Cancer is often associated with a weak immune response, so many approaches to treating the disease involve stimulation of immune cells called dendritic cells. When dendritic cells encounter tumor (or other) antigens, they process them and present them to naive T cells. This activates the T cells and 'teaches' them to identify and attack tumor cells. In most cell-based vaccination treatments, dendritic cells are isolated from the patient, activated ex vivo and then re-introduced into the patient. So far, the efficacy of this treatment has been limited; more than 90% of dendritic cells die after transplantation, and few make it to the lymph nodes, where the T cells reside. Furthermore, the treatment is costly and cumbersome, requiring two patient procedures.

Now, a study led by David J. Mooney (Harvard University and Wyss Institute for Biologically Inspired Engineering, Cambridge, MA) suggests that an effective cancer vaccine that works directly in the body may be within reach. The researchers developed porous, biodegradable polymer 'scaffolds': small, sponge-like discs that can be filled with materials and then implanted in the body, where the materials are gradually released. In a series of experiments, the investigators loaded the scaffolds with a protein known to stimulate recruitment and proliferation of dendritic cells (Nat. Mater. 8, 151–158; 2009). Recruited dendritic cells entered the scaffold's pores, where they were activated and housed until release. To test the structure's potential as a cancer vaccine, Mooney and colleagues added melanoma tumor lysates to the scaffold so that dendritic cells that entered the structure would be loaded with tumor antigens.

The researchers implanted these structures into subcutaneous pockets in the backs of mice. Two weeks later, they injected the implanted mice with highly aggressive and metastatic melanoma cells. All mice that were implanted with 'empty' scaffolds developed tumors within 18 days and had to be euthanized shortly afterward. Mice that were implanted with scaffolds containing antigen alone fared somewhat better, though all died by day 40. In mice that were implanted with scaffolds containing both tumor antigen and the dendritic cell–stimulating protein, tumor formation was delayed by approximately 40 days in 50% of the mice, and 23% of the mice were cured.

This study could have profound implications for the development of cancer vaccines and treatments for other diseases. The scaffolds are made of materials that are safe for humans, so clinical testing may be possible in the near future.