MCP-1 exists in glycosylated and unglycosylated forms. Glycosylation reduces chemotactic potency but does not affect receptor binding . Recombinant MCP-1 (unglycosylated) is typically used in research .
MCP-1 recruits monocytes, basophils, memory T lymphocytes, and NK cells via binding to CCR2 (its primary receptor) and CCR4 . Its roles include:
Inflammation: Directs immune cell migration to injury sites.
Disease Pathogenesis: Implicated in atherosclerosis, nephropathy, rheumatoid arthritis, and psoriasis .
Atherosclerosis: MCP-1 promotes monocyte infiltration into arterial walls, initiating plaque formation .
Nephropathy: Elevated MCP-1 levels correlate with renal inflammation and fibrosis .
MCP-1 serves as a biomarker for inflammatory and cardiovascular diseases.
MCP-1 >75th percentile (≥238 pg/mL) increases 10-month risk of death or MI by 1.53× (adjusted HR) .
Independent predictors: Age, hypertension, diabetes, prior coronary disease .
MCP-1 is quantified using ELISA kits, which detect both recombinant and natural forms .
Sample Type | Intra-Assay CV% | Inter-Assay CV% |
---|---|---|
Cell culture supernates/urine | 4.2–5.9% | 4.5–5.9% |
Serum/plasma | 4.7–7.8% | 4.6–6.7% |
Data from R&D Systems Quantikine ELISA (DCP00) .
MCP-1 is induced by proinflammatory cytokines (e.g., TNF-α, IL-1β) and growth factors (e.g., PDGF) .
Cell Type | Stimuli |
---|---|
Endothelial cells | Lipopolysaccharide, TNF-α |
Fibroblasts | PDGF, IL-1β |
Monocytes/macrophages | LPS, IFN-γ |
MCP-1 levels are modifiable:
Polymorphisms in the MCP-1 gene influence susceptibility to:
Polymorphism | Disease | Mechanism |
---|---|---|
-2518G>A | PCOS, ovarian cancer | Enhanced MCP-1 transcription |
-2158GG | Ovarian cancer | Increased MCP-1 production |
-362GG | Oral SCC | Altered CCR2 signaling |
MCP-1/CCL2 is a member of the C-C chemokine family and serves as a potent chemotactic factor for monocytes. It was the first human CC chemokine to be purified and characterized, initially identified due to its monocyte chemotactic properties in human cell lines. MCP-1 is located on chromosome 17 (17q11.2-q21.1) and consists of 76 amino acids with a molecular weight of 13 kDa .
What distinguishes MCP-1 from other chemokines is its specific structural characteristics and functional role. MCP-1 belongs to a subfamily of at least four members (MCP-1/CCL2, MCP-2/CCL8, MCP-3/CCL7, and MCP-4/CCL13) that share high sequence homology (61-71%) . Unlike other chemokine subfamilies, MCPs form a distinct cluster on chromosome 17q11.2-12 in humans (chromosome 11B5-C in mice) and all interact with the CCR2 receptor .
MCP-1 is produced by a diverse range of cell types, making it ubiquitous in various tissue environments. The primary sources include:
Epithelial cells
Endothelial cells
Smooth muscle cells
Monocytes/macrophages
Fibroblasts
Osteoclasts and osteoblasts (particularly at sites of tooth and bone injuries or infections)
The expression of MCP-1 by these cells is regulated by several cytokines and environmental factors. In the context of disease, both tissue-resident cells and infiltrating immune cells can produce MCP-1, creating amplification loops that sustain inflammatory responses. For instance, in breast cancer, both tumor cells and stromal cells produce MCP-1, which recruits macrophages to the tumor microenvironment .
MCP-1 plays several crucial roles in normal human physiology:
Monocyte recruitment: MCP-1 selectively attracts monocytes from the bloodstream across the vascular endothelium, which is essential for routine immunological surveillance of tissues .
Immune cell activation: Beyond chemotaxis, MCP-1 activates lymphocytes, basophils, and natural killer (NK) cells .
Regulation of T cell differentiation: MCP-1 modulates Th1 immune responses by selectively suppressing the differentiation of naïve T cells into Th1 effector cells through regulation of IL-12 release from dendritic cells .
Enhancement of type 2 immune responses: MCP-1 augments IL-4 production by T cells by activating the IL-4 promoter, which enhances type 2 immune responses .
