Low‐dose anti‐CD20 veltuzumab given intravenously or subcutaneously is active in relapsed immune thrombocytopenia: a phase I study

Low doses of the humanized anti‐CD20 monoclonal antibody, veltuzumab, were evaluated in 41 patients with immune thrombocytopenia (ITP), including 9 with ITP ≤1 year duration previously treated with steroids and/or immunoglobulins, and 32 with ITP >1 year and additional prior therapies. They received two doses of 80–320 mg veltuzumab 2 weeks apart, initially by intravenous (IV) infusion (N = 7), or later by subcutaneous (SC) injections (N = 34), with only one Grade 3 infusion reaction and no other safety issues. Thirty‐eight response‐assessable patients had 21 (55%) objective responses (platelet count ≥30 × 10⁹/l and ≥2 × baseline), including 11 (29%) complete responses (CRs) (platelet count ≥100 × 10⁹/l). Responses (including CRs) occurred with both IV and SC administration, at all veltuzumab dose levels, and regardless of ITP duration. Responders with ITP ≤1 year had a longer median time to relapse (14·4 months) than those with ITP >1 year (5·8 months). Three patients have maintained a response for up to 4·3 years. SC injections resulted in delayed and lower peak serum levels of veltuzumab, but B‐cell depletion occurred after first administration even at the lowest doses. Eight patients, including 6 responders, developed anti‐veltuzumab antibodies following treatment (human anti‐veltuzumab antibody, 19·5%). Low‐dose SC veltuzumab appears convenient, well‐tolerated, and with promising clinical activity in relapsed ITP.( Clinicaltrials.gov identifier: NCT00547066.)