MERS – Viral Vector relevant bottlenecks
This is not a well-advanced area of research. The original reservoir of MERS is thought to be in bats in Africa, then moving into camels in Africa, with camels being traded with the Middle East. MERS was first detected in immunocompromised individuals in the Middle East, who suffered from chronic infections with a high mortality rate. We now know that the majority of camels in the Middle East are seropositive, but virus shedding has only been detected in young animals. It is not known if re-infection is possible in camels or if immunity is lifelong, and the correlates of protection are not known. The rate of seropositivity in those occupationally exposed to camels is higher than the general population, and from a hospital outbreak in South Korea it was clear that healthy people can suffer extremely mild acute infections, but can transmit the infection to others.
A vaccine could be used in camels, to reduce or potentially eliminate or eradicate the disease in the animal reservoir (camels) and therefore prevent human exposure. A vaccine could also be used in those who work with camels to prevent human infections which may then be transmitted in the wider community and infect immunocompromised people. The group who suffer the greatest burden of disease, namely immunocompromised people suffering chronic infections, are not the best population to target for vaccination since the vaccine is less likely to be effective in this group. Most human immunology has concentrated on studying those with chronic infections, whereas a prophylactic vaccine will be required to prevent acute infections.
In the absence of correlates of protection, the aim for a prophylactic vaccine is to induce neutralising antibody responses against the MERS coronavirus, and thereby prevent infection. CD4+ T cell responses may also be required to improve the duration of antibody production, and CD8+ T cells would be expected to be beneficial in aiding recovery from infection and reducing virus shedding and onward transmission.
A lab in Marburg is able to perform neutralising antibody assays. At the Jenner Institute we have produced recombinant protein for use in ELISAs, can use a pseudotyped lentivirus assay as a surrogate neutralisation assay and have peptides to measure T cell responses in ELISpot assays. Other than the Marburg assay which relies on one lab receiving serum for testing, none of the assays are standardised.
A number of animal challenge models have been tested, all with disadvantages. The majority of species do not express a DPP4 receptor (which the virus requires for cell entry) which is homologous to the human receptor. A number of different transgenic mice have been produced, either expressing the human DPP4 receptor on all cells or only in some tissues. Non-human primates can be infected but suffer extremely mild disease, as do most humans. Marmosets suffer more severe disease, probably because of general immunosuppression in marmosets. Camels can be experimentally infected and virus shedding measured as the endpoint. However containment facilities for camels must be large and are expensive, and sourcing seronegative camels for study can be difficult in some countries. It will be necessary to standardise stocks of virus for challenge and the dose of challenge virus to use to ensure infection without employing such a stringent challenge that vaccines appear to underperform.
Since MERS causes mild disease in healthy adults, it may be possible to establish a human challenge model in future. However this would require high containment and may not be permitted until a highly effective drug to treat MERS infection is available, in order to treat all those undergoing MERS exposure prior to leaving quarantine, minimising the risk of spreading the virus outside of the quarantine facility.
3. Ethical/Regulatory approval (Clinical Development)
4. Vaccines classified as GMOs (Clinical Development)
5. Availability of overseas trial sites (Clinical Development)
The bottlenecks here are relevant. Obtaining ethical approval can be slow and hampered by the lack of capacity of ethical committees to keep up with demand. Within the UK there are multiple ethical committees who may request different wording on trial documents for very similar trials. Obtaining generic approval for phase I trial documents at a national level would be beneficial. The generic documents could then be adopted for specific trials. Regulatory approval is fairly rapid.
HRA is not working for small, early phase clinical trials. It takes far too long to obtain approval initially and non-substantial protocol amendments, which are common in early phase clinical development should not need to be re-reviewed. HRA can be avoided if no NHS facilities are required and this is preferable but not always possible. Approval for GMOs should become national, so that once a facility is licensed to work with GMOs at BSL1, and a national committee has approved a particular vaccine as requiring BSL1, no further specific approval to use that GMO vaccine at a particular clinical centre would be necessary. Currently approvals must be given locally and it can be difficult to find appropriately qualified individuals to assess the request.
Availability of trial sites in other countries can be a major bottleneck if there is no existing infrastructure or history of clinical development.
Pre-clinical development – stages that areNOT bottlenecks due to the use of viral vector platform technology.
From the research grade material it is necessary to go through a process of pre-GMP stock generation. This is done in the process development labs of our GMP manufacturing facility, following the principles of GMP, but without using a clean room. Some of this stock is then used to test the standard production process for replication-deficient adenoviral vaccines, some is used to test genetic stability and some will be taken into the clean room after appropriate QC testing in order to generate the master virus seed stock.
In general, this map does not apply to using platform technologies. Additionally our standard approach is to generate a master virus seed stock and small GMP batch for phase I testing within the same clean room campaign which also includes fill and finish, and proceed immediately to Phase I trials. No process validation is required for this scale of manufacture. Process development for scale up can occur in parallel with phase I and possibly phase II trials (first in human in the UK, further trials in other countries as appropriate). A small bridging study will then be required to compare the Phase I/II material with vaccine manufactured using the scaled up process.
The majority of assays required relate to the platform rather than the antigen. Antigen specific assays are used to test expression of the antigen (Western blot using serum developed in the pre-clinical stage) and to sequence the antigen in the viral vector (generic technique, antigen-specific primers required).
For this case study, a replication-deficient viral vectored vaccine expressing the major external antigen, the spike protein, is presented. This type of vaccine is safe to use in humans, can be manufactured at large scale and thermostabilised, is known to induce antibodies against the vaccine antigen in camels as well as humans, and also induce both CD4+ and CD8+ T cells against the vaccine antigen. The spike protein was chosen as it is the major external antigen of coronaviruses and infection can be blocked by neutralising antibodies to the receptor binding domain of this protein.
No development work necessary as we are using a platform technology. A viral vectored vaccine (ChAdOx1) expressing MERS S was produced using standard techniques, tested for antigen expression by Western blot of the lysate from vaccine-infected cells, and then for induction of antibodies, neutralising antibodies (Marburg lab plus pseudotype neutralisation) and T cell responses after immunising mice. We were able to demonstrate high titre neutralising antibodies after one intramuscular dose of ChAdOx1 MERS, at the same level as that induced by two doses of MVA expressing the same antigen. Another group has shown partial protection of camels against MERS challenge after two doses of MVA (given by the intramuscular AND intranasal route at the same time).
Our lead candidate is ChAdOx1 MERS. Based on clinical development of other adenoviral vectored vaccines against Ebola virus it is expected that a single dose will induce high titre neutralising antibodies as well as CD4+ and CD8+ T cell responses in humans. There is also the option of boosting that response with a subsequent dose of MVA expressing the same antigen (this is being taken into clinical development by another group and we wish to collaborate once both vaccines are in clinical development).