Dendritic cell differentiation: MCP-1 regulates the differentiation of monocytes into dendritic cells, influencing subsequent adaptive immune responses .
These functions highlight MCP-1's importance in maintaining immune homeostasis and orchestrating appropriate immune responses to various stimuli in healthy individuals.
The sandwich ELISA (Enzyme-Linked Immunosorbent Assay) is the most widely used and reliable method for quantifying MCP-1 in human samples. Specifically:
Sandwich ELISA: Utilizes a capture antibody (such as purified 10F7 antibody) and a biotinylated detection antibody (like clone 5D3-F7) to create a sensitive and specific detection system .
Chemiluminescent assays: Systems like the Q-Plex offer high sensitivity with a detection range of 2,000 – 2.74 pg/mL and a lower limit of detection (LLD) of 2.60 pg/mL .
Performance characteristics of a typical MCP-1 assay include:
Sample | Concentration (pg/ml) | %CV |
---|---|---|
Sample 1 | 325.97 | 7% |
Sample 2 | 19.72 | 5% |
Sample 3 | 8.37 | 9% |
Average CV: 7% |
Sample | Concentration (pg/ml) | %CV |
---|---|---|
Sample 1 | 345.54 | 7% |
Sample 2 | 23.93 | 6% |
Sample 3 | 8.99 | 7% |
Average CV: 7% |
Dilution Factor | % Recovery |
---|---|
Cell Culture Supernatant | |
2 | 96% |
4 | 106% |
8 | 102% |
Average percent linearity: 108% (range: 96-118%) |
For research requiring multiplex analysis, assays that can simultaneously measure MCP-1 alongside other inflammatory markers are available and beneficial for comprehensive analysis of inflammatory profiles.
When measuring MCP-1 levels in human samples, researchers should consider the following critical factors:
Sample type compatibility: Common sample types include human serum, EDTA plasma, and cell culture supernatants. Each may require specific handling protocols .
Sample volume requirements: Typically, a minimum of 25μL per well is required for ELISA-based assays .
Storage and handling of recombinant standards:
Upon initial thawing, recombinant human MCP-1 should be aliquoted into polypropylene microtubes and frozen at -80°C
Alternatively, dilute in sterile neutral buffer containing 0.5-10 mg/mL carrier protein (human or bovine albumin)
For ELISA standards, carrier-protein concentrations of 5-10 mg/mL are recommended
For in vitro biological assays, carrier-protein concentrations ≥0.5 mg/mL are suggested
Carrier protein considerations: Pre-screen carrier proteins for possible effects in your experimental system, as they may influence results due to toxicity, high endotoxin levels, or blocking activity .
Dilution protocols: Ensure proper dilution series for standard curves. To obtain linear standard curves, use doubling dilutions of the human MCP-1 standard .
Freeze-thaw cycles: Minimize freeze-thaw cycles of samples as this can degrade chemokines and affect measurement accuracy.
Timing of collection: For disease studies, the timing of sample collection relative to disease onset or progression can significantly impact measured MCP-1 levels.
Adhering to these considerations will help ensure reliable and reproducible measurements of MCP-1 in research settings.
When interpreting variations in MCP-1 levels across different sample types, researchers should consider several important factors:
Baseline differences between sample types: MCP-1 levels naturally vary between serum, plasma, urine, and tissue homogenates. For example, the dilutional linearity data shows different recovery percentages for cell culture supernatant (96-106%), activated plasma (109-112%), pooled serum (100-118%), and serum HF (107-112%) .
Biological variability:
Circulating MCP-1 levels may differ significantly from tissue-specific concentrations
Expression can vary between healthy individuals due to genetic polymorphisms, age, sex, and other demographic factors
Diurnal variations may impact measurements in time-course studies
Sample-specific confounding factors:
Disease-specific patterns:
Technical considerations:
Use consistent sample types when comparing across groups or time points
Develop tissue-specific reference ranges for accurate interpretation
Consider normalizing measurements to total protein content or other relevant parameters when comparing tissue homogenates
Researchers should interpret variations cautiously, always considering the biological context and technical limitations of the assays used.
