Differences in the stimulating capacity of immobilized anti-CD3 monoclonal antibodies: variable dependence on interleukin-1 as a helper signal for T-cell activation.

Monoclonal antibodies to the CD3 antigen on human T lymphocytes have been shown to induce accessory cell-dependent T-cell activation. One function of the accessory cells is cross-linking of CD3 by Fc receptor-binding of the anti-CD3 antibodies. Whether additional accessory signals are still required when anti-CD3 is presented in immobilized form is controversial. In the present study we stimulated purified human T cells with several anti-CD3 monoclonal antibodies, which were immobilized by coating the culture wells with goat anti-mouse IgG. A first group of immobilized anti-CD3 antibodies (anti-Leu-4, UCHT1, anti-T3, WT32 and 64.1) induced vigorous T-cell proliferation in the complete absence of monocytes, even when anti-interleukin-1 beta antiserum was added to the cultures. Other immobilized anti-CD3 antibodies (OKT3, WT31) required interleukin-1 beta in order to induce T-cell proliferation. However, when OKT3 was immobilized by direct coating of the culture wells with OKT3, it was also able to induce accessory cell-independent production of interleukin-2 and T-cell proliferation. Interleukin-1 beta further enhanced the interleukin-2-dependent proliferative response and it could provide help to induce proliferation at doses of immobilized OKT3 which, by themselves, were insufficient for full T-cell activation. We conclude that the requirement for interleukin-1 beta to induce interleukin-2-dependent proliferation of T cells when stimulated with anti-CD3 antibodies is not absolute, but depends on the CD3 epitope recognized, on the way of antibody presentation, on the antibody concentration and on other, still undefined, characteristics of the monoclonal antibodies used.     

Differential response of CD4+ V7+ and CD4+ V7− T cells to T cell receptor-dependent signals: CD4+ V7+ T cells are co-stimulation independent and anti-V7 antibody blocks the induction of anergy by bacterial superantigen

V7 is a novel cell surface glycoprotein that is expressed on 25% of circulating T lymphocytes. This molecule appears to play a critical role in T cell activation based on the observation that a monoclonal anti-V7 antibody inhibits T cell receptor (TCR)-dependent interleukin-2 (IL-2) production and proliferation of T cells. In the current study, CD4⁺ V7+ and CD4⁺ V7? T cells were separated from one another and their response to various stimuli analyzed. Although there were only minor differences between the two subsets in the expression of activation/differentiation markers, including CD45RA and R0 isotypes, when exposed to immobilized anti-CD3 or anti-TCR antibodies in the absence of APC, CD4⁺ V7+ T cells alone produced IL-2 and proliferated vigorously. By contrast, CD4⁺ V7? cells responded poorly to such stimuli, but they recovered their capacity to respond if antigen-presenting cells (APC) or anti-CD28 antibody were added to the cultures. The enhancement of the V7? T cell response by APC appears to be related to augmentation of TCR signals because the effect could be blocked by antibodies against molecules on APC [major histocompatibility (MHC) class II, CD86] that are known to up-regulate such signals through their interaction with counter-receptors on T cells. To assess the role of V7 in a system independent of co-stimulation, CD4⁺ T cells were stimulated with the bacterial superantigens, staphylococcal enterotoxins A and B. The cells responded by proliferating and then becoming anergic. Addition of anti-V7 antibody at the initiation of culture with superantigen did not inhibit cellular proliferation but prevented T cells from becoming anergic, while addition of anti-CD28 antibody had no effect on either proliferation or anergy induction. These results indicate that V7 and CD28 mediate distinct intracellular signals and suggest that V7 functions to preserve T cell reactivity whether the stimulus is mitogenic or anergizing.     

