The manipulation of cellular immunity by monoclonal antibodies in cancer patients.
thesisposted on 19.11.2015, 08:49 by James. Hollingworth
The role of an immune response in the development and regulation of tumour growth is outlined. The historical development of immunotherapy in the treatment of human cancer is reviewed and the mechanisms by which immunity may be manipulated in vitro and in vivo with respect to improving cancer immunotherapy are discussed. The experimental studies and laboratory methods finally used are presented and validated in chapter 3. Non-major histocompatibility-restricted cellular cytotoxicity was assessed in a standard 4-hour 51chromium-release assay and peripheral blood cell populations were examined using fluoresceine-conjugated monoclonal antibodies and flow cytometry. Initially in vitro studies of cellular cytotoxicity against cultured tumour cells were undertaken using peripheral blood mononuclear cells (PBMC) obtained from healthy volunteers. Extremely variable levels of cellular cytotoxicity were documented in these healthy donors which were unrelated to age or sex but were positively correlated with numbers of circulating natural killer (NK) cells. The effect on cytotoxicity, of preincubating PBMC with monoclonal antibodies (mAb) and interleukin 2 (IL-2) was studied. Various mAb including those to the CD3 antigen were found to enhance cellular cytotoxicity in vitro. The mechanism of enhancement remained unproven. However, preliminary studies suggested that mAb redirected effector cells by interacting with Fc receptors on the surface of tumour cells. Combinations of mAb had a partially additive effect on enhancement of cytotoxicity. IL-2 also enhanced cytotoxicity in a dose dependent manner although synergy between IL-2 and anti-CD3 was not demonstrated. PBMC were then studied from patients with advanced gastrointestinal tract cancer. Levels of cellular cytotoxicity were not significantly related to tumour extent and were similar to cytotoxicity in healthy donors. Cytotoxicity was mediated mainly by NK cells although lymphocytes coexpressing the CD3 antigen and NK surface antigens were significantly increased in cancer patients compared with healthy donors and also in patients with liver metastases compared to those without liver involvement. In cancer patients with liver metastases, lymphocytes coexpressing the CD3 antigen and NK antigens may play a more significant role in K562 cytotoxicity. Cytotoxicity was also enhanced in vitro by anti-CD3 mAb and I1-2. A clinical study was undertaken to investigate the safety and the immunomodulating properties of administering between 50 mug and 0.5 mug of OKT3 or normal saline to patients with advanced cancer. Patients experienced minimal and self- limiting dose-related side effects. Only one patient developed evidence of cytokine release following OKT3 when assessed by enzyme-linked immunosorbent assays. Depletion of circulating T cells and NK cells occurred following OKT3 which was proportional to the dose administered. Lymphocyte activation assessed by interleukin 2 receptor expression was not detected. Considerable individual variation in cytotoxicity was related to variation in NK cell numbers in blood in both OKT3 and normal saline treated patients. 50 mug OKT3 was associated with a rapid decline in both circulating NK cells and cytotoxicity at 4 hours compared with lower doses of OKT3. The lower doses of OKT3 had a variable effect on cytotoxicity at 24 hours. 20 mug and 5 mug OKT3 was associated with a significant rise in cellular cytotoxicity at 24 hours compared with untreated controls and the 10 mug dose. These results demonstrate that anti-CD3 mAb enhance cellular cytotoxicity in vitro. The effect of OKT3 on lymphocyte function in vivo is dose-related and variable. Low doses of OKT3 may either enhance or depress cellular immunity depending upon the precise dose and time of study following administration. The relationship between the in vitro effects of anti-CD3 mAb on cellular cytotoxicity and their effects in vivo are uncertain. Although low doses of OKT3 may be safely administered to cancer patients further studies are needed to define its potential in human cancer immunotherapy.