Dendritic cells in immune and gene therapy against cancer

Abstract

Dendritic cells (DC) are extensively used for vaccine therapy due to their superior T cell stimulatory capacity. However, the modest therapeutic effects reported by most clinical trials using DC, together with the rapid developing field of DC biology suggests important considerations for improvement of the clinical outcome. The general aim of this thesis is to develop DC-based cancer vaccines thereby facilitating the translation of such therapeutic approaches to the clinic.

An ancillary aim of this study is to better understand the factors that affect the apoptosis of DC particularly during their differentiation from monocyte precursors. Mature DC are effectively resistant to Fas-mediated apoptosis. One of the underlying mechanisms that mediate this resistance is the observed upregulation of Bcl-XL that accompanies DC maturation. These results provide additional support for the use of mature DC as cellular adjuvants since they not only represent a more potent T cell stimulatory population, but also may mediate a more protracted effect due to their resistance to Fas induced apoptosis.

The mode of antigen delivery is pivotal to the generation of specific immunity. In this study, a comparison of viral and non-viral gene delivery techniques to human DC derived from peripheral blood precursors or CD34+ stem cells were performed. DC differentiated from both types progenitor cells were receptive to non-viral transfection using mRNA and electroporation. In addition, the number of transfected cells was comparable to what could be achieved by adeno- and retro-viral transduction. These findings encourage the use of non-viral methods for transfection of DC as problem of neutralizing antibodies and prohibitively expensive safety tests associated with viral delivery may limit their use in the clinic.

Certain viruses can lead to inhibition or maturation of DC or even induce their apoptosis. Furthermore, the effect of viral transduction on cell physiology and APC activity has not been satisfactorily elucidated. Transduction of monocyte derived-DC using adenovirus (AdV) results in generation of DC that are phenotypically and functionally "activated". Taken together, the transfer of antigenic epitopes at high efficiency to human monocyte-derived DC as well as the DC- activating effects are strong arguments for their clinical application of AdV-transduced DC-based vaccines.

The final aspect of the thesis utilizes prostate specific antigen (PSA) as a model tumor antigen for generation of specific T cell response, using DC transfected with different delivery methods. Stimulation with AdV transduced TNFalpha treated DC resulted in the generation of PSA-specific T cells that predominantly produced IL10. However, stimulation with untreated, lipopolysaccharide, or anti-CD40 treated AdV transduced DC resulted in generation of IFNgamma, but not IL-10, producing PSA-specific T cells indicating that the predominant population was Th1 T cells.

In conclusion, conventional antigen delivery and DC maturation methods may influence the functional characteristics of the generated DC and may produce T cell populations with aberrant functions, that in certain instances may be counter productive to the anti-tumor immune response desired with vaccination strategies.