EBV infection of B-CLL cells in vitro potentiates their allostimulatory capacity if accompanied by acquisition of the activated phenotype

Restricted expression of EBV encoded proteins in in vitro infected CLL cells

CLL is not associated with EBV. CLL cells separated from blood express CR2, the complement receptor that serves also as EBV receptor. Thus CLL cells can be infected in vitro with the virus, however, in contrast to normal B lymphocytes, only rare CLL clones yield transformed lines. This is due to a restricted EBV encoded protein expression in the CLL cells, they express EBNAs, the virus encoded proteins that are localized in the nucleus, but not the cell membrane associated LMP-1, that is also pivotal for the virus induced transformation of B lymphocytes. This expression pattern seems to be unique to a defined B cell maturation window that is represented by the CLL cells. We named this restricted viral expression as Type IIb. Such B lymphocytes have been encountered in lymphoid tissues of infectious mononucleosis (IM) and in post transplant lymphoproliferative disease (PTLD). Moreover, they were shown in tissues of EBV infected "humanized" mice. The EBV encoded protein expression pattern may serve as a marker for the B cell differentiation stage from which CLL clones can develop.

Dendritic cells, pulsed with lysate of allogeneic tumor cells, are capable of stimulating MHC-restricted antigen-specific antitumor T cells

A variety of approaches have been used to deliver tumor-associated antigens (TAA) in conjunction with dendritic cells (DC) as cellular adjuvants. DC derived from monocytic precursors have been pulsed with whole tumor antigen using a variety of strategies and have been demonstrated to induce CD4+ and CD8+ antitumor responses. In the present study, monocyte-derived DC have been pulsed with lysate from an allogeneic melanoma cell line, A-375, and used to repeatedly stimulate T cells. The resultant T cells were examined for cytotoxic activity against A-375 targets as well as the HLA A2-positive melanoma cell line DFW. Uptake of FITC-labeled melanoma lysate by DC established that lysate of melanoma cells was efficiently endocytosed. Stimulation with lysate-pulsed DC resulted in strong proliferative responses by T cells, which could be inhibited by antibodies against both MHC class I and class II. T cells stimulated in vitro with lysate-pulsed DC demonstrated potent cytotoxicity against the melanoma targets which were blocked by antibodies against MHC class I. Lysate-pulsed DC also elicited IFN-gamma secretion by T cells as measured in an ELISPOT assay. We have also examined the ability of lysate-pulsed DC to present melanoma-associated antigens to T cells. ELISPOT assays with synthetic peptides of melanoma-associated antigens, such as gp100, mage1, NY-ESO, and MART-1, revealed that lysate-pulsed DC could stimulate T cells in an antigen-specific manner. The results demonstrate that lysate from allogeneic tumor cells may be used as a source of antigens to stimulate tumor-specific T cells in melanoma.

EBV infection induces expression of the transcription factors ATF-2/c-Jun in B lymphocytes but not in B-CLL cells

B cell type chronic lymphocytic leukaemia (B-CLL) cells carry the Epstein-Barr virus (EBV) receptor CD21 and can be infected in vitro with the virus. The infected cells exhibit an unusual EBV program, they express the nuclear proteins but not latent membrane protein 1 (LMP-1). Similar cells were encountered in lymphoid tissues of infectious mononucleosis (IM) patients and in lymphoproliferations of immunosuppressed patients. EBV infected B-CLL cells can be regarded as model for this viral program. In B cells the regulation of LMP-1 is executed mainly by EBV encoded nuclear antigen 2 (EBNA-2), interacting with several cellular proteins and these complexes bind to specific sequences in the LMP-1 promoter. ATF2 and c-Jun were shown to be among the interacting partners of EBNA-2. These molecules can be detected in experimentally infected B lymphocytes. We found c-Jun and/or phosphorylated ATF-2 (p-ATF-2) expression in some B-CLL ex vivo samples. They disappeared or their expression declined promptly in explanted cells, even if they were infected with EBV in vitro. Activation of the infected B-CLL cells by exposure to CD40L was accompanied by p-ATF-2 and c-Jun but not by LMP-1 expression. In one of three clones tested, subsequent treatment with histone deacetylase inhibitors (HDACi), TSA or n-butyrate, could induce LMP-1. Treatment with phorbol-12, 13-dibutyrate (PDB) induced LMP-1 expression in three of four clones. Neither the HDACi nor the PDB treated cells survived.

