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 × 10(9) /l and ≥2 × baseline), including 11 (29%) complete responses (CRs) (platelet count ≥100 × 10(9) /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.).