Regulation of hematopoiesis in vitro by alloreactive natural killer cell clones.

Natural killer (NK) cells lyse autologous and allogeneic target cells even in the absence of major histocompatibility complex (MHC) class I antigens on the target cells. Recently, however, human allospecific NK cell clones have been generated that recognize at least five distinct specificities inherited recessively and controlled by genes linked to the MHC. Because the genetic specificity of these alloreactive NK cells in vitro appears analogous to that of in vivo NK cell-mediated murine hybrid resistance, i.e., the rejection of parental bone marrow in irradiated F1 animals, we tested the ability of human alloreactive NK clones to recognize allogeneic hematopoietic progenitor cells. NK cells from two specificity 1 alloreactive NK clones, ES9 and ES10, significantly and often completely suppressed colony formation by purified peripheral blood hematopoietic progenitor cells from specificity 1-susceptible donors, but had no significant effect on the cells of specificity 1-resistant donors. Activated polyclonal NK cells were less efficient than the NK clones in inhibiting colony formation and had a similar effect on cells from both specificity 1-susceptible and -resistant donors. The alloreactive NK clones produced cytokines with a suppressive effect on in vitro hematopoiesis, such as interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha), when exposed to phytohemagglutinin blasts from specificity 1-susceptible, but not -resistant donors. However, the mechanism by which alloreactive NK cells inhibit colony formation is more consistent with a direct cytotoxic effect than with the production of inhibitory cytokines because antibodies (anti-IFN-gamma, alpha-TNF-alpha, and -lymphotoxin) that completely blocked the inhibition by polyclonal NK cells had only a minimal effect on the inhibition by the alloreactive clones. Moreover, the alloreactive clones were directly cytolytic in a 51Cr release assay against enriched preparations of peripheral blood progenitor cells from specificity 1-susceptible donors. These data indicate that the alloreactive NK cells are likely the human counterpart of the cells mediating murine hybrid resistance and that these cells might play clinically important roles in rejection or in graft-versus-leukemia reactions after allogeneic bone marrow transplantation.

Identification of four subsets of human CD3-CD16+ natural killer (NK) cells by the expression of clonally distributed functional surface molecules: correlation between subset assignment of NK clones and ability to mediate specific alloantigen recognition.

In previous studies we identified a surface molecule (termed GL183) capable of mediating cell activation and selectively expressed by a subset of human CD3-CD16+ natural killer (NK) cells. In this study we analyzed whether other subset-specific functional molecules were expressed in GL183- NK cells. To this end, mice were immunized with the PE29 (CD3-CD16+GL183-) NK clone. Monoclonal antibodies (mAbs) were selected by screening the hybridoma supernatants for their ability to trigger the cytolytic activity of clone PE29 against the human myelomonocytic leukemia U937. The EB6 mAb (IgG1) triggered the PE29 clone, but not a GL183+ clone used as a control. EB6+ cells ranged between 1 and 13% of peripheral blood lymphocytes and were largely included in the CD3-CD16+CD56+ cell populations (only less than 2% of EB6+ cells were CD3+). Analysis of resting or activated CD3-CD16+ populations, or clones for the expression of EB6 or GL183 mAbs, allowed us to identify four distinct, phenotypically stable, NK subsets (EB6+GL183-; EB6+GL183+; EB6-GL183+; EB6-GL183-). Similar to GL183 mAb, the EB6 mAb selectively triggered the NK subset expressing the corresponding surface antigen to lyse human tumor cell lines including U937, IGROV-I, M14, and A549. In addition, EB6 mAb sharply inhibited the cytolytic activity of EB6+ clones against P815, M12, and P3U1 murine target cells. In EB6+GL183+ ("double-positive") clones both EB6 and GL183 mAb inhibited the redirected killing of P815 cells induced by anti-CD16, anti-CD2 mAbs and phytohemagglutinin (PHA). Similar to GL183 molecules, molecules precipitated by EB6 mAb were represented by either single 58-kD chain or double chains of 55 and 58 kD (with no detectable differences in EB6+GL183- or EB6+GL183+ clones). In sequential immunoprecipitation experiments using the double-positive clones CEG52 and CA25.50, preclearing of cell lysates with EB6 or GL183 mAb removed only EB6 or GL183 molecules, respectively, thus indicating that the two antigenic determinants are carried by two distinct molecules. Peptide map analysis indicated that EB6 (or GL183) molecules precipitated from double-positive clones were identical to the corresponding molecules isolated from single-positive ones. On the other hand, comparison of the EB6 and GL183 maps revealed peptides that were unique to each molecule, although most of the major peptides migrated to identical positions. We further investigated whether correlation existed between the phenotypic assignment of NK clones and their ability to mediate specific lysis of normal allogeneic cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Antigen recognition by human T cell receptor gamma-positive lymphocytes. Specific lysis of allogeneic cells after activation in mixed lymphocyte culture.