Differential effects of CD4 and CD8 engagement on the development of cytokine profiles of murine CD4+ and CD8+ T lymphocytes

A simple culture system devoid of antigen-presenting cells was used to examine the ability of immobilized antibodies to lymphocyte function-associated antigen-1 (LFA-1) (CD11a), CD28 and CD4 or CD8 to modulate the responses of normal murine CD4+ and CD8+ lymph node T cells to immobilized anti-CD3 antibody and interleukin-2 (IL-2). All the antibodies enhanced proliferative responses to limiting anti-CD3 antibody. Both CD4+ and CD8+ cells produced substantial titres of IL-3 and interferon-gamma (IFN-gamma) in primary and secondary cultures regardless of the coactivating antibodies used for priming. By contrast, the combination of anti-CD4 with anti-CD3 antibody stimulated significantly higher titres of IL-4 than any other antibody combination in cultures of CD4+ cells. This CD4-dependent IL-4 response was induced in CD4+ T cells of naive (CD44low) phenotype and was similar in magnitude to the response induced by exogenous IL-4 but, unlike the latter, was not associated with elevated IL-3 synthesis. A comparable effect of anti-CD8 antibodies on CD8+ cells was not observed: although IL-4 production by CD8+ cells was induced by exogenous IL-4, it was not detected following coactivation with anti-CD8 or any other antibodies. We conclude that anti-CD4 antibody is a potent inducer of IL-4-secreting CD4+ T cells whose effects can be distinguished from those of anti-CD8 antibody on CD8+ T cells and from those of IL-4 on either subset.     

Hyporesponsiveness of "naive" (CD45RA+) human T cells to multiple receptor-mediated stimuli but augmentation of responses by co-stimuli

Much remains to be clarified the functional capacities of the two major reciprocal subsets of human CD4+ cells which we interpret to be naive and memory cells. CD4+ naive (CD45RA+, LFA-3-) and memory (CD45R0+, LFA-3+) cells were rigorously purified by immunomagnetic negative selection. Their proliferation was measured in response to four protocols of receptor-mediated activation: soluble anti-CD3 mAb, plastic-immobilized anti-CD3 mAb, activating pairs of anti-CD2 mAb, and "superantigens" staphyloccocal enterotoxins A and B (SEA and SEB). Naive cells proliferated much less than memory cells to each of these four regimens although their capacity to respond was demonstrated by strong PHA-induced proliferation. Although three of the regimens depend on autologous monocytes, poorer naive cell responses are also observed to anti-CD3 mAb immobilized on plastic in the absence of monocytes; this implies an intrinsic hyporesponsiveness of naive cells, independent of their potentially weaker interaction with monocytes. Naive cells proliferated less than memory cells to superantigens SEA and SEB over a wide dose range; this assumes particular importance because such superantigens are believed to more closely mimic antigen-specific stimulation than anti-CD3 mAb. The possibility was explored that hyporesponsiveness of naive cells reflects the fact that naive cells require additional co-stimuli to facilitate their activation. In support of this concept, we observed that proliferation of naive cells to anti-CD3 mAb and SEA or SEB (but not to anti-CD2 mAb pairs) was consistently enhanced by pre-activation of monocytes present in the culture. Naive cell proliferative responses were augmented further in cultures supplemented with interleukin (IL) 1 beta and IL 6 or exposed to the co-stimulating mAb anti-CD28 and anti-CD44. The pattern of augmentation was dependent on the specific triggering regimen: anti-CD44 mAb was particularly effective in augmenting the response to superantigens, anti-CD28 mAb for the anti-CD3 response and IL 1 beta/IL 6 for that induced by anti-CD2 mAb pairs. With particular combinations of stimulus/co-stimuli naive cell proliferation was as strong as that of memory cells. We interpret these findings to indicate that naive cells are capable of responding to antigen, but that such responses are critically dependent on the available co-stimuli in vivo.     

Accessory Cell-Dependent T-Cell Activation via Ti-CD3

The activation of resting T cells to interleukin 2 (IL-2) production and DNA synthesis via Ti-CD3 is dependent on accessory cells (AC). Using positively selected, resting T cells activated with particle-bound anti-CD3, we investigated the ability of various cell lines to function as AC. We found that cell lines able to act as AC all expressed LFA-3, while cell lines not expressing LFA-3 were unable to provide AC signals. This applied to CD3+, CD4+, and CD8+ T cells. Sheep red blood cells (SRBC), which express LFA-3-like molecules, also had a weak, but significant AC function in this test system. Both CD4+ and CD8+ T cells activated with particle-bound anti-CD3 could be induced to enter DNA synthesis in the absence of AC when monoclonal antibodies reacting with CD2 were present instead of AC. IL-2 production could be detected in the latter cultures but not when positively selected CD3+ or CD2+ T cells were cultured alone. Our data suggest that activation of resting T cells via CD3 will lead to IL-2 receptor expression, while the interactions between LFA-3 and its ligand CD2 provide the necessary secondary signals for IL-2 production and induction of DNA synthesis.     

