Today we report the use of base editing in patient-derived cells and in mice to correct the most common cause of progeria, the devastating rapid aging disease. Progeria is typically caused by a dominant negative C•G-to-T•A point mutation in LMNA. 1/11…
The mutation (discovered by @NIHDirector’s lab in 2003) results in progerin, a toxic protein that damages nuclei. So providing more healthy LMNA is not a solution, and cutting the mutated gene with nucleases is also challenging due to indel mixtures & similarity with wt LMNA.2/11
We used an adenine base editor to convert the T•A that causes progeria back to C•G at the key position in LMNA. Base editing in cells from progeria children corrected the mutation efficiently (~90%) with minimal indels or off-target edits, and restored nuclear morphology. 3/11
We then performed in vivo base editing of a mouse model of human progeria developed by @NIHDirector’s lab. These mice have two copies of the mutated human LMNA gene, and develop heart disease, age rapidly, & die early (~7 mo.), resembling symptoms of the disease in children. 4/11
A single injection of AAV9 (10^11-10^12 total vg) encoding the base editor into the circulatory system of these mice resulted in ~10-60% correction of the mutation in various organs, corrected the RNA missplicing of LMNA, and reduced progerin protein levels in tissues. 5/11
Base editor-treated mice showed profound rescue of aorta pathology. While saline-injected control progeria mice lose >90% of their vascular smooth muscle cells by 6 mo., and accumulate thick fibrosis around the aorta, base editor-treated aortas are normal in these respects. 6/11
Consistent with this rescue of aorta pathology, aortas of base editor-treated mice at 6 mo. show little human progerin, but abundant normal human Lamin A protein in vascular smooth muscle cells by immunofluorescence. 7/11
Control progeria mice had a median lifespan of 215 d. Mice injected with base editor at 14 d (corresponding roughly to a 5-year-old human in maturation level, though not necessarily in disease progression) had a median lifespan of 510 d, approaching “old age” in normal mice. 8/11
Here are videos of an untreated progeria mouse at 7.5 mo. (near end-of-life), and of three base editor-treated progeria mice at 11 mo. old. You can see the treated mice have much more normal coats, activity levels, & little apparent spinal curvature. 9/11…
These findings show that a one-time base editor injection can directly correct the mutation and rescue of several of the consequences of the disease. Additional work optimizing editor, delivery vector, dosing, & timing towards potential clinical use are underway. 10/11
This work was a collaboration with multiple institutions including @BroadInstitute, @NIH, @VanderbiltU, @Progeria; investigators including @NIHDirector, Jonathan Brown, Leslie Gordon; and researchers including lead authors @LukeKoblan and Mike Erdos. Congrats to the team! 11/11

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More from @davidrliu

27 Aug 20
Bizarrely, @CDCgov now says Americans don’t need to get tested even if they have been in close contact with a #COVID19 infection, and that asymptomatic people do not need a test. More Americans will needlessly die as a result. Here's a thread on why testing is essential. (1/12)
From one of the most accurate #COVID19 models to date (@youyanggu's…), about 1 in 75 Americans today has an active #COVID19 infection. Many of these are asymptomatic and unaware they are infected, but can still infect others. (2/12)…
Without identifying the 1/75 who has an active infection and separating them from the 74/75 who do not, we either allow the 1/75 to mix with others, causing new outbreaks and adding to 180,000 US deaths, or we lockdown, even though 74/75 lack the virus. Neither is acceptable.3/12
Read 12 tweets
24 Aug 20
A new report by Hong Kong University documents an apparent case of #COVID19 reinfection by two different #SARSCoV2 strains. A 33-year-old male presented symptoms and tested positive by RT-PCR on Mar 26. Hospitalized Mar 29, discharged Apr 14 after two negative PCR tests. (1/6)
He returned to Hong Kong from Spain and upon RT-PCR entry screening at the HK airport tested positive again by RT-PCR on Aug 15 (4.5 months after his initial positive test), with Ct=26.7, a fairly high viral load. No symptoms the second time. Hospitalized again. (2/6)
Viral load declined while hospitalized. Tested negative for IgG from hospitalization day 1-3, but seroconverted (became IgG+) on day 5. Sequencing of the virus from March and August saliva samples show two distinct #SARSCoV2 viruses from different clades (V/19A vs G/20A). (3/6)
Read 6 tweets
8 Jul 20
Today we report in @nature, in collaboration with the labs of Joseph Mougous and @VamsiMootha, the development of a new class of CRISPR-free base editors that enable precision editing of mitochondrial DNA (mtDNA) for the first time.… 1/7
The team discovered DddA, an interbacterial toxin that is a novel cytidine deaminase enzyme that operates on *double-stranded* DNA (dsDNA), unlike all previously known cytidine deaminases, which require single-stranded DNA (ssDNA). 2/7
Previous efforts to precisely edit mtDNA have been stymied by the fact that CRISPR requires guide RNAs, which have not been effectively delivered into the mitochondria. mtDNA can be cut with ZFNs or TALENs, but doing so results in mtDNA destruction rather than precise editing.3/7
Read 7 tweets
8 May 20
A key piece of the #COVID19 #SARSCoV2 origin puzzle emerges: where did the virus's unusual spike protein RBD—the receptor-binding domain that engages human ACE2 protein and allows the virus to enter human cells—come from? A new study from Shen & coworkers provides an answer.(1/5)
The authors isolated coronaviruses from pangolins dying from respiratory disease in a wildlife rescue center in Mar-Aug 2019. One CoV-positive pangolin had antibodies that cross-reacted with #SARSCoV2 antigens, suggesting the animal was infected with a SARS-CoV-2-like virus.(2/5)
The pangolin #coronavirus was highly similar to #SARSCoV2 in several key proteins, including a remarkably similar spike protein RBD that differs from the SARS-CoV-2 RBD at only ONE amino acid position out of ~457 amino acids. (3/5)
Read 6 tweets
27 Apr 20
As some communities begin to lift #COVID19 stay-at-home orders, let’s talk about #masks. There is extensive evidence that masks protect you, and thus protect those around you. For example, this meta-analysis of 51 studies and 49 publications:… (1/9)
But what type of mask should you wear? Any type of mask that serves as a barrier between your nose/mouth and the environment will likely help and is better than no mask, but data has been published on cloth masks vs surgical (medical) masks vs N95 masks (respirators). (2/9)
In the above meta-study, surgical masks reduce the average odds of being infected with #SARSCoV, the virus that causes SARS and a cousin of the #SARSCoV2 virus that causes #COVID19, by 68%—even better than frequent hand washing (55%)—of course, best is to do both. (3/9)
Read 9 tweets
5 Apr 20
Let’s estimate the total # of people in the US who have been infected by #COVID19 #SARSCoV2 as of Apr 4, and the number of US fatalities that will result from these infections. To avoid testing coverage uncertainty, we will use fatality data, rather than positive test data. (1/9)
Importantly, the # of fatalities that we end up estimating from the infections through Apr 4 turns out to be independent of the infection fatality rate we use, as shown below. The infection fatality rate only changes our estimate of how many people in the US are infected. (2/9)
As of 10 pm US eastern time Apr 4, there were 8,476 reported US deaths from #COVID19 (…). Let’s assume an infection fatality rate of 1%. While there has been some debate about this number, most estimates are around 1%. (3/9)
Read 9 tweets

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