These experiments were designed to define the ability of human TCR-gamma+ cells to recognize allogeneic cells. TCR-gamma+-enriched populations were obtained by treating peripheral blood E-rosetting cells with anti-CD4 and anti-CD8 mAbs. The resulting populations were CD2+4-8- expressed variable proportions of CD3+ cells (40-90%), and did not react with the WT31 mAb, which is specific for a framework determinant of the alpha/beta heterodimer that serves as receptor for antigen on most human T lymphocytes. After mixed lymphocyte culture with irradiated allogeneic cells for 7 d and 3 additional days in rIL-2 (100 U/ml), cells underwent proliferation in three of five individuals tested. In addition, MLC-derived cells lysed 51Cr-labeled PHA-induced blasts derived from the allogeneic cells used as stimulator, but not allogeneic unrelated or autologous blast cells. No cytotoxicity against autologous or allogeneic target cells could be induced by culturing CD3+4-8-WT31- lymphocytes in MLC with irradiated autologous cells. Surface iodination of allogeneic MLC-activated CD3+4-8-WT31- cells followed by lysis in 1% digitonin and immunoprecipitation with anti-CD3 mAb indicated that the CD3-associated molecules consisted of a major 45-kD band and a minor band of 43 kD. Northern blot analysis showed that mRNA for the gamma chain was expressed at high levels, whereas mRNAs for alpha and beta chains were missing. These data support the notion that TCR-gamma rather than TCR-alpha/beta is expressed in allospecific CD3-4-8-WT31- cell populations. Clones were further derived from MLC-stimulated CD3+4-8-WT31- populations. All the seven clones studied in detail maintained the surface phenotype as well as the cytolytic pattern of the original MLC populations, thus only specific allogeneic PHA-induced blasts were lysed. NK-sensitive as well as NK-resistant tumor targets were variably susceptible to lysis; therefore, specific cytolytic activity against allogeneic cells was not necessarily linked to the expression of MHC-nonrestricted cytotoxicity against tumor cells.

A monoclonal antibody specific for a common determinant of the human T cell receptor gamma/delta directly activates CD3+WT31- lymphocytes to express their functional program(s).

In an attempt to select mAbs specific for human TCR-gamma/delta, a polyclonal CD3+ 4-8-WT31- (TCR-gamma/delta+) cell line (MV1) was used for mice immunization. An mAb, termed BB3, reacted with MV1 cells but not with a large panel of CD3+ WT31+ (TCR-alpha/beta+) cell populations or clones. In addition, BB3 mAb reacted with the majority of CD3+ WT31- clones derived from six different donors. Double-color fluorescence experiments and FACS analysis showed that BB3+ cells were restricted to the CD3+ fraction of peripheral blood lymphocytes; in addition, in several donors the percentages (0.5-8% of total PBL) of BB3+ cells paralleled those of CD3+ WT31- cells. Surface molecules recognized by BB3 were susceptible to antibody-induced modulation; in addition, cell treatment with either BB3 or anti-CD3 mAb caused the simultaneous downregulation of the two molecules. That BB3 molecules are physically linked to CD3 antigen was further supported by immunoprecipitation experiments. Thus, under conditions that preserve the TCR-CD3 association, both BB3 and anti-CD3 mAb precipitated from 125I-labeled MV1 cells the same set of molecules. These consisted in the 18-28-kD CD3 molecules and in three bands of approximately 44, 42, and 38 kD under reducing conditions. When cell lysis was performed in 1% NP-40, the molecules immunoprecipitated by BB3 mAb were represented by an 80-kD band under nonreducing conditions, which resolved, under reducing conditions, in the three 44-, 42-, and 38-kD bands. Similar disulphide-linked forms of the TCR molecules were revealed in all of the other eight CD3+ WT31- BB3+ clones analyzed. Analysis of TCR molecules by electrophoresis (NEPHGE) showed that BB3 or anti-CD3 precipitated a 44-kD molecule displaying a basic PI (approximately 7.5) and two more acidic proteins (PI approximately 6) with a mol mass of 42 and 38 kD. Studies aimed to define whether stimuli directly acting on TCR-gamma/delta could induce CD3+ WT31- cell activation revealed that (a) In the presence of PMA, soluble BB3 mAb induced IL-2 production by MV1 cell line and by three other CD3+ WT31- BB3+ clones analyzed. (b) BB3 mAb-producing hybridoma used as triggering target, was efficiently lysed by CD3+ WT31- BB3+ effector cells (but not by CD3+ WT31+ BB3- conventional CTL). (c) Soluble BB3 mAb induced CD3+ WT31- BB3+ effector cells to lyse the Fc receptor-positive P815 target cells. (d) BB3-TCR-gamma/delta interaction on CD3+ WT31- BB3+ cells induced a rapid increase of [Ca2+]i levels, similar to that observed in response to anti-CD3 mAbs.

