Elevated CD38 Expression and a Concomitant Reduction in NAD+ Levels Underlie CD8+ T Cell Dysfunction in STAT1 GOF

Background and Aims STAT1 gain-of-function (GOF) patients experience severe fungal and viral infections and autoimmunity. CD8+ T cells are key mediators of the adaptive immune response by combating infections. CD8+ T cell dysfunction, in turn, contributes to autoimmune pathogenesis and chronic viral infections. We therefore hypothesized that CD8+ T cell dysfunction contributes to STAT1 GOF pathophysiology and sought to identify the underlying mechanisms. Methods We collected high-dimensional immunophenotyping and cellular indexing of transcriptomes and epitopes sequencing (CITE-Seq) data on 24 STAT1 GOF patients and age-matched healthy control PBMCs. In addition, T cell function and metabolic data were collected on untreated and in vitro-treated patient and healthy control PBMCs. Results In patients with STAT1 GOF, CD8+ T cell dysfunction was best defined as reduced production of IFN-γ, TNF-α, and IL-2 upon αCD3/αCD28 stimulation. High-dimensional immunophenotyping identified CD38 as a significantly upregulated activation marker on CD8+ T cells and most immune cell populations, from patients with STAT1 GOF. CD38 expression could be further induced by αCD3/αCD28 stimulation and was correlated with the levels of total STAT1 protein. CD38 is an ectoenzyme that consumes nicotinamide adenine dinucleotide (NAD+), and low NAD+ levels have been linked to immune dysregulation. Our CITE-Seq data confirmed that STAT1 GOF CD8+ T cells have transcriptional evidence of broadly altered NAD+ metabolism, with both NAD-consuming enzymes such as CD38 and PARP9 as well as NAD+ salvage pathway proteins such as NAMPT being increased. Using an NAD+ enzymatic assay, we confirmed that NAD+ levels were indeed reduced in STAT1 GOF CD8+ T cells while the NADH levels were comparable. By increasing NAD+ levels in patient PBMCs, it was possible to partially normalize CD8+ T cell function in CD8+ T cells from patients with STAT1 GOF. Finally, STAT1 GOF patients receiving JAK inhibitors show reduced CD38 RNA and protein expression and reduced PARP9 and NAMPT transcription. Conclusion Elevated CD38 expression and reduced NAD+ levels contribute to CD8+ T cell dysfunction in CD8+ T cells from patients with STAT1 CD8+ T cells, which can be partially normalized by providing increased NAD+ levels.