Deficiency of adenosine deaminase 2 (DADA2) is a rare autosomal recessive disease caused by loss‐of‐function variants in the ADA2 gene. DADA2 typically presents in childhood and is characterized by vasculopathy, stroke, inflammation, immunodeficiency, as well as hematologic manifestations. ADA2 protein is predominantly present in stimulated monocytes, dendritic cells, and macrophages. To elucidate molecular mechanisms in DADA2, CD14+ monocytes from 14 patients and 6 healthy donors were analyzed using single‐cell RNA sequencing (scRNA‐seq). Monocytes were purified by positive selection based on CD14 expression. Subpopulations were imputed from their transcriptomes. Based on scRNA‐seq, monocytes could be classified as classical, intermediate, and nonclassical. Further, we used gene pathway analytics to interpret patterns of up‐ and down‐regulated gene transcription. In DADA2, the frequency of nonclassical monocytes was higher compared with that of healthy donors, and M1 macrophage markers were up‐regulated in patients. By comparing gene expression of each monocyte subtype between patients and healthy donors, we identified upregulated immune response pathways, including IFNα/β and IFNγ signaling, in all monocyte subtypes. Distinctively, the TNFR2 noncanonical NF‐κB pathway was up‐regulated only in nonclassical monocytes. Patients’ plasma showed increased IFNγ and TNFα levels. Our results suggest that elevated IFNγ activates cell signaling, leading to differentiation into M1 macrophages from monocytes and release of TNFα. Immune responses and more general response to stimuli pathways were up‐regulated in DADA2 monocytes, and protein synthesis pathways were down‐regulated, perhaps as stress responses. Our identification of novel aberrant immune pathways has implications for therapeutic approaches in DADA2 (registered at clinicaltrials.gov NCT00071045).

IMPORTANCEOlmsted syndrome is a rare and disabling genodermatosis for which no successful treatment is currently available. OBJECTIVE To evaluate the clinical response to the mammalian target of rapamycin (mTOR) inhibitor sirolimus and/or the epidermal growth factor receptor (EGFR) inhibitor erlotinib among patients with Olmsted syndrome. DESIGN, SETTING, AND PARTICIPANTSThis case series focused on 4 children with treatment-refractory Olmsted syndrome. These children received treatments (initiated in 2017 and 2018) at the outpatient dermatology clinic at the Children'

T-cell large granular lymphocyte leukemia (T-LGLL) is a lymphoproliferative disease and bone marrow failure syndrome which responds to immunosuppressive therapies. We show single-cell TCR coupled with RNA sequencing of CD3+ T cells from 13 patients, sampled before and after alemtuzumab treatments. Effector memory T cells and loss of T cell receptor (TCR) repertoire diversity are prevalent in T-LGLL. Shared TCRA and TCRB clonotypes are absent. Deregulation of cell survival and apoptosis gene programs, and marked downregulation of apoptosis genes in CD8+ clones, are prominent features of T-LGLL cells. Apoptosis genes are upregulated after alemtuzumab treatment, especially in responders than non-responders; baseline expression levels of apoptosis genes are predictive of hematologic response. Alemtuzumab does not attenuate TCR clonality, and TCR diversity is further skewed after treatment. Inferences made from analysis of single cell data inform understanding of the pathophysiologic mechanisms of clonal expansion and persistence in T-LGLL.