Cytokine-induced killer cell trafficking to tumors: A chemokine-directed migration

Abstract

Cytokine-induced killer (CIK) cells are ex vivo expanded T-cells with immune effector function capable of in vitro and in vivo anti-cancer activity. The tumoricidal activity of CIK cells is attributed to a CD3+CD56+ population expressing the NKG2D receptor. The TALL-104 cell line exhibits characteristics similar to those observed in CIK cells. TALL-104 cells are CD3+CD56+, NKG2D+, and exhibit strong tumoricidal activity. Localization of CIK and TALL-104 cells into tumors has been revealed in mouse models using in vivo bioluminescence and fluorescence imaging. To better understand the trafficking potential of CIK and TALL-104 cells we sought to define their chemokine receptor expression. A comprehensive analysis of CC, CXC, and CX₃C receptors was carried out using antibody staining and flow cytometric analysis. Calcium mobilization and chemotaxis assays were used to assess function of the identified receptors. Human derived CIK cells and TALL. 104 cells express and respond to ligand stimulation for CCRS, CCR6, and CCR7 along with CXCR3 and CXCR4, additionally, TALL-104 cells express functional CCR3. We have identified a unique expression pattern of chemokine receptors on CIK and TALL-104 cells, which we believe contributes to the tissue specific trafficking patterns observed in in vivo models of cancer. Understanding the role these chemokine receptors play in the control of CIK cell trafficking to tumor sites required an in vivo model amenable to imaging modalities and chemokine perturbation. A mouse model of adenocarcinoma was chosen to study mouse CIK cell trafficking and homing into tumors. Before beginning in vivo studies we had to ensure that mouse CIK cells expressed the pattern of chemokine receptors identified on human CIK cells. Mouse derived CIK cells, analyzed for the expression of chemokine receptors patterned on human CIK cells, were found to express RNA message and respond in migration assays for CCRS, CCR6, CCR7, CXCR3, and CXCR4. It has been established that CXCR3 plays a critical role in NK and T-cell homing to tumors and so we chose to investigate the effects of CXCR3 perturbation in CIK cell tumor homing. Studies using CIK cells derived from CXCR3 knockout mice show a significant reduction in trafficking to tumor sites and tumor cell killing. The reduction in tumor killing is can be attributed to a decrease in CIK cells capable of escaping circulation and extravasating into the tumor. This suggests that CXCR3 plays a key role in the initial control of CIK cell homing into orthotopic mammary tumors.