Antibodies recognizing CD24 LAP epitope on human T cells enhance CD28 and IL-2 T cell proliferation

Membrane expression of the CD24 molecule on activated T lymphocytes is not elucidated fully. We previously described the intracellular and cell-surface expression of the CD24 sialic acid-dependent epitope(s) on phytohemagglutinin-activated peripheral blood mononuclear cells. However, the CD24 core protein was not detected previously on human T cells. This study reinvestigated the expression and role of CD24 in T cell subsets. We analyzed binding of anti-CD24 monoclonal antibodies (mAbs) to sialic and leucine-alanine-proline (LAP) epitopes in resting and activated, normal T lymphocytes. CD24 LAP and CD24 sialic epitopes were detected on activated CD4- and CD8-positive cells. Although expression of CD24 sialic epitopes remained stably expressed in interleukin (IL)-2-dependent cultures, T cell expression of the LAP epitope was transient. Anti-LAP antibodies strongly enhanced the response of T cells to a combination of anti-CD3/CD28 mAbs and enhanced proliferative response induced by recombinant IL-2. We found similarities in the tissue distribution and function of the human CD24 LAP molecule and the murine, heat-stable antigen, which suggests that CD24 might function as a signaling molecule on human T cells.     

Induction of interleukin 2 receptiveness and proliferation in resting peripheral T cells by monoclonal anti-CD3 (T3) antibodies does not require the presence of macrophages

In this study, we sought to elucidate the sequence of events by which mitogenic monoclonal anti-CD3 antibodies (anti-CD3-MoAb) initiate T cell activation. In cultures of monocyte-depleted resting T cells, two anti-CD3-MoAb, OKT3 and anti-Leu 4, induced a state of interleukin 2 (IL-2) receptiveness which culminated in T lymphocyte proliferation when recombinant IL-2 was provided. Evidence that Fc-receptor mediation by monocytes did not contribute to this mitogenesis was supported by studies showing that polyclonal F(ab')2 anti-mouse IgG Fc antibody did not alter the magnitude of the IL-2 driven T cell proliferative response, and by the use of T cells from donors whose monocytes were unable to assist in the induction of anti-Leu 4 (IgG1 subclass) initiated proliferation. Anti-CD3-MoAb, in the absence of IL-2, induced IL-2 receptor expression on purified T cells, and anti-IL 2 receptor antibodies inhibited T cell proliferation in the presence of this growth factor. Furthermore, following modulation of the CD3 molecular complex in the presence of monocytes, depletion of accessory cells rendered the modulated T cells mitogenically dependent on exogenous IL-2. IL-2 itself did not suffice to promote T cell proliferation in the absence of anti-CD3-MoAb. These results indicate that the binding of monoclonal antibody to CD3 is capable of initiating, in an accessory cell-independent manner, premitotic alterations in T cells which can culminate in proliferation when exogenous IL-2 is provided.     

Role of CD95-activated caspase-1 processing of IL-1beta in TCR-mediated proliferation of HIV-infected CD4(+) T cells.

