Releasing the Immune System Brakes Using siRNAs Enhances Cancer Immunotherapy

Therapeutic dendritic cell (DC) cancer vaccines rely on the immune system to eradicate tumour cells. Although tumour antigen-specific T cell responses have been observed in most studies, clinical responses are fairly low, arguing for the need to improve the design of DC-based vaccines. The incorporation of small interfering RNAs (siRNAs) against immunosuppressive factors in the manufacturing process of DCs can turn the vaccine into potent immune stimulators. Additionally, siRNA modification of ex vivo-expanded T cells for adoptive immunotherapy enhanced their killing potency. Most of the siRNA-targeted immune inhibitory factors have been successful in that their blockade produced the strongest cytotoxic T cell responses in preclinical and clinical studies. Cancer patients treated with the siRNA-modified DC vaccines showed promising clinical benefits providing a strong rationale for further development of these immunogenic vaccine formulations. This review covers the progress in combining siRNAs with DC vaccines or T cell therapy to boost anti-tumour immunity.