Induction of synthesis of the cytolytic C9 (ninth component of complement)-related protein in human peripheral mononuclear cells by monoclonal antibody OKT3 or interleukin 2: correlation with cytotoxicity and lymphocyte phenotype

CD8 T cell-mediated killing of Cryptococcus neoformans requires granulysin and is dependent on CD4 T cells and IL-15

Granulysin is located in the acidic granules of cytotoxic T cells. Although the purified protein has antimicrobial activity against a broad spectrum of microbial pathogens, direct evidence for granulysin-mediated cytotoxicity has heretofore been lacking. Studies were performed to examine the regulation and activity of granulysin expressed by CD8 T cells using Cryptococcus neoformans, which is one of the most common opportunistic pathogens of AIDS patients. IL-15-activated CD8 T cells acquired anticryptococcal activity, which correlated with the up-regulation of granulysin. When granules containing granulysin were depleted using SrCl(2,) or when the gene was silenced using 21-nt small interfering RNA duplexes, the antifungal effect of CD8 T cells was abrogated. Concanamycin A and EGTA did not affect the antifungal effect, suggesting that the activity of granulysin was perforin independent. Following stimulation by the C. neoformans mitogen, CD8 T cells expressed granulysin and acquired antifungal activity. This activity required CD4 T cells and was dependent upon accessory cells. Furthermore, IL-15 was both necessary and sufficient for granulysin up-regulation in CD8 T cells. These observations are most consistent with a mechanism whereby C. neoformans mitogen is presented to CD4 T cells, which in turn activate accessory cells. The resultant IL-15 activates CD8 T cells to express granulysin, which is responsible for antifungal activity.

Expression of granzyme A and perforin in mouse heart transplants immunosuppressed with donor-specific transfusion and anti-CD4 monoclonal antibody

Granzyme A and perforin are produced by activated cytotoxic T lymphocytes and their expression correlates with the appearance of cytotoxicity. Using in situ hybridization and immunohistochemistry, we examined the phenotype of cellular infiltration and the appearance of granzyme A+ and perforin+ cells in a mouse cardiac transplant model where the recipients were pretreated with donor-specific transfusion, anti-CD4 monoclonal antibody, or both. While the profiles of cellular infiltration failed to correlate with graft survival, tolerized grafts, as compared with untreated allografts, showed a decreased frequency of granzyme A and perforin expression. These functional markers of cytotoxic T lymphocytes can differentiate between rejecting and indefinitely surviving grafts and may be of value in dissecting the immunological events involved in tolerance induction.

CD30-antigen-specific targeting and activation of T cells via murine bispecific monoclonal antibodies against CD3 and CD28: potential use for the treatment of Hodgkin's lymphoma

Cross-linking of specific tumor antigens with the T-cell-associated CD3 and CD28 antigens can increase IL-2 secretion, proliferation and antigen-specific cytotoxicity in resting T cells. This cross-linking can be achieved effectively by bispecific monoclonal antibodies (BiMAb) with specificity for both the tumor antigen and CD3 or CD28 antigen, respectively. To take advantage of the enhanced activation of CD3 pre-activated T cells by additional activation via the CD28 antigen, BiMAb OKT3/HRS-3 with reactivity to both CD3 and the Hodgkin's-lymphoma-associated CD30 antigen and the BiMAb 15E8/HRS-3 with reactivity to both CD28 and CD30 antigen were generated by hybridoma fusion. Resting T cells, represented by Jurkat cells (CD3+/CD28+) were specifically activated to produce IL-2 by co-cultivation with an EBV-transformed B-cell line (LAZ509, CD30+/CD19+) only in the presence of the CD30/CD28 cross-linking BiMAb and an additional cross-linking anti-CD3/CD19 BiMAb (OKT3/6A4). Neither the cross-linking BiMAbs alone nor any combination of the monospecific parental MAbs induced a comparable IL-2 production by Jurkat cells in the presence of LAZ509. In addition, using a combination of these BiMAbs, an antigen-dependent cytotoxicity was induced by targeting APC-depleted peripheral blood lymphocytes to CD30+ L540 cells. T cells, previously specifically activated by CD3/CD30 in the presence of CD30 antigen, were cytotoxic to CD30+ cell lines only after incubation with BiMAb anti-CD28/CD30. Neither of the BiMAbs nor any of the parental antibodies induced a comparable effect. Our results indicate that such BiMAbs may offer a new approach for specific immunotherapy of Hodgkin's lymphoma, which takes advantage of cytokine secretion and cytotoxicity of activated T cells.

