Background Abatacept is a human soluble recombinant fusion protein composed of the extracellular domain of cytotoxic T-lymphocyte antigen 4 (CTLA4) and the Fc domain of human IgG1. It targets T cell activation by inhibiting the interaction of CD28 with CD80-CD86 molecules.
Objectives To monitor and predict the efficacy of Abatacept treatment in rheumatoid arthritis (RA) patients with failure to biotherapies.
Methods 18 patients with failure to TNFa inhibitors or anti-CD20 mAb, were selected for treatment with Abatacept. DAS-28, ESR, and pain/joint scores were used to monitor the clinical response. Blood samples were collected at day 0 and at 1, 3, 6 and 12 months, using Paxgene tubes for mRNA analysis. PBMC were prepared by Ficoll gradient density. Samples were frozen, and thawed for longitudinal studies, either at 1 year treatment in responders, or before, if Abatacept had been stopped due to failure. mRNA expression was analyzed by qRT-PCR, using cyclophilin B (CPB) as a house keeping gene. Functional assays were performed using PHA as stimulus. Results were longitudinally analyzed and compared with those of healthy blood donor controls (HC).
Results Among the 18 patients included in the study, 50% remained on Abatacept at 1 year, whereas Abatacept was stopped at 3 to 6 months in the other 50% patients, due to clinical failure. Functional assays were performed in 6 patients (3 responders and 3 non responders). In the responders, T cell response to PHA was observed either from day 0, or upon time of treatment. In the 3 non responder patients, PHA did not induce any significant response at any time, unless anti-CD28 mAb was added. This led us to focus on Th-1, Th-2, Treg, Th-17, but also CD28, and CTLA-4 gene expression. Longitudinal qRT-PCR analysis of whole blood samples did not show any significant difference upon time, i.e: from day 0 to year 1, of Th- or Treg gene expression, in responders. However, a significant increase upon time of the CD3e/CPB mRNA ratio (p=0.0430), together with a statistical decrease in CD28/CD3e and CTLA-4/CD3e ratios (p=0.0399, 0.0004, respectively) was observed in responders, but not non responders. This resulted in a marked increase of the CD28/CTLA4 ratio (p=0.0448). Of particular interest is the analysis of these ratios at 1, 3 and 6 months, which demonstrated in responders, but not non responders, a significant decrease in the mRNA ratio of CTLA4/CD3e, in association with an increase of CD28/CTLA-4 (p=0.022, and 0.0098, respectively). Finally, the mRNA ratios at day 0 of CD28/CD3e and CTLA-4/CD3e were found to be significantly increased in RA patients, as compared with HC (p=0.0040, and 0.0003, respectively), supporting thus an abnormal regulation of these genes in RA.
Conclusions Response to Abatacept was correlated with an increase at one year of the CD3/CPB, and a decrease of CD28/CD3e and CTLA-4/CD3e mRNA ratios. This resulted in an increase of the CD28/CTLA-4 mRNA ratios, which is likely to improve the ability of T cells to respond to Ag upon time, as opposed with the well known inhibitory effect of Abatacept on short-term T cell activation.Our results also showed that CTLA-4/CD3e and CD28/CTLA-4 mRNA ratios were either down-or up-regulated as soon as 3 months, respectively, which designates them as putative predictive markers of the response to Abatacept.
Disclosure of Interest A. Eljaafari: None Declared, M.-L. Tartelin: None Declared, H. Aissaoui: None Declared, P. Miossec Grant/Research support from: Bristol MyersSquibb support
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