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.     

CD95 (Fas) ligand-expressing vesicles display antibody-mediated, FcR-dependent enhancement of cytotoxicity

Bioactive Fas ligand (FasL)-expressing vesicles were generated (vesicle preparation, VP) from two cell lines overexpressing FasL. The effect of NOK-1 anti-FasL mAb (mouse IgG1) on the cytotoxicity of FasL VP against various targets was determined. At high concentrations (1-10 microg/ml), NOK-1 inhibited the cytotoxicity. By contrast, NOK-1 in the dose range of 1-100 ng/ml significantly enhanced cytotoxicity against the FcR(+) LB27.4, M59, and LF(+) targets, but not the FcR(-) Jurkat and K31H28 hybridoma T cell targets. The ability to enhance FasL VP-mediated cytotoxicity could be blocked by the FcR-specific mAb 2.4G2. Enhancement was also observed with FcR(+) A20 B lymphoma but not with the FcR(-) A20 variant. Enhancement of FasL VP cytotoxicity was observed with five IgG anti-FasL mAbs, but not with an IgM anti-FasL mAb. Inhibition was observed with high doses of all mAb except the IgG anti-FasL mAb G247-4, which is specific to a segment outside the FasL binding site. Interestingly, under identical conditions but in the presence of 2.4G2, G247-4 inhibited the cytotoxicity of FasL VP. In addition, G247-4 inhibited the FasL VP-mediated killing of FcR(-) Jurkat. The data demonstrate that FasL-expressing bioactive vesicles display a property heretofore unknown in bioactive agents that express FasL-mediated cytotoxicity. The mechanism of the Ab-mediated, FcR-dependent enhancement of cytotoxicity of bioactive vesicles and its physiological significance are discussed.     

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.     

Cutting edge: RANTES regulates Fas ligand expression and killing by HIV-specific CD8 cytotoxic T cells.

Based on the previous observation that RANTES mediates the cytotoxic activity of human HIV-specific CD8+ T cells via the chemokine receptor CCR3, we studied the effect of this chemokine on different effector CD8+ cytolytic cells requiring Fas/Fas ligand (FasL) or perforin-dependent pathway. In CTLs derived from PBMCs of HIV-infected patients, both the spontaneous and the RANTES-induced cytotoxicity were inhibited by anti-FasL neutralizing Abs. In contrast, allogeneic CTLs or NK cells killing through perforin were not affected by RANTES and anti-FasL Ab. Accordingly, RANTES enhanced the expression of FasL in a concentration- and time-dependent manner in HIV-specific CTLs, whereas anti-RANTES Ab decreased markedly FasL expression. Finally, cell surface expression of FasL protein in HIV-specific CTLs was also up-regulated by eotaxin, a selective ligand for CCR3. Our observations show that the action of RANTES via CCR3 is necessary to regulate FasL expression on HIV-specific CD8+ T cells that kill through the Fas/FasL pathway.     

Expression and regulation of Fas and Fas ligand on thyrocytes and infiltrating cells during induction and resolution of granulomatous experimental autoimmune thyroiditis.

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced by mouse thyroglobulin-sensitized spleen cells activated in vitro with mouse thyroglobulin, anti-IL-2R, and IL-12. G-EAT lesions reach maximal severity 19-21 days after cell transfer, and lesions almost completely resolve by day 35. Depletion of CD8+ cells delays resolution and reduces Fas ligand (FasL) mRNA expression in thyroids. This study was undertaken to analyze Fas and FasL protein expression in the thyroid during induction and resolution of G-EAT and to determine whether CD8+ cells might regulate Fas or FasL expression in the thyroid. Fas and FasL expression was analyzed by immunohistochemical staining or in situ hybridization in thyroids of mice with or without depletion of CD8+ cells. Fas and FasL proteins were not detectable in normal thyroids, but expression of both proteins increased during development of G-EAT. Fas was expressed primarily by inflammatory cells; some enlarged thyrocytes were also Fas+. Thyrocytes had intense FasL immunoreactvity, and many CD8+ cells were also FasL positive. Depletion of CD8+ cells resulted in decreased FasL expression by thyrocytes and inflammatory cells, but had no effect on Fas expression. TUNEL assay detected many apoptotic inflammatory cells in proximity to thyrocytes. CD8-depleted thyroids had ongoing inflammation with fewer apoptotic infiltrating cells at day 35. Administration of a neutralizing anti-FasL mAb had no apparent effects on development of G-EAT, but anti-FasL was as effective as anti-CD8 in preventing G-EAT resolution. These results suggested that CD8+ T cells and thyrocytes may kill inflammatory cells through the Fas pathway, contributing to G-EAT resolution.     

