Anti-CD2 antibodies induce T cell unresponsiveness in vivo

Revisiting T-cell adhesion molecules as potential targets for cancer immunotherapy: CD226 and CD2

Cancer immunotherapy aims to initiate or amplify immune responses that eliminate cancer cells and create immune memory to prevent relapse. Immune checkpoint inhibitors (ICIs), which target coinhibitory receptors on immune effector cells, such as CTLA-4 and PD-(L)1, have made significant strides in cancer treatment. However, they still face challenges in achieving widespread and durable responses. The effectiveness of anticancer immunity, which is determined by the interplay of coinhibitory and costimulatory signals in tumor-infiltrating immune cells, highlights the potential of costimulatory receptors as key targets for immunotherapy. This review explores our current understanding of the functions of CD2 and CD226, placing a special emphasis on their potential as novel agonist targets for cancer immunotherapy. CD2 and CD226, which are present mainly on T and NK cells, serve important functions in cell adhesion and recognition. These molecules are now recognized for their costimulatory benefits, particularly in the context of overcoming T-cell exhaustion and boosting antitumor responses. The importance of CD226, especially in anti-TIGIT therapy, along with the CD2‒CD58 axis in overcoming resistance to ICI or chimeric antigen receptor (CAR) T-cell therapies provides valuable insights into advancing beyond the current barriers of cancer immunotherapy, underscoring their promise as targets for novel agonist therapy.

Clinical application of immune repertoire sequencing in solid organ transplant

Background

Measurement of T cell receptor (TCR) or B cell receptor (BCR) gene utilization may be valuable in monitoring the dynamic changes in donor-reactive clonal populations following transplantation and enabling adjustment in therapy to avoid the consequences of excess immune suppression or to prevent rejection with contingent graft damage and to indicate the development of tolerance.

Objective

We performed a review of current literature to examine research in immune repertoire sequencing in organ transplantation and to assess the feasibility of this technology for clinical application in immune monitoring.

Methods

We searched MEDLINE and PubMed Central for English-language studies published between 2010 and 2021 that examined T cell/B cell repertoire dynamics upon immune activation. Manual filtering of the search results was performed based on relevancy and predefined inclusion criteria. Data were extracted based on study and methodology characteristics.

Results

Our initial search yielded 1933 articles of which 37 met the inclusion criteria; 16 of these were kidney transplant studies (43%) and 21 were other or general transplantation studies (57%). The predominant method for repertoire characterization was sequencing the CDR3 region of the TCR β chain. Repertoires of transplant recipients were found to have decreased diversity in both rejectors and non-rejectors when compared to healthy controls. Rejectors and those with opportunistic infections were more likely to have clonal expansion in T or B cell populations. Mixed lymphocyte culture followed by TCR sequencing was used in 6 studies to define an alloreactive repertoire and in specialized transplant settings to track tolerance.

Conclusion

Methodological approaches to immune repertoire sequencing are becoming established and offer considerable potential as a novel clinical tool for pre- and post-transplant immune monitoring.

CD2 Immunobiology

The glycoprotein CD2 is a costimulatory receptor expressed mainly on T and NK cells that binds to LFA3, a cell surface protein expressed on e.g., antigen-presenting cells. CD2 has an important role in the formation and organization of the immunological synapse that is formed between T cells and antigen-presenting cells upon cell-cell conjugation and associated intracellular signaling. CD2 expression is upregulated on memory T cells as well as activated T cells and plays an important role in activation of memory T cells despite the coexistence of several other costimulatory pathways. Anti-CD2 monoclonal antibodies have been shown to induce immune modulatory effects in vitro and clinical studies have proven the safety and efficacy of CD2-targeting biologics. Investigators have highlighted that the lack of attention to the CD2/LFA3 costimulatory pathway is a missed opportunity. Overall, CD2 is an attractive target for monoclonal antibodies intended for treatment of pathologies characterized by undesired T cell activation and offers an avenue to more selectively target memory T cells while favoring immune regulation.

T-cell functionality testing is highly relevant to developing novel immuno-tracers monitoring T cells in the context of immunotherapies and revealed CD7 as an attractive target

Cancer immunotherapy has proven high efficacy in treating diverse cancer entities by immune checkpoint modulation and adoptive T-cell transfer. However, patterns of treatment response differ substantially from conventional therapies, and reliable surrogate markers are missing for early detection of responders versus non-responders. Current imaging techniques using ¹⁸F-fluorodeoxyglucose-positron-emmission-tomograpy (¹⁸F-FDG-PET) cannot discriminate, at early treatment times, between tumor progression and inflammation. Therefore, direct imaging of T cells at the tumor site represents a highly attractive tool to evaluate effective tumor rejection or evasion. Moreover, such markers may be suitable for theranostic imaging.

Methods: We mainly investigated the potential of two novel pan T-cell markers, CD2 and CD7, for T-cell tracking by immuno-PET imaging. Respective antibody- and F(ab´)₂ fragment-based tracers were produced and characterized, focusing on functional in vitro and in vivo T-cell analyses to exclude any impact of T-cell targeting on cell survival and antitumor efficacy.

Results: T cells incubated with anti-CD2 and anti-CD7 F(ab´)₂ showed no major modulation of functionality in vitro, and PET imaging provided a distinct and strong signal at the tumor site using the respective zirconium-89-labeled radiotracers. However, while T-cell tracking by anti-CD7 F(ab´)₂ had no long-term impact on T-cell functionality in vivo, anti-CD2 F(ab´)₂ caused severe T-cell depletion and failure of tumor rejection.

Conclusion: This study stresses the importance of extended functional T-cell assays for T-cell tracer development in cancer immunotherapy imaging and proposes CD7 as a highly suitable target for T-cell immuno-PET imaging.

Anti-CD2 producing pig xenografts effect localized depletion of human T cells in a huSCID model

BACKGROUND

We investigated whether graft produced anti-human CD2, mediated by adenovirus (Adv) transduction of pig neonatal islet cell clusters (pNICC), would protect xenografts in a humanized mouse model from immune attack and whether such immunosuppression would remain local.

METHODS

A mouse anti-human CD2 Ab (CD2hb11) previously generated by us was genetically engineered to produce chimeric and humanized versions. The three forms of CD2hb11 were named dilimomab (mouse), diliximab (chimeric) and dilizumab (humanized). All 3 forms of CD2hb11 Ab were tested for their ability to bind CD3(+) human T cells and to inhibit a human anti-pig xenogeneic mixed lymphocyte reaction (MLR). They were administered systemically in a humanized mouse model in order to test their ability to deplete human CD3(+) T cells and whether they induced a cytokine storm. An adenoviral vector expressing diliximab was generated for transduction of pNICC. Humanized mice were transplanted with either control-transduced pNICC or diliximab-transduced pNICC and human T cells within grafts and spleens were enumerated by flow cytometry.

RESULTS

Dilimomab and diliximab inhibited a human anti-pig xenogeneic response but dilizumab did not. All 3 forms of CD2hb11 Ab bound human T cells in vitro though dilimomab and diliximab exhibited 300-fold higher avidity than dilizumab. All 3 anti-CD2 Abs could deplete human CD3(+) T cells in vivo in a humanized mouse model without inducing upregulation of activation markers or significant release of cytokines. Humanized mice transplanted with diliximab-transduced pNICC afforded depletion of CD3(+) T cells at the graft site leaving the peripheral immune system intact.

CONCLUSIONS

Local production of a single Ab against T cells can reduce graft infiltration at the xenograft site and may reduce the need for conventional, systemic immunosuppression.

Polyclonal rabbit antithymocyte globulin exhibits consistent immunosuppressive capabilities beyond cell depletion

BACKGROUND

Polyclonal antithymocyte globulins (ATGs) are used clinically to prevent and treat acute allograft rejection and are believed to modulate the immune response primarily by depleting T cells. However, nondepleting mechanisms may also be important mediators of graft survival. In the present study, 14 lots of thymoglobulin (rabbit ATG) were analyzed and compared for nondepletive immunomodulatory activities in vitro.

METHODS

Coincubation of human peripheral blood mononuclear cells with thymoglobulin induces CD4+CD25(high)Foxp3+ regulatory T cells, which were evaluated for consistent ability to suppress T-cell activation in mixed lymphocyte reactions. The consistency of CD2, CD3, CD11a, and CD45 antigen specificities in thymoglobulin was determined using flow cytometry to measure inhibition of fluorescent monoclonal antibody binding to Jurkat T cells. A transwell chemotaxis assay was established and used to evaluate ATG-mediated inhibition of stromal cell-derived factor (SDF)-1alpha-driven Jurkat T-cell migration.

