What is the process of stem cell collection (apheresis or harvesting)? How long does it take? Why chew Tums during stem cell harvest?

What's involved in the stem cell collection process?

There's generally a central line placed. It's usually an upper body central line which will be utilized for the stem cell collection process. Stem cell collection is not surgery. It's done on the bloodstream. So, it's on the peripheral blood. Once the patients have that central line placed, they are given growth factor shots. It's usually G-CSF for a certain number of days. And we are monitoring the CD34 cells in the peripheral blood. So that's a surface marker on blood stem cells. When you have a certain sufficient number of CD34 cells in the bloodstream and you've made calculations that right, if the CD34 counts get to this number, I would be able to collect this many amount of stem cells. And that's when you bring patients in to the apheresis center. And that central line is hooked up to an apheresis machine, which functions very much like the hemodialysis machine. So the blood flows through that machine and the machine plucks out the stem cells and stores them away in the bag. And then once that process is done, the stem cell processing lab, which is a separate component processes those stem cells and freezes those bags for future use. And those stem cells can be used five, ten, 15, 20 years from now. Given how the process is now is nowadays.

The actual collection process is performed on something called apheresis machine, which is basically a machine where blood from the patient is removed. It's circulated through tubes without actually touching the machine, but through sterile tubes and inside the machine there is a centrifugation process where the white cells or the cells that contain the stem cell population are removed and the blood is returned back to the patient. Then that type of procedure typically takes 3 to 4 hours a day. And generally patients can collect sufficient stem cells within anywhere between one and five consecutive days of this type of apheresis procedure.

What is apheresis? How does a cell sorter work?

So if apheresis is just a word, that means that collecting something from the blood. So when a patient has to collect stem cells from their blood, or in the case of CAR-T cells, T cells from their blood, they go through apheresis. So when we collect stem cells or T cells, we call it leukapheresis because we are collecting white blood cells from the blood. So any patient with myeloma should actually be prepared for apheresis if they're going to have a stem cell transplant or if they're going to have CAR-T cells made from their own immune cells or T cells. So apheresis is an important kind of marker or it's like something that you have to do, if these highly advanced cell therapies are going to be used in your case.

For apheresis, we use a machine called a cell sorter or a cell separator. It's a machine that collects blood from the veins into the chamber and then spins it around in a centrifuge, and then returns the blood back to you after centrifugation to another vein. So basically, you have to have two veins that are punctured with needles and good flow of blood from each one vein into the machine, and then from the return blood comes back from the machine to the other vein. Sometimes it can be done with a what we call a double lumen line. The machine itself separates the blood and using a laser, it basically when the blood is spun in the machine or centrifuged in the machine, the white blood cells separate and move up to the top. And then the white blood cells can be the desired amount of white blood cells can be taken off with a laser, which basically sucks out the only the layer of blood that you need. We can actually tune it to take plasma if you want, from the same machine. You can take platelets off the blood, you can take white cells off the blood. So when we are collecting for stem cells, they are in the white blood compartment. When you are collecting for T cells for CAR-T, they are also in the white blood compartment. So in those cases we just take the white cells off and the machine comes back.

For peripheral blood stem cell transplantation or auto transplantation, you need a lot of cells because the number of stem cells in the blood is actually very low. Even if you use agents such as Neupogen or G-CSF or plerixafor (Mozobil) to boost the stem cells, even then, the number of stem cells is very low. It's usually in the 5 to 10%, even after using these, the using these medicines in the resting states is actually even less than 1%. So you have to collect a lot of white cells to get enough stem cells that are enough for doing a transplant. So therefore, the procedure can take sometimes two or three days. And we always collect for more than one transplant. And which is the ideal thing to do because these stem cells can come in handy later in the course of disease if something, you know, they are sometimes you do need for a dual transplant, sometimes you need it for a later second transplant. Sometimes you need it as a rainy day with cell collection because you can use if some treatment causes the bone marrow to get too suppressed.

So in all of these cases, I would advise that you need as many cells as you can collect in the first scope at least very minimum for true transplant. So it could take two or three days. The most important complication, I would think, would be that a person has difficult venous access, which means that to get a good flow from a vein, it's very difficult in that person. So they may need a venipuncture or a tube going into a big blood vessel in the neck, which then goes down into one of the bigger blood vessels in the chest. And that, again, is a temporary thing. You can get that tube taken out the day after the collection is complete. So typically for T cells the same day and for stem cells two or three days of keeping that tube, that would be the single most annoying thing about this.

The second most annoying thing is that you need to stay still and find some entertainment when this is all going on. The third thing is that sometimes it can drop your blood counts a little bit, sometimes it can take out calcium from the blood and cause some problems because the blood needs to be kept in a non-clotting situation. So for that they add a chemical that can take out the calcium. So that is another complication that can happen. But these are all relatively minor complications. You can take some Tums or get some IV calcium and the calcium problems are immediately fixed. So these are some of the complications but this is an important thing to do. Apheresis, the need for apheresis should by itself not deter anyone from pursuing a stem cell transplant or a CAR-T procedure.

Why might I be asked to chew TUMS during my harvest?

So when you are harvesting as your blood is going through all this tubing, and through the machine and the collection process, you will actually lose a lot of electrolytes, calcium and magnesium and potassium. And so the apheresis nurses will be replacing you to prevent you from having cramping and sort of tetany and all these uncomfortable things that you can experience because of the loss of those electrolytes. So TUMS, of course, being giving your calcium back.