Well, it's been a very big day for us here! So big, we're going to break it up over a couple of entries.
This was the first day in the Experimental Sequence Test (EST) for our T-cell experiment and by far our busiest. Today we isolated our cells, filled the experimental containers and handed them over to to be loaded for the "launch" tomorrow. Of course, since this is a test run, our T-cells aren't actually headed to the ISS. Instead, they will be taken to another building on the ESA campus, where a surrogate crew member will perform our experiment. Then, the cells will be frozen, packed up, and returned to us back here on "earth" (that is, the lab) so that we can collect our samples.
Our preparations are on a tight deadline. Since the cells must be alive for our experiment to work, we need to load them within a very narrow window of time. If we prepare them too early, they will all be dead before they reach the space station. Too late, and they miss their ride. Depending on the launch schedule, this can call for some very early days -- today we beat the sun getting up.
Once we arrived at ESTEC, we all had a cup of coffee to wake up and set to work. The first step in isolating T-cells involves separating out a subpopulation of blood cells, called peripheral blood mononuclear cells or PBMCs for short, from whole blood. PBMCs are blood cells with round nuclei and include T-cells and several other types of cells. We use a technique called density gradient centrifugation for separation. First, we layer the blood over a viscous solution called Ficoll. This is done carefully so that the blood and Ficoll do not mix. Next, we put all of our samples in a centrifuge and spin them. Cells separate depending on their size and density, and at the end of the spin we have a nice puffy layer of PBMCs (we like to call it the 'cheese'). We remove this layer, wash and filter it to get rid of debris, and count the cells.
T-Cells are one kind of PBMC, but there are many other kinds too -- macrophages, monocytes, B-cells and Natural Killer cells, to name a few. We only want T-cells for the experiment, so we perform a second separation step, called a negative selection, to isolate them. This involves a very clever trick - we first add a solution of antibodies that bind to all the cells that we don't want. Next we add a solution of magnetic beads that bind to all the antibodies that are bound to those cells. Finally, we put the tube onto a magnet. All the cells that we don't want are attached to magnetic beads and get pulled to the sides of the magnet. Our T-cells are left floating in the solution, untouched. All we have to do now is remove them and wash them and voilà, clean isolated T-cells.
Of course this all sounds easy on paper -- preparing five samples (for the real flight, it will be ten) takes several hours of work. After a successful isolation, we decided to take a break for lunch. And it seems like a good place to take a break here as well.
Coming up next...filling the experimental cassettes!