MCP-1 plays multiple roles in cancer progression and metastasis through complex mechanisms involving tumor cells, stromal cells, and immune cells:
Recruitment of tumor-associated macrophages (TAMs):
Promotion of angiogenesis:
Direct effects on tumor cell invasion:
Facilitation of metastasis:
Recruitment of mesenchymal stem cells:
Establishment of pre-metastatic niches:
MCP-1 may help create favorable environments in distant organs for subsequent metastatic seeding
The multiple functions of MCP-1 in cancer highlight its potential as both a biomarker and therapeutic target. Blocking MCP-1 signaling pathways might reduce tumor-promoting inflammation and inhibit metastatic spread in various cancer types.
MCP-1 plays a central role in both insulin resistance development and diabetic complications:
Understanding these relationships has important clinical implications, as MCP-1 could serve as both a biomarker for disease progression and a potential therapeutic target in managing diabetic complications.
MCP-1 plays complex roles in infectious diseases, with effects that can be either protective or detrimental depending on the context:
Role in tuberculosis:
Modulation of immune cell recruitment and function:
MCP-1 directs migration and infiltration of monocytes, microglia, and memory T lymphocytes to sites of infection
It regulates the differentiation of monocytes into dendritic cells, influencing subsequent adaptive immune responses
MCP-1 modulates Th1 immune responses by selectively suppressing naïve T cell differentiation into Th1 effector cells
Impact on T cell polarization and cytokine production:
MCP-1 can enhance IL-4 production by T cells by activating the IL-4 promoter
This results in enhancement of type 2 immune responses, which may be beneficial for some parasitic infections but detrimental for intracellular pathogens
MCP-1 produced by neutrophils in a Th1 microenvironment has been implicated in Th1 adaptive responses
Context-dependent protective vs. pathological effects:
Role in COVID-19:
The multifaceted functions of MCP-1 in infectious diseases highlight the importance of context-specific analysis when studying its role in host defense and immunopathology. Therapeutic approaches targeting MCP-1 must consider these complex interactions to achieve beneficial outcomes without compromising protective immunity.
When designing experiments with MCP-1 knockout or conditional knockout models, researchers should consider several critical factors:
Model selection and verification:
Systemic vs. conditional knockouts: Systemic MCP-1 knockout mice (MCP-1 KO) show global deletion, while conditional knockouts using Cre-loxP systems allow cell-type specific deletion
Verification methods: Confirm knockout status through Southern blotting or PCR using appropriate primer sets
Background strain considerations: Genetic background can influence phenotypes; use appropriate controls matched for genetic background
Interpreting compensatory mechanisms:
Cell-specific targeting considerations:
For conditional knockouts, carefully select appropriate Cre driver lines based on the cell types of interest
Consider that MCP-1 is produced by multiple cell types including macrophages, fibroblasts, epithelial cells, and endothelial cells
Determine which cellular source of MCP-1 is most relevant to your disease model
Experimental readouts:
Include measurements of:
Monocyte/macrophage recruitment (flow cytometry, immunohistochemistry)
Inflammatory cytokine production
Disease-specific pathological changes
Functional outcomes relevant to the model
Control considerations:
Include both wild-type and heterozygous controls when possible
For conditional knockouts, include Cre-only and floxed-only controls
Consider including MCP-1 receptor (CCR2) knockout controls for comparison
Technical challenges and solutions:
Potential embryonic lethality: Use inducible systems if constitutive deletion causes developmental issues
Genotyping complexity: Design robust PCR protocols to distinguish between wild-type, floxed, and deleted alleles
Phenotypic variability: Increase sample sizes to account for variability in knockout phenotypes
Researchers studying specific diseases should also refer to existing literature on MCP-1 knockout phenotypes in relevant disease models to inform their experimental design and interpretation.
