Background
Lung cancer (LC) remains the worldwide leading cause of death from cancer. Unfortunately, approximately 75% of patients are diagnosed at an advanced stage of the disease (III, IV) [
1]. Despite significant investment and advancement in LC research, only 16% of LCs are detected at the early stages [
2]. Thus, even with recent advancements in treatment, survival remains poor. Developing early detection diagnostic methods, especially non-invasive methods, is a critical component in raising the overall survival rate and prognosis for lung cancer [
3].
Current diagnostic methods (e.g., Computed Tomography—CT, Positron Emission Tomography—PET, Low-dose CT- LDCT, radiography) have high sensitivity but low specificity. False positive rates of 96.4% for LDCT and 94% for radiography [
4‐
7] lead to a large number of unnecessary follow-up procedures. These procedures are expensive, invasive and can have significant complication risks. These can be pronounced in the elderly where para-physiological changes occur in the lungs which can lead to inappropriate interpretation of radiological findings that put patients at risk of over or under treatment as Baratella et al. report [
8]. Recent work demonstrates that core-needle biopsy performed under CT leads to accurate histological diagnosis of LC with high sensitivity and specificity [
9]. While it is less invasive than other procedures used to obtain tissue from the lung nodule, it is not without complication risks [
9]. Invasive follow-up procedures are expensive and can have significant complication risks. Nuñez et al. reported [
10] high frequency of complication rates, and factors associated with complications in a national sample of veterans screened for lung cancer by invasive procedures such as bronchoscopy, transthoracic needle lung biopsy and thoracic surgery. Shin et al. [
11] demonstrated that after lung cancer surgery, pulmonary function and patient-reported outcomes noticeably decreased in the immediate postoperative period and improved thereafter, except for dyspnea and lack of energy. Hence, in recent years, several alternative liquid biopsy approaches such as metabolomic, transcriptomic, genomic, and proteomic [
1,
12‐
16] for the identification of cancerous biomarkers have been explored for the early detection of LC. These approaches use different pathological, molecular, and biochemical analyses. Unlike invasive lung tissue biopsy to detect LC biomarkers, a liquid biopsy such as blood sample or other body fluid is non-invasive. For example, biomarkers as circulating cell-free tumor DNA (cf DNA), cell-free RNA (cf RNA), exosomes, tumor-educated platelets (TEP), and circulating tumor cells (CTCs) can be detected in blood to detect LC [
17,
18]. Common to all of these diverse methods is that the detection of LC in its early stage has low sensitivity and/or specificity. Klein et al. validated a targeted methylation-based test to detect cancer and reported sensitivities of 16.8% to detect stage I and 40.4% to detect stage II [
19,
20]. Xue et al. stated in their review of molecular technologies in liquid biopsy that early detection still needs to be improved [
21].
Studies show that activation of immune cells requires changes in the way metabolic energy (ATP molecules) is generated. Immune system cells alter their energy generation in order to obtain an effector function. Usually, the shift is from the oxidative phosphorylation cycle into an aerobic glycolysis cycle. This shift provides immediate energy that gives the immune system the ability to attack the foreign antigen [
22‐
24]. Hence, it appears that the activation state of the immune system, in response to tumor development, differs from the non-cancerous state [
25‐
30]. These important discoveries corroborate our hypothesis that changes caused by cancer are reflected in different metabolic activity profiles of immune cells such as Peripheral Blood Mononuclear Cells (PBMCs) in response to various antigenic stimulants. In general, an effective in vitro response of the immune cells to re-stimulation with a LC tumor-associated antigen (TAA) stimulant indicates that the immune cells were previously exposed to the specific stimulant. Importantly, it indicates that the cells are able to produce an immunological response to it.
