Enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA = alglucosidase alfa) is available since 2006, and has been shown effective in IOPD and LOPD; however the treatment response is variable and imperfect. This has prompted the development of a next-generation rhGAA with increased glycosylation and improved muscle cell uptake (avalglucosidase alfa). The efficacy of ERT significantly depends on the glycosylation status of the enzyme determining muscle cell uptake via the mannose-6-phosphate (M6P) receptor, and on the formation of antibodies directed against the recombinant enzyme. The impact of immunological factors on efficacy is highlighted by the occurrence of high sustained antibody titers (HSAT) in IOPD patients producing no GAA at all (CRIM-negative), that result in a worse outcome similar to that of untreated patients, if no immunomodulating medication is given. Such HSAT can also occur in IOPD patients synthesizing a non-functional GAA (CRIM-positive) and in some late onset Pompe Disease (LOPD) patients.~In the first part of this study, the investigators aim to characterize the molecular structure of wildtype GAA and, in particular, of mutated GAA variants with and without HSAT, in order to learn how mutation impairs uptake of GAA into the cell via the M6P receptor. To accomplish this, 5 healthy subjects and 45 Pompe disease patients will be studied (15 IOPD and 30 LOPD). The investigators will identify antibody epitopes in the sera of patients with rhGAA antibodies and determine and compare quantitatively their binding affinities, by using a combination of proteolytic affinity-mass spectrometry and surface plasmon resonance biosensor analysis. The investigators reason that specific mutations may affect the epitope status differently. Related to this, the investigators also speculate that glycosylations and M6P residues could modify epitopes in their close vicinity. These results will help to understand where the antibody binding epitopes are located.~In the second part of the study the investigators aim to learn to which epitopes antibodies bind and to which not. To accomplish this the epitope peptides will be synthesized and chemically modified, in order to block effectively antibodies directed against the therapeutic enzyme. Applying high affinity GAA epitope peptides capable of binding neutralizing antibodies is expected to potentially improve efficacy and safety of ERT, thereby providing a new targeted and personalized immunotolerance approach.
In the first part of this study, the aim is to characterize the molecular structure of wildtype GAA and, in particular, of mutated GAA variants with and without HSAT, in order to learn how mutation impairs uptake of GAA into the cell via the M6P receptor. In the second part of the study the aim is to learn to which epitopes antibodies bind and to which not. To accomplish this the investigators will synthesize and chemically modify the epitope peptides, in order to block effectively antibodies directed against the therapeutic enzyme.