1:CIEMAT; 2:Instituto de Investigación Sanitaria Fundación Jiménez Díaz; 3:Universitat Internacional de Catalunya; 4:Hospital Universitario Virgen del Rocío; 5:Bloodgenetic S.L.; 6:Ospedale Maggiore Policlinico, Milan; 7:VIVEbiotech

Congenital dyserythropoietic anemia type II (CDAII) is a rare inherited disorder that affects red blood cell development. CDAII patients show hypercellular in the bone marrow, erythroid hyperplasia and the presence of binucleated erythroid cells. CDAII is caused by mutations in the SEC23B gene. SEC23B is involved in protein processing and Golgi-reticulum trafficking. CDAII management is generally limited to blood transfusion and iron chelation, being allogeneic hematopoietic stem cell transplant (HSCT) the only curative option. Consequently, autologous HSCT of genetically corrected cells can offer a definitive treatment for CDAII.

To develop a gene therapy for CDAII, we have designed two lentiviral vectors carrying the wild type or the codon optimized SEC23B cDNA (wtSEC23B LV and coSEC23B LV). We had generated SEC23B knock-out human hematopoietic progenitors (SEC23Bᴷᴼ CD34⁺ cells) using the CRISPR/Cas9 system to assess the efficacy of the lentiviral vectors.  SEC23Bᴷᴼ CD34⁺ cells reproduced the erythroid defects observed in CDAII patients. Moreover, LV transduced SEC23Bᴷᴼ CD34⁺ cells increased SEC23B protein expression and restored their normal capacity for in vitro erythroid differentiation. Similarly, in vivo erythroid differentiation in NBSGW mice showed a selection of the transduced cells, accompanied by a reduction in binucleated cells. Furthermore, SEC23B LV transduction of peripheral blood CD34⁺ cells from CDAII patients improved their erythroid differentiation potential with a reduction in the percentage of binucleated erythroid cells.

In summary, SEC23B LVs compensate for the SEC23B deficiency in SEC23Bᴷᴼ CD34⁺ cells and in patients’ hematopoietic progenitor cells, which opens the possibility of future treatment of CDAII by gene therapy.