Hey Julie. I was wondering the same thing.
It might be from a talk the Cornell team gave at a conference recently. I didn't attend (I wish I had!), but the abstract is below. Note: the talk was mostly about a different, newer therapy, but it's likely that they talked about the therapy ("first generation") currently being trialed, as background to the discussion of the newer therapy.
Apologies for not giving the URL to the source of the abstract, but I forgot to note it, and now I can't "google up" the abstract page. Arg!
339. Second Generation APOE2+APOE4‾
AAV-Mediated Gene Therapy for APOE
Homozygotes at Risk for Alzheimer’s Disease
Rachel Montel, Esther Frenk, Ronald G. Crystal, Katie
Genetic Medicine, Weill Cornell Medical College, New York, NY
Alzheimer’s disease (AD) is a progressive degenerative neurological disorder associated with a strong genetic risk in polymorphisms of the apolipoprotein E (APOE) allele. Inheritance patterns of APOE alleles demonstrate that APOE4/4 homozygotes have a 14.5-fold increased risk of developing AD, while APOE2/2 homozygotes are protected against developing AD. The knowledge that the presence of APOE2 in APOE2/4 heterozygotes markedly reduces the APOE4 risk led to the development of a 1st generation preventative AD gene therapy delivering APOE2 to the brain of APOE4 homozygotes. In the present study, we hypothesized that a 2nd generation gene therapy using an adeno-associated virus (AAV) expressing therapeutic APOE2 with artificial microRNAs (miRNA) targeting endogenous APOE4 may further mitigate the risk and limit AD development of APOE4 homozygotes. To test this hypothesis, we evaluated silencing of APOE4 expression using a series of siRNAs targeting APOE4 in the U-87 human glioblastoma cell line. Of these siRNAs, one sequence (siRNA2) significantly silenced APOE expression and was selected for generating novel APOE-targeting miRNAs that were incorporated into an artificial miRNA cassette for expression in the AAV vector. These miRNAs were cloned into the intron in the CAG promoter 5’ of the transgene or in the 3’ untranslated region (UTR) of the pAAV expression cassette. To determine the efficiency of silencing by the miRNAs, the APOE4 target site was cloned into the pmirGLO-luciferase plasmid and cotransfected into 293T cells with pAAV expression plasmids containing APOE-targeting miRNAs. There was a >40% reduction in luciferase activity (representing APOE4 expression) in the presence of APOEtargeting miRNA compared to the control scrambled miRNA. In parallel, an APOE2 expression cassette was designed that was resistant to silencing by the miRNAs. To test expression of the modified APOE2 cDNA, 293T cells were transfected, followed by analysis of APOE2 expression by quantitative PCR and Western analysis. The mRNA and protein expression levels from the miRNA resistant APOE2 cDNA were similar to unmodified APOE2. These observations demonstrate that APOE4 can be targeted for silencing by miRNA incorporation into an AAV expression cassette with a therapeutic APOE2 as a 2nd generation gene therapy for the APOE2+APOE4- treatment of APOE4 homozygous individuals at high risk for the development of Alzheimer’s disease.