In the previous blog post, we explored the complexities of Primary Immunodeficiency Diseases (PIDs) and discussed the various diagnostic and management strategies available. We also introduced the promising potential of novel therapies like hematopoietic stem cell transplantation (HSCT).
In this blog, we delve deeper into the exciting world of gene therapy for PIDs. We’ll explore ongoing clinical trials and the encouraging results that are paving the way for a future where gene therapy can revolutionise the treatment landscape for these debilitating conditions. While much of the research remains in very early stages, tremendous progress is already being made.
X-SCID
Treatment of X-SCID, a genetic disease caused by mutations in the IL2RG gene, leads to a lack of functional T and NK cells and non-functional B cells. Gene therapy trials have shown promise in treating X-SCID, but initial attempts using gamma retroviral vectors resulted in serious adverse events like leukaemia, due to insertional oncogenesis. To improve safety, researchers have transitioned to using safer SIN (self-inactivating) lentiviral vectors. These vectors integrate less frequently near cancer-causing genes and have not caused leukaemia in X-SCID patients so far. Recent trials have further optimised the approach by using autologous stem cell sources and reduced-intensity conditioning through the administration of busulfan to improve hematopoietic stem cell engraftment and immune cell production. Current studies using SIN lentiviral vectors with conditioning have shown positive short-term results in terms of immune cell restoration and lack of vector-related complications. Long-term follow-up is still needed to confirm the safety and efficacy of this approach, yet initial results are promising.
Art-SCID
Artemis-Deficient Severe Combined Immunodeficiency (Art-SCID) is another PID that shows promise for gene therapy. The first clinical trial using gene therapy is currently underway. Patients receive low dose busulfan conditioning followed by an infusion of autologous CD34+ stem cells genetically modified using a self-inactivating lentiviral vector. This vector delivers a functional copy of the DCLRE1C gene under the control of its natural promoter. Early results from this trial are encouraging. Three infant patients showed successful engraftment of edited stem cells, restored lymphocyte proliferation, and were able to recover from viral infections. Notably, a single side effect of autoimmune haemolytic anaemia was observed in some patients but resolved later. The success of this initial trial paves the way for further exploration of gene therapy for Art-SCID. Research on new vectors and even gene editing strategies are ongoing, aiming to provide a safer and more definitive cure for this debilitating disease.
WAS-syndrome
Another PID showing exciting results for gene therapy application is Wiskott-Aldrich Syndrome (WAS), a genetic disorder affecting males, characterised by a triad of symptoms: eczema, bleeding due to small platelets, and recurrent infections. WAS is caused by mutations in the WAS gene, leading to abnormalities in a critical protein called WASP, affecting the proper functioning of various blood cells, including immune cells and those responsible for blood clotting. Recent trials investigating the use of lentiviral vectors are encouraging. Patients experienced improved immune function, reduced infections, and the ability to discontinue immunoglobulin therapy in most cases. While platelet counts improved modestly, some patients still required occasional transfusions for bleeding episodes. Importantly, no cases of leukaemia or abnormal cell growth have been reported so far with this approach.
The road ahead for gene editing in PIDs
Primary immunodeficiencies (PIDs) present a unique opportunity for the application of gene editing therapies. The ease of harvesting target cells (usually HSCs) and their ability to engraft after editing make PIDs ideal candidates for this approach. Additionally, edited autologous cells eliminate the risk of graft-versus-host disease associated with traditional bone marrow transplants. The recent emergence of CRISPR/Cas9 editing has significantly accelerated progress in this field. However, several hurdles remain before widespread clinical applications can be realised.
Safety concerns regarding off-target effects are paramount, especially considering past incidents of malignant transformation in SCID and WAS gene therapy trials. While our ability to predict and minimise these risks is improving, the inherent genetic variability between individuals means a certain level of mutagenesis risk will always be present with gene editing.
Another challenge lies in the longevity of edited cells, particularly when using AAV vectors. Although strategies to reduce HSC death after editing have been explored, further evaluation is needed for approaches that involve introducing additional factors during the editing process.
Optimising cell homing to the bone marrow niche is another crucial aspect. Current cell culture conditions often inadvertently promote differentiation or alter the expression of homing molecules on HSCs. This can hinder their ability to return to their proper location after editing. Strategies like transient cytokine upregulation or mRNA delivery could be beneficial in addressing this issue.
With these challenges addressed, the next decade could see the initiation of phase I human trials in PIDs. Careful trial design will be critical, including considerations for conditioning regimes. Regulatory frameworks for cell-based therapies are still evolving, with different countries developing their own. International collaboration to establish a more unified regulatory landscape would be crucial to streamline and expedite multinational clinical trials.
Blog written by Caroline Beltran, Scientific Consultant at Synexa
About Synexa and Scientific Strategies
Synexa Life Sciences is a global provider of biomarker and bioanalytical services, specialising in the development, validation and delivery of a wide range of complex and custom-designed assays. With a team of 150 across five global laboratory locations; Cape Town, London, Berlin, Turku (Finland) and Rockville (Maryland USA), we provide innovative solutions to support our customers in achieving their clinical milestones.
Synexa’s Scientific Strategies team specialises in navigating the complexities and mitigating the risks associated with advancing compounds into clinical development. Our expertise is centred on critical biomarker and bioanalytical considerations, ensuring a streamlined path toward clinical trials. By offering bespoke consulting support, we deliver clear, actionable insights that address your unique biomarker and bioanalytical challenges, becoming a true strategic partner in your development journey.
Learn more about Synexa’s biomarker consulting service.
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