A murine very late activation antigen-like extracellular matrix receptor involved in CD2- and lymphocyte function-associated antigen-1-independent killer-target cell interaction

CD2 and lymphocyte function-associated antigen (LFA)-1 are well known as T cell adhesion molecules involved in killer-target cell interactions. However, our recent study revealed that molecule(s) other than CD2 and LFA-1 might be involved in the lymphokine-activated killer (LAK) cell cytotoxicity against certain target cells. In order to characterize such unknown molecules, we established a mAb (RMV-7) which could inhibit CD2/LFA-1-independent LAK cell cytotoxicity and binding to target cells at the effector site. The Ag identified by RMV-7 appeared on splenic T cells late after mitogenic stimulation and was a noncovalently linked heterodimer composed of a 140-kDa alpha-chain and a 95-kDa beta-chain. RMV-7 blocked LAK cell binding to fibronectin (FN), fibrinogen, and vitronectin but not that to laminin or type IV collagen, indicating that the RMV-7-defined molecule is a unique extracellular matrix receptor for FN, fibrinogen, and vitronectin. One of its ligand, FN, was found on the surface of several target cells, and LAK cell cytotoxicity against them was blocked by anti-FN antibody at the target site. Similarly, cytotoxicity of a H-2d-specific CTL clone was inhibited by RMV-7 and anti-FN antibody as well. These results indicate that a unique very late activation Ag-like extracellular matrix receptor on murine CTL and LAK cells contributes to target cell binding and cytotoxicity.     

Localization of Fas ligand in cytoplasmic granules of CD8+ cytotoxic T lymphocytes and natural killer cells: participation of Fas ligand in granule exocytosis model of cytotoxicity

Fas ligand (FasL) has been implicated in cytotoxic T lymphocyte (CTL)- and natural killer (NK) cell-mediated cytotoxicity. In the present study, we investigated the localization of FasL in murine CTL and NK cells. Immunocytochemical staining showed that FasL was stored in cytoplasmic granules of CD8+ CTL clones and in vivo activated CTL and NK cells, where perforin and granzyme A also resided. Immunoelectron microscopy revealed that FasL was localized on outer membrane of the cytoplasmic granules, while perforin was localized in internal vesicles. Western blot analysis showed that the membrane-type FasL of 40 kDa was stored in CD8+ CTL clones but not in CD4+ CTL clones. By utilizing a granule exocytosis inhibitor (TN16), we demonstrated that FasL translocated onto cell surface upon degranulation of anti-CD3-stimulated CD8+ CTL clones. Moreover, TN16 markedly inhibited the FasL-mediated cytotoxicity by CD8+ T cell clones and NK cells. These results suggested a substantial contribution of FasL to granule exocytosis-mediated target cell lysis by CD8+ CTL and NK cells.     

Interaction of CD2 with its ligand, LFA-3, in human T cell proliferation

Recently, it has been demonstrated that lymphocyte function-associated Ag (LFA-3) is a natural ligand for CD2 and that this receptor-ligand interaction functions in cell-cell adhesion. In this report, we demonstrate that LFA-3 plays a role in T cell activation. L cells were transfected with human genomic DNA and sorted for expression of LFA-3. We demonstrate that LFA-3+ L cells, together with anti-CD3 mAb or with suboptimal doses of PHA, stimulate proliferation of human peripheral blood T cells. Furthermore, thymocyte proliferation was induced by LFA-3+ L cells and suboptimal doses of PHA. Proliferation was inhibited by mAb directed against either CD2 or LFA-3. Stimulation of thymocytes by the combination of PHA and LFA-3+ L cells resulted in the increased expression of the IL-2R, as well as of the surface Ag 4F2, transferrin receptor, and HLA-DR. These data support the conclusion that LFA-3 plays a role in CD2-dependent T cell activation. LFA-3 is widely distributed and is expressed on all APC and target cells. Thus, the ability of the CD2/LFA-3 interaction to costimulate with an anti-CD3 mAb suggests that the CD2/LFA-3 interaction may be involved not only in an Ag-independent alternate pathway of T cell activation but also in Ag-specific T cell activation.     

A novel functional cell surface dimer (Kp43) expressed by natural killer cells and gamma/delta TCR+ T lymphocytes. II. Modulation of natural killer cytotoxicity by anti-Kp43 monoclonal antibody.

