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THU0043 The Alternative CD20 Transcript Variant is not Expressed in B Cells and Synovial Tissue from Patients with Rheumatoid Arthritis
  1. C. Gamonet1,
  2. M. Deschamps1,
  3. B. Gaugler1,
  4. P. Saas1,
  5. I. Auger2,
  6. C. Ferrand1,
  7. E. Toussirot3,
  8. CIC BT 506
  1. 1INSERM UMR1098, Etablissement Français du Sang / Université de Franche Comté, Besançon
  2. 2INSERM UMR1097, Université Aix Marseille, Marseille
  3. 3Clinical Investigation Center Biotherapy, University Hospital, Besançon, France

Abstract

Background determining predictive factors for response to biologics may help to select appropriate treatment in patients with RA. Rituximab (RTX) is a chimeric monoclonal antibody directed against the membrane CD20 protein present on B cells. Predictive factors for good response to RTX therapy in RA have been identified and included the presence of rheumatoid factors and anti -CCP antibodies. A spliced mRNA transcript of CD20 (ΔCD20) has been observed in B cell lines from patients with lymphoma and leukaemia (1). This transcript is coding for a non anchored membrane protein and its expression is associated with resistance to RTX in patients with haematological malignancies.

Objectives to determine whether ΔCD20 is expressed by circulating B cells and synovial tissue from patients with RA and whether it could be a factor for non response to RTX therapy in RA.

Methods 23 RA patients (17 F, age (mean ± SEM): 60.1 ± 2.7 years; disease duration: 13.3 ± 1.7 years, positive rheumatoid factors: 19/23; positive anti- CCP antibodies: 19/23) and 20 healthy controls (HC) (15 F, age: 59.6 ± 2.5 years) were evaluated. Patients were under DMARDs, low corticosteroids (< 10 mg/j) or anti TNFa agents, but none received or had received RTX. Five patients with RA requiring treatment with RTX were also evaluated prior to the first RTX infusion and during a one year follow- up study. CD20 mRNA expression study was performed using RT-PCR assay allowing first to discriminate full length CD20 (membrane CD20) from ΔCD20 transcripts. A more sensitive RT-PCR assay, using a specific primer spanning the splice fusion area was then used to detect specifically only the ΔCD20 transcript. This analysis was performed on peripheral blood B cells from patients with RA and HC and synovial tissue from RA patients obtained during surgery.

Results RA patients had mild active disease (DAS28 score: 3.3 ± 0.3; CRP levels: 6.8 ± 1.9 mg/l). Number of circulating B cells per µl was not different between RA patients and controls (mean ± SEM, range: 184± 22, 18-437 vs 211± 27, 63-408, respectively). Among all the 23 RA samples, although full length CD20 expression was always detected, we were unable to detect ΔCD20, even with the more sensitive RT-PCR assay permitting to identify the spliced transcript form. Among the 5 patients who received RTX, 4 well responded to the treatment. -Both responders and non responder patients did not express ΔCD20 before RTX administration and during the follow-up study. ΔCD20 was also not detected in synovial tissue samples from 5 patients with RA.

Conclusions The present study showed that, on the contrary of leukemic or lymphoma B cells, RA B-cells and synovial tissue from RA patients do not express ΔCD20, suggesting that this transcript may be a molecular marker of malignancies rather than a factor predictive to RTX responses in auto-immune diseases like RA. We are currently examining whether B cell stimulation may help to evidence ΔCD20 expression in RA B-cells

References

  • Henry C et al., Blood, 2010;115:2420-9

Disclosure of Interest None Declared

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