AbstractsBiology & Animal Science

Indirect effector mechanisms on antibodies in hemodialysis patients

by Till Jakob Koch

Institution: Christian-Albrechts-Universität zu Kiel
Department: Medizinische Fakultät
Degree: PhD
Year: 2015
Record ID: 1102255
Full text PDF: http://macau.uni-kiel.de/receive/dissertation_diss_00016658


Patients suffering from chronic kidney failure undergoing regular hemodialysis (DP) have been shown to suffer from increased incidence of solid tumors (e.g. colorectal carcinoma), which indicates a reduced immune status. At the same time, their immune system is constantly activated to a state of slight inflammation, likely due to the continuous interaction of leukocytes with the foreign surface of the dialysis filters. In the last decades, several novel antibody drugs have been approved for the treatment of tumors, most of them of the IgG isotype. Major effects of these drugs in defense against tumor cells are mediated through indirect effector mechanisms such as ADCC. These indirect effector mechanisms depend not only on the target cell (tumor) and the antibody but also on the effector cell (leukocyte). It is yet unclear in which way regular hemodialysis influences the leukocytes ability to defend against tumor cells using antibodies. In this study, we investigated this with the mediation of antibodies. We used in vitro methods like 51Cr release assay or immunofluorescence to investigate the in vivo tumor defense and compared DP to healthy individuals (HI). We found an increased ability of DP’s peripheral blood mononuclear cells (PBMC) to kill EGFR coated tumor cells when ADCC was mediated by anti-EGFR antibodies of the IgG2 isotype. When ADCC was mediated by antibodies of the IgG1 isotype, DP and HI showed no significant difference. In order to examine whether the observed effect was restricted to ADCC or also occurred in antibody-dependent phagocytosis by cells such as PMN, we then strove to establish an assay using EGFR-coated microspheres. Principal conductibility and practicability of the chosen method could be demonstrated, and we determined optimal experimental conditions to maximize the observed phagocytosis effect. However, we were unable to show the antibody-dependency of phagocytosis, likely due to an alteration of the EGFR-molecule in the coupling procedure. To investigate further the effect of increased IgG2-mediated ADCC capacity in DP, we then experimented with subpopulations of leukocytes such as monocytes and NK-cells. In the heterogeneous PBMC population, we identified monocytes as the major faction contributing to the observed effect. An expression of FcγRII on the surface of NK-cells of DP or HI could be ruled out. The proportion of monocytes from all PBMC was numerically raised in DP and their monocytes were shown to be more potent in ADCC, suggesting a heightened activation status. The activation of monocytes seems not to be due to changes in the FcR expression, as both DP and HI showed the same level of FcR expression, but seems to be due to an effect downstream the signaling-cascade. Our experiments indicate that cytotoxic effector cells of patients with end-stage renal disease undergoing dialysis are fully capable of antibody mediated tumor cell killing. We did not find any evidence that DP’s ability to perform ADCC is diminished compared to HI. Furthermore, our studies indicate that…