In the present study we provide the first evidence supporting the fact that the Kp43 NK-associated cell-surface dimer may be involved in regulating MHC-unrestricted cytotoxicity. Our results indicated that incubation of IL-2-activated NK cells in a 51Cr-release assay with either the Kp43-specific mAb or its F(ab')2 fragments induced a significant cytolytic activity directed against normal autologous and allogeneic T cell blasts, which are relatively resistant to NK cell-mediated lysis. The cytotoxic effect was not observed in fresh CD3- CD16+ CD56+ Kp43+ lymphocytes and was only substantiated in IL-2-preactivated NK cells. Although stimulation with the Kp43-specific mAb did not significantly change the intracellular Ca2+ concentration, both Ca2+ and Mg2+ were required for the induction of cytotoxicity. The anti-Kp43-mediated activation of cytolysis was inhibited by anti-CD18 and CD11a mAb, whereas it was not significantly altered by either CD11b, CD11c, CD2, or LFA-3-specific mAb, rendering unlikely the participation of the latter. In contrast to these results the Kp43-specific mAb did not enhance the high levels of spontaneous cytotoxicity mediated by IL-2-activated NK cells against a panel of different tumor cell lines. An inhibitory effect mediated by anti-Kp43 mAb on the IL-2-dependent proliferation of NK cells was previously reported and appears, at least partially, secondary to the induction of an autolytic mechanism that is synergistically enhanced by anti-CD16 mAb. Altogether our results point out that interaction of the Kp43 dimer with its specific mAb is capable of inducing cytolytic activity and suggest that the molecule may play an important functional role in lymphokine-activated NK cells.     

Expression and function of TNF-related apoptosis-inducing ligand on murine activated NK cells.

TNF-related apoptosis-inducing ligand (TRAIL), a new member of TNF family, induces apoptotic cell death of various tumor cells. We recently showed that TRAIL mediates perforin- and Fas ligand (FasL)-independent cytotoxic activity of human CD4+ T cell clones. In the present study, we investigated the expression and function of TRAIL on murine lymphocytes by using newly generated anti-murine TRAIL mAbs. Although freshly isolated T, B, or NK cells did not express a detectable level of TRAIL on their surface, a remarkable level of TRAIL expression was induced preferentially on CD3- NK1.1+ NK cells after stimulation with IL-2 or IL-15. In contrast, TRAIL expression was not induced by IL-18, whereas it efficiently potentiated lymphokine-activated killer activity of NK cells. In addition to perforin inactivation and neutralization of FasL by anti-FasL mAb, neutralization of TRAIL by anti-TRAIL mAb was needed for the complete inhibition of IL-2- or IL-15-activated NK cell cytotoxicity against mouse fibrosarcoma L929 target cells, which were susceptible to both FasL and TRAIL. These results indicated preferential expression of TRAIL on IL-2- or IL-15-activated NK cells and its potential involvement in lymphokine-activated killer activity.     

Anti-CD3 + IL-2-stimulated murine killer cells. In vitro generation and in vivo antitumor activity

The growth, phenotype, in vitro cytolytic characteristics, and in vivo antitumor activity of murine splenocytes stimulated with anti-murine CD3 mAb in combination with IL-2 as compared with IL-2 alone was investigated. When cultured for 12 days with anti-CD3 mAb + IL-2, murine splenocytes increased 100- to 4000-fold in number compared with only 6- to 20-fold for cultures stimulated with IL-2 alone. Anti-CD3 mAb + IL-2 activated cultures developed high lymphokine-activated killer activity against NK-resistant targets including the P815 mastocytoma cell line and fresh MCA 106 sarcoma. Peak cytotoxicity on a per cell basis developed by day 8 after anti-CD3 mAb + IL-2 activation. A large proportion of the total cytolytic activity of long term anti-CD3 mAb + IL-2-stimulated cultures was related to the presence of anti-CD3 in the assay, indicating enhancement of cytotoxicity by activated CD3+ T cells. Phenotypic analysis indicated that anti-CD3 mAb + IL-2-stimulated cultures contained heterogeneous populations of T cells with increased percentages of both CD4+ and CD8+ phenotypes compared with cultures stimulated with IL-2 alone. Anti-CD3 mAb + IL-2-stimulated cells were tested for their in vivo antitumor activity by using C57BL/6 mice bearing MCA 106 sarcoma pulmonary metastases. IL-2-activated murine killer cells were given in combination with in vivo IL-2 and indomethacin, the latter of which was shown to potentiate the antitumor effect of IL-2. When given on day 5 after tumor inoculation, cell doses as low as 5 x 10(6) anti-CD3 mAb + IL-2-stimulated cells per mouse significantly reduced the number of pulmonary metastases (p less than 0.005). Thus, activation with the combination of anti-CD3 mAb + IL-2 produces rapidly expanding cultures of cytolytic cells with demonstrated in vivo antitumor efficacy.     

