The low affinity Fc receptor for IgG functions as an effective cytolytic receptor for self-specific CD8 T cells

The Role of Fc Receptors in the Innate Immune System of Flounders Purported to Be Homologs of FcγRII and FcγRIII

FcγR is a significant opsonin receptor located on the surface of immune cells, playing a crucial role in Ab-dependent cell-mediated immunity. Our previous work revealed opposite expression trends of FcγRII and FcγRIII in flounder mIgM+ B lymphocytes after phagocytosis of antiserum-opsonized Edwardsiella tarda. This observation suggests that FcγRII and FcγRIII might serve distinct functions in Ig-opsonized immune responses. In this study, we prepared rFcγRIII as well as its corresponding Abs to investigate the potential roles of FcγRII and FcγRIII in the Ab-dependent immune response of IgM+ B cells. Our findings indicate that, unlike FcγRII, FcγRIII does not participate in Ab-dependent cellular phagocytosis. Instead, it is involved in cytokine production and bacterial killing in mIgM+ B lymphocytes. Additionally, we identified platelet-derived ADAM17 as a key factor in regulating FcγRIII shedding and cytokine release in mIgM+ B lymphocytes. These results elucidate the functions of FcγRII and FcγRIII in the innate immunology of mIgM+ B lymphocytes and contribute to an improved understanding of the regulatory roles of FcγRs in the phagocytosis of teleost B lymphocytes.

Potentiating antibody-dependent killing of cancers with CAR T cells secreting CD47-SIRPα checkpoint blocker

Chimeric antigen receptor (CAR) T-cell therapy has shown success in the treatment of hematopoietic malignancies; however, relapse remains a significant issue. To overcome this, we engineered "Orexi" CAR T cells to locally secrete a high-affinity CD47 blocker, CV1, at the tumor and treated tumors in combination with an orthogonally targeted monoclonal antibody. Traditional CAR T cells plus the antibody had an additive effect in xenograft models, and this effect was potentiated by CAR T-cell local CV1 secretion. Furthermore, OrexiCAR-secreted CV1 reversed the immunosuppression of myelomonocytoid cells both in vitro and within the tumor microenvironment. Local secretion of the CD47 inhibitor bypasses the CD47 sink found on all cells in the body and may prevent systemic toxicities. This combination of CAR T-cell therapy, local CD47 blockade, and orthogonal antibody may be a combinatorial strategy to overcome the limitations of each monotherapy.

Terminally Differentiated Effector Memory CD8+ T Cells Identify Kidney Transplant Recipients at High Risk of Graft Failure

BACKGROUND

Identifying biomarkers to predict kidney transplant failure and to define new therapeutic targets requires more comprehensive understanding of the immune response to chronic allogeneic stimulation.

METHODS

We investigated the frequency and function of CD8⁺ T cell subsets-including effector memory (EM) and terminally differentiated EM (TEMRA) CD8⁺ T cells-in blood samples from 284 kidney transplant recipients recruited 1 year post-transplant and followed for a median of 8.3 years. We also analyzed CD8⁺ T cell reactivity to donor-specific PBMCs in 24 patients who had received living-donor kidney transplants.

RESULTS

Increased frequency of circulating TEMRA CD8⁺ T cells at 1 year post-transplant associated with increased risk of graft failure during follow-up. This association remained after adjustment for a previously reported composite of eight clinical variables, the Kidney Transplant Failure Score. In contrast, increased frequency of EM CD8⁺ T cells associated with reduced risk of graft failure. A distinct TEMRA CD8⁺ T cell subpopulation was identified that was characterized by expression of FcγRIIIA (CD16) and by high levels of proinflammatory cytokine secretion and cytotoxic activity. Although donor-specific stimulation induced a similar rapid, early response in EM and TEMRA CD8⁺ T cells, CD16 engagement resulted in selective activation of TEMRA CD8⁺ T cells, which mediated antibody-dependent cytotoxicity.

CONCLUSIONS

At 1 year post-transplant, the composition of memory CD8⁺ T cell subsets in blood improved prediction of 8-year kidney transplant failure compared with a clinical-variables score alone. A subpopulation of TEMRA CD8⁺ T cells displays a novel dual mechanism of activation mediated by engagement of the T-cell receptor or of CD16. These findings suggest that TEMRA CD8⁺ T cells play a pivotal role in humoral and cellular rejection and reveal the potential value of memory CD8⁺ T cell monitoring for predicting risk of kidney transplant failure.

Tumor microenvironment dictates regulatory T cell phenotype: Upregulated immune checkpoints reinforce suppressive function

Background

Regulatory T (T_reg) cells have an immunosuppressive function in cancer, but the underlying mechanism of immunosuppression in the tumor microenvironment (TME) is unclear.

