Topical application of imiquimod induces alterations in peripheral blood lymphocytes in healthy individuals

The aim of this study was to determine whether imiquimod, a Toll-like receptor-7/8 agonist, in addition to its well-known topical action on the cutaneous immune response, might also induce alterations in the peripheral blood lymphocytes. A 62.5 mg quantity of imiquimod (5% cream) was applied topically under occlusion once daily every second day for 3 weeks to the skin of 10 healthy volunteers, age range 30-57 years. Ten sex- and age-matched healthy controls applied corresponding quantities of the vehicle under occlusion. Before, and one and 3 weeks after the start of treatment, peripheral blood lymphocyte subpopulations were measured by flow cytometry. Statistically significant alterations in the percentage or absolute numbers of peripheral blood lymphocyte subpopulations were found in the imiquimod-treated group compared with the control group. These alterations indicate for the first time that topical application of imiquimod induces alterations in peripheral blood lymphocyte subsets in healthy individuals, which may be of importance in the immunotherapy of neoplastic and infectious disorders and should be taken into careful consideration in patients who are treated with imiquimod.