E Becerra

Total serum immunoglobulin levels in patients with RA after multiple B-cell depletion cycles based on rituximab: relationship with B-cell kinetics

OBJECTIVE To investigate whether the incidence of secondary hypogammaglobulinaemia in patients with RA following rituximab was related to patterns of B-cell return and relapse. METHODS CD19(+) B-cell and serum immunoglobulin (sIg) determinations were done every 2 or 3 months in 137 consecutive patients treated with one or more courses of rituximab-based B-cell depletion therapy. The pattern of B-cell return, either concordant or discordant with relapse, was also recorded. RESULTS There were 119 responders. Before treatment, three patients had low IgM and four had low IgG. After the first cycle, low IgM or IgG was present in 9.2% (11/119) and 11.8% (14/119) of the patients, respectively, increasing to 38.8% (8/18) and 22.2% (4/18) after five cycles. The mean percent maximum sIg decrease/cycle was relatively constant. The CD19(+) B-cell count at repopulation was not correlated with immunoglobulin (Ig) levels after each cycle. Patients discordant for B-cell return and relapse developed significantly lower serum IgM and more low IgM episodes than concordant patients (P < 0.05). CONCLUSION Patients with lower baseline sIg levels tended to develop persistent IgM and IgG hypogammaglobulinaemia, resulting from an accumulation of incremental decreases after repeat cycles. This was not due to lower numbers of returning B cells in those developing low sIgs. The association of low IgM in patients with a discordant pattern of relapse suggests that underlying defects in B cells relating to survival and maturation into Ig-secreting cells, as well as attrition of IgG plasma cells may be contributing to low sIg levels in some patients.

Effect of rituximab on B cell phenotype and serum B cell-activating factor levels in patients with thrombotic thrombocytopenic purpura.

Autoantibodies inhibiting the activity of the metalloproteinase, ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), underlie the pathogenesis of thrombotic thrombocytopenic purpura (TTP). Rituximab (RTX) combined with plasma‐exchange (PEX) is an effective treatment in TTP. Patients can remain in remission for extended periods following PEX/RTX, and this is associated with continuing reduction in antibodies to ADAMTS13. Factors controlling B cell differentiation to autoantibody production, including stimulation through the B cell receptor and interactions with the B cell‐activating factor (BAFF), may thus impact length of remission. In this cross‐sectional study, we measured naive and memory B cell phenotypes [using CD19/immunoglobulin (Ig)D/CD27] following PEX/RTX treatment in TTP patients at B cell return (n = 6) and in 12 patients in remission 10–68 months post‐RTX. We also investigated relationships among serum BAFF, soluble CD23 (sCD23– a surrogate measure of acquiring B memory (CD27+) phenotype) and BAFF receptor (BAFF‐R) expression. At B cell return after PEX/RTX, naive B cells predominated and BAFF‐R expression was reduced compared to healthy controls (P < 0·001). In the remission group, despite numbers of CD19+ B cells within normal limits in most patients, the percentage and absolute numbers of pre‐switch and memory B cells remained low, with sCD23 levels at the lower end of the normal range. BAFF levels were correlated inversely with BAFF‐R expression and time after therapy. In conclusion, the long‐term effects of RTX therapy in patients with TTP included slow regeneration of memory B cell subsets and persistently reduced BAFF‐R expression across all B cell subpopulations. This may reflect the delay in selection and differentiation of potentially autoreactive (ADAMTS13‐specific) B cells, resulting in relatively long periods of low disease activity after therapy.

B cell phenotypes in patients with rheumatoid arthritis relapsing after Rituximab: Expression of B cell activating factor-binding receptors on B cell subsets

