Alpha-mannosidosis (α-mannosidosis) is a lysosomal storage disease characterized by accumulation of oligosaccharides in various tissues leading to symptoms such as coarse facial features, dysostosis multiplex, hearing disabilities, mental developmental delay and skeletal involvement (dysostosis multiplex). Without treatment, the severe infantile onset form of this autosomal recessive disease leads to progressive neurodegeneration and sometimes to early death. Stem cell transplantation has been shown to be an effective treatment. In the five patients published so far, correction of skeletal abnormalities and improvement of neuropsychological capabilities have been observed. We report the first patient who received a T-cell-depleted peripheral blood stem cell transplantation (PBSCT) for α-mannosidosis. The diagnosis of α-mannosidosis was made at the age of 14 months. At the age of 24 months, he underwent PBSCT with T-cell depletion by CD34-positive selection from his HLA phenotypically identical mother. Conditioning was carried out with busulfan (20 mg/kg), cyclophosphamide (200 mg/kg), OKT3 and methylprednisolone. The patient is alive and well 27 months after PBSCT and has made significant developmental progress. The pattern of urinary oligosaccharides has returned to almost normal. CD34-positive-selected PBSCT is a feasible option to reduce risk for GVHD for these patients.
Mannosidosis (α-mannosidosis, MIM *248500) is a rare autosomal recessive disease characterized by a deficiency of lysosomal α-mannosidosis (EC 22.214.171.124). The impaired degradation of glycoproteins leads to accumulation of oligosaccharides in multiple tissues including central nervous system (CNS), liver and bone marrow.1,2,3
Clinically, α-mannosidosis presents with progressive mental deterioration, dysostosis multiplex, impaired hearing, immunodeficiency and coarse facial features. A continuum of clinical severity is observed between type I (infantile onset), with symptoms usually occurring before the age of 12 months with progressive deterioration and death between 3 and 12 years of age, and type II (juvenile onset) with milder symptoms and normal life expectancy.1,4,5
Bone marrow transplantation (BMT) has been shown to lead to stabilization of neurological function in some lysosomal storage diseases such as mucopolysaccharidosis type I-H (M. Hurler).6,8 In a feline model of α-mannosidosis Walkley et al9 could demonstrate little or no progression of neurological symptoms in transplanted animals. Immunohistochemical staining showed α-mannosidase activity in the CNS after BMT. This was thought to be attributable to bone marrow-derived microglial cells.10 The first BMT in a patient with α-mannosidosis from a matched family donor was reported in 1987. The child died of bronchopneumonia 18 weeks post transplantation. Autopsy revealed normal enzyme activity in spleen and liver, but only 7% of normal activity in the brain.11 To date, another five patients have been successfully engrafted with bone marrow for α-mannosidosis. All are still alive with at least stabilization of their neurological symptoms.2,8 We report the first patient with this disease who received a CD34-positive-selected (T-cell-depleted) graft from peripheral blood stem cells.
The boy first came to clinical attention due to a contracture of the Achilles tendon at the age of 14 months. A moderate mental developmental delay was noted. He had learned to sit at 12 months and was not able to stand or walk at the age of 23 months when he was referred to our hospital. No expressive language except for a few two-syllable words could be found by that age. He exhibited additional characteristic clinical manifestations such as coarse facial features with frontal bossing, skeletal abnormalities (Figure 1a), hearing impairment, recurrent otitis and vacuolated lymphocytes.
The diagnosis of α-mannosidosis was confirmed by virtually absent α-mannosidase enzyme activity in leukocytes (0.35 nmol/mg protein/h, normal range: 70–244 nmol/mg protein/h) and a typical pattern of urinary mannose-rich oligosaccharide excretion (Figure 2). An MRI scan of the brain revealed moderate delay of white matter myelination.
At the age of 24 months, the boy underwent peripheral blood stem cell transplantation (PBSCT) from his HLA phenotypically identical mother. She was chosen as the stem cell donor inspite of being identified as a heterozygous carrier of the disease (α-mannosidase activity in leukocytes: 89 nmol/mg protein/h, normal range: 70–244 nmol/mg protein/h). It is generally believed that even low enzyme activities can be sufficient to correct disease manifestations in α-mannosidosis.9
Conditioning was carried out with busulfan 5 mg/kg p.o. in four divided doses daily for 4 days (total dose 20 mg/kg) on days −9 to −6, cyclophosphamide 50 mg/kg i.v. once daily for 4 days (total dose 200 mg/kg) on days −5 to −2. OKT3 was administered i.v. once daily at the following doses: 0.0125 mg/kg on day −4, 0.025 mg/kg on day −3, 0.05 mg/kg on day −2, 0.1 mg/kg from day −1 to day +10, 0.05 mg/kg on day +11, 0.025 mg/kg on day +12 and 0.0125 mg/kg on day +13. Methylprednisolone was given i.v. in two divided doses daily at the following doses: 5 mg/kg on day −4, 4 mg/kg from day −3 to day −1, 2 mg/kg from day 0 to day +10, 1 mg/kg on days +11 and +12, 0.5 mg/kg on day +13, 0.25 mg/kg on days +14 and +15 and 0.125 mg/kg on days +16 and +17.
Following G-CSF stimulation (12 μg/kg daily for 5 days), the mother was submitted to a leukapheresis procedure using a Cobe Spectra Auto PBSC apheresis equipment (Gambro BCT, Lakewood, CO, USA) on day -1. T-cell depletion was achieved by CD34+cell selection using the CliniMacs device (Miltenyi Biotec, Bergisch Gladbach, Germany). A total of 21.3 × 106 CD34+ cells/kg recipient body weight and 5.9 × 103 CD3+-cells/kg were given to the patient on day 0. Owing to the T-cell depletion, no GVHD prophylaxis was administered.