Human natural killer cell adhesion molecules. Differential expression after activation and participation in cytolysis.

Cell adhesion molecules (CAM) participate in interactions between lymphocytes, accessory cells, and target cells that are critical in the generation of effective immune responses. To characterize the involvement of CAM in NK and lymphokine activated killer (LAK) activities, we examined the expression of several CAM by freshly isolated human NK cells and by NK cells activated in vitro with IL-2, and compared this to CAM expression by T lymphocytes under similar conditions. Freshly isolated human NK cells were uniformly LFA-3 (CD58)+ and expressed two to three-fold higher surface levels of LFA-1 (CD11a/CD18) than resting T lymphocytes. More NK cells than T cells also expressed phenotypically detectable levels of intercellular adhesion molecule-1 (CD54). After in vitro incubation with IL-2, human NK cells demonstrated four- to sixfold increases in surface levels of CD11a/CD18, CD2, CD54, CD58, and the NK cell-associated Ag NKH-1 (CD56). Furthermore, essentially all NK cells became CD54+ within 3 days of exposure to IL-2. T cells did not demonstrate comparable up-regulation of CAM after incubation with IL-2. Increases in NK cell CAM expression were associated with enhanced formation of E:T cell conjugates, enhanced killing of NK-sensitive targets, and the induction of cytotoxicity for previously NK-resistant targets (LAK activity). The LAK activity induced by exogenous IL-2 could be partially inhibited by anti-CD2, anti-CD11a, or anti-CD54 antibodies and almost completely abrogated by anti-CD2 and anti-CD11a in combination. These studies suggest that CAM play a central role in the regulation of NK cytolysis, and that changes in CAM expression may alter the target cell specificity of activated NK effectors.     

Involvement of CD28 in MHC-unrestricted cytotoxicity mediated by a human natural killer leukemia cell line.

NK cells and certain CTL can recognize and lyse targets without restriction by the MHC. NK cells do not express CD3/TCR complexes and the membrane receptors participating in MHC-unrestricted cytotoxicity are largely unknown. We demonstrate that YT2C2, a human NK leukemia cell line, expresses the CD28 differentiation Ag and can spontaneously lyse both murine and human cell lines expressing B7, a B cell- activation Ag that is a ligand for CD28. The participation of CD28/B7 interactions in MHC-unrestricted cytotoxicity mediated by YT2C2 cells was demonstrated by correlation of target sensitivity with levels of B7 expression, inhibition of cytotoxicity by anti-CD28 or anti-B7 mAb, and by making both murine and human cell lines susceptible to YT2C2-mediated lysis by genetic transfection with expression vectors containing B7 cDNA. However, CD28/B7 interactions alone were insufficient to initiate cytotoxicity. mAb inhibition experiments and selection of CD54- (intercellular adhesion molecule-1) deficient B cell targets indicated that CD11a/18 (lymphocyte function-associated Ag-1) also cooperated in CD28/B7-dependent cytotoxicity. The requirement for both CD28/B7 and lymphocyte function-associated Ag-1/intercellular adhesion molecule-1 interactions in YT2C2-mediated MHC-unrestricted cytotoxicity was confirmed by demonstrating that efficient lysis of murine L cells required cotransfection with both B7 and intercellular adhesion molecule-1. These findings support the concept that MHC-unrestricted cytotoxicity may not be due to a unique receptor, but may result from interactions between an appropriate array of "adhesion" molecules with their ligands.     

