Despite the identification of tumour antigens and their subsequent generation in subunit form for use as cancer vaccines, whole tumour cells remain a potent vehicle for generating anti-tumour immunity. This is because tumour cells express an array of target antigens for the immune system to react against, avoiding problems associated with major histocompatibility complex (MHC)-restricted epitope identification for individual patients. Furthermore, whole cells are relatively simple to propagate and are potentially efficient at contributing to the process of T cell priming. However, whole cells can also possess properties that allow for immune evasion, and so the question remains of how to enhance the immune response against tumour cells so that they are rejected. Scenarios where whole tumour cells may be utilised in immunotherapy include autologous tumour cell vaccines generated from resected primary tumour, allogeneic (MHC-disparate) cross-reactive tumour cell line vaccines, and immunotherapy of tumours in situ. Since tumour cells are considered poorly immunogenic, mainly because they express self-antigens in a non-stimulatory context, the environment of the tumour cells may have to be modified to become stimulatory by using immunological adjuvants. Recent studies have re-evaluated the relative roles of direct and cross-priming in generating anti-tumour immunity and have highlighted the need to circumvent immune evasion.

No abstract

SUMMARYAntigenic cross-reactivity between certain tumours has allowed the development of more widely applicable, major histocompatibility complex-disparate (allogeneic) whole-cell vaccines. This principle should also allow heat shock proteins (hsp) derived from certain tumours (and carrying cross-reactive antigens) to be used as vaccines to generate anti-tumour immunity in a range of cancer patients. Here, hsp70 derived from gp70-antigen B16 melanoma generated cytotoxic-T-lymphocyte-mediated immune protection in BALB/c mice against challenge with gp70-antigen CT26 colorectal tumour cells. Using ovalbumin as a model tumour antigen, it is shown that hsp70 enhances peptide re-presentation by dendritic cells via class I over equimolar whole ovalbumin antigen. However, while transfection of tumour cells with inducible hsp70 increases hsp yield from tumours, it does not enhance antigen recognition via puri®ed hsp70 nor via whole cells or their lysate.

BackgroundRNA interference is an evolutionary conserved immune response mechanism that can be used as a tool to provide novel insights into gene function and structure. The ability to efficiently deliver small interfering RNA to modulate gene expression in vivo may provide new therapeutic approaches to currently intractable diseases.MethodsIn vitro, siRNA targeting IL-12p40 was delivered to the murine macrophage cell line (J774A.1) encapsulated in a liposome with an IL-12 inducing agent (LPS/IFN-γ) over a number of time points. Controls included a variety of non-target specific siRNA reagents. Supernatants were analyzed for cytokine production while the cells were removed for mRNA profiling.In vivo, siRNA-targeting IL-12p40 was delivered to the murine peritoneal cavity in a therapeutic fashion, after endotoxin (LPS) challenge. Cells from the peritoneal cavity were removed by lavage and analyzed by flow cytometry. Levels of IL-12 present in lavage and in serum were also examined by ELISA.ResultsIn this report, we show that IL-12p40 siRNA can specifically silence macrophage expression of IL-12p40 mRNA and IL-12p70 protein in vitro. We extend this finding to demonstrate that delivery of liposome encapsulated siRNA targeting IL-12p40 to the murine peritoneal cavity can modulate an inflammatory stimulus in vivo. Furthermore, specific siRNA can be used therapeutically after endotoxin challenge to reduce both the local and systemic inflammatory response. Thus, the delivery of siRNA can be used to elicit specific non-permanent inhibition of endogenous protein expression.ConclusionIn vitro silencing of IL-12p40 using siRNA at selected doses leads to specific knockdown of IL-12p70 protein production without inducing type I interferons. Furthermore, siRNA targeting murine IL-12p40 can be used therapeutically to counter an inflammatory response in vivo.