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Archive for the ‘Vaccines’ Category

HIV & Measles – double hit pathogenesis?

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ResearchBlogging.org

Despite ongoing worldwide eradication efforts, measles infection still results in significant morbidity and mortality. Although, throughout most of the developed world measles infection has been considerably reduced there still exists massive (and deadly) outbreaks in areas such as Africa and South-East Asia. Investigation of the reasons why this disparity occurs therefore  is of major medical, political and social interest.

Many factors are likely to be behind this major difference – and all of which deserve our attention if we are ever to remove measles from the human population. There exists problems in rolling out vaccines in countries with poor infrastructure such as roads and transport facilities; disruption to what is known as the vaccine ‘cold-chain’ (vaccines have to be kept cold to avoid rendering them unusable) is likely to occur; general poor health of the population in these regions and possible interference of vaccination in children with high levels of passively acquired maternal antibody.

Measles vaccination efforts in Africa may not be entirely effective

Today in PLoS Pathogens, Nilsson and Chiodi highlight in a featured opinion article, another possible source: the link between co-infection with HIV-1 and Measles infection. They point out that HIV-1 infection and replication may result in impaired immune responses in both mothers and children leaving open the possibility of measles infection (no immune system, no protection). HIV-1, as I’m sure you will all know, is a potentially deadly pandemic retrovirus – particularly a major problem in sub-Saharan Africa- which infects humans where it resides in the bodies own immune system: T cells, dendritic cells and macrophages. Viral replication results in the death of these immune cells and destruction of important lymphoid tissues resulting in an individual without key immune functions.

The authors note that children born to mothers who are HIV-1 positive or are HIV-1 positive themselves develop lower levels of anti-measles antibody upon vaccination -a big deal if we’re looking to protect these kids through vaccination. They show that memory B cells may be impaired and lower protection will result through failure to mount a B cell-generated antibody response. Immunity is a highly regulated system, if you remove one aspect-  in this case T cells – you will affect another pathway , in this case B cells. Thus there exists a major  problem with HIV-1 infected people and infection with other pathogens in the environment; HIV-1 infection significantly alters the host immune system weakening it to other invading pathogens such as measles which is endemic in these areas.

So how do we overcome this problem? Well, the authors suggest that on top of increasing vaccination coverage through catch-up programs it would be wise to administer anti-retroviral drugs  to mothers and children prior to vaccination to allow sufficient immune function; this should hopefully make a difference in combating both measles and HIV in the developing world, especially in an area where both cause so much pain. Hopefully, strategies such as this will aid treatment efforts for other pathogens rife in the developing world – targeting both HIV and the individual agents may be more effective.

Sadly, there exists another interaction between HIV and co-infection with other pathogens. Infection usually results in increased levels of immune cells in the blood and tissues yet these very cells are the target for HIV and if these cells increase, HIV replication will also. There exists a deadly interaction between multiple pathogens which must be broken.

Nilsson, A., & Chiodi, F. (2011). Measles Outbreak in Africa—Is There a Link to the HIV-1 Epidemic? PLoS Pathogens, 7 (2) DOI: 10.1371/journal.ppat.1001241

Written by Connor

February 11, 2011 at 3:05 pm

Measles, Papua New Guinea and the brain

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This post was chosen as an Editor's Selection for ResearchBlogging.orgYou may not have realised that – since most people nowadays have been vaccinated against it and have never seen it – but measles is a very serious illness. Generally an acute disease of children, measles is spread by the measles virus where it infects the body via the respiratory route and establishes a systemic infection – involving multiple organ systems – via your bodies own immune cells leading to the typical rash, mild to severe respiratory distress and immunosuppression (Rima and Duprex 2006).

Measles virus replicative cycle

In the ‘developed’ world we tend not to think about infectious disease in the same way as people in other parts of the world; national vaccination campaigns have largely removed the threat (not considering some minor outbreaks) of the some of the biggest human killers and we no longer worry ourselves over whether a family member will come down with these diseases.

Subacute Sclerosing Panencephalitis or SSPE is one of the most serious complications of measles resulting from viral infection of the central nervous system; SSPE is rare (1 in 10,000-25,000 measles infections) but is almost always fatal. Following infection at a particularly young age and on average 8 years following acute infection, a progressive deterioration of neurological function presents : loss of attention span, uncontrolled movements, behavioural changes, cognitive impairment and in all cases vegetative state is entered and death occurs.

