Depletion of T and B cells in lymphoid tissues of mice induced by oclacitinib, a Janus kinase inhibitor.

The main purpose of the study was to determine the safety of oclacitinib (OCL), a Janus kinase inhibitor, with respect of its effect on CD4 + and CD8 + T cells as well as B cells in the lymphoid tissue. The mice were treated orally with OCL at a dose of 2.7 mg/kg for 14 days and peripheral blood, head and neck lymph nodes (HNLNs), mediastinal lymph nodes (MLNs) and spleen were collected. The study found that OCL induced depletion of CD4 + T cells in the HNLNs and MLNs, while it did not affect the absolute count of CD8 + T cells in these tissues. Also OCL caused a loss of B cells in the HNLNs, although not in the MLNs. Moreover, OCL depleted B cells in the peripheral blood, but did not affect the absolute count of CD4 + and CD8 + T cells. Thus, it can be concluded that OCL may induce a depletive effect on CD4 + and CD8 + T cells as well as B cells in the lymphoid tissue. This effect should be seen as an unfavorable one, especially in patients with infections. Therefore, a clinical implication is that in such patients, the benefit/risk ratio should be thoroughly considered by clinicians. Moreover, OCL reduced the absolute count of eosinophils, basophils, neutrophils and monocytes. However, it is uncertain whether this effect should be considered to be of clinical importance because the levels of these cells were within the physiological range. It is possible that the depletive effect of OCL toward T and B cells, as well as eosinophils and basophils may contribute to the beneficial effects of the drug in the treatment of skin allergic diseases.