Dissecting the mechanism of cytokine release induced by T-cell engagers highlights the contribution of neutrophils

T cell engagers represent a novel promising class of cancer-immunotherapies redirecting T cells to tumor cells and have some promising outcomes in the clinic. These molecules can be associated with a mode-of-action related risk of cytokine release syndrome (CRS) in patients. CRS is characterized by the rapid release of pro-inflammatory cytokines such as TNF-α, IFN-γ, IL-6 and IL-1β and immune cell activation eliciting clinical symptoms of fever, hypoxia and hypotension. In this work, we investigated the biological mechanisms triggering and amplifying cytokine release after treatment with T cell bispecific antibodies (TCBs) employing an in vitro co-culture assay of human PBMCs or total leukocytes (PBMCs + neutrophils) and corresponding target antigen-expressing cells with four different TCBs. We identified T cells as the triggers of the TCB-mediated cytokine cascade and monocytes and neutrophils as downstream amplifier cells. Furthermore, we assessed the chronology of events by neutralization of T-cell derived cytokines. For the first time, we demonstrate the contribution of neutrophils to TCB-mediated cytokine release and confirm these findings by single-cell RNA sequencing of human whole blood incubated with a B-cell depleting TCB. This work could contribute to the construction of mechanistic models of cytokine release and definition of more specific molecular and cellular biomarkers of CRS in the context of treatment with T-cell engagers. In addition, it provides insight for the elaboration of prophylactic mitigation strategies that can reduce the occurrence of CRS and increase the therapeutic index of TCBs.

JAK and mTOR inhibitors prevent cytokine release while retaining T cell bispecific antibody in vivo efficacy

Background

T cell engaging therapies, like chimeric antigen receptor T cells and T cell bispecific antibodies (TCBs), efficiently redirect T cells towards tumor cells, facilitating the formation of a cytotoxic synapse and resulting in subsequent tumor cell killing, a process that is accompanied by the release of cytokines. Despite their promising efficacy in the clinic, treatment with TCBs is associated with a risk of cytokine release syndrome (CRS). The aim of this study was to identify small molecules able to mitigate cytokine release while retaining T cell-mediated tumor killing.

Methods

By screening a library of 52 Food and Drug Administration approved kinase inhibitors for their impact on T cell proliferation and cytokine release after CD3 stimulation, we identified mTOR, JAK and Src kinases inhibitors as potential candidates to modulate TCB-mediated cytokine release at pharmacologically active doses. Using an in vitro model of target cell killing by human peripheral blood mononuclear cells, we assessed the effects of mTOR, JAK and Src kinase inhibitors combined with 2+1 T cell bispecific antibodies (TCBs) including CEA-TCB and CD19-TCB on T cell activation, proliferation and target cell killing measured by flow cytometry and cytokine release measured by Luminex. The combination of mTOR, JAK and Src kinase inhibitors together with CD19-TCB was evaluated in vivo in non-tumor bearing stem cell humanized NSG mice in terms of B cell depletion and in a lymphoma patient-derived xenograft (PDX) model in humanized NSG mice in terms of antitumor efficacy.

Results

The effect of Src inhibitors differed from those of mTOR and JAK inhibitors with the suppression of CD19-TCB-induced tumor cell lysis in vitro, whereas mTOR and JAK inhibitors primarily affected TCB-mediated cytokine release. Importantly, we confirmed in vivo that Src, JAK and mTOR inhibitors strongly reduced CD19-TCB-induced cytokine release. In humanized NSG mice, continuous treatment with a Src inhibitor prevented CD19-TCB-mediated B cell depletion in contrast to mTOR and JAK inhibitors, which retained CD19-TCB efficacy. Ultimately, transient treatment with Src, mTOR and JAK inhibitors minimally interfered with antitumor efficacy in a lymphoma PDX model.

Conclusions

Taken together, these data support further evaluation of the use of Src, JAK and mTOR inhibitors as prophylactic treatment to prevent occurrence of CRS.

