T cell phenotyping of a mouse model of Activated PI3Kdelta syndrome

Activated PI3Kdelta Syndrome (APDS) is immunodeficiency caused by a heterozygous gain-of-function mutation (E1021K) in the PIK3CD gene, encoding for the p110delta catalytic subunit of phosphoinositide 3-kinase (PI3K). APDS patients are lymphopenic, suffer from sinopulmonary infections and from increased susceptibility to bacterial and herpes group virus infections. Following T cell receptor (TCR) stimulation, T cells from these patients undergo increased activation induced cell death, which can be reversed by selective PI3Kdelta inhibitors. I used a new conditional knock-in mouse (T-p110delta E1020K) in order to investigate the effect of hyperactive p110delta on T cell function. Hyperactivation of p110delta led to increased PIP3 and pAKT levels following TCR stimulation that was reduced using a selective p110delta inhibitor. Following in vitro TCR stimulation, T cells proliferated normally but showed increased apoptosis that was reversed by a p110delta specific inhibitor. Despite enhanced apoptosis, CD8+ T cells displayed enhanced activation that was associated with increased levels of cytokines and granzyme B. CD4+ T cells with hyperactive p110delta produced increased Th1, Th2, Th17 and Tfh cytokines but showed reduced Treg differentiation in vitro. Conditional T-p110delta E1020K mice have reduced Tregs in the thymus but increased peripheral Tregs. These mice also have increased numbers of T follicular helper cells and germinal centre (GC) B cells upon immunisation with a T cell dependent antigen (NP-KLH). Reduced antigen specific IgG1+ cells within GC B cells was detected in mice harbouring hyperactive p110delta mutation in B cells, implying that the antibody deficiencies observed in APDS patients is due to an intrinsic defect within B cells rather than limited help from T cells. T-p110delta E1020K mice mounted normal primary responses to acute infections .However adoptive transfer of ovalbumin-specific T cell receptor transgenic CD8 T cells (OT1) revealed an intrinsic defect in the primary expansion of CD8+ T cells with hyperactive p110delta. This defect in primary expansion was found to be rescued in the presence of wild type OT1 cells. Following infection with acute pathogens, CD8+ T cells with hyperactive p110delta displayed normal to increased effector function with phenotypically reduced memory cells as indicated by reduced memory precursor effectors cells (MPECs). In contrast, following chronic infection, T-p110delta E1020K displayed increased signs of T cell exhaustion that is also characteristic of APDS patients as they suffer from chronic herpes virus infections. This set of work therefore shows that the mouse model recapitulates key aspects of APDS patients and give insights into the role of p110delta signaling in different T cell subsets influenced by hyperactive p110delta activity. Further, in depth analysis of proteomics and gene array data of in vitro stimulated T cells generated during this study, can provide a better understanding of the mechanisms behind the T cell phenotype observed