Detection and characterization of HLA class I molecules in the supernatant of an hepatocarcinoma cell line and of EBV-transformed B cell lines

The Potential of Soluble Human Leukocyte Antigen Molecules for Early Cancer Detection and Therapeutic Vaccine Design

Human leukocyte antigen (HLA) molecules are essential for anti-tumor immunity, as they display tumor-derived peptides to drive tumor eradication by cytotoxic T lymphocytes. HLA molecules are primarily studied as peptide-loaded complexes on cell membranes (mHLA) and much less attention is given to their secretion as soluble HLA–peptide complexes (sHLA) into bodily fluids. Yet sHLA levels are altered in various pathologies including cancer, and are thus of high interest as biomarkers. Disconcordance in results across studies, however, hampers interpretation and generalization of the relationship between sHLA levels and cancer presence, thereby impairing its use as a biomarker. Furthermore, the question remains to what extent sHLA complexes exert immunomodulatory effects and whether shifts in sHLA levels contribute to disease or are only a consequence of disease. sHLA complexes can also bear tumor-derived peptides and recent advancements in mass spectrometry now permit closer sHLA peptide cargo analysis. sHLA peptide cargo may represent a “liquid biopsy” that could facilitate the use of sHLA for cancer diagnosis and target identification for therapeutic vaccination. This review aims to outline the contradictory and unexplored aspects of sHLA and to provide direction on how the full potential of sHLA as a quantitative and qualitative biomarker can be exploited.

Infection of human endothelial cells by Japanese encephalitis virus: increased expression and release of soluble HLA-E

Japanese encephalitis virus (JEV) is a single stranded RNA virus that infects the central nervous system leading to acute encephalitis in children. Alterations in brain endothelial cells have been shown to precede the entry of this flavivirus into the brain, but infection of endothelial cells by JEV and their consequences are still unclear. Productive JEV infection was established in human endothelial cells leading to IFN-β and TNF-α production. The MHC genes for HLA-A, -B, -C and HLA-E antigens were upregulated in human brain microvascular endothelial cells, the endothelial-like cell line, ECV 304 and human foreskin fibroblasts upon JEV infection. We also report the release/shedding of soluble HLA-E (sHLA-E) from JEV infected human endothelial cells for the first time. This shedding of sHLA-E was blocked by an inhibitor of matrix metalloproteinases (MMP). In addition, MMP-9, a known mediator of HLA solubilisation was upregulated by JEV. In contrast, human fibroblasts showed only upregulation of cell-surface HLA-E. Addition of UV inactivated JEV-infected cell culture supernatants stimulated shedding of sHLA-E from uninfected ECV cells indicating a role for soluble factors/cytokines in the shedding process. Antibody mediated neutralization of TNF-α as well as IFNAR receptor together not only resulted in inhibition of sHLA-E shedding from uninfected cells, it also inhibited HLA-E and MMP-9 gene expression in JEV-infected cells. Shedding of sHLA-E was also observed with purified TNF-α and IFN-β as well as the dsRNA analog, poly (I:C). Both IFN-β and TNF-α further potentiated the shedding when added together. The role of soluble MHC antigens in JEV infection is hitherto unknown and therefore needs further investigation.

Soluble MHC I and soluble MIC molecules: potential therapeutic targets for cancer

It has become clear that soluble MHC I (sMHC I) and soluble MIC (sMIC), which are highly elevated in sera of cancer patients, can be viewed to be tolerogenic, and that metalloproteinases are involved in their generation process. In this review, an overview is provided of the recent progress made in the sMHC I and sMIC fields, with emphasis on their structure, formation, and function, and the key-questions that still await answers are addressed. Understanding better their formation mechanism, it will become more feasible to modulate the immune responses in cancer patients by targeting molecules involved in their generation process.

Identification of differential HLA-binding peptide between two hepatoma cell lines HepG2 and HepG2.2.15

AIM: To screen the differential HLA-binding peptides between HepG2 and HepG2.2.15 cell lines, and to find some HLA-binding peptides correlated with hepatitis B virus (HBV) infection.

METHODS: HepG2 and HepG2.2.15 cells were harvested (108 cells), and the peptides were isolated from the cell membrane by mild acid elution, respectively. Then the mixture of peptides was fractionated by high performance liquid chromatography (HPLC) and the differential fractions only expressed in HepG2.2.15 cell line were identified by nanoESI-MS/MS analysis. Bioinformatic analysis and MASCOT index were used to investigate the sequence and source of the peptides. Finally the expression of mRNA was detected by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS: HPLC fractions were markedly different between HepG2 and HepG2.2.15 cells. A peptide, SPDDPSRYISPDQ, from enolase 1 (ENO1) was obtained, which was only expressed in HepG2.2.15 cells, by nanoESI-MS/MS analysis. The result of RT-PCR confirmed that ENO1 expression was significantly higher in HepG2.2.15 cells than that in HepG2 cells.

