Dose-Dependent Effect of Enzyme Replacement Therapy on Neutralizing Antidrug Antibody Titers and Clinical Outcome in Patients with Fabry Disease

Abstract

Background: Use of enzyme replacement therapy (ERT) to treat Fabry disease, caused by deficient lysosomal α-galactosidase A activity, can lead to formation of neutralizing antidrug antibodies (ADAs). These antibodies are associated with increased accumulation of plasma globotriaosylceramide (Gb3) and disease progression. Because agalsidase ERT can saturate ADA-binding sites during infusions (achieving agalsidase/antibody equilibrium), we investigated in this open cohort study whether saturated patients (who have excess agalsidase after infusions) experience better clinical outcomes compared with not saturated patients (who have excess ADAs after infusions).

Methods: We isolated ADAs from sera of 26 men with Fabry disease receiving ERT (for a median of 94 months) and determined the amount of agalsidase necessary for antibody saturation. Clinical and biochemical outcomes included measurements of eGFR, interventricular septum thickness, and lyso-Gb3.

Results: ADA titers decreased significantly in all patients during infusion. Agalsidase-α and agalsidase-β had similar ADA-binding capacity and comparable ADA saturation frequency. Fourteen patients with saturated ADAs presented with mild (but significant) loss of eGFR, stable septum thickness, and significantly decreased lyso-Gb3 levels. The 12 not saturated patients had a more pronounced and significant loss of eGFR, increased septum thickness, and a smaller, nonsignificant reduction in lyso-Gb3, over time. In three patients, dose escalation resulted in partially elevated ADA titers, but importantly, also in reduced lyso-Gb3 levels.

Conclusions: A not saturated ADA status during infusion is associated with progressive loss of eGFR and ongoing cardiac hypertrophy. Dose escalation can result in saturation of ADAs and decreasing lyso-Gb3 levels, but may lead to increased ADA titers.

Keywords: Fabry disease; chronic kidney disease; complexes; glomerular filtration rate; immune; left ventricular hypertrophy.

Graphical abstract

Figure 1.

The required amount of recombinant enzyme for antibody saturation can be calculated using patients' purified total IgGs. (A) Determination of the individual antibody status before and after infusion. (B) Effect of infused ERT amounts (gray) on antibody titer (black) during infusion and agalsidase activity (green). The longitudinal measurement of ADA titers during infusions allows estimating the amount of enzyme required to saturate ADAs. (C) Titration of purified total IgG against ERT allows calculating the required amount of enzyme from one serum sample. The determination of the individual amount of recombinant GLA to saturate ADAs was performed using titration and subsequent calculation. First, a titration was performed to identify the required amount of enzyme to saturate 90% of 5 µg total IgGs (see Methods). ERT inhibition was plotted against the amount of enzyme. The amount required can be identified on the y-axis (here 10 ng, dashed orange line), showing that 2 ng is sufficient to saturate 1 µg total IgG. In the example shown, the patient’s measured IgG concentration was 9.5 mg/ml serum. Because each patient has approximately 3 L of serum, the total amount of patient’s IgGs per total volume of serum was calculated with 28.5 g. Therefore, the amount of enzyme required to saturate 90% of all IgGs was 57 mg (28.5 g×2/1000=57 mg). (D) Crosstitration of agalsidase-α and agalsidase-β demonstrates similar ADA saturation of either type of enzyme.

Figure 2.

Antibody titer determination allows a classification in saturated and not saturated patients during infusion. Positive values represent residual infused enzyme after ADA saturation (green, agalsidase excess). Negative values represent additional theoretical infused enzyme necessary to saturate ADA titers (red, antibody excess).

Figure 3.

Antibody saturation due to enzyme excess is associated with better outcomes over time. (A) Change in eGFR. (B) Change of interventricular septum thickness. (C) Change of plasma lyso-Gb3 levels. Green lines: saturated patients with agalsidase excess during infusion. Red lines: not saturated patients with antibody excess (agalsidase deficit) during infusion. Solid lines represent ERT-naïve patients at baseline. * indicates patients excluded for eGFR calculations because of renal transplantation or dialysis. ^# indicates a patient excluded from eGFR calculation because of newly adjusted renin-angiotensin-aldosterone system blockers. 95% CI, 95% confidence interval.

Figure 4.

Dose increase results in antibody saturation but may also trigger further ADA formation. (A) Saturation of ADAs due to dose increase. (B) Short-term effect of dose increase due to switch of product. (C) Effect of dose increase due to stepwise escalation/product switch (396th infusion). (D) Long-term effect of dose increase due to product switch (260th infusion) resulted in increased ADA titers, but titers could be saturated. (E) Long-term effect of dose increase due to product switch (185th infusion) resulted in stable ADA titers, which could be saturated. Green bars indicate saturation (agalsidase excess), red bars indicate no saturation (antibody excess) during infusion. Dotted lines represent plasma lyso-Gb3 levels.

Figure 5.

Schematic model of ERT and neutralizing antibodies during infusion. If antibodies are present, they neutralize ERT activity by binding. In addition, IgG-tagged agalsidase will be internalized and digested by macrophages. If more antibodies than ERT are present (antibody excess/agalsidase deficit), this results in a decreased cellular Gb3-clearance (left). If ERT overcomes antibody titers (agalsidase excess), more ERT can enter lysosomes of target cells (right).