Biomedical Research

Abstract

Many advances in local and systemic therapies have noticeably improved outcomes in breast cancer in women. However, early and late relapses continue to occur. Thus, novel therapeutic approaches are necessary. An understanding of the mechanisms of immune escape employed by tumour cells and the ability to regulate immune checkpoints with immunomodulatory monoclonal antibodies will provide very promising clinical results in different tumour types. In this review, we specify the rationale for targeting immune checkpoints in breast cancer and discuss their prospective use for the design of novel clinical trials.

Keywords

Breast cancer, Immunotherapy, Immune checkpoints, CTLA-4, PD-1

Introduction

According to published reports, the number of new breast cancer patients reached 1.67 million in 2012, accounting for 25% of total cancer patients [1-3]. Moreover, breast cancer has become the main cause of death in women cancer patients worldwide, including both low and middle-income countries [2]. Despite the fact that the less aggressive variants of this disease may be treated through surgery and other intensive therapies, the prognosis of patients remains dismal, and approximately one-third of women will develop metastases and die [4]. For example, inflammatory breast cancer and triple-negative breast cancer currently do not benefit from well-regarded treatments because of their aggressiveness and lack of defined molecular targets. Recently, the impacts of immunologic system targets on cancer have been extensively debated and have acquired increasing relevance in the context of cancer [5]. It is widely known that the primary function of immune cells is to eradicate transforming cells, and immune cells may exhibit antitumor or tumour-promoting activities during carcinogenesis [6]. Immunomodulation and immuno­therapy have been shown to be beneficial in breast cancer treatment, such as the effects of pembrolizumab (MK-3475) in triple-negative breast cancer, which were reported by Nanda et al. [7]. The fine balance between co-stimulatory and co-inhibitory factors has an impact on the immune responses and the efficacy of immune responses, which are also referred to as immune checkpoints [8]. Immune checkpoint-targeted agents are new therapeutic drugs in the field of medicine. This review focuses on immune checkpoints and the monoclonal antibodies that block the Cytotoxic T-Lymphocyte-associated Antigen-4 (CTLA-4) and Programmed Death 1 (PD-1) pathway. We provide an overview of the rationale for targeting immune checkpoints in breast cancer, as well as the most recent developments in immune checkpoint inhibitors.

Checkpoint blockade

To date, the genomic revolution has enabled a comprehensive understanding of the molecular mechanism of tumour-associated immunologic responses. First, an antigen of the Major Histocompatibility Complex (MHC) is recognized by the T-Cell Receptor (TCR) immune response. Second, its quality and magnitude are determined by signals that are transmitted by immune checkpoints of the cell surface [9]. The checkpoints maintain the homeostasis of the host to avoid autoimmune reactions through a process that is regulated by the immune system. Ultimately, these checkpoints function in limiting the extension and severity of the immune response, particularly regarding the adaptive immune system [5].

Based on numerous studies regarding immunotherapies, it is generally accepted that CTLA-4 and PD-1 inhibitors lead to the most promising results and have been the most extensively tested in patients with breast cancer [10].

The CTLA-4 receptor

CTLA-4 (also referred to as CD152) is a protein receptor that is widely regarded as an archetypal T-cell intrinsic inhibitory checkpoint. It is expressed on most immune cells, particularly CD4+ and CD8+ T-lymphocytes. As a member of the immune regulatory system, CTLA-4 is homologous to the T-cell costimulatory protein CD28. Both of them can combine with CD80/CD86 on antigen presenting cells (APCs) [11,12]. CD28 on T cells combines with CD80/CD86 on the surface of APCs and stimulates T-lymphocyte proliferation and activation, whereas the binding of CD80/CD86 to CTLA-4 on T cells leads to an anergic phenotype. CTLA-4 combines CD80/CD86 with a stronger affinity than CD28, giving rise to competition [13]. The tumour-specific target antigen stimulates the body, and specific antitumour T cells are activated by TCR and CD28. CTLA-4 is subsequently up-regulated and blocks the CD28 signalling pathway. In addition, the interaction between CTLA-4 and CD80/CD86 will induce the phosphorylation of the intracellular segment of CTLA-4, which results in a negative signal that blocks the activation and function of T-lymphocytes. As previously discussed, CTLA-4 is important for maintaining the normal immune homeostasis of the organism. This function has been demonstrated by the finding that a lack of CTLA-4 can cause mice to die from fatal lymphoproliferation [14,15]. Moreover, in preclinical models, the CTLA-4 antibody blockade resulted in antitumour immunity in various cancers, such as prostate, kidney, and urothelial cancers [16-18]. In breast cancer cells, higher CTLA-4 expression is associated with a poor prognosis, whereas a higher density of interstitial CTLA-4+ lymphocytes is associated with a good prognosis. However, when the tumour had a low expression of CTLA-4, a high density of CTLA-4+ lymphocytes was significantly correlated with a good prognosis [19].