RESULTS

Physiologic levels of thymoglobulin produced nondepletive immunomodulatory activities, which were consistent from batch to batch. All lots of thymoglobulin induced functionally immunosuppressive regulatory T cells and inhibited monoclonal antibody binding to key T-cell surface antigens. In addition, these studies provide the first demonstration that thymoglobulin effectively inhibits CXCR4/SDF-1alpha-driven T-cell chemotaxis.

CONCLUSIONS

This novel, systematic in vitro analysis of 14 different manufactured lots of thymoglobulin demonstrates the overall consistency of this product and provides further insights into nondepletive mechanisms by which thymoglobulin may generate durable immunoregulation and allograft survival.

Monoclonal antibodies generated by DNA immunization recognize CD2 from a broad range of primates

Using heterologous prime-boost (DNA immunization followed by immunization with transfected cells), we have generated depleting mouse anti-baboon CD2 monoclonal antibodies (mAb). These anti-CD2 mAb recognized a diverse range of primate CD2 from New World monkeys and Old World monkeys to humans and have potent immunosuppressive activity for human allo-MLR responses and anti-tetanus-toxoid recall responses. There was no upregulation of activation markers or release of cytokines when the mAb were incubated with human peripheral blood mononuclear cells. Using chimeric NOD-SCID IL2rgamma(null) mice, the mAb were shown to deplete human and cynomolgus monkey T cells in vivo. These anti-CD2 mAb may therefore be important immunological tools in allo- and xenotransplantation.

CD2 activation of human lamina propria lymphocytes reduces CD3 responsiveness

Lamina propria lymphocytes (LPLs) are thought to be antigen-activated memory T cells. Yet, they respond better to ligation of the CD2 receptor than the CD3 receptor by mitogenic antibodies. This study defines their constitutive state of activation and relates it to their CD3 hyporesponsiveness. The activated state of LPLs was demonstrated by their heightened display of the activated CD2 epitope, T11(3). Constitutive CD2 activation was shown by the reduction in spontaneous proliferation when the CD2-CD58 interaction was blocked. LPLs preferentially recognized CD58 rather than the major histocompatibility complex molecules on monocytes, triggering proliferation and interferon-gamma (IFN-gamma) secretion that was inhibited by blocking the CD2-CD58 interaction. To determine whether CD2 activation of LPLs contributes to their CD3 hyporesponsiveness, they were first stimulated with mitogenic CD2 antibodies and then tested for CD3-induced proliferation. The responses were greatly reduced by prior CD2 stimulation compared with LPLs cultured in medium alone. This effect was not caused by apoptosis or by changes in CD3 expression induced by CD2 triggering. This study shows that LPLs are constitutively activated through CD2, that they preferentially recognize CD58 on monocytes and that CD2 stimulation leads to CD3 hyporesponsiveness.

Alpha CD 2 mAb treatment safely attenuates adoptive transfer colitis

Increased proliferation, defective apoptosis, and cytokine dysregulation of T lymphocytes are thought to be important for the pathogenesis of inflammatory bowel disease. Since these phenomena can be corrected by alpha CD 2 mAb, we asked whether CD2 directed immunotherapy safely prevents and/or ameliorates adoptive transfer colitis. Colitis was induced by transfer of CD4(+) T cell blasts to syngenic RAG 1(-/-) mice or CD 45 RB(high) CD4(+) T cells to SCID mice. The alpha CD 2 mAb 12-15 or rat IgG was given, starting either initially or upon first signs of colitis. Disease activity was assessed by clinical monitoring, microscopic scoring, hemoccult, endoscopy, and blood count analysis. Cytokine production of stimulated LPL was measured by ELISA and cell proliferation by [(3)H]-thymidine incorporation. Parasite control was analyzed in a murine model of infection with Toxoplasma gondii. The alpha CD 2 mAb significantly increased mean survival time when starting at transfer of blasts (survival >35 days: alpha CD 2 69% vs 0% of controls, P<0.001). In the SCID colitis model hematochezia and macroscopic colitis were delayed. When used in established T-cell blast colitis, the benefit was less pronounced, even in combination with dexamethasone (mean survival+/-s.e.m.: alpha CD 2+dexa: 13.5+/-2.9 vs dexa+IgG: 6.3+/-1.0, P<0.05). In the preventive experiment the alpha CD 2 mAb markedly reduced IL-2 secretion and T-cell proliferation. The immune response towards Toxoplasma gondii was not impaired. These studies show for the first time that CD2 directed immunotherapy can attenuate or delay adoptive transfer colitis and ameliorate established colitis. Most likely inhibition of IL-2 secretion and T-cell proliferation are responsible for these effects. Still, immune defence towards T. gondii is maintained.

A novel role for CD28 in thymic selection: elimination of CD28/B7 interactions increases positive selection

While the importance of the CD28/B7 costimulation pathway is well established for mature T cells, the role of CD28 in thymocyte selection is less well defined. The role of CD28 in both negative and positive selection was assessed using H-Y-specific TCR-transgenic (Tg) RAG-2-deficient (H-Yrag) mice. Negative selection in male H-Yrag mice was not affected by deficiency in CD28 or B7. Surprisingly, absence of CD28 or B7 in H-Yrag females resulted in increased numbers of CD8 single-positive (SP) thymocytes. The CD8 SP thymocytes found in these females were mature and functionally competent. Furthermore, double-positive (DP) thymocytes from CD28-knockout (CD28KO) or B7.1/B7.2 double-KO (B7DKO) females had higher levels of both CD5 and TCR than those from WT females, consistent with a stronger selecting signal. CD28KO H-Yrag fetal thymic organ cultures also had elevated numbers of thymic CD8 SP cells, reflecting increased thymic differentiation and not recirculation of peripheral T cells. Finally, increased selection of mature CD4 and CD8 SP T cells was observed in non-TCR-Tg CD28KO and B7DKO mice, indicating that this function of CD28-B7 interaction is not unique to a TCR-Tg model. Together these findings demonstrate a novel negative regulatory role for CD28 in inhibiting differentiation of SP thymocytes, probably through inhibition of thymic selection.

Differentiation of regulatory T cells 1 is induced by CD2 costimulation

Induction and maintenance of peripheral tolerance is an important phenomenon for the control of homeostasis in the immune system. There is now compelling evidence for CD4(+) T cells that prevent immune pathology, both in autoimmunity and in transplantation. However, the mechanisms involved in the specific differentiation of these T cells are unknown. We had previously shown that repetitive stimulations of naive T cells in the presence of IL-10 induce the differentiation of T regulatory cells 1. We further dissected the mechanism of IL-10 function and demonstrated that IL-10 acts by the down-regulation of most costimulatory molecules without modifying the expression of CD58. Using artificial APCs expressing various costimulatory molecules, we demonstrated that, in contrast to other costimulation patterns, costimulation via CD2 alone, in the absence of costimulations through CD28- or LFA-1, induced T cell anergy in an IL-10-independent pathway along with the differentiation of Ag-specific regulatory T cells. T regulatory cell-1 differentiation via CD2 was very efficient as both high IL-10 secretion and regulatory function were observed after the first stimulation of naive T cells with CD32-CD58 L cells. The possibility to rapidly induce the differentiation of Ag-specific regulatory T cells will certainly accelerate their characterization and their potential use as regulators of T cell-mediated diseases.

Mechanisms of tolerance induction: blockade of co-stimulation

Induction of tolerance to transplantation antigens is believed to be a promising way to achieve long-term allograft survival without a deleterious immunosuppressive regimen. T-cell activation, which is an essential feature of graft rejection, requires a first signal provided by T-cell receptor (TCR) ligation and a second signal provided by engagement of co-stimulatory molecules with their respective ligands on antigen-presenting cells. The coordinated triggering of these two independent signalling systems ensures the full T-cell activation, including proliferation and acquisition of effector function. TCR occupancy in the absence of co-stimulatory signals leads to a sustained loss of antigen responsiveness called clonal anergy, which could be of major importance in transplantation. In vivo, co-stimulation blockade was indeed shown to allow for long-term allograft survival in several transplantation models. However, the current continuous identification of new co-stimulatory molecules suggests that a functional redundancy of the system exists and that tolerance to transplantation antigens might be achieved more easily through the combined blockade of two or several co-stimulatory signals. In this review, we analyse the biological effects of the disruption of some co-stimulation pathways in vitro and in vivo and discuss their potential interest for tolerance induction.

