Field of Science

Showing posts with label systems biology. Show all posts
Showing posts with label systems biology. Show all posts

Should vaccinology embrace systems biology?

Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius -- and a lot of courage -- to move in the opposite direction.

E. F. Schumacher (1911-1977) British Economist

Vaccines represent one of the most cost effective methods around to prevent loss of life and disease in a whole range of animals, including the human population. Over the last 200 years or so, we've become pretty adept at producing them and so the science of vaccinology - or how to generate these complex pharmaceuticals  - has led to the eradication (and near eradication) of many viral pathogens.

This is one network in your immune response following influenza vaccination (Kokke et al 2011) as id'd through systems biology approaches. Knowledge of key mediators in these pathways may allow for the rational design of new vaccines - but is it worth it?

But, it hasn't succeeded for a number of currently killer viruses (respiratory synycitial virus and HIV to name but two) and we have begun to think that maybe the method of 'isolate, attenuate, vaccinate' or the synthesis of single virus antigen molecules isn't gonna cut it anymore. So what are we going to do?

We are wanting to rationally generate vaccines - taking a wild-type, disease-causing isolate and through some genetic engineering, make it sufficiently weak so as to generate an effective immune response in patients while not causing disease. Yet, this is harder than it looks and so some researchers are now turning to systems biology to offer a glimpse into how some of our most successful vaccines function so as we can reconstruct these processes for the numbers of viral pathogens we are yet to protect against.

*I have explored how we may attempt to do this from the viruses perspective (mumps virus versus vaccine, here), more precisely: how come the vaccine strain is less deadly than the 'wild' strains. Both are valid approaches and probably just as difficult to carry out as each other.*

Systems biology affords us a chance to more fully understand the complexity of living systems. Through the collection of reams of data (DNA sequences, gene expression changes, protein levels - and other 'omics' technologies) we are now able to adequately model what is going on in the organism/cell through now more common bioinformatic and statistical analyses. As in the quote I used above, it is not about making the study of life more complex, it is really about realizing this fact and doing something to understand it better under a broader way of thinking. This allows us to 'see' changes and functional differences that we would never have observed had we gone about such an experiment using our a priori knowledge and this global, holistic view may just be the savior that vaccinology needs now.

Example of the complex data collected during a typical 'systems' experiment - what does it all mean, and how can we find something important and worthwhile to study?

I am aware of a number of papers that are currently using this process as a primer to develop improved vaccine products (see here, here and review here of virus vaccine examples). These guys - for example: Bali Pulandran of the Emory Vaccine Centre in Atlanta, USA - are interested in comparing the immune response (humoral response, innate immunity and gene expression changes) of human subjects administered with vaccines. The response to the yellow fever virus vaccine as well as two types of influenza vaccines have been approached and through complex bioinformatic modelling they were able to pull out some significant correlates of immune response - this they hope will aid in the future testing of novel vaccines and facilitate a rational take on vaccine generation by identifying a gene(s)/protein with a functional role in the immune response. This they have begun to do in some of ther papers above - it is nice to see this kind of work being used as a basis for experimental biology.

These types of studies hail a new way of thinking about viruses, vaccines and the immune response to them; if only we can realize the power in taking a step back and looking at the diversity in each. And this type of work could be applied to any number of mechanisms such as vaccine safety or applying it to different tissues during an infection.

Saying that - this stuff isn't particularly easy, cheap or quick as you might think. But as each study generates so much data, might it not take but a few such investigations to lead us on the way of rationally attenuated and protective vaccines? So, should vaccinology embrace systems biology? I think if you have the abilities to do such a study - which from a pharma perspective definitely yes, do it as the more information we have at our disposal the better position we are in. We await further results from these groups to compare how well systems thinking goes up against human ingenuity, that has worked well in the past.

ResearchBlogging.orgNakaya HI, Wrammert J, Lee EK, Racioppi L, Marie-Kunze S, Haining WN, Means AR, Kasturi SP, Khan N, Li GM, McCausland M, Kanchan V, Kokko KE, Li S, Elbein R, Mehta AK, Aderem A, Subbarao K, Ahmed R, & Pulendran B (2011). Systems biology of vaccination for seasonal influenza in humans. Nature immunology, 12 (8), 786-95 PMID: 21743478

The ‘interactome’ of a host/pathogen triad

This post was chosen as an Editor's Selection for ResearchBlogging.orgIn order to survive and replicate within their hosts, viruses must manipulate those pathways and systems in which their host relies upon for its own survival. However, this model gets more complicated with those viruses successfully infecting multiple host species. For example, Dengue virus (DENV) – an emerging pathogen which causes over 50 million cases a year of a mild to deadly disease – infects both humans and mosquito species of the Aedes genus. Thus to accomplish survival, DENV must interact with proteins from these two distantly related hosts. Given this complexity, understanding this dual-host/pathogen system is considerably difficult yet as Doolittle and Gomez (2011) show, computational approaches based on structural predictions of viral and host proteins may allow for the accurate prediction of the complex in vivo ‘interactome’.

Transmission of DENV - the principle mode is direct mosquito to human

The group set out to understand the interactions between both DENV encoded proteins and those of its hosts – humans and Aedes mosquitos. Using previously determined structural information for human and fly (relatively closely related insect to Aedes) and how these proteins interact with each other, they were able to map these back on to host infection. They searched databases for structural similarities between dengue proteins and those from its host (human or fly) – these ‘dengue similar host proteins’ were used to search for host-host protein interactions as a surrogate for host-dengue interactions. 

 “The computational methodology employed to generate this map assumes that proteins with comparable structures will share interaction partners. Therefore, we predict that DENV2 proteins may merge into the host protein interactome at the points normally occupied by structurally similar host proteins, creating an interface for the manipulation of downstream host processes.”

Using this approach, they built up a network of possible host/pathogen interactions, assuming that DENV proteins can participate in the same interactions as host proteins. Of course, this method over estimates interactions so to counter this, they prioritised particular interactions for further study based on previously published, validated in vivo work and those interactions still left hopefully were functionally accurate and important. This approach had previously been used to study human-HIV-1 protein interactions.


DENV capsid structure
Following significantly limiting their map down to those that had been previously validated the biological functions of host target proteins and dengue-similar proteins were analysed to determine whether the predicted functions matched those that would be important for viral infection in both humans and mosquitoes. As shown above, DENV-like proteins participate in interactions involved in diverse processes – importantly including cell death, signalling cascades, immune response and metabolism. They focus the investigation into DENV manipulation of host apoptosis and innate immune signalling and also those proteins which are shared between both insect and human hosts.

They suggest that due to the disparity in the known molecular biology of dengue/host interactions this computational methodology has its limitations in this system yet these data should be used as a springboard for future investigations and hypotheses. This study highlights the importance of global computational analysis in determining basic host/pathogen biology especially in a system which has been poorly studied like DENV.

Doolittle, J., & Gomez, S. (2011). Mapping Protein Interactions between Dengue Virus and Its Human and Insect Hosts PLoS Neglected Tropical Diseases, 5 (2) DOI: 10.1371/journal.pntd.0000954

Dyer MD, Murali TM, & Sobral BW (2007). Computational prediction of host-pathogen protein-protein interactions. Bioinformatics (Oxford, England), 23 (13) PMID: 17646292