Cytotoxic T lymphocyte triggering via CD16 is regulated by CD3 and CD8 antigens. Studies with T cell receptor (TCR)-alpha beta+/CD3+16+ and TCR-gamma delta+/CD3+16+ granular lymphocytes

The role of CD3 and CD8 Ag in CD16-mediated CTL triggering was studied in TCR-alpha beta+ and TCR-gamma delta+ granular lymphocytes (GL). In TCR-alpha beta+/CD3+4-8+16+ GL obtained from patients with GL-proliferative disorders, antibody-dependent cellular cytotoxicity was inhibited by anti-CD3 and anti-CD8 mAb. Anti-CD3 mAb also inhibited antibody-dependent cellular cytotoxicity activity of TCR-gamma delta+/CD3+4-8-16+ GL from a patient and that of TCR-gamma delta+/CD3+4-8+/-16+ T cell clones established from patients with proliferating TCR-gamma delta+ GL. In TCR-gamma delta+ T cell clones, cytotoxicity against Fc gamma R+ targets was induced by stimulation of CD16 Ag with anti-CD16 mAb, and such cytotoxicity was also inhibited by anti-CD3 mAb. These results indicate that CD3 and CD8 molecules play a regulatory role in CD16-mediated CTL triggering.     

Inhibition of cytotoxic T cell lysis by anti-CD8 monoclonal antibodies: studies with CD3-targeted cytolysis of nominal antigen-negative targets

The function of the CD8 molecule in lympholysis mediated by cytotoxic T cells was investigated by examining possible contributions of ligands on the target cell to the inhibition of lysis observed with CD8-specific mAb. In order to evaluate a variety of target cells, including those not expressing the nominal Ag (NA) for which the CTL was specific, lysis was effected by cross-linking the CTL and the target cells with anti-CD3 mAb. Such CD3 redirected cytotoxicity was demonstrated to be inhibited by anti-CD8 mAb when low anti-CD3 mAb concentrations were used. The possibility that inhibition by anti-CD8 mAb resulted for competition for the FcR between the anti-CD3 mAb and anti-CD8 mAb was eliminated by targeting TNP-modified cells with an antibody heteroconjugate prepared from Fab fragments of anti-CD3 and anti-DNP antibodies. Inhibition of the lysis of target cells not expressing NA including those deficient in class I expression, demonstrated that neither NA nor class I expression was required for anti-CD8 mAb inhibition. Whether the anti-CD8 mAb inhibition required CD8 Ag interaction with any ligand on the target cell was further investigated by measuring exocytosis of enzyme granule from CTL activated with CD3-coated poly-styrene beads. CD8-specific mAb inhibited such CTL activation in this target cell-free system. A CD8(+), MHC class II-specific CTL clone, was used to show differential inhibition by anti-CD8 mAb, depending on the target cell, therefore providing evidence that anti-CD8 mAb binding does not generate an absolute off signal. These data are consistent with the hypothesis that anti-CD8 mAb affect the lytic process independent of the recognition of a ligand on the target cell by CD8.     

Analysis of the role of leukocyte function-associated antigen-1 in activation of human influenza virus-specific T cell clones

The role of leukocyte function-associated Ag-1 (LFA-1) in intercellular adhesion is well documented. Previously, we demonstrated that the LFA-1 molecule (CD11a/CD18) can also regulate the induction of proliferation of peripheral blood T cells. In these studies, we observed opposite effects of antibodies against CD11a (LFA-1-alpha-chain) or CD18 (LFA-1-beta-chain). Here, we determined the effects of anti-CD11a and anti-CD18 mAb on proliferation of cloned influenza virus-specific T cells. Anti-CD18 mAb had similar inhibiting effects on the proliferative response of T cell clones induced by immobilized anti-CD3 mAb as it had on the response of peripheral blood T cells. In contrast to its costimulatory effect on resting peripheral blood T cells, anti-CD11a mAb did not increase the proliferation of cloned T cells. Similar differences in effects of anti-CD11a and anti-CD18 mAb were observed when proliferation of the T cell clones was induced by immobilized anti-TCR mAb. When proliferation was induced by influenza virus presented by monocytes as APC, both anti-CD11a and anti-CD18 mAb inhibited T cell proliferation. However, when EBV-transformed B cells were used as APC, neither anti-CD11a nor anti-CD18 mAb inhibited proliferation. These results demonstrate that the effects of antibodies against CD11a (LFA-1-alpha) or CD18 (LFA-1-beta) on T cell proliferation depend on 1) the stage of activation of the T cells, 2) the activation stimulus and its requirement for intercellular adhesion involving LFA-1, and 3) the type of cell used to present Ag.     