CD95 plays a critical role in the homeostasis of the immune system, and has been reported to participate in T cell death during HIV infection. Here we report that the response to CD3-TCR stimulation of CD4(+) T cells from HIV-infected individuals and CD4(+) T cells from healthy donors incubated in vitro with HIV-1(Lai) depends on the manner the CD3-TCR complex is engaged. While stimulation by anti-CD3 antibodies in solution induced CD4 T cell apoptosis both in the absence or presence of anti-CD95 antibodies, stimulation by immobilized anti-CD3 antibodies rendered CD4(+) T cells resistant to CD95-mediated death and led to increased CD4 T cell proliferation in response to CD95 ligation. CD95 ligation of CD4(+) T cells led to the activation of caspases, while costimulation induced by anti-CD3 and anti-CD95 mAb prevented the full processing of caspase-3 and caspase-8. Proliferation of CD4(+) T cells induced by CD3-TCR and CD95 costimulation was decreased by treatments with a caspase-1 inhibitor or with neutralizing antibodies to IL-1ss, indicating a requirement for caspase-1-mediated IL-1beta processing and secretion. Our findings suggest a novel mechanism whereby in addition to its role in inducing T cell apoptosis, CD95 signaling during HIV infection may also provide a costimulatory signal leading to an enhancement of CD4 T cell proliferation in response to CD3-TCR complex engagement.     

Cross-linking of the T cell receptor complex with the subset-specific differentiation antigen stimulates interleukin 2 receptor expression in human CD4 and CD8 T cells

Nonpolymorphic interactions between the T cell differentiation antigens CD4 or CD8 and major histocompatibility complex (MHC)-encoded molecules have been postulated to participate in antigen recognition of MHC-restricted T cells. This would imply simultaneous binding of CD4/8 and of the T cell receptor complex (Ti/CD3) to MHC molecules on the stimulator or target cell. In this report experimental evidence is provided that simultaneous binding by antibodies of Ti/CD3 and of CD4 or CD8 leads to the expression of interleukin 2 (IL 2) receptors in resting human T cells and to their subsequent proliferation in the presence of recombinant IL 2 (rIL 2). This could be shown by using a novel anti-CD3 monoclonal antibody (BMA 030) which alone only marginally stimulates highly purified human T cells even when applied in cross-linked form. However, human T cell subpopulations could be stimulated to grow in the presence of rIL 2 when BMA 030 was fixed to a solid support in combination with antibodies to either CD4 or CD8. In limiting dilution experiments, the frequencies of CD4 and CD8 T cells activated by the antibody combinations were similar to those activated by phytohemagglutinin in the presence of irradiated adherent cells. No stimulation was achieved if both or one antibody was applied in soluble form. In contrast, soluble antibodies inhibited activation by solid-phase antibodies. Taken together, cross-linking of Ti/CD3 with CD4/8 seems to be essential for T cell activation in cases of ligands that bind but do not activate T cells on their own--a situation that may reflect the interaction of T cell receptors with MHC-encoded molecules in association with antigen.     

Clonal analysis of CD4 mediated accessory function on the effector activity of human CD4+ T cell subsets

Background: It has been reported for the peripheral T cell repertoire that CD4 molecules may enhance adhesion between T cells and antigen presenting cells and, through their physical association with T cell antigen receptors, contribute to signal transduction. Objective: The aims of this study were to determine if the modulation of CD4 molecules had differential effects on T cell recognition, antigen induced cytokine (IL-4 and IFNγ), release and the induction of specific anergy for human TH-0, TH-1 and TH-2 cells. Methods: A panel of anti-CD4 antibodies was examined for its ability to modulate T cell proliferation, cytokine production and tolerance induction in house dust mite (TH-0 and TH-2) and influenza haemagglutinin (TH-1) specific human CD4+ T cell clones all restricted by DRB1^*1101 and isolated from dust mite allergic individuals. Results: We observed that anti-CD4 antibodies may inhibit or enhance antigen mediated T cell proliferation, which may reflect the differential requirements of T cells for selective functions of CD4. Furthermore, IFNγ and IL-4 production was differentially modulated depending on the specificity of the anti-CD4 antibody and the clone of T cells. However, pretreatment of T cells with anti-CD4 antibody alone neither induced nor enhanced the susceptibility of T cells to peptide mediated anergy. Conclusion: Antigen recognition by different subsets of human CD4+ T cells has differential requirements on CD4, whereas the induction of specific anergy appeared to be independent of the functions of CD4 molecules. Antigen induced IFNγ production was more susceptible than IL-4 to the inhibitory effects of anti-CD4 antibodies. Furthermore, it appeared that certain anti-CD4 antibodies can dissociate antigen induced IFNγ and IL-4 production, and may downregulate IFNγ synthesis without inhibiting antigen dependent proliferation.     

