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454 Part V: Therapeutic Principles Chapter 30: Regenerative Medicine: Multipotential Cell Therapy for Tissue Repair 455

delivery methodology in conjunction with the use of the StemRegenin suggest that karyotypic abnormalities may occur in as many as one of
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1 aryl hydrocarbon receptor antagonist and/or 16,16-dimethyl- every three cell lines. Trisomy 12 is the most common abnormality in
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prostaglandin E (dmPGE ) 168,169 allowed for HR in HSCs that normally human ESCs and iPSCs, and chromosome 17 trisomy occurs frequently
2
2
preferentially employ NHEJ. These data provide a strong platform for in murine ESCs. 182,183
first-in-human studies. By definition, engineered nucleases are designed to recognize a
The NHEJ arm of DNA repair also holds potential for therapeu- specific DNA sequence; however, they may also exhibit off-target (OT)
tic use. A promising avenue of investigation to use NHEJ to perma- effects due to overlapping or low-complexity sequence recognition
nently disrupt genes has been employed clinically in T cells from HIV between the primary target and the OT site. Unbiased genome-level
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patients. However, because of the ability of HIV to infect non–T-cell screens are a powerful way to assess putative OT sites, and ZFN, TALEN,
subsets, studies have also investigated CCR5 disruption in a preclin- and CRISPR/Cas9 have shown excellent safety profiles to date 184,185 ;
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ical humanized mouse model and showed that the modified cells are however, this high-resolution methodology will need to be performed
resistant to HIV-1 infection. 172,173 These data are especially relevant due for each gene target candidate. In summary, engineered nucleases allow
to the recent treatment of patients using HCT of grafts with homozy- for unparalleled specificity and flexibility that complement the attrib-
gous CCR5Δ32 mutations that disrupt cellular entry of the HIV parti- utes of progenitor cells. The ability to precisely manipulate the genome
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cles. This treatment protocol was initiated for an individual with HIV/ will support individualized ex vivo therapies and will allow for more
AIDS who developed acute myeloid leukemia (the “Berlin patient”) in uniform disease modeling in vitro.
an attempt to cure both the malignancy and the HIV infection. 174,175
Because of the paucity of CCR5Δ32/CCR5Δ32 donors, ZFN-modified
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