The immune system recognizes and is poised to eliminate cancer but is held in check by inhibitory receptors and ligands. These immune checkpoint pathways, which normally maintain self-tolerance and ...limit collateral tissue damage during anti-microbial immune responses, can be co-opted by cancer to evade immune destruction. Drugs interrupting immune checkpoints, such as anti-CTLA-4, anti-PD-1, anti-PD-L1, and others in early development, can unleash anti-tumor immunity and mediate durable cancer regressions. The complex biology of immune checkpoint pathways still contains many mysteries, and the full activity spectrum of checkpoint-blocking drugs, used alone or in combination, is currently the subject of intense study.
Summary Checkpoint blockade immunotherapy has received mainstream attention as a result of striking and durable clinical responses in some patients with metastatic disease and a reasonable response ...rate in many tumour types. The activity of checkpoint blockade immunotherapy is not restricted to melanoma or lung cancer, and additional indications are expected in the future, with responses already reported in renal cancer, bladder cancer, and Hodgkin's lymphoma among many others. Additionally, the interactions between radiation and the immune system have been investigated, with several studies describing the synergistic effects on local and distant tumour control when radiation therapy is combined with immunotherapy. Clinical enthusiasm for this approach is strengthened by the many ongoing trials combining immunotherapy with definitive and palliative radiation. Herein, we discuss the biological and mechanistic rationale behind combining radiation with checkpoint blockade immunotherapy, with a focus on the preclinical data supporting this potentially synergistic combination. We explore potential hypotheses and important considerations for clinical trial designs. Finally, we reintroduce the notion of radiosensitising immunotherapy, akin to radiosensitising chemotherapy, as a potential definitive therapeutic modality.
Highlights ► PD-1/B7-H1 are pivotal in maintaining an immunosuppressive tumor microenvironment. ► PD-1 and CTLA-4 play distinct roles in regulating immunity. ► B7-H1 upregulation on tumor cells ...likely reflects ‘adaptive resistance’. ► PD-1 blockade is active against NSCLC, thought to be a ‘non-immunogenic’ tumor. ► Monotherapies blocking PD-1 may be more effective in combinatorial regimens.
Ipilimumab (MDX-010, Yervoy; Bristol-Myers Squibb), a fully human monoclonal antibody against CTL antigen 4 (CTLA-4), was recently approved by the U.S. Food and Drug Administration (FDA) for the ...treatment of metastatic melanoma. In both early- and late-phase trials, ipilimumab has shown consistent activity against melanoma. For example, in a randomized phase III trial that enrolled patients with previously treated metastatic disease, ipilimumab, with or without a peptide vaccine, improved overall survival: Median overall survival was 10.1 and 10.0 months in the ipilimumab and ipilimumab plus vaccine arms, respectively, versus 6.4 months in the vaccine-alone group (hazard ratio, 0.68; P ≤ 0.003). Serious (grade 3-5) immune-related adverse events occurred in 10% to 15% of patients. Thus, although it provides a clear survival benefit, ipilimumab administration requires careful patient monitoring and sometimes necessitates treatment with immune-suppressive therapy. Here, we review the mechanism of action, preclinical data, and multiple clinical trials that led to FDA approval of ipilimumab for metastatic melanoma.
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