阻断型CD154抗体和CD80抗体生物学作用的研究

为比较阻断型抗人CD154单克隆抗体(1B1)和抗人CD80单克隆抗体(3H8)的单独及联合应用在调节CD4+T细胞对同种抗原的初次和再次免疫应答中的作用。采用免疫磁珠阴性选择法分离获得人外周血CD4+T细胞、将纯化的CD4+T细胞与刺激细胞体外共培养,通过检测培养上清IL-2、IFN-γ水平以及CD4+T细胞的增殖来评价1B1和3H8的生物学作用。结果显示,1B1和3H8单独或联合应用能不同程度地抑制混合淋巴细胞反应中CD4+T细胞对同种抗原刺激的增殖,下调CD4+T细胞分泌IL-2和IFN-γ,并且在再次反应中能有效诱导CD4+T细胞对同种抗原的免疫低反应性。因此,1B1和3H8的单独及联合应用在移植排斥的免疫干预及同种抗原免疫耐受的诱导中具有潜在的应用前景。     

In vitro induction of regulatory T cells by anti-CD3 antibody in humans

Therapy with anti-CD3 antibody is effective in controlling models of autoimmune diseases and can reverse or prevent rejection of grafts. We studied the in vitro immunomodulatory effect of anti-CD3 treated human T cells. CD4(+) T cells were stimulated with plate-bound anti-CD3 and cultured for 12 days after which they were cultured with autologous peripheral blood mononuclear cells (PBMCs) and stimulated with soluble anti-CD3. We found that CD4(+) T cells that were stimulated with anti-CD3 (T(alphaCD3)) markedly suppressed the proliferation and cytokine production of autologous PBMCs. These regulatory T cells were not induced by incubation with isotype control (T(control)) antibody or when anti-CD3 was combined with high doses of anti-CD28 (T(alphaCD3/CD28)). T(alphaCD3) regulatory cells were anergic and produced lower levels of IFN-gamma, TNF-alpha and IL-2, and higher levels of TGF-beta than T(control) or T(alphaCD3/CD28). There were no differences in the expression of CD25 or CTLA4 on T(alphaCD3) as compared to T(control) or T(alphaCD3/CD28), and CD4(+) CD25(-) T(alphaCD3) cells were identical to CD4(+) CD25(+) T(alphaCD3) cells in their in vitro suppressive properties. Recombinant IL-2 in vitro abrogated the suppressive effect of T(alphaCD3). The suppressive effect was not related to apoptosis, was independent of HLA since T(alphaCD3) also suppressed allogeneic PBMCs, and was not related to soluble factors. Finally, no suppression was observed when non-T cells were removed from culture or when cultures were stimulated with plate-bound anti-CD3, consistent with the ability of T(alphaCD3) to downregulate CD80 on dendritic cells in co-culture experiments. Thus, we have identified human T cells with strong in vitro regulatory properties induced in vitro by anti-CD3 which appear to act in a non-HLA restricted fashion by affecting antigen presenting cells.     

Blocking CD40 - CD154 and CD80/CD86 - CD28 interactions during primary allogeneic stimulation results in T cell anergy and high IL-10 production.

Although CD28 triggering provides an important co-stimulatory signal to T cells, blocking the CD80/CD86 - CD28 interaction with CTLA-4lg fusion protein is not sufficient for tolerance induction in vivo or in vitro. According to more recent data, interruption of the CD40 - CD154 interaction might complement the effect of CTLA-4lg and induce graft acceptance. We studied the effects of a blocking anti-CD40 monoclonal antibody (mAb) and/or blocking anti-CD80/anti-CD86 mAb in cultures of human peripheral blood mononuclear cells (PBMC) stimulated with allogeneic PBMC. T cells activated by alloantigens in the presence of anti-CD80, anti-CD86 and anti-CD40 entered a state of alloantigen-specific non-responsiveness as evidenced upon restimulation by lack of proliferation, cytotoxic activity, and IL-2, IL-5 and IL-13 production. IFN-gamma production during restimulation was less than in the control cultures, while the production of IL-10 was enhanced. Addition of recombinant IL-2 during the restimulation rescued alloantigen-specific activity. We conclude that the simultaneous blocking of the CD40 - CD154 and CD80/CD86 - CD28 interaction during allogeneic T cell activation induces T cell anergy. Since anergic cells induced by this treatment still produce high levels of IL-10, the latter could contribute to modulation of antigen-presenting cell activity and to bystander suppression of residual reactive T cells.     

