Rare Cell Isolation: Gentle and Viable Cell Separation Method for Isolation of Rare Immune Cells

Gentle and Viable Rare Cell Isolation

As research continues, we are able to learn about a variety of different diseases and biological processes. To find out more about how this works, scientists need to isolate and study rare cells.

What Are Rare Cells?

Rare cells are less common cells that occur amongst a large population of background cells. A cell type is considered rare if less than 1000 can be found in a one milliliter sample. Certain techniques are limited in their ability to separate rare cells because of sample loss and low selectivity. Some rare cells can also change in size over time based on the environment they exist in, making it difficult for many conventional cell separation methods to accurately categorize them by their physical characteristics.

While unique cell types can help us learn through research and experimentation, they are often difficult to isolate because of their fragility and scarcity.

Rare Cell Populations

Rare cells can be found anywhere, including inside the human body. Being able to identify and study these unique cell populations can provide insight into how a person’s health is being affected by a disease, what stage of development they’re at, and other more specific information such as the status of a fetus in a pregnant woman.

Circulating Tumor Cells (CTCs)

One of the most sought-after rare cell populations is the circulating tumor cell (CTC). CTCs exist in individuals with cancerous tumors in low concentrations. A CTC is a fragment of a tumor that has fallen off during the tumor’s natural life cycle and entered the bloodstream. These cells are capable of spreading cancer to different parts of the body and can tell us a lot about the tumor they came from, such as the approximate size or location of a primary mass. CTCs can also be used to identify the presence of a tumor before imaging, which play a vital role in the early diagnosis and treatment of cancer.

Beyond studying CTCs in individuals, researchers can also test these cells to get a better idea of how cancer spreads and metastasizes in the body, how different cancers affect the body, and how specific treatments can be more beneficial to specific patients. With medicine in the future becoming more and more individualized, the ability to understand what behaviors stem from cancer and which diseases stem from an individual’s genome will be an integral part of providing medical treatment.

These cells are very useful, but difficult to isolate with high viability from samples of whole blood. A gentle cell separation method can make all the difference in protecting CTCs and enabling experimentation.

Circulating Fetal Cells (CFCs)

Another important type of cell is a CFC, or a circulating fetal cell. CFCs are found in pregnant women and carry the entire genomic code of a fetus. These cells can be used as biomarkers for noninvasive prenatal testing. Limitations for CFC testing come from the need to enrich a high volume of pure cells. If researchers were capable of isolating CFCs more efficiently, it would be simpler to identify and prepare for certain genetic issues or diseases from the fetus during pregnancy.

Stem Cells

Stem cells are undifferentiated cells that can develop into a multitude of different cell types. They are an increasingly vital asset to medical research and treatment. Stem cells are capable of being manipulated or intentionally differentiated to carry out a particular function. Stem cells can replace cells that were damaged by disease or chemotherapy to replenish an individual’s tissue, organ, or immune cells. In the scope of individualized medical treatment, this cell type has one of the widest ranges of applications.

Isolating stem cells is not an easy task. By the time an individual is an adult, many of their stem cells have already differentiated into a specific role, making them hard to find. Stem cells are more abundant in earlier stages of development, such as embryonic stem cells, that are derived from embryos in the blastocyst stage. However, these cells are very fragile and still found in small amounts. When isolating stem cells with cell separation, you must make sure that the method you use is gentle, accurate, and maintains cell health and physiology without sacrificing efficiency.

Infected Cells

Another valuable unique cell subtype is infected cells. Infected cells can be any cell within the body that was infected by a disease or parasite. When you get an infection, a foreign pathogen will attach itself to cells in your body and destroy them or take them over. That infected host cell can be collected to learn more about what said disease is and how it affects cells in the body.

Isolation of infected cells can be difficult due to the variety of types that can be infected. As mentioned above, many rare cells change in shape over time, especially when they become infected. The fragility of cells that have a parasite or disease is also higher because they are already weakened, meaning that the cell separation method used must be gentle and accurate.

What is Cell Viability?