It is caused by persistent measles infection i.e one that the isn’t removed when your immune system kicks in, which spreads throughout the  cells found within the brain causing cell death and inflammation. Strangely, no infectious virus can be recovered from infected brains and when this was investigated further they found that many mutations occurred throughout the genome rendering many of the genes nonfunctional. Although the major replicative functions (replication and gene expression) were left intact, the genes required for normal particles formation were those mutated suggesting that the virus may exploit the unique cellular environment in the CNS to spread, replicate and survive.

Green Fluorescent Protein expressing measles virus infection of neuronal cell

As I mentioned previously, due to increased transmission of virus, poverty and poor nutrition, measles infection is extremely serious in developing countries and it is no surprise that SSPE occurs here in higher numbers. In Papua New Guinea there exists a very high incidence of SSPE, THE highest incidence – roughly 3 – 20 times as many cases are reported (98 per million people versus 5 per million people). Manning et al (2011) have attempted to further characterise SSPE behaviour in this country between 1997 and 2008 and highlights the significant burden that measles is in many developing countries. They measured SSPE incidence, measles infection rates and time of birth of each patient presenting with SSPE finding a direct correlation between time of birth, measles epidemics and presenting with SSPE. The group emphasises the requirement

Why is SSPE incidence so high here and what can we do about it? SSPE rates are linked to measles infections in a population and hence have been significantly reduced following measles vaccination campaigns. Sadly, only half of children in Papua New Guinea receive two measles vaccines prior to 1st birthday – not enough to sufficiently protect an individual nor a population from measles infection and hence SSPE; there is insufficiently low-level of herd immunity in regions such as papua New Guinea. The level of vaccine effectiveness of measles vaccine in this region is also particularly low – possibly reflecting damage to the vaccine from cold-chain disruption (in tropical climates it is difficult to keep vaccines refrigerated), population genetic effects or persistence of low-level non-neutralising maternal antibody.

We can no longer afford to ignore the importance of measles in developing countries like Papua New Guinea and we must stress the need for adequate vaccine effectiveness and coverage in already susceptible human populations. Studies like these with SSPE emphasise the real-world need for the investigation of the molecular mechanisms of measles virus persistence and we should look forward to a time when we can adequatly treat measles CNS complications – or maybe with better vaccination coverage we may not have to worry about this.

Manning, L., Laman, M., Edoni, H., Mueller, I., Karunajeewa, H., Smith, D., Hwaiwhanje, I., Siba, P., & Davis, T. (2011). Subacute Sclerosing Panencephalitis in Papua New Guinean Children: The Cost of Continuing Inadequate Measles Vaccine Coverage PLoS Neglected Tropical Diseases, 5 (1) DOI: 10.1371/journal.pntd.0000932

Rima, B., & Duprex, W. (2006). Morbilliviruses and human disease The Journal of Pathology, 208 (2), 199-214 DOI: 10.1002/path.1873

Written by Connor

January 10, 2011 at 8:50 pm

Posted in Measles, Vaccines

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Viral nanotechnology – at the virus-chemistry interface

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Viruses cause death and disease – Avian Influenza, Swine-origin Influenza, HIV, HPV, measles….. its hard to imagine viruses doing anything else – right?

But viruses don’t have to cause disease – they can infect, replicate and exit without the host even realising it was there. Another view of viral infection is that we can exploit this very nature of viruses for our own means – meet: viral engineering (one flavour of biologically inspired nanotechnology).

Viral nanoparticles: the diversity

Viruses are basically self-assembling storage containers that can enter and exit cells and deliver their contents, they are very small, are biodegradable, can be modified (relatively) easily and have an excellent ability to travel around the human body – one big bonus is that in some cases (plant viruses) they are also extremely cheap.

A recent review describes these ‘viral-nanoparticles’ (VNPs) as:

….dynamic, self-assembling systems that form highly symmetrical, polyvalent, and monodisperse structures. They are exceptionally robust, they can be produced in large quantities in short time, and they present programmable scaffolds. VNPs offer advantages over synthetic nanomaterials, primarily because they are biocompatible and biodegradable. VNPs derived from plant viruses and bacteriophages are particularly advantageous, because they are less likely to be pathogenic in humans and therefore less likely to induce undesirable side effects.

Of course there are many caveats with these applications such as we would have to thoroughly test the toxicity (including cell death and immunogenicity) of such VNPs as human pathogens may have been used as the basis of the design, although the use of plant viruses may circumvent these dangers. The pharmacokinetics, infectivity and replication of viruses will be assessed in animal models prior to use as so will the stability in both a physical and genetic sense. Yet there are plenty of uses for VNPs that would not have to be anywhere near a human patient.

