Immune system-mediated tumor killing has revolutionized anti-tumor therapies,providing long-term and durable responses in some patients.The phosphoinositide 3-kinase (PI3K) pathway controls multiple biological processes and is frequently dysregulated in malignancies.Enormous efforts have been made to develop inhibitors against class Ⅰ PI3K.Notably,with the increasing understanding of PI3K,it has been widely accepted that PI3K inhibition not only restrains tumor progression,but also reshapes the immunosuppressive tumor microenvironment.In this review,we focus on the pivotal roles of class Ⅰ PI3Ks in adaptive and innate immune cells,as well as other stromal components.We discuss the modulation by PI3K inhibitors of the tumor-supportive microenvironment,including eliminating the regulatory immune cells,restoring cytotoxic cells or regulating angiogenesis.The potential combinations of PI3K inhibitors with other therapies to enhance the anti-tumor immunity are also described.