Natural killer cell sensitivity of human lymphoid lines of B-cell origin does not correlate with tumorigenicity or with the expression of certain differentiation markers

HLA-A11-mediated protection from NK cell-mediated lysis: role of HLA-A11-presented peptides

The capacity of MHC class I to protect target cells from NK is well established, but the mechanism by which these molecules influence NK recognition and the physical properties associated with this function remain poorly defined. We have examined this issue using as a model the HLA-A11 allele. HLA-A11 expression correlated with reduced susceptibility to NK and interferon-activated cytotoxicity in transfected sublines of the A11-defective Burkitt's lymphoma WW2-BL and the HLA class I A,B-null C1R cell line. Protection was also achieved by transfection of HLA-A11 in the peptide processing mutant T2 cells line (T2/A11), despite a very low expression of the transfected product at the cell surface. Induction of surface HLA-A11 by culture of T2/A11 cells at 26 degrees C or in the presence of beta 2m did not affect lysis, whereas NK sensitivity was restored by culture in the presence of HLA-All-binding synthetic peptides derived from viral or cellular proteins. Acid treatment rendered T2/A11 and C1R/A11 cells sensitive to lysis, but protection was restored after preincubation with peptide preparations derived from surface stripping of T2/A11 cells. Similar peptide preparations from T2 cells had no effect. The results suggest that NK protection is mediated by HLA-A11 molecules carrying a particular set of peptides that are translocated to the site of MHC class I assembly in the ER in a TAP-independent fashion.

Search for the critical characteristics of phenotypically different B cell lines, Burkitt lymphoma cells and lymphoblastoid cell lines, which determine differences in their functional interaction with allogeneic lymphocytes

Burkitt lymphoma (BL) lines can be grouped according to phenotypic characteristics. Group I cells exhibit the phenotype of resting B cells and grow as single cells. Such lines can be Epstein-Barr-virus(EBV)-negative or -positive. Group II and group III cells are always EBV-positive, they express B cell activation markers, grow in aggregates and resemble in varying degrees lymphoblastoid cell lines (LCL). We studied three groups of BL lines for their capacity to interact with allogeneic lymphocytes. The results showed that as long as the lines have the group I phenotype, they do not stimulate allogeneic T lymphocytes irrespective whether they carry the EBV genome. The group II and III cells are stimulatory. Generally there was no correlation between sensitivity ot lymphocyte-mediated lysis and the phenotype of the lines. In one set of lines, the group I cells had higher sensitivity to both natural killer and lymphokine-activated killer effectors compared to the group II or III lines. However, such correlation could not be seen with the other two sets of lines. Among the phenotypic features investigated, expression of the adhesion molecules LFA-1 and LFA-3 correlated with the tendency for cell aggregation.

Down-regulation of class I HLA antigens and of the Epstein-Barr virus-encoded latent membrane protein in Burkitt lymphoma lines

Epstein-Barr virus (EBV)-carrying Burkitt lymphoma (BL) cells are relatively or completely resistant to the lytic effect of major histocompatibility complex class I HLA antigen-restricted cytotoxic T lymphocytes (CTLs) generated by stimulating lymphocytes of EBV-seropositive donors with the autologous EBV-transformed lymphoblastoid cell line (LCL). We previously found that EBV-negative and EBV-carrying BL lines derived from HLA-A11-positive donors were not only resistant to lysis by the HLA-A11-restricted CTL generated by stimulation with the autologous LCL, but also to HLA-A11-specific CTL derived from lymphocytes of an EBV-seronegative donor stimulated with an allogeneic LCL. Using the same and additional cell lines, we now show that the CTL resistance of the BL lines is probably due to a selective down-regulation of HLA-A11. We also show that the EBV-encoded latent membrane protein is expressed at a lower level in the EBV-carrying BL lines than in EBV-transformed LCLs. Only one of eight in vitro EBV-converted BL lines that shifted to a more LCL-like growth pattern expressed LMP at a high level. This line also reexpressed the HLA-A11 antigen that was undetectable in its EBV-negative progenitor. Our findings suggest that the typical BL cell phenotype is associated with low expression of both proteins.

Differential activation of cytotoxic responses by Burkitt's lymphoma (BL)-cell lines: relationship to the BL-cell surface phenotype

Epstein-Barr (EB) virus-positive Burkitt's lymphoma (BL) cell lines, recently established from tumour biopsies and displaying chromosomal translocations indicative of their malignant origin, can be classified into two broad sets: (i) lines growing predominantly as single cells/small clumps whose cell surface markers remain close to those of the original tumour cells, and (ii) lines whose growth pattern and cell surface markers have progressed closer to the more "lymphoblastoid" phenotype displayed by all in vitro transformed B-cell lines (LCLs) of normal origin. When compared to LCLs derived from normal B cells of the same patient, BL-cell lines in set (i) generally showed a lower expression of HLA class I and class II antigens and a reduced ability to activate both allospecific and nonspecific (natural killer-like) cytotoxic responses when cocultured with peripheral blood lymphocytes. By contrast, the HLA antigen expression and in vitro stimulatory capacity of most BL-cell lines in set (ii) were much closer to the values displayed by their corresponding LCLs. Since set (i) rather than set (ii) BL cell lines are phenotypically representative of the malignant cells as they exist in vivo, this work suggests that successful outgrowth of the virus-carrying tumour cells in the affected host may be facilitated by the inability of these cells to stimulate strong cytotoxic responses.

Differentiation-dependent sensitivity of human B-cell-derived lines to major histocompatibility complex-restricted T-cell cytotoxicity

Sets of Burkitt lymphoma lines and Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCLs) derived from the same individuals were compared for sensitivity to cytotoxic T-lymphocyte (CTL) clones. Major histocompatibility complex class I antigen-restricted CTL clones were generated by stimulating the lymphocytes of an EBV-seropositive individual with the autologous LCL. One clone (BK-20) lysed the autologous and allogeneic HLA-A11-expressing LCLs but not mitogen-induced B lymphoblasts. Thus the clone was selectively cytotoxic for LCLs. Allospecific CTL clones directed against the HLA-A11 antigen were generated from an EBV-seronegative individual. One clone (WP-36) was selectively cytotoxic for the appropriate allospecific LCL, whereas another clone (WP-21) lysed also T and B lymphoblasts. None of the four Burkitt lymphoma lines established in parallel with the CTL-sensitive LCLs were lysed. Two of the Burkitt lymphoma lines were EBV-negative, and EBV-positive sublines were derived from these by in vitro infection. One but not the other of the two convertants became sensitive to all three types of CTL clones. The CTL-sensitive converted line had also acquired some LCL characteristics: increased cell size, aggregation, and a shift in several of the B-cell-specific surface markers. The CTL-resistant convertant expressed EBV antigens but showed no phenotypic change. These findings suggest that the cellular phenotype plays a decisive role in the sensitivity of B-cell-derived lines to the lytic effect of LCL-selective autologous and allogeneic CTLs.