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Saturday, 13 April 2019

Looking good: industry sets its sights on retinal disease treatments

End stage retinitis pigmentosa

Some while back, I posted on the challenge, and lack of progress, in the development of drug treatments for the most common cause of adult blindness- “dry” age-related macular degeneration - dAMD (Roche’s lampalizumab disappoints- is the "dry" AMD pipeline about to dry up?). 

But, as a recent article in Nature Outlook reminded me, while pharmaceutical development may be lagging, a host of technologies now in clinical and commercial development offer hope for individuals with previously untreatable forms of inherited and non-inherited retinal degeneration. Author Simon Meakin lists four technologies with the potential to revolutionise treatment: retinal prosthetics (“bionic eyes”); gene therapy; optogenetics, and cell regeneration.

The “bionic eye” approach involves fooling the brain into interpreting electrical signals delivered by an implanted microchip placed over the retina as spots of light. A microprocessor converts images captured by a miniature camera worn on a spectacles frame to electrical impulses relayed by wireless to the implant. While this cannot match the resolution achieved by the millions of photoreceptors in a healthy retina, with training, recipients can distinguish light from dark and identify high contrast objects. 

The first commercial product (Argus II: Second Sight) received regulatory approval in 2011 in Europe (2013 in the US) for use in individuals with end-stage retinitis pigmentosa (RP).The device cost is widely cited as around $150,000, excluding surgical and training costs. Two other prosthetic systems in clinical development use implants placed underneath the retina; Prima (Pixium Vision) and Alpha AMS, a camera-free system developed by Retinal Implants AG, although the latter has recently entered administration. Pixium intends to begin trials of Prima in dAMD patients before the end of 2019. Second Sight is evaluating the feasibility of bypassing the retina by implanting electrodes into the visual cortex with its Orion system. 

Gene therapy is now established as a viable means of bringing some degree of vision improvement to those with certain inherited conditions, with the landmark approval of Luxturna® (Spark Therapeutics) in both the US (December 2017) and Europe (November 2018). Clinical trials of other gene therapies are underway, with the aim of correcting RP-associated defects and inherited retinal conditions including Leber’s hereditary optic neuropathy; Leber’s congenital amaurosis; Stargardt disease; achromatopsia, and X-linked retinoschisis.

While not associated with any single gene detect, the “wet” (neovascular) form of AMD is also the subject of gene therapy trials aimed at neutralizing a protein (vascular endothelial growth factor- VEGF) involved in blood vessel formation. Success could replace the current treatment of regular injection of anti-VEGF antibodies into the eye.

Treatments in development require injection of viral vectors to insert functioning genes but other strategies, including gene editing and gene silencing, could potentially expand the range of treatable conditions. At a cost of around $425,000 per eye, Luxturna® has featured in the “fair value” debate around drug pricing, although the recent acquisition of NightstaRx, a gene therapy developer with a portfolio of early and clinical-stage assets by Biogen for a headline value of around $800 million, and the acquisition of Quethera and its pre-clinical glaucoma programme by Astellas are likely only the beginning of big pharma interest in next generation ophthalmology.
Optogenetic approaches, which exploit light sensitive proteins (“opsins”) to modulate biological processes, are still in early clinical development but have the potential to address a number of ophthalmologic conditions in which there are too few cells left to exploit or repair through either restoring function or inducing other types of retinal cell to become light-sensitive. A start-up company, RetroSense, initiated the first clinical studies of a viral vector delivered opsin in RP patients and was acquired by Allergan in 2016: an early-stage clinical study is ongoing.

The downside of opsins is that they respond to a limited range of light conditions. Gensight Biologics, hopes to get around this by combining video capture and electrical stimulation of retinal ganglion cells made light-sensitive through insertion of a gene coding for opsin production. The first RP patient was treated in October 2018 and the ongoing clinical study will evaluate different doses of the viral vector bearing the opsin gene.

The replacement of damaged retinal pigment epithelium (RPE) through stem cell therapy may eventually become a viable treatment for RP and AMD. Mixed results have been obtained with injected cell suspensions but implantation of pre-formed sheets of RPE cells secured within a biocompatible matrix could prove to be a significant improvement. Early clinical studies have been completed in subjects with both the wet and dry forms of AMD, and a start-up, Regenerative Patch Technology, formed to take up the challenge of financing and commercialising development.