CD27-mediated activation of murine NK cells

CD27, a member of the TNF receptor superfamily, has been implicated in T cell activation, T cell development, and T cell-dependent Ab production by B cells. In the present study we examined the expression and function of CD27 on murine NK cells. Murine NK cells constitutively expressed CD27 on their surface. Stimulation with immobilized anti-CD27 mAb or murine CD27 ligand (CD70) transfectans solely could induce proliferation and IFN-gamma production of freshly isolated NK cells and enhanced the proliferation and IFN-gamma production of anti-NK1.1-sutimulated NK cells. Although NK cell cytotoxicity was not triggered by anti-CD27 mAb or against CD70 transfectants, prestimulation via CD27 enhanced the cytotoxic activity of NK cells in an IFN-gamma-dependent manner. These results suggest that CD27-mediated activation may be involved in the NK cell-mediated innate immunity against virus-infected or transformed cells expressing CD70.     

IL-10: a novel cytotoxic T cell differentiation factor

A previous report concluded that a new cytokine, designated IL-10, is a growth cofactor for thymocytes, spleen, and lymph node cells. In this report, we have focused on the effects of IL-10 on CD8+ spleen T cells. We first observed that IL-10 enhances the growth of CD8+ T cells to IL-2. We then investigated the effect of murine rIL-10 on the induction of murine effector CTL from CTL precursors (CTL-p) using both bulk and filler cell-free limiting-dilution cultures. IL-10 alone could not induce Con A-activated FACS-sorted CD8+ T cells either to proliferate or to generate effector CTL. In combination with IL-2, however, IL-10 augmented the cytolytic activity of effector CTL generated from Con A-activated spleen CD8+ T cells in bulk cultures incubated for 5 days. In limiting-dilution cultures (using solid-phase anti-CD3 mAb as stimulus), IL-10, in combination with IL-2, substantially increased the CTL-p frequency and augmented the cytolytic activity per clone expanded from one CD8+ T cell when compared with cells cultured in IL-2 alone. Kinetic studies showed that IL-10 is required at both early and late culture stages for optimal generation of effector CTL. The potentiating effects of IL-10 on CTL function were neutralized by an anti-IL-10 mAb. These results indicate that IL-10 has direct effects on mature T cells, and suggest that IL-10 also functions as a cytotoxic T cell differentiation factor, which promotes a higher number of IL-2-activated CTL-p to proliferate and differentiate into effector CTL. In contrast, IL-10 did not enhance significantly the lymphokine-activated killer cell activity of IL-2-grown CD8+ cytotoxic T cells.     

Triggering of co-mitogenic signals in T cell proliferation by anti-LFA-1 (CD18, CD11a), LFA-3, and CD7 monoclonal antibodies

Proliferative T cell responses were elicited in a comitogenic assay when purified mAb against CD 18, CD11a, LFA-3, and CD7 were immobilized onto solid plastic surfaces together with submitogenic doses of mAb against the CD3 complex. The proliferative response was associated to the production of IL-2 and to the expression of IL-2R. We explored the possibility that a second signal provided by either PMA or a Ca2+ ionofore could replace the anti-CD3 mAb in the comitogenic assay. Interestingly, our data clearly indicate that PMA but not the ionofore was capable of mediating the co-mitogenic effect in conjunction with solid-bound mAb (CDw18, CD11a, LFA-3, and CD7). We also demonstrate that the mAb (anti-CD4 and anti-CD2) which have been previously described as co-mitogenic in combination with anti-CD3 are capable of eliciting this activating signal in the presence of PMA. These data indicate that mAb to certain cell surface differentiation Ag that in soluble form inhibit T cell function such as LFA-1, LFA-3, and CD2 can under appropriate conditions induce co-mitogenic signals on T cells. Our results support the hypothesis that several cell surface differentiation Ag may participate in conjunction with the T3-Ti complex in the transmembrane signal transduction leading to T cell activation.     

