NKG2A inhibits NKG2C effector functions of γδ T cells: implications in health and disease

The CD94/NKG2 complex is expressed on T and NK lymphocytes. CD94 molecules covalently associate to activating or inhibitory NKG2 molecules, and their expression finely tunes cell responses. Human γδ T cells express several NKRs. Expression of these receptors is confined to the cytolytic Vδ2 subset, which coexpresses the FcγRIII CD16 and CD45RA and has been defined as Vγ9Vδ2 T(EMRA) cells. We show that the CD94/NKG2C complex, associated with KARAP/DAP12, is fully functional in γδ T cells, as determined by measuring IFN-γ production, T cell proliferation, and cytolytic activity by γδ lymphocytes. In contrast, NKG2A expression was found on all γδ T cell memory subsets, suggesting a crucial role of the inhibitory signal provided by this receptor on γδ T cell responses. Moreover, we found Vγ9Vδ2 T(EMRA), NK, and CD8+ αβ T cells coexpressing NKG2A and NKG2C receptors. Functional experiments showed that the inhibitory signal mediated by the NKG2A receptor prevails when double-positive cells are activated. Finally, NKG2A expression on γδ LDGL correlates with asymptomatic pathology, even in the presence of NKG2C coexpression, whereas in symptomatic patients affected by severe disease, the inhibitory NKG2A receptor is absent, and a variety of activatory NKRs was found. We propose that the silent behavior of γδ cells in LDGL patients is a result of effective inhibitory HLA class I receptors.

Increased frequency of human leukocyte antigen-E inhibitory receptor CD94/NKG2A-expressing peritoneal natural killer cells in patients with endometriosis

OBJECTIVE

To analyze the frequency of peritoneal natural killer (NK) cells expressing the human leukocyte antigen (HLA)-E receptor CD94/NKG2A in patients with endometriosis.

DESIGN

Case-control study.

SETTING

University hospital.

PATIENT(S)

Stage III and stage IV endometriosis, according to the revised American Society for Reproductive Medicine classification, was laparoscopically and histologically confirmed in 11 and 9 patients, respectively; 13 subjects without endometriosis were selected for the control group.

INTERVENTION(S)

Collection of peripheral venous blood, peritoneal fluid, endometriotic tissue, and normal endometrium in subjects undergoing laparoscopy.

MAIN OUTCOME MEASURE(S)

Surface expression levels of CD94/NKG2A and CD94/NKG2C were detected by three-color cytofluorometric analysis. Semiquantitative HLA-E messenger RNA expression analysis was performed in endometriotic lesions and in eutopic endometrium. NK cell-mediated cytotoxic activity toward HLA-E positive target, DT360 cell line, was also determined.

RESULT(S)

In women with endometriosis, the percentage of CD94/NKG2A-positive peritoneal NK cells was significantly higher than in the control group. The CD94/NKG2A ligand, HLA-E, was detected at high levels in endometriotic tissue as messenger RNA transcript. Target cells bearing HLA-E were resistant to NK cell-mediated lysis in a CD94/NKG2A-dependent manner.

CONCLUSION(S)

Increased expression of CD94/NKG2A in peritoneal NK cells may mediate the resistance of endometriotic tissue to NK cell-mediated lysis, thus contributing to the progression of the disease.

High-efficient lentiviral vector-mediated gene transfer into primary human NK cells

OBJECTIVE

The long-term transfection of genes into primary natural killer (NK) cells without disrupting normal cellular functions has been proven to be difficult with currently available gene-transfer methods. In this study, we establish a lentiviral vector-based technique for improved gene transfer into human NK cells in vitro and we report on high-efficient transduction of freshly isolated as well as cultured primary NK cells.

METHODS

Freshly isolated or primary cultured human NK cells, as well as the human NK cell line YTS, were transduced with replication-incompetent human immunodeficiency virus (HIV)-based lentiviral vector bearing a GFP reporter gene or a gene of interest under the control of the elongation factor 1alpha (EF1alpha) promoter. Transduction efficiencies were monitored by flow cytometry.