Human peripheral blood lymphocytes bearing T cell receptor gamma/delta. Expression of CD8 differentiation antigen correlates with the expression of the 55-kD, C gamma 2-encoded gamma chain.

We analyzed the CD3-associated molecules present on peripheral blood-derived TCR-gamma/delta+ clones that express CD8 surface antigens. Clones were derived by limiting dilution from CD3+WT31- FACS-purified populations derived from several donors. Eight of greater than 300 TCR-gamma/delta+ clones analyzed expressed CD8 and reacted with delta-TCS-1 mAb. Cell numbers suitable for more detailed analyses could be obtained from four clones, including one derived from thymus. Analysis of CD3-associated TCR molecules immunoprecipitated by anti-Leu-4 (anti-CD3) mAb under conditions that preserve the CD3/TCR association (1% digitonin) showed a predominant 55-60-kD molecule both under reducing and nonreducing conditions. On the other hand, the delta-TCS-1-reactive molecules immunoprecipitated from 25 CD3+ delta-TCS-1+ CD8- clones, in all instances, displayed a 40-44-kD mol mass. In two-dimensional PAGE, TCR-gamma molecules precipitated from delta-TCS-1+ CD8+ clones appeared more acidic than those of BB3+ or delta-TCS-1+ CD8+ clones. Southern analysis confirmed that this type of non-disulphide-linked TCR-gamma/delta is also coded for by the C gamma 2 gene segment.

Specific recognition of human CD3-CD16+ natural killer cells requires the expression of an autosomic recessive gene on target cells.

We analyzed the recently defined ability of CD3-CD16+ cells to specifically recognize and lyse normal allogeneic target cells (PHA-induced blasts). The susceptibility to lysis by a given alloreactive natural killer (NK) clone ("1 anti-A") was expressed by PHA blasts derived from 9 of 38 random donors analyzed. In all instances, the specific lysis of "susceptible" target cells was greater than 35% while that of "nonsusceptible" targets was less than 6% at an E/T cell ratio of 5:1. In addition to 1 anti-A, A anti-1 specific CD3-CD16+ clones could also be isolated from the reverse MLC combination. The relationship existing between lysis of normal allogeneic cells or tumor cells by the same CD3-CD16+ effector cell has been investigated: 1 anti-A specific CD3-CD16+ clones lysed PHA blasts of three of six cancer patients, while they lysed fresh tumor cells (ovarian carcinoma) from all six patients. The type of inheritance of the character "susceptibility to lysis" was analyzed in representative families. This analysis revealed that the character is inherited in an autosomic recessive fashion, and it is therefore different from MHC. We further investigated the type of segregation of the opposite character "resistance to lysis" (which is inherited in a dominant mode). The finding that this character segregated in all donors expressing given MHC haplotypes indicated that the gene regulating the expression of the NK-defined alloantigen is present on chromosome 6.

Specific lysis of allogeneic cells after activation of CD3- lymphocytes in mixed lymphocyte culture.