The PD-1 receptor

Similar to CTLA-4, PD-1 (also referred to as CD279) is an inhibitory receptor that negatively regulates the immune system. However, CTLA-4 mainly affects T cells, whereas PD-1 is more broadly expressed on B cells, Tregs and Natural Killer (NK) cells and regulates mature T-cell activity in the tumour microenvironment and peripheral tissues [8,20]. The PD-1 receptor combines two types of ligands. The ligands interact with CD28 and CTLA-4, respectively. PD-L1 binds CD80 with a substantially greater affinity than CD28, giving rise to competition [25]. The docking of CD80 causes the down-regulation of downstream pathways, which leads to cytokine release and T-cell activation [20]. Accordingly, by inhibiting this signalling pathway, the PD-1/PD-L1 interaction induces T-cell tolerance [25-27]. The intracellular enzymatic pathways of PD-1 and CTLA-4 are slightly different. However, they exert a similar immunosuppressive effect because both pathways induce an ineffective anergic T-cell response [28]. PD-L1 is expressed on many cancers, including ovarian cancer, hepatocellular carcinoma, renal cell carcinoma and gastric cancer [29,30]. PD-L1 expression in breast cancer has been detected by Ghebeh et al. who identified PD-L1 expression in 22 (50%) of the 44 tumours evaluated in their study. In 18 of these tumours (41%), PD-L1 was identified in tumour-infiltrating lymphocytes, and in 15 tumours (34%), it was restricted to the tumour epithelium [30]. Furthermore, PD-L1 mRNA expression was detected in substantially larger subsets of breast cancer, and the expression of PD-L1 was correlated with the clinicopathological parameters of highly proliferative breast cancer [31-36].

Other Checkpoint Molecules

LAG-3

LAG-3 (lymphocyte activation gene-3) is a cell surface molecule, also referred to as CD223, whose structure is similar to CD4 and is present on many immune cells [37]. It can be expressed by Tumour-Infiltrating Lymphocytes (TILs) and suppresses the activation of APCs [38]. Murine disease models and ovarian cancer patients showed synergism between the LAG-3 and PD-1 blockade. Both studies indicate that the antibody could block PD-1, and in combination with LAG-3 blockade, it showed higher efficacy than either factor alone. This method may become a useful strategy in some malignancies [38-40].

TIM-3

T-cell Immunoglobulin Mucin 3 (TIM-3) is a marker of Interferon-γ producing CD4+ and CD8+ T cells, which were first identified in mice and humans in 2002 [41,42]. The TIM-3 receptor may be combined with Gal-9 and subsequently plays a negative regulatory role in the survival and function of T cells [12]. TIM-3 is associated with nuclear grade, TNM stage, Progression-Free Survival (PFS) and recurrence-free survival by univariate analysis. The percentages of CD4+ T cells and TIM-3+PD-1+CD8 T cells were substantially higher in the tumour infiltrate than the peripheral blood obtained from patients with renal cell carcinoma [43]. However, to date, there are no sustained TIM-3 blockade clinical trials in patients with cancer [44].

KIR

The Killer-cell Immunoglobulin-like Receptor (KIR) is a receptor for MHC class I molecules located on NK cells, and it participates in the down-regulation of the immunological activity of NK cells [20]. In contrast to adaptive T and B cells, NK cells modulate and conduct their killing capacity independent of several activating and inhibitory receptors [45]. In addition, their cytotoxicity against multiple tumour cell lines is increased as a result of a mismatched KIR-ligand or NK cells that do not express the KIR-ligand [46,47].

