PI3Kδ

PI3Kδ is a class I PI3K isoform that generates PIP3, a second messenger used by cell-surface receptors to control immune-cell movement, growth, survival, and differentiation^[1]. Mechanistically, PI3Kδ acts in adaptive immunity, and both loss-of-function and gain-of-function defects in this pathway cause primary immunodeficiency, showing that PI3Kδ activity requires precise dynamic regulation^[2]. In B-lineage models, p110δ and p110α are essential for pre-B-cell receptor signaling and B-cell development, while p110α, but not p110β, can compensate for p110δ loss during early bone-marrow B-cell development^[3]. Compared with related isoforms, PI3Kα and PI3Kβ are relatively ubiquitous, whereas PI3Kδ is mostly confined to myeloid and lymphoid lineages, making high PI3Kδ expression a characteristic of immune cells^[1]. In disease and experimental applications, idelalisib is an orally active selective PI3Kδ inhibitor with antitumor activity in previously treated indolent non-Hodgkin lymphoma and relapsed chronic lymphocytic leukemia^[4][5]. Therefore, PI3Kδ supports research designs focused on immune signaling, B-cell receptor biology, primary immunodeficiency, inflammatory models, and selective PI3Kδ inhibitor pharmacology^{[1][2][3][4][5]}.