CD34 and deficiency of adenosine deaminase 2: Next, we investigated the ability of lentiviral-ADA2 gene transfer to restore ADA2 protein expression and enzymatic activity in CD34+HSPC derived from a 3-month-old severe DADA2 patient with bone marrow involvement presenting with Pure Red-Cell Aplasia (PRCA) (genotype ADA2 p.G47W/p.G47W; see Table 1 for clinical characteristics).