Introduction
Nowadays, immunotherapeutic applications are widely used for treating cancer. Specific parts of immune system of person is used to fight with specific diseases for instance cancer. The war between immune system and cancer can be done in several ways. The first way is to evoke the patient’s immune system to function smarter and more successful in order to attack cancer cells. The second way is to give immune system components to patient. Importantly, immunotherapy has been used to cure some types of cancer in the last few decades and the scientists are now testing the newer types of immune treatments. Lots of treatments are involved in immunotherapy and these treatments work in different ways. Very simply, some treatments are used to enhance the immune system of the body in general and other treatments are used to help the immune system for training in order to fight with cancer cells. In some types of cancers, using immunotherapy is better. It is effective to use immunotherapy by itself in these types of cancers. However for other types of cancers, immunotherapy is more effective when other treatments are used as well.
To understand the immunotherapy, the function of the immune system should be understood. Immune system consists of organs, specific cells, protective substances against infections and several other diseases. The substances that are normally found in the body are followed by the immune system. If a new substance is detected and if the immune system does not recognize it, the immune system will attack to it. The immune response has its ability to annihilate anything including strange substance and germs and cancer cells are the examples. Specifically when the cells are altered and these cells are growing out of control, cancer starts. However, sometimes the immune system can not recognize cancer cells as foreign cells. Thus, the ability of immune system to fight with cancer on its own is limited. Sometimes the immune system can not recognize the cancer cells. Sometimes it recognizes the cancer cells but the response of the immune system might not be enough to annihilate the cancer cells. To overcome thşs problem, researchers have been studying several ways to help immune system to recognize the cancer cells and to make the immune system’s response to be enough for destruction of cancer cells.
Immunotherapeutic applications can be categorized into five groups. The first group is cancer vaccines. The cancer vaccine category relies on the viral and bacterial immunization’s advantageous effects. Patients are immunized with the cancer vaccines in order to make the patients’ immune systems active against the specific tumor antigen. The second group of immunotherapy is targeted monoclonal antibodies. This is one of the antibody based approach. Monoclonal antibodies can be constructed from human or murine antibody components. These components bind to the specific tumor-associated antigens. The third group of immunotherapy is immune checkpoint regulation. The immune checkpoint regulation is an antibody based approach. Immune checkpoint inhibitors and checkpoint blockade immunotherapy are included in this strategy. The fourth group is immunotoxin therapy. Immunotoxin is a protein, it is human-made and the toxin kills the cell when it binds to the sepecific cell and taken into the cell by endocytosis. The fifth and the last category of immunotherapy is adoptive cell therapy. In this strategy, the immune cells of the patient are modified with specific cancer cells and then they are given to the patient again. Natural killer cell immunotherapy and chimeric antigen receptor therapy are the types of adoptive cell therapy. In this review, an overview of these five strategies will be given with focusing on their applications in non-small cell lung cancer.
Cancer Vaccines
The aim of the immunotherapy with cancer vaccines is to create or increase the immune response against tumors by using a whole cell that is biologically active or by using specific protein antigen. The administration of cancer vaccine to the patient is done in order to augment the reactivity of immune system. The cancer vaccines for non-small cell lung cancer can be categorized into two as cell based vaccines and antigen specific vaccines.
Cell Based Vaccines
Belagenpumatucel-L (Lucanix) is a cell based vaccine. Allogenic non-small cell lung cancer cell lines that exposure to radiation and that is transfected with a TGF-β2 antisense gene plasmid are used to produce Lucanix. This strategy is based upon the knowledge that the level of TGF-β is interrelated with the poor prognosis in the non-small cell lung cancer patients and it includes immunosuppressive effects. A phase III clinical trial evaluated the overall survival in patients that are in the period after completing 12 weeks of chemotherapy. Acording to the analysis, the overall survival was improved (20.7-13.4 months) and 40 vs. 10 months was the median survival of patients treated with radiotherapy. (21)
Tergenpumatucel-L is another cell based vaccine composed of three genetically modified allogenic lung tumor cell lines with the α-galactosyltransferase moiety on the cell surfaces. This enzyme creates a congenital immune reaction and this reaction kills the foreign non-small cell lung cancer tumor cells. In a phase II clinical trial, 28 patients that have metastatic non-small cell lung cancer or recurring disease received the vaccine with a median overall survival of 11.3 months. Patients that received chemotherapy after vaccinated with Tergenpumatucel-L had much better overall response to ensuing chemotherapy treatments compared to the patients that were not vaccinated with the prior Tergenpumatucel-L.
