Novel RNA Interference (RNAi)-Based Nanomedicines for Treating Viral Infections - Harnessing Biomaterials in Nanomedicine: Preparation, Toxicity, and Applications - page 220

months, all patients remained in remission from lymphoma and had
gene marking frequencies between 0.2 and 0.32% of peripheral blood
mononuclear cells (PBMCs). Vector expressed RNAs were detectable
up to 24 months following infusion and marking was seen in T
cells, monocytes, B cells, and Lin - subsets indicating that HSC were
truly transduced. A second pilot study is now recruiting patients
who have failed anti-retroviral therapy for infusion of autologous
T-cells transduced with the same vector in multiple doses [24].
The natural resistance of CCR5 Δ 32 homozygous individuals
to HIV [27, 58] has made CCR5 a promising target for both small
molecule inhibitors, such as the FDA-approved maraviroc, and RNAi
based interventions. Clinical proof-of-principle was provided by
transplantation of stem cells from a CCR5 Δ 32 homozygous donor
into a HIV + leukemic patient [59]. Following transplant, HIV levels
have remained undetectable even after discontinuing HAART.
As only ~1% of Caucasians are homozygous for the CCR5 Δ 32
mutation and there is currently no infrastructure to track these
individuals, RNAi targeting CCR5 is being explored as an alternative
to homozygous donor stem cell transplantation. In a preclinical
experiment with non-human primates Rhesus macaque CD34 + HSC
transduced ex vivo with a lentiviral vector encoding a H1 driven
shRNA targeting the macaque CCR5 was stably maintained for up
to 14 months after transplantation into autologous recipients with
no toxicity [2]. Surface levels of CCR5 decreased 3-10-fold and CCR5
mRNA levels decreased 5-10-fold. Lymphocytes isolated from these
animals demonstrated a higher resistance to in vitro challenge with
SIV mac239 .
Viral vectors capable of specifically transducing only the desired
cell type after systemic administration have also been investigated
to alleviate the high costs and sophisticated manipulations
associated with ex vivo transduction protocols. Lentiviral vectors
expressing shRNA targeting CCR5 were pseudotyped with a Sindbis
virus envelope that expresses the Fc binding domain (ZZ) of S.
aureus protein A [4]. Conjugation of this ZZ-SIN vector to a α -CCR5
monoclonal antibody enabled targeting of CCR5-expressing CD3 +
T cells and CD14 + macrophages but not CD19 + B cells upon i.v.
administration into NOD-SCID-IL2r γ mice reconstituted with human
PBMC.
Synthetic siRNAs allow for varying siRNA sequences to keep
pace with the mutating virus if the need arises during the course of