Understanding a cell’s density provides vital insights into its condition. As cells grow, differentiate, or die, they can either absorb or expel water and other molecules, leading to noticeable changes in density.
While monitoring these subtle shifts in cellular states on a large scale is challenging, MIT researchers have developed a quick and accurate method for measuring cell density—capable of analyzing up to 30,000 cells in just one hour.
The researchers demonstrated that changes in density can help predict crucial outcomes, such as whether immune T cells are activated to combat tumors or if tumor cells respond to specific drugs.
“These predictions stem from minor alterations in the physical attributes of cells, indicating their responses,” states Scott Manalis, the David H. Koch Professor of Engineering in the departments of Biological Engineering and Mechanical Engineering, who is also part of the Koch Institute for Integrative Cancer Research.
Manalis is the senior author of the study published today in Nature Biomedical Engineering, with MIT Research Scientist Weida (Richard) Wu as the lead author.
Innovative Density Measurement Techniques
As cells transition between states, the concentration of molecules like lipids, proteins, and nucleic acids can fluctuate. Measuring a cell’s density offers insights into this molecular crowding.
The new density measurement technique builds upon extensive research conducted by Manalis’ lab over the last two decades. In 2007, his team introduced a suspended microchannel resonator (SMR)—a microfluidic device consisting of a microchannel across a tiny silicon cantilever that vibrates at a designated frequency. When a cell passes through the channel, the vibration’s frequency shifts slightly, allowing researchers to calculate the cell’s mass.
In 2011, they adapted this technique for density measurement. This involves sending cells through the device twice, suspended in two fluids of distinct densities. Since a cell’s buoyant mass varies based on its mass and volume, measuring two buoyant masses allows the determination of its mass, volume, and density.
Though effective, the original method was slow, enabling the measurement of only a few hundred cells at a time due to the time-consuming fluid swaps. To enhance efficiency, researchers paired their SMR device with a fluorescent microscope to measure cell volume. The microscope is positioned at the device’s entrance, allowing cells to flow through while suspended in a non-absorbing fluorescent dye. A decrease in the fluorescent signal indicates cell volume, which is calculated before cells enter the resonator for mass measurement. This streamlined method enables rapid density calculations, facilitating measurements of tens of thousands of cells within an hour.
“Instead of rerouting cells back and forth through the cantilever multiple times to determine density, we aimed for a more efficient approach, allowing cells to pass through just once,” Wu explains. “From the mass and volume, we can derive density, maintaining both precision and throughput.”
Insights into T Cell Activation
The researchers employed their innovative technique to observe density changes in T cells after activation by signaling molecules.
They discovered that as T cells shift from a resting to an active state, they absorb new molecules and water, leading to a decrease in density—from an average of 1.08 grams per milliliter to 1.06 grams per milliliter—indicative of reduced crowding as water influx surpasses the absorption of other molecules.
“This suggests that cell density likely reflects an increase in water content as T cells transition from a dormant state to one of heightened growth,” Wu notes. “These findings propose that cell density is a notable biomarker that changes during T-cell activation and may correlate with their proliferation capacity.”
Travera, a clinical-stage company co-founded by Manalis, is focused on employing SMR mass measurements to anticipate the responsiveness of individual cancer patients’ T cells to drugs aimed at boosting anti-tumor immunity. Preliminary studies indicate that combining mass and density measurements yields more precise predictions than either method alone.
“Both metrics reveal significant insights regarding the competence of immune cells,” says Manalis.
Utilizing physical measures of cells to monitor immune activation is an exciting development that may introduce a novel method for assessing changes in circulating immune cells, according to Genevieve Boland, an associate professor of surgery at Harvard Medical School. She asserts that this unique approach could serve as an innovative tool for clinical decision-making regarding cancer therapies, response monitoring, and early detection of side effects from immune therapies.
Predicting Tumor Cell Responses
This new methodology may also serve in anticipating how tumor cells respond to various cancer treatments. In previous research, Manalis revealed that tracking alterations in cell mass post-treatment could predict drug-induced apoptosis in tumor cells. In this study, he found that density measurements can similarly indicate these responses.
In experiments involving pancreatic cancer cells, the team applied two different drugs—one effective and one ineffective against the cells. Findings showed that density changes after treatment accurately reflected the cells’ responses.
“We capture crucial information about the cells that allows for predictive insights within days after they are extracted from the tumor,” Wu notes. “Cell density acts as an immediate biomarker for assessing in vivo drug response.”
Manalis’ lab is currently exploring how mass and density measurements can help evaluate the vitality of cells involved in synthesizing complex proteins, such as therapeutic antibodies.
“As cells produce these proteins, tracking markers related to cell vitality and metabolic conditions could facilitate predictions about their protein production efficiency, and potentially guide strategies to enhance these yields,” Wu concludes.
This research was supported by the Paul G. Allen Frontiers Group, the Virginia and Daniel K. Ludwig Fund for Cancer Research, the MIT Center for Precision Cancer Medicine, the Stand Up To Cancer Convergence Program, Bristol Myers Squibb, and the Koch Institute Support (core) Grant from the National Cancer Institute.
Photo credit & article inspired by: Massachusetts Institute of Technology