Activation of T cells by cross-linking an anti-CD3 antibody with a second anti-T cell antibody: mechanism and subset-specific activation

Binding of anti-CD3 antibody BMA030-F(ab')2 to T cells is not able to induce T cell proliferation even after additional cross-linking by plastic-bound goat anti-mouse Ig antibodies (panning) and addition of either interleukin (IL) 1 or IL2. In search for agents able to complement the signals provided by BMA030-F(ab')2, several antibodies directed against CD2, CD4, CD5, CD6 and CD8 were used. Neither of these caused T cell proliferation either by themselves or when simply added together with BMA030-F(ab')2. However, if BMA030-F(ab')2 and any other of these anti-CD2, CD4, CD5, CD6 or CD8 antibodies were cross-linked, then proliferation of T cells occurred. The mitogenic effect of cross-linking BMA030-F(ab')2 and a second anti-T cell antibody is dependent on the presence of monocytes or exogenously added IL2. The enhancing effect of monocytes could not be replaced by addition of IL1, suggesting that other soluble factors or monocyte contact might be involved in induction of activation signals. The mechanism leading to this mitogenic effect is dependent on combining cross-linking of BMA030 with the second anti-T cell antibody, whereby the second antibody appears to act as an "anchor" for the CD3 antibody, controlling and/or changing the signal transduction via the CD3 structure. This "anchor" hypothesis could be substantiated by the following observations: the best stimulatory signals were obtained at a BMA030/anti-T cell antibody ratio of 1:1; the effect is independent of the antibody isotype and the epitope recognized by the second antibody; the binding of BMA030 and separate cross-linking of the anti-T cell antibody was not sufficient to trigger T cell mitogenesis; immobilization by direct binding of the CD3 antibody alone or of the CD3 and second membrane structure/antibody complex separately was not sufficient to stimulate T cell proliferation. A further interesting aspect of this finding is the fact that a selective T cell stimulation is possible, since cross-linking BMA030-F(ab')2 plus anti-CD4 antibodies induced a selective stimulation of T4 cells, while cross-linking BMA030-F(ab')2 plus anti-CD8 activated solely T8 cells. It is thus possible to selectively activate T cell subsets in vitro.     

T cell activation by cross-linking anti-CD3 antibodies with second anti-T cell antibodies: dual antibody cross-linking mimics physical monocyte interaction

The anti-CD3 antibody BMA030 (IgG2a isotype) induces T cell activation and proliferation if an interaction with monocytes is provided. In contrast to other anti-CD3 antibodies, it is unable to induce interleukin (IL)2 responsiveness through cross-linking by plastic-bound goat anti mouse Ig antibodies (panning). Cross-linking BMA030 with a second anti-T cell antibody is, however, able to induce IL 2 responsiveness in monocyte-depleted T cell cultures. In this report we show that a large number of different antibodies are suitable for this dual antibody stimulation, and that the extent of proliferation corresponds to the percentage of T cells expressing the respective T cell antigen. Proliferation induced by low concentrations (0.1-1 ng/ml) of other anti-CD3 antibodies requires also cross-linking with second anti-T cell antibodies. The proliferative response of monocyte-depleted T cells to two cross-linked anti-T cell antibodies plus added IL 2 is of the same magnitude as the one induced by anti-CD3 antibodies plus monocytes. On the other hand, if monocytes are present, soluble anti-CD2, -CD4, -CD8, -LFA-1 antibodies (IgG1 or F(ab')2 fragments) can inhibit OKT3 or BMA030-induced T cell activation. Anti-CD6 antibodies do not interfere with this monocyte-dependent T cell stimulation. We conclude that dual antibody stimulation mimics the physical contact of T cells with monocyte membranes, where the T cell receptor CD3 complex is cross-linked with neighboring structures (mainly so-called adhesion molecules) through the interaction with respective counter-structures on monocyte membranes. Dual antibody cross-linking bypasses this interaction and can be used to stimulate IL 2 responsiveness of antibody-defined T cells.     

