Oxidant-induced cell death in lymphocytes: mechanisms of induction and resistance

Reactive oxygen species (oxidants, oxygen radicals) produced by the phagocytic NADPH oxidase have pivotal roles in immunity. Patients lacking a functional NADPH oxidase suffer from chronic granulomatous disease, which is characterized by recurring bacterial infections and thus manifesting the importance of reactive oxygen species in host defense against bacteria. However, NADPH oxidase-derived radicals also efficiently inhibit lymphocyte-mediated immunity. Oxidant-induced inactivation of lymphocytes is reportedly a control mechanism for autoreactive lymphocytes and hence prevents autoimmunity. In malignant diseases, oxygen radicals have been proposed to contribute to the characteristic state of anergy of cytotoxic lymphocytes, which prevents immune-mediated rejection of the tumor. Studies of the mechanisms of radical-induced inactivation of lymphocytes may therefore be helpful in understanding the pathophysiology of important disease entities. The first paper in this thesis shows that oxidant-induced functional inhibition and cell death in cytotoxic lymphocytes is critically dependent on cooperation between a nuclear enzyme involved in DNA repair, PARP-1, and a mitochondrion-derived protein, AIF. The results presented in Paper II demonstrate that pharmacological inhibition of the PARP-1 enzyme not only prevents oxidant-induced cell death, but also preserves functions of cytotoxic lymphocytes, such as cytotoxicity against malignant cells, cytokine production, and proliferation. Paper III shows that subsets of natural killer (NK) cells display differential sensitivity to oxygen radicals: the cytotoxic CD56dimCD16+ NK cells were found to be highly sensitive to oxidative inactivation and apoptosis, while the immunoregulatory, cytokine-producing CD56brightCD16- NK cells were highly resistant to the toxicity of oxidants. These data were extended in Paper IV, in which the effect of oxygen radical-producing phagocytes on the expression of the activating NK cell receptors, NKp46 and NKG2D, was investigated. The expression of both receptors was efficiently downregulated on CD56dim NK cells, while the expression remained intact on CD56bright cells. Recent data imply that reciprocal interactions between NK cells and dendritic cells (DCs) are important for the development of adaptive immunity. The results presented in Paper V demonstrate that DCs are equipped with an antioxidative system that efficiently protects cytotoxic cells from oxidant-induced inactivation

Determinants for Effective ALECSAT Immunotherapy Treatment on Autologous Patient-Derived Glioblastoma Stem Cells.

Glioblastoma (GBM) is the most aggressive primary brain tumor with a median survival of less than 15 months, emphasizing the need for better treatments. Immunotherapy as a treatment for improving or aiding the patient's own immune defense to target the tumor has been suggested for GBM. A randomized clinical trial of adoptive cell transfer using ALECSAT (Autologous Lymphoid Effector Cells Specific Against Tumor Cells) is currently ongoing in Sweden. Here we performed a paired pre-clinical study to investigate the composition and in vitro effect of ALECSAT and identify determinants for the effect using autologous GBM-derived cancer stem cells (CSC), immunocytochemistry and flow cytometry. We show a clear dose-response relationship of ALECSAT on CSC, suggesting that the number of infused cells is of importance. In addition, the in vitro effect of ALECSAT on CSC correlated significantly to the blood count of T helper (Th) cells in the patient indicating a potential benefit of collecting cells for ALECSAT preparation at an even earlier stage when patients generally have a better blood count. The factors identified in this study will be important to consider in the design of future immunotherapy trials to achieve prolonged survival