Immune Checkpoint Blockade

Anti CTLA-4

Two monoclonal antibodies that target the CTLA-4 receptor are currently being investigated in breast cancer patients, namely, ipilimumab and tremelimumab.

Ipilimumab

Ipilimumab is a type of fully humanized IgG1 monoclonal antibody. It was recently used to treat metastatic melanoma [48]. Treatment with ipilimumab (3 mg/kg every 3 weeks) improved the median survival by 3.7 months in metastatic melanoma phase III clinical trials [49]. Ipilimumab was reported to prolong the lifespan of some patients, and approximately 24% of the patients were alive after 2 y [50].

In addition, ipilimumab is being evaluated in breast cancer patients in active clinical trials. One aim is to evaluate the safety of ipilimumab alone or a combined application with cryoablation in women with curable early-stage breast cancer [51]. The other on-going clinical trial uses ipilimumab in stage IV breast cancer patients whose conditions are still developing although being treated with primary treatment [52]. In murine breast cancer models, the activity of ipilimumab was associated with fractionated radiotherapy [5,53,54]. Moreover, another study showed that 40% of mice underwent EMT6 breast cancer tumour regression when treated with ipilimumab only, whereas 100% of the mice treated with both ipilimumab and ixabepilone experienced complete tumour regression [55].

Tremelimumab

Tremelimumab is a fully humanized IgG2 monoclonal antibody that blocks the binding of CTLA-4 to CD80 and CD86 and enhances human T-cell activation [8]. Tremelimumab has antitumour activity in patients with advanced melanoma [56]. In addition, tremelimumab was the first CTLA-4 abrogating agent, and its activity in combination with the aromatase inhibitor exemestane has shown mild adverse reactions (constipation, diarrhoea, fatigue and pruritus) in 42% of breast cancer cases [57]. As a result of the low response rate to tremelimumab, it is no longer used as a single immunotherapeutic agent in patients with advanced solid tumours, and the evaluation of the combination of tremelimumab with the anti-PD-L1 antibody MEDI-4736 is on-going.

Anti PD-1 signalling

Various monoclonal antibodies that block PD-1 signalling are under evaluation in clinical trials. Compared with anti-CTLA-4 agents, anti-PD-1 agents have more advantages, such as high tumour specificity and weak immune toxicity [58].

Nivolumab

Nivolumab was the first monoclonal anti-PD-1 antibody and showed minimal toxicity in large phase I research in small-cell lung cancer, renal cell carcinoma, advanced melanoma and other solid tumours [59-61]. Melanoma patients treated with ipilimumab and nivolumab showed a 32% overall response rate compared with an 11% response rate for chemotherapy (dacarbazine or carboplatin/paclitaxel) [62]. The objective response was approximately 18% in non-small cell lung cancer, 27% in renal cell carcinoma and 28% in melanoma. Moreover, this response is associated with the PD-L1 positivity of tumour cells [63]. However, no preclinical or clinical data are available for breast cancer treatment to date.

BMS-936558

BMS-936558 (formerly MDX-1106) is another monoclonal anti-PD-1 antibody that blocks the activity of PD-1 [64]. In previous research, 39 patients with advanced colorectal cancer, non-small cell lung cancer, metastatic melanoma, renal cell carcinoma or castrate-resistant prostate cancer were treated with BMS-936558. The results provided good safety and ideal evidence in support of its clinical application [65]. BMS-936558 exhibited a high response rate, which was approximately 18% in non-small cell lung cancer, 27% in renal cell carcinoma and 28% in melanoma [59]. It has been reported that BMS-936558 and MPDL3280A are both specific monoclonal antibodies of PD-L1, which showed substantially better safety than ipilimumab in clinical trials, including breast cancer trials (NCT00729664 and NCT01375842) [64].

Pidilizumab (CT-011)

Pidilizumab is a humanized IgG-1k recombinant monoclonal antibody that specifically blocks PD-1. It is currently approved for the treatment of metastatic non-small cell lung cancer by the US Food and Drug Administration (FDA) [66]. A phase II trial, which investigated its use for diffuse large B-cell lymphoma treatment, also evaluated the activity of pidilizumab in different tumours, including colorectal cancer, melanoma and many other solid tumours [67]. Pembrolizumab showed an acceptable toxicity profile in melanoma, non-small cell lung cancer and advanced renal cell carcinoma in an initial early phase trial [68]. Currently, many clinical trials are on-going for breast cancer treatment with pidilizumab, whose activity is associated with a p53 vaccine as a combinatorial therapy.

