Correlation between urinary GAG and anti-idursulfase ERT neutralizing antibodies during treatment with NICIT immune tolerance regimen: A case report

INTRODUCTION

Antibodies to intravenous idursulfase enzyme replacement therapy (ERT) for patients with Hunter syndrome (mucopolysaccharidosis type II, MPS II) can have a harmful clinical impact, including both increasing risk of infusion reactions and inhibiting therapeutic activity. Thus, failure to monitor anti-idursulfase antibodies and neutralizing antibodies, and delays in reporting results, may postpone critical clinical decisions.

HYPOTHESIS

Urinary glycosaminoglycan (GAG) levels may be used as a biomarker for anti-idursulfase antibodies and neutralizing antibodies to improve timeliness in monitoring and managing ERT.

METHODS

This is a case report describing a patient with MPS II with high levels of neutralizing antibodies and worsened clinical status who was treated for five years with a non-immunosuppressive and non-cytotoxic immune tolerance (NICIT) regimen, consisting of intravenous immune globulin and frequent infusions of idursulfase. Neutralizing antibodies and total anti-idursulfase antibodies were measured by two different methods, the direct 1,9-dimethylmethylene blue (DMB) assay and cetylpyridinium chloride carbazole-borate (CPC) assay.

RESULTS

Neutralizing antibodies, measured as percent inhibition of enzyme activity and also by total neutralizing antibody titer, were correlated with quantitative urinary GAG measured by DMB assay (p=0.026, p=0.0067), and quantitative urinary GAG by CPC assay with percent inhibition of enzyme activity by neutralizing antibodies (p=0.0475). The NICIT regimen showed a sustained immune tolerance after five years and was well-tolerated.

CONCLUSIONS

Urinary GAG, measured by DMB assay, may be a biomarker for anti-idursulfase neutralizing antibodies and is useful for managing immune tolerance regimens for patients with MPS II who have high levels of anti-idursulfase neutralizing antibodies. This study highlights the importance of regular and frequent monitoring of urinary GAG in patients with MPS II who are receiving ERT. The NICIT regimen, with less drug toxicities, may be preferred in patients with MPS who have a high risk of infections and whose disease progresses less rapidly than some other lysosomal storage diseases, such as infantile Pompe disease.

Non-myeloablative preconditioning with ACK2 (anti-c-kit antibody) is efficient in bone marrow transplantation for murine models of mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disease caused by the deficient activity of iduronate 2-sulfatase (IDS), which is involved in the lysosomal catabolism of the glycosaminoglycans (GAGs) dermatan and heparan sulfate. Such a deficiency leads to the accumulation of undegraded GAGs in some organs. Although enzyme replacement therapy is available as a treatment of MPS II, there are some limitations, such as the requirement of weekly administration for whole life. To avoid such limitations, hematopoietic cell transplantation (HSCT) is a possible alternative. In fact, some report suggested positive effects of HSCT for MPS II. However, HSCT has also some limitations. Strong conditioning regimens can cause severe side effects. For overcome this obstacle, we studied the efficacy of ACK2, an antibody that blocks KIT, followed by low-dose irradiation as a preconditioning regimen for HSCT using a murine model of MPS II. This protocol achieves 58.7±4.92% donor chimerism at 16weeks after transplantation in the peripheral blood of recipient mice. GAG levels were significantly reduced in liver, spleen, heart and intestine. These results indicated that ACK2-based preconditioning might be one of the choices for MPS II patients who receive HSCT.

