Data about efficacy and safety of daratumumab in iTTP refractory or intolerant to standard immunosuppressive treatments are scarce. Therefore, the investigators aim at collecting evidence on a larger number of patients through a collaborative, international study.

iTTP in an autoimmune disease caused by autoantibodies directed against the metalloproteinase ADAMTS13. Rituximab is the standard immune suppressive treatment suggested from international guidelines. However, 10-15% of patients do not achieve a sustained ADAMTS13 remission with rituximab, and a significant portion of responders eventually need re-treatment after 12 months or less. Other therapeutic options are scarce and based on old immunosuppressive agents or splenectomy, all burdened by relevant toxicity and lack of solid efficacy data. Recently, targeting CD20-negative long-lived plasma cells appears to be a promising strategy in refractory iTTP. The anti-CD38 monoclonal antibody daratumumab has been employed in selected iTTP patients with good results. However, evidence stems only from isolated case reports.

The DarTTP study aims to collect evidence on a larger number of patients about the efficacy and safety of daratumumab in iTTP subjects who are refractory or intolerant to previous immunosuppressive treatments. The primary endpoint is the proportion of patients with ADAMTS13 activity levels above 20% of normal at 6 months from the first daratumumab administration.

Inclusion Criteria:

• patients with a confirmed diagnosis of iTTP (i.e., ADAMTS13 activity <10% with anti-ADAMTS13 antibodies detected);
• aged ≥ 18 years;
• male and female patients;
• treated with daratumumab for iTTP.

Exclusion Criteria:

• patients unwilling or unable to provide their informed consent;
• follow-up < 6 months after daratumumab administration.

The study includes adult iTTP patients who were treated with daratumumab in the acute phase of disease (i.e., with plasma exchanges and/or caplacizumab ongoing) or during remission (i.e., due to ADAMTS13 relapse or ADAMTS13 activity plasma levels persistently <20%) from January 2010 to 6 months before the time of data collection. It includes iTTP patients receiving daratumumab either for refractory disease or in ADAMTS13 remission but intolerant to other immune suppressive agents.