Dendritic cells loaded with apoptotic tumour cells induce a stronger T-cell response than dendritic cell-tumour hybrids in B-CLL

Dendritic cells (DC) are professional (specialised) antigen-presenting cells that can capture antigen from apoptotic tumour cells and induce MHC class I- and II-restricted responses. Also, DC fused with tumour cells may be effective for immune response induction. Both cell preparations may be considered as vaccine candidates in a therapeutic approach. We examined autologous T-cell activation by DC that had endocytosed leukaemic B-cell apoptotic bodies (Apo-DC) and compared it to the T-cell stimulatory capacity of DC that were fused with tumour cells. Following incubation, 22.6+/-6.2 (mean+/-s.e.m.) of DC had endocytosed leukaemic cells, while the frequency of DC-leukaemic cell hybrids was 10.5+/-2.6%. Apo-DC and hybrid cells both demonstrated the ability to stimulate a tumour-specific T-cell immune response in vitro. A T-cell proliferation response was also observed in four out of five CLL patients when using Apo-DC. However, fusion hybrids lacked the ability to elicit a proliferative response. Apo-DC also induced an IFN-gamma response, as did hybrid cells. The cytokine response induced by Apo-DC was significantly higher than that induced by fusion (P<0.05). This study shows that endocytosed apoptotic tumour cells induced a significantly stronger T-cell response than DC hybrids; and as such should be a better candidate for vaccine production.

Leukemia-associated monoclonal and oligoclonal TCR-BV use in patients with B-cell chronic lymphocytic leukemia

T-cell receptor-B-variable (TCR-BV) gene usage and the CDR3 size distribution pattern were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) in patients with B-cell chronic lymphocytic leukemia (B-CLL) to assess the T-cell repertoire. The use of TCR-BV families in CD4 and CD8 T cells stimulated with autologous activated leukemic cells was compared with that of freshly obtained blood T cells. Overexpression of individual TCR-BV families was found in freshly isolated CD4 and CD8 T cells. Polyclonal, oligoclonal, and monoclonal TCR-CDR3 patterns were seen within such overexpressed native CD4 and CD8 TCR-BV families. In nonoverexpressed TCR-BV families, monoclonal and oligoclonal populations were noted only within the CD8 subset. After in vitro stimulation of T cells with autologous leukemic B cells, analyses of the CDR3 length patterns showed that in expanded TCR-BV populations, polyclonal patterns frequently shifted toward a monoclonal/oligoclonal profile, whereas largely monoclonal patterns in native overexpressed TCR-BV subsets remained monoclonal. Seventy-five percent of CD8 expansions found in freshly obtained CD8 T cells further expanded on in vitro stimulation with autologous leukemic B cells. This suggests a memory status of such cells. In contrast, the unusually high frequency of CD4 T-cell expansions found in freshly isolated peripheral blood cells did not correlate positively to in vitro stimulation as only 1 of 9 expansions continued to expand. Our data suggest that leukemia cell-specific memory CD4 and CD8 T cells are present in vivo of patients with CLL and that several leukemia cell-associated antigens/epitopes are recognized by the patients' immune system, indicating that whole leukemia cells might be of preference for vaccine development.

High level of transgene expression in primary chronic lymphocytic leukemia cells using helper-virus-free recombinant Epstein-Barr virus vectors

OBJECTIVE

Epstein-Barr virus (EBV)-based vectors have favorable features for gene transfer, including a high transduction efficiency especially for B cells, large packaging capacity up to 150 kb pairs, and ability to infect postmitotic cells. Recombinant EBV was explored for transduction of primary human B-cell chronic lymphocytic leukemia (CLL) cells.

MATERIAL AND METHODS

EBV vectors deleted for all oncogenic sequences and encoding terminal repeats (TR) essential for encapsidation, the lytic origin of replication (oriLyt) for DNA amplification, and the enhanced green fluorescent protein (EGFP) were packaged using an optimized, helper-virus-free method. Infectious EBV virions encoding EGFP (EBV/EGFP) with an infectious titer up to 2 x 10(6) per milliliter were generated. Primary leukemic cells from 14 patients with CLL were successfully transduced with EBV/EGFP at a very low multiplicity of infection (< 1).

