Researchers Discover Mechanism that Helps Turn a Subset of CD4+ Helper Cells into a Cancer-Fighting Tool

Cleveland clinic researchers recently uncovered the transcription factor that regulates the differentiation of CD4+ T helper cells into a subset known as tumor-specific CD4+ T helper 9 (Th9) cells. Th9 cells — which get their name because they secrete the cytokine interleukin-9 — display anti-tumor activity and could potentially be used in cancer immunotherapy. The researchers also found that the newly uncovered transcription factor regulates the enhancement of Th9 cells anti-tumor capabilities.

“My lab has been interested in whether we can identify additional T cells that can be used to treat cancer,” says Qing Yi, MD, PhD, Chair of Cancer Biology, Lerner Research Institute, Cleveland Clinic. Dr. Yi is the senior author on the study, which was recently published in the journal Science Signaling.

Interleukin 7 boosts anti-tumor effects of Th9 cells

In the past, researchers have focused on Th1 and Th17 cells for cancer immunotherapy. Five years ago, Dr. Yi and colleagues published a paper showing that Th9 cells had even stronger anti-tumor effects compared with Th1 cells after adoptive transfer to tumor-bearing mice.

After that paper was published, Dr. Yi and one of his post-doctoral students, Enguang Bi, decided to try pretreating murine CD4+ cells in vitro with the cytokine Interleukin-7 (IL-7), which is important for T cell growth. Dr. Bi did a pilot study in which he pretreated CD4+ T cells with IL-7 and then polarized them to Th9 cells using the cytokines IL-4 and TGF-β.

“We found that this enhanced the Th9 cells,” Dr. Yi says. “They displayed even stronger anti-tumor effects compared with ordinary Th9 cells in tumor-bearing mice.”

Effect also seen in tumor-induced mice

After that preliminary work, the researchers injected OT II mice — transgenic mice whose CD4+ T cells have only one type of T-cell receptor which can recognize certain artificial tumor antigens — with B16 (melanoma) tumor cells. After four days, they transferred IL-7 pretreated Th9 cells to some mice and plain Th9 cells to other mice.

“Consistent with the in-vitro data, the mice treated with IL-7 pretreated Th9 cells displayed much stronger anti-tumor effects,” Dr. Yi says. “You see much less tumor burden in these mice compared with mice treated with ordinary Th9 cells.”

Positive and negative regulators found

Lastly, the researchers followed the signaling pathway downstream of IL-7. They found that IL-7 markedly increased the abundance of the histone acetyltransferase p300 by activating the STAT5 and PI3K-AKT-mTOR signaling pathways and promoting the acetylation of histone at the IL-9 promotor.

This dephosphorylated and translocated the transcriptional regular Foxo1 to the nucleus, bound it to the IL-9 promotor and induced the production of IL-9 protein. Foxo1 also outcompeted Foxp1, which normally binds to the IL-9 promotor in naive CD4+ T cells and inhibits IL-9 expression. In addition, Foxp1 was translocated to the cytoplasm.

“To our surprise those two transcription factors play different roles in regulating IL-9,” Dr. Yi says. “One is a positive regulator for IL-9 gene expression and one is a negative regulator for IL-9 gene expression.”

Dr. Yi says the production of IL-9 and IL-21 are important for the anti-tumor functions of Th9 cells and that this latest research showed that the IL-7-pretreated Th9 cells produced more IL-21 than the regular Th9 cells. He points out that clinical trials using IL-21 alone or combined with chemotherapy or biological agents are ongoing and have good therapeutic potential. Thus, he says, using IL-7-pretreated Th9 cells could have even better treatment possibilities.

“One day soon,” he says, “We hope we can transfer what we have learned from the laboratory to the clinic.”