Repairing the circuitry linking photoreceptors to the brain presents an altogether different level of technical challenge but, on the basis that non-mammalian species are capable of some degree of retinal neuron regeneration, it’s not impossible that means of reproducing this trick in humans might be developed, possibly through re-programming other cells present in the eye to regenerate lost neurons.

Complexity, cost and necessary caution over gene therapy and stem cell procedures make it likely that only a small number of individuals will initially benefit from these treatments, but advances in viral vector and stem cell-derived product manufacture, together with growing industry involvement should eventually make these life-changing treatments available to a significant minority of vision-impaired individuals.

Photo credit: Christian Hamel [CC BY 2.0]

Saturday, 6 April 2019

HPV vaccination just keeps on giving

HPV vaccination has the potential to eliminate
 cervical cancer in future generations

As a keen follower of developments in cancer immunotherapy (and occasional commentator), it’s easy to forget the quiet impact of past advances in cancer treatment and prevention which are now a routine element of healthcare.

A publication from the Giovanni Lorenzini Foundation, a not for profit health educator,”HPV Vaccination Concepts in the Reality of Today, reminded me that, while effective therapeutic cancer vaccines remain elusive, prophylactic vaccination against human papilloma viruses (HPV) has achieved the initial public health goal of significantly reducing the risk of cervical cancer and, in time, will have a similar impact on other HPV infection related cancers, notably cancers of the head and neck.

HPV infection is not uncommon, with viral DNA being detectable in around 10% individuals (and up to 30% in some populations). Over 200 types of HPV have been identified, with 15 or so being linked to cancer. These “high risk” types have a propensity to integrate their DNA with that of host cells, resulting in the expression of two particular proteins (E6 and E7) with cancer-causing potential. HPV-related cancers are a significant burden, accounting for an estimated 4.5% of all cancers, most commonly cervical cancer, followed by head and neck cancers, anal and male and female genital cancers.

Cervical cancer development is generally slow: the first HPV vaccines were deployed just over a decade ago so the absolute reduction in cancer cases is unknown. Meta-analysis of studies in women receiving either an HPV vaccine or a placebo found that pre-cancerous changes in the cervix were present in 2 of every 10,000 vaccinated women and in 164 of every 10,000 unvaccinated women. In women aged 15 to 26 years (but not those aged 25 to 45 years) vaccination reduced the risk of cervical pre-cancerous changes associated with the highest risk HPV types from 341 to 157 per 10,000. 

Early HPV vaccines were only capable of protecting against two or four high risk HPV types associated with cervical cancer, with vaccines introduced in the last four years addressing nine HPV types to provide broader protection against a range of HPV-related cancers, particularly head and neck cancers arising from or orpharyngeal infection with HPV. 

While the overall incidence of head and neck cancers is declining in developed economies, largely due to decreasing tobacco use, the incidence of HPV-positive cancers has risen over the last two decades. Extending routine HPV vaccination to young males (a policy in place in the UK since July 2018) should eventually reverse this trend, while also further reducing the prevalence of HPV-associated genital cancers.

HPV vaccination has not been without controversy. A meta-analysis of 73,000 participants in HPV vaccine studies did not encounter any evidence to support much publicized claims that “debilitating illness” (including rapid increase in heart rate on sitting or standing up- postural orthostatic tachycardia syndrome) was a common side effect in girls. The uptake of HPV vaccination in the US is low relative to overall vaccination rates. Parental concern that vaccination would somehow encourage promiscuity has been proposed as one reason, although studies suggest that lack of knowledge about the purpose and benefits of HPV vaccination; a three dose vaccine schedule which may have resulted in missing doses, and vaccine cost are key contributors.

HPV vaccination may have benefits outside of cancer prevention. The prevalence of HPV in seminal fluid is twice as high in infertile men when compared with the general population. Laboratory studies have identified several mechanisms by which HPV can detrimentally alter sperm, with the presence of sperm-bound viral DNA being a predictive factor for early miscarriage. Vaccination has been shown to increase the rate of HPV clearance from infected semen and might contribute to higher success rates for couples undergoing assisted reproduction.