T-cell immunity in the induction and maintenance of a tumour dormant state

We conclude from animal tumour model studies that T cell immunity can play an essential role in the induction and maintenance of tumour dormancy. Evidence was found in tumour dormancy situations for active control of proliferating tumour cells by CD8 memory T cells leading to a long-term balance in the bone marrow between low numbers of tumour cells and immunological memory. In breast cancer patients, too, the bone marrow may represent a privileged compartment for tumour dormancy and immunological memory. Upon restimulation with tumour antigen pulsed autologous dendritic cells, bone marrow-derived memory T cells from cancer patients could be shown to exist and to become activated into potent anti-tumour effector cells.

p62dok negatively regulates CD2 signaling in Jurkat cells

p62(dok) belongs to a newly identified family of adaptor proteins. In T cells, the two members that are predominantly expressed, p56(dok) and p62(dok), are tyrosine phosphorylated upon CD2 or CD28 stimulation, but not upon CD3 ligation. Little is known about the biological role of Dok proteins in T cells. In this study, to evaluate the importance of p62(dok) in T cell function, we generated Jurkat clones overexpressing p62(dok). Our results demonstrate that overexpression of p62(dok) in Jurkat cells has a dramatic negative effect on CD2-mediated signaling. The p62(dok)-mediated inhibition affects several biochemical events initiated by CD2 ligation, such as the increase of intracellular Ca(2+), phospholipase C gamma 1 activation, and extracellular signal-regulated kinase 1/2 activation. Importantly, these cellular events are not affected in the signaling cascade induced by engagement of the CD3/TCR complex. However, both CD3- and CD2-induced NF-AT activation and IL-2 secretion are impaired in p62(dok)-overexpressing cells. In addition, we show that CD2 but not CD3 stimulation induces p62(dok) and Ras GTPase-activating protein recruitment to the plasma membrane. These results suggest that p62(dok) plays a negative role at multiple steps in the CD2 signaling pathway. We propose that p62(dok) may represent an important negative regulator in the modulation of the response mediated by the TCR.

Anti-CD2 monoclonal antibodies prevent the induction of experimental autoimmune myocarditis

We investigated the effect of a monoclonal antibody against CD2 molecules (OX34) in preventing the induction of experimental autoimmune myocarditis (EAM) induced by immunizing Lewis rats with cardiac myosin. Administration of OX34 before immunization, on Days -6, -4, -2 and 0, completely prevented EAM. On the other hand, treatment with OX34 just before the appearance of myocardial lesions, on Days 9, 11, 13 and 15, had only a partial effect in preventing the disease. Flow cytometric analysis of lymph node cells showed that CD3+ T cells were immediately depleted with the administration of OX34 but had largely recovered on Day 21. Lymph node cells in OX34-treated rats had no proliferative responses to cardiac myosin-rod, but the proliferation was restored when recombinant IL-2 was added. Ultimate production of the anti-myosin antibody was not inhibited by the treatment with OX34. These results suggest that the prevention of EAM by administering the anti-CD2 monoclonal antibody OX34 resulted from T cell depletion during the induction phase, and might in addition result from T cell anergy of Th1, but not Th2 cells.

The experimental (in vitro) and clinical (in vivo) immunosuppressive effects of a rat IgG2b anti-human CD2 mAb, LO-CD2a/BTI-322

BACKGROUND

CD2 is a cell surface glycoprotein expressed on most human T cells and natural killer (NK) cells, working as a cell adhesion and costimulatory molecule. The aim of this paper is to analyze the mechanism of action of a rat IgG2b anti-human CD2 monoclonal antibody (mAb) (LO-CD2a/BTI-322 mAb), which is a potent immunosuppressive agent and inducer of cell death. In vivo, this mAb is able to prevent or treat kidney allograft rejection.

METHODS

The mechanisms by which the LO-CD2a/BTI-322 mAb is able to induce inhibition of cell activation and cell death were analyzed by mixed lymphocyte reactions and by flow cytometry. After in vivo treatment, levels of circulating mAb were measured by ELISA as well as anti-rat immunization and cytokine release.

RESULTS

We show that the inhibition of cell activation induced by LO-CD2a/BTI-322 mAb after allogeneic or OKT3 stimulation is due to an Fcgamma receptor-dependent CD2 down-modulation and to T-cell depletion through an antibody-dependent cell-mediated cytotoxicity mechanism mediated by NK cells or activated monocytes. Peripheral T- and NK-cell depletion was observed after in vivo treatment with LO-CD2a/BTI322. Cytokine release (TNFalpha) was correlated with some side effects, but only after the first injection, and the effects were never severe or life threatening.

CONCLUSION

The correlation between the in vitro and in vivo data suggests that T-cell depletion, especially of activated cells, and inhibition of cell activation after CD2 down-modulation are the main mechanisms of action of the LO-CD2a/BTI-322 mAb.

Infection of mice by a Toxoplasma gondii isolate from an AIDS patient: virulence and activation of hosts' immune responses are independent of parasite genotype

Virulence of a Toxoplasma gondii isolate from an AIDS patient (designated as PTN) was compared with that of PLK, a variant of P-strain. Virulence was assessed in term of host survival upon inoculation in different strains of mice. All C57BL/6 mice died of acute toxoplasmosis by 7-10 days following intraperitoneal infection with 1 x 105 tachyzoites of PTN and 40% of BALB/c died on day 23 of infection, whereas 100% CBA/J infected with the same dose of PTN survived, as did outbred Swiss Webster mice. All C57BL/6, BALB/c, CBA/J, or Swiss Webster died of acute toxoplasmosis by 3-9 days postinfection upon inoculation with same dose of tachyzoites of the PLK strain. Further studies in CBA/J mice demonstrated that mice infected with PTN elicited a significantly higher lymphoproliferative response to crosslinked anti-CD3 mAb or Con A than PLK infected mice, and augmented production of TNFalpha, lower levels of nitrite and a higher number of NK cells. Genetical analysis indicated that both PLK and PTN strains of T. gondii are from type ll. Interestingly, being of the same genotype, the later showed less virulence upon inoculation in mice and had greater capacity to activate host immune system than the PLK strain.

CD2 sets quantitative thresholds in T cell activation

It has been proposed that CD2, which is highly expressed on T cells, serves to enhance T cell-antigen presenting cell (APC) adhesion and costimulate T cell activation. Here we analyzed the role of CD2 using CD2-deficient mice crossed with transgenic mice expressing a T cell receptor specific for lymphocytic choriomeningitis virus (LCMV)-derived peptide p33. We found that absence of CD2 on T cells shifted the p33-specific dose-response curve in vitro by a factor of 3-10. In comparison, stimulation of T cells in the absence of lymphocyte function-associated antigen (LFA)-1-intercellular adhesion molecule (ICAM)-1 interaction shifted the dose-response curve by a factor of 10, whereas absence of both CD2-CD48 and LFA-1-ICAM-1 interactions shifted the response by a factor of approximately 100. This indicates that CD2 and LFA-1 facilitate T cell activation additively. T cell activation at low antigen density was blocked at its very first steps, as T cell APC conjugate formation, TCR triggering, and Ca(2+) fluxes were affected by the absence of CD2. In vivo, LCMV-specific, CD2-deficient T cells proliferated normally upon infection with live virus but responded in a reduced fashion upon cross-priming. Thus, CD2 sets quantitative thresholds and fine-tunes T cell activation both in vitro and in vivo.

Prediction of graft prolongation by mixed lymphocyte culture following anti-CD4 monoclonal antibody treatment among different donor-recipient combinations

This study was conducted to examine whether mixed lymphocyte culture (MLC) could be used as a predictor of the efficacy of anti-CD4 monoclonal antibody (MAb) immunosuppression in vivo in a mouse model. C57BL/10 or BALB/c hearts were transplanted into C3H.He recipients. Anti-CD4 MAb administration prolonged graft survival, but there was a clear difference between the two donor-recipient combinations studied, the median survival time (MST) being >100 days in the C57BL/10 --> C3H group, and 17 days in the BALB/c --> C3H group. Anti-CD8 MAb prolonged the survival of C57BL/10 hearts slightly to a MST of 22 days, but the BALB/c hearts were rejected at control rates. Combining anti-CD4 and anti-CD8 antibody therapy prolonged the survival of C57BL/10 hearts indefinitely, but had little effect on the survival of BALB/c grafts, achieving an MST of only 24 days. Next, MLCs were performed in the presence and absence of the MAbs and compared with the graft survival data. The inhibition rates in the MLC, being the C3H lymph node cell responder, correlated well with graft survival. When three kinds of C3H responder cells, namely lymph node (LN) cells, T cells, and CD4+ cells, were examined to determine which was the most suitable for predicting graft survival, the MLC results showed that the responses of LN cells correlated most closely with graft outcome. In conclusion, MLC using LN cells as the responder is a useful tool for predicting allograft survival induced by anti-CD4 MAb therapy.

