Cytolytic activity score (CYT), designed to quantify the amount of killing activity of immune cells against cancer, may be useful as a marker of immune checkpoint blockade success in patients with colorectal cancer, according to new research.
“The cytolytic activity score associates with the number of immune cells that infiltrate into the tumor, improved survival and higher expression of immune checkpoint molecules, which are targets for several immunotherapeutic agents,” said lead study author Sumana Narayanan, MD, a clinical fellow in the Department of Surgical Oncology at Roswell Park Comprehensive Cancer Center, in Buffalo, N.Y., at the time of the study. “In the future, we may be able to use CYT as a predictive biomarker of the efficacy of immune checkpoint blockade or a tumor’s responsiveness to immunotherapy.”
The study was presented at the 2018 Society of Surgical Oncology Annual Cancer Symposium (abstract 68) and later published in the Annals of Surgical Oncology (2018;25:2323-2231).
In an interview, Dr. Narayanan explained that immune checkpoint inhibitors improve survival in colorectal cancer involving microsatellite instability (MSI)—especially MSI high—and that elevated tumor-infiltrating lymphocytes (TILs) within the tumor microenvironment are a known positive prognostic factor in colorectal cancer. In the study, Dr. Narayanan and her colleagues obtained genomic expression data from 456 untreated colorectal tumor samples in the Cancer Genome Atlas and used the analytical tool CIBERSORT to evaluate intratumoral immune cell composition. To define CYT, the researchers used the expressions of two proteins: pro-apoptotic granzyme (GZMA), as cytotoxic immune cells destroy cancer cells through the GZMA pathway, as well as perforin, which mediates the entry of GZMA into the cell membrane, cleaving caspases and inducing apoptosis, Dr. Narayanan explained, “thereby making granzyme and perforin expression a good marker for cytolytic activity.”
The researchers found that patients with high CYT had more right-sided tumors, early-stage cancers and high MSI. Compared with samples of normal colonic tissue, colorectal cancer samples had lower CYT, indicating lower cytolytic activity from TILs. Tumors with high mutation load and high MSI had high CYT. The gene KRAS, frequently mutated in colorectal cancer, had a low association with CYT, likely due to its lack of association with MSI and TILs. Less frequently mutated genes, including BRAF, which is known to associate with deficient mismatch repair genes and MSI, had greater association with high CYT.
Tumors with high CYT expression, compared with those with low expression, had high ratios of activated memory CD4-positive T cells; gamma delta T cells, a type of cytotoxic T cell; and M1 macrophages, which release pro-inflammatory cytokines and are antitumoral.
They also had significantly better overall survival (median overall survival, 101 vs. 67 months; P=0.019) and disease-free survival (73 vs. 41 months; P=0.016).
“There was an even greater improvement in survival in CYT-high patients that were TIL-positive,” Dr. Narayanan said. For those patients, both the CYT-high group’s median overall and median disease-free survival were not reached at 125 months, she said, compared with 64 and 48 months, respectively, in the CYT-low group.
High CYT was directly associated with immune checkpoint molecules: programmed death-1 (PD-1; Spearman’s rho, 0.7), programmed death ligand-1 (PD-L1; Spearman’s rho, 0.675), cytotoxic T-lymphocyte–associated antigen 4 (Spearman’s rho, 0.637), and regulatory T-cell markers FOXP3 (Spearman’s rho, 0.517) and CCR4 (Spearman’s rho, 0.47) (all P<0.0001). High CYT was a positive prognostic factor, independent of age, sex, lymphovascular invasion, tumor location, MSI-high status and TIL positivity.
“Patients with high CYT and low checkpoint molecule expression had significantly superior survival, which was seen in checkpoint molecules PD-1, PD-L1, LAG-3, TIM-3 and IDO-1,” Dr. Narayanan said.
Conversely, high checkpoint molecule expression reduced survival, even in patients who were high in PD-1, PD-L1, LAG-3, TIM-3 and IDO-1. And “the overall poorest survival [was] in patients who had low CYT and high checkpoint expression,” Dr. Narayanan said.
“Given the association between CYT and immune checkpoint molecules, we may be able to use CYT as a predictive biomarker of the efficacy of immune checkpoint blockade,” Dr. Narayanan said. The researchers are investigating whether similar associations exist for other tumors, such as breast cancer.
Asked to comment on the research, Adam Snook, PhD, an assistant professor in the Department of Immunology and Microbial Pathogenesis at Thomas Jefferson University, in Philadelphia, said the study’s biggest limitation was the strength of the relationship between CYT and immune checkpoint molecules. “It is corollary. It can’t and doesn’t really look any deeper into understanding what is really happening, but the study does add to the knowledge of immune biomarkers in colon cancer,” Dr. Snook said.
He noted that a new technology, Immunoscore, has been in development for the past 10 years to use immune characterization to predict what will happen to patients with colorectal cancer and improve treatment. Recent validation research supports its implementation as a new component of TNM-Immune classification of cancer (Lancet 2018;391:2128-2139). Dr. Snook said the CYT research “adds a little bit more nuance to that characterization. It adds some additional markers that might make sense to look at when characterizing the immune infiltrate in colorectal tumors.”