Natural killer cells in cancer : studies on migration and cytotoxicity

Sammanfattning: The role of natural killer (NK) cells in cancer development has been studied extensively over the last four decades and the increasing knowledge on NK cell regulation has improved both safety and efficacy of treatment. Despite these recent advances the clinical success has to date been modest in treatment of solid tumors, owing both to suboptimal directed migration of NK cells and the tumor cell’s resistance to NK cell-mediated lysis. This thesis focuses on strategies to overcome these critical issues thus improving the anti-tumor effect of adoptive NK cell therapy. In paper I, we have studied the sensitizing effect of doxorubicin on tumor cells to NK cell and T cell-mediated lysis. The potential clinical advantage of using doxorubicin as a preconditioning agent was highlighted in a xenograft mouse model, where mice receiving low-doses of doxorubicin prior to NK cell infusion had a stronger anti-tumor effect of a subsequent NK cell treatment compared to mice receiving only NK cell treatment. Further, we identified TRAIL-signaling as the main pathway responsible for the tumor sensitization due to decreased expression of the anti-apoptotic protein cFLIP. In paper II we have established that the cytotoxicity of NK cells can be augmented by co-culturing them with monocytes in presence of the biphosphonate zoledronic acid (ZA). We observed an upregulated expression of TRAIL on NK cells, through increased levels of monocyte-derived IFNγ in the culture. Thus, NK cells primed with ZA were able to lyse TRAIL-sensitive tumors both in vitro and in vivo. In paper III, we studied CXCL10-mediated migration of NK cells toward solid tumors. We found that ex vivo expansion of NK cells induced a 10-fold increase in CXCR3-receptor expression, which allowed them to migrate towards tumor cells in a CXCL10-dependent manner. In two separate xenograft models we could demonstrate the anti-tumor effect of CXCL10-induced migration of adoptively transferred CXCR3-positive NK cells by their selective targeting of CXCL10-producing tumors, which resulted in reduced tumor progression and prolonged survival. In paper IV, we identified anaplastic thyroid carcinoma (ATC) as a potential novel target for NK cell therapy. We found that ATC cells were sensitive to NKG2D-mediated lysis due to high expression of ULBP2 on tumor cells. In addition, tumor cells produced high levels of CXCL10 which attracted CXCR3-positive NK cells in vitro. In ATC tumor samples we found a suppressed NK cell population although enriched for CXCR3 expression suggesting that CXCL10 may have been involved in the chemoattraction of the NK cells. In conclusion, we have studied some of the important aspects of how NK cells interact with tumor cells and suggested approaches that could improve the use of NK cells in cancer therapy. Moreover, we have identified the highly aggressive tumor ATC as being uniquely sensitive to NK cell lysis and have studied the prospects of developing NK cell therapies for ATC patients.