RESULTS

A long-term transgene expression was detected in up to 98% of YTS NK cells, whereas in freshly isolated or primary cultured NK cells exposed to interleukin (IL)-2 plus IL-12 upon infection, efficiency was in the range of 50% to 90%. Moreover, in freshly isolated quiescent NK cells a transfection efficiency of 18% to 20% was achieved without stimulation. Notably, no major phenotypic and functional modifications were observed in transduced cells with respect to control cells: the expression levels of activating receptors, CD69-antigen induction as well as cytotoxic function were unaffected.

CONCLUSION

Results of our study demonstrate that NK cells can be efficiently transduced by lentiviral vectors.

Arf6: a new player in FcγRIIIA lymphocyte-mediated cytotoxicity

The activation of phosphoinositide metabolism represents a critical step in the signaling pathways leading to the activation of cytolytic machinery, but its regulation is partially understood. We report here that the stimulation of the low-affinity receptor for immunoglobulin G (IgG) (FcγRIIIA, CD16) on primary human natural killer (NK) cells induces a phosphatidylinositol 3-kinase (PI3K)–dependent activation of the small G protein Arf6. We first demonstrate a functional role for Arf6-dependent signals in the activation of the antibody-dependent cellular cytotoxicity (ADCC) attributable to the control of secretion of lytic granule content. We also show that Arf6 couples CD16 to the lipid-modifying enzymes phosphatidylinositol4phosphate 5-kinase type I alpha (PI5KIα) and phospholipase D (PLD) that are involved in the control of granule secretion; Arf6, but not Rho family small G proteins RhoA and Rac1, is required for receptor-induced PI5KIα membrane targeting as well as for PI5KIα and PLD activation. Our findings suggest that Arf6 plays a crucial role in the generation of a phosphatidylinositol4,5-bisphosphate (PIP2) plasma membrane pool required for cytolytic granule-mediated target cell killing.

SH2-containing inositol phosphatase (SHIP-1) transiently translocates to raft domains and modulates CD16-mediated cytotoxicity in human NK cells

Membrane recruitment of the SH2-containing 5' inositol phosphatase 1 (SHIP-1) is responsible for the inhibitory signals that modulate phosphatidylinositol 3-kinase (PI3K)-dependent signaling pathways. Here we have investigated the molecular mechanisms underlying SHIP-1 activation and its role in CD16-mediated cytotoxicity. We initially demonstrated that a substantial fraction of SHIP-1-mediated 5' inositol phosphatase activity associates with CD16 zeta chain after receptor cross-linking. Moreover, CD16 stimulation on human primary natural killer (NK) cells induces the rapid and transient translocation of SHIP-1 in the lipid-enriched plasma membrane microdomains, termed rafts, where it associates with tyrosine-phosphorylated zeta chain and shc adaptor protein. As evaluated by confocal microscopy, CD16 engagement by reverse antibody-dependent cellular cytotoxicity (ADCC) rapidly induces SHIP-1 redistribution toward the area of NK cell contact with target cells and its codistribution with aggregated rafts where CD16 receptor also colocalizes. The functional role of SHIP-1 in the modulation of CD16-induced cytotoxicity was explored in NK cells infected with recombinant vaccinia viruses encoding wild-type or catalytic domain-deleted mutant SHIP-1. We found a significant SHIP-1-mediated decrease of CD16-induced cytotoxicity that is strictly dependent on its catalytic activity. These data demonstrate that CD16 engagement on NK cells induces membrane targeting and activation of SHIP-1, which acts as negative regulator of ADCC function.