Co-stimulation with 4-1BB ligand allows extended T-cell proliferation, synergizes with CD80/CD86 and can reactivate anergic T cells

Activation of T cells requires co-stimulation, in addition to signals through the antigen-receptor complex. Antigen encounter without adequate co-stimulation results in T-cell desensitization or anergy, a mechanism of peripheral tolerance and an apparent obstacle to cancer immunotherapy. One important co-stimulatory pathway involves CD28 engagement by CD80 or CD86. However, other ligand-receptor pairs can also provide co-stimulation and may have important functions modulating the immune response. Previous reports indicated that co-stimulation using 4-1BB ligand (4-1BBL) or agonistic anti-4-1BB antibodies could prolong T-cell responses, avoid activation-induced cell death and promote anti-tumour responses in mice. To further investigate the potential for cancer immunotherapy, we studied the effects of CD80/CD86 and 4-1BBL in repeated stimulation of human T cells and asked whether 4-1BBL might be capable of reversing anergy. We expressed CD80, CD86 and 4-1BBL in A549 lung carcinoma cells using adenovirus vectors and co-cultured these with human T cells stimulated with anti-CD3 antibody. Proliferation co-stimulated by CD80 or CD86 was transient; however, 4-1BBL-co-stimulated cultures continued to proliferate for up to 5 weeks, with repeated stimulation. Combined co-stimulation with CD80/CD86 and 4-1BBL also allowed continuous proliferation at a faster rate than either signal alone. Co-stimulation with 4-1BBL did not suppress expression of the inducible, inhibitory CD80/CD86R, CTLA-4. Significantly, we show that T cells that had become non-responsive to anti-CD3, either alone or together with CD80/CD86 co-stimulation, and thus were anergic, could be reactivated to proliferate when costimulated with 4-1BBL, either alone or combined with CD80/CD86.     

Signals delivered via the Qa-2 molecule can synergize with limiting anti-CD3-induced signals to cause T lymphocyte activation.

Qa-2 is a glycolipid anchored, MHC encoded class I molecule expressed at high levels on all murine peripheral T lymphocytes. Anti-Qa-2 antibodies have previously been found to stimulate T cells to proliferate in the presence of crosslinking antibody and PMA. We have examined the effect of anti-Qa-2 antibodies on T cells stimulated with a suboptimal concentration of immobilized anti-CD3. When anti-Qa-2 antibodies were co-immobilized with limiting anti-CD3, in the absence of PMA, a clear augmentation of T cell proliferation was seen. Interestingly, the co-stimulatory anti-Qa-2 antibodies could be directed against epitopes mapped to either the alpha 3 or the alpha 1/alpha 2 Qa-2 domains. As was the case with activation induced by soluble/crosslinked anti-Qa-2 antibodies plus PMA, CD8+ T cells were less able to be costimulated with anti-Qa-2 antibodies than CD4+ cells. Surprisingly, Ca2+ mobilization was only seen when two anti-Qa-2 antibodies reactive to separate structural domains were co-crosslinked on the surface of Indo-1 loaded T cells with a suboptimal concentration of anti-CD3. Collectively these results raise questions regarding the mechanism of Qa-2 mediated signaling and its potential role in T cell activation.     

