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Under the Microscope: Lentiviral-Gene corrected Hematopoietic Stem Cells


Under the Microscope: Lentiviral-Gene corrected Hematopoietic Stem Cells

Begoña Díez Cabezas, PhD

María Fernández-García, PhD

Sala de producción celular CliniStem.


Madrid, Spain

Disclaimer/Conflict of interest statement. None.

Phase contrast image of lentiviral gene-corrected human Hematopoietic stem cells in culture, after transduction with lentiviral vectors.


Lentiviral-gene corrected hematopoietic stem cells (HSC) are defined as modified self-renewing, multipotent cells that can generate hematopoietic progeny of all lineages carrying a specific therapeutic gene. These cells are being tested as a medicinal product for the treatment of certain life-threatening monogenic diseases, including primary immunodeficiencies, red blood disorders and bone marrow failure syndromes (1).


HSCs are the source of all mature blood cells that constitute a healthy hematopoietic system. For this reason, targeted gene modification and subsequent transplant of HSCs offers a source of self-renewing stem cells, with the promise of a life-long therapeutic effect, making these cells perfect candidates to treat the full complement of hematopoietic diseases, regardless of the specific hematopoietic cell type affected (2).


HSC was reported in the 60’s by Till and McCulloch in a series of experiments to characterize radiation sensitivity, in which a transplant from donor adult bone marrow into syngeneic irradiated murine recipients was capable of protecting the recipients from lethal irradiation by regenerating the irradiation-ablated hematopoietic system (3). The first clinical trials using lentiviral vectors (LV) in HSC began in mid-2000 by Cartier et al (4) and Cavazzana-Calvo et al (5). The main driving force pushing the investigation, testing and release of this new category of medicinal products was found in Academia. However, the main limitations of these therapies are the logistics, as each disorder requires its specific vector and the entire pre-clinical and clinical drug development package.


The most widely used LV system, based on self-inactivated vectors, was first developed in 1996 by Naldini et al (6). Later, in 2009 lentiviral gene-corrected HSCs were used for the first time in a clinical trial for the treatment of a neurological disorder and in 2013 for a hematological disorder. Since then, LVs have become the most used vector for ex vivo gene therapy clinical trials. In 2019, the European Medicines Agency (EMA) gave conditional marketing authorization to the medicinal product Zynteglo, based on gene-corrected HSC for patients with transfusion-dependent β-thalassaemia (7), although the marketing-authorization holder has withdrawn this authorization and the product is no longer available for these patients.   



Nowadays, more than 60 clinical trials using LV modified HSCs are registered on the website, most of them in Europe and USA. From these, one medicinal product received conditional marketing authorization for β-thalassaemia and another one a complete marketing authorization for the treatment of metachromatic leukodystrophy in Europe. None of them has been authorized in USA yet.



HSCs are usually isolated from mobilized peripheral blood using the presence of CD34 in their membrane by immunomagnetic separation, which enables 30- to 50-fold enrichment of HSCs. The main difficulty in producing this kind of product is the reduced number of the CD34-expressing progenitor cells and their propensity to differentiation in culture. As such, modification should be conducted in the shortest period of time possible. Moreover, as cells are modified using LVs, it is important to test each batch of viral vector production in order to adjust the multiplicity of infection (MOI) to target the desired number of cells and control the vector copy number introduced in each cell (8).

Did you know that… genomic modifications in HSCs using lentiviral vectors have been used not only to treat hematological disorders but also as delivery vehicles for the treatment of inherited neurometabolic disorders and acquired diseases. They have been used to treat certain lysosomal storage disorders such as metachromatic leukodystrophy, a disease in which myelinic nervous cells are very affected, leading to a decrease in neurocognitive and motor function. As a result of the therapeutic benefit observed in clinical trials conducted in this disease setting, the medicinal product Libmeldy was approved in October 2020 in Europe for treatment of metachromatic leukodystrophy. To date, this is the only lentiviral gene-correct HSC-based product commercially available in Europe.


  1. Bueren JA, Quintana-Bustamante O, Almarza E, Navarro S, Río P, Segovia JC, et al. Advances in the gene therapy of monogenic blood cell diseases. Clin Genet [Internet]. 2020 Jan 1 [cited 2022 Jun 21];97(1):89–102. Available from:

  2. Sagoo P, Gaspar HB. The transformative potential of HSC gene therapy as a genetic medicine. Gene Ther [Internet]. 2021 [cited 2022 Jun 21]; Available from:

  3. Till JE, McCulloch EA. A direct measurement of the radiation sensitivity of normal mouse bone marrow cells. 1961. Radiat Res [Internet]. 2011 Feb [cited 2022 Jun 21];175(2):145–9. Available from:

  4. Cartier N, Hacein-Bey-Abina S, Bartholomae CC, Veres G, Schmidt M, Kutschera I, et al. Hematopoietic stem cell gene therapy with a lentiviral vector in X-linked adrenoleukodystrophy. Science [Internet]. 2009 Nov 6 [cited 2022 Jun 21];326(5954):818–23. Available from:

  5. Cavazzana-Calvo M, Payen E, Negre O, Wang G, Hehir K, Fusil F, et al. Transfusion independence and HMGA2 activation after gene therapy of human β-thalassaemia. Nature [Internet]. 2010 [cited 2022 Jun 21];467(7313):318–22. Available from:

  6. Naldini L, Blömer U, Gallay P, Ory D, Mulligan R, Gage FH, et al. In vivo gene delivery and stable transduction of nondividing cells by a lentiviral vector. Science [Internet]. 1996 Apr 12 [cited 2022 Jun 21];272(5259):263–7. Available from:

  7. Ferrari G, Thrasher AJ, Aiuti A. Gene therapy using haematopoietic stem and progenitor cells. Nat Rev Genet [Internet]. 2021 Apr 1 [cited 2022 Jun 21];22(4):216–34. Available from:

  8. Morgan RA, Gray D, Lomova A, Kohn DB. Hematopoietic Stem Cell Gene Therapy: Progress and Lessons Learned. Cell Stem Cell [Internet]. 2017 Nov 2 [cited 2022 Jun 21];21(5):574–90. Available from:


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