Researchers have discovered a possible target for cancer immunotherapy.

The research, directed by Professor Massimiliano Mazzone, discovered that the CDA gene is one of the most elevated metabolic genes in immunotherapy-resistant cancer. Inhibiting this gene through pharmacological or genetic intervention resulted in improved T-cell infiltration, enhancing the efficacy of immunotherapy in PDAC, a type of pancreatic cancer.

Study done by VIB-KU Leuven Center for Cancer Biology and the findings were published in Nature Cancer.

At present, immunotherapy treatments, including adoptive T-cell transfer, cancer vaccines and immune checkpoint blockade (ICB), represent a promising option for cancer patients.

Despite the high response rates with prolonged survival in subsets of melanoma, lung, and renal cancer patients, ICB struggles to show clinical benefit in several other tumours such as in most of the colorectal cancer and pancreatic ductal adenocarcinoma (PDAC) patients.

PDAC is one of the most aggressive and lethal cancers with an overall 5-year survival rate of 9%. In Belgium alone, pancreatic cancer is the 9th most common cancer with 2242 diagnoses in 2021.

Most patients are diagnosed at advanced stages with distant organ metastases, resulting in less than 20% of patients being eligible for surgery at the time of diagnosis. Most therapies, including ICB, are not effective and many patients who undergo surgery ultimately relapse.

A team led by Professor Massimiliano Mazzone at the VIB-KU Leuven Center for Cancer Biology investigates ways to bypass immunotherapy resistance.

In their most recent study, co-authored by Tommaso Scolaro, Marta Manco, Mathieu Pecqueux and Ricardo Amorim, the team studied the role of an enzyme called cytidine deaminase or CDA in pancreatic ductal adenocarcinoma.

Professor Massimiliano Mazzone, "CDA is an enzyme that helps recycle parts of DNA and RNA. It also deactivates some cancer drugs, which can make these treatments less effective. While the consensus is that CDA plays a role in resistance to chemotherapy, its role in immunotherapy resistance was never studied. We decided to take a closer look and to determine if CDA is indeed a roadblock for treatments such as ICB."

By analysing multiple datasets of PDAC tumours that were both responsive and resistant to ICB treatment, the team proved that the presence of CDA in cancer cells results in the creation of uridine-diphosphate (UDP). UDP is a molecule that can signal certain immune cells known as tumour-associated macrophages (TAMs). In doing so, UDP can hijack TAMs, turning them immunosuppressive.

This an important finding, because TAMs make up approximately 50% of tumour mass and are widely associated with tumour progression.

Tommaso Scolaro, the first author of the research paper said, "To our excitement, our study showed that CDA indeed contributes to immunotherapy resistance. This led to our next hypothesis that inhibiting the gene responsible for creating CDA could in turn weaken the immunosuppressive properties of PDAC tumors that are typically resistant to treatments such as ICB."

As a next step, the team looked at ways to inhibit the CDA gene in cancer cells. Through pharmacologic and genetic interventions, the team was able to disrupt the interactions between CDA-expressing cancer cells and TAMs. This led to better infiltration of T-cells and a higher susceptibility for immunotherapy treatments in resistant PDAC tumours, confirming that targeting CDA in cancer cells (or the UDP receptor in TAMs) can overcome the immunosuppressive qualities of a tumour. Better yet, the team also noted the same results in other cancer types such as melanoma.

Massimiliano Mazzone, "The results of this study are very positive, to say the least. Not only does this propose a new potential target to enable immunotherapy in resistant cancer types, but it also improves our understanding of what drives immunosuppression in tumours. PDAC is one of the deadliest cancers out there. While our results give hope, more research is needed before we can bring this to the patient."