When people discuss “fat stem cells” they usually mean something called “stromal vascular fraction” or SVF. While references to fat or adipose stem cells can sometimes mean non-SVF materials, these days adipose SVF gets the most attention. But, does anyone have a clear picture of this biologic?
What exactly is Stromal Vascular Fraction (SVF)?
In a nutshell, stromal vascular fraction is a cellular extract made in a laboratory from fat. While methods to produce the SVF extract vary, the basic idea is that the wide variety of cells within fat tissue are separated from the actual gloppy fat tissue itself. Those cells are then concentrated to make SVF.
That’s about it.
However, getting cells out of fat requires a molecular sledgehammer. This extraction process generally uses something called an enzyme, most often one called collagenase. Enzymes like these chew up proteins that run through the fat tissue and connect with cells.
Imagine your spaghetti and meatballs are stuck together in a giant web of sticky cheese. You are on a paleo diet or something so you only want the meatballs. In this analogy the enzyme used to make SVF would release the meatballs (the cells) from the spaghetti and over-abundant pounds of cheese. Except with cells within fat tissue, they are tiny and sparsely present throughout.
The end product of SVF is not a naturally occurring substance. While all the cells in SVF did mostly exist in the body fat, they weren’t together. Also the exposure of the cells to the enzyme can change their behavior and inherent nature in some ways. The stress of the process could even generate cells with new properties.
It’s not well-understood. In principle SVF could be made from almost any tissue to isolate its stromal and vascular cells. It’s basically just done almost always with fat these days.
What cells are in SVF?
Many different cells end up in SVF.
The exact numbers and types are going to vary a lot from patient to patient. Also, lab or clinic making the SVF preparation and the individual person doing it will influence what comes out of it. Overall, some cells are likely to be in every stromal vascular fraction prep. Fibroblasts will make up a good number of SVF cells too. It’s important to note that there different kinds of fibroblasts as well. There may even be some primitive fibroblasts that are more like progenitor cells.
A few fat cells or adipocytes will be there along with some fat cell progenitors called pre-adipocytes.
Blood vessel cells will also be in SVF, including endothelial cells and smooth muscle cells. Also in SVF are really interesting cells called pericytes that hug the exterior of blood vessels. They may have some stem cell like properties, perhaps being able to make smooth muscle cells and a few other types.
There are also going to be actual white blood cells in SVF too including macrophages.
The National Cancer Institute (NCI) has its own definition of stromal vascular fraction here, but I think they are a bit generous on their description of the known functional properties.
There are likely to be fragments of many cells in SVF preps too depending on how it is made and purified. Those could pose risks.
What about MSCs in SVF?
Wait a minute, you might say, what about mesenchymal stem cells (MSC)? Often folks use the terms SVF and MSCs interchangeably. So aren’t MSCs in fat? There are some MSCs in SVF, but not as many you might think based on the rhetoric out there by some. Many “MSCs” may be more like a cross between stromal and stem cells, which is why some folks think the acronym MSC should stand for, “mesenchymal stromal and/or stem cells.”
Lipogems vs. SVF
Something called lipogems are also made from fat. They sometimes get discussed together with SVF and MSCs. Certain folks have suggested that lipogems basically functionally are fat stem cells, but that’s not clear. Here are a few articles in Pubmed on lipogems.
Looking ahead on stromal vascular fraction
Overall, I believe that cellular medicine products from fat have real potential, but haven’t been proven safe and effective for particular applications in rigorous clinical trials.