Were monocytes responsible for initiating the cytokine storm in the TGN1412 clinical trial tragedy?

CD28 is expressed by macrophages with anti-inflammatory potential and limits their T-cell activating capacity

CD28 expression is generally considered to be T lymphocyte specific. We have previously shown CD28 mRNA expression in M-CSF-dependent anti-inflammatory monocyte-derived macrophages (M-MØ), and now demonstrate that CD28 cell surface expression is higher in M-MØ than in GM-CSF-dependent macrophages, and that macrophage CD28 expression is regulated by MAFB and activin A. In vivo, CD28 was found in tumor-associated macrophages and, to a lower extent, in pro-inflammatory synovial fluid macrophages from rheumatoid arthritis patients. Analysis of mouse macrophages confirmed Cd28 expression in bone-marrow derived M-MØ. Indeed, anti-CD28 antibodies triggered ERK1/2 phosphorylation in mouse M-MØ. At the functional level, Cd28KO M-MØ exhibited a significantly higher capacity to activate the OVA-specific proliferation of OT-II CD4+ T cells than WT M-MØ, as well as enhanced LPS-induced IL-6 production. Besides, the Cd28KO M-MØ transcriptome was significantly different from WT M-MØ regarding the expression IFN response, inflammatory response, and TGF-β signaling related gene sets. Therefore, defective CD28 expression in mouse macrophages associates to changes in gene expression profile, what might contribute to the altered functionality displayed by Cd28KO M-MØ. Thus, CD28 expression appears as a hallmark of anti-inflammatory macrophages and might be a target for immunotherapy.

"Cytokine storm", not only in COVID-19 patients. Mini-review

Cytokine storm is a form of uncontrolled systemic inflammatory reaction activated by a variety of factors and leading to a harmful homeostatic process, even to patient's death. Triggers that start the reaction are infection, systemic diseases and rarely anaphylaxis. Cytokine storm is frequently mentioned in connection to medical interventions such as transplantation or administration of drugs. Presented mini-review would like to show current possibilities how to fight or even stop such a life-threatening, immune-mediated process in order to save lives, not only in COVID-19 patients. Early identification of rising state and multilevel course of treatment is imperative. The most widely used molecule for systemic treatment remains tocilizumab. Except for anti IL-6 treatment, contemporary research opens the possibilities for combination of pharmaceutical, non-pharmaceutical and adjunctive treatment in a successful fight with consequences of cytokine storm. Further work is needed to discover the exact signaling pathways that lead to cytokine storm and to determine how these effector molecules and/or combination of processes can help to resolve this frequently fatal episode of inflammation. It is a huge need for all scientists and clinicians to establish a physiological rational for new therapeutic targets that might lead to more personalized medicine approaches.

Different players generate positive responses in two in vitro cytokine assay formats with aqueous and immobilized TGN1412 analog

To detect potential risk of severe cytokine release syndrome, in vitro assay formats with human cells have been developed. The two major testing platforms are a combination of whole blood with aqueous-phase test articles (whole blood cytokine assay, WBCA) and peripheral blood mononuclear cells with solid-phase articles (PBMC assay). Significant induction of cytokines was seen in both assays after treatment with a widely used control agent, TGN1412 or its analog CD28SA, but the WBCA cytokine profile differed from what was expected from clinical experience. In the WBCA, potential risk of CD28SA was detected by elevation of IL-8 whereas IL-2, a key cytokine after stimulation of CD28, was not induced in approximately 40% of donor samples. Therefore, further mechanistic understanding of the different responses in the in vitro assay was needed. In this study of donor samples treated with CD28SA, we compared the induction of cytokines and identified the cytokine-producing cells in the two assays. IL-2 was markedly elevated in all the donors in the PBMC assay but only in 1 of 3 donors in the WBCA. IL-8, the most sensitive biomarker in the WBCA, was produced by monocytes and granulocytes. T cells, the most relevant player in the PBMC assay with CD28SA, did not contribute to the positive response seen in two donors in the WBCA, which suggests that different players caused the positive cytokine responses to CD28SA in the two assays.

Animal extrapolation in preclinical studies: An analysis of the tragic case of TGN1412

According to the received view, the transportation view, animal extrapolation consists in inductive prediction of the outcome of a mechanism in a target, based on an analogical mechanism in a model. Through an analysis of the failure of preclinical studies of TGN1412, an innovative drug, to predict the tragic consequences of its first-in-man trial in 2006, the received view is challenged by a proposed view of animal extrapolation, the chimera view. According to this view, animal extrapolation is based on a hypothesis about how human organisms work, supported by the amalgamation of results drawn from various experimental organisms, and only predicting the 'predictive grid', that is, a global framework of the effects to be expected.

Enhancing the safety of antibody-based immunomodulatory cancer therapy without compromising therapeutic benefit: Can we have our cake and eat it too?

