Lung cancer is the leading cause of global cancer deaths, with 1.6 million deaths annually (World Health Organization, International Agency for Cancer Research, 2017). Non-small cell lung cancer (NSCLC) covers most of the diagnosis of lung cancer and the disease is metastatic at the time of diagnosis for most patients (National Cancer Institute, 2017).
Despite an improvement in overall survival by platinum-based chemotherapy (NSCLC Collaborative Group meta-analyses, 2008), the prognosis remains unsatisfactory for patients with advanced NSCLC, with a median survival of 8 to 12 months (Schiller, 2002; Sandler, 2006). The development in the molecular characterization of NSCLC, especially in the histological subtypes of adenocarcinoma, has allowed the identification of key genetic aberrations in NSCLC, which can be addressed with molecular targeted therapy (Pao, 2011). Genetic aberrations in EGFR, ALK, ROS1, RET, BRAF and NTRK have predictive value for susceptibility to receptor tyrosine kinase inhibitors (Mok, 2009; Solomon, 2014; Shaw, 2014; Planchard, 2016). Despite the success of molecular diagnostics, acquired resistance and disease progression are inevitable (Camidge, 2014; Hirsch, 2016). The treatment options for patients with small cell lung cancer (SCLC), when the disease progressed after platinum-based chemotherapy, are even more limited.
Immunotherapy in cancer has been described as any therapy that interacts with immunity. Immunotherapy in cancer can be classified into passive and active types. Passive immunotherapy has been described as the administration of an active agent produced or generated outside the patient’s body. Theoretically, such an approach does not depend on the host’s own immune system to have an effect. Examples of passive immunotherapy include the use of monoclonal antibodies such as trastuzumab or rituximab (Slamon, 2001; Coiffier, 2002), and adoptive cell therapy, such as tumor infiltrating lymphocyte infusion, TCR (Morgan, 2006; Maude, 2014).
Active immunotherapy involves stimulating or determining the host’s immune system to recognize a tumor as a foreign. Examples of active immunotherapy include vaccination against cancer with tumor antigens and an adjuvant enhancement of immune cell function with cytokines, as well as targeting of immune control regulators with immune control inhibitor control.
Inhibitors targeting cytotoxic T lymphocyte (CTLA-4) associated protein 4 and programmed cell death (PD-1)/programmed cell death ligand-1 (PD-L1) are used in NSCLC and SCLC.
The studies that examined the efficacy of cytokines such as interferon alpha and interleukin-2 (IL-2) in lung cancer patients didn’t prove any benefit and will not be discussed (Jansen, 1992; Schiller, 1995).
Vaccines against cancer
Therapeutically active vaccines in cancer are designed to eliminate cancer cells by increasing their own immune responses. This type of vaccine contrasts with prophylactic vaccines, which are usually administered to healthy people. Cancer vaccines can be classified into several major types, such as cellular vaccines, peptide vaccines and genetic vaccines (Cuppens, 2014; Decoster, 2012).
Cellular vaccines may be either autologous, or allogeneic. Autologous tumor cell vaccines are developed by isolating tumor cells from an individual (patient), creating a vaccine that is administered back to the same patient, usually in combination with an adjuvant that stimulates the immune system. These vaccines have been among the first types of cancer vaccines tested and have the advantage of provoking an immune response to a wide range of tumors. Antigens expressed by the patient’s own tumor result in tumor destruction. Although similar to autologous vaccines, allogeneic vaccines are obtained by administering tumor cells to a patient, creating a vaccine that is then administered to another patient with the same type of cancer. Unlike cellular vaccines that are made directly from patient tumors, peptide vaccines are often synthesized in vitro to mimic tumor associated proteins in order to elicit an immune response against tumor cells expressing that protein.
Genetic vaccines are composed of DNA molecules or synthetic RNAs encoding tumor-associated proteins and are administered either alone, or packaged in a non-pathogenic virus. The genetic material is taken up by the recipient cells, translated into proteins encoded, processed and presented to the immune system to elicit the immune response against tumor-associated proteins.
