The beta-hemoglobinopathies are the most prevalent genetic disorders worldwide and serve as an important paradigm for the development of safe and effective approaches to hematopoietic gene therapy. In the past several years, substantial advances have been made towards this goal, from original vector design to the sustained correction of relevant mouse models, culminating with the first Phase I/II clinical trial of a lentiviral vector aimed at the gene therapy of a genetic disease. While the first patient treated show sustained expression of the transferred globin gene 4 months post-transplantation, the latest time assessed, we are now asking whether therapeutic globin expression within virtually all red blood cells can be safely achieved in sub-myeloablated recipients even when only partial chimerism with transduced hematopoietic stem cells (HSCs) would be obtained by current measures.
In Specific Aim 1, we will devise an ex-vivo selection procedure for genetically corrected HSCs by means of a novel nerve growth factor receptor (NGF-R) variant devoid of residual activity and compatible with clinically-applicable bulk cell purification in a magnetic field. Importantly, we will assess whether the previously unavoidable loss of HSC content that occurs in vitro during such a procedure can be alleviated by means of novel HOX fusion proteins that penetrate cell membranes directly to induce HSC maintenance and expansion without the potentially oncogenic risk posed by the transfer of genetic material.
In Specific Aim 2, we will investigate whether self-controlled in vivo amplification of genetically corrected red blood cells can be provided by co-expression of a natural erythropoietin (Epo) receptor variant with enhanced sensitivity to endogenous Epo. The rationale is based on the benign natural history of the familial erythrocytosis caused by this genetic variant and extensive preliminary data.
In Specific Aim 3, we will turn to a non-human primate, Macaca fascicularis, whose cell transducibility by human lentiviral vectors is similar to that of human cells. This model will circumvent the low permissivity of most non-human primates for HIV vectors and make thus possible the critical evaluation of novel globin lentiviral vectors and aforementioned transplantation strategies in a large animal model closely related to humans.
