Multi-Year Registry Study of Elapegademase Treatment in Patients With Adenosine Deaminase Severe Combined Immunodeficiency (ADA-SCID) Requiring Enzyme Replacement Therapy

The safety and tolerability of elapegademase (elapegademase-lvlr; Revcovi^®) a PEGylated recombinant adenosine deaminase (ADA), were demonstrated in two Phase 3 clinical trials in the U.S. and Japan in patients with ADA-deficient severe combined immunodeficiency (ADA-SCID). Elapegademase replaced Adagen^® (pegademase, a PEGylated bovine ADA) in 2018. This registry study (NCT03878069) was conducted as a post-marketing requirement to bolster the limited safety and effectiveness data on elapegademase in patients with ADA-SCID and to study patients starting on enzyme replacement therapy (ERT) de novo.

Patients were managed by routine clinical care and treating physicians’ judgement from September 2019 to January 2023. Primary endpoints included trough plasma ADA activity and total trough erythrocyte deoxyadenosine nucleotides (dAXP). Secondary outcomes included lymphocyte counts, hospitalizations, infections, and safety outcomes.

Thirty-two patients were grouped as ERT-naïve (n = 7; infants and children with no prior ERT [EN]); pegademase-transitioning (n = 21; from pegademase to elapegademase [PT]); and patients who had participated in the Phase 3 clinical trial (n = 4; STP-2279-002; [STP]). The EN group maintained optimal plasma ADA activity, increased lymphocyte counts, had manageable infections, and had no mortality for up to 30 months while on elapegademase. The STP group and 66.7% of the PT group continued to maintain satisfactory levels of both ADA and dAXP with stable rates of infections and hospitalizations and stable lymphocyte counts for up to 48.6 months. Variability on all measures was seen, but overall, patients did not deteriorate while on elapegademase.

Effectiveness of elapegademase was maintained up to 4 years of use and with no new safety concerns.