Other modulators

There are other checkpoint modulators, such as BMS-663513, which is specific for CD137 (4-1BB). Moreover, monoclonal anti-PD-1 antibodies, such as CT-011, AMP-224, MK-3475 and MPDL3280A, have been evaluated in phase II clinical trials in melanoma. Moreover, an agonist, an anti-OX-40 antibody, has been evaluated in prostate cancer [69]. There are no published data regarding the predictive value of PD-L1 expression in breast cancer for immune checkpoint inhibitor therapy. However, all phase I trials in breast cancer that reported clinical outcomes required PD-L1 expression for eligibility.

Conclusions

The human immune system functions as an immune surveillance, exhibiting a protective role against cancer by identifying and eliminating abnormal cells. However, tumour cells may escape attack through immune checkpoints as described in this review. Therefore, checkpoint blockade has emerged as a promising approach to renovate antitumour immunity. Reactivation of effector T cells through checkpoint blockade may overcome the development of resistant mutations and benefit cancer patients. Immune checkpoint inhibitors, which target regulatory immune cells to enhance antitumour immune responses, have achieved promising results and demonstrate significant clinical efficacy in various malignancies, including breast cancer. To date, the treatment of breast cancer remains challenging, as the research on breast cancer is limited, and most research is in the basic research stage. Thus, there are many problems that remain to be solved. However, we have reason to believe that with continued research and clinical validation of immune checkpoint inhibitors, immunotherapy will bring more hope to breast cancer patients in the near future.

Conflict of Interest

The authors confirm that this article content has no conflict of interest.