Methods

We compared the phenotypes of T cell subsets, including T_reg cells, obtained from peripheral blood, malignant effusion, and tumors of 103 cancer patients. Our primary focus was on the expression of immune checkpoint (IC)-molecules, such as programmed death (PD)-1, T-cell immunoglobulin and mucin-domain containing (TIM)-3, T cell Ig and ITIM domain (TIGIT), and cytotoxic T lymphocyte antigen (CTLA)-4, on T_reg cells in paired lymphocytes from blood, peritumoral tissue, and tumors of 12 patients with lung cancer. To identify the immunosuppressive mechanisms acting on tumor-infiltrating T_reg cells, we conducted immunosuppressive functional assays in a mouse model.

Results

CD8⁺, CD4⁺ T cells, and T_reg cells exhibited a gradual upregulation of IC-molecules the closer they were to the tumor. Interestingly, PD-1 expression was more prominent in T_reg cells than in conventional T (T_conv) cells. In lung cancer patients_, higher levels of IC-molecules were expressed on T_reg cells than on T_conv cells, and T_reg cells were also more enriched in the tumor than in the peri-tumor and blood. In a mouse lung cancer model, IC-molecules were also preferentially upregulated on T_reg cells, compared to T_conv cells. PD-1 showed the greatest increase on most cell types, especially T_reg cells, and this increase occurred gradually over time after the cells entered the TME. PD-1 high-expressing tumor-infiltrating T_reg cells displayed potent suppressive activity, which could be partially inhibited with a blocking anti-PD-1 antibody.

Conclusions

We demonstrate that the TME confers a suppressive function on T_reg cells by upregulating IC-molecule expression. Targeting IC-molecules, including PD-1, on T_reg cells may be effective for cancer treatment.

Mass cytometry dissects T cell heterogeneity in the immune tumor microenvironment of common dysproteinemias at diagnosis and after first line therapies

Dysproteinemias progress through a series of clonal evolution events in the tumor cell along with the development of a progressively more “permissive” immune tumor microenvironment (iTME). Novel multiparametric cytometry approaches, such as cytometry by time-of-flight (CyTOF) combined with novel gating algorithms can rapidly characterize previously unknown phenotypes in the iTME of tumors and better capture its heterogeneity. Here, we used a 33-marker CyTOF panel to characterize the iTME of dysproteinemia patients (MGUS, multiple myeloma—MM, smoldering MM, and AL amyloidosis) at diagnosis and after standard of care first line therapies (triplet induction chemotherapy and autologous stem cell transplant—ASCT). We identify novel subsets, some of which are unique to the iTME and absent from matched peripheral blood samples, with potential roles in tumor immunosurveillance as well as tumor immune escape. We find that AL amyloidosis has a distinct iTME compared to other dysproteinemias with higher myeloid and “innate-like” T cell subset infiltration. We show that T cell immune senescence might be implicated in disease pathogenesis in patients with trisomies. Finally, we demonstrate that the early post-ASCT period is associated with an increase of senescent and exhausted subsets, which might have implications for the rational selection of post-ASCT therapies.

Pros and cons of the immunogenicity of monoclonal antibodies in cancer treatment: a lesson from autoimmune diseases

The aim of this review is to report the current evidence on immunogenicity of monoclonal antibodies (moAbs) used in cancer compared with autoimmune diseases, focusing on local microenvironment. English abstracts were identified in Medline and www.clinicaltrials.gov . A total of 82 papers were selected. The percentage of immunogenicity of moAbs used for cancer therapy, evaluated as the serum concentration of antidrug antibodies, is significantly lower than that of moAbs used for the treatment of autoimmune diseases. This condition may rely on a different immunologic background characterized by a hyperactivation of immune cells in autoimmune diseases. The formation of complexes between antidrug antibodies and non-neutralizing moAbs bound to neoplastic antigens may allow more efficient elimination of cancer cells, but additional studies are needed.

Tumor antigen CA125 suppresses antibody-dependent cellular cytotoxicity (ADCC) via direct antibody binding and suppressed Fc-γ receptor engagement

Cancers employ a number of mechanisms to evade host immune responses. Here we report the effects of tumor-shed antigen CA125/MUC16 on suppressing IgG1-mediated antibody-dependent cellular cytotoxicity (ADCC). This evidence stems from prespecified subgroup analysis of a Phase 3 clinical trial testing farletuzumab, a monoclonal antibody to folate receptor alpha, plus standard-of-care carboplatin-taxane chemotherapy in patients with recurrent platinum-sensitive ovarian cancer. Patients with low serum CA125 levels treated with farletuzumab demonstrated improvements in progression free survival (HR 0.49, p = 0.0028) and overall survival (HR 0.44, p = 0.0108) as compared to placebo. Farletuzumab’s pharmacologic activity is mediated in part through ADCC. Here we show that CA125 inhibits ADCC by directly binding to farletuzumab that in turn perturbs Fc-γ receptor engagement on effector cells.