Tumor Therapy with Bispecific Antibody: The Targeting and Triggering Steps Can Be Separated Employing a CD2-Based Strategy

For tumor therapy with unprimed effector cells, we developed a novel combination of a CD2 × tumor Ag bispecific targeting Ab and an anti-CD2 triggering Ab. These Ab constructs were derived from two novel CD2 mAbs, termed M1 and M2 that, together, but not individually activate T cells. Unlike many other CD2 Abs, M1 and M2 do not interfere with TCR/CD3 triggering nor do they inhibit binding of CD2 to its ligand CD58, thus preserving the physiological functions of these important effector cell molecules. M2 was chemically conjugated with an Ab recognizing the epidermal growth factor-receptor (EGF-R). Incubation of unprimed peripheral blood mononuclear cells with the bispecific F(ab′)2 construct (M2xEGF-R) in the presence of trigger Ab M1 led to efficient selective lysis of EGF-R-positive targets by CTL and NK cells. Importantly, the need for trigger Ab M1 for effector cell stimulation allowed to separate targeting from triggering steps in vitro and should thus enable to focus immune responses to sites of target Ag expression in vivo.

CD48-deficient mice have a pronounced defect in CD4(+) T cell activation

We have generated mice deficient in the expression of the lymphocyte cell surface antigen CD48 (Blast-1, BCM1, sgp-60) by gene targeting in embryonic stem cells. Mice homozygous for the CD48 mutation (CD48(-/-) mice) are severely impaired in CD4(+) T cell activation. Proliferative responses to mitogens, anti-CD3 mAb, and alloantigen are all reduced. Experiments in which T cells and antigen-presenting cells from either wild-type or CD48(-/-) mice were cocultured reveal that CD48 is important on both T cells and antigen-presenting cells. The most dramatic impairment was observed in experiments in which highly purified T cells were stimulated through the T cell receptor in the presence of the phorbol ester, phorbol 12-myristate 13-acetate. The results of these experiments raise the possibility that CD48 plays a role in signaling through the T cell receptor.

Alteration of Intracellular Calcium Flux and Impairment of Nuclear Factor-AT Translocation in T Cells During Acute Toxoplasma gondii Infection in Mice

Down-regulation of host immune response to Toxoplasma gondii is associated with the expression of specific cytokines, in particular IL-10, and the induction of CD4+ T cell anergy. In the present study we report that the expression of both CD4 and CD2 antigen is down-regulated during the acute phase of infection. A decrease in the expression of CD2 was apparent during the acute phase of T. gondii infection in three genetically distinct strains of mice, CBA/J, C57BL/6, and BALB/c. The lymphoproliferative response induced by cross-linked anti-CD3 mAb or by Con A was markedly depressed. This suppressed response was associated with a reduction in the influx of Ca2+. We have examined whether lymphocytes from T. gondii mice maintain NF-AT transcription factors in the nucleus where they participate in the Ca2+-dependent induction of genes required for lymphocyte activation and proliferation. Immunofluorescence with confocal microscopy using an Ab to NF-ATc demonstrates a decrease in translocation of NF-ATc in T lymphocytes from acutely infected mice. Together, these results suggest that the defect in T cell expansion that occurs during acute murine toxoplasmosis is related to reduced activity of NF-AT, a calcium-dependent transcription factor required for T cell proliferation.

A Critical Role for CD48 Antigen in Regulating Alloengraftment and Lymphohematopoietic Recovery After Bone Marrow Transplantation

The binding of CD2, present on T cells, to its counterreceptor CD48 facilitates adhesion, signaling, alloantigen-induced cytokine production, and cytotoxic T-lymphocyte responses. Because these T-cell functions have been implicated in graft-versus-host disease (GVHD) pathogenesis, we have analyzed the effects of the CD2:CD48 pathway on GVHD mediated by CD4+ and CD8+ T cells infused into sublethally irradiated recipients. CD4+ T-cell–mediated, and to a lesser extent, CD8+ T-cell–mediated GVHD was inhibited by CD2 + 48 monoclonal antibody (MoAb) infusion. To assess the effects of combined MoAb infusion on alloengraftment, two different alloengraftment bone marrow transplantation (BMT) models were used. In both, MoAb infusion markedly inhibited alloengraftment and hematopoietic recovery post-BMT. To determine if the adverse effects on lymphohematopoiesis in the allogeneic BMT recipients were caused by an immune or nonimmune mechanism, studies were performed in congenic BMT recipients to preclude an immune mechanism as the cause for delayed recovery post-BMT. MoAb infusion resulted in impaired lymphohematopoietic recovery in congenic BMT recipients and markedly reduced day 12 colony-forming unit–spleen formation in syngeneic BMT recipients, consistent with a nonimmune mediated mechanism. Because the spleen is a site of early hematopoietic recovery post-BMT, studies were performed using adult splenectomized syngeneic BMT recipients. MoAb infusion delayed recovery in both nonsplenectomized and splenectomized recipients post-BMT, indicating that the delayed hematopoietic recovery was not the consequence of an abnormal homing pattern of hematopoietic progenitors to the spleen early post-BMT. CD48 MoAb was necessary and sufficient for the inhibition of GVHD lethality and delayed lymphohematopoietic effects of the combined MoAb regimen. CD48 MoAb was found to induce a profound modulation of CD48 antigen expression on BM cells, suggesting that the CD48 antigen may have an important function in hematopoiesis in the BM compartment. Taken together, these data provide evidence that the CD48 antigen plays a critical role in regulating hematopoiesis in post-BMT.

A Critical Role for CD48 Antigen in Regulating Alloengraftment and Lymphohematopoietic Recovery After Bone Marrow Transplantation

The binding of CD2, present on T cells, to its counterreceptor CD48 facilitates adhesion, signaling, alloantigen-induced cytokine production, and cytotoxic T-lymphocyte responses. Because these T-cell functions have been implicated in graft-versus-host disease (GVHD) pathogenesis, we have analyzed the effects of the CD2:CD48 pathway on GVHD mediated by CD4+ and CD8+ T cells infused into sublethally irradiated recipients. CD4+ T-cell–mediated, and to a lesser extent, CD8+ T-cell–mediated GVHD was inhibited by CD2 + 48 monoclonal antibody (MoAb) infusion. To assess the effects of combined MoAb infusion on alloengraftment, two different alloengraftment bone marrow transplantation (BMT) models were used. In both, MoAb infusion markedly inhibited alloengraftment and hematopoietic recovery post-BMT. To determine if the adverse effects on lymphohematopoiesis in the allogeneic BMT recipients were caused by an immune or nonimmune mechanism, studies were performed in congenic BMT recipients to preclude an immune mechanism as the cause for delayed recovery post-BMT. MoAb infusion resulted in impaired lymphohematopoietic recovery in congenic BMT recipients and markedly reduced day 12 colony-forming unit–spleen formation in syngeneic BMT recipients, consistent with a nonimmune mediated mechanism. Because the spleen is a site of early hematopoietic recovery post-BMT, studies were performed using adult splenectomized syngeneic BMT recipients. MoAb infusion delayed recovery in both nonsplenectomized and splenectomized recipients post-BMT, indicating that the delayed hematopoietic recovery was not the consequence of an abnormal homing pattern of hematopoietic progenitors to the spleen early post-BMT. CD48 MoAb was necessary and sufficient for the inhibition of GVHD lethality and delayed lymphohematopoietic effects of the combined MoAb regimen. CD48 MoAb was found to induce a profound modulation of CD48 antigen expression on BM cells, suggesting that the CD48 antigen may have an important function in hematopoiesis in the BM compartment. Taken together, these data provide evidence that the CD48 antigen plays a critical role in regulating hematopoiesis in post-BMT.