Human CD3- lymphocyte populations were obtained by treating peripheral blood lymphocytes with mAbs directed to CD3, CD4, and CD8 surface antigens. The resulting populations were cultured with irradiated allogeneic cells; at day 4, 100 U/ml IL-2 were added and cultures continued for an additional 10 d. The resulting populations were CD3-CD2+CD7+ and displayed cytolytic activity against PHA-induced blast cells bearing the stimulating alloantigens but not against autologous or unrelated allogeneic blast cells. When CD3- populations were cultured with irradiated autologous cells, no cytolytic activity could be detected either against autologous or allogeneic blast cells. On the other hand, K562 target cells were lysed by both MLC-derived CD3- cell populations regardless of the origin (autologous or allogeneic) of the stimulating cells. CD3- clones were further derived from MLC-stimulated CD3- populations. These clones displayed a cytolytic pattern similar to the original MLC populations as only specific PHA blasts could be lysed. These clones did not express detectable surface TCR-alpha/beta or -gamma/delta molecules and lacked productive mRNA for TCR alpha and beta chains, while small amounts of TCR-gamma mRNA were detectable in one of four clones tested. Also mRNA for CD3 gamma and delta chains were undetectable in all clones, however, CD3 epsilon mRNA was consistently present.

Evidence of a natural killer (NK) cell repertoire for (allo) antigen recognition: definition of five distinct NK-determined allospecificities in humans.

Previous studies indicated that CD3-CD16+ natural killer (NK) cells are capable of specific alloantigen recognition. Thus, alloreactive NK clones lysed normal allogeneic target cells (phytohemagglutinin [PHA] blasts) bearing the stimulating alloantigen but did not lyse autologous cells or the majority of unrelated allogeneic cells. In this study we investigated whether NK cells isolated from single individuals could exhibit different allospecificities. To this end, we derived large numbers of CD3-CD16+ clones (in the presence of PHA) from fresh CD3- peripheral blood lymphocytes. Cloning efficiencies ranged between 5 and 10%. The resulting CD3-CD16+ clones were tested for their reactivity against a panel of allogeneic PHA blasts (derived from six donors). In a given individual (A), four distinct groups of clones could be identified according to their pattern of reactivity (over 400 clones have been analyzed). Clones that could be assigned to one or another group of specificity represented 36% of all clones derived from this donor. The remaining clones did not display cytolytic activity against any of the allogeneic target cells used in the panel. None of the clones lysed autologous (A) PHA blasts, yet, these cells were lysed by the representative clones G10 and H12 specific for donor A. Clones displaying a cytolytic pattern of reactivity identical to that defined for donor A were present in other individuals studied, however not all groups of allospecific clones were necessarily represented in different individuals. Allospecific clones belonging to the various groups were homogeneous in the expression of EB6/GL183-triggering surface molecules, and could thus be assigned to one or another of the previously defined subsets of NK cells. Genetic analysis of the new NK-defined alloantigens was performed in representative families. The corresponding characters were found to segregate independently and, at least for three of them, an autosomic recessive type of inheritance could be demonstrated. Moreover, the comparative analysis of the segregation of the major histocompatibility complex haplotypes and the recessive or dominant alleles of the genes governing the five specificities analyzed indicated that there is no independent sampling between the two genetic traits, thus suggesting that the genes regulating the NK-defined specificities are carried by chromosome 6. Finally, some donors expressed more than one specificity, thus providing evidence for an NK-defined complex haplotype.

Involvement of HLA class I alleles in natural killer (NK) cell-specific functions: expression of HLA-Cw3 confers selective protection from lysis by alloreactive NK clones displaying a defined specificity (specificity 2).

