Immunotherapy is a new class of cancer treatment that works to harness the innate powers of the immune system to fight cancer. Because of the immune system’s unique properties, these therapies may hold greater potential than current treatment approaches to fight cancer more powerfully, to offer longer-term protection against the disease, to come with fewer side effects, and to benefit more patients with more cancer types. From the preventive vaccine for cervical cancer to the first therapy ever proven to extend the lives of patients with metastatic melanoma, immunology has already led to major treatment breakthroughs for a number of cancers. Every cancer type is unique, though, and immunology and immunotherapy are impacting each cancer in different ways.
The tumour microenvironment is an important aspect of cancer biology that contributes to tumour initiation, tumour progression and responses to therapy. Cells and molecules of the immune system are a fundamental component of the tumour microenvironment. Importantly, therapeutic strategies can harness the immune system to specifically target tumour cells and this is particularly appealing owing to the possibility of inducing tumour-specific immunological memory, which might cause long-lasting regression and prevent relapse in cancer patients.
The composition and characteristics of the tumour microenvironment vary widely and are important in determining the anti-tumour immune response. For example, certain cells of the immune system, including natural killer cells, dendritic cells (DCs) and effector T cells, are capable of driving potent anti-tumour responses. However, tumour cells often induce an immunosuppressive microenvironment, which favours the development of immunosuppressive populations of immune cells, such as myeloid-derived suppressor cells and regulatory T cells. Understanding the complexity of immunomodulation by tumours is important for the development of immunotherapy. Various strategies are being developed to enhance anti-tumour immune responses, including DC-based vaccines and antagonists of inhibitory signalling pathways to overcome ‘immune checkpoints’. Existing therapies are also being investigated for their ability to induce an anti-tumour immune response, which could lead to the administration of combination immunotherapies that provide a more efficacious and enduring response. However, there are issues that remain to be understood. In particular, it is clear that there is variability in the ability of a tumour to induce an immune response and hence there is debate about the determinants of tumour immunogenicity. It will be important to resolve these issues in order to predict or modulate responses to immunotherapies.
In just the past few years, the rapidly advancing field of cancer immunology has produced several new methods of treating cancer that increase the strength of immune responses against tumors. These therapies either stimulate the activities of specific components of the immune system or counteract signals produced by cancer cells that suppress immune responses.
The journal Science designated “immunotherapy of cancer” as its Breakthrough of the Year in 2013 to recognize the progress made in this area. These advances are the result of long-term basic scientific research on the immune system.