References

1. Zhang G, Zhang W, Li B, Stringer-Reasor E, Chu C, Sun L, Bae S, Chen D, Wei S, Jiao K, Yang WH, Cui R, Liu R, Wang L. MicroRNA-200c and microRNA-141 are regulated by a FOXP3-KAT2B axis and associated with tumor metastasis in breast cancer. Breast Cancer Res 2017; 19: 73.
2. Zhao T, Li C, Wu Y, Li B, Zhang B. Prognostic value of PD-L1 expression in tumor infiltrating immune cells in cancers: A meta-analysis. PLoS One 2017; 12: 0176822.
3. Volders JH, Haloua MH, Krekel NM, Meijer S, van den Tol PM. Current status of ultrasound-guided surgery in the treatment of breast cancer. World J Clin Oncol 2016; 7: 44-53.
4. Newman LA. Epidemiology of locally advanced breast cancer. Semin Radiat Oncol 2009; 19: 195-203.
5. Ravelli A, Reuben JM, Lanza F, Anfossi S, Cappelletti MR, Zanotti L, Gobbi A, Milani M, Spada D, Pedrazzoli P, Martino M, Bottini A, Generali D. Immune-related strategies driving immunotherapy in breast cancer treatment: a real clinical opportunity. Expert Rev Anticancer Ther 2015; 15: 689-702.
6. Mellman I, Coukos G, Dranoff G. Cancer immunotherapy comes of age. Nature 2011; 480: 480-489.
7. Nanda R, Chow LQ, Dees EC, Berger R, Gupta S, Geva R, Pusztai L, Pathiraja K, Aktan G, Cheng JD, Karantza V, Buisseret L. Pembrolizumab in patients with advanced triple-negative breast cancer: Phase Ib Keynote-012 Study. J Clin Oncol 2016; 34: 2460-2467.
8. Pardoll DM. The blockade of immune checkpoints in cancer immunotherapy. Nat Rev Cancer 2012; 12: 252-264.
9. Weber J. Immune checkpoint proteins: a new therapeutic paradigm for cancer-preclinical background: CTLA-4 and PD-1 blockade. Semin Oncol 2010; 37: 430-439.
10. Ernst B, Anderson KS. Immunotherapy for the treatment of breast cancer. Curr Oncol Rep 2015; 17: 5.
11. Greenwald RJ, Freeman GJ, Sharpe AH. The B7 family revisited. Annu Rev Immunol 2005; 23: 515-548.
12. Kim ES, Kim JE, Patel MA, Mangraviti A, Ruzevick J, Lim M. Immune checkpoint modulators: An emerging antiglioma armamentarium. J Immunol Res 2016; 2016: 4683607.
13. Li L, Chao QG, Ping LZ, Xue C, Xia ZY, Qian D, Shi-ang H. The prevalence of FOXP3+ regulatory T-cells in peripheral blood of patients with NSCLC. Cancer Biother Radiopharm 200; 24: 357-367.
14. Waterhouse P, Penninger JM, Timms E, Wakeham A, Shahinian A, Lee KP, Thompson CB, Griesser H,Mak TW. Lymphoproliferative disorders with early lethality in mice deficient in Ctla-4. Sci 1995; 270: 985-988.
15. Tivol EA, Borriello F, Schweitzer AN, Lynch WP, Bluestone JA, Sharpe AH. Loss of CTLA-4 leads to massive lymphoproliferation and fatal multiorgan tissue destruction, revealing a critical negative regulatory role of CTLA-4. Immunity 1995; 3: 541-547.
16. Leach DR, Krummel MF, Allison JP. Enhancement of antitumor immunity by CTLA-4 blockade. Sci 1996; 271: 1734-1736.
17. van Elsas A, Hurwitz AA, Allison JP. Combination immunotherapy of B16 melanoma using anti-cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and granulocyte/macrophage colony-stimulating factor (GM-CSF)-producing vaccines induces rejection of subcutaneous and metastatic tumors accompanied by autoimmune depigmentation. J Exp Med 1999; 190: 355-366.
18. Alme AK, Karir BS, Faltas BM, Drake CG. Blocking immune checkpoints in prostate, kidney, and urothelial cancer: An overview. Urol Oncol 2016; 34: 171-181.
19. Yu H, Yang J, Jiao S, Li Y, Zhang W, Wang J. Cytotoxic T lymphocyte antigen 4 expression in human breast cancer: implications for prognosis. Cancer Immunol Immunother 2015; 64: 853-860.
20. Reck M, Paz-Ares L. Immunologic checkpoint blockade in lung cancer. Semin Oncol 2015; 42: 402-417.