Scientists have tested the peptide vaccines in solid tumors for instance a peptide vaccine against the indoleamine 2,3-dioxygenase enzyme. In a phase I trial, a partial response was progressed after one year of treatment with the vaccine and in six patients long lasting stable disease was detected. The median of overall survival was 25.9 months.
Antigen Specific Vaccines
MAGE-A3 is a type of antigen specific vaccine and it was developed against melanoma-associated antigen-A3. MAGE-A3 is a tumor specific antigen and 35-50 % of non-small cell lung cancer have expression of melanoma-associated antigen A3.According to the results from a phase II clinical trial when MAGE-A3 vaccine was utilized in non-small cell lung cancer, the interrelation between the expreesion of a gene and immune related transcripts was observed. And tha trial showed that they are connected with better outcome.
Tecemotide (Stimuvax, L-BLP25) is another antigen specific vaccine. It targets the mucin-1 (MUC-1) glycoprotein. The overexpression of MUC-1 occures in lung cancer and it is connected with poor prognosis. According to the preclinical studies, a strong immune response is provided by this glycoprotein against lung cancer. The results from “Stimulating Targeted Antigenic Response to Non-Small Cell Lung Cancer (NSCLC)” clinical trial shows that no significant difference occured in the overall survival between placebo and tecemotide vaccinated patients.
TG4010 is produced from a modified vaccinia virus. The sequence that encode the MUC-1 and IL-2 is included in the vaccinia virus. According to the results of a Phase IIB trial, an increase occured in 6 months progression free survival in the patients immunized with the TG4010 vaccine in comparison to the patients who received chemotherapy alone.
Monoclonal Antibodies
Specific mutations of tumor cells were identified in non-small cell lung cancer. The notion of the monoclonal antibody (mAb) therapy was led to the identification of mutations. The production of antibody was done by using mouse/human (chimeric) or human fragments. These antibodies bind to the target and then inhibit the target’s function. Thus, they block the mutation induced signaling pathway effect.
Antibodies that Target the Epidermal Growth Factor Receptor
In clinical practice, various monoclonal antibodies are utilized. Because they function by inhibitting the epidermal growth factor receptor (EGFR), thereby inhibiting the interaction locus of the receptor with the epidermal growth factor. Then, the receptor became internalized and the internalization of the receptor makes the surface expression of EGFR down regulated. It blocks the abnormal growth signals and the progress of the cancer is stopped. Cetuximab (ERBITUX) is an example of anti-EGFR antibody. If Cetuximab is used with chemotherapy, it will provide extraordinary advantages for the treatment of advanced non-small cell lung cancer. Necitumumab is another antibody and its sutructure is similar to cetuximab. The only difference is that necitumumab is a fully human antibody while cetuximab is human/murine antibody. There are two ongoing Phase III clinical trials to evaluate the necitumumab. According to the results of trial 1, a significant improvement occured in overall survival when necitumumab is used as first line treatment with chemotherapy. The overall survival increased from 9.9 months to 11.5 months in comparison to chemotherapy alone.
Antibodies that Blocks MET Receptor
In 40% of non-small cell lung cancer, MET receptor is overexpressed. It is a tyrosine kinase related with survival, proliferation and invasion. Onartuzumab and ficlatuzumab are monoclonal antibodies that aim this pathway. A Phase III trial was done to analyse the function of onartuzumab in combination with erlotinib in MET-postive non-small cell lung cancer. Since it was proven that onartuzumab did not enhance the overall survival, the trial was stopped. However, onartuzumab makes the cMET receptor to inhibit activation and ficlatuzumab makes the cMET ligand hepatocyte growth factor inhibit the signaling pathway. Phase IB trial was done to analyse the function of ficlatuzumab plus gefitinib in non-small cell lung cancer. A partial decrease occured in 5 patients out of 12. A Phase II trial was done to analyse the function of ficlatuzumab in combination with erlotinib compared to placebo and erlotinib alone. This is an ongoing trail and based on the principle of EGFR inhibition in EGFR mutant non-small cell lung cancer.
Antibodies that Target the Vascular Endothelial Growth Factor
Angiogenesis favouring tumor metastasis is evoked by vascular endothelial growth factor (VEGF) and because of the function of VEGF, it is used in monoclonal antibody therapy. Bevacizumab is an antibody that is the most studied monoclonal antibody. According to the trial of The Eastern Cooperative Oncology Group, paclitaxel/carboplatin/bevacizumab provided benefits for the survival when compared to paclitaxel/carboplatin in non-small cell lung cancer patients. A Phase III trial was done to analyse the function of bevacizumab when low and high doses of it were added to cisplatin/gemcitabine chemotherapeutic diet. The trial was demonstrated that bevacizumab improved the progression-free survival. Ramucirumab is a fully human monoclonal antibody. It inhibits the interaction between vascular endothelial growth factor receptor (VEGFR) and VEGF by binding the extracellular part of VEGFR. A Phase III trial was done to evaluate ramucirumab in combination with docetaxel compared to placebo plus docetaxel. It was determined that an increase occured in median overall survival and in progression-free survival.