This study was designed to identify the target molecules of the natural killer (NK) cell-mediated recognition of normal allogeneic target cells. As previously shown, the gene(s) governing the first NK-defined allospecificity (specificity 1) were found to be localized in the major histocompatibility complex region between BF gene and HLA-A. In addition, the analysis of a previously described family revealed that a donor (donor 81) was heterozygous for three distinct NK-defined allospecificities (specificities 1, 2, and 5). HLA variants were derived from the B-Epstein-Barr virus cell line of donor 81 by gamma irradiation followed by negative selection using monoclonal antibodies specific for the appropriate HLA allele. Several variants were derived that lacked one or more class I antigen expressions. These variants were analyzed for the susceptibility to lysis by NK clones recognizing different allospecificities. The loss of HLA-A did not modify the phenotype (i.e., "resistance to lysis"). On the other hand, a variant lacking expression of all class I antigens became susceptible to lysis by all alloreactive clones. Variants characterized by the selective loss of class I antigens coded for by the maternal chromosome became susceptible to lysis by anti-2-specific clones. Conversely, variants selectively lacking class I antigens coded for by paternal chromosome became susceptible to lysis by anti-1 and anti-5 clones (but not by anti-2 clones). Since the Cw3 allele was lost in the variant that acquired susceptibility to lysis by anti-2 clones and, in informative families, it was found to cosegregate with the character "resistance to lysis" by anti-2 clones, we analyzed whether Cw3 could represent the element conferring selective resistance to lysis by anti-2 clones. To this end, murine P815 cells transfected with HLA Cw3 (or with other HLA class I genes) were used as target cells in a cytolytic assay in which effector cells were represented by alloreactive NK clones directed against different specificities. Anti-2-specific clones efficiently lysed untransfected or A2-, A3-, and A24-transfected P815 cells, while they failed to lyse Cw3-transfected cells. NK clones recognizing specificities other than specificity 2 lysed untransfected or Cw3-transfected cells. Thus, the loss of Cw3 resulted in the de novo appearance of susceptibility to lysis, and transfection of the HLA-negative P815 cells with Cw3 resulted in resistance to lysis by anti-2 clones. Therefore, we can infer that Cw3 expression on (both human and murine) target cells confers selective protection from lysis mediated by anti-2 NK clones.

Alloantigen recognition by two human natural killer cell clones is associated with HLA-C or a closely linked gene.

Human natural killer (NK) cells with the CD3- CD16+ phenotype recognize allospecificities on normal T-cell blasts. The NK-defined specificity 1 (NK-1) is recessively inherited and has been mapped to the major histocompatibility complex between the complement gene cluster and HLA-A. A gene for NK-1, however, has not been identified. Here we demonstrate that NK-1 and the recently defined NK specificity 2 (NK-2) are reciprocally associated with homozygosity for a diallelic polymorphism at amino acid positions 77 and 80 in the putative peptide-binding site of HLA-C (P less than 10(-5)). NK-cell recognition of allogeneic cells may, therefore, be controlled by HLA-C itself or by a closely linked gene(s), which dominantly prevents (resistance alleles) or recessively permits (susceptibility alleles) recognition of still-unknown target determinants.

Specificity of human T lymphocytes expressing a gamma/delta T cell antigen receptor. Recognition of a polymorphic determinant of HLA class I molecules by a gamma/delta clone.

Alloreactive clones expressing T cell receptor (TcR) gamma/delta were derived by limiting dilution from CD3+ CD4- CD8- WT31- populations stimulated in allogeneic mixed lymphocyte culture. These clones specifically lysed phytohemagglutinin-induced blast cells bearing the stimulating alloantigens, whereas they had no effect on autologous or allogeneic unrelated target cells. Analysis of the reactivity with monoclonal antibodies (mAb) specific for two different subsets of TcR gamma/delta (BB3 and delta-TCS-1) showed that five out of nine clones were BB3+, whereas the remaining reacted with delta-TCS-1. Therefore, we can conclude that both subsets of TcR gamma/delta+ cells are able to specifically recognize and lyse allogeneic cells. mAb directed against the CD3-TcR gamma/delta molecular complex strongly inhibited the specific cytolytic activity of TcR gamma/delta+ clones, whereas they had no effect on the lysis of the natural killer-sensitive K-562 target cells mediated by the same clones. An alloreactive delta-TCS-1+ clone (LM12) was further characterized for its specificity. LM12 clone had been derived after stimulation in mixed lymphocyte culture against donor M.M. (HLA typing: Aw68, 24; B35, w55; DR1, 7). The analysis of a large panel of phytohemagglutinin-induced target cells revealed that only the HLA-A24+ target cells were lysed. The direct evidence that the A24 molecule represented the restriction element was provided by experiments using A24-transfected murine P815 target cells. Thus, clone LM12 efficiently lysed A24-transfected P815 cells, but not the same cells untransfected or transfected with the Cw3 gene. Therefore, it appears that polymorphic determinants of class I major histocompatibility complex molecules can be the target of TcR gamma/delta+ alloreactive cell recognition.

Surface molecules involved in CD3-negative NK cell function. A novel molecule which regulates the activation of a subset of human NK cells.

