A novel bispecific antibody format enables simultaneous bivalent and monovalent co-engagement of distinct target antigens

Bispecific antibodies based on full-length antibody structures are more optimal than fragment-based formats because they benefit from the favorable properties of the Fc region. However, the homodimeric nature of Fc effectively imposes bivalent binding on all current full-length bispecific antibodies, an attribute that can result in nonspecific activation of cross-linked receptors. We engineered a novel bispecific format, referred to as mAb-Fv, that utilizes a heterodimeric Fc region to enable monovalent co-engagement of a second target antigen in a full-length context. mAb-Fv constructs co-targeting CD16 and CD3 were expressed and purified as heterodimeric species, bound selectively to their co-target antigens, and mediated potent cytotoxic activity by NK cells and T cells, respectively. The capacity to co-engage distinct target antigens simultaneously with different valencies is an improved feature for bispecific antibodies with promising therapeutic implications.     

Cutting edge: monovalency of CD28 maintains the antigen dependence of T cell costimulatory responses

CD28 and CTLA-4 are the major costimulatory receptors on naive T cells. But it is not clear why CD28 is monovalent whereas CTLA-4 is bivalent for their shared ligands CD80/86. We generated bivalent CD28 constructs by fusing the extracellular domains of CTLA-4 or CD80 with the intracellular domains of CD28. Bivalent or monovalent CD28 constructs were ligated with recombinant ligands with or without TCR coligation. Monovalent CD28 ligation did not induce responses unless the TCR was coligated. By contrast, bivalent CD28 ligation induced responses in the absence of TCR engagement. To extend these findings to primary cells, we used novel superagonistic and conventional CD28 Abs. Superagonistic Ab D665, but not conventional Ab E18, predominantly ligates CD28 bivalently at low CD28/Ab ratios and induces Ag-independent T cell proliferation. Monovalency of CD28 for its natural ligands is thus essential to provide costimulation without inducing responses in the absence of TCR engagement.     

Valency of CD3 binding and internalization of the CD3 cell-surface complex control T cell responses to second signals: distinction between effects on protein kinase C, cytoplasmic free calcium, and proliferation

We have studied the relationship of valency of CD3 stimulation and modulation of the CD3 receptor complex with biochemical and proliferative responses of T cells. Anti-CD3 Fab, as well as F(ab')2 and whole antibody caused rapid modulation of the CD3 antigen, whereas anti-CD3 conjugated to Sepharose did not. In the absence of monocytes, T cells stimulated with anti-CD3 Fab, F(ab')2, or F(ab')2-Sepharose showed differences in their ability to respond to second signals given by PMA, IL 1, IL 2, or antibodies to Tp67 and Tp44. None of the anti-CD3 signals alone caused resting T cells to produce IL 2, and only the Sepharose-bound anti-CD3 F(ab')2 caused T cells to express high levels of functional IL 2 receptors. Anti-CD3 F(ab')2-Sepharose-stimulated T cells produced IL 2 and proliferated in response to each of the second signals. Because anti-CD3-Sepharose did not cause modulation of the CD3 antigen, the ability of the Sepharose-bound antibody to induce T cells to express IL 2 receptors and to respond to individual second signals may be related to lack of modulation rather than valency of binding. Anti-CD3 Fab-stimulated T cells responded to PMA but required combinations of other second signals. T cells stimulated with unmodified anti-CD3 antibody or F(ab')2 fragments responded to PMA but did not respond to any other second signals alone or in combination. Stimulations that resulted in modulation (i.e., anti-CD3 whole antibody, anti-CD3 F(ab')2, or anti-CD3 Fab fragments) caused an increase in cytoplasmic calcium levels in resting T cells but blocked proliferation of T cells in response to mitogenic lectins or CD2 stimulation. Anti-CD3 F(ab')2 on Sepharose, however, did not block T cell proliferation. Whole bivalent anti-CD3 antibody or F(ab')2 fragments, but not monovalent Fab fragments, caused a rapid translation of protein kinase C activity from cytosol to membrane in the Jurkat T cell line. Because all of these modulate the receptor, these data indicate that the functional difference between monovalent and bivalent binding to CD3 is related to antibody valency and not to antigenic modulation. The use of Fab anti-CD3 stimulation that requires combinations of second signals for proliferation allowed an analysis of the functional relationships between IL 1, anti-Tp67, and anti-Tp44.     