Fc Receptors and Fc Receptor-Like Molecules within the Immunoreceptor Family

Receptors for the Fc portion of immunoglobulins (FcRs) account for most cell-mediated biological activities of antibodies. The majority of FcRs are encoded by a set of genes, clustered in the fcr locus, on chromosome 1 in humans and on chromosome 1 and 3 in mice. Eight (in humans) and six (in mice) new genes were found, intermixed with FcR genes in corresponding fcr loci, which encode FcR-like molecules (FcRLs). FcRs and FcRLs are genetically, phylogenetically, structurally, and functionally related. FcRs and FcRLs, however, markedly differ by their ligands, their tissue distribution, and, therefore, by the biological functions they control. A systematic comparison of their biological properties leads to the conclusion that FcRLs are not like FcRs. They altogether form a single family within the immunoreceptor family, whose members fulfill distinct but complementary roles in immunity by differentially controlling innate and adaptive responses.

Fc Receptors in Immune Responses

Antibodies are major molecular effectors of adaptive immune responses. Most, if not all, biological activities of antibodies, however, depend on the functional properties of cells that express receptors for the Fc portion of antibodies (FcR). Most FcR are activating receptors; some are inhibitory. When engaged by antibodies and antigen, the various FcR expressed by a given cell trigger a mixture of positive and negative signals whose integration determines cellular responses. Responses of cell populations can be either protective or pathogenic. As a consequence, FcR are potential target/tools in a variety of diseases including infection, allergy, autoimmune diseases, and cancer.

Fc receptors as adaptive immunoreceptors

Most biological activities of antibodies depend on their ability to engage Receptors for the Fc portion of immunoglobulins (FcRs) on a variety of cell types. As FcRs can trigger positive and negative signals, as these signals control several biological activities in individual cells, as FcRs are expressed by many cells of hematopoietic origin, mostly of the myeloid lineage, as these cells express various combinations of FcRs, and as FcR-expressing cells have different functional repertoires, antibodies can exert a wide spectrum of biological activities. Like B and T Cell Receptors (BCRs and TCRs), FcRs are bona fide immunoreceptors. Unlike BCRs and TCRs, however, FcRs are immunoreceptors with an adaptive specificity for antigen, with an adaptive affinity for antibodies, with an adaptive structure and with an adaptive signaling. They induce adaptive biological responses that depend on their tissue distribution and on FcR-expressing cells that are selected locally by antibodies. They critically determine health and disease. They are thus exquisitely adaptive therapeutic tools.

Ligand binding but undetected functional response of FcR after their capture by T cells via trogocytosis

Intercellular transfer of cell surface proteins by trogocytosis is common and could affect T cell responses. Yet, the role of trogocytosis in T cell function is still elusive, and it is unknown whether a molecule, once captured by T cells, harbors the same biological properties as in donor APC. In this study, we showed that FcgammaR as well as the associated FcRgamma subunit could be detected at high levels on murine and human T cells after their intercellular transfer from FcgammaR-expressing APC. Capture of FcgammaR occurred during coculture of T cells with FcgammaR-expressing APC upon Ab- or Ag-mediated T cell stimulation. Once captured by T cells, FcgammaR were expressed in a conformation compatible with physiological function and conferred upon T cells the ability to bind immune complexes and to provision B cells with this source of Ag. However, we were unable to detect downstream signal or signaling-dependent function following the stimulation of FcgammaR captured by T cells, and biochemical studies suggested the improper integration of FcgammaR in the recipient T cell membrane. Thus, our study demonstrates that T cells capture FcgammaR that can efficiently exert ligand-binding activity, which, per se, could have functional consequences in T cell-B cell cooperation.