The adaptor protein shc is involved in the negative regulation of NK cell-mediated cytotoxicity

The activation of protein tyrosine kinase(s) (PTK) is a critical event required for the development of NK cell-mediated cytotoxicity. Here we demonstrate that the adaptor protein shc undergoes tyrosine phosphorylation during the generation of antibody-dependent cellular cytotoxicity (ADCC) and natural killing. In addition, we report that, upon direct or antibody-dependent target cell interaction, shc coprecipitates with the Src homology 2 (SH2)-containing inositol phosphatase, SHIP. To gain information on the functional role of shc in NK cytotoxicity, we overexpressed wild-type or dominant negative shc constructs in the human NKL cell line. Our findings show a consistent shc-mediated down-regulation of ADCC and natural killing. Such functional effect correlates with a perturbation of the phosphoinositide (PI) metabolism by means of a shc-mediated negative regulation of inositol 1,4,5 triphosphate (IP3) generation and intracellular calcium flux upon CD16 ligation. Furthermore, our data show that dominant-negative shc-mediated perturbation of shc/SHIP interaction leads to inhibition of ligand-dependent SHIP recruitment to CD16 zeta chain. We suggest that shc plays a role of negative adaptor by modulating SHIP recruitment to activation receptors involved in the generation of NK cytotoxic function.

The GTPase rho controls a p53-dependent survival checkpoint during thymopoiesis

During the early stages of thymopoiesis, cell survival is controlled by cytokines that regulate the expression of antiapoptotic proteins such as Bcl-2. At the pre-T cell stage, a critical checkpoint for beta chain selection is monitored by the tumor suppressor p53: pre-T cells can survive and differentiate when p53 is removed genetically or when its proapoptotic function is inactivated physiologically as a consequence of signaling through the pre-T cell receptor complex. Previous work has shown that the guanine nucleotide binding protein Rho controls cell survival in T cell progenitors. Here we define the survival pathways controlled by Rho in pre-T cells and show that this GTPase is a pivotal regulator of the p53-mediated checkpoint operating at the time of beta selection: loss of Rho function results in apoptosis in pre-T cells, but this cell death is prevented by loss of p53. The prevention of cell death by loss of p53 restored numbers of early T cell progenitors but did not fully restore thymic cellularity. Further analysis revealed that loss of Rho function caused survival defects in CD4/8 double-positive thymocytes that is independent of p53 but can be prevented by ectopic expression of Bcl-2. These studies highlight that the GTPase Rho is a crucial component of survival signaling pathways in at least two different thymocyte subpopulations: Rho controls the p53 survival checkpoint in pre-T cells and is also crucial for a p53 independent survival signaling pathway in CD4/8 double positives.

Role for the Rac1 exchange factor Vav in the signaling pathways leading to NK cell cytotoxicity

Here we investigate the activation of and a possible role for the hematopoietic Rac1 exchange factor, Vav, in the signaling mechanisms leading to NK cell-mediated cytotoxicity. Our data show that direct contact of NK cells with a panel of sensitive tumor targets leads to a rapid and transient tyrosine phosphorylation of Vav and to its association with tyrosine-phosphorylated Syk. Vav tyrosine phosphorylation is also observed following the activation of NK cells through the low-affinity Fc receptor for IgG (Fc gamma RIII). In addition, we demonstrate that both direct and Ab-mediated NK cell binding to target cells result in the activation of nucleotide exchange on endogenous Rac1. Furthermore, Vav antisense oligodeoxynucleotide treatment leads to an impairment of NK cytotoxicity, with Fc gamma RIII-mediated killing being more sensitive to the abrogation of Vav expression. These results provide new insight into the signaling pathways leading to cytotoxic effector function and define a role for Vav in the activation of NK cell-mediated killing.