Early studies on Calmett bacillus vaccine in adjuvant and neoadjuvant were negative (Bakker, 1986; Miller, 1982; Matthay, 1986). In the modern age, multiple-stage, locally advanced and advanced NSCLC advanced vaccine studies have been conducted. The recombinant protein-associated anti-melanoma-antigen (MAGE) A3 vaccine has been extensively studied in adjuvant therapy after complete resection. A randomized phase II trial showed that for patients with stage IB-II, MAGE-A3 in NSCLC, who did not receive any adjuvant chemotherapy, there was a tendency towards survival gain. And survival without signs of disease was positively influenced by the MAGE-A3 vaccine compared to placebo after a median follow-up of 70 months (HR: 0.75; CI 95%: 0.46-1.23; p=0.254) (Vansteenkiste, 2016).
However, the clinical benefit was not found in the randomized, double-blind, placebo-controlled phase III (MAGRIT) study in fully NSCLC IB-IIIA MAGE-A3, with or without adjuvant chemotherapy. Subsequently, for the total population in this study, median disease-free survival was 60.5 months for the MAGE-A3 vaccine group and 57.9 months for the placebo group (HR: 1.02; CI 95%: 0.89-1.18, p=0.74). In the subgroup that performed adjuvant chemotherapy, median disease-free survival was 58 months in the vaccine group and 56.9 months in the placebo group (HR: 0.97; 95% CI: 0.8-1.18; p=0.76) (Vansteenkiste, 2016).
Tecomydoid (L-BLP25) is a peptide vaccine based on a sequence of 25 amino acids of the mucosal glycoprotein-1 protein (MUC1), which demonstrated promising activity in locally advanced NSCLC in a phase II study (Butts, 2005). The results led to the initiation of two randomized trials. One was a complete phase III trial, START, in which the placebo tebeotide was compared for patients with stage III NSCLC without disease progression after chemoradiation therapy (Butts, 2014). The second study, INSPIRE, was a randomized phase II study on Asian patients (Wu, 2011). The START trial showed that there was no significant difference in the median overall survival between the teemotide arm and the placebo arms (25.6 months versus 22.3 months, adjusted HR: 0.88; 95% CI: 0.75-1.03; p=0.123). However, following a pre-specified subgroup analysis, median overall survival was different between the vaccine arm and the placebo arm for patients receiving concomitant chemoradiation therapy (30.8 months versus 20.6 months, HR: 0.78; 95% CI: 0.64-0.95; p=0.016) compared with patients receiving sequential chemoradiation therapy (19.4 months versus 24.6 months, HR: 1.12; 95% CI: 0.87-1.44; p=0.38). INSPIRE was stopped in 2014 after Merck announced this plan to discontinue the clinical development of tecemotide as monotherapy for patients with stage III NSCLC due to disappointing results from the Japanese I/II phase EMR 63325-009 study (Merck KgaA, 2014).
In the advanced stage of the disease, the TG4010, another vaccine targeting MUC1, used a viral vector to express both MUC1 and IL-2 (a T cell stimulus). The results were promising.
The NSCLC (TIME) study, phase IIb results, part of the randomized, double-blind, placebo-controlled, phase IIb/III study, showed that in the overall population, the disease-free survival was 5.9 months for the TG4010 group and 5.1 months for placebo (HR: 0.74; 95% CI: 0.55-0.98; p=0.019) (Quoix, 2016).
Belagenpumatucel-L is an allogeneic cell tumor vaccine derived from four cell lines. NSCLC cell lines with different histologies also express an antisense transgene for transforming beta2 growth factor that reduces the regulation of immunosuppressive transformation of beta2 growth factor. The results of a phase II study suggested clinical efficacy in patients with advanced NSCLC (Nemunaitis, 2006), and a randomized phase III study (STOP) was initiated. Patients with stage III/IV NSCLC in whom the disease did not progress after platinum-based chemotherapy received either belagenpumatum-L or placebo (Giaccone, 2015). There was no significant difference in overall survival between the two arms (20.3 months versus 17.8 months, HR: 0.94, p=0.594); there was also no difference in progression-free survival (4.3 months versus 4 months, HR: 0.99, p=0.947).
The epidermal growth factor receptor (EGFR) is an important signaling pathway in NSCLC, and a vaccine has been developed against its related EGF ligand, using recombinant human EGF coupled to a carrier protein. In a randomized phase II trial, patients with stage IIIB/IV NSCLC were randomly assigned to receive the best supportive treatment or EGF vaccines after first-line chemotherapy (Neninger, 2008). There was a trend towards improved overall survival and a significant survival advantage for patients who had a good response to EGF antibodies.
