High Sustained Antibody Titers in Patients with Classic Infantile Pompe Disease Following Immunomodulation at Start of Enzyme Replacement Therapy

OBJECTIVE

To evaluate whether immunomodulation at start of enzyme replacement therapy induces immune tolerance to recombinant human acid alpha-glucosidase (rhGAA) in patients with classic infantile Pompe disease.

STUDY DESIGN

Three patients (1 cross reactive immunologic material negative, 2 cross reactive immunologic material positive) were treated with 4 weekly doses of rituximab, weekly methotrexate, and monthly intravenous immunoglobulin and enzyme replacement therapy at 40 mg/kg/week. Antibody titers were measured using enzyme-linked immunosorbent assay. Neutralizing effects on rhGAA activity and cellular uptake were determined and combined with pharmacokinetic analysis. Clinical efficacy was evaluated by (ventilator-free) survival, reduction in left ventricular mass index, and improvement of motor function.

RESULTS

Immunomodulation induced B cell depletion that was accompanied by absence of antibody formation in all 3 patients. Upon cessation of rituximab treatment, all 3 patients showed B cell recovery, which was accompanied by formation of very high sustained antibody titers in 2 patients. Neutralizing effects on infused rhGAA were low to mild/moderate. All patients were alive at study end, learned to walk, and showed (near) normalization of left ventricular mass index.

CONCLUSIONS

Immunomodulation as recommended in the literature prevented formation of rhGAA antibodies only during B cell depletion but failed to induce immune tolerance in 2 out of 3 patients.

A new assay for fast, reliable CRIM status determination in infantile-onset Pompe disease

Pompe disease is caused by a deficiency of acid α-glucosidase (GAA; EC, 3.2.1.20), and the infantile-onset form is rapidly fatal if left untreated. However, recombinant human GAA (rhGAA) enzyme replacement therapy (ERT) extends survival for infantile Pompe patients. Although cross-reactive immunologic material (CRIM)-negative patients, who lack detectable endogenous GAA, mount an immune response to rhGAA that renders the therapy ineffective, timely induction of immune tolerance in these patients may improve clinical outcomes. Previously, CRIM status has been determined by Western blot analysis in cultured skin fibroblasts, a process that can take a few weeks. We present a blood-based CRIM assay that can yield results within 48 to 72 h. Results from this assay have been confirmed by GAA Western blot analysis in fibroblasts or by GAA sequencing in a small number of Pompe disease patients. Rapid classification of CRIM status will assist in identifying the most effective treatment course and minimizing treatment delays in patients with infantile-onset Pompe disease.

B-Cell depletion and immunomodulation before initiation of enzyme replacement therapy blocks the immune response to acid alpha-glucosidase in infantile-onset Pompe disease

OBJECTIVE

To evaluate whether B-cell depletion before enzyme replacement therapy (ERT) initiation can block acid alpha-glucosidase (GAA) antibody responses and improve clinical outcomes.

STUDY DESIGN

Six subjects with Pompe disease (including 4 cross-reacting immunologic material-negative infants) aged 2-8 months received rituximab and sirolimus or mycophenolate before ERT. Four subjects continued to receive sirolimus, rituximab every 12 weeks, and intravenous immunoglobulin monthly for the duration of ERT. Sirolimus trough levels, IgG, CD3, CD4, CD8, CD19, CD20, N-terminal pro-brain natriuretic peptide, creatine kinase, creatine kinase-MB, C-reactive protein, platelets, alkaline phosphatase, gamma-glutamyl transferase, aspartate aminotransferase, and alanine aminotransferase were measured regularly.

RESULTS

Immunomodulation achieved B-cell depletion without adverse effects. After 17-36 months of rituximab, sirolimus and ERT, all subjects lacked antibodies against GAA, 4 continued to gain motor milestones, yet 2 progressed to require invasive ventilation. The absence of infusion-associated reactions allowed the use of accelerated infusion rates.

CONCLUSION

B-cell depletion and T-cell immunomodulation in infants naïve to ERT was accomplished safely and eliminated immune responses against GAA, thereby optimizing clinical outcome; however, this approach did not necessarily influence sustained independent ventilation. Importantly, study outcomes support the initiation of immunomodulation before starting ERT, because the study regimen allowed for prompt initiation of treatment.