Role for the Rac1 Exchange Factor Vav in the Signaling Pathways Leading to NK Cell Cytotoxicity

Here we investigate the activation of and a possible role for the hematopoietic Rac1 exchange factor, Vav, in the signaling mechanisms leading to NK cell-mediated cytotoxicity. Our data show that direct contact of NK cells with a panel of sensitive tumor targets leads to a rapid and transient tyrosine phosphorylation of Vav and to its association with tyrosine-phosphorylated Syk. Vav tyrosine phosphorylation is also observed following the activation of NK cells through the low-affinity Fc receptor for IgG (FcγRIII). In addition, we demonstrate that both direct and Ab-mediated NK cell binding to target cells result in the activation of nucleotide exchange on endogenous Rac1. Furthermore, Vav antisense oligodeoxynucleotide treatment leads to an impairment of NK cytotoxicity, with FcγRIII-mediated killing being more sensitive to the abrogation of Vav expression. These results provide new insight into the signaling pathways leading to cytotoxic effector function and define a role for Vav in the activation of NK cell-mediated killing.

Selective binding of shc-SH2 domain to tyrosine-phosphorylated zeta but not gamma-chain upon CD16 ligation on human NK cells

Fc gamma RIII (CD16) is a hetero-oligomeric receptor composed of a ligand-binding alpha subunit associated with homo- or heterodimers of the TCR zeta- and Fc epsilon RI gamma-chains. We have previously demonstrated that CD16 ligation promotes complex formation between tyrosine-phosphorylated shc and Grb2, leading to activation of ras signaling pathway in human NK cells. Here we report that CD16 engagement induces rapid shc association with the tyrosine-phosphorylated receptor complex in human NK cells. In vitro binding studies demonstrate that this interaction is mediated by the shc-SH2 domain, and immunodepletion experiments indicate that the zeta- but not the gamma-chain has the capability to mediate this association. Jurkat cell clones expressing CD16-zeta or -gamma homodimers have been used to gain more information about the mechanism of shc/CD16 association. Our data show that, while engagement of both receptors induces tyrosine phosphorylation of shc and Grb2 recruitment, shc-SH2/receptor complex association is evident only in CD16-zeta but not in CD16-gamma transfectants. Overall, our data demonstrate that the adaptor protein shc can be recruited to the activated CD16 complex by interaction with tyrosine-phosphorylated zeta-chain in a SH2-dependent manner. These results also provide further support to the notion that zeta- and gamma-chains might couple to different biochemical pathways.

Selective binding of shc-SH2 domain to tyrosine-phosphorylated zeta but not gamma-chain upon CD16 ligation on human NK cells

Fc gamma RIII (CD16) is a hetero-oligomeric receptor composed of a ligand-binding alpha subunit associated with homo- or heterodimers of the TCR zeta- and Fc epsilon RI gamma-chains. We have previously demonstrated that CD16 ligation promotes complex formation between tyrosine-phosphorylated shc and Grb2, leading to activation of ras signaling pathway in human NK cells. Here we report that CD16 engagement induces rapid shc association with the tyrosine-phosphorylated receptor complex in human NK cells. In vitro binding studies demonstrate that this interaction is mediated by the shc-SH2 domain, and immunodepletion experiments indicate that the zeta- but not the gamma-chain has the capability to mediate this association. Jurkat cell clones expressing CD16-zeta or -gamma homodimers have been used to gain more information about the mechanism of shc/CD16 association. Our data show that, while engagement of both receptors induces tyrosine phosphorylation of shc and Grb2 recruitment, shc-SH2/receptor complex association is evident only in CD16-zeta but not in CD16-gamma transfectants. Overall, our data demonstrate that the adaptor protein shc can be recruited to the activated CD16 complex by interaction with tyrosine-phosphorylated zeta-chain in a SH2-dependent manner. These results also provide further support to the notion that zeta- and gamma-chains might couple to different biochemical pathways.

Different functions of the GTPase Rho in prothymocytes and late pre-T cells

Mice lacking thymic function of the GTPase Rho show severe defects in fetal and adult thymopoiesis. Rho thymi are deficient in CD44+ CD25+ pro-T cells and CD44- CD25+ early pre-T cells because Rho function is required for survival but not G1/S phase cell cycle progression in these populations. The selective apoptosis defect in Rho prothymocytes can be rescued by expression of a bcl-2 transgene. A second function for Rho is seen in CD44- CD25- late pre-T cells: Rho regulates cell cycle progression but not survival of this population. These studies show that the critical processes of proliferation and survival are independently regulated during thymopoiesis and establish two different functions for Rho in the development of early thymic progenitors.