Photo credit: chinnapong/shutterstock.com

Tuesday, 12 March 2019

(Un)-Natural Born Killers

Human natural killer (NK) cell.
Add CAR for extra killing.

Cancer immunotherapy, although far from offering universal cure, continues to rack up some remarkable successes. Immune checkpoint inhibitor treatment has transformed expectation in metastatic melanoma, non-small cell lung cancer and other advanced solid tumours, with new agents and novel combination therapies likely to further improve outcomes.

Cell-based therapies in which patient T cells are genetically engineered to express a protein construct (“chimeric antigen receptor”, hence CAR-T) specific for a target cancer antigen, then expanded and infused to bring about tumour destruction and long-term anti-tumour immunity. CAR-T treatment has achieved unprecedented complete response rates in certain types of otherwise untreatable childhood and adult leukaemia, although not without the risk of life-threatening adverse events resulting from cytokine release and relapse through the escape of cancer cells that do not express the selected target antigen. 

Clinical experience with CAR-T therapies is limited and so far confined to haematological cancers (Kymriah® developed by Novartis and Yescarta®, developed by Kite Pharma and since aquired by Gilead, only received FDA approval in August 2017 and October 2017, respectively), but the potential of cell-based cancer treatment  is such that substantial industrial and academic effort is focused on development of next generation therapies capable of tackling solid tumours, and which do not require  complex and expensive patient-specific product manufacture.

T cells are not the only components of the immune system capable of tumour recognition and destruction. So-called “natural killer” (NK cells- there’s a clue to their purpose in the name) are part of the innate immune system, a first-line defence that does not require the recognition and processing of foreign antigens to function. NK cells possess a variety of tumour-recognising receptors with interaction resulting in cancer cell destruction and upregulation of innate and adaptive immune systems.

In contrast to donated T cells (even when matched by tissue type), donated NK cells are not identified as foreign, opening up the possibility of off-the-shelf (“allogeneic”) treatments. NK cells are readily isolated from cord or peripheral blood and can be maintained as a cell line. Human stem cell-derived NK cells might one day prove suitable for industrial scale production. Moreover, as with T cells, NK cells are amenable to transformation by viral vectors encoding chimeric antigen receptor DNA.

A number of CAR-NK clinical studies are underway, utilising NK cells from donors or cell lines modified to express different cancer antigen receptors specific for lymphoma and various forms of leukaemia; glioblastoma; non-small cell lung cancer, and other solid tumours. Notably, several of these studies are sponsored by Chinese clinical investigators and biopharma companies, echoing the country’s substantial efforts in CAR-T product development.

CAR-NK product development is not without problems, such as the efficiency of cell production and need to optimise CAR design to minimise toxicity through “off target” effects and to improve the specificity of intracellular signalling which kicks NK cells into fighting mode. It’s too early to determine which of the available sources of NK cells, if any, will result in superior outcomes. NK cells are relatively short-lived and products based on a subset of longer-lived NK cells may be required to induce lasting anti-tumour effects.

However, as regulatory and clinical acceptance of CAR-T cell products demonstrates, the complexities of cell-based therapy can be mastered: CAR-NK products will undoubtedly benefit from this expanding knowledge base and through entering an environment with growing payer acceptance of high-ticket cancer treatments.

Photo credit: NIAID

Thursday, 29 November 2018

Linking the brain, gut and bacteria in neurological disease.

The lifetime risk of developing neurological disease is influenced by variety of factors: genetics, cardiovascular health, and of course, age and neuroscience research continues to uncover more subtle links. 

Recent work elaborates on a long-suspected connection between that occasionally troublesome leftover, the appendix, and Parkinson’s disease risk, while other researchers have raised the possibility of the brain having its own microbiome, with implications for a bacterial influence on the risk and course of neurological disease.