Functional heterogeneity among herpes simplex virus-specific human CD4+ T cells.

One hundred thirteen HSV-specific CD4+ T cell clones were established from the PBL of a healthy person and their functional heterogeneity was investigated. All clones proliferated in response to stimulation with HSV in the presence of autologous APC. Among those, 48 clones showed cytotoxic activity to HSV-infected autologous EBV-transformed lymphoblastoid cell line, but not to HSV-infected autologous fibroblasts, HSV-infected allogeneic cells, or K562 cells (group 1). Five clones showed cytotoxicity against HSV-infected autologous cells as well as HSV-infected allogeneic cells and K562 cells (group 2). The cytotoxicity of these clones was found to be mediated by the direct killing but not by the "innocent bystander" killing of target cells. Sixty clones showed no cytotoxic activity, however, among these, 23 revealed HLA-unrestricted and nonspecific cytotoxicity in the presence of PHA in culture (group 3), and the remaining 37 did not show any cytotoxic activity even in the presence of PHA (group 4). The cytotoxic patterns of these clones did not change in activated and resting phases, suggesting that the difference in cytotoxic ability does not depend on cell cycles. The cytotoxic activity of group 1 was inhibited by addition of anti-HLA-DR or anti-CD3 mAb to the culture, whereas these mAb had no effect on the cytotoxicity of group 2. All four groups of clones had helper activity for anti-HSV antibody production by autologous B cells. Moreover it was found that all groups of clones simultaneously produced IL-2, IL-4, and IFN-gamma after culture with APC followed by HSV Ag stimulation. The surface phenotype of all clones was uniformly CD2+, CD3+, CD4+, CD8-, CD29+, CD45RA-, but expression of Leu 8 was varied. These data therefore indicate that HSV-specific human CD4+ T cells are classified into at least four groups according to the presence and specificity of cytotoxicity, i.e., Th cells with HSV-specific and HLA-class II-restricted cytotoxicity, Th cells with HLA-unrestricted and nonspecific cytotoxicity, Th cells with lectin-dependent cytotoxicity, and Th cells without cytotoxic activity. The present finding of functional heterogeneity among virus-specific human CD4+ T cells might shed light on the pathogenesis of CD4+ T cell immunodeficiency, such as human retrovirus infections.     

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.     

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.     

Phenotypic and functional characterization of cytotoxic cells derived from endomyocardial biopsies in human cardiac allografts.

This study was undertaken to characterize the phenotype and function of lymphocytes derived from endomyocardial biopsies in heart transplant patients. To this aim, tissue infiltrating lymphocytes were derived from seven heart transplant patients and were analyzed for the expression of a panel of markers, including CD3, CD4, CD8, CD16, CD56, CD45RA, CD45RO, alpha/beta and gamma/delta T cell receptor, and for their ability to lyse a series of targets, including NK-sensitive K-562 targets, NK-resistant Raji targets, donor related, and unrelated normal splenocytes. Our data show that the majority of cultured lymphocytes expressed the CD3+ phenotype and the alpha/beta T cell receptor. The CD4 and CD8 molecules were heterogeneously expressed among T cell lines tested. Concerning cytotoxic related markers, a significant percentage of cells were CD56+. The evaluation of CD45 isoforms showed that both "naive" and "memory" cells were present among heart TIL. Cytotoxic in vitro studies demonstrated that all our T cell lines showed an efficient cytotoxic machinery when tested against NK-sensitive targets. A marked lysis of donor-related splenocytes was demonstrated in all patients tested. To investigate the role of CD3 and HLA class I molecules in the cytotoxic mechanisms taking place in human heart allograft rejection mechanisms, TIL were assessed for their lytic activity against different targets in the presence of anti-CD3 and anti-HLA class I monoclonal antibodies (mAbs). Although donor-specific cytotoxicity was considerably inhibited by the anti-CD3 mAb, no inhibitory effect was displayed by this antibody on TIL-mediated cytotoxicity against donor-unrelated splenocytes. Anti-HLA class I mAb was able to inhibit both allospecific and nonallospecific cytotoxicity. These data suggest that different types of cytotoxic cells may be propagated from biopsy specimens of heart transplant patients.     