When conducting MCP-1 inhibition studies to evaluate therapeutic potential, researchers should consider a comprehensive approach that addresses both efficacy and safety:
Inhibition strategy selection:
Direct MCP-1 neutralization: Monoclonal antibodies against MCP-1
Receptor antagonism: CCR2 receptor antagonists
Gene expression inhibition: siRNA, antisense oligonucleotides, or CRISPR-based approaches
Small molecule inhibitors: Compounds that disrupt MCP-1/CCR2 interaction
In vitro validation studies:
Monocyte chemotaxis assays to confirm functional inhibition
Dose-response relationships to determine optimal inhibitor concentrations
Cell viability assays to assess potential cytotoxicity
Specificity testing to ensure minimal off-target effects on other chemokines/receptors
In vivo experimental design considerations:
Treatment timing: Preventive (before disease onset) vs. therapeutic (after disease established)
Dosing regimen: Based on pharmacokinetic/pharmacodynamic properties
Route of administration: Systemic vs. local/targeted delivery
Duration: Acute vs. chronic treatment paradigms
Appropriate controls: Vehicle, isotype control antibodies, scrambled RNA sequences
Outcome measures:
Primary disease-specific endpoints (e.g., tumor size, glucose tolerance, plaque formation)
Biomarker assessments (circulating MCP-1 levels, downstream inflammatory mediators)
Immune cell infiltration (quantity and phenotype of monocytes/macrophages)
Functional outcomes relevant to the disease model
Safety parameters (organ function, immune competence against infections)
Potential challenges and mitigation strategies:
Redundancy in chemokine systems: Measure other chemokines that might compensate for MCP-1 inhibition
Timing-dependent effects: Test intervention at multiple disease stages
Context-dependence: Evaluate in multiple disease models if relevant
Balancing efficacy vs. impaired host defense: Include infection challenge studies
Translational considerations:
Species differences in MCP-1 biology between rodents and humans
Use of humanized models when appropriate
Application of findings from human genetic studies (e.g., MCP-1 polymorphisms)
Correlation with clinical biomarker data when available
By following this structured approach, researchers can generate robust preclinical evidence regarding the therapeutic potential of MCP-1 inhibition in specific disease contexts, while also identifying potential limitations and safety concerns.
When studying MCP-1 expression dynamics in human tissue samples, researchers should implement the following best practices:
Sample collection and preservation:
Optimize tissue preservation with appropriate fixatives (for immunohistochemistry) or snap-freezing (for RNA/protein extraction)
Minimize ischemia time to prevent artifactual changes in chemokine expression
Document clinical parameters and treatment history that might influence MCP-1 expression
Include matched control tissues whenever possible
Multiple detection methods:
Combine protein and mRNA detection approaches:
Immunohistochemistry/immunofluorescence for spatial localization
ELISA/Western blot for quantitative protein measurement
qRT-PCR for mRNA expression levels
In situ hybridization for cellular localization of MCP-1 transcripts
Single-cell RNA sequencing for cell-specific expression patterns
Cellular source identification:
Use multi-color immunofluorescence with cell type-specific markers to identify MCP-1 producing cells
Consider that MCP-1 is produced by various cell types including epithelial cells, endothelial cells, smooth muscle cells, monocytes/macrophages, fibroblasts, astrocytes, and microglial cells
Laser capture microdissection can isolate specific cell populations for expression analysis
Analytical considerations:
Temporal dynamics assessment:
When possible, obtain serial samples to assess temporal changes
In cross-sectional studies, stratify samples by disease stage/duration
Correlate MCP-1 expression with disease activity markers
Consider circadian variations in expression
Validation and controls:
Include positive and negative controls for each detection method
Validate antibody specificity using appropriate controls
Consider measuring other MCPs (MCP-2/CCL8, MCP-3/CCL7, MCP-4/CCL13) to assess potential compensatory mechanisms
Include receptor (CCR2) expression analysis to provide context for MCP-1 signaling potential
Functional correlation:
Correlate MCP-1 expression with monocyte/macrophage infiltration
Assess relationship between MCP-1 levels and clinical outcomes
Consider ex vivo functional assays with patient-derived samples
By implementing these methodological approaches, researchers can generate more comprehensive and reliable data on MCP-1 expression dynamics in human tissues, facilitating better understanding of its role in both normal physiology and disease pathogenesis.
