progressive GVHD or receives steroids.
Duration of therapy for IA is not well defined.  Experienced clinicians usually opt for prolonged treatment courses, taking into consideration the host’s immune system function and administered immunosuppressive therapies (e.g. steroids for GVHD etc).  The availability of oral antifungal agents with activity against Aspergillus spp. (e.g. voriconazole, posaconazole) have significantly facilitated our treatment decision making in patients with IA in the outpatient setting.

Clinical Outcomes

IA among HSCT recipients has been associated with high mortality, in the range of 70-90% [Denning, 1996; Wald 1993].  However, survival appears to have significantly improved, with 12-week overall survival ranging from 44% to 64.5% [Neofytos et al, 2009, Upton et al, 2007, Nivoix et al, 2008].  This may be attributed to earlier diagnosis, in part, due to higher clinical suspicion and better non-invasive diagnostic modalities, and prompt treatment initiation with effective, well tolerated antifungal therapies.  Notably, in two recently published studies administration of voriconazole was found to be significantly associated with improved survival [Upton et al, 2007, Nivoix et al, 2008].


Carolyn Alonso and Dionissios Neofytos
Transplant and Oncology Infectious Disease Program
Johns Hopkins School of Medicine, Division of Infectious Diseases
1830 E Monument Street, Suite 421, Baltimore, MD 21205 
Tel: (410) 502 9521
Fax: (410) 614 0714
E-mail Address: [email protected] 
E-mail Address: [email protected]

November 2010