Over the past two decades, Dr. Wilcox’ laboratory has been focused on developing a means to address genetic-based inherited platelet defects leading to hematological disorders. From that effort, we have developed an ex-vivo lentiviral-based gene therapy technology that isolates the patient’s own stem cells, then introduces a normal gene to replace defective genetic material into those cells, which, after being incorporated into the patient’s stem cells, functionally generates modified cells specifically designed to eradicate the genetic disease. Platelet Targeted Therapeutics was formed in 2012 as a holding company for the intellectual property created through this research to bring these discoveries to the clinical arena.
Using a lentivector, we have performed pre-clinical studies using tissue cultured human cells, murine and canine models for both Hemophilia A and Glanzmann Thrombasthenia and have entered Phase I clinical trials in Hemophilia A patients with a history of inhibitory antibodies to recombinant and plasma derived Factor VIII infusion therapy. This lentiviral vector technology serves as a model for platelets to serve as “transport vehicles” to synthesize, store and deliver replacement genes products, potentially for a variety of disorders affecting and accessible to platelets. We are currently assessing possible applications.
ADVANTAGE OF LENTI-BASED GENE TRANSFER VECTORS IN CLINICAL APPLICATIONS
Lentivectors have several potential advantages in the clinical arena. These include:
- Therapy can target therapeutic agents to specific cellular sites, such as the α-granule compartments inside the platelet, inaccessible to recognition by the immune system until secreted into the blood stream following platelet activation.
- Patients who may produce antibodies that destroy other viral vectors have not been shown to develop antibodies to lentivectors.
- Using lentivector technology, stem cells may be safely collected from the body, genetically modified, and reinfused as has been developed and performed for over 30 years.
- ≈100% of hemophilia A patients, including those who elicit antibodies to Factor 8 (FVIII) should not produce inhibitory antibodies to plasma FVIII, a potential with plasma-based therapies.
- Lentivector HSC may also be used in patients with some forms of liver damage.
- Lentivector HSC can include a diverse (age, gender) population with exception of some medical conditions. It may also be applied to patients less than 18 years old, as bone marrow proliferates and replicates for life.
- Lentivector insertion into the genomic DNA has a very low probability to lead to insertional mutagenesis, clonal expansion, or cancer.
CLINICAL APPLICATION OF EX-VIVO GENE THERAPY
The Platelet-Targeted gene transfer treatment involves a series of steps whereby hematopoietic stem cells (HSC) are mobilized with cytokines to permit HSC to travel from bone marrow into the blood, which allows the HSC to be collected by apheresis. HSC are then incubated with a lentiviral gene transfer vector (LV) encoding FVIII under the control of a fragment of a megakaryocyte-specific gene promoter (ITGA2B) that preferentially allows synthesis of FVIII within the platelet‑lineage. For example, the genetically modified HSC are transplanted back into the patients with a low dose of pre‑conditioning to create space for the genetically altered HSC to take up residence within the bone marrow, leading to the production of Pleightlet™ theoretically for the lifetime of the individual.
This protocol has been successful in human megakaryocytes (parental cells of platelets) and platelets produced in a xeno‑transplant mouse model. Activated platelets have also been shown capable of restoring hemostasis in hemophilia A mice, and in dogs.
INDUCIBLE PLURIPOTENT STEM CELLS
Inducible Pluripotent Stem Cells (iPSC), first developed in late 2007, are stem cells produced by a number of cells that have been re-engineered back to their pluripotent state, The capability to generate somatic cells to iPSCs may provide significant opportunity to develop patient-specific cell lines to better understand human disorders.
Platelet Targeted Therapeutics’ approach also has potential applications for lentivectors to genetically modify iPSC as a transient application technology we are developing in collaborative effort with investigators from around the world.
Currently, we have collaborations with a number of universities to investigate potential clinical applications of lentivector-based stem cells in several areas, such as ischemia, angiogenesis, growth factors, myocardial tissue, coagulation, bone fracture, and promotion of immunity against bacterial and viral pathogens.
An ongoing concern with systemic delivery of chemotherapy has been that such therapy can have deleterious and/or off-target effects on healthy cells. Since platelets play a direct role in cancer progression, we hypothesized that megakaryocytes can be induced to express an anti-oncogenic agent that can be delivered directly to tumors. It has been established that activated platelets secrete agents (e.g., cytokines) that can promote solid tumor growth & cancer metastasis.