When performing cell separation there are metrics that must be monitored such as yield, recovery, and throughput. One of the most important statistics when isolating rare or unique cell populations is cell viability. Cell viability refers to the amount of healthy, functional cells contained in an enriched sample. By measuring dead cells, you can calculate the viability ratio by subtracting the dead cells from the total quantity of cells, then divide by the total quantity of cells and multiply by 100 for the percentage.

Why is High Cell Viability Cell Separation Important?

Cell viability is important for the same reasons that cell separation is important–to properly study the specific behavior of a cell type, all experiments must be performed exclusively with said cells. Damaged and dead cells will not function the same way and could potentially skew results.

Isolation of Rare Cells

When it comes to the actual process of enriching rare cells there are a multitude of factors that must be considered for optimal performance. Here are some of the details you should pay attention to if isolating rare cell types:

• Sample site – The location blood is sampled from can affect the rare cell count outcome. Extracting blood from an area the cell type is more likely to be prevalent in can benefit the experiment by starting off with a higher initial population.
• Variable markers – Sometimes biochemical markers on rare cell surfaces may be expressed differently on a cell membrane than other cells of the same type. This can lead to missing cells or overall statistics being determined by the cell subtypes as opposed to the cell population itself.
• Cell sizes – Due to the largeness of certain unique cells, they are sometimes filtered by small capillaries in the body before reaching the sample site. This is another consideration when choosing the sample site to ensure that the desired cell type can reach that specific area.
• Cell masking – Platelets or other coagulation factors can mask rare cells, hiding them from certain affinity-based isolation methods. This problem can be reduced by purifying the sample to remove these additional substances before performing primary cell separation.
• Downstream applications – The isolation method used should typically be gentle enough to preserve the cell membrane and nucleus for subsequent culturing or molecular analysis. If you have plans to use the rare cell culture once it is enriched, you must take care of it.

Due to small sample sizes, researchers often use isolation methods such as single-cell sequencing and microfluidics to ensure accurate enrichment. These separation techniques are preferred to more traditional techniques because they can be done in a smaller space and focus more on specific characteristics. However, because rare cells often exist with many subtypes it may require multiple isolation steps to properly sort them. Many times, these methods will have to be used in conjunction with other purification methods for the best possible outcome.

Traditional Separation Methods

Other traditional cell separation methods like fluorescence activated cell sorting (FACS) and magnetic bead-based cell sorting not perform well in rare cell isolation.

FACS sort cells one-by-one based on their physical characteristics. As mentioned above, rare cells have multiple variations in their size and shape depending on time spent in their environments. Along with cells being sorted inaccurately, sort-times for rare cells are very high when dealing with rare cells. The flow cytometer has difficulty identifying low-volume populations.

Buoyancy Activated Cell Sorting (BACS)

Buoyancy activated cell sorting (BACS) is an innovative technology developed by Akadeum Life Sciences that represents a breakthrough in cell separation. The microbubbles are small, solid particles with a hollow core that allow researchers to leverage the power of gravity for quick and gentle removal of captured cells from a complex biological mixture. Because gravity is the driving force behind the microbubbles, they provide consistent results without requiring extraneous equipment like magnets or columns, which enables reliable separations that are exceptionally gentle on delicate cells, like rare immune cells of low abundance.

The microbubbles are simply mixed into the sample, directly in the sample container, where they bind to the unwanted cells, floating them gently to the top of the container while the untouched cells of interest are pelleted at the bottom. The microbubbles, microbubble-bound cells, and supernatant are removed using vacuum aspiration, and the highly-enriched cells of interest are ready for downstream use. The microbubble workflow maintains the health and physiology of the cells of interest, allowing for fast, easy, and exceptionally gentle isolation of target cells.

Microbubbles and Naïve T Cell Isolation

When it comes to enriching rare immune cells, Akadeum offers many kits including the Mouse Naïve T Cell Isolation Kit that can be used to extract a high throughput, viable sample for downstream applications. This kit is used to negatively select naïve T cells from mouse splenocytes.

If you’d like to perform large sample rare cell isolation while maintaining cell health and physiology for downstream applications, Akadeum’s microbubble kits are the simplest way to achieve that at the best price. Check out our app note on Combining Microbubbles and Cell Sorting for Quick & Gentle Isolation of Unique Cell Populations for more information on how BACS can improve your workflow, or set up a meeting with one of our scientists today.