The abstract starts out saying that treating these disorders with gene therapy is “based on transplantation of autologous hematopoietic stem cells” (HSC). What does that mean, and why do you think that could be useful for these types of hemoglobinopathies?
Gene therapy for hemoglobinopathies is currently based on this. Hematopoietic stem cells are modified by integrating lentiviral vectors expressing a globin gene under the control of globin transcriptional regulatory elements.
Traditional curative therapy is represented by allogeneic hematopoietic stem cell transplantation hemoglobinopathies offers a disease free survival of 80%, up to 93%. However, availability of a well-matched donor is critical for a favorable outcome (Lidonnici, 2018).
127 our experts are availableright now
Although there are successes with this approach, there are complications/limitations to a more general application, such as the development of efficient vectors. This also includes the nature, source and age of repopulating hematopoietic stem cells.
Studies of gene therapy approach for treating hemoglobinopathies have been made possible by the availability of transgenic and know-out murine strains models for SCD and β-thalassemia (Lidonnici, 2018).
Transplantation of BM cells transduced with LV carrying anti-sickling Hb variants and β-LCR resulted in correction of the pathology in SCD mouse models . The transduced cell dose, as well as the stem cell course, are critical factors that might affect transplantation outcomes (Lidonnici, 2018).
The image below shows “Scheme representing the stepwise procedure of gene therapy: autologous transplantation of cells genetically modified by gene replacement or gene editing in patients affected by β-thalassemia or sickle cell disease.” (Gene therapy and gene editing strategies for hemoglobinopathies).
Find an article that discusses a specific gene therapy approach for treating either sickle cell anemia or beta-thalassemia in an animal model, not a human clinical trial. (There are directions for retrieving full-text articles through JHU in the “Useful links” tab.) Which disease did you choose to learn about for this discussion?
I chose beta-thalassemia.
Objective of paper: “This study explored whether TALENs‐mediated non‐homologous end joining (NHEJ) targeting the mutation site can correct the aberrant β‐globin RNA splicing, and ameliorate the β‐thalassaemia phenotype in β654 mice. “
Conclusion of paper: “These results suggest effective treatment of the anaemia phenotype in TALENs+/β654 mice following deletion of the mutation site by TALENs, demonstrating a simple and straightforward strategy for gene therapy of β654‐thalassaemia in the future.”
There are many types of animal models used for preclinical gene therapy studies. Which one was used in this paper?
Gene therapies were studied with mouse models.
- Gene therapy studies on SCD mouse models.
- Gene therapy studies on improved transduction methods.
- Gene therapy safety studies.
What general gene therapy strategy was used for the gene therapy treatment in this paper? Did it involve autologous HSC transplant or a different method of correcting the disorder?
This paper covers a number of gene transfer techniques, which lists benefits and current limitations of each. This includes gene editing techniques (CRISPR, TALENs, etc.) and gene additions with viral vectors.
Gene therapy has been proposed as theoretically feasible in a large number of patients, since it relies on an autologous transplant with no need for a matched donor (aka gene addition).
In gene therapy studies on SCD, transplantation of BM cells transduced with LV carrying anti-sickling Hb variants and B-LCR resulted in correction of pathology in SCD mouse models. Gene therapy with autologous HSCs using RV or LV have been successfully applied to primary immunodeficiencies. Stem cell procurement, transduction efficiency and patient conditioning were found to be the most critical factors that need improving in order to achieve clinical benefit (Lidonnici, 2018).
In gene therapy, determining the optimal genetically modified cell dose to reach therapeutic effectiveness remains unclear, especially in disease with no selective advantage. The transduced cell dose, as well as the stem cell source, are critical factors that might affect the transplantation outcomes (Lidonnici, 2018).
There are complications with gene addition. Such as:
- Variable and low level expression
- Unstable vectors with multiple arrangements
- Vectors with low titers
In the context of β-hemoglobinopathies, different gene editing strategies have been successful. This includes induction of endogenous fetal, correction of β-globin gene mutation. However, gene targeting in primary immunodeficiencies showed that a high gene targeting efficiency in HSCs by homologous recombination at disease-causing loci is difficult to obtain (Lidonnici, 2018). Overall, results from gene editing methods to correct β-hemoglobinopathies show promising results and the use for clinical applications needs to be reviewed in preclinical genotoxicity and safety studies (Lidonnici, 2018).
What conclusions do the authors make about their strategy? Is it something that could potentially be used in human clinical trials? Are there any practical limitations that they mention addressing before clinical trials could be attempted?
They end their conclusion by stating that there are several barriers to gene therapy — it’s far from being understood.
They say the results from gene editing methods to correct β-hemoglobinopathies are promising and the potential clinical translation needs to be evaluated in preclinical genotoxicity and safety studies, in the best available models (Lidonnici, 2018).
Future studies need to assess potential toxicity of genome editing in human HSCs and minimize potentially unsafe off-target mutations before clinica translation (Lidonnici, 2018).
Reference
- Lidonnici, M., & Ferarri, G. (2018, May). Gene therapy and gene editing strategies for hemoglobinopathies. Retrieved January 29, 2019, from https://www-sciencedirect-com.proxy1.library.jhu.edu/science/article/pii/S1079979617304291?via=ihub
- Gene therapy and gene editing strategies for hemoglobinopathies. (n.d.). Retrieved from https://www-sciencedirect-com.proxy1.library.jhu.edu/science/article/pii/S1079979617304291?via=ihub
- Treatment of β654‐thalassaemia by TALENs in a mouse model. (n.d.). Retrieved from https://onlinelibrary-wiley-com.proxy1.library.jhu.edu/doi/full/10.1111/cpr.12491