A subsequent phase III study included patients with stage IIIB/IV NSCLC, who were randomly assigned to the first line of chemotherapy to make the vaccine or the best supportive care. In the safety population, overall survival was 10.83 months for the vaccine arm and 8.86 months for the control arm (Rodriguez, 2016). For patients who received at least four doses of vaccine, overall survival differed significantly between the vaccine group and the supportive treatment group (12.43 months versus 9.43 months, HR: 0.77, p=0.036). Furthermore, overall survival was longer (14.66 months) for patients vaccinated with high concentrations of EGF at baseline.
Immunotherapy through immune control site inhibitors
Recently, a profound understanding of the interaction between the immune system and the malignant tumors has led to the identification of CTLA-4 and PD-1/PD-L1 as key factors by which tumors avoid host immune response (Pardoll, 2012). This discovery has led to the development of a new generation of immunotherapy agents targeting these molecules. The inhibitors of immune control points represent an important breakthrough in the treatment of cancer. Multiple studies have shown that control bridge inhibitors are very active in a variety of solid tumors including NSCLC. Immunocompromised immunoassay inhibitors include CTLA-4 inhibitors, PD-1 inhibitors and PD-L1 inhibitors. Other immunotherapeutic inhibitors in development include lymphocyte activation, 3 (LAG3) genes and immunoglobulin receptor-like inhibitors such as killer cells, control-stimulating agents such as OX40, 4-1BB and GITR agonists (Sundar, 2014 ).
Ipilimumab is a recombinant human IgG1 monoclonal antibody that binds to CTLA-4 and prevents negative T cell deregulation in the early stages of T cell activation. The activity of ipilimumab in advanced melanoma was clearly demonstrated in two large phase III studies (Hodi, 2010; Robert, 2011), that led the FDA in 2011 to approve this drug in metastatic malignant melanoma. Ipilimumab determines long-term sustained survival in responders with a significantly higher survival rate of 5 years for ipilimumab plus dacarbazine compared to placebo plus dacarbazine (18.2%, 95% CI: 13.6% to 23.4%) versus 8.8% (95% CI; 5.7% to 12.8%, p=0.0002) (Maio, 2015). Ipilimumab in combination with chemotherapy has been studied in patients with advanced NSCLC who have not received previous treatment. In this phase II triple arm study, patients were randomly assigned to chemotherapy (carboplatin plus paclitaxel), sequential chemotherapy with ipilimumab or chemotherapy with concomitant ipilimumab.
The primary endpoint of the study was overall survival and progression-free survival, which were 4.6 months for the chemotherapy arm, 5.7 months for the sequential ipilimumab chemo arm (HR: 0.72, p=0.05) and 5.5 months for the ipilimumab arm concomitantly with chemotherapy (HR: 0.81, p=0.13) (Lynch, 2012). Progression-free survival was better in NSCLC patients with squamous histology than in patients with non-squamous NSCLC. To confirm these results, a larger phase III trial (NCT02279732) was initiated for patients with squamous NSCLC.
PD-1 inhibitors include agents such as nivolumab and pembrolizumab. Nivolumab is a fully human human immunoglobulin G4 (IgG4) monoclonal antibody that disrupts PD-1-mediated signaling, thus releasing T cells from their inhibitory interaction with PD-L1 and PD-L2.
Pembrolizumab is a monoclonal antibody, the humanized IgG4/kappa isotype, which also blocks the binding of PD-L1 and PD-L2 to PD-1 on T cells, resulting in activation of tumor-specific cytotoxic T cells. Cytotoxicity is complement-dependent (CDC) (Homet, 2015). Action may be important because cytotoxicity can cause an exhaustion of activated T cells and infiltrating lymphocytes into tumors. PD-1 is expressed on effector T cells and other immune cells (Chen, 2012).
Nivolumab has been observed for the first time in early-stage studies to be active in melanoma (Topalian, 2012). The results of the subsequent phase III studies confirmed the superiority of nivolumab as the standard of therapy, leading to its approval by the Food and Drug Administration (FDA) for the treatment of melanoma. Recently, the combination of nivolumab and ipilimumab has been approved as a first-line treatment for patients with advanced melanoma, regardless of the BRAF V600E status (Larkin, 2015).
Nivolumab is also active in a variety of solid tumors and has been approved by the FDA for the treatment of advanced NSCLC, advanced renal cell carcinoma and classical Hodgkin’s lymphoma (Motzer, 2015; Ansell, 2015).