Phenotypic non-equivalence of murine (monocyte-) macrophage cells in biomaterial and inflammatory models

Cells of the mononuclear phagocytic system including monocytes and macrophages (e.g., pooled human monocytes, bone marrow-derived macrophages, etc.) are often employed for in vitro assessment of novel biomaterials and to assay anti-inflammatory drug activity. In this context, numerous macrophage cells are treated interchangeably in the literature despite a lack of demonstrated equivalence among immortalized cell lines and further, between cell lines and primary-derived macrophages of different species. Three murine (monocyte-) macrophage cell lines (IC-21, J774A.1, and RAW 264.7), commonly utilizedin biomaterial and pharmaceutical screening research, have been compared with primary-derived murine bone marrow macrophages. Significant differences were discovered in the expression of cell surface proteins requisite for cell adhesion and activation among cell lines and primary-derived cells as well as between the different cell lines. Results demonstrate activation but with reduced cytokine expression to chemical stimulus (lipopolysaccharide) by cell lines compared with that of primary-derived macrophages. Limited correlation between cultured primary and immortalized cells in cytokine production, phenotype and intrinsic activation states has relevance to fidelity for in vitro testing. These differences warrant justification for selection of various cell lines for specific assay purposes, and merit caution if comparisons to primary cell types (i.e., for biocompatibility) are required.

The FGL2-FcgammaRIIB pathway: a novel mechanism leading to immunosuppression

Fibrinogen-like protein 2 (FGL2) is a multifunctional protein, which has been implicated in the pathogenesis of allograft and xenograft rejection. Previously, FGL2 was shown to inhibit maturation of BM-derived DC and T-cell proliferation. The mechanism of the immunosuppressive activity of FGL2 remains poorly elucidated. Here, we focus on identification of FGL2-specific receptor(s) and their ability to modulate APC activity and allograft survival. Using flow cytometry and surface plasmon resonance analysis, we show that FGL2 binds specifically to Fc gamma receptor (FcgammaR)IIB and FcgammaRIII receptors, which are expressed on the surface of APC, including B lymphocytes, macrophages and DC. Antibody to FcgammaRIIB and FcgammaRIII, or deficiency of these receptors, abrogated FGL2 binding. FGL2 inhibited the maturation of BMDC from FcgammaRIIB+/+ mice but not from FcgammaRIIB(-/-) mice and induced apoptosis in the FcgammaRIIB+ mouse B-cell line (A20) but not the A20IIA1.6 cell line that does not express FcgammaRIIB. Recombinant FGL2 infused into FcgammaRIIB+/+ (C57BL/6J, H-2b) mice but not FcgammaRIIB(-/-) mice inhibited rejection of fully mismatched BALB/cJ (H-2d) skin allografts. The identification of specific receptor binding has important implications for the pathogenesis of immune-mediated disease and suggests a potential for targeted FGL2 therapy.

Inhibition of prostate carcinogenesis by combined active immunoprophylaxis

The aim of this study is to investigate whether an active immunoprophylactic approach combining specific antigens and adjuvant stimuli would be able to inhibit prostate carcinogenesis in transgenic TRAMP mice. A vaccine consisting of allogeneic large T antigen (TAg)-positive SV40-transformed cells combined with systemic recombinant IL-12 was administered to TRAMP mice, starting from when they were still tumor-free at 5-6 weeks of age. The combined vaccine significantly inhibited prostate carcinogenesis, giving a more than doubled median latency time of prostatic tumors (53 weeks in comparison to 26 weeks in control mice). Vaccination with cells alone or IL-12 treatment alone was poorly effective (median latency of 30 and 39 weeks, respectively). The combined vaccine induced a very high CD4 response biased toward the Th1 pathway, with the induction of a humoral response that included TAg-specific antibodies. Therefore, such active immunoprophylactic approach based on the combination of allogeneic SV40 TAg-positive cells and systemic administration of recombinant IL-12 significantly delayed autochthonous urogenital carcinogenesis driven by SV40 TAg in TRAMP mice.

Self-antigen maintains the innate antibacterial function of self-specific CD8 T cells in vivo

Self-specific CD8 T cells, which are selected by high-affinity interactions with self-Ags, develop into a lineage distinct from conventional CD8 T cells. We have previously shown that these self-specific cells acquire phenotypic and functional similarities to cells of the innate immune system including the expression of functional receptors associated with NK cells. In this study, we show that these self-specific cells have the ability to produce large amounts of IFN-gamma in response to infection with Listeria monocytogenes in a bystander fashion. The rapid production of IFN-gamma is associated with a dramatic reduction in the number of viable bacteria at the peak of infection. Self-specific CD8 T cells provide only marginal innate protection in the absence of self-Ag; however, the presence of self-Ag dramatically increases their protective ability. Exposure to self-Ag is necessary for the maintenance of the memory phenotype and responsiveness to inflammatory cytokines such as IL-15. Significantly, self-specific CD8 T cells are also more efficient in the production of IFN-gamma and TNF-alpha, thus providing more cytokine-dependent protection against bacterial infection when compared with NK cells. These findings illustrate that self-reactive CD8 T cells can play an important innate function in the early defense against bacterial infection.