The transplantation period was uneventful with mild mucositis, full donor engraftment on day +10 and no acute GVHD. However, on day +46, the patient developed mixed chimerism with 40% cells of recipient origin in the peripheral blood mononuclear cell fraction as demonstrated by fluorescence in situ hybridization for X and Y chromosomes (XY-FISH). This has remained stable at a level of approximately 50–60% donor cells until the last assessment at 27 months post transplantation (Figure 3). He has always had more than 95% donor-derived peripheral blood neutrophils. Enzyme activity of α-mannosidase in peripheral blood leukocytes has reached a stable level at about 40–80 nmol/mg protein/h (normal range: 70–244 nmol/mg protein/h). This reflects the mixed chimerism status of donor cells with an activity of about 50% of normal and recipient cells with no activity.
The patient is alive and well 24 months after T-cell-depleted PBSCT with normal growth and no signs of chronic GVHD. His slightly coarse facial features have smoothened.
The patient has made remarkable progress in functional as well as in social skills. His playing is about appropriate for his chronological age. After surgical correction of the Achilles tendon contracture, he has learned to walk. Marked improvements as to language skills as well as hearing capability were observed. At the age of 4 years, his expressive language was about that of a 3-year old.
In a Snijders–Oomen nonverbal intelligence test (SON-R 2 1/2–7) carried out at the age of 4.2 years (27 months post transplantation), he showed a slightly below average score of 94 (normal 85–115) with slightly lower scores in the action- and higher scores in the thinking scale. The SON-R tests are individual intelligence tests for general application that do not require the use of spoken or written language.13
No more episodes of otitis were noted after transplantation. Skeletal abnormalities have improved significantly, most notably in the metacarpals (Figure 1b). Delayed myelination as demonstrated by MRI before transplantation has normalized after 12 months.
The pattern of urinary excretion of mannose-rich oligosaccharides has slowly decreased and had virtually resolved completely 13 months after transplantation (Figure 2). The vacuolated lymphocytes have also disappeared.
Stem cell transplantation was first shown to be an effective treatment for α-mannosidosis in a feline animal model.9 Decreasing glycoprotein substrate accumulation in skeleton and brain was noted after transplantation. This was thought to be mediated by donor peripheral blood mononuclear cells carrying normal enzyme activity.9 Microglial cells derived from donor peripheral blood monocytes seem to be responsible for glycoprotein substrate degradation in the CNS.10 The fact that patients with α-mannosidosis show better correction of neurological symptoms after transplantation than patients with other lysosomal storage diseases might be explained by an increased secretion of α-mannosidase from microglial cells as compared with other lysosomal enzymes.14 These experiments also suggested better correction of neurological function if the transplantation is carried out early in life.9
Five patients have been transplanted with bone marrow successfully and show correction of the skeletal abnormalities and improvement of mental capabilities.8 Bony deformations seem to show a much better response to BMT than observed in mucopolysaccharidosis type I-H (M. Hurler). To date, it is unclear to what this effect is attributable.8 In our patient we could also demonstrate rapid normalization of skeletal changes, improved myelination in the CNS and almost normal patterns of urinary oligosaccharide excretion after PBSCT. Most notably his neurological status has not only stabilized but we could observe good progress in his motor, social and intellectual capabilities as well as in his speech development. This is well documented by an intelligence test score of 94 (normal 85–115) at 27 months post transplantation.
To reduce the risk for GVHD in this nonmalignant disease, a profound T-cell depletion was carried out by CD34-positive selection. This approach results in little acute toxicity as no additional immunosuppression is necessary to prevent GVHD. However, T-cell depletion has been associated with an increased rate of graft rejection. Although the patient received a very high dose of CD34+ cells (>20 × 106/kg), we observed a partial rejection soon after transplantation. This mixed chimerism state has remained stable without any further intervention for 27 months now and is obviously sufficient in delivering α-mannosidase activity. If regular chimerism testing should reveal a further decline pointing towards complete rejection, an intervention with low-dose donor lymphocyte infusions could be applied.15
We chose the mother as the stem cell donor because of prompt availability and the excellent HLA-match (6/6) despite the fact that she is a heterozygous carrier of α-mannosidosis with enzyme activity levels slightly below normal. It is debatable whether our patient could have fared even better with a normal homozygous donor instead, which would probably have resulted in a higher enzyme activity post transplantation. It is believed, however, that even low levels of enzyme activity are sufficient to improve disease manifestations in α-mannosidosis and other lysosomal storage disorders.9 This is further supported by the fact that our patient has made remarkable improvements with α-mannosidase activity in leukocytes of about 40–80 nmol/mg protein/h (normal range: 70–244 nmol/mg protein/h). Therefore, heterozygous carriers (ie parents, siblings) can be considered as suitable donors especially if HLA-matched. There are also data suggesting that haploidentical family donors can be used for the transplantation of patients with genetic diseases. This approach may however imply an increased risk for graft rejection.16,17
Enzyme replacement therapy which is available for Gaucher and Fabry's disease and impending for other storage diseases is not in sight for α-mannosidosis.6,7,18 Therefore stem cell transplantation represents a good therapeutic option for these patients.3,6,8 CD34+ PBSCT is a feasible option to reduce the risk of GVHD, but may carry an increased risk for graft rejection. As outlined, transplantation results can be expected to be best when carried out in early childhood.
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Albert, M., Schuster, F., Peters, C. et al. T-cell-depleted peripheral blood stem cell transplantation for α-mannosidosis. Bone Marrow Transplant 32, 443–446 (2003) doi:10.1038/sj.bmt.1704148
- peripheral blood stem cell transplantation
- lysosomal storage disease
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