Immunotherapies are steadily gaining traction in cancer treatment. The strategies often depend on the migration of immune cells from primary tumors to secondary tumor sites and lymphoid organs that induce antitumor responses. Much attention has been paid to the infiltration of immune cells into tumors, but the subsequent fate of the tumor-infiltrating immune cells remains understudied.

Researchers developed a photoconversion-based model capable of labeling immune cells in tumors to follow the migration pathways of tumor-transiting immune cells. The authors injected cancerous cells into mice to induce primary tumors, and observed that a variety of myeloid cells, as well as some lymphocytes, made up the population of tumor-infiltrating cells.

However, following the initial tumor infiltration, T cells, rather than myeloid cells, comprised the largest population of tumor-transiting cells in draining lymph nodes and secondary tumors.

Further analysis revealed that a subset of T cells, including CD4⁺ and CD8⁺ T cells, was among those that transited primary tumor sites more rapidly than other T-cell types, which were preferentially retained.

The findings suggest that specific molecular mechanisms direct immune cell migration from tumors to the surrounding tissue and metastatic sites. According to the authors, the findings might be relevant to T-cell–based cancer immunotherapy. 

http://www.pnas.org/content/early/2017/05/10/1618446114