Alzheimer’s disease (AD) and Parkinson’s disease (PD) are characterised by the accumulation of mis-folded proteins in the brain: amyloid β and tau proteins in the case of AD, and α-synuclein in PD, where it is the main constituent of “Lewy bodies”- clumps of aggregated protein found within neurons and a hallmark of PD and other dementias. Mutations within the α-synuclein gene are found in familial PD and efforts are ongoing to determine the normal function of α-synuclein and whether preventing its aggregation or accumulation in the brain might be of benefit
PD causes both motor and non-motor symptoms and gut-associated problems such as constipation and impaired emptying of the stomach are common years before the onset of motor symptoms. That the aberrant form of α-synuclein can be found throughout the gastrointestinal tract in individuals with PD has been known for several years, although this also the case in those who don’t develop PD.
The highest levels of aberrant α-synuclein are found the appendix, raising the possibility that it serves as reservoir for dysfunctional protein which makes its way to the brain via the vagus nerve and potentiates the transformation of normal α-synuclein into the aggregated form. Circumstantial evidence for a link between the appendix and PD risk has been found in a large epidemiological study, with individuals who had undergone surgical severing of the vagus nerve (usually to manage hard to treat chronic duodenal ulcers) being at  lower risk of developing PD.
Defining the role of the appendix in PD has proved elusive, and three recent epidemiological studies failed to find any obvious link. By analysing medical records from over 1.6m Swedes from 1964, a research group at the Van Andel Institute has established that appendectomy reduces the risk of developing PD by around 20%, although this protective effect was only apparent in individuals living in rural areas. Pesticide and herbicide exposure are linked with a higher risk of PD and appendectomy may in some way mitigate environment-related PD risk.  Further analysis indicated that appendectomy delayed the onset of PD by an average of more than three and a half years in those who had undergone appendix removal 30 years or more before.

Biochemical analysis of appendix samples from healthy individuals and those with PD identified aberrant forms of α-synuclein. These were present in 46 of 48 normal individuals.  Mixing normal appendix tissue with normal α-synuclein resulted in the protein being broken down into forms resembling those found in PD brain samples.
Although far from being a recommendation for elective appendectomy, the finding that aberrant α-synuclein is common in healthy people suggests that PD risk requires its migration to the brain. Finding ways of confining, or even eliminating, the protein from the appendix could conceivably reduce PD risk.

It’s postulated that appendix might play a role in monitoring and restoring the gut microbiome and that inflammation results in changes which favour bacteria which generate “pro-PD” metabolites. That the gut flora might directly influence the neurological environment is not as far-fetched as it once would have seemed although a poster presentation given at the Society for Neuroscience annual meeting suggests the possibility that a local, rather than distant, microbiome might potentially influence conditions in the brain.

University of Alabama researchers have found that rod-shaped structures first observed on electron microscopic examination of brain samples from schizophrenics are, in fact, bacteria. These were most abundant in the substantia nigra, hippocampus and prefrontal cortex but rarer in the striatum. Bacteria were also found within brain cells, particularly in the ends of astrocytes closest to the blood-brain barrier locations, in dendrites, glial cells and in and around myelinated axons.

To rule out sample contamination, the group compared fresh brain samples from mice raised in a normal environment and those born and maintained in a germ-free environment: bacteria were only found in the former. Nucleic acid sequencing indicated that most of the bacteria belonged to groups commonly found in the gut, although their means of passage to the brain- whether from blood, the nose or through the nervous system.

Since bacteria were found in the brains of both normal individuals and those with schizophrenia, there’s no obvious causal relationship, but, as the study of gut, oral and skin microbiomes has shown, bacterial nutrients and metabolites can cause subtle but important changes in cell and organ function. Whether the presence of bacteria in the brain truly indicates a permanent ecosystem and not merely a post-mortem artefact remains to be established. But, as with the appendix and PD, confirmation that the brain is indeed influenced by local (or distant) bacteria may help better define neurological disease risk and uncover new means of treatment and prevention.

Sunday, 11 November 2018

Melanoma immunotherapy: Can vaccines and cell therapies expand on immune checkpoint inhibitor successes?