RESULTS

Transgene expression was detected in up to 85% of cells 48 hours after infection. Transduction was specifically mediated by EBV vectors because gene transfer was inhibited by an antibody (72A1) directed against the viral envelope glycoprotein gp350/220. Furthermore, transduction of CLL cells with packaged EBV vectors coding for EGFP but deleted for TR sequences (TR-) did not result in EGFP expression compared to TR+ vector constructs (p = 0.009).

CONCLUSION

Helper-virus-free EBV-based gene transfer vectors hold promise for development of genetic therapies for CLL patients.

Intracellular T cell cytokines in patients with B cell chronic lymphocytic leukaemia (B-CLL)

Analysis of cytokine production is a tool to functionally characterise T cells. In this study, spontaneous and polyclonal activation induced cytokine production in T cells were assessed by flow cytometry in patients with B-CLL. Patients with progressive disease had a significantly increased number of T cells spontaneously producing IL-2, IL-4 and GM-CSF as compared to healthy donors and patients with non-progressive CLL, which was not the case for TNF-alpha and IFN-gamma producing T cells. However, no difference in the frequency of T cells producing these cytokines was seen comparing patients with non-progressive disease to control donors. Polyclonal activation of B-CLL T cells in vitro induced an increased proportion of T cells producing these five cytokines in patients as well as in control donors, indicating that T cells in CLL patients might have a relatively well preserved functional capacity. However, the increase in GM-CSF, TNF-alpha and IL-4 producing T cells was more marked in CLL patients than in controls. Furthermore, following activation, a higher frequency of cytokine-producing T cells was noted in patients with progressive disease as compared to those with non-progressive disease. The augmented number of cytokine-producing T cells in CLL may indicate an up-regulated capability of T cells to secrete cytokines, especially in patients with progressive CLL. The increased production of the T cell derived cytokines GM-CSF, TNF-alpha, IL-4 and IL-2 is interesting, as these cytokines have previously been shown to support growth of B-CLL leukaemic cells in vitro and as T cells might specifically recognise the autologous leukaemic B cells in vivo. The findings may suggest a role for T cells in the pathogenesis of B-CLL.

Significance of phosphotyrosine proteins, Bcl-2 and p53 for apoptosis in resting B-chronic lymphocytic leukemia (CLL) cells

Signal transduction and apoptosis in B-cell chronic lymphocytic leukemia (CLL) cells with a post-germinal center (GC) phenotype were studied. Specific activation of the cells was induced by a combination of soluble anti-CD40 monoclonal antibody and interleukin-4 (CD40/IL-4) and nonspecific activation with a combination of phytohemagglutinin, phorbol-12-myristate-13-acetate and ionomycin (chemical mixture). Less than 5% of these leukemia cells entered the cell cycle after activation, as indicated by the number of cells in G0/G1 phase. The protein tyrosine phosphorylation pattern and expression of the Bcl-2 protein were specific in ex vivo CLL cells of each individual patient. Expression of the p53 protein was not detectable in these leukemia cells. Cross-linking of the CD40/IL-4 receptors on CLL cells significantly upregulated phosphotyrosine proteins and the p53 protein. In the presence of chemical mixture, downregulated phosphotyrosine proteins were detected. Alterations in Bcl-2 expression were independent of cross-linking with CD40/IL-4 or chemical mixture. A high frequency of apoptotic cells was detected in cells that had downregulated phosphotyrosine proteins and Bcl-2 protein. There was no correlation between induction of apoptosis and expression of p53 protein. Our results suggest that apoptosis in resting leukemia cells could occur prior to the cell cycle progression. Alterations in phosphotyrosine proteins and Bcl-2 but not p53 might play an important role in the regulation of apoptosis in resting G0/G1 memory post-GC B-CLL cells.