A Phase II Study of BTI-322, a Monoclonal Anti-CD2 Antibody, for Treatment of Steroid-Resistant Acute Graft-Versus-Host Disease

BTI-322, a rat monoclonal IgG2b directed against the CD2 antigen on T cells and natural killer (NK) cells, blocks primary and memory alloantigen proliferative responses in vitro. We have evaluated the pharmacokinetics and safety of BTI-322 during treatment of 20 transplant recipients with steroid-refractory acute graft-versus-host disease (GVHD). Treatment consisted of BTI-322 by intravenous (IV) bolus or 30-minute infusion at approximately 0.1 mg/kg/d for 10 days in addition to continuing high-dose steroids and tacrolimus or cyclosporine. Pharmacokinetic sampling was performed in 10 patients; the t1/2 ± SE was 9.1 ± 1.3 hours, the Cmaxwas 2,549 ± 291 ng/mL, the Vd was 3.97 ± 0.95 L, and the Vd/kg was 0.05 ± 0.01 L/kg. Ten patients experienced transient dyspnea sometimes accompanied by nausea, vomiting, diarrhea, and tachycardia shortly after the initial bolus dose of drug, but serious drug-related adverse events were not seen during the remainder of the infusions. At the end of treatment (day 11), there were six patients with complete responses and five with a reduction in grade of GVHD for a total response rate of 55% (95% confidence interval [CI], 32% to 77%). Antibodies targeting CD2 may be active in the treatment of acute GVHD, and evaluation of a humanized form of BTI-322 is warranted.

A Phase II Study of BTI-322, a Monoclonal Anti-CD2 Antibody, for Treatment of Steroid-Resistant Acute Graft-Versus-Host Disease

BTI-322, a rat monoclonal IgG2b directed against the CD2 antigen on T cells and natural killer (NK) cells, blocks primary and memory alloantigen proliferative responses in vitro. We have evaluated the pharmacokinetics and safety of BTI-322 during treatment of 20 transplant recipients with steroid-refractory acute graft-versus-host disease (GVHD). Treatment consisted of BTI-322 by intravenous (IV) bolus or 30-minute infusion at approximately 0.1 mg/kg/d for 10 days in addition to continuing high-dose steroids and tacrolimus or cyclosporine. Pharmacokinetic sampling was performed in 10 patients; the t1/2 ± SE was 9.1 ± 1.3 hours, the Cmaxwas 2,549 ± 291 ng/mL, the Vd was 3.97 ± 0.95 L, and the Vd/kg was 0.05 ± 0.01 L/kg. Ten patients experienced transient dyspnea sometimes accompanied by nausea, vomiting, diarrhea, and tachycardia shortly after the initial bolus dose of drug, but serious drug-related adverse events were not seen during the remainder of the infusions. At the end of treatment (day 11), there were six patients with complete responses and five with a reduction in grade of GVHD for a total response rate of 55% (95% confidence interval [CI], 32% to 77%). Antibodies targeting CD2 may be active in the treatment of acute GVHD, and evaluation of a humanized form of BTI-322 is warranted.

Enhanced murine CD4+ T cell responses induced by the CD2 ligand CD48

The physiological functions of murine CD2 and its ligand CD48 are uncertain. We have examined the role of the CD2-CD48 interaction in murine T cell activation using a series of Chinese hamster ovary (CHO) cell transfectants. CHO cells expressing I-Ad together with CD48 induced more potent activation of OVA-specific, I-Ad-restricted DO11.10-transgenic T cells than CHO cells expressing I-Ad alone. CD48 augmented proliferation and IL-2 production in response to antigen. The enhancing effect of CD48 was of the same magnitude as that seen for CD80 (B7-1). Conjugate assays revealed the ability of CD48 to increase adhesion between T cells and CHO transfectants. The enhancing effects of CD48 on T cell-antigen-presenting cell adhesion and T cell activation were inhibited by anti-CD2 monoclonal antibody. This report provides the first evidence that the CD2 ligand CD48 contributes to the interactions of murine CD4+ T cells with antigen-presenting cells.

The role of ICAM-1/LFA-1 and VCAM-1/VLA-4 interactions on T helper 2 cytokine production by lung T cells of Toxocara canis-infected mice

In order to study the effect of costimulatory signals on T helper type 2 (Th2) cytokine production, monoclonal antibodies (mAb) against cell adhesion molecules (CAM) were added to cells in culture obtained from the lungs of Toxocara canis (Tc)-infected mice followed by the determination of interleukin-5 (IL-5) and IL-4 in the supernatants of the culture. ES-stimulated IL-5 production in the supernatant of total lung cells was reduced by 25% when anti-intercellular adhesion molecule-1 (anti-ICAM-1) mAb, anti-CD11a mAb, or both anti-ICAM-1 and anti-CD11a mAb together were added to the culture. The addition of anti-CD18 mAb had no effects. Anti-vascular cell adhesion molecule-1 (anti-VCAM-1) mAb addition also reduced IL-5 production by 60%, although the addition of anti-very late activation antigen-4 (anti-VLA-4) mAb or both anti-VCAM-1 and anti-VLA-4 mAb together were less effective. In the case of anti-CD3 mAb stimulation, similar effects of mAb to CAM were observed. In contrast, IL-4 production induced by anti-CD3 mAb was reduced more markedly by the addition of either anti-ICAM-1 or anti-CD11a mAb than the combination of anti-VCAM-1 and anti-VLA-4 mAb. Similar effects of mAb to CAM were observed on the production of IL-5 and IL-4 by CD4+ T cells purified using a fluorescence-activated cell sorter. Coincubation with adherent cells was necessary for the significant production of IL-5 and IL-4 by CD4+ T cells. These results suggest that the VCAM-1/VLA-4 interaction is more important for IL-5 production by CD4+ T cells in the lungs of Tc-infected mice, and that the ICAM-1/lymphocyte function-associated antigen-1 interaction is more important for the production of IL-4.

Association of p59(fyn) with the T lymphocyte costimulatory receptor CD2. Binding of the Fyn Src homology (SH) 3 domain is regulated by the Fyn SH2 domain

Human CD2 is a 50-55-kDa cell surface receptor specifically expressed on the surface of T lymphocytes and NK cells. Stimulation of human peripheral blood T cells with mitogenic pairs of anti-CD2 monoclonal antibodies (mAbs) is sufficient to induce interleukin-2 production and T cell proliferation in the absence of an antigen-specific signal through the T cell receptor. CD2 has been shown previously to associate physically with the Src family protein-tyrosine kinases p56(lck) and p59(fyn). We now report that stimulation of T cells with mitogenic pairs of anti-CD2 mAbs enhanced the association of the Fyn polypeptide with the CD2 complex, whereas stimulation with single anti-CD2 mAb had minimal effect. Using glutathione S-transferase (GST) fusion proteins, we found that CD2 bound to the Src homology (SH) 3 domain of Fyn. Interestingly, the CD2-Fyn association was negatively regulated by the Fyn SH2 domain; CD2 bound poorly to GST fusion proteins expressing both the SH2 and SH3 domains of Fyn. However, the inhibitory effect of the Fyn SH2 domain on binding of the Fyn SH3 domain to CD2 was relieved by peptides containing a phosphorylated YEEI sequence that bound directly to the Fyn SH2 domain. In addition, we found that the ability of the Fyn SH2 domain to precipitate tyrosine-phosphorylated proteins, including the CD3zeta chain, was enhanced after T cell stimulation with mitogenic pairs of CD2 mAbs. Finally, overexpression of a mutated Fyn molecule, in which the ability of the Fyn SH2 domain to bind phosphotyrosine-containing proteins was abrogated, inhibited CD2-induced transcriptional activation of the nuclear factor of activated T cells (NFAT), suggesting a functional involvement of the Fyn SH2 domain in CD2-induced T cell signaling. We thus propose that stimulation through the CD2 receptor leads to the tyrosine phosphorylation of intracellular proteins, including CD3zeta itself, which in turn bind to the Fyn-SH2 domain, allowing the direct association of the Fyn SH3 domain with CD2 and the initiation of downstream signaling events.

Selective reduction in CD2 expression on CD2bright/CD8+ lymphocytes from cynomolgus monkeys (Macaca fascicularis) in response to acute stress

Numerous reports have demonstrated a link between stressful stimuli and immune suppression. However, the cellular mechanisms by which stress impairs immune function are largely unknown. We have examined the effects of an acute stressor on the T cell population, specifically, the number and phenotype of T cells in a nonhuman primate model. In nonstressed adult monkeys, we found differences in the level of expression of CD2 on T cells, revealing two distinct subsets of T cells, CD2dim and CD2bright cells, with CD2bright cells predominately coexpressing CD8. In response to acute stress, we observed a significant loss in the number and percent of CD2bright/CD8+ cells, with percent of CD2bright cells returning to pre-stress values within 24 h.

