Katarína Poláková

Analysis of HLA-G expression in malignant hematopoetic cells from leukemia patients.

It has been suggested that HLA-G antigens may provide tumor cells with an effective immune escape mechanism. So far mostly solid tumors have been analyzed; HLA-G antigen was only exceptionally detected. To further examine HLA-G expression, patients were chosen with different forms of leukemia: AML (25), CML (4), ALL (9), CLL (8), HCL (2) and NHL (3). Using flow cytometry with three HLA-G specific mAbs (87G, 01G and MEM-G/9), western blotting with two specific mAbs (4H84 and MEM-G/1) and RT-PCR, neither HLA-G antigen nor mRNA for any HLA-G isoform was detected. These results strongly suggest that HLA-G antigen is not expressed in freshly isolated human leukemia cells and therefore is not involved in their escape from immune attack.

Mild acid treatment induces cross-reactivity of 4H84 monoclonal antibody specific to nonclassical HLA-G antigen with classical HLA class I molecules.

Mild acid treatment by releasing beta(2)m and antigenic peptides leaves human leukocyte antigen (HLA) class I free heavy chains attached to the cell surface. Acid treatment thus allows detection of the cell surface class I antigens by monoclonal antibodies (mAbs) specific to HLA-free heavy chains. We found that acid treatment also enables detection of the cell surface non-classical HLA-G class I antigen with mAbs specific for HLA-G free heavy chains, including 4H84 mAb recognizing all isoforms. Furthermore, we found that 4H84 mAb, but not other mAbs specific to HLA-G free heavy chains, binds to the surface of 8 out of 16 acid-treated leukemia cell lines. Nevertheless, HLA-G antigen is not present in any of these leukemia cells. This was demonstrated by failure to detect any antigen with 4H84 mAb in immunoblotting as well as by inability to detect HLA-G mRNA by RT-PCR. The antigen recognized by 4H84 mAb in some acid treated leukemia cells was identified by immunoprecipitation as a 45 kDa protein. A number of observations indicate that 45 kDa proteins are none other than classical class I heavy chains. Acid treatment thus induces the ability of the 4H84 mAb to recognize some classical HLA class I molecules. Remarkably, 4H84 determinant on HLA-G is linear but corresponding determinant present on some partially folded classical HLA class I free heavy chains is conformational. In view of the unexpected cross-reactivity, detection of HLA-G with this mAb must be carefully evaluated to avoid false detection.

Dissociation of β2-microglobulin is responsible for selective reduction of HLA class I antigenicity following acid treatment of cells

Beta 2-Microglobulin (beta 2 m) dissociated from surface HLA class I complex following exposure of cells to low pH and was detected in supernatant by radioimmunoprecipitation with specific monoclonal antibodies (mAbs). As the concn of beta 2m in supernatant increased, the binding of mAbs, specific for HLA class I heavy chains associated with beta 2m, to the cell surface declined. Binding of mAb specific for free HLA class I heavy chain to the cell surface increased after acid treatment. Reassociation with exogenous beta 2m confirmed increase in the number of free HLA class I heavy chains on surface of the cells after their exposure to low pH and also at least partially restored the reactivity with mAbs specific to HLA class I heavy chains associated with beta 2m. Dissociation of beta 2m from CD1 complex following acid treatment was also accompanied with the changes in antigenicity of cell surface CD1 molecules.

Genetically engineered mesenchymal stromal cells producing TNFα have tumour suppressing effect on human melanoma xenograft

Mesenchymal stromal cells (MSC) are a promising tool for targeted cancer therapy due to their tumour‐homing ability. Intrinsic resistance enables the MSC to longer tolerate therapeutic factors, such as prodrug converting enzymes, cytokines and pro‐apoptotic proteins. Tumour necrosis factor alpha (TNFα) is known to be cytotoxic to a variety of cancer cells and exert a tumour‐destructive capacity.

The molecular weight determination of proteins and glycoproteins of RNA enveloped viruses by polyacrylamide gel electrophoresis in SDS

Abstract The apparent molecular weights for glycoproteins of four RNA enveloped viruses — influenza virus, NDV, VSV and AMV, calculated relative to protein standards depend upon the percent of acrylamide used. Such anomaly is not observed for other proteins of these viruses. The irregular behaviour of glycoproteins resulted from their lesser capacity to bind SDS.

Antibodies to PB1-F2 protein are induced in response to influenza A virus infection.

PB1-F2 is a small influenza A virus (IAV) protein encoded by an alternative (+1) reading frame of the PB1 gene. While dispensable for IAV replication in cultured cells, PB1-F2 has been implicated in IAV pathogenicity. To better understand PB1-F2 expression in vivo and its immunogenicity, we analyzed anti-PB1-F2 antibodies (Abs) in sera of mice infected intranasally (i.n.) with A/PR/8/34 (H1N1) virus and human acute and convalescent sera collected from the influenza H3N2 winter 2003–2004 epidemic. We explored a number of methods for detecting anti-PB1-F2 Abs, finding that PB1-F2-specific Abs could clearly be detected via immunoprecipitation or immunofluorescence assays using both immune mouse and human convalescent sera. Importantly, paired human sera exhibited similar increases in HI titers and PB1-F2-specific Abs. This study indicates that PB1-F2 is expressed in sufficient quantities in mice and humans infected with IAV to elicit an Ab response, supporting the biological relevance of this intriguing accessory protein.