Src/lck inhibitor dasatinib reversibly switches off cytokine release and T cell cytotoxicity following stimulation with T cell bispecific antibodies

Background

T cell engagers are bispecific antibodies recognizing, with one moiety, the CD3ε chain of the T cell receptor and, with the other moiety, specific tumor surface antigens. Crosslinking of CD3 upon simultaneous binding to tumor antigens triggers T cell activation, proliferation and cytokine release, leading to tumor cell killing. Treatment with T cell engagers can be associated with safety liabilities due to on-target on-tumor, on-target off-tumor cytotoxic activity and cytokine release syndrome (CRS). Tyrosine kinases such as SRC, LCK or ZAP70 are involved in downstream signaling pathways after engagement of the T cell receptor and blocking these kinases might serve to abrogate T cell activation when required (online supplemental material 1). Dasatinib was previously identified as a potent kinase inhibitor that switches off CAR T cell functionality.

Methods

Using an in vitro model of target cell killing by human peripheral blood mononuclear cells, we assessed the effects of dasatinib combined with 2+1 T cell bispecific antibodies (TCBs) including CEA-TCB, CD19-TCB or HLA-A2 WT1-TCB on T cell activation, proliferation and target cell killing measured by flow cytometry and cytokine release measured by Luminex. To determine the effective dose of dasatinib, the Incucyte system was used to monitor the kinetics of TCB-mediated target cell killing in the presence of escalating concentrations of dasatinib. Last, the effects of dasatinib were evaluated in vivo in humanized NSG mice co-treated with CD19-TCB. The count of CD20⁺ blood B cells was used as a readout of efficacy of TCB-mediated killing and cytokine levels were measured in the serum.

Results

Dasatinib concentrations above 50 nM prevented cytokine release and switched off-target cell killing, which were subsequently restored on removal of dasatinib. In addition, dasatinib prevented CD19-TCB-mediated B cell depletion in humanized NSG mice. These data confirm that dasatinib can act as a rapid and reversible on/off switch for activated T cells at pharmacologically relevant doses as they are applied in patients according to the label.

Conclusion

Taken together, we provide evidence for the use of dasatinib as a pharmacological on/off switch to mitigate off-tumor toxicities or CRS by T cell bispecific antibodies.

CAR-J cells for antibody discovery and lead optimization of TCR-like immunoglobulins

T-cell bispecific antibodies (TCBs) are a novel class of engineered immunoglobulins that unite monovalent binding to the T-cell receptor (TCR) CD3e chain and bivalent binding to tumor-associated antigens in order to recruit and activate T-cells for tumor cell killing. In vivo, T-cell activation is usually initiated via the interaction of the TCR with the peptide-HLA complex formed by the human leukocyte antigen (HLA) and peptides derived from intracellular proteins. TCR-like antibodies (TCRLs) that recognize pHLA-epitopes extend the target space of TCBs to peptides derived from intracellular proteins, such as those overexpressed during oncogenesis or created via mutations found in cancer. One challenge during lead identification of TCRL-TCBs is to identify TCRLs that specifically, and ideally exclusively, recognize the desired pHLA, but not unrelated pHLAs. In order to identify TCRLs suitable for TCRL-TCBs, large numbers of TCRLs have to be tested in the TCB format. Here, we propose a novel approach using chimeric antigen receptors (CARs) to facilitate the identification of highly selective TCRLs. In this new so-called TCRL-CAR-J approach, TCRL-candidates are transduced as CARs into Jurkat reporter-cells, and subsequently assessed for their specificity profile. This work demonstrates that the CAR-J reporter-cell assay can be applied to predict the profile of TCRL-TCBs without the need to produce each candidate in the final TCB format. It is therefore useful in streamlining the identification of TCRL-TCBs.