INTRODUCTION

Monoclonal antibodies (mAbs) targeting checkpoint inhibitors have demonstrated clinical benefit in treating patients with cancer and have paved the way for additional immune-modulating mAbs such as those targeting costimulatory receptors. The full clinical utility of these agents, however, is hampered by immune-related adverse events (irAEs) that can occur during therapy.

AREAS COVERED

We first provide a general overview of tumor immunity, followed by a review of the two major classes of immunomodulatory mAbs being developed as cancer therapeutics: checkpoint inhibitors and costimulatory receptor agonists. We then discuss therapy-associated adverse events. Finally, we describe in detail the mechanisms driving their therapeutic activity, with an emphasis on interactions between antibody fragment crystallizable (Fc) domains and Fc receptors (FcR).

EXPERT OPINION

Given that Fc-FcR interactions appear critical in facilitating the ability of immunomodulatory mAbs to elicit both therapeutically useful as well as adverse effects, the engineering of mAbs that can effectively engage their targets while limiting interaction with FcRs might represent a promising future avenue for developing the next generation of immune-enhancing tumoricidal agents with increased safety and retention of efficacy.

Failure to upregulate cell surface PD-1 is associated with dysregulated stimulation of T cells by TGN1412-like CD28 superagonist

The CD28 superagonist (CD28SA) TGN1412 was administered to humans as an agent that can selectively activate and expand regulatory T cells but resulted in uncontrolled T cell activation accompanied by cytokine storm. The molecular mechanisms that underlie this uncontrolled T cell activation are unclear. Physiological activation of T cells leads to upregulation of not only activation molecules but also inhibitory receptors such as PD-1. We hypothesized that the uncontrolled activation of CD28SA-stimulated T cells is due to both the enhanced expression of activation molecules and the lack of or reduced inhibitory signals. In this study, we show that anti-CD3 antibody-stimulated human T cells undergo time-limited controlled DNA synthesis, proliferation and interleukin-2 secretion, accompanied by PD-1 expression. In contrast, CD28SA-activated T cells demonstrate uncontrolled activation parameters including enhanced expression of LFA-1 and CCR5 but fail to express PD-1 on the cell surface. We demonstrate the functional relevance of the lack of PD-1 mediated regulatory mechanism in CD28SA-stimulated T cells. Our findings provide a molecular explanation for the dysregulated activation of CD28SA-stimulated T cells and also highlight the potential for the use of differential expression of PD-1 as a biomarker of safety for T cell immunostimulatory biologics.

Dynamics of a cytokine storm

Six volunteers experienced severe inflammatory response during the Phase I clinical trial of a monoclonal antibody that was designed to stimulate a regulatory T cell response. Soon after the trial began, each volunteer experienced a “cytokine storm”, a dramatic increase in cytokine concentrations. The monoclonal antibody, TGN1412, raised serum concentrations of both pro- and anti-inflammatory cytokines το very hiγh values during the first day, while lymphocyte and monocyte concentrations plummeted. Because the subjects were healthy and had no prior indications of immune deficiency, this event provided an unusual opportunity to study the dynamic interactions of cytokines and other measured parameters. Here, the response histories of nine cytokines have been modeled by a set of linear ordinary differential equations. A general search procedure identifies parameters of the model, whose response fits the data well during the five-day measurement period. The eighteenth-order model reveals plausible cause-and-effect relationships among the cytokines, showing how each cytokine induces or inhibits other cytokines. It suggests that perturbations in IL2, IL8, and IL10 have the most significant inductive effect, while IFN-γ and IL12 have the greatest inhibiting effect on other cytokine concentrations. Although TNF-α is a major pro-inflammatory factor, IFN-γ and three other cytokines have faster initial and median response to TGN1412 infusion. Principal-component analysis of the data reveals three clusters of similar cytokine responses: [TNF-α, IL1, IL10], [IFN-γ, IL2, IL4, IL8, and IL12], and [IL6]. IL1, IL6, IL10, and TNF-α have the highest degree of variability in response to uncertain initial conditions, exogenous effects, and parameter estimates. This study illuminates details of a cytokine storm event, and it demonstrates the value of linear modeling for interpreting complex, coupled biological system dynamics from empirical data.

After TGN1412: recent developments in cytokine release assays

The failure of regulatory science to keep pace with and support the development of new biological medicines was very publically highlighted in March 2006 when the first-in-man Phase I clinical trial of the immunomodulatory CD28-specific monoclonal antibody (mAb) TGN1412 ended in disaster when all six volunteers suffered a life-threatening adverse reaction termed a 'Cytokine Storm'. The poor predictive value of standard pre-clinical safety tests and animal models applied to TGN1412 demonstrated the need for a new generation of immunotoxicity assays and animal models that are both sensitive and predictive of clinical outcome in man. The non-predictive result obtained from pre-clinical safety testing in cynomolgus macaques has now been attributed to a lack of CD28 expression on CD4+ effector memory T-cells that therefore cannot be stimulated by TGN1412. In contrast, high levels of CD28 are expressed on human CD4+ effector memory T-cells, the source of most TGN1412-stimulated pro-inflammatory cytokines. Standard in vitro safety tests with human cells were also non-predictive as they did not replicate in vivo presentation of TGN1412. It was subsequently shown that, if an immobilized therapeutic mAb-based assay or endothelial cell co-culture assay was used to evaluate TGN1412, then these would have predicted a pro-inflammatory response in man. New in vitro assays based on these approaches are now being applied to emerging therapeutics to hopefully prevent a repeat of the TGN1412 incident. It has emerged that the mechanism of pro-inflammatory cytokine release stimulated by TGN1412 is different to that of other therapeutic mAbs, such that standard pro-inflammatory markers such as TNFα and IL-8 are not discriminatory. Rather, IL-2 release and lymphoproliferation are optimal readouts of a TGN1412-like pro-inflammatory response.

