Cancer immunotherapies harness the power of the patient’s own immune system to fight cancer. One type of immunotherapy, called adoptive T cell therapy, uses immune cells called CD8+ Killer T cells to target and destroy tumors. These T cells are made in the spleen and lymph nodes and they can migrate to different locations in the body through a part of our circulatory system known as the lymphatic system.

CD8+ T cells can also leave the circulation and travel into the body’s tissues to fight infection and cancer. Scientists from the Scripps Research Institute and UC San Diego are interested in learning how these killer T cells do just that in hopes of developing better immunotherapies that can specifically target solid tumors.

In a study published last week in the journal Nature, the teams discovered that a gene called Runx3 acts as a switch that programs CD8+ T cells to set up shop within tissues outside of the circulatory system, giving them access to solid tumors.

“Runx3 works on chromosomes inside killer T cells to program genes in a way that enables the T cells to accumulate in a solid tumor,” said Matthew Pipkin, co-senior author and Associate Professor at The Scripps Research Institute.

Study authors Adam Getzler, Dapeng Wang and Matthew Pipkin of The Scripps Research Institute collaborated with scientists at the University of California, San Diego.

They discovered Runx3 by comparing what genes were expressed in CD8+ T cells found in the lymphatic system to CD8+ T cells that were found in tissues outside of the circulation. They then screened thousands of potential factors for their ability to influence CD8+ T cells to infiltrate solid tumors.

“We found a distinct pattern,” Pipkin said. “The screens showed that Runx3 is one at the top of a list of regulators essential for T cells to reside in non-lymphoid tissues.”

The team then set out to prove that Runx3 was a key factor in getting CD8+ T cells to localize at the site of solid tumors. To do this, they took T cells that either overexpressed Runx3 or did not express Runx3 in these cells. The T cells were then transplanted into mice with melanoma through a process known as adoptive cell transfer. Overexpression of Runx3 in T cells not only reduced tumor size but also extended lifespan in the mice. On the other hand, removing Runx3 expression had a negative impact on their survival rate.

This research, which was supported in part by CIRM funding, offers a new strategy for developing better cancer immunotherapies for solid tumors.

Pipkin concluded in a Scripps Research Institutes News Release,

“Knowing that modulating Runx3 activity in T cells influences their ability to reside in solid tumors opens new opportunities for improving cancer immunotherapy. We could probably use Runx3 to reprogram adoptively transferred cells to help drive them to amass in solid tumors.”