Discussion
MPB, WAS and beta-thalassemia, neutropenia, transfusion dependency
DISEASE, NEUTROPENIA, GRAFT VERSUS HOST DISEASE
MPB is widely employed as HSPC source for ex vivo gene-correction approaches and HSCTPrevious studies comparing total BM vs. total G-CSF MPB sources in the context of HSCT were mainly focused on the overall outcome (i.e. survival, incidence of graft versus host disease and relapse or immune reconstitution)Thanks to the similarities between the two groups of WAS-GT patients in terms of disease background, transduction protocol and conditioning regimen settings we were able to assess the performance of engineered purified BM or MPB-HSPC reducing substantially the confounding factors generating several original information over the previous HSCT studies. Firstly, the faster recovery from neutropenia and reduced time for platelet transfusion dependency observed in the MPB-GT group (Fig. In-depth phenotypic characterization was not foreseen at infusion since the markers exploited for HSPC identification are not reliable after ex vivo culture due to the down-regulation of CD38 markerIt has been previously hypothesized that the distinct in vivo performance of the two sources were due to differences in the intrinsic properties of resident vs. mobilized HSPC, with MPB CD34+ cells displaying a more quiescent state and primitive gene signatureThe possibility of tracing the dynamics of infused gene-corrected HSPC through IS provided unique evidences with respect to previous HSCT reports, where there is no marking of the cells contained in the graft. Indeed, no study was conducted in order to evaluate whether the rapid hematopoietic recovery observed in MPB-based HSCT might have occurred at the expenses of the overall clonality of the hematopoietic system. In our model, we could assess that the use of MPB as source was associated with an overall higher complexity of the hematopoietic system and diversity of HSPC pool with respect to BM CD34+cells. This observation is particularly relevant in the clinical practice since it was reported that reduction of HSPC clonality lead to premature cellular senescence in HSCTOur results are in accordance with a recent work on a limited number of patients with 2 different disease backgrounds (WAS and beta-thalassemia) treated with HSPC-GTFinally, we have observed the maintenance of a highly polyclonal pool of engineered multipotent stem cells that sustained stable production of gene-corrected cells in all hematopoietic lineages, up to 3 years after GT in all the patients analyzed (Fig. In conclusion, our results validate also from the biological point of view the preferred use of MPB as HSPC source in the context of HSPC-GT and generate new references for future interpretation of clinical data and transplantation outcome.