Immune Checkpoint Inhibition
The immune checkpoint blockade is opposite to the monoclonal antibody therapy. When inhibitory signals are up regulated, cytotoxic T-cell weakness occured and antibodies that are used by immune checkpoint blockade hinders cytotoxic T-cell weakness. Programmed cell death protein 1 (PD-1), programmed cell death ligand 1 (PDL-1) and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) are blocked by immune checkpoint inhibitors.
PD-1 Inhibition
Programmed cell death protein 1 is an inhibitory protein. Natural killer (NK) cells, T-activated cells, monocytes and B cells include PD-1 inhibitory protein. PD-1 receptor binds to its ligands, PDL-1 and PDL-2. When PD-1 binds to one of its ligands, it causes the inhibition of the downstream transcription of NF-κB and it causes also the inhibition of proliferation. According to the study of PD-1, it was observed that when the expression of PD-1 was increased, the function of the T cell degenerated. The specific antibodies for PD-1 are Nivolumab and Pembrolizumab and the clinical trials for these antibodies are ongoing.
Nivolumab is a human immunoglobulin G4 anti PD-1 agent. And Nivolumab does not have antibody dependent cellular cytotoxicity activity. According to the ongoing and completed clinical trials, it was approved that the Nivolumab is beneficial for the second line chemotherapy treatment in non-small cell lung cancer. A Phase II trial was done to analyse the function and safety of Nivolumab in the non-small cell lung cancer (NSCLC). According to the results, 4% of the patients have tiredness, diarrhea and pneumonitis as adverse effects. This trial demonstrated that the overall survival increased and nivolumab provided long-term safety in the patients with NSCLC.
Pembrolizumab is an antibody that neutralizes the PD-1. The antibody has 19.4% objective response rate in the patients with NSCLC and it has remarkable activity of antitumor. The recently completed clinical trial demonstrated that when pembrolizumab was used in the patients with NSCLC, the response to PD-1 inhibition was improved. The ongoing trials have being done to analyse the clinical efficiancy of the antibody plus carboplatin/paclitaxel or the antibody plus carboplatin/pemetrexed. According to the current results, the preliminary overall response rate in cured patients was 30-67%.
CTLA-4 Inhibition
The expression of cytotoxic T-lymphocyte antigen-4 is done by regulatory T cells and activated T cells. The antigen presenting cells express B7 molecules. When CTLA-4 binds to co-stimulatory B7 molecules, the interactive relation with the T-cell receptor that activates CD28 is blocked and the direct inhibitory signals are initiated by CTLA-4. These inhibitory signals reduces the function of T cells. CTLA-4 also causes a restrictive pathway in antigen specific cells. Ipilimumab and tremelimumab are fully human antibodies which are being tested at the present time. These two antibodies are the first agents of immune checkpoint inhibition.
Ipilimumab is the only agent that has been confirmed by the European Medical Agency (EMA) and Food and Drug Administration (FDA) for utilizing in NSCLC. However, tremelimumab is being tested yet. Tremelimumab attaches to CTLA-4. A Phase II trial was done to analyse tremelimumab as platinum based first line therapy. Acording to the results, patients who have advanced NSCLC had objective response rate of 4.8%. And there was no increase observed in the progression free survival in comparision with the best supportive therapy. Ipilimumab inhibits CTLA-4 to evoke immune response for antitumor. According to the Phase II trial about ipilimumab, it was proven that the immune related progression free survival was improved in ipilimumab plus paclitaxel and carboplatin in comparison with only chemotherapy.
