Proteins That Provide Key Information to Identify Patients with Poor Prognosis Found

In recent years, immune-based cancer treatment methods have given doctors and patients a lot of hope. Drugs called immune checkpoint inhibitors have provided life-saving benefits to more and more people suffering from melanoma, lung cancer, bladder cancer, and many other types of cancer. Although these drugs are exciting, a frustrating sticking point is that doctors cannot predict who will benefit from these drugs and who will not.

In a new study, researchers from Memorial Sloan-Kettering Cancer Center in the United States have found that specific patterns or "signatures" of markers on the surface of immune cells in the blood may be biomarkers of immune checkpoint immunotherapy response. In this immune signature, the LAG-3 molecule provides critical information for identifying patients with a poor prognosis. The relevant research results were published in the journal Science Translational Medicine on August 25, 2021. The title of the paper is "LAG-3 expression on peripheral blood cells identifies patients with poorer outcomes after immune checkpoint blockade".

This connection was found in a group of patients with metastatic melanoma and was validated in a second group of patients with metastatic bladder cancer, indicating that this potential biomarker may be widely applicable to various cancer patients.

According to Margaret Callahan, the corresponding author of the paper and a researcher at the Parker Institute for Cancer Immunotherapy at Memorial Sloan-Kettering Cancer Center, the large patient cohort, strong clinical follow-up, and strict statistical methods in this study made her “enthusiastically believe this immune label tells us important information about who responds to immunotherapy and why."

These findings paved the way for prospective clinical trials designed to test whether incorporating this biomarker into patient care can improve the prognosis of patients who are unlikely to benefit from existing therapies.

These authors had data to support the findings of this study. As one of the earliest cancer centers in the world to start treating a large number of patients with immunotherapy, Memorial Sloan-Kettering Cancer Center has stored blood from hundreds of patients treated over the years, pioneered by its researchers Jedd Wolchok and PhilWong. They derived their findings using pretreatment blood samples collected from patients recruited from seven different clinical trials open at Memorial Sloan-Kettering Cancer Center between 2011 and 2017.

To dig up clues in the blood, the authors used a technique called flow cytometry. Flow cytometry is a tool that rapidly analyzes the properties of individual cells as they flow through the laser. Their goal is to identify markers found on the surface of patients' immune cells that are associated with the response of these patients to immunotherapy—mainly PD-1 targeted drugs such as nivolumab (trade name Opdivo) and pembrolizumab (trade name Keytruda).

Ronglai Shen, lead author of the paper and statistician in the Department of Epidemiology and Biostatistics at Memorial Sloan-Kettering Cancer Center, said, "When you think of the fact that hundreds of thousands of blood cells are collected from patients, and we are mapping the composition of nearly 100 different immune cells, it is a real challenge to effectively extract clinically relevant information. This is where we as data scientists can help Dr. Callahan and other physician researchers in this study. Perfect combination of skills."

The statistical tools developed by Dr. Shen and other data scientist Katherine Panageas in this study allowed the Callahan team to classify patients into three characteristic immune signatures, or immunotypes, based on the unique patterns of blood markers.

A prominent immunophenotype is a group of patients who express a protein called LAG-3 at high levels on the surface of multiple T cell subpopulations. These researchers found that patients with this LAG+ immunophenotype had a much shorter survival time than patients with LAG-immunophenotype: for melanoma patients, the difference in median survival was more than four years (the former is 22.2 months, the latter is 75.8 months), and this difference is statistically significant.

LAG-3 (the full name is lymphocyte-activation gene 3) belongs to a family of molecules called immune checkpoints. Like the more well-known immune checkpoints CTLA-4 and PD-1, LAG-3 has an inhibitory effect on the immune response, which means it can suppress the immune response. Several drugs targeting LAG-3 are currently in clinical development, although determining who might benefit the most from these drugs has been a challenge.

When Dr. Callahan and her colleagues started this research, they did not intend to pay particular attention to LAG-3. She said, "We let the data guide us, and LAG-3 is our goal."

One advantage of this study is that it uses both the "discovery group" and the "validation group". This means that these researchers performed a preliminary analysis of a set of blood samples from a large number of patients—188 melanoma patients in this study. Then, they asked whether the immune signatures they found in the discovery group could predict treatment outcomes for a completely different group of patients—94 bladder cancer patients.

It can, and the effect is quite good. Dr. Callahan said, “When we looked at the validated cohort of bladder cancer patients who were treated with immune checkpoint blockade, those with the LAG+ immunophenotype had a response rate of 0. None of them responded. In contrast, the response rate of patients with LAG-immune phenotype is 49%."

Due to the large amount of data, these researchers were also able to compare the patient’s LAG+ immunophenotype with other known response biomarkers—specifically, PD-L1 status and tumor mutation burden. They found that this immunophenotype provides new and independent information about the patient's prognosis, rather than just echoing other biomarkers.

Biomarkers are important in cancer for several reasons. They can help clinicians and patients choose the best treatment, and can allow patients to avoid unnecessary or impossible treatments. Dr. Panageas said, "Immunotherapy drugs are not without potential side effects. Therefore, if we can save someone from the potential risks of a certain treatment, because we know they cannot respond, this is a big improvement."

The second reason is cost. Immunotherapy drugs are expensive, so it is vital that there is a means to better match patients with existing drugs.

Since these researchers used patient blood samples to determine this biomarker, it presents a promising prospect that patients can evaluate this biomarker by simply drawing blood. Other biomarkers currently in use rely on tumor tissue that is usually obtained by biopsy.

Dr. Callahan said, "If I tell you that you can take a simple blood draw and get information within a few days to decide what treatment you get, I would say there is nothing better than this. Of course, there is still much research work to be done before these findings can be applied to clinical patients, but we are really enthusiastic about the potential to apply these findings."

A limitation of this study is that it was retrospective, which means that the data analyzed came from blood samples collected many years ago and stored in freezers. To confirm that these findings have the potential to benefit patients, one will need to test their hypothesis in a prospective study, that is, to have patients participate in a specifically designed clinical trial to test whether the use of this immunophenotype in treatment decisions can improve patient outcomes.

Dr. Callahan said, "The most exciting thing for me is to prospectively evaluate this idea, and we can not only identify those patients who do not respond well to traditional therapies, but we can also provide these patients with other treatments that may help them based on our understanding of the biological role of LAG-3.”