Study authors Ronald Levy (left) and Idit Sagiv-Barfi

Experiments in mice have shown that injecting immune-stimulating agents directly into a tumor can help the immune system eradicate tumors in other areas of the body.

The approach worked for several cancers, including lymphomas.

The researchers believe the local application of the agents could serve as a rapid and relatively inexpensive cancer therapy that is unlikely to cause the adverse effects often seen with more widespread immune stimulation.

“Our approach uses a one-time application of very small amounts of two agents to stimulate the immune cells only within the tumor itself,” said Ronald Levy, MD, of Stanford University Medical Center in California.

“In the mice, we saw amazing, body-wide effects, including the elimination of tumors all over the animal. This approach bypasses the need to identify tumor-specific immune targets and doesn’t require wholesale activation of the immune system or customization of a patient’s immune cells.”

Dr Levy and his colleagues described this approach in Science Translational Medicine.

The method involves reactivating cancer-specific T cells by injecting microgram amounts of two agents directly into the tumor site.

One of the agents is an unmethylated CG–enriched oligodeoxynucleotide (CpG)—a Toll-like receptor 9 (TLR9) ligand. It works with nearby immune cells to amplify the expression of OX40 on the surface of T cells.

The other agent is an antibody that binds to OX40. It activates the T cells to lead the charge against the cancer cells.

Because the agents are injected directly into the tumor, only T cells that have infiltrated it are activated. In effect, these T cells are “prescreened” by the body to recognize only cancer-specific proteins.

Some of these tumor-specific, activated T cells then leave the original tumor to find and destroy other identical tumors throughout the body.

The researchers found this approach worked well in mice with A20 B-cell lymphoma tumors transplanted in two sites on their bodies.

Injecting one tumor site with the agents caused regression of the untreated tumor as well as the treated one. In this way, 87 of 90 mice were cured.

Although lymphoma recurred in 3 of the mice, the tumors again regressed after a second treatment with CpG and anti-OX40.

The researchers saw similar results in mice with melanoma as well as breast and colon cancer.

Mice genetically engineered to spontaneously develop breast cancers in all 10 of their mammary pads also responded to the treatment. Treating the first tumor that arose often prevented the occurrence of future tumors and significantly increased the animals’ life span, the researchers found.

Finally, the team explored the specificity of the T cells by transplanting two types of tumors into mice.

They transplanted A20 lymphoma cells in two locations and a colon cancer cell line in a third location. Treatment of one of the lymphoma sites caused the regression of both lymphoma tumors but did not affect the colon cancer cells.

“This is a very targeted approach,” Dr Levy said. “Only the tumor that shares the protein targets displayed by the treated site is affected. We’re attacking specific targets without having to identify exactly what proteins the T cells are recognizing.”

Dr Levy and his colleagues have launched a clinical trial (NCT03410901) to test this treatment approach. The researchers hope to determine the adverse effects and optimal dose of the TLR9 agonist SD-101, the anti-OX40 antibody BMS 986178, and radiation therapy in patients with low-grade B-cell non-Hodgkin lymphomas.

If the trial is successful, Dr Levy believes the treatment could be useful for many tumor types.

“I don’t think there’s a limit to the type of tumor we could potentially treat,” he said, “as long as it has been infiltrated by the immune system.”

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