Anti-IL-6 receptor antibody (tocilizumab): a B cell targeting therapy

IL-6 mediated inflammation is induced by binding to IL-6 receptor (IL-6R) or IL-6/IL-6R complex binding gp130. Tocilizumab, a recombinant humanised monoclonal antibody that acts as IL-6R antagonist has been recently introduced for the treatment of rheumatoid arthritis (RA).

To evaluate whether tocilizumab therapy may induce B cells to undergo phenotypic changes compatible with regulatory function.

B cells from treated RA patients were isolated before and after 3 months of treatment with tocilizumab and were stained for the expression of intracellular TGF-β, IL-10, membrane CD69, and MHCII. These markers were assessed in CD25(high) B cells considered to belong to a regulatory/suppressive subset of B cells. All markers were expressed in mean flow cytometry intensity (MFI), with results given in mean ± SEM. Data was compared before and after tocilizumab treatment.

Clinical improvement was noted three months following the initiation of tocilizumab, namely: DAS improvement from 6.8 ± 0.3 at baseline to 3.1 ± 0.4, p<0.002, and ESR decrease from 44.4 ± 8.6 at baseline to 7.4 ± 2.3, p<0.006. This clinical benefit was found to occur in association with the expansion of a B cell subset with regulatory properties namely: the expression of intracellular TGF-β in CD25-high B cells was significantly increased (from 5.2 ± 2.3 at baseline to 8.1 ± 2.8; p<0.02); In addition, the expression of MHC-II and of CD69 on B cells were significantly reduced (from 9.1 ± 2.2 at baseline to 4.2 ± 0.4; p<0.04), and (from 7.6 ± 2.4 at baseline to 2.7 ± 0.7; p<0.03) respectively.

The present finding of a shift in B cell properties following tocilizumab treatment, namely the increase in TGF-β expression and the alteration in the activation status (CD69 expression) and APC properties (MHC-II expression) in CD25(high) B cells, suggests that the induction/expansion of B regulatory cells may be one of the mechanisms by which tocilizumab may possibly produce its beneficial clinical effects.