The GTPase Rho has a critical regulatory role in thymus development

The present study employs a genetic approach to explore the role of Rho GTPases in murine thymic development. Inactivation of Rho function in the thymus was achieved by thymic targeting of a transgene encoding C3 transferase from Clostridium botulinum which selectively ADP-ribosylates Rho within its effector domain and thereby abolishes its biological function. Thymi lacking functional Rho isolated from C3 transgenic mice were strikingly smaller and showed a marked (90%) decrease in cellularity compared with their normal litter mates. We also observed a similar decrease in levels of peripheral T cells in C3 transgenic mice. Analysis of the maturation status of thymocytes indicated that differentiation of progenitor cells to mature T cells can occur in the absence of Rho function, and both positive and negative selection of T cells appear to be intact. However, transgenic mice that lack Rho function in the thymus show maturational, proliferative and cell survival defects during T-cell development that severely impair the generation of normal numbers of thymocytes and mature peripheral T cells. The present study thus identifies a role for Rho-dependent signalling pathways in thymocyte development. The data show that the function of Rho GTPases is critical for the proliferative expansion of thymocytes. This defines a selective role for the GTPase Rho in early thymic development as a critical integrator of proliferation and cell survival signals.

Tyrosine kinase-dependent activation of human NK cell functions upon triggering through CD44 receptor

We recently showed evidence of CD44-mediated enhancement of natural killer (NK) cell cytotoxic activity and induction of intracellular Ca2+ flux. In this study, we evaluated whether CD44 plays a stimulatory role in NK cell functions, such as cytokine production and activation antigen expression. Our results indicate that ligation of the CD44 receptor results in the induction of expression of the CD69 surface activation antigen as well as in the enhancement of phorbol ester-induced TNF-alpha secretion. We report also evidence for the coupling of CD44 receptor to a protein tyrosine kinase(s) pathway. CD44 engagement rapidly stimulates the tyrosine phosphorylation of several cellular substrates. Pretreatment of NK cells with the tyrosine kinase inhibitor herbimycin A resulted in marked decrease of CD44-stimulated phosphorylation, indicating that it activates tyrosine kinase(s). Furthermore, the drug also prevents CD44-mediated TNF-alpha production and CD69 expression. These findings indicate that protein tyrosine phosphorylation is an early and critical event in CD44-mediated activation of NK cell functions.

CD16-mediated p21ras activation is associated with Shc and p36 tyrosine phosphorylation and their binding with Grb2 in human natural killer cells

The Src homology (SH) 2/SH3 domain-containing protein Grb2 and the oncoprotein Shc have been implicated in a highly conserved mechanism that regulates p21ras activation. We investigated the involvement of these adaptor proteins in the signaling pathway induced by CD16 or interleukin (IL) 2R triggering in human natural killer (NK) cells. Both p46 and p52 forms of Shc were rapidly and transiently tyrosine phosphorylated upon CD16 or IL-2 stimulation with different kinetics. Shc immunoprecipitates from lysates of CD16- or IL-2-stimulated NK cells contained Grb2 and an unidentified 145-kD tyrosine phosphoprotein. Grb2 immunoprecipitates from anti-CD16-stimulated NK cells contained not only Shc, but also a 36-kD tyrosine phosphoprotein (p36). The interaction between Grb2 and Shc or p36 occurred via the Grb2SH2 domain as indicated by in vitro binding assays using a bacteriologically synthesized glutathione S-transferase-Grb2SH2 fusion protein. We also present evidence that p21ras is activated by CD16 and IL-2R cross-linking. Accumulation of guanosine triphosphate-bound Ras was detected within 1 minute and occurred with kinetics similar to inductive protein tyrosine phosphorylation and Grb2 association of Shc and p36 adaptor proteins.