Functional optimization of agonistic antibodies to OX40 receptor with novel Fc mutations to promote antibody multimerization

Immunostimulatory receptors belonging to the tumor necrosis factor receptor (TNFR) superfamily are emerging as promising targets for cancer immunotherapies. To optimize the agonism of therapeutic antibodies to these receptors, Fc engineering of antibodies was applied to facilitate the clustering of cell surface TNFRs to activate downstream signaling pathways. One engineering strategy is to identify Fc mutations that facilitate antibody multimerization on the cell surface directly. From the analyses of the crystal packing of IgG1 structures, we identified a novel set of Fc mutations, T437R and K248E, that facilitated antibody multimerization upon binding to antigens on cell surface. In a NF-κB reporter assay, the engineered T437R/K248E mutations could facilitate enhanced agonism of an anti-OX40 antibody without the dependence on FcγRIIB crosslinking. Nonetheless, the presence of cells expressing FcγRIIB could facilitate a boost of the agonism of the engineered antibody with mutations on IgG1 Fc, but not on the silent IgG2σ Fc. The Fc engineered antibody also showed enhanced effector functions, including antibody-dependent cell-meditated cytotoxicity, antibody-dependent cellular phagocytosis, and complement-dependent cytotoxicity, depending on the IgG subtypes. Also, the engineered antibodies showed normal FcRn binding and pharmacokinetic profiles in mice. In summary, this study elucidated a novel Fc engineering approach to promote antibody multimerization on a cell surface, which could enhance agonism and improve effector function for anti-TNFR antibodies as well as other therapeutic antibodies.     

PEGylation and multimerization of the anti-p185HER-2 single chain Fv fragment 4D5: effects on tumor targeting

A major goal in antibody design for cancer therapy is to tailor the pharmacokinetic properties of the molecule according to specific treatment requirements. Key parameters determining the pharmacokinetics of therapeutic antibodies are target specificity, affinity, stability, and size. Using the p185HER-2 (HER-2)-specific scFv 4D5 as model system, we analyzed how changes in molecular weight and valency independently affect antigen binding and tumor localization. By employing multimerization and PEGylation, four different antibody formats were generated and compared with the scFv 4D5. First, dimeric and tetrameric miniantibodies were constructed by fusion of self-associating, disulfide-linked peptides to the scFv 4D5. Second, we attached a 20-kDa PEG moiety to the monovalent scFv and to the divalent miniantibody at the respective C terminus. In all formats, serum stability and full binding reactivity of the scFv 4D5 were retained. Functional affinity, however, did change. An avidity increase was achieved by multimerization, whereas PEGylation resulted in a 5-fold decreased affinity. Nevertheless, the PEGylated monomer showed an 8.5-fold, and the PEGylated dimer even a 14.5-fold higher tumor accumulation than the corresponding scFv, 48 h post-injection, because of a significantly longer serum half-life. In comparison, the non-PEGylated bivalent and tetravalent miniantibodies showed only a moderate increase in tumor localization compared with the scFv, which correlated with the degree of multimerization. However, these non-PEGylated formats resulted in higher tumor-to-blood ratios. Both multimerization and PEGylation represent thus useful strategies to tailor the pharmacokinetic properties of therapeutic antibodies and their combined use can additively improve tumor targeting.     