The relationship between anti-idursulfase antibody status and safety and efficacy outcomes in attenuated mucopolysaccharidosis II patients aged 5 years and older treated with intravenous idursulfase

In the pivotal phase II/III trial of idursulfase administered intravenously to treat mucopolysaccharidosis II, approximately half of the patients developed antibodies to idursulfase. This post-hoc analysis of data from the phase II/III trial and extension study examined the relationship between antibody status and outcomes. A total of 63 treatment-naïve patients received 0.5 mg/kg of intravenous idursulfase weekly for two years. Thirty-two patients (51%) were positive for anti-idursulfase IgG antibodies, 23 of whom (37%) became persistently positive. All patients who developed an antibody response did so by their scheduled Week 27 study visit. Positive antibody status appeared to have no statistically significant effect upon changes in six-minute walk test distance, percent predicted forced vital capacity, or liver and spleen volume. All patients showed significant decreases in urinary GAG levels, although the antibody positive group maintained somewhat higher urinary GAG levels than their antibody-negative counterparts at the end of study (138.7 vs. 94.7 μg/mg creatinine, p = 0.001). Antibody positivity was not associated with a higher event rate for serious adverse events. Among patients who had no prior infusion-related reactions, antibody positive patients were 2.3 times more likely to have a first infusion-related reaction than those who would remain negative (p = 0.017); the risk increased to 2.5 times more likely for those who were persistently positive (p = 0.009). These differences in risk disappeared among patients with a previous infusion-related reaction, likely because of preventive measures. A genotype analysis for the 36 patients with available data found that patients with nonsense or frameshift mutations may be more likely to develop antibodies, to experience infusion-related reactions, and to have a reduced uGAG response than those with missense mutations, suggesting the possibility that antibodies are not a driver of clinical outcomes but rather a marker for genotype.

Transplantation of fetal fibroblasts and correction of enzymatic deficiencies in patients with Hunter's or Hurler's disorders

An attempt was made at correcting the specific lysosomal enzyme deficiencies in 7 children with Hunter's or Hurler's diseases by transplantation of fetal fibroblasts. In spite of pretreating the young patients with stored blood, following a procedure employed successfully to avoid rejection of kidneys from incompatible donors, the use of serum-free media for culturing the cells before being harvested and incubation of the cells with chorionic gonadotrophin, the transplantation of fetal fibroblasts was not associated with biochemical or clinical changes. None of the seven patients showed immune reactions against the transplanted cells, HLA antigens, or the missing enzymes.

HLA alloimmunization with leukocyte concentrates from HLA-matched and HLA-non-matched donors in patients with Hunter's syndrome

The incidence and characteristics of HLA alloimmunization following transfusions of leukocyte concentrates as a source of enzyme replacement were determined in male patients with Hunter's syndrome. Five patients were given leukocyte concentrates from HLA matched donors (Group I) and another five patients received leukocyte concentrates from non-HLA matched donors (Group II). No other blood products were transfused in either group. Immune response pattern of HLA alloimmunization measured as the proportion of screening cells manifesting cytotoxicity with patient's sera obtained during the follow-up period was similar in both groups. HLA alloimmunization is seen with transfused leukocyte concentrates from either HLA-matched or non-HLA-matched donors in patients with Hunter's syndrome. There appears to be a trend for an earlier onset of HLA alloimmunization with fewer transfusions when leukocyte concentrates from non-HLA-matched donors are transfused as compared to leukocyte concentrates from HLA-matched donors. Once HLA alloimmunization occurs, immune response patterns appear similar with either leukocyte product.

Characteristics and natural history of alloimmunization following HLA-matched leukocyte transfusion in Hunter's syndrome

The characteristics and natural history of alloimmunization to HLA were studied in five patients with Hunter's syndrome receiving long term transfusions of leukocytes collected from human leukocyte antigen (HLA) matched donors. Patients were not given any other blood component transfusions. All patients became alloimmunized at an average interval of eight months following an average of 15 transfusions. All patients developed HLA alloantibodies to transfused cross-reactive HLA antigens. Antibodies to transfused incompatible HLA antigens also developed in all patients. Multispecific HLA antibodies in which specificity determination could not be made were also seen in four patients. In a small number of patients in this study, despite matching for the private HLA specificities, HLA alloimmunization was not prevented. In fact, broad alloimmunization was seen uniformly in our patients.