CD16 on human gamma delta T lymphocytes: expression, function, and specificity for mouse IgG isotypes.

We examined the expression, the signal transduction capacity and mouse IgG-isotype specificity of CD16 on human gamma delta T cells. CD16 is expressed by the majority of gamma delta T cells in peripheral blood and by part of the gamma delta T cell clones. The amount of CD16 expressed on gamma delta T cell clones varied considerably with passaging of the cells, but was always significantly less than on freshly isolated gamma delta T cells. Like CD16 on CD3- CD16+ natural killer (NK) cells, CD16 on gamma delta T cells can act as an activation site triggering cytotoxic activity. CD16+ gamma delta T cell clones exerted antibody-dependent cellular cytotoxicity (ADCC) which could be blocked by anti-CD16 mAb. ADCC activity of gamma delta T cell clones was also inhibited by anti-CD3 mAb, suggesting a functional linkage between the CD16 and CD3 activation pathways. MAb directed against CD16 induced lysis of Fc gamma R+ target cells by CD16+ gamma delta T cell clones. The mouse IgG-isotype specificity of CD16 on gamma delta T cells was analyzed using isotype switch variants of a murine anti-glycophorin A mAb in EA rosette assays, and was found to be identical to that of CD16 on CD3- CD16+ NK cells, i.e., highest affinity for mIgG2a, intermediate affinity for mIgG2b, and undetectable binding of mIgG1-sensitized erythrocytes. CD16 was partly modulated from the cell surface of both gamma delta T cells and NK cells after rosette formation with mIgG2a-sensitized erythrocytes, indicating that the rosette formation was indeed mediated via the CD16 molecule.     

Activated,but not resting,T cells can be recognized and killed by syngeneic NK cells

We demonstrate that IL-2-activated NK cells or lymphokine-activated killer cells recognize and kill syngeneic CD4(+) and CD8(+) T cells that have been activated by APCs. Induction with APC required TCR-specific Ag, and lysis was perforin mediated. Brefeldin A, which disrupts protein transport, inhibited the sensitivity induced by activation. In BALB/c, expression of NKG2D ligands correlated with lysis and could be inhibited by brefeldin A. As well, addition of anti-NKG2D mAb to a killing assay completely abrogated lysis. Transduction of mouse NKG2D into a human NK cell line, YTSeco, conferred upon it the ability to kill activated BALB/c T cells, indicating that NKG2D is necessary for recognition. Our data provide a basis for studying a role for NK cells in T cell regulation.     

Participation of the CD27 antigen in the regulation of IL-2-activated human natural killer cells.

The CD27 Ag is expressed by the majority of resting T lymphocytes and appears to play a crucial role in T cell activation. We found that some resting peripheral blood NK cells also express CD27. Furthermore, CD27 expression was up-regulated on NK cells stimulated by IL-2. The cytolytic activity of IL-2-activated, but not resting, NK cells was inhibited by an anti-CD27 mAb (anti-1A4). However, anti-1A4 did not affect conjugate formation between IL-2-activated NK cells and tumor cell targets. In contrast, anti-1A4 inhibited CD2-mediated calcium mobilization and the serine esterase activity of NK cell granules. These inhibitory effects could be mediated in part by increase in intracellular cAMP levels induced by anti-1A4. Our results suggest that the CD27 Ag plays an important role in the regulation of activated NK cells.     

A novel functional cell surface dimer (Kp43) expressed by natural killer cells and T cell receptor-gamma/delta+ T lymphocytes. I. Inhibition of the IL-2-dependent proliferation by anti-Kp43 monoclonal antibody.