21. Dong H, Zhu G, Tamada K, Chen L. B7-H1, a third member of the B7 family, co-stimulates T-cell proliferation and interleukin-10 secretion. Nat Med 1999; 5: 1365-1369.
22. Latchman Y, Wood CR, Chernova T, Chaudhary D, Borde M, Chernova I, Iwai Y, Long AJ, Brown JA, Nunes R, Greenfiled EA, Bourque K, Boussiltis VA, Carter LL, Carreno BM, Malenkovich N, Nishimura H, Okazaki T, Honjo T, Sharpe AH, Freeman GJ. PD-L2 is a second ligand for PD-1 and inhibits T cell activation. Nat Immunol 2001; 2: 261-268.
23. Moore KW, O'Garra A, de Waal Malefyt R, Vieira P, Mosmann TR. Interleukin-10. Annu Rev Immunol 1993; 11: 165-190.
24. Keir ME, Butte MJ, Freeman GJ, Sharpe AH. PD-1 and its ligands in tolerance and immunity. Annu Rev Immunol 2008; 26: 677-704.
25. Butte MJ, Keir ME, Phamduy TB, Sharpe AH, Freeman GJ. Programmed death-1 ligand 1 interacts specifically with the B7-1 costimulatory molecule to inhibit T cell responses. Immunity 2007; 27: 111-122.
26. Liang SC, Latchman YE, Buhlmann JE, Tomczak MF, Horwitz BH, Freeman GJ, Sharpe AH. Regulation of PD-1, PD-L1, and PD-L2 expression during normal and autoimmune responses. Eur J Immunol 2003; 33: 2706-2716.
27. Zou W, Chen L. Inhibitory B7-family molecules in the tumour microenvironment. Nat Rev Immunol 2008; 8: 467-477.
28. Jacobsen ED. Restoring antitumor immunity via PD-1 blockade after autologous stem-cell transplantation for diffuse large B-cell lymphoma. J Clin Oncol 2013; 31: 4268-4270.
29. Wimberly H, Brown JR, Schalper K, Haack H, Silver MR, Nixon C, Bossuyt V, Pusztai L, Lannin DR, Rimm DL. PD-L1 expression correlates with tumor-infiltrating lymphocytes and response to neoadjuvant chemotherapy in breast cancer. Cancer Immunol Res 2015; 3: 326-332.
30. Mittendorf EA, Philips AV, Meric-Bernstam F, Qiao N, Wu Y, Harrington S, Su X, Wang Y, Gonzalez-Angulo AM, Akcakanat A, Chawla A, Curran M, Hwu P, Sharma P, Litton JK, Molldrem JJ, Alatrash G. PD-L1 expression in triple-negative breast cancer. Cancer Immunol Res 2014; 2: 361-370.
31. Soliman H, Khalil F, Antonia S. PD-L1 expression is increased in a subset of basal type breast cancer cells. PLoS One 2014; 9: e88557.
32. Ali HR, Glont SE, Blows FM, Provenzano E, Dawson SJ, Liu B, Hiller L, Dunn J, Poole CJ, Bowden S, Earl HM, Pharoah PD, Caldas C. PD-L1 protein expression in breast cancer is rare, enriched in basal-like tumours and associated with infiltrating lymphocytes. Ann Oncol 2015; 26: 1488-1493.
33. Esteva FJ, Wang J, Lin F, Mejia JA, Yan K, Altundag K, Valero V, Buzdar AU, Hortobagyi GN, Symmans WF, Pusztai L. CD40 signalling predicts response to preoperative trastuzumab and concomitant paclitaxel followed by 5-fluorouracil, epirubicin, and cyclophosphamide in HER-2-overexpressing breast cancer. Breast Cancer Res 2007; 9: 87.
34. Sabatier R, Finetti P, Mamessier E, Adelaide J, Chaffanet M, Ali HR, Viens P, Caldas C, Birnbaum D, Bertucci F. Prognostic and predictive value of PDL1 expression in breast cancer. Oncotarget 2015; 6: 5449-5464.
35. Schalper KA, Velcheti V, Carvajal D, Wimberly H, Brown J, Pusztai L, Rimm DL. In situ tumor PD-L1 mRNA expression is associated with increased TILs and better outcome in breast carcinomas. Clin Cancer Res 2014; 20: 2773-2782.
36. Ghebeh H, Mohammed S, Al-Omair A, Qattan A, Lehe C, Al-Qudaihi G, Elkum N, Alshabanah M, Bin Amer S, Tulbah A, Ajarim D, Al-Tweigeri T, Dermime S. The B7-H1 (PD-L1) T lymphocyte-inhibitory molecule is expressed in breast cancer patients with infiltrating ductal carcinoma: correlation with important high-risk prognostic factors. Neoplasia 2006; 8: 190-198.
37. Goldberg MV, Drake CG. LAG-3 in Cancer Immunotherapy. Curr Top Microbiol Immunol 2011; 344: 269-278.
