Abstract: The efficacy and safety of caplacizumab in individuals with acquired thrombotic thrombocytopenic purpura (aTTP) have been established in the phase 2 TITAN and phase 3 HERCULES trials. Integrated analysis of data from both trials was conducted to increase statistical power for assessing treatment differences in efficacy and safety outcomes. Caplacizumab was associated with a significant reduction in the number of deaths (0 vs 4; P & lt; .05) and a significantly lower incidence of refractory TTP (0 vs 8; P & lt; .05) vs placebo during the treatment period. Consistent with the individual trials, treatment with caplacizumab resulted in a faster time to platelet count response (hazard ratio, 1.65; P & lt; .001), a 72.6% reduction in the proportion of patients with the composite end point of TTP-related death, TTP exacerbation, or occurrence of at least 1 treatment-emergent major thromboembolic event during the treatment period (13.0% vs 47.3%; P & lt; .001), and a 33.3% reduction in the median number of therapeutic plasma exchange days (5.0 vs 7.5 days) vs placebo. No new safety signals were identified; mild mucocutaneous bleeding was the main safety finding. This integrated analysis provided new evidence that caplacizumab prevents mortality and refractory disease in acquired TTP and strengthened individual trial findings, with a confirmed favorable safety and tolerability profile. These trials were registered at www.clinicaltrials.gov as #NCT01151423 and #NCT02553317.

Abstract: Introduction: Acquired or immune-mediated thrombotic thrombocytopenic purpura (aTTP) is a life-threatening thrombotic microangiopathy characterized by severe thrombocytopenia, microangiopathic hemolytic anemia, and organ ischemia. Inhibitory autoantibodies cause a severe deficiency of the von Willebrand factor (vWF) cleaving enzyme ADAMTS13, leading to intravascular vWF-platelet aggregation and microvascular thrombosis. The mainstays of treatment are plasma exchange (PE) and immunosuppression. Caplacizumab, a bivalent Nanobody, targets the A1 domain of vWF, inhibiting the interaction between ultra-large vWF and platelets. Methods: Patients with an acute episode of aTTP who had received one PE treatment were randomized 1:1 to placebo or 10 mg caplacizumab, in addition to daily PE and corticosteroids. A single IV dose of study drug was given before the first on-study PE and a SC dose was given daily during the PE period and 30 days thereafter. If at the end of this period there was evidence of ongoing disease, such as suppressed ADAMTS13 activity, investigators were encouraged to extend the blinded treatment for a maximum of 4 weeks together with optimization of immunosuppression. All patients entered a 28-day treatment-free follow up period after the last dose of study drug (Figure 1). Primary endpoint was time to platelet count response, defined as platelet count ≥ 150×109/L with stop of daily PE within 5 days. There were 4 key secondary endpoints, hierarchically ranked. The 1st was a composite of aTTP-related death, aTTP recurrence, or major thromboembolic event during the study drug treatment period. A blinded, independent committee adjudicated aTTP-related deaths and major thromboembolic events. The 2nd looked at recurrences during the entire study period, including the follow up period. The 3d evaluated refractoriness to therapy, defined as absence of platelet count doubling after 4 days of treatment and LDH still above normal. The 4th was the time to normalization of 3 organ damage markers: LDH, cardiac troponin I and serum creatinine. Results: 145 patients were randomized, 73 to placebo and 72 to caplacizumab. Demographics and baseline disease characteristics were balanced between groups, except for a higher proportion of initial episodes in the caplacizumab arm. Compared to patients treated with placebo, those on caplacizumab were & gt;50% more likely to achieve a platelet response at any given time point (platelet count normalization rate 1.55, 95% CI 1.10 - 2.20, p & lt;0.01). During the study drug treatment period, treatment with caplacizumab resulted in a 74% reduction in TTP-related death, recurrence of TTP, or a major thromboembolic event (p & lt;0.0001, Table 1). During the overall study period, 28 patients in the placebo group experienced a recurrence versus 9 patients in the caplacizumab group, a 67% reduction (p & lt;0.001, Table 2). In all 6 caplacizumab-treated patients with a relapse during the follow up period, ADAMTS13 activity was still & lt;10% at