A multimorphic variant in ThPOK causes an inborn error of immunity with T cell defects and fibrosis [fibroblasts]

ThPOK is a transcription factor which acts as a master regulator of CD4+ T cell lineage commitment. We report the first human disease caused by genetic alteration in ThPOK, specifically, a damaging heterozygous de novo variant in ThPOK (NM_001256455.2: c.1080A>C, p.K360N). This patient exhibited the unusual constellation of persistent CD4+ T cell deficiency, allergy, interstitial lung disease, corneal vascularization and scarring, developmental delay, and growth failure. The ThPOKK360N variant displayed abnormal multimorphic activity, interfering with ThPOKWT (antimorph), failing to bind wild-type ThPOK consensus sequences (amorph), and showing novel DNA-binding specificity (neomorph). Single-cell RNA sequencing revealed defects in CD4+ and CD8+ T cell maturation and activation (hypomorph). Recapitulated in lentivirally transduced healthy control T cells and fibroblasts, transcriptomic analysis showed ThPOKK360N-transduced T cells had impaired TCR activation, and ThPOKK360N-transduced fibroblasts with increased pro-fibrotic gene expression. This novel human disease confirms ThPOK's role in CD4+ T cell development but also uncovers novel roles in TCR activation and regulation of fibrotic pathways in fibroblasts. Fibroblasts were grown from patient and healthy control lung tissue biopsy before lenti virus transduction and RNA was studied via RNA seq.