Sickle cell disease (SCD) is a chronic inflammatory disease associated with multiple organ damage, chronic anemia, and infections. SCD patients have a high rate of alloimmunization against red blood cells (RBCs) following transfusion and may develop autoimmune diseases. Studies in mouse models have suggested that regulatory T cells (Treg) play a role in alloimmunization against RBC antigens. We characterized the phenotype and function of the Treg cell population in a homogeneous cohort of transfused SCD patients. We found that the distribution of Treg subpopulations differed significantly between SCD patients and healthy blood donors. SCD patients have a particular Treg phenotype, with strong CTLA-4 and CD39 expression and weak HLA-DR and CCR7 expression. Finally, we show that this particular phenotype is related to SCD rather than alloimmunization status. Indeed, we observed no difference in Treg phenotype or function in vitro using autologous feeder cells between strong and weak responders to alloimmunization.

Hydroxyurea (HU) is useful for treating sickle cell anemia because of its ability to reduce some of the severe clinical events such as painful crises and acute chest syndrome. It may also reduce the need for blood transfusions and frequent hospitalizations and reduce mortality. Nevertheless, no consistent recommendations regarding its therapeutic schedule are defined. Our aim was to improve and validate a high performance liquid chromatography (HPLC) technique to measure HU and to study HU levels in serum and urine of sickle cell anemia patients and relate this to treatment efficacy and compliance. Thirty-seven patients received 1,128 +/- 333 mg of HU per day (8.0 to 28.0 mg/kg/day). Plasma and/or urine were sampled and HU was measured using an HPLC method coupled with UV detection. We validated a specific, sensitive assay with good reproducibility and linearity, and showed a positive relationship between plasma HU concentrations and time elapsed between oral HU intake and sampling. We observed plasma HU concentrations were positively correlated with change in mean corpuscular volume (MCV) before and during the treatment. No correlation was obtained between HU concentration and Hb F level.

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Sperm parameters are known to be impaired in men with sickle cell disease (SCD). Although treatment with hydroxyurea (HU) impacts sperm quality, sperm preservation is impossible before puberty. The present study's primary objective was to analyze and compare sperm parameters in male SCD patients exposed (or not) to HU before puberty. Twenty-six sperm samples from 15 patients (median (range) age: 17 (16-23)) treated with HU during childhood were compared with 46 samples from 23 HU-naïve patients (median (range) age: 20 (16-24)). The median (range) age at HU initiation was 6 years (1-14), the median duration of HU treatment was 4 years (0.5-10) and the mean ± standard deviation dose of HU was 22.4 ± 3.7 mg/kg/day. Although we observed substantial quantitative and qualitative semen abnormalities in all patients, there were no significant differences in semen volume, sperm concentration, total sperm count, and spermatozoa motility, morphology and vitality between the HU-exposed and HU-naïve groups. At the time of the semen analysis, respectively 100% and 52% of the patients in the HU-exposed and HU-naïve groups were on transfusion therapy. Hydroxyurea's specific effect on spermatogenesis in very young infants and the putative value of transfusion for reversing HU's toxicity warrant further investigation.