Systemic RNA delivery to dendritic cells exploits antiviral defence for cancer immunotherapy.

Lymphoid organs, in which antigen presenting cells (APCs) are in close proximity to T cells, are the ideal microenvironment for efficient priming and amplification of T-cell responses. However, the systemic delivery of vaccine antigens into dendritic cells (DCs) is hampered by various technical challenges. Here we show that DCs can be targeted precisely and effectively in vivo using intravenously administered RNA-lipoplexes (RNA-LPX) based on well-known lipid carriers by optimally adjusting net charge, without the need for functionalization of particles with molecular ligands. The LPX protects RNA from extracellular ribonucleases and mediates its efficient uptake and expression of the encoded antigen by DC populations and macrophages in various lymphoid compartments. RNA-LPX triggers interferon-α (IFNα) release by plasmacytoid DCs and macrophages. Consequently, DC maturation in situ and inflammatory immune mechanisms reminiscent of those in the early systemic phase of viral infection are activated. We show that RNA-LPX encoding viral or mutant neo-antigens or endogenous self-antigens induce strong effector and memory T-cell responses, and mediate potent IFNα-dependent rejection of progressive tumours. A phase I dose-escalation trial testing RNA-LPX that encode shared tumour antigens is ongoing. In the first three melanoma patients treated at a low-dose level, IFNα and strong antigen-specific T-cell responses were induced, supporting the identified mode of action and potency. As any polypeptide-based antigen can be encoded as RNA, RNA-LPX represent a universally applicable vaccine class for systemic DC targeting and synchronized induction of both highly potent adaptive as well as type-I-IFN-mediated innate immune mechanisms for cancer immunotherapy.

FLT3 ligand enhances the cancer therapeutic potency of naked RNA vaccines.

Intranodal immunization with antigen-encoding naked RNA may offer a simple and safe approach to induce antitumor immunity. RNA taken up by nodal dendritic cells (DC) coactivates toll-like receptor (TLR) signaling that will prime and expand antigen-specific T cells. In this study, we show that RNA vaccination can be optimized by coadministration of the DC-activating Fms-like tyrosine kinase 3 (FLT3) ligand as an effective adjuvant. Systemic administration of FLT3 ligand prior to immunization enhanced priming and expansion of antigen-specific CD8(+) T cells in lymphoid organs, T-cell homing into melanoma tumors, and therapeutic activity of the intranodal RNA. Unexpectedly, plasmacytoid DCs (pDC) were found to be essential for the adjuvant effect of FLT3 ligand and they were systemically expanded together with conventional DCs after treatment. In response to FLT3 ligand, pDCs maintained an immature phenotype, internalized RNA, and presented the RNA-encoded antigen for efficient induction of antigen-specific CD8(+) T-cell responses. Coadministration of FLT3 ligand with RNA vaccination achieved remarkable cure rates and survival of mice with advanced melanoma. Our findings show how to improve the simple and safe strategy offered by RNA vaccines for cancer immunotherapy.

Linking transgene expression of engineered mesenchymal stem cells and angiopoietin-1-induced differentiation to target cancer angiogenesis.

OBJECTIVE: To specifically target tumor angiogenesis by linking transgene expression of engineered mesenchymal stem cells to angiopoietin-1-induced differentiation. BACKGROUND: Mesenchymal stem cells (MSCs) have been used to deliver therapeutic genes into solid tumors. These strategies rely on their homing mechanisms only to deliver the therapeutic agent. METHODS: We engineered murine MSC to express reporter genes or therapeutic genes under the selective control of the Tie2 promoter/enhancer. This approach uses the differentiative potential of MSCs induced by the tumor microenvironment to drive therapeutic gene expression only in the context of angiogenesis. RESULTS: When injected into the peripheral circulation of mice with either, orthotopic pancreatic or spontaneous breast cancer, the engineered MSCs were actively recruited to growing tumor vasculature and induced the selective expression of either reporter red florescent protein or suicide genes [herpes simplex virus-thymidine kinase (TK) gene] when the adoptively transferred MSC developed endothelial-like characteristics. The TK gene product in combination with the prodrug ganciclovir (GCV) produces a potent toxin, which affects replicative cells. The homing of engineered MSC with selective induction of TK in concert with GCV resulted in a toxic tumor-specific environment. The efficacy of this approach was demonstrated by significant reduction in primary tumor growth and prolongation of life in both tumor models. CONCLUSION: This "Trojan Horse" combined stem cell/gene therapy represents a novel treatment strategy for tailored therapy of solid tumors.

The analysis of metastasis in transgenic mouse models.

Human metastasis has been modeled mostly by xenotransplantation of cell lines in immunodeficient mice. Since this approach frequently uses cell lines derived from metastases, it ignores the significant role of cellular selection processes before and during metastatic progression and, in fact, models metastasis from metastasis and not metastasis from primary tumours. While the importance of the latter for the fate of patients is proven, the existence and clinical relevance of metastasis from metastasis is still unsettled. On the other hand, transgenic or gene knockout models of cancer offer novel experimental approaches to dissect the metastatic cascade from its very beginnings. Here, we briefly review the attempts to model metastatic progression and the strengths and limitations of the different experimental approaches and describe how transgenic mouse models recently helped to promote our understanding of systemic cancer progression.

Systemic spread is an early step in breast cancer.

It is widely accepted that metastasis is a late event in cancer progression. Here, however, we show that tumor cells can disseminate systemically from earliest epithelial alterations in HER-2 and PyMT transgenic mice and from ductal carcinoma in situ in women. Wild-type mice transplanted with single premalignant HER-2 transgenic glands displayed disseminated tumor cells and micrometastasis in bone marrow and lungs. The number of disseminated cancer cells and their karyotypic abnormalities were similar for small and large tumors in patients and mouse models. When activated by bone marrow transplantation into wild-type recipients, 80 early-disseminated cancer cells sufficed to induce lethal carcinosis. Therefore, release from dormancy of early-disseminated cancer cells may frequently account for metachronous metastasis.