Enhancement by monocytes of perforin production and its gene expression by human CD8+ T cells stimulated with interleukin-2

Pore‐forming protein (PFP) is an important effector molecule for cytotoxicity mediated by cytotoxic T cells and NK cells. In the present study, the effect of monocytes on PFP production by inter‐leukin‐2 (IL‐2)‐stimulated T lymphocytes was examined. Highly purified lymphocytes (>99%) and monocytes (> 90%) were isolated by centrifugal elutriation from peripheral blood of healthy donors, and, CD4+ and CD8+ cells were isolated from the purified lymphocytes by using antibody‐bound magnetic beads. PFP production was quantitated with a universal microspectrophotometer in combination with immunostaining using anti‐PFP antibody. Monocytes did not produce any PFP. High levels of PFP production were observed in CD8+ cells, but not CD4+ cells after incubation for 4 days with IL‐2. Addition of monocytes to cultures of CD8 + cells resulted in significant augmentation of PFP production after 3 days’ stimulation with IL‐2. Monokines (TNFα and IL‐6) caused a significant increase in PFP production by IL‐2‐stimulated CD8+ cells. Northern blot analysis revealed that the PFP mRNA level was enhanced by stimulation with IL‐2, and that addition of monocytes to cultures of CD8 + cells plus IL‐2 augmented their PFP mRNA expression. These observations suggest that monocytes are important in in situ regulation of the CD8 + T cell‐mediated cytotoxic response through production of PFP.

Interleukin 2 induction of pore-forming protein gene expression in human peripheral blood CD8+ T cells

Our studies have analyzed pore-forming protein (PFP) mRNA expression in resting and stimulated human peripheral blood CD3- large granular lymphocytes (LGL), CD3+ T cells, and their CD4+ or CD8+ subsets. Signals that stimulate T cells to develop cytotoxic activity (i.e., IL-2 or OKT-3 mAb) led to the induction of PFP mRNA in T cells. The data indicated that IL-2 directly increased PFP mRNA in the CD8+ subset of T cells, in the absence of new DNA or protein synthesis. Abrogation of IL-2-induced PFP mRNA expression and cytotoxic potential of T cells by the anti-p75 IL-2 receptor mAb suggested that low numbers of p75 IL-2 receptors on CD8+ T cells were capable of transducing signals responsible for these IL-2-induced effects. The induction of T cell PFP mRNA via CD3, using OKT-3 mAb, was less rapid but greater than that caused by IL-2; however, a combination of PMA and ionomycin, which bypasses crosslinking of the TCR/CD3 complex, could not mimic this increase in PFP mRNA levels in T cells. The role of second messenger systems in regulating PFP mRNA expression remains to be determined. In contrast, high constitutive PFP mRNA expression was observed in CD3- LGL and these mRNA levels could not be enhanced by stimulation with IL-2. The cytotoxic potential of peripheral blood T cells and LGL induced in response to IL-2 correlated with IL-2-induced PFP mRNA levels in these cells and was consistent with PFP being one of several important molecules involved in the effector function of cytotoxic lymphocytes.

Expression of HRF20, a regulatory molecule of complement activation, on peripheral blood mononuclear cells

HRF20 is a homologous restriction factor of 20,000 MW that prevents cells from membrane attack by homologous complement. HRF20 has been identified by a monoclonal antibody (mAb), 1F5, and is one of the phosphatidylinositol(PI)-anchored cell-surface glycoproteins. We analysed the distribution of HRF20 expressed on subsets of peripheral blood lymphocytes using 1F5. HRF20 is expressed in relatively large amounts on T cells. In contrast, adherent cells possess smaller amounts of HRF20 while having large quantities of decay-accelerating factor (DAF). Although DAF was shown to be deficient or present at rather low levels on NK cells, HRF20 was detected in 95% of large granular lymphocytes (LGL), as described by FACS analysis. We also determined the effect of 1F5 on both mononuclear leucocytes and T cells in terms of their growth response. The results show that 1F5 induces T-cell proliferation when cells are stimulated with interleukin-2 (IL-2). In addition, induction of proliferation is facilitated by cross-linking 1F5 with a second antibody. These results suggest that HRF20 expressed on T cells not only protects them from cytotoxic attack by homologous complement, but also may initiate intracellular signals leading to cell activation when they happen to be cross-linked.