The anti-lymphoma activities of anti-CD137 monoclonal antibodies are enhanced in FcγRIII−/− mice

Agonistic monoclonal antibodies (mAbs) directed against the co-signaling molecule CD137 (4-1BB) elicit potent anti-tumor immunity in mice. This anti-tumor immunity has traditionally been thought to result from the ability of the Fab portion of anti-CD137 to function as an analog for CD137L. Although binding of CD137 by anti-CD137 mAbs has the potential to cross-link the Fc fragments, enabling Fc engagement of low to moderate affinity Fc gamma receptors (FcγR), the relative import of such Fc–FcγR interactions in mediating anti-CD137 associated anti-tumor immunity is unknown. We studied the ability of a rat anti-mouse CD137 mAb (2A) to mediate the anti-tumor response against the EL4E7 lymphoma in WT and FcγR^?/? strains. 2A-treated FcRγ^?/? mice had improved anti-tumor immunity against EL4E7, which could be completely recapitulated in FcγRIII^?/? animals. These improved anti-tumor responses were associated with increased splenic CD8β T cell and dendritic cell (DC) populations. Furthermore, there was an increase in the number of DCs expressing high levels of the CD40, CD80, and CD86 molecules that are associated with more effective antigen presentation. Our results demonstrate an unexpected inhibitory role for FcγRIII in the anti-tumor function of anti-CD137 and underscore the need to consider antibody isotype when engineering therapeutic mAbs.     

T cell activation through TCR/-CD3 complex. IL-2 production of T cell clones stimulated with anti-CD3 without cross-linkage.

To elucidate the Th cell activation mechanism through the TCR/CD3 complex, we examined the reactivity of T cell clones to soluble monovalent and divalent anti-CD3 without accessory cells or costimulatory factor. All T cell clones tested produced IL-2 in response to monovalent anti-CD3, although reactivity to divalent anti-CD3 was variable depending upon clones. IL-2 production of T cell clones induced by monovalent anti-CD3 was suppressed by cross-linking of the antibody with anti-hamster IgG. IL-2 mRNA expression and the increment of intracellular Ca2+ concentration were consistent with the IL-2 production. When T cell clones were stimulated with monovalent anti-CD3, they increased in size, although divalent anti-CD3 stimulation did not affect their size irrespective of their IL-2 production. These results indicate that monovalent anti-CD3 is more efficient than divalent anti-CD3 in induction of IL-2 production and that the cross-linkage of the TCR/CD3 complex is not necessarily required for the T cell clone activation.     

Established T cell-driven germinal center B cell proliferation is independent of CD28 signaling but is tightly regulated through CTLA-4

CD4 T cell activation is positively (CD28) and negatively (CTLA-4) regulated by the costimulatory ligands CD80 and CD86. A central question is how the balance between these two opposing forces is controlled as T cells differentiate. We have previously shown that CD28 signaling is absolutely required to prime naive CD4 T cells to differentiate into effectors that provide help for germinal centers and class-switched Ab responses. In this study, we show that the requirement for CD28 signaling is transient and effector CD4 T cells do not require CD28 signals to sustain their function. The CD28 independence of effector T cells within germinal centers suggested that a key function for CD80/CD86 under these circumstances might be to provide negative regulatory signals via the CD28 homologue CTLA-4. By examining germinal center responses in mice where the ability to signal through T cell CTLA-4 was compromised, we provide data that supports a critical role for CTLA-4 in down-regulating T cell help for germinal center B cells.     

Ligation of CD80 is critical for high-level CD25 expression on CD8+ T lymphocytes

CD80 and CD86 have been shown to play a critical role in the optimal activation of T cells. Although these two molecules bind the same ligand, CD28, the question of whether CD80 and CD86 provide unique signals or serve redundant roles remains controversial. Previous studies have suggested that CD80 binding to CD28 may be superior to CD86 for the activation of naive CD8+ T cells. This study provides a potential mechanism to explain these observations. Our study demonstrates a previously unappreciated role for CD80, its superiority over CD86 in promoting CD25 expression, increasing both the number of cells that express CD25 and the level expressed on a per cell basis. These findings provide new insights into the role of CD80 vs CD86 and have important implications for the design of vaccines and immunotherapeutics aimed at the generation of a robust CD8+ T cell response in vivo.     