Autologous T lymphocytes may specifically recognize leukaemic B cells in patients with chronic lymphocytic leukaemia

This study analysed a naturally occurring specific cellular immunity against tumour cells in chronic lymphocytic leukaemia (CLL) patients. Five out of eight patients had blood T lymphocytes able to recognize spontaneously and specifically the autologous tumour B cells (proliferation assay). In these five patients, detection of cytokines by real-time reverse transcription polymerase chain reaction (RT-PCR) revealed that granulocyte-macrophage colony-stimulating factor (GM-CSF) was the most abundant cytokine gene expressed by the T cells that recognized the autologous tumour B cells. Other activated cytokine genes were gamma-interferon (IFN), interleukin (IL)-2 and tumour necrosis factor (TNF)-alpha, but not IL-4. This profile suggests a type 1 anti-B-CLL T-cell response. CD80 and CD54 were relatively downregulated on the native tumour B cells compared with control normal B cells. Upregulation of CD80 on the leukaemic cells was mandatory for the induction of such a specific T-cell response. CD80 and CD54 monoclonal antibodies inhibited the specific T-cell DNA synthesis proliferation. The proliferative T-cell response was either MHC class I or class II restricted (inhibition by monoclonal antibodies). The specific cytokine gene expression could be found in isolated CD4, as well as CD8, T-cell subsets. This study demonstrated the presence of a potential natural specific CD4, as well as a CD8 type 1 T-cell immunity against the leukaemic CLL tumour B cells in CLL. A further detailed analysis of the spontaneous anti-CLL T-cell immunity is warranted that may facilitate the development of effective anti-tumour vaccines in CLL.

LMP-1, the Epstein-Barr virus-encoded oncogene with a B cell activating mechanism similar to CD40

Many details in the expression pattern of Epstein-Barr virus (EBV)-encoded proteins, their role in blast and growth transformation in infected B lymphocytes are known, but 'black holes' still exist. The two main types of virus-B lymphocyte interactions are denoted as Type I and Type III. These are characterized by the difference in the EBV protein expression which is related to the phenotype of the cell. The difference was first detected in comparisons between Burkitt lymphoma cells (BL) and lymphoblastoid cell lines, LCLs, which arise from normal B lymphocytes after experimental infection and are growth transformed by EBV. A third type of interaction can be seen in B-CLL cells which carry the EBV receptor CD21 and can be thus infected with the virus in vitro. The infected cells express the EBV-encoded proteins with a pattern which is different from the above mentioned two types, in that they express the nuclear proteins but not the membrane localized LMP-1. Importantly, the infected B-CLL cells do not enter DNA synthesis and they do not growth transform. Normal B lymphocytes with similar expression pattern have been seen in analysis of the lymphoreticular tissues of patients which responded to the primary EBV infection with development of the infectious mononucleosis symptoms.

Recognition of B-CLL cells experimentally infected with EBV by autologous T lymphocytes

We compared 5-day-old cultures of two B-CLL clones experimentally infected with EBV for their interaction with autologous T lymphocytes. The clone which was strongly activated by the virus stimulated autologous T cells. It was also damaged by the cytotoxic T cells which were generated in mixed cultures with autologous lymphoblastoid cell lines (LCL). Cultured, non-infected CLL cells were not lysed by these effectors. The other B-CLL clone, which was activated to considerably lesser extent by the virus, did not stimulate the autologous T lymphocytes. While, also in this case cytotoxic function was generated in the mixed T cell-LCL culture, the effectors did not damage the EBV-infected CLL cells. The results with B-CLL cells can be regarded as a model for the EBV genome carrier normal B lymphocytes. They substantiate the current concept that such cells persist in seropositive healthy individuals undisturbed by the specific immune response as long as they maintain the phenotype of resting cells. However, after activation they can be recognized and eliminated by T cells.

B-CLL cells with unusual properties

In studies concerning the interaction of B-CLL cells and Epstein-Barr virus (EBV), we encountered one patient whose cells had several unusual properties. In addition to the B-cell markers, the CLL cells expressed the exclusive T-cell markers CD3 and CD8 and carried a translocation t(18,22)(q21;q11), involving the bcl-2 and Ig lambda loci. The patient represents the 4th reported CLL case with this translocation. The CLL cells could be infected and immortalized by the indigenous and by the prototype B958 virus in vitro. The T-cell markers were not detectable on the established lines. In all experiments the immortalized lines originated from the CLL cells. Their preferential emergence over virus-infected normal B cells may be coupled to the high expression of the bcl-2 gene due to the translocation. In spite of the sensitivity of CLL cells to EBV infection in vitro, no EBNA-positive cells were detected in the ex vivo population. In vitro, we could generate cytotoxic function in T-lymphocyte cultures which acted on autologous EBV-infected CLL cells. Therefore we assume that if such cells emerged in vivo they were eliminated by the T-cell response.