Ameliorating effect of anti-Fas ligand MAb on wasting disease in murine model of chronic colitis

Fas/Fas ligand (FasL) interaction has been implicated in the pathogenesis of various diseases. To clarify the involvement of Fas/FasL in the pathogenesis of intestinal inflammation, we investigated the preventive and therapeutic effects of neutralizing anti-FasL monoclonal antibody (MAb) on the development of chronic colitis induced by adaptive transfer of CD4+CD45RBhigh T cells to SCID mice. Administration of anti-FasL MAb from 1 day after T cell transfer (prevention study) resulted in a significant improvement of clinical manifestations such as wasting and diarrhea. However, histological examination showed that mucosal inflammation in the colon, such as infiltration of T cells and macrophages, was not improved by the anti-FasL MAb treatment. In vitro studies showed that anti-FasL MAb did not inhibit IFN-gamma production by anti-CD3/CD28-stimulated lamina propria CD4+ T cells but suppressed TNF-alpha and IL-1beta production by lamina propria mononuclear cells. Therapeutic administration of anti-FasL MAb from 3 wk after T cell transfer also improved ongoing wasting disease but not intestinal inflammation. These results suggest that the Fas/FasL interaction plays a critical role in regulating systemic wasting disease but not local intestinal inflammation.     

Signaling from LFA-1 contributes signal transduction through CD2 alternative pathway in T cell activation.

LFA-1, a member of the integrin family of molecules, is involved in mediating cellular adhesion in all phases of the immune response, playing a role in the interaction of helper T cells as well as in killing of target cells by both cytotoxic T cells and natural killer cells. We have developed a monoclonal antibody, anti-HVS6B6, which recognizes a functionally unique epitope of the LFA-1 molecule. Although this mAb itself was not mitogenic against T cells, it induced a strong proliferative response when added to T cells with submitogenic concentrations of anti-CD2 (anti-T11(2) and anti-T11(3)) mAbs. In contrast, other anti-LFA-1 mAbs (CD11a and CD18) suppressed this anti-CD2 mAb-induced T cell proliferation. Kinetic studies showed that anti-HVS6B6 acts on an early event in CD2-mediated T cell activation. Although T11(3)-epitope expression induced by anti-T11(2) mAb was not affected by treatment of cells with anti-HVS6B6, both Ca2+ influx and phosphatidylinositol turnover induced by anti-CD2 mAbs were markedly enhanced by the pretreatment of T cells with anti-HVS6B6 mAb. These results indicate that the LFA-1 mediating signal contributes to a very early phase of signal transduction during CD2-mediated T cell activation.     

An HIV-1-infected T cell clone defective in IL-2 production and Ca2+ mobilization after CD3 stimulation

A chronically HIV-1-infected T cell clone (J1.1) derived from Jurkat cells was developed that possesses defects in CD3 signaling. This clone was phenotypically determined to be CD4- and express a reduced surface density of CD3 as compared with a pool of uninfected Jurkat clones. Although J1.1 could be induced with TNF-alpha to produce HIV-1 particles, stimulation via the CD3 (T3-Ti) complex, using mAb cross-linking, had no effect on viral production. Further investigation revealed that J1.1 secreted approximately 20-fold less IL-2 than did uninfected Jurkat cells after anti-CD3 treatment. In addition, a separate defect in Ca2+ mobilization was noted in the HIV-1-infected J1.1 line when compared with uninfected Jurkat cells after anti-CD3 cross-linking. The cell line described offers a new model in which to study the mechanisms of several defects directly imposed by HIV-1 on CD3+ cells.     

Triggering of cytotoxic T lymphocytes and NK cells via the Tp103 pathway is dependent on the expression of the T cell receptor/CD3 complex

The expression and function of the T cell activation molecule Tp103 on human cloned cytotoxic CD3+ and CD3- cells were studied. All in vitro growing CD3+ and CD3- clones expressed Tp103 regardless of their phenotype and the expression of a CD3-associated TCR complex. Whereas the CD2 pathway was functional in all these clones, only CD3-expressing clones could be triggered via Tp103 to kill target cells. In contrast, both CD2 and Tp103 pathways were suppressed after modulation of the TCR complex with anti-CD3 mAb. This indicates that the function of Tp103 but not of CD2 is dependent on the expression of a functional Ag receptor on cytotoxic T cells. Furthermore, modulation of the Ag receptor induces a state of unresponsiveness in cytotoxic T cells that cannot be attributed to just the removal of the CD3/TCR complex from the cell membrane.     