Interaction of natural killer cells with extracellular matrix induces early intracellular signalling events and enhances cytotoxic functions

NK cells are endowed with a wide array of adhesion molecules which mediate their interaction with endothelium and extracellular matrix components. We have shown that cross-linking of beta 1 integrins and CD44 on human NK cells induces a signal transduction pathway involving both tyrosine kinase activation and the modulation of intracellular calcium levels. Our studies have also demonstrated the ability of beta 1 integrins and CD44 to upregulate both the spontaneous and the CD16-triggered cytotoxic activity of human NK cells. Although the molecular mechanisms responsible for this costimulatory activity have not been defined yet, our studies indicate that the simultaneous cross-linking of beta 1 integrins and CD44 results in a synergistic effect on CD16-mediated enhancement of intracellular free calcium concentration, and suggest that this may be relevant for the cooperation observed.

CD44 triggering enhances human NK cell cytotoxic functions

CD44, a major hyaluronate receptor, is involved in a variety of lymphocyte functions including lympho-hemopoiesis, adhesion to high endothelial venules or the extracellular matrix, and T cell activation. Here we investigated the ability of CD44 to affect the cytotoxic functions of human NK cells. Ligation of CD44 by selected mAb (J173 and F10442) resulted in a rapid, dose-response-dependent enhancement of NK cytotoxic activity against a panel of tumor target cells that varied in their sensitivity to NK killing. Neither enhanced killing against NK-resistant target cells nor CD44 mAb-mediated redirected lysis was not observed. CD44 cross-linking also was found to up-regulate CD16-mediated lysis. In an attempt to investigate the early biochemical events that occur after CD44 ligation, we found that optimal cross-linking conditions induce a rapid increase of intracellular free calcium levels, which is abrogated by extracellular Ca2+ chelation. Moreover, enhanced and more sustained Ca2+ rise resulted from CD16 and CD44 coengagement. In contrast, no inositol 1,4,5-trisphosphate generation was found after optimal CD44 cross-linking. These results suggest that although CD44 is not capable of delivering a lytic signal in human NK cells, it coactivates spontaneous or CD16-mediated NK cytotoxicity. The variation in intracellular free calcium may be one of the signals that account for the costimulation of the lytic activity.

CD44 triggering enhances human NK cell cytotoxic functions

CD44, a major hyaluronate receptor, is involved in a variety of lymphocyte functions including lympho-hemopoiesis, adhesion to high endothelial venules or the extracellular matrix, and T cell activation. Here we investigated the ability of CD44 to affect the cytotoxic functions of human NK cells. Ligation of CD44 by selected mAb (J173 and F10442) resulted in a rapid, dose-response-dependent enhancement of NK cytotoxic activity against a panel of tumor target cells that varied in their sensitivity to NK killing. Neither enhanced killing against NK-resistant target cells nor CD44 mAb-mediated redirected lysis was not observed. CD44 cross-linking also was found to up-regulate CD16-mediated lysis. In an attempt to investigate the early biochemical events that occur after CD44 ligation, we found that optimal cross-linking conditions induce a rapid increase of intracellular free calcium levels, which is abrogated by extracellular Ca2+ chelation. Moreover, enhanced and more sustained Ca2+ rise resulted from CD16 and CD44 coengagement. In contrast, no inositol 1,4,5-trisphosphate generation was found after optimal CD44 cross-linking. These results suggest that although CD44 is not capable of delivering a lytic signal in human NK cells, it coactivates spontaneous or CD16-mediated NK cytotoxicity. The variation in intracellular free calcium may be one of the signals that account for the costimulation of the lytic activity.