38. Matsuzaki J, Gnjatic S, Mhawech-Fauceglia P, Beck A, Miller A, Tsuji T, Eppolito C, Qian F, Lele S, Shrikant P, Old LJ, Odunsi K. Tumor-infiltrating NY-ESO-1-specific CD8+ T cells are negatively regulated by LAG-3 and PD-1 in human ovarian cancer. Proc Natl Acad Sci USA 2010; 107: 7875-7880.
39. Woo SR, Turnis ME, Goldberg MV, Bankoti J, Selby M, Nirschl CJ, Bettini ML, Gravano DM, Vogel P, Liu CL, Tangsombatvisit S, Grosso JF, Netto G, Smeltzer MP, Chaux A, Utz PJ, Workman CJ, Pardoll DM, Korman AJ, Drake CG, Vignali DA. Immune inhibitory molecules LAG-3 and PD-1 synergistically regulate T-cell function to promote tumoral immune escape. Cancer Res 2012; 72: 917-927.
40. Nirschl CJ, Drake CG. Molecular pathways: co-expression of immune checkpoint molecules: signalling pathways and implications for cancer immunotherapy. Clin Cancer Res 2013; 19: 4917-4924.
41. Sakuishi K, Jayaraman P, Behar SM, Anderson AC. Kuchroo VK. Emerging Tim-3 functions in antimicrobial and tumor immunity. Trends Immunol 2011; 32: 345-349.
42. Zhu C, Anderson AC, Kuchroo VK. TIM-3 and its regulatory role in immune responses. Curr Top Microbiol Immunol 2011; 350: 1-15.
43. Dannenmann SR, Thielicke J, Stöckli M, Matter C, von Boehmer L, Cecconi V, Hermanns T, Hefermehl L, Schraml P, Moch H, Knuth A, van den Broek M. Tumor-associated macrophages subvert T-cell function and correlate with reduced survival in clear cell renal cell carcinoma. Oncoimmunol 2013; 2: e23562.
44. Alme AK, Karir BS, Faltas BM, Drake CG. Blocking immune checkpoints in prostate, kidney, and urothelial cancer: An overview. Urol Oncol 2016; 34: 171-181.
45. Pegram HJ, Andrews DM, Smyth MJ, Darcy PK, Kershaw MH. Activating and inhibitory receptors of natural killer cells. Immunol Cell Biol 2011; 89: 216-224.
46. Tam YK, Martinson JA, Doligosa K, Klingemann HG. Ex vivo expansion of the highly cytotoxic human natural killer-92 cell-line under current good manufacturing practice conditions for clinical adoptive cellular immunotherapy. Cytother 2003; 5: 259-272.
47. Klingemann HG. Natural killer cell-based immunotherapeutic strategies. Cytotherap 2005; 7: 16-22.
48. Kim DW, Trinh VA, Hwu WJ. Ipilimumab in the treatment of advanced melanoma-a clinical update. Expert Opin Biol Ther 2014; 14: 1709-1718.
49. Hodi FS, O'Day SJ, McDermott DF, Weber RW, Sosman JA, Haanen JB, Gonzalez R, Robert C, Schadendorf D, Hassel JC, Akerley W, van den Eertwegh AJ, Lutzky J, Lorigan P, Vaubel JM, Linette GP, Hogg D, Ottensmeier CH, Lebbé C, Peschel C, Quirt I, Clark JI, Wolchok JD, Weber JS, Tian J, Yellin MJ, Nichol GM, Hoos A, Urba WJ. Improved survival with ipilimumab in patients with metastatic melanoma. N Engl J Med 2010; 363: 711-723.
50. Su M, Huang CX, Dai AP. Immune checkpoint inhibitors: therapeutic tools for breast cancer. Asian Pac J Cancer Prev 2016; 17: 905-910.
51. Memorial Sloan Kettering Cancer Center. Pre-operative, single-dose ipilimumaband/or cryoablation in early stage/resectable breast cancer. 2014.
52. Bristol-Myers Squibb. Study of MDX-010 in stage IV breast cancer. 2012.
53. Dewan MZ, Galloway AE, Kawashima N, Dewyngaert JK, Babb JS, Formenti SC, Demaria S. Fractionated but not single-dose radiotherapy induces an immune-mediated abscopal effect when combined with anti-CTLA-4 antibody. Clin Cancer Res 2009; 15: 5379-5388.
54. Demaria S, Kawashima N, Yang AM, Devitt ML, Babb JS, Allison JP, Formenti SC. Immune-mediated inhibition of metastases after treatment with local radiation and CTLA-4 blockade in a mouse model of breast cancer. Clin Cancer Res 2005; 11: 728-734.
