2, lower panel E and F). These results demonstrated that the T cells now harboured a mutant and a wild-type sequence, confirming the in vivo reversal of the mutation in one allele of the ADA gene. We also measured ADA activity at this time (Table 2, 50 months old) and found that RBC had some (although still very low compared with a healthy control) and continued to show a modest but lower levels of dAXP than previously observed. However, this ADA selleck chemicals activity was almost 3 times higher when compared to reference values (Table 2, age 50 months). This suggested that the revertant T cells could have contributed to mildly improve the immune function in the patient allowing him to survive

longer. For ADA-deficient patients in whom immune reconstitution by HSCT or GT is not feasible, ERT with PEG-ADA is an option that leads to rapid improvement in lymphocyte counts within several weeks to few months after the initiation of therapy [13, 17]; this has been used also even in situations in which

a somatic mosaicism caused by a reversion of an inherited mutation is detected. At the age of 50 months, our patient was not eligible for HSCT or GT therefore, we started him on ERT at the dose of 30 U/kg of weight, and just after 2 weeks, the ADA activity in PBL increased from 0.9 to 12.6 nmol/h per mg and dAXP decreased from 10.4% to 2.7% (not shown). However, difficulties Mdm2 antagonist in adherence to treatment led to some fluctuations in ADA activity and dAXP; therefore, we increased the dose to 50 U/kg after 10 months of treatment, and

this quickly led to normal ADA activity and undetectable dAXP (not shown). To monitor the treatment with PEG-ADA, we phenotyped all main lymphocyte populations in PB at several intervals after the initiation of therapy. As mentioned earlier, by the age of 50 months, SPTLC1 our patient had normal PBL counts with normal CD3+, CD8+ and CD16/56+ NK lymphocytes, and although CD4+ T cells also increased, they were still below normal values; in contrast, CD19+ B cells remained unchanged (Table 1, age 50 months). After 2 weeks on PEG-ADA we observed a rapid increase in PBL counts exceeding the reference values for the patient’s age, including CD3+, CD8+ T cells as well as NK cells (12,637, 10,880, 2154 and 1643 cells/μl, respectively; see Fig. 3). CD4+ T cells also increased to normal values but transiently (1284 cells/μl); moreover, CD19+ B cells also increased yet these always remained below normal (25 cells/μl). Interestingly, lymphocyte (and subset) counts returned to normal or just below normal after 3 months of therapy and remained stable for the next 14 months (Fig. 3). These results demonstrated that the ERT resulted in a transient expansion in total counts for most lymphocyte populations in PB. The mature pool of T lymphocytes in PB in humans is comprised of clonally derived TCRαβ+ and TCRγδ+ T cells in a proportion of 90% vs.