A Novel Immune-based Cancer Therapy Using Gene-Silenced Dendritic Cells
Dendritic cells (DCs) are specialized antigen-presenting cells (APCs) that play a critical role in anti-tumour specific immune responses 1-3. The use of tumour antigen-loaded DCs (tumour vaccines) for cancer immunotherapy is an area of considerable interest and progress 1,3. For example, more than 100 clinical trials (phase I and II) of therapeutic DC-based cancer vaccines have been reported4. Unfortunately, outcomes from clinical trials have been disappointing 2. It is now apparent that expression of immunosuppressive molecules in DCs is responsible, at least in part, for poor outcomes. These immunosuppressive molecules diminish desirable DC-mediated immune responses: this is a primary mechanism for acquisition of immune privilege by cancer cells and represents a major hurdle for immune-based cancer therapy 5. An important and recently-characterized immune suppressive molecule is indoleamine 2,3-deoxygenase (IDO), which is over-expressed in subtypes of DCs, in many different human tumour cell types, and in non-tumour cells found in lymph nodes 6. IDO may therefore play a critical role in the protecting tumours from immune recognition and attack 6, and in the maintenance of local and systemic tolerance of cytotoxic T lymphocytes (CTLs) toward cancer cells 7,8. Thus, inhibition of immune-suppressive molecules, such as IDO, in DCs is expected to overcome immunosuppression, restore anti-tumour immunity, and enhance DC-based immunotherapy.
To date, small interfering RNA (siRNA) is among the most effective techniques to selectively knock down gene expression9. Tolerotech developed a new method to treat cancer through silencing “immunosuppressive” molecules expressed in cancer or/and in DCs. There are two products are being generated in ToleroTech:
1. siCancer—Silencing tumour-derived immunosuppressive molecules using siRNA. Recently, we have successfully inhibited tumour growth by using siRNA to knock down IDO expression in mouse melanoma cells (J Immunol 2006, 177:5639). We have successfully inhibited tumor growth using IDO-siRNA in a murine melanoma model. Silencing IDO in melanoma resulted in the prevention of tumor-induced T cell apoptosis and increased T-cell-directed tumor lysis. The in vitro IDO-silenced melanoma B16 cells delayed in vivo tumor formation after inoculation into syngeneic and allogeneic recipients. Finally, treatment with IDO-siRNA in melanoma-bearing mice successfully delayed tumor onset time and significantly decreased tumor size.
2. siCancerVaccine-- More recently, we silenced IDO expressing on DCs. Using siRNA-silenced DC triggered strong anti-tumour immune response against melanoma (PCT Patent Application, WO 2006/133561). Access to funding available through Phase I of the CIHR Proof-of Program will utilized to demonstrate that the silencing of IDO can improve the effectiveness of DC-based immune therapies for the treatment of cancer. The anticancer effects of IDO-silenced DC therapy, compared with non-silenced, conventional control DC vaccine, were evidenced by i) postponed melanoma tumor onset time, and ii) decreased tumor size. In addition, after immunization with IDO-silenced DC, the number of CD8+ T cells was significantly increased while CD4+ and CD8+ T cell apoptosis in draining lymph nodes was remarkably reduced. Furthermore, immunization with IDO-silenced DC enhanced tumor antigen-specific T cell proliferation and CTL activity, and decreased numbers of CD4+CD25+FoxP3+ regulatory T cells (Treg).