Improved monovalent TNF receptor 1-selective inhibitor with novel heterodimerizing Fc

The development of alternative therapeutic strategies to tumor necrosis factor (TNF)-blocking antibodies for the treatment of inflammatory diseases has generated increasing interest. In particular, selective inhibition of TNF receptor 1 (TNFR1) promises a more precise intervention, tackling only the pro-inflammatory responses mediated by TNF while leaving regenerative and pro-survival signals transduced by TNFR2 untouched. We recently generated a monovalent anti-TNFR1 antibody fragment (Fab 13.7) as an efficient inhibitor of TNFR1. To improve the pharmacokinetic properties of Fab 13.7, the variable domains of the heavy and light chains were fused to the N-termini of newly generated heterodimerizing Fc chains. This novel Fc heterodimerization technology, designated “Fc-one/kappa” (Fc1κ) is based on interspersed constant Ig domains substituting the CH3 domains of a γ1 Fc. The interspersed immunoglobulin (Ig) domains originate from the per se heterodimerizing constant CH1 and CLκ domains and contain sequence stretches of an IgG1 CH3 domain, destined to enable interaction with the neonatal Fc receptor, and thus promote extended serum half-life. The resulting monovalent Fv-Fc1κ fusion protein (Atrosimab) retained strong binding to TNFR1 as determined by enzyme-linked immunosorbent assay and quartz crystal microbalance, and potently inhibited TNF-induced activation of TNFR1. Atrosimab lacks agonistic activity for TNFR1 on its own and in the presence of anti-human IgG antibodies and displays clearly improved pharmacokinetic properties.     

CD152 ligation by CD80 on T cells is required for the induction of unresponsiveness by costimulation-deficient antigen presentation

Two apparently contradictory observations have been made concerning peripheral T cell tolerance; costimulation-deficient Ag presentation leads to unresponsiveness, and CTLA4 (CD152) ligation is required for unresponsiveness to be induced. This issue was addressed using a CD80- CD86low B cell line to present Ag to DO.11.10 naive CD4+ T cells. Proliferation was substantially enhanced by anti-CD80 or anti-CD152, but was inhibited by anti-CD86. Furthermore, anti-CD80 partially, and anti-CD152 totally protected cloned DO.11.10 T cells from the induction of unresponsiveness following culture with peptide and Chinese hamster ovary H2-Ad+ CD80- CD86- cells. Fab of anti-CD80 caused similar enhancement, and coimmobilized anti-CD80 failed to costimulate the anti-CD3 response of purified T cells, indicating that direct signaling by anti-CD80 was not responsible for these effects. The possibility that anti-CD80 liberated CD28 molecules that were sequestered by the T cell-expressed CD80, enabling them to coaggregate with TCR:CD3 complexes was excluded by finding that anti-CD80 and anti-CD152 individually caused maximal enhancement, rather than having additive effects. These data suggest that T cell-expressed CD80 has a regulatory function and plays a key role in the induction of unresponsiveness due to costimulation-deficient Ag presentation by the ligation of CD152 on neighboring, or even the same, T cell.     