stop of study drug, reflecting ongoing disease. No caplacizumab-treated patients were refractory to therapy, while 3 patients on placebo were (p =0.057). Treatment with caplacizumab was associated with a trend toward faster normalization of the 3 organ damage markers. Safety is summarized in Table 3. In the caplacizumab group, the most common study drug-related TEAEs were epistaxis, gingival bleeding, and bruising. During the study drug treatment period, 3 patients on placebo died. One death occurred during the follow up period in a caplacizumab-treated patient and was assessed by the investigator as not related to study drug. Conclusions: Results of the Phase 3 HERCULES study confirm that treatment with caplacizumab reduces the time to platelet count response, resulting in faster resolution of aTTP. Treatment with caplacizumab also resulted in a highly clinically meaningful reduction in aTTP-related death, recurrence of aTTP, or a major thromboembolic event during study drug treatment. The relapses after stop of study drug in patients with ADAMTS13 activity & lt;10% suggest that treatment should be continued until complete resolution of the underlying disease. Caplacizumab has a favorable safety profile, with mucocutaneous bleeding the most frequently reported AE. Caplacizumab, through rapid blocking of vWF-mediated platelet aggregation, represents a novel treatment option for patients with aTTP. (clinicaltrials.gov: NCT02553317) Disclosures Scully: Ablynx: Honoraria, Research Funding; Shire: Honoraria, Research Funding; Novartis: Honoraria; Alexion: Honoraria. Cataland:Ablynx NV: Membership on an entity's Board of Directors or advisory committees. Peyvandi:Ablynx, Roche: Membership on an entity's Board of Directors or advisory committees; Ablynx, Bayer, Grifols, Novo Nordisk, Sobi: Speakers Bureau;Freeline, Kedrion, LFB, Octapharma: Consultancy. Coppo:Ablynx: Membership on an entity's Board of Directors or advisory committees; Alexion: Membership on an entity's Board of Directors or advisory committees; Octapharma: Membership on an entity's Board of Directors or advisory committees; Shire: Membership on an entity's Board of Directors or advisory committees. Knöbl:Novo Nordisk: Consultancy, Research Funding; Shire: Consultancy, Research Funding. Kremer Hovinga:Baxalta/Shire: Other: unrestricted grant hereditary TTP registry; Ablynx NV: Membership on an entity's Board of Directors or advisory committees. Metjian:Ablynx NV, Shire, Omeros: Research Funding; Shire: Membership on an entity's Board of Directors or advisory committees. de la Rubia:Amgen: Other: Honoraria; Celgene: Other: Honoraria; Janssen: Other: Honoraria. Pavenski:Alexion Pharmaceuticals: Honoraria; Novartis: Honoraria; Ablynx: Other: participation in industry sponsored RCT; CSL Behring: Research Funding. Callewaert:Ablynx NV: Employment. Biswas:Ablynx NV: Employment. De Winter:Ablynx NV: Employment. Zeldin:Ablynx NV: Employment.

Abstract: Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a potentially fatal thrombotic microangiopathy caused by autoantibody-mediated severe deficiency of ADAMTS13. Standardized definitions of response, exacerbation, remission, and relapse were initially proposed in 2003 and modified by the International Working Group for TTP in 2017. These definitions, which have been widely used in clinical practice and research, are based primarily on the platelet count and are benchmarked against the timing of discontinuation of therapeutic plasma exchange (TPE). They do not incorporate ADAMTS13 activity or the temporizing effects on the platelet count of caplacizumab, a novel anti–von Willebrand factor (VWF) nanobody. In light of these limitations, the IWG aimed to develop revised consensus outcome definitions that incorporate ADAMTS13 activity and the effects of anti-VWF therapy, by using an estimate-talk-estimate approach. The updated definitions distinguish clinical remission and clinical relapse (defined primarily by platelet count) from ADAMTS13 remission and ADAMTS13 relapse (defined by ADAMTS13 activity). The revised definitions of exacerbation and remission are benchmarked against not only the timing of discontinuation of TPE but also that of anti-VWF therapy. Retrospective validation of the revised definitions is described, although they have yet to be prospectively validated. Clinical implications of the updated outcome definitions are also discussed and an example of their application to clinical practice is provided to highlight their clinical relevance.