In a phase II trial (CheckMate 153), 824 patients with advanced NSCLC were treated for one year with nivolumab. The partial response and stable disease rates were 12% and 44%, respectively. The answers were independent of PD-L1 (Hussein, 2015). The second treatment line with nivolumab was superior to docetaxel in two subsequent phase III randomized phase in advanced NSCLC patients receiving double-blind platinum chemotherapy.
Recently, in a phase III study, first-line nivolumab, compared to a platinum-based dual platinum-based chemotherapy for tumors with a PD-L1 expression of 5% or greater (CheckMate 026), showed a greater progression-free survival for the chemotherapy arm, but overall survival was better for the nivolumab arm (Socinski, 2016). The objective response rate was lower for the nivolumab arm.
Activity in SCLC
Small cell lung cancer (SCLC) is most often in an extended stage disease at the time of diagnosis. Although the first line of platinum-based chemotherapy has activity, the disease progresses inevitably and the response rates in the second treatment line are low and not sustainable. The activity and safety of nivolumab with or without ipilimumab in previously treated SCLCs was evaluated in CheckMate 032. The objective response rate was 10% with nivolumab 3 mg/kg alone, 23% with 1 mg/kg of nivolumab in combination with 3 mg/kg of ipilimumab and 19% with 3 mg/kg of nivolumab in combination with 1 mg/kg of ipilimumab (Antonia, 2016A). PD-L1 expression was not associated with responses.
Pembrolizumab is active in a variety of solid tumors, including melanoma, colorectal cancer, NSCLC, gastric cancer and urothelial cancer, as well as Merkel cell cancer and Hodgkin’s lymphoma (Robert, 2015; Le, 2015; Muro, 2016; Seiwert, 2016; Nghiem, 2016; Armand, 2016).
The agent has been approved by the FDA for the treatment of advanced metastatic malignant melanoma, advanced stage NSCLC, both as a first-line treatment and in subsequent treatment lines in recurrent or metastatic head and neck carcinoma.
Activity in NSCLC
The efficacy and safety of pembrolizumab at two different doses in previously untreated patients, advanced NSCLC, were reported in the Keynote-001 study. The objective response rate was 19.4% and the median response time was 12.5 months. The progression-free survival was 3.7 months, and overall survival was 12 months (Garon, 2015). The objective response rate was 18% in those treated previously and 24.8% in untreated patients. The objective response rate was 45.2% and no time to progression was 6.3 months. The objective response rate was similar regardless of dose, schedule and histology subtype. The response rate was higher among smokers than non-smokers. Treatment-related adverse events of any grade occurred in 70.9% of patients, 9.5% having a grade 3 or higher adverse event.
Pembrolizumab was evaluated in a phase II/III study of patients previously treated with advanced NSCLC (Keynote-010). A total of 1,034 patients were randomized to receive either a 2 mg/kg dose, or 10 mg/kg pembrolizumab or 75 mg/m2 of docetaxel every three weeks (Herbst, 2016). All patients had at least 1% tumor cells that were positive for PD-L1. Overall survival was improved with both doses of pembrolizumab compared to docetaxel. Among patients with at least 50% of the tumor cells expressing PD-L1, overall survival was 14.9 and 17.3 months with pembrolizumab at doses of 2 mg/kg and 10 mg/kg, respectively, compared to 8.2 months with docetaxel.
Any degree of treatment-related adverse events occurred in 63% of pembrolizumab 2 mg/kg and 66% of patients receiving 10 mg/kg. The treatment-related toxicity was higher (81%) in the docetaxel arm.
Activity in SCLC
Preliminary data from a multicohort phase Ib study on pembrolizumab in patients with previously treated PDL-L1 positive controls included a 25% objective response rate and a 31% disease control rate (Ott, 2015).
PD-L1 inhibitors also inhibit PD-1/PD-L1 interactions, but leave the PD-1/PD-L2 pathway intact. PD-L1 inhibitors include atezolizumab, durvalumab and avelumab. Atezolizumab and durvalumab are human IgG1 anti-PD-L1 antibodies with mutations in their Fc domains to eliminate both antibody-dependent cell-mediated cytotoxicity (ADCC) activity and CDC (complement-dependent cytotoxicity) activity. Avelumab is a fully human IgG1 anti-PD-L1 monoclonal antibody and, unlike another PD-1/PD-L1 inhibitor, it has been shown to retain ADCC and CDC activity in preclinical studies (Boyerinas, 2015). Several PD-L1 inhibitors showed promising activity in Merkel cell carcinoma, urothelial cancer and NSCLC (Rosenberg, 2016; Kaufman, 2016; Massard, 2016). Phase III studies confirming the activity of these agents in various solid tumors are ongoing.