In the present study we describe a novel functional cell surface molecule, designated as Kp43, which is expressed among leukocytes by NK cells, TCR-gamma/delta + T lymphocytes, and some CD8+ CD56+TCR-alpha/beta + T cell clones. The Kp43 Ag is a 70-kDa disulfide-linked dimer, which migrates in SDS-PAGE under reducing conditions as a single 43-kDa band. Two-color immunofluorescence staining of fresh PBL revealed that only a fraction of CD16+, and of TCR-gamma/delta + T lymphocytes expressed the Ag. The analysis of TCR-alpha/beta + T cell clones showed that a small proportion (2 out of 20) weakly expressed Kp43 together with the CD8 and CD56 molecules. By immunoperoxidase staining of different tissues the anti-Kp43, reactivity was detected exclusively in lymphoid organs, where a minority of scattered cells was stained, and in some liver sinusoidal cells. Essentially all NK cells acquired Kp43 when stimulated with a B lymphoblastoid cell line. By contrast, the pattern of distribution of Kp43 remained stable upon in vitro culture of T-gamma/delta lymphocytes, thus delineating two subsets according to its expression. In lymphokine-activated killer populations, obtained by culturing either PBL or NK cells with high concentration of IL-2, most CD16+ and CD56+ cells became Kp43+. The Kp43-specific mAb inhibited the IL-2-dependent proliferative response of cultured NK and TCR-gamma/delta + T cells without affecting their non-MHC-restricted cytotoxicity. The partial inhibitory effect, which was mediated as well by pepsin digested F(ab')2 fragments, was lost upon reduction to Fab. The anti-Kp43 mAb did not interfere with the specific binding of IL-2 to its surface receptors. Altogether the data point out that the Kp43 dimer is involved in the regulation of the IL-2-dependent proliferative response of NK cells and a subset of TCR-gamma/delta + T lymphocytes.     

Generation propagation, and targeting of human CD4+ helper/killer T cells induced by anti-CD3 monoclonal antibody plus recombinant IL-2. An efficient strategy for adoptive tumor immunotherapy.

We developed a culture system for the rapid generation of CD4+ T cells that have both helper and killer functions. CD4+ T cells isolated from human PBL did not proliferate or develop significant cytotoxicity when treated with rIL-2 because of the lack of p75 IL-2R expression. However, culture of isolated CD4+ T cells with immobilized anti-CD3 mAb plus rIL-2 resulted in a marked proliferation (500-fold increase in 14 days) of CD4+ T cells. The proliferating CD4+ T cells produced IL-2 (92 U/ml) and showed strong cytotoxicity against OKT3 hybridoma cells and Daudi, K562, and U937 tumor cells in an anti-CD3 mAb-dependent manner. The CD4+ T cells contained significant amounts of cytolytic granule-related proteins such as serine esterase and perforin. Activated CD4+ helper/killer cells can be generated from both healthy donors and tumor patients and can be propagated in vitro for 14 to 35 days by biweekly restimulation with immobilized anti-CD3 mAb plus rIL-2. This culture yielded about 20,000-fold increase in cell number after a 21-day culture. Bispecific antibody containing anti-CD3 and anti-glioma Fab components enhanced the cytotoxicity of activated CD4+ helper/killer cells against IMR32 glioma cells. Moreover, the activated CD4+ helper/killer cells showed both helper and antitumor activity in vivo and prevented growth of anti-CD3 hybridoma cells in nude mice whether or not IL-2 was administered. These results indicate that anti-CD3 mAb plus IL-2-activated CD4+ helper/killer cells may provide an effective strategy for adoptive tumor immunotherapy of cancer.     

Functional CD2 mutants unable to bind to, or be stimulated by, LFA-3.

To define epitopes on the CD2 (T11, the T cell erythrocyte receptor) molecule that are necessary for interaction with lymphocyte function-associated Ag-3 (LFA-3), we have expressed the human wild-type CD2 cDNA and mutant CD2 cDNA in a murine Ag-specific T cell hybridoma that responds to human HLA-DR Ag. Here we have expressed mutations at amino acid 91 and 92 of CD2 in the T cell hybridoma. The mutated CD2 molecules were functional in that pairs of anti-CD2 mAb that continued to bind were able to stimulate IL-2 production by the hybridomas. However, CD2 mutants with either the 91 or 92 amino acid substitution had lost the ability to bind to or be activated by either SRBC, which bear an LFA-3 homologue, or by murine L cells expressing human LFA-3. Unlike hybridomas expressing the wild-type CD2 molecule, there was no enhanced response to Ag stimulation. Taken together, these data suggest that the mutated CD2 molecules were no longer able to bind to, or to utilize, LFA-3 for activation. We have previously demonstrated that a mutation at amino acid 51 of CD2 results in loss of binding to LFA-3. Whether these two regions of CD2, discrete and separable by amino acid sequence, form one or more binding sites for LFA-3 remains to be determined.