CD45R-stained IHC image depicting B cells within a tertiary lymphoid structure in a triple-treated cholangiocarcinoma tumor. Image credit: Greten lab
Adding a vascular endothelial growth factor (VEGF) inhibitor to a treatment regimen of two therapies known as immune checkpoint inhibitors stimulated the immune system more effectively and led to better tumor control than the two treatments alone, according to new research published in Immunity on April 8, 2025. This seemed to be due to increased activation of immune system B cells as well as several other types of immune cells in cholangiocarcinoma, a rare type of bile duct cancer, the study found.
VEGF is a protein that helps promote the growth of new blood vessels, a process known as angiogenesis. In cancer cells, VEGF is often present at unusually high levels, and it can cause expansive blood vessel growth which helps tumors grow by providing oxygen and nutrients. Many cancer treatments have therefore been developed to target VEGF and stop it from working.
“A lot of data suggests that anti-VEGF drugs, which were initially developed as anti-angiogenic drugs, may also affect the immune system,” said Tim F. Greten, M.D., Deputy Chief of the Thoracic and GI Malignancies Branch and lead author of the study. “But ultimately it’s never really been clear what type of immunological effects these drugs have.”
To answer this question, the researchers added an anti-VEGF drug to two immune checkpoint inhibitors in mouse and human studies. Immune checkpoints are proteins on the surface of immune cells that prevent an immune response from getting too strong, which could lead to the immune system destroying the body’s own healthy cells. Cancer often suppresses immune responses, so immune checkpoint inhibitors essentially remove the “off switch” from the body’s immune system, which can lead to the immune system attacking cancer more effectively. The specific immune checkpoint inhibitors used in this study targeted two proteins called CTLA4 and PD-L1.
In the first steps of their experiments, the researchers studied mice to see if adding anti-VEGF treatment to anti-CTLA4 and anti-PD-L1 medications would help control tumor growth more effectively than the immune checkpoint inhibitors alone. The researchers also repeated these analyses in a phase 2 clinical trial that enrolled people with cholangiocarcinoma. Their initial findings, based on six people enrolled in the study, showed similar molecular and clinical outcomes to what they saw in mice.
What the researchers ultimately determined was that the treatment created a chain of events: the drugs sparked different modes of activity which were dependent on a protein called BAFF, or B-cell activating factor. These activities led to an inflammatory response by an increased number of B cells that also caused production of interleukin-12 (IL-12) proteins. BAFF and IL-12 then helped rewire a type of suppressive immune cell, regulatory T cells, to become active immune cells.
“We saw an activation of CD8 T cells, which we expected, but the increase of B cells and regulatory T cells were unexpected,” said Greten.
Overall, the studies showed that treatment with the triple therapy regimen resulted in delayed tumor growth and prolonged survival compared to other treatments, including anti-CTLA4 and anti-PD-L1 alone in mice and people with cholangiocarcinoma, due to this cascade of immune system effects.
Greten and his team hope to study this treatment in more people and determine if there are any ways it can be modified or improved. Additionally, the research team has completed initial studies of this treatment in mice with pancreatic cancer and aims to explore whether it can be effective for even more types of cancer.