When confronted with discrepancies in MCP-1 measurements across different detection platforms, researchers should implement a systematic approach to identify sources of variation and establish standardization protocols:
Identify potential sources of variation:
Antibody specificity: Different assays may use antibodies recognizing distinct epitopes on MCP-1
Detection of glycosylated forms: Various assays may differentially detect glycosylated vs. unglycosylated forms of MCP-1
Cross-reactivity: Some antibodies might cross-react with other MCP family members that share 61-71% sequence homology
Sample matrix effects: Components in serum, plasma, or tissue lysates may interfere differently with various assay platforms
Detection range differences: Different assay sensitivities (e.g., lower limit of detection of 2.60 pg/mL for some ELISA kits)
Implement standardization protocols:
Reference standards: Use common recombinant MCP-1 standards across platforms
Spike-recovery experiments: Add known amounts of recombinant MCP-1 to samples and measure recovery across platforms
Dilutional linearity assessment: Perform serial dilutions of samples and compare linearity profiles (expected range: 96-118%)
Internal controls: Include consistent positive controls across all experimental runs
Standard curves: Compare standard curves across platforms to identify systematic biases
Cross-validation strategies:
Bland-Altman analysis: Plot differences between methods against their means to identify systematic biases
Passing-Bablok regression: Non-parametric method for method comparison that doesn't assume error-free reference method
Sample splitting: Analyze identical aliquots across multiple platforms
Sequential measurements: Test the same samples first with one method, then another
Platform-specific considerations:
ELISA vs. multiplex: Multiplex assays may show different sensitivity due to potential antibody cross-reactions
Automated vs. manual: Evaluate variability introduced by automation
Different ELISA formats: Compare sandwich vs. competitive ELISAs
Mass spectrometry approaches: Consider as reference method for absolute quantification
Reporting recommendations:
Clearly document the detection method, including antibody clones (e.g., 10F7 as capture antibody and 5D3-F7 as detection antibody)
Report both intra-assay (typically ~7% CV) and inter-assay variability (typically ~7% CV)
Specify the detection range and lower limit of detection
Document any sample preparation or handling procedures that might affect results
By systematically addressing these factors, researchers can better understand the source of discrepancies, implement appropriate correction factors when comparing across studies, and select the most suitable platform for their specific research question.
When analyzing MCP-1 in clinical samples, researchers must control for numerous confounding factors that can influence results and interpretation:
Demographic and physiological factors:
Age: MCP-1 levels may increase with aging due to chronic low-grade inflammation
Sex: Hormonal influences may affect MCP-1 expression
Body mass index (BMI): Adipose tissue is a significant source of MCP-1
Circadian rhythm: Consider potential diurnal variations in chemokine levels
Exercise status: Recent physical activity can transiently alter MCP-1 levels
Nutritional status: Fasting/fed state may influence inflammatory markers
Pre-analytical variables:
Sample collection method: Differences between serum (higher due to release during clotting) and plasma
Anticoagulant type: EDTA, heparin, or citrate may differently affect MCP-1 measurements
Processing time: Delayed processing may increase MCP-1 due to ex vivo activation
Storage conditions: Temperature and duration of storage before analysis
Freeze-thaw cycles: Multiple cycles can degrade chemokines
Clinical and medication confounders:
Concurrent infections or inflammatory conditions: Even subclinical inflammation can elevate MCP-1
Renal function: Impaired kidney function affects MCP-1 clearance and urinary levels
Medications: Many drugs affect inflammatory pathways (e.g., statins, corticosteroids)
Comorbidities: Conditions like diabetes or cardiovascular disease independently influence MCP-1
Disease duration and activity: Stage and activity of primary disease being studied
Genetic factors:
Statistical approaches to address confounding:
Multivariate analysis: Adjust for known confounders in statistical models
Propensity score matching: Match cases and controls based on confounding variables
Stratification: Analyze subgroups separately when confounding effects are strong
Repeated measures designs: Use subjects as their own controls when appropriate
Sensitivity analyses: Test robustness of findings with different analytical approaches
Reporting recommendations:
Document all potential confounding variables
Specify inclusion/exclusion criteria related to confounders
Report both unadjusted and adjusted analyses
Discuss limitations related to unmeasured confounders
By systematically addressing these confounding factors through study design, sample handling, and statistical analysis, researchers can enhance the validity and reproducibility of clinical MCP-1 studies and enable more meaningful cross-study comparisons.