Combinatorial blockade of calcineurin and CD28 signaling facilitates primary and secondary therapeutic gene transfer by adenovirus vectors in dystrophic (mdx) mouse muscles

Recombinant adenovirus vectors (AdV) have been considered a potential vehicle for performing gene therapy in patients suffering from Duchenne muscular dystrophy but are limited by a cellular and humoral immune response that prevents long-term transgene expression as well as effective transduction after AdV readministration. Conventional immunosuppressive agents such as cyclosporine and FK506, which act by interfering with CD3-T-cell receptor-mediated signaling via calcineurin, are only partially effective in reversing these phenomena and may also produce substantial organ toxicity. We hypothesized that activation of redundant T-cell activation pathways could limit the effectiveness of these drugs at clinically tolerable doses. Therefore, we have tested the ability of immunomodulatory immunoglobulins (Ig) with different modes of action to facilitate AdV-mediated gene transfer to adult dystrophic (mdx) mice. When used in isolation, immunomodulatory Ig (anti-intercellular adhesion molecule-1, anti-leukocyte function-associated antigen-1, anti-CD2, and CTLA4Ig) were only mildly effective in mitigating cellular and/or humoral immunity against adenovirus capsid proteins and the therapeutic transgene product, dystrophin. However, the combination of FK506 plus CTLA4Ig abrogated the immune response against adenovirus proteins and dystrophin to a degree not achievable with the use of either agent alone. At 30 days after AdV injection, >90% of myofibers could be found to express dystrophin with little or no evidence of a cellular immune response against transduced fibers. In addition, the humoral immune response was markedly suppressed, and this was associated with increased transduction efficiency following vector readministration. These data suggest that by facilitating both primary and secondary transduction after AdV administration, combined targeting of CD3-T-cell receptor-mediated signaling via calcineurin and the B7:CD28 costimulatory pathway could greatly increase the potential utility of AdV-mediated gene transfer as a therapeutic modality for genetic diseases such as Duchenne muscular dystrophy that will require long-term transgene expression and repeated vector delivery.

Potent Apoptotic Signaling and Subsequent Unresponsiveness Induced by a Single CD2 mAb (BTI-322) in Activated Human Peripheral T Cells

Manipulation of CD2 molecules with CD2 mAb pairs has been shown to deliver apoptotic signals to activated mature T cells. We show that BTI-322, a CD2 mAb directed at a peculiar epitope of CD2, can trigger on its own the apoptotic death of IL-2-activated peripheral T cells and of OKT3-stimulated T cells, contrasting in this respect with a series of other mouse or rat CD2 mAb. F(ab′)2 fragments were as potent as the whole Ab. BTI-322-induced apoptosis proceeded in a few hours and was independent of the Fas/Fas ligand system. Less than 5 ng/ml of BTI-322, added at the begining of culture, were able to eliminate within 4 days most CD3+ cells from OKT3- and IL-2-stimulated lymphocytes, the only cells remaining being CD16+CD2− NK cells. T cell proliferative responses induced by a mitogenic CD2 mAb pair or by PHA-P (which mainly binds to CD2) were not inhibited by BTI-322. In this case, the apoptotic effect was successfully counteracted by simultaneous enhancement of T cell divisions. Thus, the killing effect of BTI-322 was most effective when T cells were exclusively stimulated through the CD3/TCR complex. Apoptosis of the responding T cells may explain why T cells recovered from a primary MLC performed in the presence of BTI-322 responded to third party cells but not to the primary stimulatory cells. These data constitute the rational basis for the use of BTI-322 for inducing tolerance in human allotransplantation.

Deletion of a CD2-like gene, 8-DR, from African swine fever virus affects viral infection in domestic swine

An African swine fever virus (ASFV) gene with similarity to the T-lymphocyte surface antigen CD2 has been found in the pathogenic African isolate Malawi Lil-20/1 (open reading frame [ORF] 8-DR) and a cell culture-adapted European virus, BA71V (ORF EP402R) and has been shown to be responsible for the hemadsorption phenomenon observed for ASFV-infected cells. The structural and functional similarities of the ASFV gene product to CD2, a cellular protein involved in cell-cell adhesion and T-cell-mediated immune responses, suggested a possible role for this gene in tissue tropism and/or immune evasion in the swine host. In this study, we constructed an ASFV 8-DR gene deletion mutant (delta8-DR) and its revertant (8-DR.R) from the Malawi Lil-20/1 isolate to examine gene function in vivo. In vitro, delta8-DR, 8-DR.R, and the parental virus exhibited indistinguishable growth characteristics on primary porcine macrophage cell cultures. In vivo, 8-DR had no obvious effect on viral virulence in domestic pigs; disease onset, disease course, and mortality were similar for the mutant delta8-DR, its revertant 8-DR.R, and the parental virus. Altered viral infection was, however, observed for pigs infected with delta8-DR. A delay in spread to and/or replication of delta8-DR in the draining lymph node, a delay in generalization of infection, and a 100- to 1,000-fold reduction in virus titers in lymphoid tissue and bone marrow were observed. Onset of viremia for delta8-DR-infected animals was significantly delayed (by 2 to 5 days), and mean viremia titers were reduced approximately 10,000-fold at 5 days postinfection and 30- to 100-fold at later times; moreover, unlike in 8-DR.R-infected animals, the viremia was no longer predominantly erythrocyte associated but rather was equally distributed among erythrocyte, leukocyte, and plasma fractions. Mitogen-dependent lymphocyte proliferation of swine peripheral blood mononuclear cells in vitro was reduced by 90 to 95% following infection with 8-DR.R but remained unaltered following infection with delta8-DR, suggesting that 8-DR has immunosuppressive activity in vitro. Together, these results suggest an immunosuppressive role for 8-DR in the swine host which facilitates early events in viral infection. This may be of most significance for ASFV infection of its highly adapted natural host, the warthog.

Differential immunosuppressive activity of monoclonal CD2 antibodies on allograft rejection versus specific antibody production

CD2 is a co-stimulatory receptor involved in T cell activation. Here we report on immunosuppressive effects of three mouse CD2 monoclonal antibodies (OX34, OX54, OX55) directed against non-overlapping epitopes of the rat CD2 receptor on various modes of T cell activation in vitro and in vivo. Although non-ligand-blocking OX54 and OX55, in concert, activated T cells through CD2 in vitro, they individually suppressed the mixed lymphocyte reaction (MLR) and significantly prolonged allograft survival after rat heart transplantation in vivo. Phenotype analysis revealed that OX55 significantly down-modulated CD2 in vivo, whereas OX54 depleted T cells. Graft rejection coincided with re-expression of CD2 and clearance of OX55 from serum, whereas T cell depletion by OX54 outlasted the period of graft survival. The most suppressive antibody, OX34, down-modulated CD2 and inhibited T cell activation through the TCR or CD2 and the MLR and prolonged median allograft survival time from 7 days in controls to 45 days in the absence of any additional treatment. Graft survival was clearly dose dependent and correlated with the duration of CD2 down-modulation and the presence of circulating CD2 antibody in serum. Importantly, the specific antibody production to a T cell-dependent antigen as demonstrated by immunization with keyhole limpet hemocyanin in vivo remained unaffected after treatment with OX34. These results demonstrate the pivotal role of CD2 signaling in mediating allogeneic immune reactions after vascularized organ transplantation while allowing specific humoral immune responses in vivo.

Generation of an Inhibitory Circuit Involving CD8+ T Cells, IL-2, and NK Cell-Derived TGF-β: Contrasting Effects of Anti-CD2 and Anti-CD3

Although the phenomenon of immunosuppression is well established, the mechanisms involved in the generation of lymphocytes with down-regulatory activity are poorly understood. Unlike anti-CD3 antibodies, mitogenic combinations of anti-CD2 antibodies do not stimulate human PBL to produce IgM or IgG. In determining the reason for this difference, we have found that anti-CD2 triggers an inhibitory circuit facilitated by TGF-β provided by NK cells. Stimulation of PBL with anti-CD2, but not anti-CD3, generated substantial amounts of active TGF-β. NK cells were found to be a significant source of TGF-β and were the only lymphocyte population that constitutively produced this cytokine. Anti-CD2 enhanced the production of active TGF-β by purified NK cells. TGF-β. After the removal of NK cells or the addition of anti-TGF-β, anti-CD2 could stimulate Ig production. Anti-TGF-β had to be added within the first 24 h for a maximal effect. Moreover, a short, overnight exposure of CD8+ T cells to TGF-β could prime them for suppressor activity provided that IL-2 was also present. Thus, the presence of active TGF-β coincident with CD8+ T cell activation can condition these cells to mediate down-regulatory activity, and NK cells can serve as the source of this cytokine.

