NEW YORK – Researchers from the Singapore-MIT Alliance for Research and Technology (SMART) have developed a new test to measure an individual's immune response, potentially offering a tool for clinicians to determine the status of an infection in a patient without a blood culture.
SMART, established by the Massachusetts Institute of Technology in partnership with the National Research Foundation of Singapore, is a research hub with five interdisciplinary research groups. The test, from the Critical Analytics for Manufacturing Personalized-Medicine interdisciplinary research group within SMART uses deterministic lateral displacement (DLD) microfluidics to quantitatively measure immune cell biophysical signatures in relation to real-time activation levels of white blood cells, which can aid in early diagnosis of infectious diseases before a patient is admitted to the intensive care unit.
Part of the appeal of the test, according to researcher Kerwin Kwek, senior postdoctoral associate at the SMART CAMP Interdisciplinary Research Group, is the speed – the test can return results in 15 minutes, much faster than the hours needed for traditional tests measuring leukocytes or blood serum cytokine profiles. It also requires no dilution or sample handling and only 20 microliters of unprocessed blood. It's fast because "everything is within the device," he said.
In a paper published in Small in February, the researchers note that the test uses a polydimethylsiloxane device with three open reservoirs and a single outlet tubing attached to a syringe pump. The reservoirs allow for easy sample loading and resuspension to prevent settling of cells and to facilitate the washing of the reservoirs for reusing the device. The device has unconventional L and inverse-L pillar structures that can sort white blood cells differently by using different flow velocities, the researchers wrote.
Kwek said the user only has to drop the blood sample onto the device's chip and let it flow through the device to run the test. The chip uses negative pressure to draw the blood through 21 device segments and separates out white blood cells, profiling them by size, deformability, distribution, and cell count.
These biophysical changes occur when the immune cells sense a trigger in the body and migrate into tissue, Kwek said. As the white blood cells migrate and generate products to kill the bacteria, changes in their size and shape occur, and the test measures the degree of those changes to correlate back to the immune response of the patient, he said.
A camera is on the end of the chip to count the number of cells and allow a researcher or clinician to see their distribution. Low-cost, compact machine vision cameras or smartphone optical sensors could be used in developing a point-of-care system for tests using whole blood samples, researchers added.
Kwek said this information allows clinicians to classify a patient's immune activity as high or low, which can help determine how a patient's immune response is developing and the course of the disease. It can be used when a patient enters an emergency room to determine the appropriate treatment before immune dysregulation becomes clinically evident and requires admission to the ICU, the researchers wrote in Small. Patients in the emergency room "frequently show non-specific symptoms and signs, which pose a challenge for physicians to assess the presence of infection and possibility of deterioration into organ dysfunction," they added.
In a preliminary study with National University Hospital, Singapore, researchers evaluated the diagnostic capabilities of the test on 85 blood samples from healthy people, people with non-infection symptoms such as cardiac conditions, and patients presenting to the emergency department with two or more components of the systemic inflammatory response syndrome. The test "resulted in distinction between infection and non-infection group with a detection sensitivity of .91 and specificity of .92," they wrote.
The goal of the test is to see what the immune state of the patient is and how the immune response is adjusting to the therapy that's being given, Kwek said. It doesn't compete with any other specific tests but adds a new method to measure the response, he said, noting there are a few standard biomarkers that are often used to determine immune response, such as procalcitonin.
However, most of those biomarkers aren't very specific and require a panel of multiple biomarkers to determine the immune response. Because the cells need time to generate those biomarkers, it can be a lagging indicator, Kwek said.
Because the DLD test measures the immune cell itself, it can "shed new light" on the immune response, he added. Jongyoon Han, a co-author of the paper and principal investigator at the SMART CAMP Interdisciplinary Research Group, said it is meaningful because the test looks at cell factors where the response begins and can measure the degree of activation. The assay "might be a little bit more upstream in terms of the information chain," providing information earlier in the course of an infection than other tests.
Although the focus of this study was on sepsis and the inflammatory response, Kwek said the test could have many other applications, such as in immunotherapy.
Andrew Conway Morris, a senior research associate and Wellcome Trust Clinical Career Development fellow in the division of anesthesia at the University of Cambridge, said that though the findings of the paper are intriguing, it "needs to be seen very much as preliminary results." He added that the receiver operating characteristic curve "is almost certainly significantly overestimating the diagnostic performance of these markers" because the researchers compared patients with no clinical suspicion of infection to those with clinical suspicion. "If patients can be discriminated between on clinical grounds, then one does not need a test to demonstrate this," he continued.
Conway Morris said future stages, such as validation with a larger cohort of patients, would be needed before "it was even close to a clinically usable test." The test would also need to be able to discriminate at an early point between patients with clinical suspicion of infection who go on to develop severe infection or sepsis and those who don't.
Han noted that in infectious disease testing, the presence of a pathogen may not always translate to the severity of the disease. The real risk is the immune system getting triggered and damaging organs, which can be as deadly as fully blown sepsis, he said. "People are really focused on detecting and identifying the pathogen," he said. "Once the immune system is triggered in this manner where you actually activate the systematic immune response, then it really doesn't matter what the original cause was. It's going to damage your organs at one point." Instead, "the immune response of the host might be the more relevant thing to measure in order to manage these patients properly."
Han emphasized that the immune response test shouldn't replace other diagnostic tests that detect specific pathogens but should instead work alongside them. But knowing the pathogen doesn't mean the patient won't develop sepsis or severe infections. "The immune angle is not a surrogate for detecting the bacteria or pathogen, it's actually almost as important as the detection of the original pathogen," he said.