Trafficking of tumor peptide-specific cytotoxic T lymphocytes into the tumor microcirculation

The major histocompatibility complex class I-restricted CD8(+) cytotoxic T-lymphocyte (CTL) effector arm of the adaptive immune response can specifically recognize and destroy tumor cells expressing peptide antigens. Although adoptive T-cell therapy has been successfully used for the treatment of viral and malignant diseases, little is known of the trafficking and fate of adoptively transferred antigen-specific T cells. In the present study, splenocytes derived from mice that rejected their tumors (CT26 or CT26-clone 25 tumors) in response to direct intratumor injection of disabled infectious single-cycle herpes simplex virus (DISC-HSV) encoding murine GM-CSF were restimulated with peptide in vitro. CTLs specific for the AH-1 and beta-gal peptides expressed by CT26 and CT26-clone 25 tumor cells, respectively, were generated and used for adoptive cellular therapy and trafficking studies. Intravenous administration of AH-1-specific CTLs 3 days following i.v. injection of CT26 cells resulted in significant tumor growth inhibition, whereas administration of control CTLs generated against a bacterial beta-gal peptide did not inhibit the growth of tumors. Trafficking of AH-1-specific lymphocytes and their interaction with the CT26 tumor microcirculation was analyzed using real-time in vivo microscopy (IVM). AH-1-specific but not beta-gal-specific CTLs adhered and localized in the CT26 tumor microvasculature, but neither population adhered to the endothelium of the normal microcirculation. This study provides direct visual evidence suggesting that AH-1-specific CTLs that mediate a therapeutic response traffic to and localize within the tumor microenvironment.