title: Inducible caspase 9 suicide gene to improve the safety of allodepleted T cells after haploidentical stem cell transplantation.
abstract: Addback of donor T cells following T cell-depleted stem cell transplantation (SCT) can accelerate immune reconstitution and be effective against relapsed malignancy. After haploidentical SCT, a high risk of graft-versus-host disease (GVHD) essentially precludes this option, unless the T cells are first depleted of alloreactive precursor cells. Even then, the risks of severe GVHD remain significant. To increase the safety of the approach and thereby permit administration of larger T cell doses, we used a suicide gene, inducible caspase 9 (iCasp9), to transduce allodepleted T cells, permitting their destruction should administration have adverse effects. We made a retroviral vector encoding iCasp9 and a selectable marker (truncated CD19). Even after allodepletion (using anti-CD25 immunotoxin), donor T cells could be efficiently transduced, expanded, and subsequently enriched by CD19 immunomagnetic selection to >90% purity. These engineered cells retained antiviral specificity and functionality, and contained a subset with regulatory phenotype and function. Activating iCasp9 with a small-molecule dimerizer rapidly produced >90% apoptosis. Although transgene expression was downregulated in quiescent T cells, iCasp9 remained an efficient suicide gene, as expression was rapidly upregulated in activated (alloreactive) T cells. We have demonstrated the clinical feasibility of this approach after haploidentical transplantation by scaling up production using clinical grade materials.
authors.affiliation: Center for Cell and Gene Therapy, Baylor College of Medicine, The Methodist Hospital, Houston, Texas 77030, USA. stey@bcm.tmc.edu
authors.forename: Siok-Keen
authors.initials: SK
authors.lastname: Tey
authors.forename: Gianpietro
authors.initials: G
authors.lastname: Dotti
authors.forename: Cliona M
authors.initials: CM
authors.lastname: Rooney
authors.forename: Helen E
authors.initials: HE
authors.lastname: Heslop
authors.forename: Malcolm K
authors.initials: MK
authors.lastname: Brenner
mesh_terms: D017209:Apoptosis; D053453:Caspase 9 / Q000235:genetics* / Q000378:metabolism; D005240:Feasibility Studies; D041722:Genes, Transgenic, Suicide; D005822:Genetic Vectors; D006086:Graft vs Host Disease / Q000517:prevention & control*; D006239:Haplotypes; D018380:Hematopoietic Stem Cell Transplantation / Q000379:methods; D006412:Hematopoietic Stem Cells; D006801:Humans; D016219:Immunotherapy, Adoptive / Q000379:methods; D017710:Lymphocyte Transfusion / Q000379:methods*; D012190:Retroviridae / Q000235:genetics; D013601:T-Lymphocytes / Q000145:classification / Q000637:transplantation*; D014161:Transduction, Genetic; D014184:Transplantation, Homologous
chemical_list: D053453:Caspase 9