Induction of cytotoxicity in human T cells coated with anti-glioma x anti-CD3 bispecific antibody against human glioma cells

A bifunctional hetero-F(ab')2 antibody fragment was developed that contained the Fab portions from anti-CD3 and anti-glioma monoclonal antibodies. The antibody simultaneously recognized two different molecules, the CD3 complex on effector T cells and a human glioma-associated antigen; thus, it could cross-link effector and target cells. This bispecific F(ab')2 fragment induced peripheral blood mononuclear cells (PBMC's) from healthy donors to lyse cells of the human glioma cell line, U251MG, which are resistant to natural killer cell-mediated cytolysis. The effect of the bispecific antibody on lymphokine-activated killer (LAK) cell activity was tested in patients suffering from malignant glioma. For this study, PBMC's from these patients were preactivated with recombinant interleukin-2 and their killer activity against U251MG cells was investigated in vitro with and without the bispecific antibody. The LAK cell activity of the PBMC's from patients with malignant gliomas was found to be suppressed compared with those of healthy donors. However, after preincubation with bispecific antibody, the patients' LAK cells exhibited marked cytolytic activity against U251MG cells. These findings suggest that this bispecific antibody may be a useful addition to anti-glioma immunotherapy.

Structure and function of human perforin

Perforin (P1) is a cytolytic protein with similarity to complement component C9. P1 has been described as a unique component of murine cytolytic T-cell and rat natural killer cell granules Previous studies indicated that human granules and P1 differed from murine granules and P1 in that they appeared to be cytolytically less active and lacked the haemolytic activity characteristic of P1. It has been suggested that P1, like C9, is under the control of the homologous restriction factor. Here we determine the primary structure of human P1, re-examine its functional properties, and address the question of homologous restriction.

Self-protection of cytotoxic lymphocytes: a soluble form of homologous restriction factor in cytoplasmic granules

A soluble form of homologous restriction factor (HRF) has been isolated from the cytoplasmic granules of human large granular lymphocytes that were cultured in the presence of recombinant interleukin 2 for 2-3 weeks. The granule-derived protein (approximately 65 kDa) is soluble in detergent-free solution and reacts with antibody produced to membrane HRF. HRF was first described as a 65-kDa membrane protein of human erythrocytes capable of inhibiting the formation of transmembrane channels by the membrane attack complex of complement. It has also been isolated from activated human lymphocytes and shown to confer upon these cells relative resistance to lysis by the membrane attack complex and by the complement component C9-related protein of human cytotoxic lymphocytes. The soluble HRF of lymphocyte granules inhibits reactive lysis of erythrocytes by the membrane attack complex of human complement. It was also found to be a potent inhibitor of (i) the cytolytic activity of the C9-related protein of human cytotoxic lymphocytes, (ii) human large granular lymphocyte cytotoxicity, and (iii) the cytotoxic activity of human CD8+ lymphocytes obtained by cell sorting from recombinant interleukin 2-activated peripheral blood mononuclear cells. It is proposed that granule-derived soluble HRF and cell surface-membrane-bound HRF are involved in the mechanism of self-protection of killer lymphocytes.

Appearance of granule-associated molecules during activation of cytolytic T-lymphocyte precursors by defined stimuli

Lysis of target cells by cytolytic T lymphocytes (CTL) is associated with the exocytosis of cytoplasmic granules. Purified granules from CTL cell lines contain a pore-forming protein (perforin), tree serine esterases, granzyme A (60,000 MW), granzyme B (29,000 MW), and granzyme C (27,000 MW). We have compared the kinetics of appearance of cytolytic activity with that of perforin and granzyme A activity during activation of lymphocytes from normal animals with leukoagglutinin (LA) and recombinant interleukin-2 (rIL-2). Unstimulated lymph node cells do not express any of these activities, which appear between Day 3 and Day 4 of stimulation and increase rapidly to reach a pronounced peak on Day 6. On Day 7 all the activities are considerably lower, even though the cells still proliferate exponentially. There is a good correlation between the kinetics of appearance of all of these activities. Using antisera against perforin and against granzyme C, one can detect positive cytoplasmic granules in a small fraction of cells on Day 3; by Day 5, 80-90% of the cells are stained. This proportion decreases again on Day 7.