Down-modulation of CD2 delays deletion of superantigen-responsive T cells

CD2 is a cell surface glycoprotein expressed on most T lymphocytes that is generally viewed as a cell adhesion molecule and, in this capacity, contributes to T cell receptor (TCR) signaling. CD2 has a relatively long cytoplasmic tail which associates with the src family tyrosine kinases, p56(lck) and p59(fyn), and could potentially signal directly. Down-modulation of CD2 on T cells has been shown to result in diminished proliferative capacity and interleukin (IL)-2 production. Furthermore, re-expression of CD2 can result in the restoration of these functions. This suggests that CD2 can influence the intensity of TCR signaling. As TCR signal intensity is pivotal to the induction of T cell apoptosis, we considered the hypothesis that the level of CD2 on the T cell surface may influence its propensity toward apoptosis. Using an anti-CD2 antibody, CD2 was down-modulated in vivo on mouse T lymphocytes without affecting the levels of surface CD3, TCR alphabeta, CD4 or CD8. Deletion of superantigen-responsive T cells was delayed in mice with down-modulated CD2 following the administration of staphylococcal enterotoxin B (SEB). This was paralleled by diminished apoptosis of SEB-responsive cells. The findings suggest a model whereby the level of CD2 expression influences the intensity of TCR signaling and the ability to undergo apoptosis.

Initiation and perpetuation of rat adjuvant arthritis is inhibited by the anti-CD2 monoclonal antibody (mAb) OX34

OBJECTIVE

The purpose of this study was to investigate the therapeutic potential of the anti-CD2 mAb OX34 first with regard to bone protection in established rat adjuvant arthritis (AA) and secondly with regard to prevention of AA induction.

METHODS

Established AA was treated with dexamethasone (1 mg/kg body weight) for two days plus OX34 mAb or control mAb over three days (2 mg and then 1 mg) starting at different time points of the disease. For prevention studies animals were injected as above with mAb before induction of AA. Arthritis score (AS), hindpaw thickness, and body weight were blindly measured three times per week. Flow cytometry and hindpaw radiography were performed at the end of the study (day 29).

RESULTS

Treatment of early AA with OX34 mAb combined with dexamethasone but not dexamethasone plus control mAb dramatically suppressed established AA as assessed by AS and hind paw thickness (> 65% and > 80% reduction, respectively; p < 0.05). Most importantly, early treatment in the course of AA almost completely prevented bone destruction in established AA. When given before AA induction OX34 alone prevented the initiation of arthritis compared with controls (AS reduction 83-95%, p < 0.05). In addition, OX34 plus dexamethasone treatment resulted in depletion of CD4+ T cells but not CD8+ T cells. IL2R+ and CD45RC- ('memory') T cells were significantly reduced.

CONCLUSIONS

Anti-CD2 mAb treatment prevents AA induction confirming the role of CD4+ T cells in the induction phase of AA. In addition, early OX34 plus dexamethasone treatment resulted in pronounced clinical improvement and joint protection. OX34 treatment therefore inhibits the initiation and the perpetuation of rat AA.

Ligation of CD2 provides a strong helper signal for the production of the type 2 cytokines interleukin-4 and -5 by memory T cells

In this study, we investigated the efficiency of costimulatory signaling provided by anti-CD2 monoclonal antibodies (mAbs) for the production of type 1 (IL-2 and IFN-gamma) and type 2 (IL-4, IL-5, and IL-10) cytokines by human T cells. We cultured purified human T cells (freshly isolated from blood) with immobilized anti-CD3 mAb, either alone or in combination with anti-CD28 or anti-CD2 mAbs. When compared with the standard costimulatory signal anti-CD28, anti-CD2 mAbs (9-1 plus 9.6) were shown to be more potent costimulators of IL-4 production and to have similar activity for IL-5 production, but to be less potent for costimulation of IL-2, IL-10, and IFN-gamma production. IL-4 production was completely inhibited by cyclosporin A or by blocking IL-2 activity and its receptor. IL-4 and IL-5 were produced by CD45RO+ T cells but not by CD45RA+ T cells, indicating that anti-CD2 in this system costimulated type 2 cytokine production by differentiated memory cells. In the presence of IL-12, the cytokine profile was shifted to high IFN-gamma and IL-10 production and IL-4 and IL-5 production were slightly inhibited. Our data thus suggest that CD2 ligation plays an important role in the upregulation of Th2-like T cell activity (especially IL-4 production), but they also show that this effect is strongly modulated by IL-12, resulting in predominant IL-10 and IFN-gamma production instead.

A dimeric form of soluble recombinant sheep LFA-3(CD58) inhibits human T-cell proliferation by generating regulatory T cells

We recently observed that the soluble recombinant from of sheep LFA-3, termed sLFA-3 is biologically active as determined by E-rosette inhibition and inhibition of human T-cell proliferation in response to the recall antigen. In the present study, we examined the immunosuppressive properties of a derivative of sLFA-3, a dimeric form of the first domain (D1) of sLFA-3, named sD1Hcys dimer which was made by oxidative binding of the two D1 molecules through disulfide bonds formed between the SH side chains of a cysteine which was added to the C-terminal of the D1 domain. By investigating the suppressive properties of the sD1Hcys dimer, we obtained evidence that antigen-stimulated T-cell proliferation was inhibited by the suppressor T cell, mainly CD4 + CD45RA - CD45RO + and CD8 + CD45RA - CD45RO + T cells, generated by incubating PBLs with a low dose (0.5 microgram/ml) of sD1Hcys dimer in the presence of a low dose of IL-2 and GM-CSF. Flow cytometric analysis showed that the expression of some surface molecules on T cells were modulated by a high dose (5 micrograms/ml) of sD1Hcys dimer such as downregulation of CD3 and upregulation of IL-2R, but were not modulated by a low dose (0.5 microgram/ml) of the sD1Hcys dimer. These findings suggest that the sD1Hcys dimer exerts its suppressive effects on the antigen-induced proliferation assay by generating suppressor T cells. The sD1Hcys dimer might therefore have potential as an immunotherapeutic agent to inhibit and/or anergize antigen-specific T-cell responses.

CD84 Leukocyte Antigen Is a New Member of the Ig Superfamily

cDNA isolated from a human B-cell line Raji library was analyzed and shown to encode the full-length cDNA sequence of a novel cell-surface glycoprotein, initially termed HLy9-β. The predicted mature 307-amino acid protein was composed of two extracellular Ig-like domains, a hydrophobic transmembrane region, and an 83-amino acid cytoplasmic domain. The extracellular Ig-like domains presented structural and sequence homology with a group of members of the Ig superfamily that included CD2, CD48, CD58, and Ly9. Northern blot analysis showed that the expression of HLy9-β was predominantly restricted to hematopoietic tissues. Chromosome localization studies mapped the HLy9-β gene to chromosome 1q24, where other members of this Ig superfamily (CD48 and HumLy9) have been mapped. CD84 monoclonal antibodies (MoAbs) were shown to react with cells transfected with the cloned cDNA. These MoAbs were further used to show that CD84 is expressed as a single chain cell-surface glycoprotein of Mr 64,000 to 82,000, which was highly glycosylated. CD84 had a unique pattern of expression, being found predominantly on lymphocytes and monocytes. Thus, the glycoprotein HLy9-β is recognized by MoAbs previously clustered as CD84 and represents a newly identified member of the Ig superfamily that may play a significant role in leukocyte activation.