Mestastatic melanoma cells

Tracking the major cancer meetings has kept me occupied throughout October and into November but left me with plenty of material for this, and future, blog articles. A presentation at the UK’s NCRI conference on the increasing mortality rate from melanoma in men (but not women, where mortality rates are generally declining or stabilising), while alarming, did remind me of just how far melanoma treatment has advanced in a few short years.  
Prior to the availability of anti-CLTA-4 and anti-PD-1 immune checkpoint inhibitors, overall survival from metastatic melanoma in developed countries was around 25% after three years: combination immune checkpoint inhibitor treatment has stretched this to over 60%, and use following surgery (“adjuvant” use) significantly improves recurrence free survival.
Despite these successes, a significant need remains for alternative treatments for those who fail, or are intolerant of, current immune inhibitor checkpoint regimens and a gamut of investigational immunotherapies including “personalized” or “individualised” peptide and mRNA therapeutic vaccines, cell therapies and oncolytic virus therapies are in active clinical development.
That the immune system recognises melanoma as being “not self” has been known for decades and means of usefully exploiting this distinction long precede the discovery of immune checkpoints. Attempts to effectively boost the anti-melanoma immune response through injection of the Bacille Calmette–Guérin (BCG) tuberculosis vaccine were made in the 1970s, with mixed success. The potent immunomodulators, interferon alpha (IFNα) and interleukin 2 (IL-2), were approved for use in melanoma in the 1990s and still have a role in the treatment of metastatic disease and adjuvant therapy.
Melanoma has long been an attractive target for cancer vaccine development. A variety of melanoma antigens common to a majority of tumours - “tumour-associated antigens” (TAAs), including gp100, GM2; tryosinase, MART-1 and MAGE-A3, have been exploited, either alone or in combination, in cell-based and peptide therapeutic vaccines.
Cell-based vaccines (as either intact or processed tumour cells or as cell-free lysates) offer the advantage of presenting a spectrum of TAAs, although neither patient-derived (autologous) nor cultured tumour cell-derived (allogeneic) cell-based melanoma vaccines, such as Melacine® (GSK/Schering) and Canvaxin® (CancerVax/Serono), have made it through pivotal studies. M-VAX (AVAX), a chemically-modified autologous cell vaccine, has been in late-stage development limbo for over a decade.
Historically, peptide vaccines have fared no better, with a pivotal study of Oncophage® (Antigenics), the manufacture of which involved isolation of heat shock protein-peptide complexes from autologous tumour cells, being abandoned, and a Phase III study of a MAGE-A3 peptide vaccine (GSK) being terminated due to lack of obvious efficacy over placebo.
Adoptive cell transfer (ACT) involves the collection, isolation, ex vivo expansion and (re)-infusion of autologous tumour-associated cytotoxic T-cells. ACT using tumour-infiltrating lymphocytes (TIL) has occasionally attained response rates of 40%-50% and complete remission in 10% to 25% of patients with extensive metastatic disease: however, the complexity of ACT has essentially confined it to clinical studies and compassionate use.
As is the case with other cancer indications, decades of disappointment and inconsistency have not curbed the academic and commercial pursuit of effective melanoma immunotherapies. Applying recent advances in technology- next generation sequencing; gene transfer and editing; nucleic acid delivery- to melanoma vaccine and cell therapy development might just make these old dogs capable of new tricks.
Cancer vaccine efficacy is blunted by the immunosuppressive tumour microenvironment: combination with immune checkpoint inhibitors is an obvious means of increasing the odds of success and a number of studies combining therapeutic vaccines with anti-PD-1 or anti-CTLA-4 immune checkpoint inhibitors are underway. These agents may eventually be joined or replaced, by one or more of the “next wave” of immune-oncology drugs directed at LAG3, CSF1-R, GITR or at targets in the innate immune systems which can fire up the immune response.
Imlygic® (T-VEC: Amgen), an oncolytic virus therapy is“vaccine-like” in effect, activating both the innate immune system and revealing hidden tumour antigens (“neoantigens”) to the adaptive immune system through tumour lysis. Combination with ipilimumab has shown improvement in response rates over Imlygic® alone, and a Phase III combination study with pembrolizumab (KEYNOTE-034) is ongoing. Early-stage studies of CAVATAK®, an investigational virotherapy acquired by Merck & Co from Viralytics earlier this year, has shown promise when combined with either pembrolizumab or ipilimumab.
The application of next generation sequencing technology and bioinformatics could offer a practical route to bespoke melanoma vaccines, with antigen selection and vaccine composition being determined by tumour and patient genetic makeup. Neon Therapeutics is currently trialling a synthetic peptide vaccine (NEO-PV-01) using sequencing of tumour biopsy material to formulate a selection of up to 20 peptide-mimicking patient-specific neoantigens. NantBioScience is pursuing a similar personalization strategy, with expression of patient-specific neoantigens in yeast cells (YE-NEO-001).
The in vivo expression of melanoma (and other cancer antigens) through the introduction of the corresponding mRNA sequence is receiving increasing attention. Lipid complex mRNA vaccines, encoding multiple melanoma TAAs or a personalised selection of antigens, are now in early clinical studies (Lipo-MERIT and RO7198457: BioNTech).
mRNA has brought a new twist to dendritic cell (DC) vaccination, where DCs isolated from the patient are loaded with melanoma antigens to optimise their processing and efficiency of presentation to the immune system. eTheRNA’s TriMix technology combines mRNA encoding melanoma antigens with mRNA encoding proteins known to enhance DC activation and maturation and to promote both helper and cytotoxic T cell production. Durable clinical responses have been achieved in melanoma patients who had failed previous treatments when the TriMix-DC-MEL vaccine was administered in combination with ipilimumab.
Gene transfer may open up additional ACT strategies for melanoma. T-cell receptor (TCR) gene transfer allows the generation of antigen-specific lymphocytes from patient T-cells Early studies with melanoma antigen-specific TCRs have shown modest response rates, although several have been marred by severe adverse events due to the “off-target” destruction of normal melanocytes.
The utility of ACT may be significantly improved through chimeric antigen receptor (CAR-T) technology, where T-cell antigen receptors are engineered to combine binding, signalling and co-stimulatory domains. Pilot CAR-T studies are underway. Improvements in TIL ACT may be possible by using CRISPR-CAS9 gene editing to increase the ability of T-cells to home in on tumours.
Next generation cell therapies, including DC vaccination, are likely to benefit from the broader expanding commercial interest in CAR-T and TCR therapies which will likely lead to further improvements in manufacture and assist in establishing the logistics necessary to delivery patient-specific treatments. Growing use of semi- or wholly-automated cell product processing will ultimately reduce costs and make the treatment of larger number of patients viable.
Effective melanoma immunotherapy had been a long time in coming, but as immune checkpoint inhibitor therapy has shown, revolution is possible. Experimental melanoma immunotherapies still have a lot to prove, but with the aid of across the board advances in immuno-oncology and other disciplines, we may finally see vaccine and cell-based approaches becoming practical and valuable treatment options.
Photo credit: Valencia, JC. NCI Center for Cancer Research