Abstract: Background: The post-HERCULES trial (NCT02878603) evaluated long-term safety and efficacy of caplacizumab in patients with acquired thrombotic thrombocytopenic purpura (aTTP; also known as immune-mediated TTP), and efficacy of repeated use of caplacizumab for aTTP recurrence. Methods: Patients who completed the HERCULES trial were invited to participate in the post-HERCULES study and attend twice-yearly visits for 3 years. In case of aTTP recurrence, patients could receive open-label (OL) caplacizumab with therapeutic plasma exchange (TPE) and immunosuppression (IST). Safety was assessed during the overall study period (intention-to-observe [ITO] population) and during recurrences. TTP-related events (recurrence, mortality, or major thromboembolic events) were assessed in the efficacy ITO population. The ITO population (n=104) included all enrolled patients, grouped by whether they received caplacizumab during HERCULES (randomized or switched to OL after exacerbation). The efficacy ITO population (n=78) included those without aTTP recurrence during HERCULES or prior to the beginning of post-HERCULES. The recurrence population (n=19) included patients with ≥1 recurrence during post-HERCULES; the repeat-use population (n=9) was a subset treated at least twice with caplacizumab (received caplacizumab in HERCULES or treated twice in post-HERCULES). Pharmacodynamics and immunogenicity were assessed in the ITO population. The study was conducted in accordance with the Declaration of Helsinki. Results: Of 104 patients enrolled in post-HERCULES, 75 were treated with caplacizumab along with TPE+IST during HERCULES (caplacizumab group) and 29 were treated with TPE+IST only (placebo group). During the overall post-HERCULES study period, incidence of adverse events (AEs) and serious AEs was similar between the groups. In the ITO population, recurrence occurred in 11/75 patients (15%) in the caplacizumab group and 8/29 patients (28%) in the placebo group. In the efficacy ITO population, TTP-related events occurred in 8% of patients (4/49) randomized to caplacizumab versus 38% (11/29) randomized to placebo (Table 1). Prior rituximab use during HERCULES was similar in both groups (21/49 patients [43%] randomized to caplacizumab and 12/29 [41%] randomized to placebo). Incidence of recurrence by prior rituximab use (with vs without) was 10% (2/21) versus 7% (2/28) among patients randomized to caplacizumab, and 17% (2/12) versus 35% (6/17) among patients randomized to placebo. Of 19 patients with ≥1 recurrence, 13 were treated with caplacizumab and 6/13 received concomitant rituximab. Recurrences were resolved (12/13) or resolving (1/13) for all patients treated with caplacizumab, including 9 patients with repeat caplacizumab use. One patient who did not receive caplacizumab in either HERCULES or post-HERCULES died as an outcome of recurrence. Safety profile of caplacizumab for treatment of recurrence was consistent with that observed in HERCULES (Table 2) . The most common treatment-emergent AEs (TEAEs) with caplacizumab during the first recurrence (n=13) were headache and constipation (n=3 each). In the repeat-use population (n=9), bleeding events were reported in 5/9 patients (56%) for the first recurrence; 2 patients had a serious treatment-related TEAE of genitourinary or gastrointestinal bleeding; 2 patients had treatment-emergent anti-drug antibodies (ADAs) positive in a functional neutralizing antibody assay. No apparent impact of treatment-emergent ADAs on RICO activity or change from baseline in von Willebrand factor antigen concentration was found. Conclusions: The long-term safety profile of patients exposed to caplacizumab together with TPE+IST was similar to those who received IST+TPE only, with no observed increases in recurrence of aTTP. Repeat caplacizumab use was efficacious, with no evidence of safety concerns or boosting of ADA response. Funding: This research was funded by Ablynx, a Sanofi company. Figure 1 Figure 1. Disclosures Scully: Shire: Research Funding; Novartis: Research Funding, Speakers Bureau; Takeda: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Octopharma: Speakers Bureau. de la Rubia: Ablynx/Sanofi: Consultancy; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen, Bristol Myers Squibb,: Honoraria, Speakers Bureau; Celgene, Takeda, Janssen, Sanofi: Honoraria; Celgene: Consultancy; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Sanofi: Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy; AbbVie: Consultancy; Bristol Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel Accommodations; GSK: Consultancy. Pavenski: Alexion: Honoraria, Research Funding; Bioverativ: Research Funding; Ablynx: Honoraria, Research Funding; Octapharma: Research Funding; Shire: Honoraria. Metjian: Momenta/Johnson & Johnson, Sanofi Aventis, Takeda: Research Funding; Ablynx/Sanofi: Consultancy; Sanofi Aventis, Takeda: Other: Advisory. Knoebl: Ablynx/Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Shire/Takeda: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; CSL Behring: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novo Nordisk: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Peyvandi: Roche: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Sobi: Consultancy, Honoraria. Cataland: Alexion: Consultancy, Research Funding; Ablynx/Sanofi: Consultancy, Research Funding; Takeda: Consultancy; Sanofi Genzyme: Consultancy. Coppo: Alexion Pharmaceuticals, Sanofi Aventis, Octapharma AG: Consultancy, Other: Advisory; Alexion Pharmaceuticals, Sandoz, Sanofi Aventis, Takeda: Other: Speakers Bureau; Ablynx/Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Shire: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Kremer Hovinga Strebel: Ablynx/Sanofi: Membership on an entity's Board of Directors or advisory committees, Other: Speaker at symposia; Shire: Membership on an entity's Board of Directors or advisory committees, Research Funding; CSL Behring: Other: Speaker at symposia; Roche: Other: Speaker at symposia; Siemens: Other: Speaker at symposia. Minkue Mi Edou: Sanofi: Current Employment, Other: May hold shares and/or stock options. de Passos Sousa: Sanofi: Current Employment, Other: May hold shares and/or stock options. Callewaert: Sanofi: Current Employment, Other: May hold shares and/or stock options. Gunawardena: Sanofi: Current Employment, Other: May hold shares and/or stock options. Lin: Sanofi: Current Employment, Other: May hold shares and/or stock options.