Multiple layers of CD80/86-dependent costimulatory activity regulate primary, memory, and secondary lymphocytic choriomeningitis virus-specific T cell immunity

The lymphocytic choriomeningitis virus (LCMV) system constitutes one of the most widely used models for the study of infectious disease and the regulation of virus-specific T cell immunity. However, with respect to the activity of costimulatory and associated regulatory pathways, LCMV-specific T cell responses have long been regarded as relatively independent and thus distinct from the regulation of T cell immunity directed against many other viral pathogens. Here, we have reevaluated the contribution of CD28-CD80/86 costimulation in the LCMV system by use of CD80/86-deficient mice, and our results demonstrate that a disruption of CD28-CD80/86 signaling compromises the magnitude, phenotype, and/or functionality of LCMV-specific CD8(+) and/or CD4(+) T cell populations in all stages of the T cell response. Notably, a profound inhibition of secondary T cell immunity in LCMV-immune CD80/86-deficient mice emerged as a composite of both defective memory T cell development and a specific requirement for CD80 but not CD86 in the recall response, while a related experimental scenario of CD28-dependent yet CD80/86-independent secondary CD8(+) T cell immunity suggests the existence of a CD28 ligand other than CD80/86. Furthermore, we provide evidence that regulatory T cells (T(REG)s), the homeostasis of which is altered in CD80/86(-/-) mice, contribute to restrained LCMV-specific CD8(+) T cell responses in the presence of CD80/86. Our observations can therefore provide a more coherent perspective on CD28-CD80/86 costimulation in antiviral T cell immunity that positions the LCMV system within a shared context of multiple defects that virus-specific T cells acquire in the absence of CD28-CD80/86 costimulation.     

CD3×CD19 bispecific antibodies and CD28 costimulation for locoregional treatment of low-malignancy non-Hodgkin’s lymphoma

 In advance of using bispecific antibodies for the treatment of B cell lymphoma in humans, we analysed CD3×CD19 bispecific antibodies for their capacity to induce T cell activiation in cell suspensions from follicular lymphoma lymph nodes. Here, we demostrate that the lack of costimulatory molecules, such as members of the B7 family, on the tumour cells resulted in insufficient activation of autologous T lymphocytes. However, stimulation and proliferation of T cells could be induced by addition of monospecific CD28 antibodies. Moreover, we show that bispecific CD3×CD19 antibodies can protect severe combined immunodeficiency (SCID) mice from human Epstein-Barr-virus (EBV)-induced B cell lymphoma growth. In these in vivo studies, CD28 costimulation did not show a significant benefit, possibly because of the high-level expression of CD80 and CD86 on the surface of the lymphoma cells. Furthermore, the treatment of SCID mice with bispecific antibodies, with or without CD28 antibodies, induced tumour-protective effects, as determined by a rechallenging experiment in long-term-surviving animals with the autologous EBV-transformed tumour B cell line. Treatment of a follicular lymphoma patient by intratumoural injection of both antibodies resulted in immunological responses with increases in the T/B ratio of peripheral blood as well as enhanced NK cell activity without toxic systemic side-effects. Accepted: 14 October 1997     

Targeting CD28, CTLA-4 and PD-L1 Costimulation Differentially Controls Immune Synapses and Function of Human Regulatory and Conventional T-Cells

CD28, CTLA-4 and PD-L1, the three identified ligands for CD80/86, are pivotal positive and negative costimulatory molecules that, among other functions, control T cell motility and formation of immune synapse between T cells and antigen-presenting cells (APCs). What remains incompletely understood is how CD28 leads to the activation of effector T cells (Teff) but inhibition of suppression by regulatory T cells (Tregs), while CTLA-4 and PD-L1 inhibit Teff function but are crucial for the suppressive function of Tregs. Using alloreactive human T cells and blocking antibodies, we show here by live cell dynamic microscopy that CD28, CTLA-4, and PD-L1 differentially control velocity, motility and immune synapse formation in activated Teff versus Tregs. Selectively antagonizing CD28 costimulation increased Treg dwell time with APCs and induced calcium mobilization which translated in increased Treg suppressive activity, in contrast with the dampening effect on Teff responses. The increase in Treg suppressive activity after CD28 blockade was also confirmed with polyclonal Tregs. Whereas CTLA-4 played a critical role in Teff by reversing TCR-induced STOP signals, it failed to affect motility in Tregs but was essential for formation of the Treg immune synapse. Furthermore, we identified a novel role for PD-L1-CD80 interactions in suppressing motility specifically in Tregs. Thus, our findings reveal that the three identified ligands of CD80/86, CD28, CTLA-4 and PD-L1, differentially control immune synapse formation and function of the human Teff and Treg cells analyzed here. Individually targeting CD28, CTLA-4 and PD-L1 might therefore represent a valuable therapeutic strategy to treat immune disorders where effector and regulatory T cell functions need to be differentially targeted.     

