Innovative Therapies for Hemoglobin Disorders

Abstract

-globin gene transfer has been used as a paradigm for hematopoietic stem cell (HSC) gene therapy, but is subject to major difficulties, such as the lack of selection of genetically corrected HSCs, the need for high-level expression of the therapeutic gene, and cell-specific transgene expression. It took more than 40 years for scientists and physicians to advance from the cloning of globin gene and discovering globin gene mutations to improving our understanding of the pathophysiological mechanisms involved, the detection of genetic modifiers, the development of animal models and gene transfer vectors, comprehensive animal testing, and demonstrations of phenotypic improvement in clinical trials, culminating in the authorization of the first gene therapy product for -thalassemia in 2019. Research has focused mostly on the development of lentiviral gene therapy vectors expressing variants of the -globin gene, or more recently targeting a -globin repressor, some of which have entered clinical testing and should soon diversify the available treatments and promote price competition. These results are encouraging, but we have yet to reach the end of the story. New molecular and cellular tools, such as gene editing or the development of induced pluripotent stem cells, are being developed, heralding the emergence of alternative products, the efficacy and safety of which are being studied. Hemoglobin disorders constitute an important model for testing the pros and cons of these advanced technologies, some of which are already in the clinical phase. In this review, we focus on the development of the advanced products, and recent technological innovations which could lead to clinical trials in the near future, and provide hope for a definitive cure of these severe conditions.

A Small Key for a Heavy Door: Genetic Therapies for the Treatment of Hemoglobinopathies

“…LVs are currently being tested for treating hemoglobinopathies as well. The main strategies can be categorized in (i) transgene addition ( Figure 3A ), (ii) short hairpin RNA (shRNA)-mediated BCL11A knockdown ( Figure 3B ) and (iii) forced chromatin looping ( Figure 3C ) (Breda et al, 2016 ; Cavazzana et al, 2017 ; Sii-Felice et al, 2020 ). The first strategy preceded the other two and is currently the most common and advanced in terms of clinical translation.…”

“…Indeed, there are a variety of efforts directed at generating LVs carrying recombinant β-like globin gene sequences with the goal of achieving therapeutic levels of transgene expression in RBCs derived from LV-transduced HSCs. To this end, the combined optimization of LCR elements, transgenes and vector genomes is permitting the achievement of efficient transduction of HSCs and subsequent therapeutic protein levels in RBCs (May et al, 2000 ; Negre et al, 2015 ; Cavazzana et al, 2017 ; Sii-Felice et al, 2020 ). For instance, concerning the optimization of LCR elements in particular, it was demonstrated that incorporating in LV genomes large sequences spanning the HS2, HS3 and HS4 elements, instead of the respective minimal core sequences, yielded sustained and high amounts of recombinant β-globin in RBCs of transplanted mice (May et al, 2000 ).…”

“…Since the initial development of the aforementioned Lentiglobin vectors HPV569 and BB305, other LV-based β-thalassemia and SCD gene therapy products have emerged and entered clinical trials, namely GLOBE, OTL-300, ARU-1801, Lenti-βAS3-FB, and DREPAGLOBE (Sii-Felice et al, 2020 ) ( Table 1 ). The genomes of these LVs differ among each other in several aspects, namely: (i) LCR HS site composition (HS2-4), (ii) type of transgene (i.e., wildtype β-globin, β T87Q -globin or hybrid βɤ-globin), (iii) absence or presence of insulators (i.e., cHS4 or FII/BEAD-A; Ramezani et al, 2008 ); and (iv) vector promoter sequences (i.e., hybrid CMV/5'LTR or wildtype 5'LTR; Cavazzana et al, 2017 ; Sii-Felice et al, 2020 ).…”

“…Although improved LV designs present reduced safety concerns associated with insertional oncogenesis (e.g., HIV-1 SIN constructs with miniaturized HBB enhancer/promoter elements), life-long monitoring for the emergence of potentially hazardous monoclonal expansions of HSC progenies, is warranted. Importantly, LV-based gene therapies are showing promising results in terms of achieving clinically relevant β-like globin expression levels in initial and ongoing clinical trials ( Table 1 ) (Sii-Felice et al, 2020 ).…”

Coordinated β-globin expression and α2-globin reduction in a multiplex lentiviral gene therapy vector for β-thalassemia

“…Several lentiviral b-globin gene therapy vectors (LVbs) encompassing elements of the locus control region (LCR) 4 are in clinical trials for b-hemoglobinopathies. 5,6 Notably, the LentiGlobin BB305 gene therapy vector, encoding b A-T87Q -globin, originally designed by Leboulch et al 7 and Pawliuk et al 8 to inhibit hemoglobin S (HbS) polymerization, has achieved clinical efficacy and safety in a large number of transfusion-dependent individuals with b-thalassemia [9][10][11][12] and sickle cell disease in phase II and III trials. 13,14 With regard to gene therapy for b-thalassemia, virtually all individuals with b-thalassemia with residual b-globin synthesis (non-b 0 /b 0 genotype) (e.g., HbE/b 0 -thalassemia), have discontinued transfusions following BB305 gene therapy, with near-normal blood Hb levels.…”