Induction of Sustained Remissions Associated with Immune Activation by Idelalisib in Patients with Follicular Lymphoma

Phosphatidylinositol-3-kinase (PI3K) inhibition has emerged as a therapeutic option against indolent lymphoma, including relapsed follicular lymphoma (FL). While inhibition of active signaling in the lymphoma cell represents the primary mode of action, PI3K inhibition also exerts immunomodulatory effects. Here we have analyzed 17 consecutive advanced treatment line FL patients treated with the delta-selective PI3K inhibitor idelalisib in a retrospective single-center observational study, with a specific focus on response and immune effects. Eleven patients achieved complete remission (CR) or partial remission (PR) with median response duration of 22 (11–88) months following a median idelalisib exposure of 15 (4–88) months. Disease response persisted in three patients for a median of 37 (21–63) months following cessation of idelalisib without another therapy being initiated. Autoimmune side effects occurred in eight of the eleven patients who responded, compared to none in six patients whose disease did not respond. In conclusion, a time-limited exposure to idelalisib may induce sustained remissions in a portion of patients with recurrent and/or refractory (r/r) FL, suggesting immunomodulatory effects of PI3K inhibition to be involved in the control of the disease.