Despite these difficulties, we have a great chance of developing improved VNPs through the application of genetic engineering and chemical modifications, allowing us to generate novel combinations of genes and properties into a single viral particle. We no longer have to rely on ‘wild-type’ virus genomes – we can improve on what is out there. By applying a better understanding of natural viral pathogenesis including cell entry, replication, gene expression, cellular tropism and immunomodulation we should be able to rationally design safer, more efficacious and cheaper VNPs for whatever purpose we want. We can now begin to think of viruses as a novel materal that can altered to generate improved properties and thinking this way should open up many possibilities for medicine, industry and science. This is a basic tenet of synthetic biology.

Synthetic biology meet virology.

As of today, this research has been moving at an extremely fast pace – viruses are now used in cancer treatments, bacteriophages have been used to kill off bacterial infections, viruses have been applied in materials science, improved electronics have been developed using viral particles and targeted viruses have been used in biomedical imaging technology. Yet as our understanding of virus/host interactions increases and research on the applications of these VNPs begins to move from in vitro to in vivo investigations we will see more and more uses for these novel materials in both the clinic and in industry. Look forward to the future of viral nanotechnology!

As the review finishes off:

The virus-chemistry interface remains an exciting place to be!

N.F. Steinmetz, Viral nanoparticles as platforms for next-generation therapeutics and imaging devices. Nanomedicine: NBM 2010;6:634-641, doi:10.1016/j.nano.2010.04.005

Written by Connor

January 4, 2011 at 4:43 pm

Massively parallel sequencing meets the vaccine industry

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Live attenuated vaccines (LAVS), such as those produced for measles, mumps and influenza viruses, must have both high safety and immunogenicity if we are ever going to prevent human infection. Those vaccines, which are deemed unsafe, will be withdrawn resulting in low uptake and increased pathogen transmission and those vaccines which are poorly immunogenic, will not be  protective and result in pathogen transmission and significant disease

The key to easily predicting how safe a vaccine is – and also how immunogenic -, may lie in our ability to infer the phenotype (safety in humans) from the genotype (nucleic acid sequence). One problem with this is the inherent genetic instability of  RNA viruses; viruses such as polio, measles and mumps which are responsible for considerable disease in humans and which we vaccinate millions of people worldwide each year. This genetic instability results in what is generally considered as a viral ‘qausipecies’; a cloud-like structure in viral genome sequence space that can have multiple phenotypic properties: one being the safety, or lack of in humans. One example is that of oral polio vaccine strains which during production in tissue culture can accumulate genomic changes resulting in neurovirulence in humans.

In order to assess the safety we must therefore assay the genetic consistency or the types and frequency of particular changes in our vaccines prior to human administration to avoid vaccine induced disease. As I mentioned previously, our ability to assess the safety relies on our means of predicting phenotype from genotype, something that for most viruses is particularly difficult and time consuming. We are therefore  in a position in which we do not know the genetic determinants of safety and so cannot predict it based on nucleic acid sequence.

MPS analysis of two batches of type 3 OPV performed by pyrosequencing. (A) The number of times each nucleotide was read in forward (green) and reverse (red) orientations. (B and C) Mutational profiles for vaccine batches that failed and passed the MNVT, respectively. Here and in all other figures the contents of mutants is shown by colored bars: mutations to A shown in orange, mutations to C in red, mutations to G in blue, and mutations to U in green. Neverov & Chumakov.(2010)

Neverov and Chumakov, from the American Food and Drug association (FDA) recently published a method in which massively parallel sequencing (MPS) is used to accurately and rapidly quantify nucleotide changes across entire poliovirus vaccine genomes.  This method proved to be very sensitive at detecting low frequency changes, changes that may have led to disease in humans. The group put forward the view that we do not truly have to know the direct relationship between genome sequence and safety but what we can do is compare the genotype and frequency of each change with previous ‘safe’ vaccine sequences. Vaccines will be allowed for human use if they have similar viral populations as a previously used strain. They offer this method as a replacement to the slower and less accurate mutant analysis by PCR and restriction enzyme cleavage (MAPREC) method.

The authors admit that the wide-scale implementation of MPS will be inhibited by the high running cost of the equipment.; a cost that they say is much less than the previously used primate neuroviruelance assay. Investment in this technology is expected to lead to a rapid decrease in price and hence will result in increased uptake of this in LAV production worldwide. Neverov and Chumakov have applied this novel sequencing technology to an important area of the vaccine industry. This application will find use in not only polio vaccines but in other LAV production and may also be implemented in the discovery of new genetic determinants of viral safety and immunogenicity.

