Serum levels of granzyme B decrease in patients with rheumatoid arthritis responding to abatacept

A possible role of granzyme B (GZMB) in the pathogenesis of joint erosions in rheumatoid arthritis (RA) has been suggested. Since CD28neg T-cells may be an important source of GZMB, and we have previously shown that co-stimulation blockade by abatacept can prevent the generation of the CD28neg T-cell populations, we evaluated the effect of abatacept therapy on GZMB serum levels in patients with RA.

The serum levels of GZMB were evaluated by an indirect solid-phase enzyme immunoassay before the start of treatment with abatacept (T0) in 53 patients with RA and after 6 months of therapy (T6) in 25 patients.

At T0, GZMB serum levels were correlated with disease activity measured by DAS28-CRP (p=0.0022) and percentages of circulating CD4+CD28neg and CD8+CD28neg T-cells (p=0.007; p=0.031). The levels of GZMB in 18 patients with a moderate or good EULAR clinical response to ABA significantly decreased from T0 to T6 (p=0.023), whereas no variation was observed in 7 non responders. The variation of GZMB levels was directly correlated with that of DAS28-PCR (p=0.040), but not with those of circulating CD28-neg T-cell subsets.

Costimulation blockade by ABA can decrease the serum levels of GZMB in RA patients responding to the treatment, suggesting that this might be one of the mechanism by which abatacept can prevent radiographic erosions. However, the lack of correlation of such decrease with the numbers of circulating CD28-neg T cells suggests that these cells probably are not the main source of serum GZMB.