Mitogenic CD28 signals require the exchange factor Vav1 to enhance TCR signaling at the SLP-76-Vav-Itk signalosome

Almost all physiological T cell responses require costimulation-engagement of the clonotypic TCR with MHC/Ag and CD28 by its ligands CD80/86. Whether CD28 provides signals that are qualitatively unique or quantitatively amplify TCR signaling is poorly understood. In this study, we use superagonistic CD28 Abs, which induce T cell proliferation without TCR coligation, to determine how CD28 contributes to mitogenic responses. We show that mitogenic CD28 signals require but do not activate the proximal TCR components TCRzeta and Zap-70 kinase. In cell lines lacking proximal TCR signaling, an early defect in the CD28 pathway is in phosphorylation of the adaptor molecule SLP-76, which we show is essential for recruitment of the exchange factor Vav leading to Ca(2+) flux and IL-2 production. Point mutations in CD28 that result in diminished Vav phosphorylation also result in defective Ca(2+) flux, IL-2 production, and Tec-kinase phosphorylation. Using Vav1-deficient mice, we further demonstrate the importance of Vav1 for efficient proliferation, IL-2 production, and Ca(2+) flux. Our results indicate that CD28 signals feed into the TCR signaling pathway at the level of the SLP-76 signalosome.     

Essential role for both CD80 and CD86 costimulation, but not CD40 interactions, in allergen-induced Th2 cytokine production from asthmatic bronchial tissue: role for alphabeta, but not gammadelta, T cells

CD80 and CD86 interact with CD28 and deliver costimulatory signals required for T cell activation. We demonstrate that ex vivo allergen stimulation of bronchial biopsy tissue from mild atopic asthmatic, but not atopic nonasthmatic, subjects induced production of IL-5, IL-4, and IL-13. Explants from both study groups did not produce IFN-gamma, but secreted the chemokine RANTES without any overt stimulation. In addition to allergen, stimulation of asthmatic explants with mAbs to CD3 and TCR-alphabeta but not TCR-gammadelta induced IL-5 secretion. Allergen-induced IL-5 and IL-13 production by the asthmatic tissue was inhibited by anti-CD80 and, to a lesser extent, by anti-CD86 mAbs. In contrast, the production of these cytokines by PBMCs was not affected by mAbs to CD80, was inhibited by anti-CD86, and was strongly attenuated in the presence of both Abs. FACS analysis revealed that stimulated asthmatic bronchial tissue was comprised of CD4+ T cells that expressed surface CD28 (75. 3%) but little CTLA-4 (4.0%). Neutralizing mAbs to CD40 ligand had no effect on the cytokine levels produced by asthmatic tissue or PBMCs. Collectively, these findings suggest that allergen-specific alphabeta T cells are resident in asthmatic bronchial tissue and demonstrate that costimulation by both CD80 and CD86 is essential for allergen-induced cytokine production. In contrast, CD86 appears to be the principal costimulatory molecule required in PBMC responses. Attenuation of type 2 alphabeta T cell responses in the bronchial mucosa by blocking these costimulatory molecules may be of therapeutic potential in asthma.     

