Abstract
AbstractActivated PI3K delta syndrome 1 (APDS1) is caused by a heterozygous germline gain-of-function (GOF) variants inPIK3CDwhich encodes the p110δ catalytic subunit of phosphoinositide 3-kinase (PI3K). APDS1 patients display a broad range of clinical manifestations and perturbations in cellular phenotype. One of the most striking features is the dysregulation of the T cell compartment characterised by an increase in memory T cells, including Tfh cells, and a concomitant decrease in naïve T cells. We have previously shown that many of these changes in T cell populations were T cell extrinsic and were also induced in WT T cells that developed in the presence of PI3K GOF cells. Here we dissected the drivers of dysregulated T cell activation using a mouse model of APDS1. This revealed PI3K GOF macrophages and DCs made little contribution to the aberrant T cell activation. Instead, the loss of naïve T cells was mostly driven extrinsically by PI3K GOF T cells, while the increase in Tfh cells was mediated by dysregulated PI3K GOF B cells. Surprisingly, despite previous reports of increased PI3K driving dysregulated inflammatory Tregs, we saw no evidence forPik3cdGOF Tregs acquiring an inflammatory phenotype and driving T cell activation. These studies provide new insights into the clinical phenotype of patients with APDS1 and new understanding of the role of PI3K in immune cells.
Publisher
Cold Spring Harbor Laboratory