Figure 1. Tumor-Induced Brain-Specific T Cell Sequestration in the Bone Marrow.
(A) S1P1+ T cells are produced in the bone marrow and normally cycle through the body where they also infiltrate tumors like those grown subcutaneously. (B) Intracranially injected tumors likely secrete a factor that promotes S1P1 loss on the T cell surface leading to T cell sequestration in the bone marrow and subsequent leukopenia. (C) Genetic blockade of S1P1 internalization on T cells in intracranial tumor-bearing SD1 P1-knockin mice (S1P1-KI) hinders S1P1 loss on the T cell surface, unlocks T cell entrapment, and thus enables T cell release into the peripheral blood.