PDL-1 Inhibition
The expression of programmed death receptor ligand 1 was done in T cells and B cells an also in surface antigen presenting cells. It has an effect on inhibitory signaling of T cell. The T cell inhibitory signaling causes decrease of cytokine production and suppression of the proliferation of T cells. It was proved that the up-regulation of PDL-1 occurs in several tumors and it causes poor prognosis in NSCLC. MPDL3280A, MEDI4736 and BMS936559 are the anti-PDL-1 antibodies that are being tested in lung cancer. MPDL3280A is a fully human PDL-1 inhibition antibody. It includes Fc-domain. The Fc-domain is engineered domain and the effect of the antibody dependent cellular cytotoxicity is reduced by means of the design of the Fc-domain. A Phase II trial that compared MPDL3280A with docetaxel in the patients who have received the PDL-1 treatment beforehand demonstrated that an increase occured in progression free survival of the patients with MPDL3280A treatment. MEDI4736 is another human antibody used to prohibit antibody dependent cellular cytotoxicity. It functions by prohibiting the binding of PDL-1 to PD-1. The evaluation of the antibody plus tremelimumab was done and according to the Phase I/II trial, the overall response rate was 14-23% in the patients with positive PDL-1 in NSCLC. BMS936559 is also a human antibody that functions by blocking the binding of PDL-1 to PD-1. A Phase I clinical trial was done to evaluate BMS936559 in 75 patients with NSCLC. According to the results, the targeted response rate was achieved in 5 patients treated with BMS936559.
Immunotoxin Therapy
An antigen targeted part is used in the immunotoxin therapy. The antibody or the growth factor receptor that is mutated binds to a competent toxin. Pseudomonas exotoxin A is the example for this toxin. The endocytosis of toxin complex is started by the binding of surface tumor antigen to the binding part. Since the complex enters into the cytosol, the protein synthesis is blocked, the cell cycle is arrested by the toxin and finally ensuing cell death was occured. However, the application of immunotoxin therapy is limited in lung cancer. SS1P is an immunotoxin that acts opposite to mesothelin and mesothelin is an antigen that is overexpressed in various tumors such as in lung tumors. It merges with a part of Pseudomonas exotoxin A. SS1P is efficient for malignant pleural mesothelioma. A Phase II trial has currently been in progress about the malignant pleural mesothelioma to evaluate the antitumor efficiancy of SS1P in lung cancer as preclinical study. In future, these studies will be a proof for the efficacy of immunotoxin therapy in NSCLC.
Adoptive Cell Therapy
Natural Killer Cell Immunotherapy
The first adoptive cell therapy is natural killer (NK) cell therapy. There are several studies of the NK cell therapy in lung cancer and they demonstrated that NK cells that are in the tumors are connected with retarded tumor progression. [4] The death receptor mediated apoptosis is activated, cytoplasmic molecules are secreted by NK cells and they also excrete effector molecules to cause the death of targeted cells. Several studies approved the convenience of the lung cancer therapy with allogeneic or autologous expanded NK cells. A Phase I trial was done to evaluate the efficiency of NK cell therapy with chemotherapy clinically. According to the observations of the NSCLC patients that received allogeneic NK cells, any type of side effects were not observed. One year survival rate was observed in the 56% of patients and the survival rate was 2 year in the 19% of the patients. [20-64] Another trial was done to evaluate the effect of autologous NK cells plus docetaxel in the patients who have advanced non-small cell lung cancer. According to the results, progression free survival was observed in a small number of patients. [20-65]
Chimeric Antigen Receptor (CAR) T-Cell Therapy
The chimeric antigen receptor therapy is used clinically as the adoptive cell therapy for lung cancer. In patients with haematological disorders, the chimeric antigen receptor T-cell therapy has been used as an efficient clinical therapy. There is an ongoing trial and the aim of the trial is to determine the targeted antigen for the solid tumors especially for lung cancer. The CAR therapy functions by several steps. Firstly, the T cells are isolated in the patient’s peripheral blood. Then T cells are modified genetically. Since T cells are modified, the gene for a chimeric antigen receptor is introduced to the T cell. When the chimeric antigen receptor gets into the specific antigen for it, the activation of T cell is done and it causes lysis of the antigen-expressing cell.
A preclinical study was done to evaluate the lung cancer with regard to mesothelin. According to the results, poor prognosis was observed in the patients with mesothelin positive tumors. And CAR T-cell therapy was found to be safe for the pleural malignancies. A Phase I trial was done to evaluate the function of mesothelin targeted chimeric antigen receptor therapy for the patients with pleural disease. When the mesothelin targeted CAR T-cells are introduced by intrapleural injection, long term decrease of malignant pleural mesothelioma is occured compared to intravenous injection. The long term remission is caused because of the early activation of antigen. (20-72)
Conclusion
According to the clinical studies and researches, immunotherapy will be a promising way to treat lung cancer. In the future, several Phase III clinical trials will be done to evaluate the immunotherapeutic approaches in cancer and a comparison with standard chemotherapy will be reported. The future studies will determine the function of immunotherapy for treating the advanced NSCLC. New neoadjuvant and adjuvant immunotherapeutic approaches will be induced with the knowledge of the future studies and these immunotherapeutic approaches can provide a long survival for the patients with surgically cured non-small cell lung cancer.