Nevertheless, there are concerns relating to how we should deliver this bacterial protein in the clinic. For one, ChABC activity is short-lived and therefore repeated injections or delivery by intrathecal catheter is needed, which is unattractive.
Gene therapy approaches may provide the answer. Modified viruses have long been used as a tool to carry inserted genes into cells, “infecting” them with a copy of the gene which in turn causes the cell to produce (express) the protein. Obviously, concerns surround gene therapy as well, but the prospect of only needing a single administration of a therapeutic viral vector which gives rise to long-term expression of the therapeutic gene is compelling.
A few years back the Bradbury lab (Kings College London, UK) presented a poster on the successful application of a gene therapy approach. I posted something on this at the time and the work was eventually published a little while after.
Sustained and widespread degradation of CSPGs was seen after a single injection of a lentiviral vector carrying a gene of ChABC. This led to a dramatic reduction of lesion pathology: sparing of neuronal tissue and dramatic reduction in cavity volume. It significantly improved signal conduction across the injury site coupled with improved performance on a horizontal ladder test
The viral vector used in this earlier work was based on a lentiviral carrier and the expression of chondroitinase was permanently on.
Yesterday two posters from the Guest lab at the Miami Project showed data from a non-human primate study using either gene therapy chondroitinase alone or in combination with autologous Schwann cell transplants [A. Y. Flores #158.26 & R. De Negri #158.25]. The gene vector system was the same as that used by the Bradbury group, i.e. always on.
Chondroitinase gene therapy in an upper cervical hemi-contusion injury resulted in improved hand function. Interestingly, the group receiving the chondroitinase + cell graft combination lost significant upper limb function. It is unfair to speculate too much as to why this combination fared so badly as the group haven't had an opportunity to look at the histology, but the take home is that gene therapy alone looked very promising in a non-human primate study which is what I'm interested in here.
In all of the above studies the gene vector used permanently produced the gene product, chondroitinase.
Today, we were treated to three posters that reported on the first controllable chondroitinase gene therapy system. Controlled (inducible) gene expression can be achieved by engineering into the vector a antibiotic responsive transactivator which only switches on the production of the gene of interest (in our case chondroitinase) when exposed to the antibiotic doxycycline. Such a system has been around for years but it can't be used in the clinic because the transactivator causes an immune reaction that damages and kills the cells containing the vector. Not good.
The Verhaagen group have produced a "stealthy" version that evades the immune system and the results were impressive and from a translational point of view, very significant.
F. De Winter [#323.09] was able to show that this stealthy, inducible system could be repeatedly switched on and off many, many times over the course of 47 weeks without losing any efficacy. This markedly contrasted with the results from a non-stealthy version which could only be switched on over three cycles before losing "switchability". In addition, histological examination of the tissue at the end of the experiment revealed a lot of cell debris and very unhealthy-looking cells in the spinal cord tissue of animals injected with the non-stealthy version; the tissue from the stealthy group look just fine!
In the above study De Winter used a reporter gene (luciferase) to characterise the system. R. Eggers on the other hand looked at a therapeutic option [#323.10]. Eggers treated an avulsion injury at L3, L4 & L5 with an inducible, stealthy GDNF gene-carrying vector. The importance of being able to induce the production GDNF in an controlled way became evident when it was shown that 12 week exposure to doxycycline (12 weeks on) resulted in exuberant regeneration of motor neuron axons in and around the site of the injection but these axons remained there and went no further. The axons became trapped by their thirst for GDNF. When doxycycline was given for only 4 weeks (4 weeks on) the axons made their way onwards towards the denervated target.
Finally, E. R. Burnside from the Bradbury lab showed further evidence of the value of being able to control the delivery of chondroitinase using this vector system [#323.11]. Using a cervical contusion injury model and treatment with the inducible, stealthy chondroitinase vector two treatment groups were studied ; (i) treatment with short-term expression (2.5 weeks exposure to doxycyline) and (ii) treatment with 8 weeks exposure. Both groups showed improved locomotor function over controls. What was most impressive was the finding that fine motor control in the forelimb improved only in the 8 week treated group. This was the first time this type of skilled motor function has been shown to recover in this injury model.
The Verhaagen and Bradbury labs are part of the CHASE-IT consortium.
Chondroitinase gene therapy in an upper cervical hemi-contusion injury resulted in improved hand function. Interestingly, the group receiving the chondroitinase + cell graft combination lost significant upper limb function. It is unfair to speculate too much as to why this combination fared so badly as the group haven't had an opportunity to look at the histology, but the take home is that gene therapy alone looked very promising in a non-human primate study which is what I'm interested in here.
In all of the above studies the gene vector used permanently produced the gene product, chondroitinase.
Today, we were treated to three posters that reported on the first controllable chondroitinase gene therapy system. Controlled (inducible) gene expression can be achieved by engineering into the vector a antibiotic responsive transactivator which only switches on the production of the gene of interest (in our case chondroitinase) when exposed to the antibiotic doxycycline. Such a system has been around for years but it can't be used in the clinic because the transactivator causes an immune reaction that damages and kills the cells containing the vector. Not good.
The Verhaagen group have produced a "stealthy" version that evades the immune system and the results were impressive and from a translational point of view, very significant.
F. De Winter [#323.09] was able to show that this stealthy, inducible system could be repeatedly switched on and off many, many times over the course of 47 weeks without losing any efficacy. This markedly contrasted with the results from a non-stealthy version which could only be switched on over three cycles before losing "switchability". In addition, histological examination of the tissue at the end of the experiment revealed a lot of cell debris and very unhealthy-looking cells in the spinal cord tissue of animals injected with the non-stealthy version; the tissue from the stealthy group look just fine!
In the above study De Winter used a reporter gene (luciferase) to characterise the system. R. Eggers on the other hand looked at a therapeutic option [#323.10]. Eggers treated an avulsion injury at L3, L4 & L5 with an inducible, stealthy GDNF gene-carrying vector. The importance of being able to induce the production GDNF in an controlled way became evident when it was shown that 12 week exposure to doxycycline (12 weeks on) resulted in exuberant regeneration of motor neuron axons in and around the site of the injection but these axons remained there and went no further. The axons became trapped by their thirst for GDNF. When doxycycline was given for only 4 weeks (4 weeks on) the axons made their way onwards towards the denervated target.
Finally, E. R. Burnside from the Bradbury lab showed further evidence of the value of being able to control the delivery of chondroitinase using this vector system [#323.11]. Using a cervical contusion injury model and treatment with the inducible, stealthy chondroitinase vector two treatment groups were studied ; (i) treatment with short-term expression (2.5 weeks exposure to doxycyline) and (ii) treatment with 8 weeks exposure. Both groups showed improved locomotor function over controls. What was most impressive was the finding that fine motor control in the forelimb improved only in the 8 week treated group. This was the first time this type of skilled motor function has been shown to recover in this injury model.
The Verhaagen and Bradbury labs are part of the CHASE-IT consortium.
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