Infliximab Induces Clonal Expansion of γδ-T Cells in Crohn's Disease: A Predictor of Lymphoma Risk?

Background: Concominant with the widespread use of combined immunotherapy in the management of Crohn's disease (CD), the incidence of hepato-splenic gamma-delta (gamma delta)-T cell lymphoma has increased sharply in CD patients. Malignant transformation of lymphocytes is believed to be a multistep process resulting in the selection of malignant gamma delta-T cell clones. We hypothesised that repeated infusion of anti-TNF-alpha agents may induce clonal selection and that concurrent treatment with immunomodulators further predisposes patients to gamma delta-T cell expansion. Methodology/Principal Findings: We investigated dynamic changes in the gamma delta-T cells of patient with CD following treatment with infliximab (Remicade (R); n = 20) or adalimumab (Humira (R); n = 26) using flow cytometry. In patients with a high gamma delta-T cell level, the gamma delta-T cells were assessed for clonality. Of these 46 CD patients, 35 had a gamma delta-T cells level (mean 1.6%) comparable to healthy individuals (mean 2.2%), and 11 CD patients (24%) exhibited an increased level of gamma delta-T cells (5-15%). In the 18 patients also receiving thiopurines or methotrexate, the average baseline gamma delta-T cell level was 4.4%. In three male CD patients with a high baseline value, the gamma delta-T cell population increased dramatically following infliximab therapy. A fourth male patient also on infliximab monotherapy presented with 20% gamma delta-T cells, which increased to 25% shortly after treatment and was 36% between infusions. Clonality studies revealed an oligoclonal gamma delta-T cell pattern with dominant gamma delta-T cell clones. In support of our clinical findings, in vitro experiments showed a dose-dependent proliferative effect of anti-TNF-alpha agents on gamma delta-T cells. Conclusion/Significance: CD patients treated with immunomodulators had constitutively high levels of gamma delta-T cells. Infliximab exacerbated clonal gamma delta-T cell expansion in vivo and induced gamma delta-T cell proliferation in vitro. Overall, young, male CD patients with high baseline gamma delta-T cell levels may be at an increased risk of developing malignant gamma delta-T cell lymphomas following treatment with anti-TNF-alpha agents.