Hyaluronate is costimulatory for human T cell effector functions and binds to CD44 on activated T cells

Lymphohematopoiesis, cell matrix adhesion, homing of leukocytes, T cell activation, and tumor metastasis are mediated through the CD44 family of cell surface receptors. We have recently shown that anti-CD44 mAb trigger protein tyrosine kinase-dependent activation of T cell effector functions. Here, we show that hyaluronate (HA), a CD44 ligand, in conjunction with CD3/TCR-mediated stimuli, is costimulatory for human peripheral blood T cell proliferation, for IL-2 production by Th clones, and for release of trypsin-like esterase by cytolytic T cell clones. A human T cell line, HUT-78, was found to bind HA and on HA coating it was used as a target for cytolytic T cell clones. After anti-CD3 stimulation, CD3+/CD8+ clones acquire the ability of lysing HA-coated HUT-78 cells more efficiently than the same HA-uncoated targets. Resting peripheral blood T cells and T cell clones do not adhere to HA-coated plates. However, 24-h anti-CD3 mAb stimulation gives them the transient ability to bind HA. HA adhesion of activated T cells and T cell clones, as well as that of T cell lines, is blocked by one anti-CD44 mAb (J-173). Two other anti-CD44 mAbs induce a 10-fold increase in HA adhesiveness of anti-CD3-stimulated peripheral blood T cells. This impressive HA adhesiveness is also readily blocked by J-173 anti-CD44 mAb. These data indicate that 1) HA is costimulatory for human T cell effector functions in conjunction with CD3/TCR-mediated stimuli, 2) the capacity to bind HA is acquired by resting T cells and T cell clones after anti-CD3 stimulation, and 3) HA binding occurs via specific interaction with CD44 molecules expressed on activated T cells.

Hyaluronate is costimulatory for human T cell effector functions and binds to CD44 on activated T cells

Lymphohematopoiesis, cell matrix adhesion, homing of leukocytes, T cell activation, and tumor metastasis are mediated through the CD44 family of cell surface receptors. We have recently shown that anti-CD44 mAb trigger protein tyrosine kinase-dependent activation of T cell effector functions. Here, we show that hyaluronate (HA), a CD44 ligand, in conjunction with CD3/TCR-mediated stimuli, is costimulatory for human peripheral blood T cell proliferation, for IL-2 production by Th clones, and for release of trypsin-like esterase by cytolytic T cell clones. A human T cell line, HUT-78, was found to bind HA and on HA coating it was used as a target for cytolytic T cell clones. After anti-CD3 stimulation, CD3+/CD8+ clones acquire the ability of lysing HA-coated HUT-78 cells more efficiently than the same HA-uncoated targets. Resting peripheral blood T cells and T cell clones do not adhere to HA-coated plates. However, 24-h anti-CD3 mAb stimulation gives them the transient ability to bind HA. HA adhesion of activated T cells and T cell clones, as well as that of T cell lines, is blocked by one anti-CD44 mAb (J-173). Two other anti-CD44 mAbs induce a 10-fold increase in HA adhesiveness of anti-CD3-stimulated peripheral blood T cells. This impressive HA adhesiveness is also readily blocked by J-173 anti-CD44 mAb. These data indicate that 1) HA is costimulatory for human T cell effector functions in conjunction with CD3/TCR-mediated stimuli, 2) the capacity to bind HA is acquired by resting T cells and T cell clones after anti-CD3 stimulation, and 3) HA binding occurs via specific interaction with CD44 molecules expressed on activated T cells.

