Using the Immune System to Eradicate Cancer
Deliver locally, act globally
Mobilizing endogenous T cells to fight tumors is the goal of many immunotherapies. Sagiv-Barfi et al. investigated a combination therapy in multiple types of mouse cancer models that could provide sustainable antitumor immunity. Specifically, they combined intratumoral delivery of a TLR9 ligand with OX40 activation to ramp up T cell responses. This dual immunotherapy led to shrinkage of distant tumors and long-term survival of the animals, even in a stringent spontaneous tumor model. Both of these stimuli are in clinical trials as single agents and could likely be combined at great benefit for cancer patients.
It has recently become apparent that the immune system can cure cancer. In some of these strategies, the antigen targets are preidentified and therapies are custom-made against these targets. In others, antibodies are used to remove the brakes of the immune system, allowing preexisting T cells to attack cancer cells. We have used another noncustomized approach called in situ vaccination. Immunoenhancing agents are injected locally into one site of tumor, thereby triggering a T cell immune response locally that then attacks cancer throughout the body. We have used a screening strategy in which the same syngeneic tumor is implanted at two separate sites in the body. One tumor is then injected with the test agents, and the resulting immune response is detected by the regression of the distant, untreated tumor. Using this assay, the combination of unmethylated CG–enriched oligodeoxynucleotide (CpG)—a Toll-like receptor 9 (TLR9) ligand—and anti-OX40 antibody provided the most impressive results. TLRs are components of the innate immune system that recognize molecular patterns on pathogens. Low doses of CpG injected into a tumor induce the expression of OX40 on CD4+ T cells in the microenvironment in mouse or human tumors. An agonistic anti-OX40 antibody can then trigger a T cell immune response, which is specific to the antigens of the injected tumor. Remarkably, this combination of a TLR ligand and an anti-OX40 antibody can cure multiple types of cancer and prevent spontaneous genetically driven cancers.