Chronic morphine treatment promotes specific Th2 cytokine production by murine T cells in vitro via a Fas/Fas ligand-dependent mechanism

Improper homeostasis of Th1 and Th2 cell differentiation can promote pathological immune responses such as autoimmunity and asthma. A number of factors govern the development of these cells including TCR ligation, costimulation, death effector expression, and activation-induced cell death (AICD). Although chronic morphine administration has been shown to selectively promote Th2 development in unpurified T cell populations, the direct effects of chronic morphine on Th cell skewing and cytokine production by CD4(+) T cells have not been elucidated. We previously showed that morphine enhances Fas death receptor expression in a T cell hybridoma and human PBL. In addition, we have demonstrated a role for Fas, Fas ligand (FasL), and TRAIL in promoting Th2 development via killing of Th1 cells. Therefore, we analyzed whether the ability of morphine to affect Th2 cytokine production was mediated by regulation of Fas, FasL, and TRAIL expression and AICD directly in purified Th cells. We found that morphine significantly promoted IL-4 and IL-13 production but did not alter IL-5 or IFN-gamma. Furthermore, morphine enhanced the mRNA expression of Fas, FasL and TRAIL and promoted Fas-mediated AICD of CD4(+) T cells. Additionally, blockade of Fas/FasL interaction by anti-FasL inhibited the morphine-induced production of IL-4 and IL-13 and AICD of CD4(+) T cells. These results suggest that morphine preferentially enhances Th2 cell differentiation via killing of Th1 cells in a Fas/FasL-dependent manner.     

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.     

Induction of lysis by T cell receptor gamma delta+/CD3+ T lymphocytes via CD2 requires triggering via the T11.1 epitope only

The requirements for activation of the lytic machinery through CD2 of TCR gamma delta+/CD3+ cells were examined, by utilizing bispecific heteroconjugates containing anti-CD2 mAb cross-linked to anti-DNP. Contrary to the CD2 activation requirements in TCR alpha beta+/CD3+ cells, cytotoxic activity in TCR gamma delta+/CD3+ clones and TCR-/CD3- NK cell clones can be induced by heteroconjugates containing a single anti-CD2 (OKT11.1) mAb. Activation of TCR gamma delta+/CD3+ cells via CD2 is independent of heteroconjugates binding to CD16 (Fc gamma RIII), because heteroconjugates prepared from Fab fragments induced equal levels of lysis. Moreover, anti-CD16 mAb did not inhibit triggering via CD2 in TCR gamma delta+/CD3+ cells. In TCR-/CD3- NK cells, however, induction of cytotoxicity via CD2 is co-dependent on interplay with CD16. Anti-CD3 mAb blocked the anti-CD2 x anti-DNP heteroconjugate-induced cytotoxicity of TCR gamma delta+/CD3+ cells, indicating a functional linkage between CD2 and CD3 on these cells. We conclude that induction of lysis via CD2 shows qualitatively different activation requirements in TCR gamma delta+/CD3+, TCR alpha beta+/CD3+ CTL and TCR-/CD3- NK cells.     

Anti-CD3 and phorbol myristate acetate regulation of MHC unrestricted T cell cytotoxicity. Lack of a requirement for CD3/T cell receptor complex expression during tumor cell lysis