The molecular basis of target cell killing by human lymphocytes and of killer cell self-protection

The cytolytic protein (C9RP) of human cytotoxic lymphocytes was isolated from large granular lymphocytes (LGL) and anti-CD3 activated cytotoxic T cells (CTL). It is immunochemically related to the channel-forming proteins of complement. Whereas LGL constitutively contain C9RP, peripheral resting CTL do not. C9RP synthesis is induced, however, in CD8+ cells upon stimulation of the T cell antigen receptor-CD3 structure. Comparison of cellular cytotoxicity and C9RP content at various times during anti-CD3 activation of CTL yielded a coefficient of correlation, r = 0.92. Isolated C9RP (Mr approximately 70,000) readily lysed a large variety of metabolically active cells tested. Certain monoclonal antibodies to C9RP inhibited target cell killing by LGL or activated CD8+ lymphocytes. Homologous restriction factor (HRF) is a normal membrane protein of blood cells that inhibits transmembrane channel formation by the membrane attack complex of complement. It has recently been found that isolated HRF (Mr approximately 65,000), bound to sheep erythrocytes, inhibited their lysis mediated by the antibody-dependent cellular cytotoxicity reaction or by isolated C9RP. Further, stimulation of resting peripheral lymphocytes with anti-CD3 resulted in increased expression of cell surface HRF. Acquisition of HRF expression conferred upon CTL relative resistance to lysis by C9RP. A soluble form of HRF (Mr approximately 65,000) was isolated from the cytoplasmic granules of LGL, which also contain C9RP, and shown to inhibit cytotoxicity of LGL and CTL. It is conceivable that HRF is opertive in self-protection of cytotoxic lymphocytes.

A comparison of the cytolytic properties of murine primary CD8+ cytotoxic T lymphocytes and cloned cytotoxic T cell lines

Lysates of many highly cytolytic murine primary CD8+ cytotoxic T lymphocytes (CTLs) have no detectable hemolytic activity and only traces of serine esterase activity, indicating a striking paucity or absence of the perforin-rich secretory granules that are abundant in the cytoplasm of murine cloned CTL cell lines. Nevertheless, the primary CTLs are almost as resistant to granule-mediated lysis as CTL cell lines. Moreover, target cells that are lysed by all CTLs so far tested, whether primary or cell lines, show similar rapid and marked increases in intracellular calcium and breakdown of DNA into nucleosome-sized fragments. A parsimonious explanation for all of these findings is that primary CTLs, like the CTL cell lines, exercise their cytolytic activity by means of perforin, but the amounts needed are extremely small and below the level of detection by the current relatively insensitive hemolytic assays.

Induction of expression of cell-surface homologous restriction factor upon anti-CD3 stimulation of human peripheral lymphocytes

Homologous restriction factor (HRF) is a 65-kDa membrane protein that inhibits transmembrane channel formation by the membrane-attack complex of complement and by the complement component C9-related cytolytic lymphocyte protein. Stimulation of resting peripheral human lymphocytes with the anti-CD3 monoclonal antibody OKT3 has been shown to induce cytotoxicity in the CD8+ subpopulation. As demonstrated here, OKT3 stimulation also induces expression of cell-surface HRF by CD4+ and CD8+ T lymphocytes. The small proportion of Leu 19+ natural killer lymphocytes present in peripheral blood mononuclear cells was found to express HRF prior to stimulation. Whereas unstimulated peripheral blood mononuclear cells were susceptible to lysis by the membrane-attack complex or by the C9-related protein, OKT3-stimulated peripheral blood mononuclear cells were relatively resistant to both the membrane-attack complex and C9-related protein. This acquired resistance was abrogated by blocking surface HRF with F(ab')2 anti-HRF, suggesting that resistance was due to lymphocyte-membrane HRF. By using solid-phase anti-HRF, a 65-kDa protein was isolated from the activated peripheral blood mononuclear cells and shown to be capable of conferring upon sheep erythrocytes the characteristic activity of human HRF.

Induction of cytotoxicity in resting human T lymphocytes bound to tumor cells by antibody heteroconjugates

An in vitro model for peripheral human T-cell activation and resultant tumor cell killing is described. Cytotoxic T lymphocytes may be generated from resting lymphocytes by incubation of human peripheral blood mononuclear cells for 3 days with the anti-CD3 monoclonal antibody OKT3. Cytotoxicity in peripheral blood mononuclear cells can also be induced by adding an anti-target-OKT3 antibody conjugate and 10% (vol/vol) fetal calf serum to the culture medium. Conjugate activation of T cells was almost completely blocked, however, when 20% (vol/vol) human serum was added to the medium. Conjugate-mediated peripheral blood mononuclear cells activation was restored to some extent by the addition of melanoma target cells to the culture and was markedly enhanced by a second conjugate containing anti-target cell and anti-CD28 antibody. Monoclonal antibody 9.3 (anti-CD28) provides a progression signal in T-lymphocyte activation when used in combination with anti-CD3. Thus, presentation by the tumor target cells of anti-CD3 and anti-CD28 to resting human lymphocytes causes T-cell activation, which is independent of monocytes, proceeds in the presence of human serum, and results in tumor cell killing.