CONCLUSION: A human peptide SPDDPSRYISPDQ from ENO1 can be presented on the surface of HepG2.2.15 cells by HLA, and ENO1 mRNA expression is significantly higher in HepG2.2.15 than that in HepG2, suggesting that HBV infection may cause the up-regualtion of ENO1 expression.

Expression of HLA-I on HepG2 cells by hepatitis B virus nucleocapsid mutants

AIM

To study the expression of HLA-I/antigen peptide complex on HepG2 cells transfected with HBV (adr) wild type and nucleocapsid protein mutants.

METHODS

The site-directed mutation was performed to introduce nucleocapsid protein point mutations V60 and L97 into 1.2 copies of HBV genome plasmid p3.8 Ⅱ. After identification of DNA sequence and biological activities, the plasmid p3.8Ⅱ and mutant plasmid constructs were subcloned respectively into EB virus based vector EBO-plpp for stable expression. The vector constructed EBO-wild type, EBO-V60, and EBO-L97 were analyzed by restriction enzyme digestion and DNA sequenceing, then transfected into HepG2 cells via the liposome technique, respectively. HBV antigen in their culture supernatants was quantified by Abbott kits. The cells were stained with murine monoclonal antibody anti-HLA-ABC conjugated directly to FITC, and expression of HLA-I on their membrane was analyzed by flow-cytometry.

RESULTS

Restriction enzyme digestion of 3 vector constructs showed two bands similar to HBV 1.2 copies genome and EBO vector, respectively. Analysis of DNA sequence confirmed the mutated nucleotides of EBO-V60 and EBO-L97 (i.e nt2078 C→G, nt2189 A→C). The expression of HBeAg S/CO in culture supernatant of EBO-wild type was much higher than that of mutant EBO-V60 and EBO-L97, while the expression of HBsAg S/N in three constructs had similar level, indicating similar transfecting rate in this experiment. The expression of HLA-I on HepG2 cells transfected with EBO empty vector was at low level. Fluorescence intensity of HLA-I expression of transfected cells was elevated by EBO-wild type (18.2), while that of L97 was increased to 34.5 and V60 declined to 3.4.

CONCLUSION

HBV might enhance the expression of HLA-I/antigen peptide complex on HepG2 cells. Hot-spot mutations of HBV nucleocapsid protein L97 and V60 could influence the expression level of HLA-I on host cells.

Size variants of beta-2-microglobulin-free human leucocyte antigen class I heavy chain make different contributions to its serum increase in multiple myeloma

We previously showed that serum beta-2-microglobulin (beta2m)-free human leucocyte antigen (HLA) class I heavy chain (FHC) levels were increased in MM and correlate with disease activity. The present investigation, carried out in 124 multiple myeloma patients, studied the expression of the three size variants of FHC, namely the 42 kDa intact heavy chain (A variant, AV), released through a shedding process, and the truncated FHC (tFHC) 39 kDa (BV) and 36-35 kDa (CV) released by means of membrane-type metalloprotease activity. The increase in FHC correlated with a high expression percentage of BV (r = 0.32, P = 0.0002) and tFHC (r = 0.42, P < 0.0001), which could help to discriminate multiple myeloma from monoclonal gammopathy of undetermined significance (tFHC mean ratio = 3.2; Mann-Whitney U-test, P < 0.0001). tFHC levels highly correlated with other disease activity markers, namely haemoglobin (r = -0.35; Spearman's rank, P = 0.0001), percentage of bone marrow plasma cells (r = 0.4, P < 0.0001) and beta2m levels (r = 0.36, P < 0.0001), while only the last barely correlated (r = 0.2, P = 0.03) with AV. Finally, the 0.4, 0.57 and 0.71 mg/l BV, tFHC and (to a lesser extent) FHC cut-off values divided patients into two groups with different survival curves (P = 0.0005, P = 0.0025 and P = 0.04 respectively). These data are in favour of a correlation between disease aggressiveness and cleavage of these variants by membrane-type metalloprotease enzymes.

Soluble HLA proteins with bound peptides are released from the cell surface by the membrane metalloproteinase

The metalloproteinase (MPase)-mediated pathway of MHC class I processing is a distinct cellular mechanism that generates soluble HLA proteins. It has been implicated in modulation of immune responses induced during transplantation events. It is, therefore, important to define the characteristics of soluble HLA species produced by the MPase pathway. We have previously shown that some mutant peptide-conformed beta(2)-microglobulin (beta(2)m) free heavy chains (HC) with lower affinity for beta(2)m can be released into supernatants by the MPase. These soluble conformed beta(2)m-free HC intermediates can re-associate with beta(2)m in solution giving rise to beta(2)m-associated HC. We now demonstrate that also nonmutant soluble conformed beta(2)m-free HC can be detected in supernatants of activated cells. These soluble HC intermediates appear to have bound peptides and readily re-associate with exogenous beta(2)m producing beta(2)m-associated HC that are stable at physiologic temperature. Thus, generation of peptide-conformed beta(2)m-free HC intermediates is an important step, which precedes generation of both soluble beta(2)m-free and beta(2)m-associated HC by the MPase pathway operating in activated cells.