A new study led by King's College London has found that chemotherapy helps attract a specific population of immune cells called stem-like T cells toward tumors. The research, published in Cell Stem Cell, found that macrophages around tumor blood vessels can act as a barrier, limiting the T cells' ability to enter. By blocking an enzyme called heme oxygenase-1 (HO-1) in these macrophages, the researchers were able to reduce this barrier, allowing more stem-like T cells to enter the tumor and contribute to an antitumor immune response.