Abstract
Botulinum toxin type A (BoNT/A) formulations differ in their content of non-toxic accessory proteins, also known as complexing proteins (CPs), which may influence immunogenicity. Some BoNT/A products share structurally similar CPs, potentially leading to antibody cross-reactivity among formulations. This prospective study investigated whether patients treated with different BoNT/A products develop cross-reactive anti-CP antibody responses. One hundred participants were allocated into five treatment groups, each receiving a single BoNT/A formulation: incobotulinumtoxinA (IncoA), onabotulinumtoxinA (OnaA), abobotulinumtoxinA (AboA), letibotulinumtoxinA (LetiA), or prabotulinumtoxinA (PraboA). Each participant received 50 units or equivalent dosing. Serum samples were collected 180 days post-injection, and anti-CP antibodies were quantified using an absorption ELISA and compared with a toxin-naïve control group. IncoA did not induce significant anti-CP antibody responses. In contrast, higher antibody levels were observed in the OnaA, LetiA, and PraboA groups against multiple CPs, suggesting structural similarity and cross-reactivity. AboA primarily induced antibodies directed against its own CPs and those of PraboA. These findings demonstrate that CP-containing formulations can induce cross-reactive antibody responses, whereas CP-free incobotulinumtoxinA exhibits minimal immunogenicity. This study highlights the importance of CP composition in guiding clinical product selection, particularly in patients requiring repeated BoNT/A administration.