Tumors generate unique, temporary cell structures in the cell to evade immunotherapy

Scientists have shown how cancer cells escape immunotherapy by generating unique, temporary structures of cells within the cell, in which the inner cells remain in good condition and can return to single tumor cells.

These results, published today in eLife, offers a new theory about how cancer cells avoid destruction by the immune system. They could also report the development of treatments that combine immunotherapy with timed inhibition of related signaling pathways in cancer cells.

“Cancer immunotherapy harnesses the body’s immune system to fight cancer. Despite its remarkable success, the majority of patients who receive immunotherapy will only see their tumors temporarily shrink in size before returning, and these relapsed tumors are likely to be resistant to immunotherapy,” he says. Says first author Amit Gutwillig, who was a doctoral student in Karmi Lab, Tel Aviv University, Israel, at the time the study was conducted and is now a senior researcher in Nucleai, Tel Aviv.

To determine how tumors relapse after immunotherapy, Karmi and the team began by comparing whole-genome genetic sequences in primary and relapsed tumors in the same patient. Their analysis suggested that relapsed tumors do not change significantly after immunotherapy.

Next, the team studied this process in breast and melanoma, using mouse models in which tumors resistant to immunotherapy had relapsed. They gave mice cells from treated tumors and allowed these cells to reach an appreciable size. The team found that the cells were just as susceptible to immunotherapy approaches as the parent tumor, although they relapsed sooner.

To better characterize the tumor cells that survived in mice after immunotherapy, the researchers isolated and studied live tumor cells. They found that most cells responded to the presence of T cells – a type of immune cell that targets foreign molecules – by organizing into temporary configurations. They consisted of clusters of many tumor cell nuclei, which were surrounded by a single multilayered membrane and a network of cortical actin filaments. The inner cell of the formation was dense and seemed to be compacted inside another cell.

To demonstrate that this finding was not due to the isolation of melanoma cells, the team also analyzed tumors using fluorescently-labeled cell nuclei and membranes. They found that in-cell formation was more prevalent in tumors treated with immunotherapy, particularly at sites associated with cancer cell death. Additional analysis indicated that approximately half of the tumor cells that survived immunotherapy were arranged in a cell-by-cell configuration. Over time, these cells reverted to a single cell state, with structural features similar to those of the parental cell line.

The team next tested whether this phenomenon occurs in human cancers. To do this, they incubated the tumor cell lineages with pre-activated T cells from healthy donors. They discovered that the vast majority of breast, colon, and melanoma cells that survived T-cell killing were organized into the cell’s intracellular structure. Three-day observation of T cells interacting with tumor cells showed that these structures were dynamic, with individual tumor cells forming and constantly spreading out from the structure.

Finally, they tested the clinical significance of this finding by analyzing tumor tissues from multiple organs of stage IV melanoma patients. These patients were undergoing surgical removal of primary and metastatic lymph nodes—that is, lymph nodes that had spread from the primary tumor. The researchers found that, in all four patients, β-cell formation was highly abundant in the T-cell region of the bleeding lymph nodes, but not in the primary tumors. Furthermore, in a patient with untreated recurrent melanoma, most cells in the primary tumor were single cells, whereas the recurrent tumors had an abundance of cell formations in the primary tumor.

This previously unknown mechanism of tumor resistance highlights the limitations of immunotherapy currently. Over the past decade, several clinical studies have used immunotherapy followed by chemotherapy. But our findings suggest that timed inhibition of relevant signaling pathways must occur in tandem with immunotherapy to prevent the tumor from becoming resistant to subsequent treatments.”

Yaron Carme, Senior writer, Principal Investigator, Department of Pathology, Sackler College of Medicine, Tel Aviv University

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Journal reference:

Gottwillig, A.; et al. (2022) Transcellular formation in the cell underlies tumor relapse and resistance to immunotherapy. eLife. doi.org/10.7554/eLife.80315.