Dowell, Alexander Charles (2010)
Ph.D. thesis, University of Birmingham.
Costimulation is required for the generation of an effective T cell based immune response. The presentation of tumour associated antigens may occur in the absence of effective costimulation, inducing tolerance. Conversely effective costimulation can overcome immunosuppressive mechanisms present within the tumour. Costimulation may therefore hold significant potential for cancer immunotherapy. Using recombinant adenoviral vectors encoding the costimulatory molecules CD80 and 4-1BBL (CD137L) and the cytokine IL-12 tumour cell lines were transduced to express these molecules individually or in combination in vitro. Using PBMC from healthy donors the effect of costimulation in response to pan-T cell stimulation with the anti-CD3 antibody OKT-3 were initially studied. The combination of CD80+4-1BBL supported the proliferation of CD8+ T cells and was superior to either molecule alone. Proliferation was further enhanced by the addition of IL-12 to the combination of CD80+4-1BBL. Unexpectedly in the absence of OKT-3 costimulation with 4-1BBL or IL-12 was observed to predominantly induced the proliferation of natural killer (NK) cells. The effects of 4-1BBL on human NK cells are not clearly defined in the literature. Further experiments were therefore conducted to investigate the ability of 4-1BBL and IL-12 to stimulate NK cells. The combination of 4-1BBL+IL-12 was superior to either stimulation alone for the activation, proliferation and function of NK cells from healthy lab donors. 4-1BBL was also shown to promote the long term expansion of NK cells. Importantly renal cell carcinoma patient NK cells were shown to require a combination of 4-1BBL+IL-12 for short and long term expansion; stimulated NK cells were also shown to be functional. These data highlight the need for understanding of the pleiotropic effects of costimulatory molecules and the necessity to choose optimal combinations for the activation of not only the adaptive III but also the innate immune response. The combined intratumoural delivery of 4-1BBL and IL-12 via adenoviral vectors could potentially stimulate beneficial T cell and NK cell responses, and therefore warrant further investigation as a potential immunotherapy.
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