CD84 Leukocyte Antigen Is a New Member of the Ig Superfamily

cDNA isolated from a human B-cell line Raji library was analyzed and shown to encode the full-length cDNA sequence of a novel cell-surface glycoprotein, initially termed HLy9-β. The predicted mature 307-amino acid protein was composed of two extracellular Ig-like domains, a hydrophobic transmembrane region, and an 83-amino acid cytoplasmic domain. The extracellular Ig-like domains presented structural and sequence homology with a group of members of the Ig superfamily that included CD2, CD48, CD58, and Ly9. Northern blot analysis showed that the expression of HLy9-β was predominantly restricted to hematopoietic tissues. Chromosome localization studies mapped the HLy9-β gene to chromosome 1q24, where other members of this Ig superfamily (CD48 and HumLy9) have been mapped. CD84 monoclonal antibodies (MoAbs) were shown to react with cells transfected with the cloned cDNA. These MoAbs were further used to show that CD84 is expressed as a single chain cell-surface glycoprotein of Mr 64,000 to 82,000, which was highly glycosylated. CD84 had a unique pattern of expression, being found predominantly on lymphocytes and monocytes. Thus, the glycoprotein HLy9-β is recognized by MoAbs previously clustered as CD84 and represents a newly identified member of the Ig superfamily that may play a significant role in leukocyte activation.

A multimeric form of soluble recombinant sheep LFA-3 (CD58) inhibits human T-cell proliferation

The rosetting of T cells by sheep erythrocytes is mediated through the interaction of the CD2 molecule on T cells with T11TS, a molecule on sheep erythrocytes homologous to lymphocyte function-associated antigen-3 (LFA-3, CD58). We cloned a T11TS cDNA from sheep leucocyte mRNA which encodes a soluble molecule comprising the distal D1 and the D2 extracellular domains, but not the transmembrane domain. cDNA for this soluble D1 + D2 form of sheep LFA-3 (sLFA-3) was expressed in Escherichia coli and the properties of the purified recombinant protein were assessed by inhibition of T-cell rosette formation. sLFA-3 inhibited rosette formation, but its activity was low, 50% inhibition occurring at 25 micrograms/ml, consistent with the observed low binding avidity of fluorescein isothiocyanate (FITC)-labelled sLFA-3, sLFA-3 was made multimeric to increase its affinity, by crosslinking biotinylated sLFA-3 to streptavidin-biotinylated dextran complexes. The binding of crosslinked sLFA-3 multimers, tested by fluorescence-activated cell sorting (FACS) analysis, was significantly increased compared to sLFA-3 monomers. Competition with monoclonal antibodies demonstrated that multimeric sLFA-3 bound to the T11(1) epitope on CD2. The multimeric form of sLFA-3 was significantly more potent than the monomer in inhibiting proliferation of human T cells in response to purified protein derivative (PPD), tetanus toxoid (TT) or allogeneic cells. Multimeric sLFA-3 might, therefore, have potential as an immunotherapeutic agent to inhibit and/or anergize antigen-specific T-cell responses.

Recent advances in graft-versus-host disease (GVHD) prevention

In the 1970s and 1980s, GVHD prevention approaches were limited in number. Recent advances in our understanding of the requirements for T-cell immune responses and for basic mechanism(s) involved in GVHD pathophysiology have led to exciting new strategies for GVHD prevention. This review focuses upon recent developments in GVHD prevention generated over the past 5 years. We have selected five different types of strategies to highlight including: 1) the in vivo targeting of GVHD-reactive T cells using either intact and F(ab')2 fragments of monoclonal antibodies directed against T-cell-surface determinants or immunotoxins which consist of antibodies linked to toxins, 2) a comparison of the in vivo immunosuppressive effects of FK506 and rapamycin on T-cell signaling, 3) the inhibition of T-cell activation through blockade of costimulatory or adhesogenic signals, 4) shifting the balance between acute GVHD-inducing T-helper-type 1 (Th1) T cells to anti-inflammatory T-helper-type 2 (Th2)-type T cells, and 5) the regulation of alloreactive T-cell activation by treatment with peptide analogs which affect either TCR/MHC, CD4/MHC class II, or CD8/MHC class I interactions. Collectively, these approaches are illustratrative of the progress made in extending our GVHD prevention armamentarium.

Decreased T cell response to anti-CD2 in systemic lupus erythematosus and reversal by anti-CD28: evidence for impaired T cell-accessory cell interaction

OBJECTIVE

To assess the ability of T cells from patients with systemic lupus erythematosus (SLE) to respond to a mitogenic combination of anti-CD2 monoclonal antibodies (MAb), and to learn the molecular basis of the documented defect.

METHODS

Peripheral blood mononuclear cell (PBMC) populations from individuals with SLE and paired controls were stimulated in vitro with anti-CD2, and the proliferative response was compared with that evoked by stimulation with phytohemagglutinin (PHA) and anti-CD3. Surface markers on lymphocyte populations were assessed by flow cytometry after staining with specific MAb.

RESULTS

The proliferative response to anti-CD2 was decreased to a greater extent than was the response to anti-CD3 or PHA in SLE patients. This defect was found in approximately one-half of the patients examined, was not associated with disease activity, and was maintained upon repeated testing. Since either monocytes or resting B cells can serve as accessory cells for T cells following activation by anti-CD2, we examined the T cell response after depletion of adherent cells. In approximately two-thirds of the individuals with a decreased response, depletion of monocytes or substitution of monocytes with allogeneic, resting B cells from normal donors corrected the defect. The addition to PBMC of anti-CD28, but not of a neutralizing antibody to interleukin-10, largely reversed the anti-CD2 proliferative defect. Significantly fewer CD8+ T cells expressed CD28 in SLE, and this defect was also documented, to a lesser extent, in CD4+ cells.

CONCLUSION

This study provides evidence that some functional T cell defects in SLE may be due, at least in part, to decreased CD28-mediated costimulatory activity following the interaction of T cells with conventional accessory cells.

CD2 Regulates the Positive Selection and Function of Antigen-Specific CD4−CD8+ T Cells

The CD2 glycoprotein has been implicated in both positive and negative regulation of T-cell mitogenesis. To study the involvement of CD2 in T-lymphocyte development and immune responses, we have analyzed two lines of CD2-null mice, each expressing a distinct class I major histocompatibility complex (MHC)-restricted T-cell receptor (TCR). In both situations, the absence of CD2 appeared to promote the positive selection of cells in a manner that is similar to that which occurs in the absence of CD5. Consistent with this, compound homozygotes that lacked both CD2 and CD5 showed evidence of enhanced positive selection even in the absence of a transgenic TCR. Despite the observed enhancement of positive selection, the lack of CD2 was associated with defects in proliferative responses and interferon-γ production when transgenic thymocytes and mature T lymphocytes were stimulated with the appropriate antigens. These findings raise the possibility that impaired sensitivity to selecting ligands in the thymus may provide a selective advantage that improves the efficiency of positive selection for certain TCRs. Furthermore, the results highlight the potential for a differential role for CD2 in thymocyte selection and T-cell immune responses.

Coexistence of Th1- and Th2-type cytokine profiles in anti-CD2 monoclonal antibody-induced tolerance

Anti-CD2 monoclonal antibody OX34 has been shown to suppress immunity in rodents in vitro and in vivo. To evaluate the effects of OX34 on vascularized allografts, Lewis (RT1(1)) hearts were transplanted heterotopically into Wistar Furth (RT1(u)) rats. A single 5 mg/kg intraperitoneal dose of OX34 administered at transplantation induced indefinite graft survival (mean survival time >140.3+/-12.3 vs. 12.7+/-0.7 control, P=0.001). The mixed lymphocyte response was partially inhibited at 60 days after transplant, returning to normal at 100 days. Donor-specific tolerance was confirmed by acceptance of second donor (>100 days, n=2) and rejection of third-party (mean survival time: 7.5+/-0.5 days, n=2) hearts. Immunohistochemical staining of allograft tissue from tolerant animals demonstrated abundant CD2+, CD4+, and CD8+ graft-infiltrating cells. To elucidate further the nature of these cells, we compared the expression of interleukin (IL)-2, IL-4, IL-10, and interferon (IFN)-gamma mRNA in allografted tissue from tolerant, acutely rejecting (AR), isografted, and naive animals using nonisotopic in situ hybridization. A significant increase in IL-2, IL-4, IL-10, and IFN-gamma mRNA was observed in graft-infiltrating cells of both tolerant and AR animals. IL-10 mRNA expression 4 days after transplant was significantly elevated in the OX34-treated compared to AR recipients. These data demonstrate that a single dose of OX34 at engraftment induces tolerance to vascularized allografts. Expression of both T helper 1 and T helper 2 cytokine mRNA profiles (IL-2/IFN-gamma and IL-4/ IL-10, respectively) are up-regulated locally in graft-infiltrating cells of AR and tolerant animal allografts.