55. Jure-Kunkel MN, Masters G, Girit E, Dito G, Lee FY. Antitumor activity of anti-CTLA-4 monoclonal antibody (mAb) in combination with ixabepilone in preclinical tumor models. J Clin Oncol 2008; 26: 3048.
56. Ribas A. Clinical development of the anti-CTLA-4 antibody tremelimumab. Semin Oncol 2010; 37: 450-454.
57. Mohit E, Hashemi A, Allahyari M. Breast cancer immunotherapy: monoclonal antibodies and peptide-based vaccines. Expert Rev Clin Immunol 2014; 10: 927-961.
58. Topalian SL, Drake CG, Pardoll DM. Immune checkpoint blockade: a common denominator approach to cancer therapy. Cancer Cell 2015; 27: 450-461.
59. Topalian SL, Hodi FS, Brahmer JR, Gettinger SN, Smith DC, McDermott DF, Powderly JD, Carvajal RD, Sosman JA, Atkins MB, Leming PD, Spigel DR, Antonia SJ, Horn L, Drake CG, Pardoll DM, Chen L, Sharfman WH, Anders RA, Taube JM, McMiller TL, Xu H, Korman AJ, Jure-Kunkel M, Agrawal S, McDonald D, Kollia GD, Gupta A, Wigginton JM, Sznol M. Safety, activity, and immune correlates of anti-PD-1 antibody in cancer. N Engl J Med 2012; 366: 2443-2454.
60. Hamid O, Robert C, Daud A, Hodi FS, Hwu WJ, Kefford R, Wolchok JD, Hersey P, Joseph RW, Weber JS, Dronca R, Gangadhar TC, Patnaik A, Zarour H, Joshua AM, Gergich K, Elassaiss-Schaap J, Algazi A, Mateus C, Boasberg P, Tumeh PC, Chmielowski B, Ebbinghaus SW, Li XN, Kang SP, Ribas A. Safety and tumor responses with lambrolizumab (anti-PD-1) in melanoma. N Engl J Med 2013; 369: 134-144.
61. Topalian SL, Sznol M, McDermott DF, Kluger HM, Carvajal RD, Sharfman WH, Brahmer JR, Lawrence DP, Atkins MB, Powderly JD, Leming PD, Lipson EJ, Puzanov I, Smith DC, Taube JM, Wigginton JM, Kollia GD, Gupta A, Pardoll DM, Sosman JA, Hodi FS. Survival, durable tumor remission, and long-term safety in patients with advanced melanoma receiving nivolumab. J Clin Oncol 2014; 32: 1020-1030.
62. Weber JS, D'Angelo SP, Minor D. Nivolumab versus chemotherapy in patients with advanced melanoma who progressed after anti-CTLA-4 treatment (CheckMate 037): a randomised, controlled, open-label, phase 3 trial. Lancet Oncol 2015; 16: 375-384.
63. Daskivich TJ, Belldegrun A. Words of wisdom. Re: Safety, activity, and immune correlates of anti-PD-1 antibody in cancer. Eur Urol 2015; 67: 816-817.
64. Emens LA. Breast cancer immuno biology driving immunotherapy: vaccines and immune checkpoint blockade. Expert Rev Anticancer Ther 2012; 12: 1597-1611.
65. Brahmer JR, Drake CG, Wollner I, Powderly JD, Picus J, Sharfman WH, Stankevich E, Pons A, Salay TM, McMiller TL, Gilson MM, Wang C, Selby M, Taube JM, Anders R, Chen L, Korman AJ, Pardoll DM, Lowy I, Topalian SL. Phase I study of single-agent anti-programmed death-1 (MDX-1106) in refractory solid tumors: safety, clinical activity, pharmacodynamics, and immunologic correlates. J Clin Oncol 2010; 28: 3167-75.
66. Pusztai L, Karn T, Safonov A, Abu-Khalaf MM, Bianchini G. New strategies in breast cancer: immunotherapy. Clin Cancer Res 2016; 22: 2105-2110.
67. Lu J, Lee-Gabel L, Nadeau MC, Ferencz TM, Soefje SA. Clinical evaluation of compounds targeting PD-1/PD-L1 pathway for cancer immunotherapy. J Oncol Pharm Pract 2015; 21: 451-467.
68. Patnaik A, Kang SP, Rasco D, Papadopoulos KP, Elassaiss-Schaap J, Beeram M, Drengler R, Chen C, Smith L, Espino G, Gergich K, Delgado L, Daud A, Lindia JA, Li XN, Pierce RH2 Yearley JH, Wu D, Laterza O, Lehnert M, Iannone R, Tolcher AW. Phase I Study of Pembrolizumab (MK-3475; Anti-PD-1 Monoclonal Antibody) in Patients with Advanced Solid Tumors. Clin Cancer Res 2015; 21: 4286-4293.
69. Weinberg AD, Morris NP, Kovacsovics-Bankowski M, Urba WJ, Curti BD. Science gone translational: the OX40 agonist story. Immunol Rev 2011; 244: 218-231.