Although the immune checkpoint protein B7-H1/PD-L1 is a commonly used cancer biomarker, controversy remains over the predictive and prognostic utility of immunohistochemical methods. Download our white paper which shows that we can reliably measure B7-H1/PD-L1 in conditioned media supernates and cell lysates from a number of cancer cell lines.
Data from our white paper indicate that:
We can reliably measure B7-H1/PD-L1 in a number of human cancer cell lines
Soluble B7-H1/PD-L1 expression levels are coincident with loss of PTEN tumor suppressor or increased activation of the phosphoinositide 3-kinase pathway
The immune system fights off pathogens, but this defensive force can be pathogenic itself when hyperactive, resulting in autoimmune diseases such as lupus and multiple sclerosis. Consequently, the body has developed multiple mechanisms to suppress the immune system when necessary.
One method of immunosuppression is the PD-1 pathway. This pathway is activated in response to the mobilization of the immune system. The receptor PD-1 is expressed on the surface of activated lymphocytes. Similarly, its ligand, PD-L1, is expressed by antigen-presenting cells in response to cytokine signaling. When PD-L1 is bound to PD-1, downstream signaling undoes the phosphorylation events associated with activation, thereby reverting lymphocytes to an inactive state [1, 2].
Tumor cells take advantage of the PD-1 pathway to evade the immune system . Consequently, many pharmaceutical companies have been developing drugs to inhibit PD-1 and PD-L1. In clinical trials, many patients have shown strong responses to these therapies [4-10]. For these drugs to be most effective, a high number of CD8+ T cells must already be at the tumor site, ready to be mobilized after inhibition of the PD-1 pathway .Recent investigations have uncovered promising methods of increasing the efficacy of PD1 inhibitors. One method is combining PD1 inhibitors with other drugs, such as HDAC inhibitors  and anti-CTLA4 antibodies . Another method is using biomarkers to predict response to therapy [13,14]. Recent work has also suggested that GSK3 inhibitors can enhance effects of immunotherapy .Though these results have been encouraging, several challenges remain, including the mitigation of autoimmune effects and how to overcome drug resistance.
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2. Haanen, J. (2013) Immunotherapy of Melanoma. EJC Suppl 11:97-105.
3. Yao et al. (2013) Advances in targeting cell surface signaling molecules for immune modulation. Nat Rev Drug Discov. 12:130-146.
4. Topalian, S. et al. (2012) Safety, activity, and immune correlates of anti-PD-1 antibody in cancer. N. Engl. J. Med. 366:2443-2454.
5. Hamid, O. et al. (2013) Safety and tumor responses with lambrolizumab (anti-PD-1) in melanoma. N. Engl. J. Med. 369:134-144.
6. Topalian, S. L. et al. (2012) Safety, activity, and immune correlates of anti-PD-1 antibody in cancer. N. Engl. J. Med. 366:2443–2454
7. Brahmer, J. R. et al. (2012) Safety and activity of anti-PD-L1 antibody in patients with advanced cancer. N. Engl. J. Med. 366:2455–2465
8. Hamid, O. et al. (2013) Safety and tumor responses with lambrolizumab (anti-PD-1) in melanoma. N. Engl. J. Med. 369:134–144
9. Wolchok, J. D. et al. (2013) Nivolumab plus ipilimumab in advanced melanoma. N. Engl. J. Med. 369:122–133
10. Topalian, S. L. et al. (2014) Survival, durable tumor remission, and long-term safety in patients with advanced melanoma receiving nivolumab. J. Clin. Oncol. 32:1020–1030
11. Tumeh, P. et al. (2014) PD-1 blockade induces responses by inhibiting adaptive immune response. Nature. 515:568-71.
12. Woods, D. et al. (2015) HDAC inhibition upregulates PD-1 ligands in melanoma and augments immunotherapy with PD-1 blockade. Cancer Immunol Res 12:1375-85.
13. Chakravarti, N., & Prieto, V. G. (2015). Predictive factors of activity of anti-programmed death-1/programmed death ligand-1 drugs: immunohistochemistry analysis. Translational Lung Cancer Research, 4:743–751.
14. Barak, V. et al. (2015) Assessing response to new treatments and prognosis in melanoma patients, by the biomarker S-100B. Anticancer Res. 35:6755-60.
15. Taylor, A. et al. (2014) Glycogen synthase kinase 3 inactivation drives T-bet-mediated downregulation of co-receptor PD-1 to enhance CD8+ cytolytic T cell responses. Immunity 44:274-86.