Serum levels of B cell‐activating factor (BAFF) rise following rituximab (RTX) therapy in patients with rheumatoid arthritis (RA). Initiation of naive B cell return to the periphery and autoreactive B cell expansion leading to relapse after RTX may therefore be linked to interactions between BAFF and BAFF‐binding receptors (BBR). Relationships between serum BAFF and BBR expression [(BAFFR, calcium signal modulating cyclophilic ligand interactor (TACI) and B cell maturation antigen (BCMA)] were determined on B cell subsets, defined using immunoglobulin (Ig)D/CD38. Twenty pre‐RTX and 18 RA patients relapsing after B cell depletion were included. Results were analysed with respect to timing of relapse up to 7 months after peripheral B cell return (≥ 5 B cells/μl) and to serum BAFF levels. After B cell return, B cell populations from relapsing patients had significantly lower BAFFR+ expression compared to HC and pre‐RTX patients. The percentage of BAFFR+ B cells increased with time after B cell return and was correlated inversely with serum BAFF levels. BAFFR expression remained reduced. The percentage of TACI+ memory B cells were lower in RA patients after RTX compared with healthy controls (HC). BCMA expression (% and expression) did not differ between patients and HC. Relapse following B cell return appeared largely independent of the percentage of BAFFR+ or percentage of BCMA+ B cells or serum BAFF levels. The lower percentage of TACI+ memory B cells may reduce inhibitory signalling for B cell differentiation. In patients relapsing at longer periods after B cell return, recovery of the B cell pool was more complete, suggesting that selection or expansion of autoreactive B cells may be needed to precipitate relapse.

FRI0042 BAFF-R expression in naÏve CD5+IGM+ B cells in rheumatoid arthritis patients repopulating after rituximab

Background Serum levels of B cell activating factor (BAFF) rise following Rituximab (RTX) therapy in patients with Rheumatoid arthritis (RA). CD5+IgM+B cells are present within transitional and naïve B cell subsets and their increased production or accumulation is associated with some autoimmune diseases. Previous studies have shown that BAFF does not enhance their survival compared with CD5- naïve B cells, suggesting that signalling pathways are important in promoting their survival. Objectives To determine serum BAFF levels and BAFF-receptor (BAFF-R) expression in CD5+IgM+B cells in healthy controls (HC), RTX-naïve RA patients (pre-RTX), and relapsing at different time points after peripheral B cell repopulation post-RTX treatment, divided into 2 groups: early relapsers (0–3 months post-B cell return) and later relapsers (>4 months post-B cell return). Methods Immunophenotyping of peripheral blood mononuclear cells was used to determine %CD5+IgM+B cells and BAFF-R (% and expression, mean fluorescence intensity (MFI)) in 5 HC, 13 pre-RTX and 12 post-RTX RA patients. Results were analyzed with respect to timing of relapse after peripheral B cell return (≥5 B cells/μL) and serum BAFF levels. Results %CD5+IgM+B cells, but not absolute numbers, were significantly higher in post-RTX early relapsers compared to HC (p<0.01), pre-RTX patients (p<0.001) and post-RTX later relapsers (p<0.01). There was a strong inverse correlation between %CD5+IgM+B cells and time after B cell return (r2=0.88, p<0.0001). BAFF-R+ expression was significantly lower in both post-RTX groups compared to HC and pre-RTX patients; early relapsers showed the lowest % and MFI BAFF-R+ expression, compared with later relapsers (p<0.01). BAFF-R+ expression increased with time after B cell return, both % (r2=0.47, p<0.002) and MFI (r2=0.76, p<0.0004). BAFF levels were significantly higher in both post-RTX groups compared to HC and pre-RTX patients, with the highest BAFF levels in early relapsers (p<0.05 compared to later relapsers). There was a significant inverse correlation between BAFF levels and % (r2=0.51, p<0.01) and MFI (r2=0.4, p<0.05) BAFF-R+ expression.Table 1 %CD5+IgM+ (median;range) %BAFF-R+ve BAFF-R+ve (MFI) BAFF levels (ng/ml) (median;range) HC 18.5 (9.1–26.8) 98.7 (97.9–99.5) 62.5 (50.5–82.4) 1.1 (0.9–1.2) Pre-RTX 5.4 (1.9–21.4) 97.3 (85.8–100) 58 (34.2–139) 1.4 (0.9–1.7) Post-RTX early relapse 44.4 (39.6–55.8) **###

SAT0055 B cell activating factor receptor (BAFF-R) expression after rituximab: Comparison of patients with rheumatoid arthritis and thrombotic thrombocytopenic PURPURA

60.6 (12.9–71.2)**###

Long-term safety of rituximab in patients with rheumatoid arthritis

15.6 (11.8–17.5)**###

Patterns of Relapse in the Rheumatoid Arthritis Cohort Treated with Rituximab at University College London

2.4 (2–6.4)**###