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Over the last thirty years, the field of gene therapy has not only persisted but also achieved significant advancements, providing lasting treatments for an increasingly varied range of diseases. Currently, active clinical trials are addressing a spectrum of inherited and acquired disorders across different organ systems. The techniques used include the ex vivo modification of haematologic stem cells (HSC), T lymphocytes, and other immune cells, as well as in vivo delivery of genes or gene editing tools to the pertinent target cells via local or systemic administration.

Why is it so hard to treat blood disorders?

Blood cells are generated through a process known as haematopoiesis, which primarily takes place in the bone marrow. Haematopoiesis involves the differentiation of haematopoietic stem cells (HSCs) into various blood cell types, including red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.

In treating blood disorders, the complexity arises from the intricate regulation of haematopoiesis. Blood disorders, including both inherited conditions (e.g., sickle cell anaemia, thalassemia) and acquired conditions (e.g., leukaemia, myelodysplastic syndromes), often involve abnormalities in the production, maturation, or function of blood cells.

Leukaemia, for example, is a type of blood cancer characterised by the uncontrolled proliferation of abnormal white blood cells. This arises from genetic mutations affecting the regulation of cell growth and differentiation in haematopoietic cells.

The challenging nature of treating blood disorders lies in the complexity of the haematopoietic system, the diversity of blood cell types, and the genetic variability underlying these disorders. Gene therapy holds promise in addressing these challenges by targeting the genetic basis of blood disorders. This approach aims to correct or replace “faulty genes”, restore normal haematopoiesis, and provide a long-term solution to these conditions.

By understanding the intricacies of haematopoiesis and the genetic factors involved, gene therapy endeavours to offer more effective and targeted treatments for a range of blood disorders, offering hope for improved outcomes and quality of life for affected individuals.

Treating blood disorders with cell and gene therapies

Treating inherited blood disorders presents considerable challenges, and innovative approaches like haematopoietic stem cell transplantation (HSCT) and haematopoietic stem cell gene therapy (HSCGT) aim to address these issues. One primary challenge is the imperative need for compatible donors. Finding suitable donors with matching tissue types is often a complex and time-consuming process. The donor must not only possess matching human leukocyte antigen (HLA) types but also be genetically compatible to minimise the risk of graft rejection. This necessity for stringent compatibility limits the availability of suitable donors, posing a significant hurdle in the widespread application of HSCT.

Additionally, HSCT introduces the risk of immunological complications. Graft rejection, where the recipient’s immune system recognises and attacks the transplanted cells as foreign, remains a concern. To mitigate this risk, recipients often receive immunosuppressive treatments, which come with their own set of challenges, including increased susceptibility to infections and other adverse effects. Graft versus host disease (GVHD) is another potential complication in HSCT. In this scenario, immune cells from the donor attack the recipient’s tissues, leading to a range of adverse effects. Controlling GVHD requires a delicate balance between suppressing the immune response and allowing the transplanted cells to engraft successfully. Despite advancements in managing GVHD, it remains a significant concern in HSCT.

In contrast, HSCGT offers a novel and promising approach to treating inherited blood disorders. One of these methods involves using the patient’s own (autologous) HSC, which are extracted from the body, genetically modified outside the body (ex vivo), and then reintroduced into the patient. The genetic modification aims to correct the defective gene responsible for the blood disorder.

HSCGT eliminates the need for external donors, addressing the challenge of finding compatible matches. Since the patient’s own cells are used, the risk of graft rejection is minimised. Furthermore, the risk of GVHD is virtually eliminated, as the transplanted cells are the patient’s own genetically modified cells.

This approach not only enhances the feasibility of treatment but also reduces the reliance on external donors, potentially making these innovative therapies more widely accessible. Notable successes include the treatment of severe combined immune deficiency (SCID) using lentiviral vectors, showcasing high survival rates and successful immune reconstitution. Additionally, metabolic disorders and hemoglobinopathies, such as sickle cell disease and β-thalassemia, have witnessed positive outcomes with HSCGT.

While challenges and complexities still exist in refining and implementing HSCGT, its unique advantages position it as a promising solution to the longstanding issues associated with treating inherited blood disorders.

As we navigate the fascinating journey of cell and gene therapy, we invite you to join us for our latest Healthcare 2.0 event: State of the Art and New Frontiers in Cell & Gene Therapy. This gathering of world-leading experts will delve into the latest advancements, breakthroughs, and promising future that cell and gene therapies hold.

For more information and ticket registration click HERE!

References:

Kohn, D.B., Chen, Y.Y., & Spencer, M.J. (2023). Successes and challenges in clinical gene therapy. Gene Therapy, 30, 738–746. https://doi.org/10.1038/s41434-023-00390-5