Natural killer cells are characterized by the lack of CD3/TCR molecules and by the expression of CD16 and CD56 (NKHI or Leu19) surface antigens. In addition to their ability to lyse certain tumor target cells, they release lymphokines including tumor necrosis factor and interferon gamma. Another unexpected functional capability of at least some NK cells is the ability to specifically recognize and lyse certain normal allogeneic cells (PHA-induced blasts). MAbs directed to CD2 or to CD16 surface molecules induced triggering of NK cells leading to target cell (p815) lysis in a redirected killing assay. Importantly, different from induction of T cell activation, single anti-CD2 MAbs were sufficient to trigger NK cell function. Another MAb (GL183) inducing NK cell triggering recognized a novel surface molecules expressed on 20-50% of resting or cultured NK cells. Cloned GL183+ cells displayed a variable degree of cytolytic activity against a number of human target cells of different histotype; moreover, this activity was strongly enhanced by the addition of GL183 MAb. On the other hand, GL183 MAb inhibited lysis of murine lines (including P815). Thus on P815 target cells GL183 MAb has an effect antithetical to that of other stimuli including PHA, anti-CD2 or anti-CD16 MAbs. GL183 MAb, added simultaneously to one or another of the stimuli above, strongly inhibited the target cell lysis induced by these stimuli. Thus, GL183 may represent an important molecule in the process of activation/regulation of phenotypically-defined NK cell subsets.

Recognition by human Vgamma9/Vdelta2 T cells of melanoma cells upon fusion with Daudi cells.

Daudi Burkitt's lymphoma cells, unlike other tumor cell lines, stimulate human T cells coexpressing the variable (V) region genes TCRG-V9 and V TCRD-V2 to proliferate and secrete lymphokines. Hybrids, derived by the fusion of Daudi cells with the human melanoma cell line MZ2-MEL 2.2, retain the morphology of melanoma cells. Unlike the parental melanoma cell line, these Daudi x MZ2-MEL 2.2 hybrids stimulate secretion of tumor necrosis factor (TNF) and granulocyte/macrophage colony stimulating factor (GM-CSF) by CD4-positive Vgamma9/Vdelta2 T-cell clones. Whereas the stimulator phenotype of Daudi cells behaves as a dominant trait in Daudi x melanoma hybrids, the expression of B-cell differentiation markers is suppressed. Thus, the gamma/delta T-cell ligand expressed by Daudi cells behaves as a dominant tumor antigen in Daudi x melanoma hybrids and is unrelated to the differentiated B-cell phenotype. Dominant expression of the Daudi ligand for human Vgamma9/Vdelta2 T cells in these hybrids may provide a basis for defining the stimulatory principle at the molecular level.

Susceptibility or resistance to lysis by alloreactive natural killer cells is governed by a gene in the human major histocompatibility complex between BF and HLA-B.

The specificity recognized on normal allogeneic cells by a given alloreactive (1-anti-A) natural killer clone is controlled by a gene locus termed EC1. Because the EC1 locus was previously shown to be located on chromosome 6, families characterized by a recombinant major histocompatibility complex haplotype were analyzed to map this locus more precisely. The breakpoint of recombination was studied by standard HLA typing, complement typing, and restriction fragment length polymorphism analysis of a series of genes located between the complement cluster genes and HLA-B within the major histocompatibility complex region. Three of 10 families analyzed were informative. From the data obtained, the EC1 locus maps between BF and HLA-B and presumably is one of the normal genes recently described in this region.

Human T cells expressing the gamma/delta T-cell receptor (TcR-1): C gamma 1- and C gamma 2-encoded forms of the receptor correlate with distinctive morphology, cytoskeletal organization, and growth characteristics.