Saturday, 22 September 2018

Zika virus: a whistle-stop tour

Zika virus (false colour transmission
electron microscope image)
In a recent piece on mRNA vaccines[mRNA vaccine technology: industry is getting the message] , I mentioned Zika virus development as an indication for this emerging technology. only to realise my ignorance of this high profile pathogen (shameful, since I spent my post-doc years working in a school of tropical medicine)

First stop in filling the knowledge gap was a visit to the ever-useful World Health Organisation website which features a comprehensive “Zika timeline”. First discovered in 1947 in monkeys living in a Ugandan forest (which gave its name to the virus), and shortly after in species of Aedes mosquito, epidemiological studies conducted in the 60s and 80s indicated widespread human exposure to the Zika virus in Africa and Asia, with infection largely associated with no, or only mild, symptoms.

The more sinister nature of Zika infection emerged in 2007 and 2008, with the first confirmed large scale outbreak on the Micronesian island of Yap, and evidence that infection could be sexually transmitted. Further outbreaks occurred on various Pacific Islands during 2013 and 2014 and pointed to a link between Zika infection and birth defects and with Guillain–Barré  syndrome, a rare autoimmune disease which affects the nervous system. A year later, an epidemic characterized by a skin rash bit otherwise mild symptoms was reported in north-eastern Brazil, but was not recognised as being due to Zika virus.

