Viruses are small biological particles that can infect humans and cause major health complications. In the case of the Human Immunodeficiency Virus (HIV), that causes the acquired immunodeficiency syndrome (AIDS) and is responsible for almost one million deaths every year worldwide, the viral particle is just 120 nm big. However, conventional microscopes are diffraction-limited, as described by the German physicist Ernst Abbe in the XIX century. This means that we are not able to resolve objects that are smaller than 250 nm, thus preventing the study of small viruses. It is however imperative that we are able to understand the molecular mechanisms governing their infection cycle and the natural responses developed by our immune system to be able to efficiently treat viral infections in the clinic, through vaccination or immune therapies.
The goal of the FILM-HIV project is to develop and apply advanced microscopy methods that can overcome the diffraction limit and observe viruses with nanometre precision. This multidisciplinary biophysics project spans from the optics fields to immunology and cell biology, and has been developed at the Leibniz Institute of Photonic Technology in Jena, Germany. The university of Jena was the alma matter of Ernst Abbe, and the city is internationally known for its long tradition on microscopy development and manufacturing. The project aims to apply these new methodologies to record the entry of HIV virions in immune cells, and how a specific type of broadly neutralising antibodies isolated from HIV patients can stop this process.
One of the main challenges when developing microscopy techniques is to make them compatible with the observation of biological samples, such as human cells, that are highly sensitive to the high laser powers required in modern microscopy proceedings. To overcome this limitation, we have applied a new methodology that consists in the constant recycling of the fluorescent molecules that allow us to visualise cells. These novel dyes, known as exchangeable dyes, not only allow us to observe cells with nanometre resolution, but also allow as to quantify their biophysical properties, such as the diffusion of single molecules or their order, which in turn offers us valuable information about key biological processes such as membrane fusion, which HIV requires to infect cells.
Finally, we have applied novel super-resolution techniques to the study of the binding of potent neutralising antibodies to HIV. We have identified key features of these antibodies responsible for their potency and found that we can naturally enhance their potency by creating engineered versions that increase their binding capacity to the HIV membrane.
