Loss of PI3Kδ Activity Drives Autoimmune Colitis by Impairing Extrathymic Treg Differentiation

Area of Science:

• Immunology
• Gastroenterology
• Pharmacology

Background:

• Peripherally derived regulatory T cells (pTregs) are vital for intestinal immune homeostasis.
• Inactivation of phosphoinositide-3-kinase delta (PI3Kδ), often due to cancer drug idelalisib, can cause gut inflammation and diarrhea.
• While PI3Kδ inactivation impacts Treg function, the tissue-specific mechanisms behind gut immune tolerance breakdown remain unclear.

Purpose of the Study:

• To investigate the specific role of PI3Kδ in maintaining gut immune tolerance.
• To elucidate the molecular basis for tissue-restricted immune tolerance breakdown upon PI3Kδ loss.
• To understand the mechanism of colitis development in PI3Kδ-deficient mice.

Main Methods:

• Systemic PI3Kδ inactivation in a mouse model.
• Analysis of regulatory T cell (Treg) populations in the colon.
• In vitro and in vivo studies of extrathymic Treg induction from naive CD4+ T cells.
• Assessment of Treg phenotype and function.

Main Results:

• Mice lacking PI3Kδ activity do not exhibit a general Treg immunosuppression defect.
• A specific failure to develop Helios-negative pTregs in the colon was observed.
• PI3Kδ inactivation reduced extrathymic Treg induction and dysregulated tissue-resident Treg phenotypes.
• These findings indicate PI3Kδ is essential for pTreg differentiation in the gut.

Conclusions:

• PI3Kδ plays a nonredundant role in the differentiation of pTregs within the colon.
• PI3Kδ-dependent pTreg development is critical for maintaining tolerance to gut commensal antigens.
• Understanding this pathway could inform strategies to prevent PI3Kδ inhibitor-induced colitis.