By October 2015, an increasing numbers of microcephaly cases (newborns with small heads, indicative of abnormal brain development) were being reported. Further Zika outbreaks occurred in several South American and Caribbean countries over the following year, with the first cases (via sexual transmission) being identified in the continental United States in 2016.

Being generally asymptomatic, the prevalence of Zika infection is not easy to quantify, but mosquito-transmitted infection has been reported in over 80 countries (with transmission ongoing in over 60 of these). Over 1.3 million people are thought to have been infected in Brazil alone during the 2015 outbreak. In common with other vector-borne diseases, the spread of Zika owes something to human mobility, although social factors, principally the inability to afford protection against mosquitoes and high population density have been identified as key drivers.

The Zika virus has several properties that contribute to its ready transmission and to its devastating effect on foetal development. The virus is highly persistent in whole blood (up to 100 days) and in the male reproductive tract, allowing sexual transmission. Zika has a preference for certain cell types that facilitate the passage of infection through the placenta; animal studies suggest that viral preference extends to neural progenitor cells essential for normal cortical development. Whether Zika infection is a direct cause of Guillain–Barré  syndrome  has not been established.

As with malaria, Zika’s vulnerability lies in its dependence on mosquito vectors: and targeted insecticide use, management of standing water and the conscientious use of bed nets and repellents can significantly reduce transmission. Like malaria, control initiatives are vulnerable to political and economic factors, including climate change-related changes in mosquito distribution and abundance. Unlike malaria, Zika has a simple lifecycle; as with other flaviviruses (including the causative agents of yellow fever and Japanese encephalitis), infection should, in theory, be preventable through vaccination.

Vaccine development efforts are almost contemporary with the Zika outbreak itself, beginning in the second half of 2015 with the genetic analysis of Brazilian Zika isolates, with the first clinical study of a Zika vaccine being reported in late 2017. Around 45 candidate vaccines have been developed through academic, governmental and industrial efforts, with nine of these reaching the clinic, representing both established (inactivated virus) and experimental approaches (DNA and mRNA vaccines). The WHO’s initial requirement is for a vaccine that can be deployed in response to outbreaks with the primary goal of preventing congenital Zika syndrome through minimizing virus carriage in the immediate population.

Early clinical studies have established that vaccination can elicit aneutralizing antibody responses, although, while an accepted hallmark of flavivirus vaccine efficacy, the importance of neutralising antibodies, and the minimum levels needed to establish protection have still to be established in the context of Zika infection. Other important unknowns include the duration of effective vaccine-induced immunity and whether the reproductive tract can be protected from infection.
Perversely, given the untold misery arising from Zika outbreaks around the globe, the virus’s propensity for neural progenitor cells may offer a new means of treating the most aggressive and intractable form of brain tumour, glioblastoma.

Chinese researchers have found that an experimental live attenuated Zika vaccine functions as an oncolytic virotherapy [Going viral] in an animal model of glioblastoma, specifically infecting and destroying glioma stem cells thought to be responsible for the inevitable recurrence of the tumour. Elimination was also observed using glioma stem cells isolated from individual patients.

Photo credit: Credit: NIH/NIAID

Thursday, 6 September 2018

Gene editing: off the bench and into the clinic

As the first sponsored CRISPR-Cas9 clinical study gets underway,
industry has high hopes that genome editing will eventually make gene
therapy a mainstream treatment for both inherited and non-inherited
Recent progress in gene therapy, with successful proof of concept being reported in a range of otherwise untreatable conditions and the grant of marketing authorisations for commercially-developed treatments makes it easy to forget that these successes were built on almost three decades of endeavour and regular disappointment.

Gene therapy restores aberrant or missing biological functions through the introduction of functional genes carried into the cell using engineered viruses or by zapping with electrical pulses. A more involved process is the alteration of specific nucleotide sequences within a faulty gene to restore or 
modify function- so-called “gene editing”. 