This article describes an improved immunometabolism blood test that measures the function of the immune cells in response to antigenic stimuli based on changes in the metabolic pathways of cells. There are several classical methods to test lymphocytes’ function. Mixed leukocyte culture (MLC) determines histocompatibility by co-culturing PBMCs of a potential donor with those of an allograft recipient. MLC takes 3–8 days to get results and involves the use of H
3 thymidine radiolabeling [
31]. Limiting dilution assay (LDA) also assesses histocompatibility between two parties. It determines the precursor frequencies of cytotoxic and helper T lymphocytes. The duration of this test is generally longer than MLC and takes 7–18 days [
32]. Lymphocyte transformation test (LTT), in contrast to MLC and LDA, measures lymphocyte responses toward nonspecific stimuli (mitogens/drugs) or specific stimuli (antigen). A proliferative response shows that antigens of the respective microorganism are presented by antigen-presenting cells, and are recognized by pre-existing, antigen-specific T lymphocytes. The duration of this test is 8–10 days [
33]. A more recent method to test the function of lymphocytes is the enzyme-linked immunospot (ELISpot) assay. It is a sensitive and quantitative method to detect cytokine production level in cell culture supernatant after growing cells with stimulant antigen. The duration of this ELISpot test, including cell culturing, is 2–12 days [
34,
35]. Various flow cytometry assays that measure lymphocyte functionality include tests that are based on the detection of cell divisions by fluorescent CFSE staining, use of multimer staining of human leukocyte antigen (HLA) restricted peptides with their T cell receptor, use of other staining of cell’s receptors, or measurement of proteins that correlate with cell activation [
36]. Like ELISpot, these types of tests need cell culturing for 2–12 days. ImmuKnow test measures the response of CD4
+ T-helper lymphocytes to the mitogen phytohaemagglutinin-L (PHA), a general stimulator. It measures the amount of ATP produced by the cells following nonspecific stimulation. The duration of this test is 2 days [
37]. While the methods described are non-invasive or devoid of the radiation risk of imaging, they all require days of execution, are cumbersome to perform, and there are no uniform standards (positive and negative controls, measurement units and working protocols) in performing these methods by different users. Therefore, the need for an assay that monitors in vitro cellular immune responses (primarily T and B cells) to antigenic stimuli with TAA, within a few hours, to determine immune activation levels is important.
In a previous publication, we presented a novel, non-invasive, cancer detection platform [
38]. Our platform, named Liquid ImmunoBiopsy™, is based on measurements of metabolic activity profiles of immune cells. In our previous study we showed that by using machine learning methods to get a multivariate prediction model and training on the metabolic profiles, we were able to differentiate between blood samples of LC patients (n = 100, all stages) and control subjects (n = 100) with 91% sensitivity and 80% specificity in a cross-validation statistical evaluation
. Since the clinical benefits for early detection of LC are demonstrated, we continued to develop the metabolic activity (MA) test protocol. The objective of this presented research is to investigate the accuracy of the metabolic activity test for lung cancer (MA-LC) in its improved protocol version versus the previous version by comparing MA-LC results from two additional clinical trials. The first clinical trial (n = 328) is referred to here as the “earlier” clinical trial, and the second additional clinical trial (n = 245) is referred to here as the “later” clinical trial. The earlier MA-LC protocol was used in the earlier clinical trial (n = 328), and an improved protocol was used in the later clinical trial (n = 245). We tested whether the improved protocol does, in fact, increase the sensitivity and specificity of the MA-LC to detect stage I and stage II LC.
Discussion
We describe an improved immunometabolism blood test that measures the function of the immune cells in response to LC antigenic stimuli based on enhancement of the glycolysis metabolic pathway of immune cells. Glycolysis enhancement is a marker for the rapid activation of most immune cells [
29].
This research article compares results from two clinical trials; in the earlier clinical trial an earlier MA-LC protocol was used and in the later clinical trial an improved protocol was used. Since the clinical benefits for early detection have been demonstrated, this current research focuses on early-stage lung cancer (stages I, II). Our results indicate that the MA-LC in its final version improves the test’s specificity from 81.7% (Table
4 – earlier clinical trial) to 94% (Table
5 – later clinical trial), while sensitivity increased from 92.3% (Table
4 – earlier clinical trial) to 94.9% (Table
5 – later clinical trial) in identifying LC stage I, and from 89.5% (Table
4 – earlier clinical trial) to 100% (Table
5 – later clinical trial), in identifying LC stage II. The higher specificity and sensitivity in the later clinical trial is the result of fine tuning the previously published protocol. These improvements include calibration of stimulants and PBMCs concentrations, selection of the most suitable stimulants, and improvements in quality control methods.