Antibodies to CD44 trigger effector functions of human T cell clones

mAb against the lymphocyte homing receptor CD44/Hermes up-regulate the proliferation of human T PBL induced by anti-CD3 or anti-CD2 mAb. Moreover, certain anti-CD44 mAb can activate human resting T cells and mouse cytotoxic T cells in the absence of anti-CD3 or anti-CD2 mAb. Here, we show that anti-CD44 mAb trigger proliferation of human CD3+/CD4+ T cell clones in a fashion similar to that observed with mAb to CD3. Such an effect is IL-2-dependent, as shown by IL-2 production induced by anti-CD44 mAb and by complete inhibition of cell proliferation in the presence of anti-IL-2 antibodies or cyclosporin A. Moreover, anti-CD44 mAb trigger human cytolytic T cell clones to lyse Fc gamma-R+ P815 cells in the absence of additional stimuli. The magnitude of the cytolytic response induced by anti-CD44 mAb is comparable to that observed in the presence of anti-CD3 mAb for both CD4+ and CD8+ TCR-alpha/beta+ clones, and for V delta 1 or V delta 2 TCR-gamma/delta+ clones. By contrast, in CD3-/CD16+ NK cell clones, no cytolytic responses to anti-CD44 mAb could be observed. Granule trypsin-like esterase enzyme (granzyme) release by cytolytic T cell clones is induced by plastic-immobilized anti-CD44 mAb. Anti-CD44 mAb-triggered proliferation ([3H]thymidine incorporation) and cytotoxicity are blocked by the protein tyrosine kinase inhibitor, genestein. In addition, ligation of the CD44 molecule induces tyrosine phosphorylation of proteins identical, by molecular mass, to those phosphorylated after anti-CD3 mAb stimulation. Notably, anti-CD44 mAb does not induce tyrosine phosphorylation of a 21-kDa protein (the phosphorylated zeta-chain of the TCR molecular complex) typically observed upon anti-CD3 mAb stimulation. In conclusion, this study shows that the ligated CD44 molecule provides the necessary stimuli for a variety of T cell-mediated functions triggered via protein tyrosine kinase-dependent signal transduction pathways at least in part similar to those that follow stimulation of the CD3/TCR complex.

Antibodies to CD44 trigger effector functions of human T cell clones

mAb against the lymphocyte homing receptor CD44/Hermes up-regulate the proliferation of human T PBL induced by anti-CD3 or anti-CD2 mAb. Moreover, certain anti-CD44 mAb can activate human resting T cells and mouse cytotoxic T cells in the absence of anti-CD3 or anti-CD2 mAb. Here, we show that anti-CD44 mAb trigger proliferation of human CD3+/CD4+ T cell clones in a fashion similar to that observed with mAb to CD3. Such an effect is IL-2-dependent, as shown by IL-2 production induced by anti-CD44 mAb and by complete inhibition of cell proliferation in the presence of anti-IL-2 antibodies or cyclosporin A. Moreover, anti-CD44 mAb trigger human cytolytic T cell clones to lyse Fc gamma-R+ P815 cells in the absence of additional stimuli. The magnitude of the cytolytic response induced by anti-CD44 mAb is comparable to that observed in the presence of anti-CD3 mAb for both CD4+ and CD8+ TCR-alpha/beta+ clones, and for V delta 1 or V delta 2 TCR-gamma/delta+ clones. By contrast, in CD3-/CD16+ NK cell clones, no cytolytic responses to anti-CD44 mAb could be observed. Granule trypsin-like esterase enzyme (granzyme) release by cytolytic T cell clones is induced by plastic-immobilized anti-CD44 mAb. Anti-CD44 mAb-triggered proliferation ([3H]thymidine incorporation) and cytotoxicity are blocked by the protein tyrosine kinase inhibitor, genestein. In addition, ligation of the CD44 molecule induces tyrosine phosphorylation of proteins identical, by molecular mass, to those phosphorylated after anti-CD3 mAb stimulation. Notably, anti-CD44 mAb does not induce tyrosine phosphorylation of a 21-kDa protein (the phosphorylated zeta-chain of the TCR molecular complex) typically observed upon anti-CD3 mAb stimulation. In conclusion, this study shows that the ligated CD44 molecule provides the necessary stimuli for a variety of T cell-mediated functions triggered via protein tyrosine kinase-dependent signal transduction pathways at least in part similar to those that follow stimulation of the CD3/TCR complex.