Helper effector function of human T cells stimulated by anti-CD3 mAb can be enhanced by co-stimulatory signals and is partially dependent on CD40-CD40 ligand interaction

In this study we have investigated whether anti-CD3-induced human T cell help for immunoglobulin production could be enhanced by co-stimulation of the T cells via other T cell surface molecules, and the contribution of CD40-CD40 ligand interaction to the execution of T helper effector function induced by these different stimulatory signals. In a system in which irradiated tonsillar T cells were stimulated with immobilized anti-CD3 monoclonal antibody (mAb), it was found that ligation of CD2 with a mitogenic pair of mAb considerably enhanced anti-CD3-induced T cell help for immunoglobulin production. Likewise, ligation of CD28 with mAb enhanced T helper activity, although to a lesser extent. Upon addition of anti-CD28 and anti-CD2 mAb together, an even higher immunoglobulin production was observed. This combination resulted in a four- to fivefold increase in immunoglobulin production as compared to cultures in which T cells were stimulated with anti-CD3 mAb alone. The effect of ligation with B7, the natural ligand of CD28, was studied in a system which utilizes the presentation of anti-CD3 mAb on human FcγRII-expressing mouse fibroblasts which were co-transfected with human B7. It appeared that B7 could stimulate help for immunoglobulin production much more efficiently than ligation of CD28 with mAb did. Physical separation of B cells from T cells led to complete abrogation of immunoglobulin production. Blocking of CD40 with specific mAb, which have no intrinsic B cell stimulatory properties, or the CD40 ligand with a soluble CD40-human IgM fusion protein, resulted in dose-dependent, but only partial, inhibition of T cell-dependent immunoglobulin production with all modes of T cell activation tested. A clear correlation was found between the induction of CD40 ligand expression on the T cells by the different modes of co-stimulation and subsequent immunoglobulin production by the B cells. It is concluded that ligation of CD28 and/or CTLA-4, and of CD2 can generate co-stimulatory signals for T cell help for immunoglobulin production, which was found to be only partially dependent on the CD40-CD40 ligand interaction.     

Stimulation of CD2-negative T cells by staphylococcal enterotoxin superantigens.

A minor fraction of CD3+ T cells lacks expression of the CD2 antigen, which is the target for an "alternative" T cell activation pathway. CD2-CD3+ T cells can be stimulated by anti-CD3 or anti-T cell receptor (TCR) antibodies, indicating that the CD3/TCR signal transduction pathway functions in the absence of cell surface CD2. In the present study we have analyzed whether CD2-CD3+ T cells also respond to antigen stimulation. We show here that cloned CD2-negative T cells expressing the alpha/beta TCR are activated by one or several staphylococcal enterotoxin "superantigens". Activation of CD2-CD3+ T cell clones by staphylococcal enterotoxins resulted in IL-2 production and/or proliferative activity, and was dependent on the presence of HLA class II-bearing feeder cells. These data demonstrate that T cells can recognize (and respond to) antigen in the absence of a functional CD2 molecule.     

Promotion of natural killer cell growth in vitro by bispecific (anti-CD3 x anti-CD16) antibodies.

Bispecific heteroconjugated F(ab')2 fragments were prepared from pepsin-digested monoclonal OKT3 (anti-CD3) and 3G8 (anti-CD16) antibodies with 5,5'-dithiobis- (2-nitrobenzoic acid). When these bispecific antibodies (BsA) were added to peripheral blood lymphocyte (PBL) cultures with 100 U/ml human recombinant interleukin-2 (rIL-2), preferable growth of natural killer cells occurred. After 3 weeks the frequencies of CD56+ and CD56+3- cells in cultures with BsA were 74 +/- 7% and 65 +/- 7%, respectively, compared with 48 +/- 6% and 29 +/- 7% in control cultures. The frequencies of CD3+ lymphocytes in the presence of BsA, cells from 1-day cultures were labelled with fluorescein isothiocyanate (FITC)-conjugated anti-CD3, CD4 and CD8 monoclonal antibodies (mAb) and propidium iodide which stains dead cells. Flow cytometry revealed that more than 95% of the dead cells in cultures with BsA were CD3+. Thirty-seven per cent of CD3+, 43% of CD4+ and 17% of CD8+ cells were dead on day 1, and after 3 days the CD4+/CD8+ ratio among viable lymphocytes was 1.6 in the control and 0.5 in BsA cultures. Taken together, these results show that bispecific (anti-CD3 x anti-CD16) F(ab')2 fragments are strongly immunomodulatory by inducing the killing of T cells by CD16+ cells.