Table 4
Sensitivity and specificity of MA-LC of the earlier clinical trial
Specificity | 81.7% | (76–86%) |
Sensitivity | 91.5% | (83–96%) |
Table 5
Sensitivity and specificity of MA-LC of the later clinical trial
Specificity | 94.0% | (89–97%) |
Sensitivity | 97.3% | (92–99%) |
I | 39 | 94.9% |
II | 21 | 100.0% |
III | 25 | 100.0% |
IV | 25 | 96.0% |
N/A | 1 | 100.0% |
The sensitivity and specificity obtained by MA-LC in detecting early-stage lung cancer is much higher than the results reported for stages I, II in the literature by using only one method [
19‐
21,
39]. The superior accuracy for early stages by MA-LC can be explained by the hypothesis that immune cells in lung-associated lymph nodes reach the malignant cells in the lung when the tumor is young, small and has yet to develop its ability to evade immune cells (stages I, II). Recognition of lung cancer TAAs (stimulants) by immune cells is possible and results in an immediate shift to the glycolysis pathway, enabling an effective local immune response. As the malignant tumor develops and grows (cancer at later stages), it activates mechanisms for evading the immune system. This results in the failure of the immune system to adequately activate and allows the tumor to escape immune detection and elimination [
40]. Tumor-exposed immune cells reach peripheral blood, and repeated in vitro exposure to TAAs will result in a shift to the glycolysis metabolic pathway. This shift is detectable by the MA-LC. Metabolic pathway shift and immune cell function are highly correlated [
29]. For example, the activation of immune receptors promotes glycolysis, which is the energy source of immune cells to fight the foreign invader tumor antigens.
Other biomarkers noninvasive tests focus on detecting circulating biomarkers, including tumor DNA, tumor antigens, tumor cells, exosomes, and extracellular vesicles. These biomarkers are released to peripheral blood primarily when the tumor reaches a certain size at a later stage of the disease.
We have previously shown [
38] that chronic obstructive pulmonary disease (COPD) or smoking habits do not affect the test results, which supports other findings that diseases produce specific signatures in the metabolic profiles, which can help distinguish between various ailments such as cancers, autoimmune diseases, and infectious diseases [
23]. To date, there are no laboratory tests for lymphocyte function that provide a quick and accurate answer. The immunometabolism assay can help diagnose early stages of cancer by using tumor associated/specific peptides.
The broad potential of this immunometabolism-based platform may also extend to other types of diseases, as well as to treatment monitoring and therapy selection. It could provide the cellular immune status of vaccinated people to SARS-COV-2 by using virus spike peptides, measure other cellular immune statuses to diseases such as allergy, autoimmune, immunodeficiency, antimicrobial immunity, follow up the effect of immunotherapy treatments, and measure drug efficacy.
Liquid ImmunoBiopsy™ is a new, promising, and non-invasive platform that measures the metabolic state of the immune system as a direct indicator of cellular immune responses (primarily T and B cells) to antigenic stimuli. The MA-LC provides results within five hours of receiving the blood sample for MA-LC. The analytical sensitivity of the test is high with a lower limit of quantification (LLOQ) of 0.000119 (d/minute) in change of acidity over time. It specifically quantifies glycolysis which is a biomarker for the activation level of immune cells that are re-exposed in vitro to lung TAA stimulants.
The present study has limitations. Not all control subjects received LDCT screening, nor were they followed-up after the blood draw, therefore, it is unknown whether lung cancer cases were already present and missed. Separately, cross validation is a widely used approach for assessment of classification performance and can address known individual confounders. However, cross-validation procedures do not control simultaneously for all confounders, and the use of an independent test set is needed to evaluate the generalizability of these results. Prospective studies are planned to validate classifier performance in an independent cohort and verify the generalization predictions from confounder-controlled CV.
The MA-LC is, inter alia, a diagnostic method to detect stage I and stage II of lung cancer, with low material costs and fast results. Furthermore, the combination of LDCT scans with MA-LC may reduce the need for follow-ups of suspected lung nodules, prevent unnecessary radiation exposure, and decrease the number of unnecessary invasive procedures with their associated complications. In addition, the MA-LC can help improve adherence to routine medical screenings in high-risk populations through the use of a patient-friendly blood test. A larger prospective clinical validation is a next step.
Acknowledgements
The authors are indebted to Dr. Ori Haberfeld, Dr. Yaron Saiet, Dr. Eran Gilad from Department of General Thoracic Surgery, Rambam Health Care Campus, Israel and to Dr. Yana Kogan, Dr. Einat Fireman Klain, Dr. Sonia Shneer and Dr. Raya Cohen from Pulmonary Division, Faculty of Medicine, Lady Davis Carmel Medical Center, Israel for their help in recruiting suitable subjects for the clinical study and explaining to them the research study and its risks and signing an informed consent form in accordance with the Helsinki Convention. The authors thank Gratzia Luzon, Irena Shahar and Mori Hay Levy for their help in coordinating the clinical studies.
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.