Atezolizumab was reported to be active in urothelial cancer in a phase I study (Powele, 2014) and was subsequently approved by FDA for the treatment of advanced urothelial cancer. In a single arm phase II study (IMpower 110), the objective response rate was 16%, regardless of PD-L1 expression of immune cells, and 28% in patients with 5% or greater expression PD-L1 (Rosenberg, 2016; Herbst 2014). In a dose escalation and expansion study, the objective response rate was 23%, the progression-free survival was 4 months, and the overall survival was 16 months for patients who received 20 mg/kg intravenously at each three weeks (Horn, 2015). In a randomized phase II study (Poplar) in patients receiving platinum-based chemotherapy, atezolizumab was associated with a higher overall survival (HR: 0.73; CI 95%: 0.53-0.99; p=0.04) (Fehrenbacher, 2016). In another phase II study (BIRCH), advanced NSCLC patients who were selected for PD-L1 expression received atezolizumab as a first line or later. The response rates ranged from 17% to 27% (Besse, 2016) and the median overall survival was 14 months for patients receiving atezolizumab as the first line of therapy. The overall survival has not yet been achieved for patients receiving atezolizumab as a subsequent therapy (Broderick, 2016).
The overall response rates ranged from 16% to 26% in a phase II trial of an advanced NSCLC population with PD-L1 expression in tumor and immune cells (Spigel, 2015). In the OAK study, a phase III trial of previously treated NSCLC patients randomly assigned to atezolizumab or docetaxel, the overall survival was significantly better for atezolizumab (13.8 months versus 9.6 months, HR: 0.73; 95% CI: 0.62-0.87, p=0.0003) (Rittmeyer, 2017). The OAK study led to FDA approval of atezolizumab for second-line therapy of advanced NSCLC.
In a phase I/II study with durvalumab in 2009 in the first line in NSCLC patients irrespective of PD-L1 status, the overall response rate was 27% and 29% for PD-L1 positive tumors (defined as ≥25% of tumor cells expressing PD-L1) and 11% in negative PD-L1 tumors (Antonia, 2016B).
In another phase I trial of previously treated advanced NSCLC patients, the response rate was 14% in total and 23% in patients with PD-L1 expression (Rizvi, 2015B).
In a phase II trial of patients with advanced NSCLC who received at least two previous systemic therapy lines, the activity was extremely encouraging. The objective response rate and survival rate at one year increased according to PD-L1 expression: 7.5% (PD-L1 expression less than 25%), 16.4% (more than 25% expression) and 30.9% (greater than 90% expression). The corresponding one-year survival rate was 34.5%, 47.7% and 50.8% (Garassino, 2016).
The results of early studies of avelumab in NSCLC were promising; the response rate was 12% for patients who had a disease progression after platinum-based chemotherapy. There was a trend towards greater activity in patients with PD-L1 positive (Gulley, 2015). Among patients treated with avelumab at the first line, the objective response rate and disease control rates were 18.7% and 64%, respectively (Verschraegen, 2016).
Combinations of immunoterapic medicines
CTLA-4 and PD-1/PD-L1 combined
CTLA-4 inhibitors are also studied in conjunction with PD-1 and PD-L1 inhibitors. Results of preclinical studies indicate that this combination can work synergistically to produce improved antitumor activity (Curran, 2010). The combination of pilimumab and nivolumab in advanced melanoma resulted in improved antitumor activity compared to single agent therapy; however, toxicity was increased with combination therapy (Larkin, 2015). Nivolumab was combined with ipilimumab for first stage NSCLC in setting up in a phase I study (CheckMate 12). The results included objective response rates ranging from 13% to 39% (Hellman, 2016). A randomized phase III trial (CheckMate 27) is ongoing to compare nivolumab plus ipilimumab with nivolumab as monotherapy, nivolumab plus platinum-based chemotherapy and platinum-based chemotherapy in PD-L1 in untreated NSCLC. In addition, durvalumab was combined with the trehalimumab CTLA-4 inhibitor in a phase Ib study of patients with advanced NSCLC. Although many adverse events occurred during the study dose phase, the antitumor activity (23% objective response rate) was evident regardless of the PD-L1 status in the evaluable patients in the dose study – the expansion phase of the study (Antonia, 2016).