Rituximab for refractory manifestations of the antiphospholipid syndrome: a multicentre Israeli experience

The clinical manifestations of the antiphospholipid syndrome (APS) are heterogeneous and related to anti-phospholipid antibodies (aPL). There is some evidence that B cells are involved in the pathogenesis of this condition. Thus the ability of rituximab (RTX) to deplete B cells makes it an appealing potential therapy for refractory antiphospholipid syndrome (APS). Real world data on RTX treatment of APS are still lacking. This study was conducted to report outcomes of RTX administration in the treatment of different aspects of APS.

This is a retrospective case series study on APS patients from 3 medical centres in Israel who were treated with RTX during 2010-2019 for refractory manifestations of APS including diffuse alveolar haemorrhage, recurrent thrombosis, cytopenia, neurological and skin manifestations. Medical records were reviewed regarding the clinical indication for RTX treatment, concomitant medications, RTX protocol, aPL status and response to treatment. Outcomes were defined as complete response if full resolution of the "indicated manifestation" was achieved and maintained for at least 12 months, partial response or no response.

We identified 40 APS patients who were treated with RTX for refractory manifestations of this condition, of whom, 24 patients (60%) were female with a mean age of 40 years, and 31 patients (78%) were diagnosed with primary APS. A favourable response to RTX was documented in 32 patients (80%) including a complete response in 22 patients (55%). Response to RTX treatment was associated with a rituximab protocol of 375mg/m2 x 4 compared to a fixed dose of 1000 mg x2 (100% vs. 65%; p=0.01). Complete response was associated with a decrease in aPL titres within 4-6 months post treatment, whereas no significant change in aPL titres was observed in patients with partial or no response.

Consistent with previous small case series, we report a good therapeutic response to RTX in patients with difficult to treat manifestations of APS. In this cohort, treatment protocols were associated with outcomes. Although further studies are required to verify our observations, our data support a plausible role for B cell depletion in refractory APS.