Anti-ADAMTS13 Antibodies Trajectory is Associated With ADAMTS13 Recovery in Immune-Mediated TTP.

Current triplet regimens associating therapeutic plasma exchange (TPE), immunosuppression with corticosteroids and rituximab, and caplacizumab have dramatically improved the outcome of immune-mediated thrombotic thrombocytopenic purpura (iTTP). However, nearly half of the patients require extended caplacizumab treatment (i.e., > 30 days) due to persistent ADAMTS13 deficiency, raising cost and tolerance concerns. Therefore, we investigated whether anti-ADAMTS13 antibodies titer and their trajectory during the acute phase of the disease could predict ADAMTS13 improvement (i.e., activity ≥ 20% before day-30 post-TPE). From a cohort of 286 patients receiving the triplet regimen, we identified on diagnosis a cut-off value for anti-ADAMTS13 IgG antibodies of 90.5 U/mL, with a modest discriminating ability (AUC: 0.57) for predicting long-term response, precluding its use to guide therapeutic strategies. Nonetheless, the analysis of anti-ADAMTS13 IgG antibodies titer trajectory from diagnosis revealed that the proportion of iTTP patients with ADAMTS13 activity improvement was higher in patients who decreased (Dec+) their antibodies titer within the 7-14 days interval post-TPE compared to those without decrease (Dec-) (65% vs. 25% of cases, respectively, p < 0.001), a finding confirmed in a validation cohort (N = 51). These results highlight the possibility of intensifying immunosuppression in an early period post-TPE to shorten time to ADAMTS13 activity recovery. Close monitoring of anti-ADAMTS13 antibodies titer may guide immunomodulation strategies, including additional courses of B-cell depleting agents when appropriate.