IPRIMYO: Immune-privileged, immortal, myogenic stem cells for gene therapy of Muscular Dystrophy

Dr. Marisa Jaconi, University of Geneva

Abstract (lay summary see below)

Duchenne muscular dystrophy (DMD) is a devastating incurable disease, affecting thousands with heavy burden on health systems. This project combines the development of a safe “immune‐privileged cell” with genetic engineering to correct many dystrophin gene mutations for an efficacious and cost affordable therapy. Systemic intra‐arterial transplantation of mesoangioblasts (blood vessel‐derived progenitors) proved safe in DMD patients and is now being implemented for efficacy in a phase II clinical trial. However, this personalized approach would prove prohibitively expensive for healthcare systems, as pricing of successful gene therapies is showing. We made the striking observation that human mesoangioblasts can be indefinitely expanded with a novel culture medium, even after genetic manipulation and cloning. Cells will be first engineered with a lentivector to silence endogenous HLA (β2‐microglubin and class II CTA) while inserting tolerogenic HLA‐E, fused to β2microglubin and, as safety device, the Herpes Simplex Thymidine Kinase suicide gene with truncated NGF receptor for selection. The vector will also express CD47 and PDL1 to further inhibit immune response to transplanted cells and a small nuclear RNA (U7) engineered to skip exon 51 of the dystrophin gene. Due to the syncytial nature of muscle fibers, the snRNA also enters and corrects the genetic defect in neighboring dystrophic nuclei, thus amplifying of one log the therapeutic effect. Five different cell lines would correct the mutation in 60% of DMD patients. Properly transduced and selected cells will be first checked for genome integrity and their capacity to generate muscle fibers in vitro. They will be then transplanted in humanized DMD mice (already available) and assessed for the ability to escape immune surveillance and to differentiate in dystrophin expressing myofibers, establishing pre‐clinical safety and efficacy for an off‐the‐shelf affordable product. Thanks to unique expertise to successfully complete this project, our strategy may be expanded to other recessive monogenic diseases, for a ground‐breaking impact in regenerative medicine.

Lay summary

Les dystrophies musculaires ne bénéficient toujours pas d'une thérapie efficace. Nous avons développé
une thérapie cellulaire permettant la correction génétique et une production élevée de dystrophine (dont
la mutation provoque la dystrophie musculaire de Duchenne, DMD). La distribution systémique de cellules
souches musculaires autologues génétiquement corrigées (mésoangioblastes) peut conduire à un bénéfice
clinique qui sera testé dans un essai clinique (San Raffaele, Milan). Néanmoins, même en cas de succès, le
coût d'un tel traitement individualisé resterait prohibitif, comme observé pour des protocoles réussis
d’autres maladies génétiques. Par conséquent, nous allons créer un unique lentivecteur spécifique qui
assurera aux mésoangioblastes de corriger le défaut génétique de la DMD et d’échapper à la destruction
par système immunitaire après transplantation. Ces cellules seront utilisées pour générer une banque
cellulaire permettant leur administration sur demande à n'importe quel patient atteint de DMD mais aussi
d'autres maladies génétiques.

Für Muskeldystrophien gibt es noch immer keine wirksame Therapie. Wir haben eine Zelltherapie
entwickelt, die eine genetische Korrektur und eine hohe Produktion von Dystrophin (dessen Mutation die
Duchenne‐Muskeldystrophie, DMD, verursacht) ermöglicht. Die systemische Verteilung von genetisch
korrigierten autologen Muskelstammzellen (Mesoangioblasten) könnte zu einem klinischen Nutzen
führen, der in einer klinischen Studie (San Raffaele, Mailand) getestet werden soll. Doch selbst wenn dies
gelänge, wären die Kosten für eine solche individualisierte Behandlung unerschwinglich, wie bei
erfolgreichen Protokollen für andere genetische Krankheiten zu beobachten ist. Deshalb werden wir einen
einzigen spezifischen Lentivor entwickeln, der sicherstellt, dass die Mesoangioblasten den DMD‐Gendefekt
korrigieren und nach der Transplantation der Zerstörung durch das Immunsystem entgehen. Diese Zellen
werden zur Erstellung einer Zellbank verwendet, die es ermöglicht, sie bei Bedarf jedem Patienten zu
verabreichen, der an DMD, aber auch an anderen genetischen Krankheiten leidet.

Le distrofie muscolari non hanno ancora una terapia efficace. Abbiamo sviluppato una terapia cellulare
che permette la correzione genetica e la produzione elevata di distrofina (la cui mutazione causa la distrofia
muscolare di Duchenne, DMD). La distribuzione sistemica di cellule staminali muscolari autologhe
geneticamente corrette (mesoangioblasti) può portare a un beneficio clinico che sarà testato in un trial
clinico (San Raffaele, Milano). Tuttavia, anche se avesse successo, il costo di un tale trattamento
individualizzato rimarrebbe proibitivo, come osservato in protocolli di successo per altre malattie
genetiche. Pertanto, creeremo un unico lentivettore specifico che assicurerà ai mesoangioblasti di
correggere il difetto genetico DMD e sfuggire alla distruzione da parte del sistema immunitario dopo il
trapianto. Queste cellule saranno utilizzate per generare una banca cellulare per la loro somministrazione
su richiesta a qualsiasi paziente affetto da DMD ma anche da altre malattie genetiche.