Human cell surface proteins selectively assembled into vesicular stomatitis virus virions

Vesicular stomatitis virus (VSV) selectively assembled proteins from human cells into progeny virions. These proteins can be surface labeled before infection with 125I, and when purified virus was examined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, only two or three bands of proteins (Mr around 100K) were seen. Antisera to these proteins were produced, using as immunizing antigen VSV tsO45 mutant, defective in assembly of G protein, which had been made at the nonpermissive temperature in the three human tumor cell lines, HeLa (cervical carcinoma), T47D (breast carcinoma), and HMB2 (melanoma). After absorption with wild-type VSV, each of the antisera displayed a different pattern of reactivity; at least three antigenic specificities were detected. Two of them, corresponding to antigens selected by VSV from HeLa and T47D, were to some extent related and they showed an association mainly with epithelial cell-derived gynecological tumors, but they were absent in carcinomas of lung or of digestive tract. These (or related) antigens were expressed in a lower level in some normal tissues, mainly in ovaries. Antigen(s) assembled by VSV from the melanoma cell line was entirely different and appeared to be associated with cell growth. The grounds for selective assembly of these specific proteins by VSV are not clear; they either share with viral surface glycoproteins some physical or structural properties, which are critical for incorporation into the viral envelope, or conceivably they even may represent uncleaved precursor proteins coded by env genes of incomplete genomes of endogenous human retroviruses.

A DNA vaccine expressing PB1 protein of influenza A virus protects mice against virus infection

Although influenza DNA vaccine research has focused mainly on viral hemagglutinin and has led to promising results, other virion proteins have also shown some protective potential. In this work, we explored the potential of a DNA vaccine based on the PB1 protein to protect BALB/c mice against lethal influenza A virus infection. The DNA vaccine consisted of pTriEx4 plasmid expressing PB1. As a positive control, a pTriEx4 plasmid expressing influenza A virus HA was used. Two weeks after three subcutaneous doses of DNA vaccine, the mice were challenged intranasally with 1 LD50 of A/Puerto Rico/8/34 (H1N1) virus, and PB1- and HA-specific antibodies, survival rate, body weight change, viral mRNA load, infectious virus titer in the lungs, cytokines IL-2, IL-4 and IL-10, and granzyme-B were measured. The results showed that (i) the PB1-expressing DNA vaccine provided a fair protective immunity in the mouse model and (ii) viral structural proteins such as PB1 represent promising antigens for DNA vaccination against influenza A.

HLA-G5 in the blood of leukemia patients and healthy individuals

In this work we focused on analysis of HLA-G5 molecules in the blood of patients with B-CLL leukemia and healthy individuals. Using sandwich ELISA, we found total soluble HLA-G, represented by sHLA-G1 and HLA-G5 in most of B-CLL patients while HLA-G5 alone was present only in few cases in both groups. These results lead us to assume that the majority of soluble HLA-G in blood is generated by proteolytic cleavage and shedding of membrane-bound HLA-G1. There is no correlation between the presence of HLA-G5 in blood of B-CLL patients and the stage of disease, age, and gender.

Expression of HLA-G transcripts in graft biopsy samples of renal transplant recipients.

BACKGROUND The HLA-G molecule has a high potential to modulate immune response towards the improvement of graft survival after transplantation. In this work, we have analyzed the total HLA-G mRNA expression in graft tissues of dysfunctional transplanted kidneys. MATERIAL AND METHODS We examined 84 kidney biopsy samples obtained from 65 renal transplant recipients with dysfunctional graft (50 males, 15 females; average age 46.8 ± 11.9 years). 52 specimens were with signs of acute rejection and 32 without any rejection characteristics (diagnosed as glomerulonephritis, ATN and IFTA). Patients with acute rejection were divided into three groups: antibody-mediated rejection (AMR; n = 23), T cell mediated rejection (TCMR; n = 16) and combined antibody and T cell-mediated rejection (AMR + TCMR; n=13). The biopsy samples were taken from a dysfunctional graft at different time periods after kidney transplantation. The relative expression of total HLA-G mRNA in biopsy specimens was determined by real time RT-PCR. The correlation between HLA-G mRNA expression and dysfunctional graft state was investigated. The impact of different factors (post-transplantation interval, gender,mismatch, induction therapy and cold ischemia time) on relative expression of total HLA-G mRNA was also studied. RESULTS We have found that the levels of HLA-G transcripts in kidneys with rejection were higher than those in non-rejected but dysfunctional grafts (P = 0.0003). The highest levels of HLA-G mRNA were detected at combined AMR + TCMR rejection (P= 0.005). The time-course analysis of total HLA-G mRNA expression was also studied. In both dysfunctional graft groups (rejected and non-rejected) the lower levels of HLA-G transcripts were detected during early post-transplant period (1–3 months), however a substantial increase of HLA-G mRNA expression was observed after an extended period of time(N3 months). It was also revealed that antibody induction therapy may reduce HLA-G expression (P=0.0004) and in female samples were higher levels of HLAG transcripts than those in male recipients (P=0.003). It was found no significant impact of age, cold ischemic time, PRA (Panel Reactive Antibody) score, and a number of HLA-mismatches on HLA-G mRNA expression. CONCLUSIONS We have demonstrated that the expression of total HLA-GmRNA in renal grafts can be influenced by different factors such as clinical state of transplanted kidney, elapsed time after transplantation, gender and antibody induction therapy. We have proved that HLA-G mRNA expression was significantly higher in recipients with acute rejection in comparison to patients with dysfunctional but non-rejected grafts.