Dysregulation of signaling pathways in CD45-deficient NK cells leads to differentially regulated cytotoxicity and cytokine production

CD45, a protein tyrosine phosphatase that regulates Src family kinases, is important for regulating T cell and B cell receptor signaling; however, little is known about how CD45 regulates immunoreceptor tyrosine-based activation motif (ITAM)-dependent natural killer (NK) cell receptor signaling and the resulting effector functions. NK cells from CD45-deficient mice are relatively competent for ITAM receptor-induced cell-mediated cytotoxicity, yet completely deficient for cytokine secretion after stimulation with ligands to or antibodies against NK1.1, CD16, Ly49H, Ly49D, and NKG2D. This deficiency in cytokine/chemokine production occurs at the level of mRNA expression. After receptor engagement, extracellular signal-regulated kinase and c-Jun N-terminal kinase activation was markedly perturbed, whereas p38 activation was not substantially affected. The pattern and amounts of basal tyrosine phosphorylation were altered in freshly isolated NK cells and were surprisingly and markedly increased in IL-2-expanded NK cells from CD45-/- mice. These findings indicate that CD45-dependent regulation of ITAM-dependent signaling pathways is essential for NK cell-mediated cytokine production but not cytolytic activity.

The role of CD8 T cells in innate immunity and in antigen non-specific protection

The role of CD8 T cells in adaptive immune responses is well understood. These lymphocytes respond through their T cell receptors to diverse antigens presented by MHC class I molecules by proliferating, secreting cytokines and chemokines, and directly lysing infected cells. Recently, a role for CD8 T cells in the innate immune response has become apparent. Independent of T cell receptor ligation, CD8 T cells can mount a response against pathogens by secreting cytokines and can defend against tumors by directly killing transformed cells. This innate response has been shown to be beneficial in controlling several types of bacterial infections. However, a subset of CD8 T cells that have innate non-antigen-specific capabilities has been implicated in self-reactivity, which could lead to autoimmunity.

Role of antibody-dependent cell-mediated cytotoxicity in the efficacy of therapeutic anti-cancer monoclonal antibodies

In recent years, interest in anti-cancer therapeutic monoclonal antibodies (mAb) has been renewed. Several of these reagents have been approved for therapy in a variety of cancer patients and many others are in different stages of development. It is believed that multiple mechanisms are involved in the anti-cancer effects of these reagents. However, several in vitro and in vivo studies have demonstrated that antibody-dependent cell-mediated cytotoxicity (ADCC) is their predominant mode of action against cancer cells. The requirement for a direct interaction between mAb and receptors for the Fc region of the antibodies (FcR) has been demonstrated for anti-tumor effects of these antibodies. Consequently, FcR-bearing immune effector cells play an important role in mediating their effects. It is not surprising that cancer cells have developed different strategies to evade these antibodies. Several strategies are proposed to potentiate the mAb-mediated ADCC in cancer patients. They may enhance anti-cancer therapeutic effects of these regents.

Negative Signaling in Fc Receptor Complexes

Cell activation results from the transient displacement of an active balance between positive and negative signaling. This displacement depends in part on the engagement of cell surface receptors by extracellular ligands. Among these are receptors for the Fc portion of immunoglobulins (FcRs). FcRs are widely expressed by cells of hematopoietic origin. When binding antibodies, FcRs provide these cells with immunoreceptors capable of triggering numerous biological responses in response to a specific antigen. FcR-dependent cell activation is regulated by negative signals which are generated together with positive signals within signalosomes that form upon FcR engagement. Many molecules involved in positive signaling, including the FcRbeta subunit, the src kinase lyn, the cytosolic adapter Grb2, and the transmembrane adapters LAT and NTAL, are indeed also involved in negative signaling. A major player in negative regulation of FcR signaling is the inositol 5-phosphatase SHIP1. Several layers of negative regulation operate sequentially as FcRs are engaged by extracellular ligands with an increasing valency. A background protein tyrosine phosphatase-dependent negative regulation maintains cells in a "resting" state. SHIP1-dependent negative regulation can be detected as soon as high-affinity FcRs are occupied by antibodies in the absence of antigen. It increases when activating FcRs are engaged by multivalent ligands and, further, when FcR aggregation increases, accounting for the bell-shaped dose-response curve observed in excess of ligand. Finally, F-actin skeleton-associated high-molecular weight SHIP1, recruited to phosphorylated ITIMs, concentrates in signaling complexes when activating FcRs are coengaged with inhibitory FcRs by immune complexes. Based on these data, activating and inhibitory FcRs could be used for new therapeutic approaches to immune disorders.