B-CLL cells experimentally infected with EBV enter DNA synthesis, produce cytokines and stimulate T-lymphocytes

Several B-chronic lymphocytic leukemia (B-CLL) clones, represented by different patients can be infected with EBV in vitro. A proportion of the cells becomes activated by the virus, but they rarely yield immortalized cell lines. We used cells from two B-CLL patients which differed in sensitivity to EBV infection. After 7 days in culture, we studied the CLL cells exposed to the B-cell activators Staphylococcus aureus, IL-2 and/or to EBV for expression of the activation markers CD23, CD39 and the adhesion and costimulatory molecules CD54 and CD80, for DNA synthesis, for production of various cytokines and for capacity to stimulate autologous and allogeneic T-lymphocytes. Generally the frequency of cells expressing cytokines in the cytoplasm correlated with the activation status of the populations and with their capacity to stimulate T-cells. It is likely that the difference between the clones with regard to sensitivity to the viral infection, is determined by the maturation state of the CLL cells. It may therefore reflect the variation in the response within a normal B-cell population. The results obtained in the present and in our earlier experiments with EBV provide information concerning the events after primary EBV infection in vivo. The T-lymphocyte stimulatory capacity of the infected CLL cells may be considered as an in vitro correlate to the syndrome of infectious mononucleosis. The detection of cytokines in the infected B-CLL cells suggests that their production by the B-blasts contributes to the level of T-lymphocytosis induced by the primary infection.

Epstein Barr virus (EBV)-carrying cells of a chronic lymphocytic leukemia (CLL) subpopulation express EBNA1 and LMPs but not EBNA2 in vivo

We have previously described an exceptional CLL patient, P.G., whose leukemic cell population contained a small fraction of Epstein-Barr virus (EBV)-carrying cells. These cells grow directly into permanent cell lines in vitro. Using RT-PCR analysis, we now show that the in vivo EBV-carrying CLL cells expressed EBNAI, LMPI, LMP2a and 2b, but not EBNA2, in 4 of 4 blood samples obtained during the last 3 years of the patient's life. Our data also show that the CLL cells used a promoter in the F/Q, but not the W or C, region. This is consistent with the fact that CLL cells resemble resting lymphocytes rather than immunoblasts. Expression of LMP1 and LMP2b differs from the exclusive EBNAI and LMP2a expression of normal resting B cells, however, and corresponds to the state defined as latency II. This form of latency was until now detected only in EBV-carrying non-B cells in vivo. Our data show that a B-cell subtype can also show this expression pattern in vivo.

Detection of two Epstein-Barr-virus (EBV)-carrying leukemic cell clones in a patient with chronic lymphocytic leukemia (CLL)

The leukemic-cell population of one CLL patient, PG, was found to contain a sub-set of EBV-genome-carrying cells. It was detected directly by the expression of EBNA (EBV-encoded nuclear antigen) and by its capacity to grow in vitro. The proportion of EBNA-positive cells (0.1%) was maintained constantly during the period of this study, the final 3 years of the patient's life. EBV-carrying clonal sibling B-cell lines were established on 5 occasions. They had identically rearranged JH bands and chromosomal markers corresponding to the ex vivo CLL cells. Analysis of the viral episomes in the lines proved that they were the descendants of one cell. On the last occasion of blood sampling, 8 B-cell lines were established; 4 of these contained the same clonal markers as the previous lines, while 4 other lines belonged to another clone with identical JH rearrangement. Their abnormal karyotypes were different from the first clone. The chromosomal markers were only partly identical, suggesting secondary diversifications. The EBV sub-strain carried by this group of lines was different from the sub-strain of the first clone, as judged by the EBNA size distributions (EBNOtype) and EBV-DNA analysis. Analysis of the terminal repeat in the viral episomes also showed that the first and the second set of clones represented 2 independent EBV-infection events in vivo.