Acute myelogenous leukemia blasts as accessory cells during in vitro T lymphocyte activation

The ability of acute myelogenous leukemia (AML) blasts to mediate costimulatory signals during T lymphocyte activation was investigated in an experimental model where monoclonal T cell populations were stimulated with standardized activation signals (anti-CD3, anti-CD2, and anti-CD28 monoclonal antibodies and phytohemagglutinin). Proliferative T cell responses were detected for all AML patients (n = 16) when irradiated leukemia blasts were used as accessory cells during activation. T cell cytokine release was also observed for all patients when nonirradiated AML accessory cells were used, and for most patients a broad cytokine response (interleukin (IL) 2, IL4, IL10, IL13, and interferon-gamma) was detected. However, both T cell proliferation and cytokine release showed a wide variation among AML patients, and T cell responsiveness was in addition dependent both on the nature of the activation signal and on differences between individual T cell clones. The accessory cell function of AML blasts showed no correlation with the release of any single immunomodulatory soluble mediator (IL1beta, IL6, TNF-alpha, soluble IL2 receptors) or the expression of any particular adhesion/costimulatory membrane molecule (CD54, CD58, CD80, and CD86) by the blasts. However, blocking studies with anti-CD58 and anti-CD80/86 monoclonal antibodies demonstrated that both pathways can be involved when AML blasts are used as accessory cells, but the relative importance and the final effects of signaling through these pathways differ between AML populations. Although there is a wide interpatient variation, we conclude that for a majority of patients the native AML blasts can mediate adequate costimulatory signals needed for accessory cell-dependent T cell activation.     

The CD28/CTLA-4-B7 signaling pathway is involved in both allergic sensitization and tolerance induction to orally administered peanut proteins

Dendritic cells are believed to play an essential role in regulating the balance between immunogenic and tolerogenic responses to mucosal Ags by controlling T cell differentiation and activation via costimulatory and coinhibitory signals. The CD28/CTLA-4-CD80/CD86 signaling pathway appears to be one of the most important regulators of T cell responses but its exact role in responses to orally administered proteins remains to be elucidated. In the present study, the involvement of the CD28/CTLA-4-CD80/CD86 costimulatory pathway in the induction of allergic sensitization and oral tolerance to peanut proteins was investigated. In both an established C3H/HeOuJ mouse model of peanut hypersensitivity and an oral tolerance model to peanut, CD28/CTLA-4-CD80/CD86 interactions were blocked using the fusion protein CTLA-4Ig. To examine the relative contribution of CD80- and CD86-mediated costimulation in these models, anti-CD80 and anti-CD86 blocking Abs were used. In the hypersensitivity model, CTLA-4Ig treatment prevented the development of peanut extract-induced cytokine responses, peanut extract-specific IgG1, IgG2a, and IgE production and peanut extract-induced challenge responses. Blocking of CD80 reduced, whereas anti-CD86 treatment completely inhibited, the induction of peanut extract-specific IgE. Normal tolerance induction to peanut extract was found following CTLA-4Ig, anti-CD86, or anti-CD80 plus anti-CD86 treatment, whereas blockade of CD80 impaired the induction of oral tolerance. We show that CD28/CTLA-4-CD80/CD86 signaling is essential for the development of allergic responses to peanut and that CD86 interaction is most important in inducing peanut extract-specific IgE responses. Additionally, our data suggest that CD80 but not CD86 interaction with CTLA-4 is crucial for the induction of low dose tolerance to peanut.     

PSMA-targeted bispecific Fab conjugates that engage T cells

Bioconjugate formats provide alternative strategies for antigen targeting with bispecific antibodies. Here, PSMA-targeted Fab conjugates were generated using different bispecific formats. Interchain disulfide bridging of an αCD3 Fab enabled installation of either the PSMA-targeting small molecule DUPA (SynFab) or the attachment of an αPSMA Fab (BisFab) by covalent linkage. Optimization of the reducing conditions was critical for selective interchain disulfide reduction and good bioconjugate yield. Activity of αPSMA/CD3 Fab conjugates was tested by in vitro cytotoxicity assays using prostate cancer cell lines. Both bispecific formats demonstrated excellent potency and antigen selectivity.