Rituximab increases peripheral natural killer cells in patients with rheumatoid arthritis

Objective The clinical response of rituximab (RTX) is related to the degree of B cell depletion, although other circulating lymphocytes may be affected. We investigated the changes in lymphocyte sub-populations in rheumatoid arthritis (RA) patients treated with RTX and their relationship with the therapeutic response, with attention to natural killer (NK) cells. Methods In fifty-one RA patients peripheral blood B and T lymphocytes and NK cells subtypes were counted by flow cytometry before and 3, 6 and 12 months after RTX administration. Patients were evaluated for disease activity with DAS28-CRP and EULAR response criteria at each visit. Results RTX significantly increased from baseline values CD56+3- cells (28 %, 19 % and 25 %; p<0.001, p=0.009 and p=0.004 respectively for month 3, 6 and 12) and CD56dimCD16+ cells (41%, 24% and 36%; p<0.001, p=0.001 and p<0.001 respectively for month 3, 6 and 12). CD56bri16- cells were unaffected by RTX treatment. The increase in both CD56+3- and CD56dimCD16+ cells was significantly greater in patients who were re-treated with another course of RTX at month 6 (p=0.046 and p=0.010 respectively). An inverse correlation between disease activity score and increase in NK cells was demonstrated. No significant changes were observed in CD3+, CD4+ and CD8+ cells during the whole observation period. Conclusion In RA patients, RTX treatment is associated with significant and persistent increase in CD56+3- and CD56dimCD16+ NK cells. A correlation with disease activity is probable, although the association with clinical response remains to be proved.