Neverov, Alexander, and Konstantin Chumakov. 2010. Massively parallel sequencing for monitoring genetic consistency and quality control of live viral vaccines. Proceedings of the National Academy of Sciences of the United States of America 107, no. 46 (November). doi:10.1073

Written by Connor

December 23, 2010 at 7:23 pm

A mothers love declines – a measles vaccine problem?

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Worldwide, measles virus infection accounts for around 200,000 deaths annually; the importance of which is emphasized given the availability of a highly effective vaccine. Vaccine effectiveness, however, is a complex matter and is subject to many problems – a major one being transfer of maternal antibodies to children during early life, a form of natural passive immunity. Although these antibodies are there for a reason and do protect offspring from infections in early life, bridging the gap until they can synthesize their own antibodies, they have been shown to inhibit the activity to certain vaccines – measles vaccine is an example (see figure below).

Antibody concentrations in child following birth showing decline in attenuation (infection attenuation)

During early childhood, maternal antibody concentrations begin to wane and eventually reach such a level as to offer little protection from microbial challenge. These antibodies however are able to dampen the ability of a child to develop protective immunity following vaccination; it is this ‘window of opportunity’ that is responsible for a great number of measles virus infections and fatalities every year. The development of an effective vaccination strategy to get around this blocking effect would therefore be of great medical interest.

Recently, Kim et al (2010) publish their investigations into understanding how and why measles virus infection, in the presence of specific antibody results in the inhibition of a protective response following vaccination. Prior to this study it was unknown whether in this situation, MeV-specific B cells were being generated at all or whether they simply failed to secrete neutralizing antibody. The group used a rat model of MeV infection and simulated maternal antibody effects by passively transferring MeV specific antibodies and measuring the immunological outcomes. They demonstrated that there is a specific failure of B cells to secrete protective antibody in the presence of transferred antibody.

B cells will only secrete antibody when 3 signals are triggered:

1.     B-cell receptor/antigen interactions

2.     B – cell/ T-cell interactions

3.     Action of soluble mediators (for example: cytokines like interferon)

Kim et al hypothesized that in this model, where both signals 1 and 2 were active, inhibition of antibody secretion may be accounted for by the interference with certain soluble mediators. This idea was attractive providing the great deal of evidence showing MeV obstruction of interferon production – a pathway that normally results in the robust development of innate and adaptive immune responses. This results in two major problems involving antibody-specific inhibition of protective immune responses (maternal antibody) combined with MeV’s natural ability to inhibit the development of immunity; cases which are shared during the ‘window of opportunity’.

To this effect, the group developed a novel vaccine vector to circumvent wild-type measles interferon inhibition. Using reverse-genetics technology, they incorporated a MeV antigen gene, the haemagglutinin (HN) glycoprotein into the Newcastle Disease virus (NDV) genome as an extra gene, generating NDV-HN. NDV is an avian virus that induces high concentrations of IFNs upon infection allowing for the possibility of an effective measles vaccine in the presence of measles antibody.

The investigation confirmed the group’s predictions in that NDV-HN induced much higher levels of IFN in rat tissues when compared to MeV and that this led to development of MeV-specific neutralizing antibodies in the presence of transferred antibody. This work further verified that role that the restoration signal 3, in the form of alpha-IFN allows for B-cell secretion of antibody in in vivo and in vitro systems.

Given how medically important vaccination has been in protecting populations from often fatal and serious infectious disease and the troubles that arise when maternal antibody concentrations drop, any work developing vaccine technology to avoid these difficulties should be welcomed. Kim et al. confirmed the basis for the immunological blocks in generating MeV antibodies and began the development of a novel vector system to rationally provide protection. The results in this rat model, although not specifically applicable to the human situation, are promising in that it provides a logical framework to advance vaccine technology and prevent thousands of childhood deaths worldwide.

Kim D, Martinez-Sobrido L, Choi C, Petroff N, García-Sastre A, Niewiesk S, Carsillo T. (2011) Induction of Type I Interferon Secretion through Recombinant Newcastle Disease Virus Expressing Measles Virus Hemagglutinin Stimulates Antibody Secretion in the Presence of Maternal Antibodies. J Virol. 2011 Jan;85(1):200-7. PMID: 20962092

Written by Connor

December 17, 2010 at 10:43 pm