Background/Purpose: Rituximab treatment has been shown to be effective in non-thrombotic manifestations of APS and refractory catastrophic APS (CAPS). However, there are conflicting results regarding the change in aPL titers and limited data on the effect on thrombotic recurrence. The aim of this study was to evaluate the change in aPL titers over time, thrombotic recurrence and mortality rates, and treatment-related adverse events in APS patients treated with rituximab.

Methods: This retrospective single center study included 43 patients with thrombotic APS (11 with primary APS, 32 with SLE+APS) who received at least 1 cycle of rituximab (1000 mg on days 0 and 15). Baseline demographic, clinical, and serologic characteristics, aCL IgG/IgM and anti-β2-glycoprotein-I (aβ2GPI) IgG/IgM titers at 6 to 12 months of rituximab treatment were reviewed. The positivity threshold for aCL and aβ2GPI IgG/IgM was accepted as >40 GPL/MPL units or >99th percentile.

Results: The demographic, clinical, and serologic characteristics of the patients are summarized in Table 1. The median follow-up period after rituximab was 3.5 (IQR: 5.8) years. Whilst the majority of patients were treated with rituximab for thrombotic APS, there were also patients who were received rituximab for lupus nephritis or non-renal SLE (Table 1). After 6-12 months of rituximab treatment, aPL positives decreased: aCL IgG from 29 (67.4%) to 13 (30.2%), aCL IgM from 9 (20.9%) to 2 (4.7%), aβ2GPI IgG from 22 (51.2%) to 9 (20.9%), and aβ2GPI IgM from 9 (20.9%) to 2 (4.7%). There was also a statistically significant decrease in aPL antibody titers (Figure 1). Five patients developed new events after rituximab and details are shown in Table 2. Five patients died during follow-up. Causes of death were sepsis in 1, traumatic intracranial hemorrhage in 1, and lupus nephritis in 1. One patient died due to recurrence of pulmonary hemorrhage 38 months after rituximab and 1 patient was lost due to treatment-refractory CAPS at 6th month of rituximab. Bacterial infections were observed in 15 patients (4 required hospitalization and 1 lost after ICU admission), COVID infections in 7 (2 required hospitalization), herpes zoster in 3. Finally, 2 patients developed allergic reactions, none of which were considered anaphylaxis.

Conclusion: In patients with thrombotic APS, rituximab treatment may prevent thrombotic recurrence with a significant decrease in aPL titers. It is noteworthy that 4 of 5 patients who developed recurrence after rituximab were not receiving effective anticoagulant therapy. These data suggest that under consideration of infectious complications, rituximab may be an effective alternative in high-risk APS patients with recurrent thrombosis.

Table 1 Baseline demographic, clinical, and laboratory characteristics and rituximab indications of the cohort

Table 2 Details of aPL-related events after rituximab

Figure 1 Change in aPL titers 6-12 months after rituximab

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/rituximab-in-antiphospholipid-syndrome-apl-titer-decline-and-clinical-outcomes/