Around the turn of the millennium, certain bacterial genomes were observed to have multiple copies of repeated DNA sequences which read the same in both directions -“clustered regularly interspaced palindromic repeats” (CRISPR), which were subsequently found to be responsible for the exquisitely specific recognition of infecting viruses. In 2012, it was shown that CRISPR could be exploited to edit genes in mammalian cells, prompting an explosion in translational science, patent wrangles and an influx of venture funding. 

Reduced to its bare bones, CRISPR gene editing utilises a short piece of “guide” RNA, designed to bind to a specific sequence of DNA, complexed with an enzyme able to cut double-stranded DNA, with the bacterial enzyme “Cas9” being widely used. Once within the nucleus, the guide RNA latches onto its complementary DNA sequence, directing the enzyme to cut in the right place: the cell’s DNA repair mechanism completes the editing process. 

CRISPR-Cas9 (and other CRISPR based systems) have brought relative simplicity and low cost to gene editing, providing a powerful research tool with application across biological disciplines and a route to significant advances in agriculture and the treatment of both inherited and non-inherited disease.

American and European regulators have been understandably cautious with respect to CRISPR clinical studies. As with other forms of gene therapy, CRISPR-Cas9 editing is not without potential risk, such as unwanted alteration of DNA sequences other than the target gene sequence, or the triggering of immune responses to the Cas9 enzyme (obtained from one or other of two common skin bacteria) or through introduced RNA being recognised as being  “foreign”. 

Chinese investigators have been less troubled by the unknowns surrounding CRISPR clinical development:  first in man studies began in 2010, with around 80 subjects being treated in cancer and HIV gene editing studies by February this year. Several Chinese research groups have explored  gene editing in non-viable, and most recently, viable human embryos.  

CRISPR Therapeutics, in partnership with Vertex,  successfully addressed undisclosed FDA concerns raised in May this year and are now recruiting beta thalassemia patients for a Phase I/II gene editing study. Like sickle cell disease, beta thalassemia arises from an inherited defect in the gene encoding the oxygen-carrying protein, haemoglobin. 

Rather than directly editing the haemoglobin gene, the CRISPR-Cas9 complex (designated CTX001) is designed to alter a DNA sequence responsible for the shutdown of foetal haemoglobin production, in the hope that turning the switch back on will produce sufficient levels of functional haemoglobin. The editing process is performed ex vivo, with blood-forming stem cells being extracted from the patient, transfected with the CRISPR-Cas9 complex, expanded and then returned by infusion. 

CRISPR Therapeutics and its peers, Editas Medicine and Intellia Therapeutics have ambitions to develop gene editing therapies for a range of genetic conditions that result in metabolic dysfunction (Hurler syndrome, glycogen storage disease, alpha-1 antitrypsin deficiency, transthyretin amyloidosis) and visual impairment (Leber congenital amaurosis, Usher syndrome), as well as cystic fibrosis and Duchenne muscular dystrophy (DMD). Exonics Therapeutics recently published data indicating that their “SingleCut” CRISPR technology was able to  restore near normal levels of dystrophin expression in an animal model of DMD. 

CRISPR may prove to be more efficient and flexible means of engineering “off the shelf” (allogeneic) cancer-fighting T cell therapies, reducing the cost and complexity of current patient-specific CAR-T therapy  [ASCO Clinical Cancer Advances 2018. And the winner is...].

Pre-CRISPR era gene editing methodologies may also prove to have therapeutic application. Sangamo Therapeutics has used a zinc finger nuclease-based approach to achieve “in body” editing of a faulty gene in four individuals with Hunter syndrome, an enzyme disorder that prevents the breakdown of complex sugars, leading to harmful accumulation. A decrease in urinary complex sugar level was observed in two individuals, although not an increase in normal enzyme levels in the blood. Full interpretation of the significance of these results will take time but importantly, “in body” editing raised no safety issues. 

Clinical development of  gene editing-based therapies will continue to advance cautiously (at least in the West), but is likely to can to benefit from experience gained in viral and non-viral vector design now being exploited in other forms of gene therapy and growing regulatory familiarity with gene therapy risk-benefit assessment. 

Image credit: Credit: Jill George, NIH.