Repopulation of blood lymphocyte sub‐populations in rheumatoid arthritis patients treated with the depleting humanized monoclonal antibody, CAMPATH‐1H

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Abstract
Patients with severe rheumatoid arthritis who had failed treatment with conventional therapies were treated with a course of five or 10 daily intravenous infusions of CAMPATH-1H, a humanized antibody against the CD52 antigen, resulting in profound depletion of peripheral blood mononuclear cells. During the subsequent 18 months, lymphocytes were analysed for subpopulations by fluorescence-activated cell sorter (FAGS) and for proliferation in response to polyclonal T-cell stimulation with anti-CD3 or staphylococcal enterotoxin B (SEE). Treatment resulted in almost complete depletion of lymphocytes from the blood followed by gradual repopulation. CD16(+) natural killer (NK) cells and CD14(+) monocytes returned to pretreatment levels within 1-2 months. CD19(+) B cells returned to within 50% of pre-treatment levels by day 66 and to within normal range by day 150, whereas CD8(+) T cells recovered to 50% of pretreatment levels by day 66, but did not show any further increase during the rest of the study period. The most profound effects were on the CD4(+) T lymphocyte sub-population, as the mean CD4(+) count did not increase above 20% of pre-treatment level at any time during the study period (550 days), at all the doses tested. The T cells which initially repopulated the blood 1-2 months after treatment, nearly all expressed the activation markers human leucocyte antigen (HLA)-DR and CD45RO, although the percentage of T cells expressing these molecules gradually declined to normal levels over time. Proliferative responses to polyclonal T-cell stimulation (anti-CD3 and SEE) were also significantly reduced in the first few months after treatment, but recovered to pre-treatment levels by day 250. The relationship between these observations and the clinical response is discussed.