The effects of anti-CD3 mAb on MHC-unrestricted cytotoxic activity of NK depleted PHA-activated human T cells were examined. Anti-CD3 mAb had variable effects on killing of K562 or Daudi targets. Whereas lower concentrations of OKT3 often inhibited lysis of either target, higher concentrations (greater than 1 micrograms/ml) frequently increased K562 killing and always augmented Daudi lysis. However, lysis of the renal cell carcinoma, Cur, was consistently inhibited by OKT3 over a broad concentration range. Such variable effects were not related to differential regulation of heterogeneous subsets of effector cells, as similar patterns of OKT3-mediated modulation of tumor cell lysis by T cell clones was also observed. Another IgG2a anti-CD3 mAb, 64.1, and either F(ab')2 fragments of OKT3 or intact OKT3 in the presence of aggregated human Ig were found to inhibit lysis of Cur, K562, and Daudi targets consistently. Additional experiments were carried out to determine whether modulation of CD3 accounted for the inhibitory effects of the anti-CD3 mAb. PMA was noted to cause modulation of CD3 from the surface of PHA or alloantigen-activated T cells, and the combination of anti-CD3 and PMA caused even more marked modulation of CD3. Whereas preincubation with PMA and/or anti-CD3 decreased alloantigen-specific cytotoxic T cell function in relative proportion to the loss of CD3 expression, no consistent relationship between CD3 expression and the capacity of PHA-activated T cells to kill Cur targets was noted. PMA alone caused no consistent alteration of Cur lysis. Moreover, in the presence of PMA, anti-CD3 mAb caused no significant inhibitory effect on Cur lysis, in spite of increased modulation and in some cases virtual total loss of surface CD3 expression. These findings indicate that when FcR interactions are prevented, anti-CD3 mAb consistently inhibit MHC-unrestricted cytotoxicity by PHA-activated T cells. Despite this, the data support the conclusion that CD3/TCR complex interactions with target cells are not required for either target cell recognition or triggering of lysis by MHC-unrestricted cytotoxic T cells.     

Antibody blockade of Thy-1 (CD90) impairs mouse cytotoxic T lymphocyte induction by anti-CD3 monoclonal antibody

Thy-1 (CD90) expressed by mouse T cells is known to have signal transducing properties, but the ability of Thy-1 to enhance cytotoxic T lymphocyte (CTL) development is not well understood. Here we show that stimulation of mouse T cells with monoclonal antibodies (mAb) to CD3, CD28 and Thy-1 (clone G7), which were coimmobilized on polystyrene microbeads, resulted in a greater proliferative response than stimulation with only anti-CD3 and anti-CD28 mAb, indicating that Thy-1 cross-linking enhanced T cell receptor/CD28-driven T cell activation. Consistent with this finding, Thy-1 blockade with a soluble nonactivating anti-Thy-1 mAb (clone 30-H12) inhibited anti-CD3-induced proliferation of CD4+ and CD8+ T cells, and the induction of cytotoxic effector cells in a dose-dependent fashion. Interleukin-2 synthesis and CD25 expression were also impaired by Thy-1 blockade. The inhibitory effect involved a defect at or before the level of protein kinase C activation because the addition of phorbol ester ablated the anti-Thy-1-mediated inhibition of anti-CD3-induced T cell activation. The CTL that were induced in the presence of blocking anti-Thy-1 mAb adhered to target cells but showed reduced expression of granzyme B and perforin. In contrast, Fas ligand expression and function was not affected by Thy-1 blockade. We conclude that Thy-1 signalling promotes the in vitro generation of CTL that kill in a granule-dependent fashion.     

Bioactivities of Fas ligand-expressing retroviral particles

Culture supernatants from retroviral packaging cells carrying the human Fas ligand (FasL) gene killed both human (Jurkat) and mouse (LB27.4) targets within 5 h of incubation. Cytotoxicity was found both in a fraction >/=500 kDa and a fraction between 50 and 500 kDa. Following ultracentrifugation, the activity in the >/=500-kDa fraction was concentrated in the pellet (FasL vector preparation (VP)), which was also infective when added to NIH-3T3 cells. Both Polybrene and poly-l -lysine significantly enhanced the cytotoxicity of FasL VP but not anti-Fas mAb, soluble FasL (sFasL), and cell-associated FasL. In the presence of Polybrene, FasL VP killed targets that are resistant to anti-Fas mAb and sFasL. The infectivity but not FasL cytotoxicity of FasL VP was sensitive to irradiation and heat shock. By contrast, cytotoxicity of FasL VP could be enhanced or inhibited depending on the doses of anti-FasL mAb. Interestingly, the infectivity of FasL VP was specifically enhanced by anti-FasL mAb, suggesting that a nonviral gene product could be used to regulate the behavior of the retroviral vector. Thus, in addition to expressing potent FasL cytotoxicity, the FasL VP exhibits unique properties heretofore not attributed to anti-Fas mAb, sFasL, and cell-associated FasL. Our study raises the possibility of using the retroviral gene-packaging technology to make powerful, versatile, and regulatable bioactive vesicles expressing a predetermined function of the protein encoded by the target gene.