Stem cell therapies of Wolman disease

Abstract

Wolman disease is a rare lysosomal storage disorder, caused by a pathogenic variant in the LIPA gene. There is complete absence or extremely low levels of the enzyme lysosomal acid lipase, thus its substrates, cholesterol esters and triglycerides, are not hydrolysed and accumulate. Patients with Wolman disease present in the first few months of life with faltering growth, develop progressive gut and liver failure and, if untreated, usually die within the first 6 months of life. Historically, the only definitive treatment of Wolman disease has been allogeneic haematopoietic stem cell transplant (HCT). The principle of this approach is based upon the efficacy of transplantation in other lysosomal storage disorders. Engrafted, donor-derived leukocytes deliver the deficient enzyme to residual enzyme-deficient, host tissues, catabolising accumulated substrate. This correction of host tissues by enzyme secreted by donor leukocytes is known as cross correction. Transplant requires intensive conditioning chemotherapy, and most patients died during transplant due to the rapidity of disease progression; there is insufficient time for the graft to deliver enough enzyme quickly enough to stabilise the illness. More recently, enzyme replacement therapy (ERT) has been manufactured which improved patient survival. Some patients do not tolerate this treatment or develop antibodies against the enzyme. It is so expensive as to preclude its use worldwide. However, ERT can be used to stabilise the disease in the short term in many patients, and it might be used as a bridging therapy to stem cell transplant, allowing disease control before more definitive enzyme-replacement can be delivered by engrafted donor cells. Our first aim was to present this multi modal approach to treating Wolman disease, with allogeneic HCT providing definitive and long-term enzyme replacement in a patient whose disease progression has first been controlled by ERT, aided by dietary substrate reduction (DSR). We described the first 5 patients in the world treated this way, overall survival is 80%, a significant improvement compared to a historical group of Wolman patients. The multi modal approach showed improvements in biomarkers (Cholestane-3,5,6-triol) and histology of the gut and liver. Histology also suggested better enzyme delivery to the gut than ERT alone, clinically demonstrated with normalisation of the patients diet. We propose this approach as the new paradigm of treatment for Wolman disease patients. This therapy continues to have its limitations. Engraftment is frequently incomplete in patients with Wolman Disease, with mixed chimerism, and this limits enzyme delivery to host tissues. HCT is a toxic procedure, requiring a matched donor, associated with significant morbidity and mortality, including from graft versus host disease. Autologous haematopoietic stem cell gene therapy (HSC-GT) has been used in other lysosomal storage disorders as it is both safer and more effective, since supraphysiological enzyme can be delivered. We proposed Wolman disease as a potential candidate for lentiviral mediated ex vivo autologous gene therapy. We developed a lentiviral (LV) vector for Wolman disease, CD11bLIPA LV, and demonstrated expression of lysosomal acid lipase via direct transduction of Wolman fibroblasts. Additionally, we are able to cross correct Wolman fibroblasts, using media from directly transduced CHME3. To explore its clinical potential, we transduced CD34+ Wolman stem cells, demonstrating supraphysiological enzyme levels. We determined the optimal lentiviral concentration (multiplicity of infection) required to transduce CD34+ Wolman stem cells, using transduction enhancers. Further preclinical research is needed with larger scale transduction of CD34+ stem cells, and assessment of the effect of overexpression of lysosomal acid lipase, before this autologous HSC-GT approach is ready for early phase clinical trials.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Brian Bigger (Supervisor) & Robert Wynn (Supervisor)