BB3 and delta-TCS1 monoclonal antibodies identify two distinct nonoverlapping populations of T-cell receptor (TcR) gamma/delta (TcR-1)-positive cells, which express a disulfide-linked and a nondisulfide-linked form of TcR, respectively. BB3+ cells represented the majority of circulating TcR-1+ cells, but they were virtually undetectable in the thymus. On the other hand, delta-TCS1+ cells were largely predominant among TcR-1+ thymocytes but represented a minority in peripheral blood (PB). Similar distributions were observed by clonal analysis of thymocytes or PB TcR-1+ populations. The use of joining region (J)-specific probes indicated that BB3+ and delta-TCS1+ clones displayed different patterns of J rearrangement. Thus, the disulfide-linked form of TcR-1 (BB3+ clones) was associated with the expression of J segments upstream to the C gamma 1 gene segment, whereas the nondisulfide-linked form (delta-TCS1+ clones) was associated with the expression of J segments upstream to C gamma 2. delta-TCS1+ clones, in most instances, exhibited a growth pattern different from that of BB3+ or conventional TcR alpha/beta+ clones as they adhered promptly to surfaces, spread, and emitted long filopodia ending with adhesion plaques. Ultrastructural analyses showed, exclusively in delta-TCS1+ cells, nuclear deformations, uropod formation, and abundant cytoskeletal structures. In addition, immunofluorescence studies of this subset of TcR-1+ cells revealed the presence of abundant microtubules, intermediate filaments, and submembranous microfilaments. Thus, our findings suggest that delta-TCS1+ cells are capable of active motility.

Antibodies to adhesion molecules inhibit the lytic function of MHC-unrestricted cytotoxic cells by preventing their activation.

We evaluated the effect of the antibodies to adhesion molecules CD2, CD11a/CD18 (LFA-1), and CD56 (N-CAM) on MHC-unrestricted cytotoxicity mediated by polyclonal NK cells and LAK cells or by CD3+ or CD3- cytolytic cell clones against a panel of tumor cell targets selected according to expression or absence of the corresponding ligands. We show that (i) antibodies to CD11a/CD18 and, to a lesser extent, antibodies to CD2 inhibit target cell lysis, whereas anti-CD56 antibodies exert little if any effect; (ii) in a model system using polyclonal NK/LAK cells as effectors and K562 or HL60-R (NK-resistant) cells as targets, inhibition of cytotoxicity occurs without a significant impairment of effector to target cell binding; (iii) the cytotoxic function of CD3+ or CD3- cytotoxic cell clones is inhibited differentially by antibodies to adhesion molecules; (iv) conjugates formed in the presence of antibodies which inhibit target cell lysis display a significant reduction of target to effector cell contact surface; and (v) this may lead to defective activation of effector cells, as indicated by lack of redistribution of the microtubular apparatus. We conclude that (i) MHC-unrestricted cytotoxicity is regulated by a number of molecular interactions that span far beyond our present knowledge and that it is strictly dependent on the surface phenotype of the effector cell and of the target cell; (ii) in certain types of effector/target cell interactions, antibodies to adhesion molecules do not prevent conjugate formation but reduce the extent of cell-to-cell surface contact which, in turn, leads to defective activation of the effector cell and, therefore, to inhibition of target cell lysis.

Self class I molecules protect normal cells from lysis mediated by autologous natural killer cells.

The surface expression of given HLA class I alleles protects target cells from lysis mediated by natural killer (NK) clones specific for these (or related) alleles. We could define two groups of NK clones specifically recognizing either Cw4 and related C alleles ("group 1") or Cw3 and related C alleles ("group 2"), respectively. Monoclonal antibodies (mAb) to class I molecules should interfere with the interaction between NK receptors and class I molecules, thus resulting in lysis of protected target cells. However, none of the numerous available mAb to class I molecules had this effect. Therefore, we attempted to select new mAb on the basis of their ability to induce lysis of Cw4- or Cw3-protected lymphoblastoid cell lines by "group 1" or "group 2" NK clones, respectively. From mice immunized with phytohemagglutinin (PHA)-activated lymphocytes expressing either Cw3 or Cw4 alleles, two mAb were selected, the 6A4 (IgG1) and the A6-136 (IgM), on the basis of their ability to induce lysis of protected target cell. Both mAb immunoprecipitated molecules which, in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gave two bands of 45 and 12 kDa, typical of the class I heavy chain and beta 2 microglobulin, respectively. It has been proposed (but not proven), that self major histocompatibility complex class I molecules protect normal cells from autologous NK cell lysis. Thus, we used the 6A4 and A6-136 mAb to assess this possibility directly. Cw4-specific ("group 1") and Cw3-specific ("group 2") NK clones were isolated from donors expressing the corresponding (or related) protective C alleles. None of these clones lysed autologous PHA-induced blasts, used as target cells. However, addition of the F(ab')2 of 6A4 mAb or the A6-136 mAb resulted in lysis of autologous target cells by "group 1" or "group 2" NK clones, respectively. These data provide direct evidence that the expression of class I molecules protects normal cells from lysis by autologous NK cells.