Differentiating MCP-1-specific effects from redundant chemokine pathway activation requires a multi-faceted experimental approach:
Molecular specificity approaches:
Selective neutralization: Use highly specific anti-MCP-1 antibodies that don't cross-react with other MCPs
Receptor antagonism profiling: Compare effects of selective CCR2 antagonists with broader chemokine receptor blockade
Gene silencing specificity: Use siRNA or CRISPR techniques targeting MCP-1 specifically, with appropriate controls for off-target effects
Rescue experiments: Re-introduce MCP-1 in knockout/knockdown systems to confirm phenotype reversal
Comprehensive chemokine profiling:
Expression analysis: Measure multiple chemokines simultaneously (MCP-1, MCP-2/CCL8, MCP-3/CCL7, MCP-4/CCL13, and others)
Temporal dynamics: Assess sequential activation patterns of different chemokines
Cell-specific production: Identify which cells produce which chemokines using single-cell approaches
Receptor expression mapping: Profile the expression of CCR2 and other chemokine receptors on relevant cell populations
Functional redundancy assessment:
Combinatorial inhibition: Compare effects of blocking MCP-1 alone versus MCP-1 plus other chemokines
Additive vs. synergistic effects: Use formal interaction analysis to determine relationship between multiple chemokine systems
Cell-specific response assays: Measure chemotaxis of different monocyte subsets to various chemokines
Receptor desensitization experiments: Test whether pre-exposure to one chemokine affects response to others
Genetic model approaches:
Knockout comparison: Compare phenotypes of MCP-1 knockout with CCR2 knockout mice (receptor knockout should show more profound effects if multiple ligands signal through CCR2)
Conditional and inducible models: Use temporal and spatial control of gene deletion to minimize compensatory changes
Compound mutants: Create double or triple knockout models to address redundancy
Human genetic variation: Study individuals with polymorphisms affecting specific chemokines or receptors
Advanced analytical strategies:
Network analysis: Use systems biology approaches to map chemokine network interactions
Principal component analysis: Identify major patterns of variation in chemokine profiles
Machine learning algorithms: Develop models that predict cellular responses based on complex chemokine signatures
In silico modeling: Use computational approaches to predict redundancy based on structural similarities and receptor binding patterns
Translational validation:
Ex vivo human samples: Test responses in patient-derived samples with selective inhibitors
Biomarker correlation: Identify which chemokines best correlate with disease activity or response to therapy
Clinical trial data mining: Analyze outcomes from trials targeting specific chemokine pathways
By implementing these strategies, researchers can more confidently attribute biological effects to MCP-1 specifically, rather than to redundant chemokine pathways, enhancing the precision of both basic mechanistic studies and therapeutic targeting approaches.
Monocyte Chemotactic Protein-1 (MCP-1), also known as CCL2 (C-C motif chemokine ligand 2), is a small cytokine belonging to the CC chemokine family. It plays a crucial role in the immune system by recruiting monocytes, memory T cells, and dendritic cells to sites of inflammation caused by tissue injury or infection .
The CCL2 gene is located on chromosome 17 (17q11.2-q21.1) in humans and spans 1,927 bases. It consists of three exons and two introns . The protein precursor contains a signal peptide of 23 amino acids, and the mature CCL2 protein is 76 amino acids long, with a predicted molecular weight of approximately 11.025 kilodaltons (kDa) .
CCL2 is primarily secreted by monocytes, macrophages, and dendritic cells. It is also expressed in endothelial cells and smooth muscle cells in response to various stimulants such as platelet-derived growth factor (PDGF), interleukin-1β (IL-1β), and oxidized low-density lipoprotein . The expression of CCL2 is tightly regulated by cellular mechanisms and is upregulated during monocyte differentiation into macrophages .
CCL2 exhibits chemotactic activity for monocytes and basophils but does not attract neutrophils or eosinophils . It binds to chemokine receptors CCR2 and CCR4, which mediate its effects . CCL2 plays a significant role in the pathogenesis of diseases characterized by monocytic infiltrates, such as psoriasis, rheumatoid arthritis, and atherosclerosis . It also augments monocyte anti-tumor activity and is essential for the formation of granulomas .
Recombinant human CCL2 is produced using E. coli expression systems. The recombinant protein is typically purified to a high degree of purity (>97%) and is available in both carrier-free and carrier-containing formulations . The carrier protein, usually Bovine Serum Albumin (BSA), enhances protein stability and shelf-life . Recombinant CCL2 is used in various research applications, including cell culture and as an ELISA standard .
CCL2 has been implicated in the pathogenesis of several diseases, including psoriasis, rheumatoid arthritis, and atherosclerosis . Its role in recruiting monocytes to sites of inflammation makes it a potential therapeutic target for modulating immune responses in these conditions. Additionally, CCL2’s involvement in tumor immunity suggests its potential use in cancer immunotherapy .