CD28 ligation increases macrophage suppression of T-cell proliferation

When compared to spleen or lymph node cells, resident peritoneal cavity cells respond poorly to T-cell activation in vitro. The greater proportional representation of macrophages in this cell source has been shown to actively suppress the T-cell response. Peritoneal macrophages exhibit an immature phenotype (MHC class II(lo), B7(lo)) that reduces their efficacy as antigen-presenting cells. Furthermore, these cells readily express inducible nitric oxide synthase (iNOS), an enzyme that promotes T-cell tolerance by catabolism of the limiting amino acid arginine. Here, we investigate the ability of exogenous T-cell costimulation to recover the peritoneal T-cell response. We show that CD28 ligation failed to recover the peritoneal T-cell response and actually suppressed responses that had been recovered by inhibiting iNOS. As indicated by cytokine ELISpot and neutralizing monoclonal antibody (mAb) treatment, this 'cosuppression' response was due to CD28 ligation increasing the number of interferon (IFN)-γ-secreting cells. Our results illustrate that cellular composition and cytokine milieu influence T-cell costimulation biology.Cellular & Molecular Immunology advance online publication, 23 April 2012; doi:10.1038/cmi.2012.13.

Granzyme B- and Fas ligand-mediated cytotoxic function induced by mitogenic CD28 stimulation of human memory CD4+ T cells

Some human memory CD4(+) T cells have cytotoxic functions best understood in the context of viral infections; however, their possible role in pathologic processes is understudied. The novel discovery that mitogenic CD28 antibodies induced proliferation and expansion of Tregs offered therapeutic promise for autoimmune disorders. However, the failed TGN1412 trial forced reassessment of this concept. As memory CD4(+) T cells are known to produce toxic molecules, including granzyme B (GrzB) and FasL, we wondered whether mitogenic CD28 was able to induce these cytotoxic molecules. A commercially available mitogenic human CD28 mAb (clone ANC28.1) was used to determine whether mitogenic CD28 induces cytotoxic function from human memory CD4(+) T cells. We found that stimulation of memory CD4(+) T cells by ANC28.1, as well as by conventional costimulation (CD3/CD28 mAb), robustly induced enzymatically active GrzB, along with increased surface expression of FasL. These functional phenotypes were induced in association with increased expression of T cell activation markers CD69 and CD25, and elimination of target cells by ANC28.1-activated memory CD4(+) T cells involved both GrzB and FasL. Additionally, ANC28.1-activated memory CD4(+) T cells caused disruption of epithelial cell monolayer integrity, which was partially mediated by GrzB. These findings reveal functions of memory CD4(+) T cells previously unknown to be induced by mitogenic CD28, and suggest that these pathogenic mechanisms may have been responsible for some of the widespread tissue destruction that occurred in the TGN1412 trial recipients.

A predictive biomimetic model of cytokine release induced by TGN1412 and other therapeutic monoclonal antibodies

Human peripheral blood mononuclear cells (PBMC) are routinely used in vitro to detect cytokine secretion as part of preclinical screens to delineate agonistic and antagonistic action of therapeutic monoclonal antibodies (mAbs). Preclinical value of standard human PBMC assays to detect cytokine release syndrome (CRS) has been questioned, as they did not predict the "cytokine storm" that occurred when healthy human volunteers were given a CD28-specific super-agonist mAb, TGN1412. In this article, we describe a three-dimensional biomimetic vascular test-bed that can be used as a more physiologically relevant assay for testing therapeutic Abs. For developing such a system, we used TGN1412 as a model mAb. We tested soluble TGN1412 on various combinations of human blood components in a module containing endothelial cells grown on a collagen scaffold and measured cytokine release using multiplex array. Our system, consisting of whole leukocytes, endothelial cells, and 100% autologous platelet-poor plasma (PPP) consistently produced proinflammatory cytokines in response to soluble TGN1412. In addition, other mAb therapeutics known to induce CRS or first infusion reactions, such as OKT3, Campath-1H, or Herceptin, generated cytokine profiles in our model system consistent with their in vivo responses. As a negative control we tested the non-CRS mAbs Avastin and Remicade and found little difference between these mAbs and the placebo control. Our data indicate that this novel assay may have preclinical value for predicting the potential of CRS for mAb therapeutics.