Tumor-targeted 4-1BB agonists for combination with T cell bispecific antibodies as off-the-shelf therapy

Endogenous costimulatory molecules on T cells such as 4-1BB (CD137) can be leveraged for cancer immunotherapy. Systemic administration of agonistic anti-4-1BB antibodies, although effective preclinically, has not advanced to phase 3 trials because they have been hampered by both dependency on Fcγ receptor-mediated hyperclustering and hepatotoxicity. To overcome these issues, we engineered proteins simultaneously targeting 4-1BB and a tumor stroma or tumor antigen: FAP-4-1BBL (RG7826) and CD19-4-1BBL. In the presence of a T cell receptor signal, they provide potent T cell costimulation strictly dependent on tumor antigen-mediated hyperclustering without systemic activation by FcγR binding. We could show targeting of FAP-4-1BBL to FAP-expressing tumor stroma and lymph nodes in a colorectal cancer-bearing rhesus monkey. Combination of FAP-4-1BBL with tumor antigen-targeted T cell bispecific (TCB) molecules in human tumor samples led to increased IFN-γ and granzyme B secretion. Further, combination of FAP- or CD19-4-1BBL with CEA-TCB (RG7802) or CD20-TCB (RG6026), respectively, resulted in tumor remission in mouse models, accompanied by intratumoral accumulation of activated effector CD8⁺ T cells. FAP- and CD19-4-1BBL thus represent an off-the-shelf combination immunotherapy without requiring genetic modification of effector cells for the treatment of solid and hematological malignancies.

Abstract 957: Design of CD19-4-1BBL, a novel CD19-targeted 4-1BB ligand for combination therapy with CD20 T-cell bispecific antibodies and CD20 antibodies

Co-stimulation through 4-1BB has shown promising anti-tumor activity in preclinical models, but the development of 4-1BB agonistic antibodies in the clinic has been hampered by Fc-mediated liver toxicity. Here, we describe a novel CD19-targeted 4-1BB ligand designed to deliver a safe but potent 4-1BB agonist to effector T and NK cells with the goal to improve treatment of B cell malignancies. The antibody fusion protein is composed of split trimeric 4-1BB ligands and a tumor antigen targeting moiety recognizing CD19 fused to a silent Fc part (CD19-4-1BBL). The construct is devoid of FcgR-mediated crosslinking responsible for Fc-mediated toxicity and reintroduces 4-1BB hyperclustering upon binding to CD19 on B cells exclusively. In mice and cynomolgus monkeys, CD19-4-1BBL shows IgG-like pharmacokinetic properties. When cross-linked via CD19 on Non-Hodgkin Lymphoma cell lines or normal B cells, CD19-4-1BBL is biologically active in co-stimulating T cells. As 4-1BB is an inducible protein on activated T cells and NK cells, we combined CD19-4-1BBL with a T cell bispecific Ab targeting CD20 (CD20-TCB) to provide initial T cell activation while engaging with CD19+CD20+ tumor cells. In vitro, pre-treatment with CD20-TCB mediates the clustering of CD19-4-1BBL molecules to the interaction synapse of T cells and tumor cells. Live imaging revealed that the addition of CD19-4-1BBL induces significantly prolonged T cell-tumor contact (>30 min), leading to fast and efficient killing of tumor cells. In vivo in WSU-DLCL2-bearing human stem cell engrafted NSG mice (HSC-NSG) mice, CD20-TCB treatment quickly up-regulates 4-1BB on activated T cells, resulting in tumor growth inhibition. The combination of CD19-4-1BBL and CD20-TCB (used at a suboptimal dose) synergizes to eradicate the tumor completely. The combination induces strong T cell infiltration into the tumor, accompanied by an elevated CD8/Treg ratio, as compared to the monotherapies. Similarly, the combination also induces complete remission in a “difficult-to-treat” Nalm6 tumor model associated with low and patchy CD20 expression, mimicking patterns seen in the ABC subtype of DLBCL. Finally, the combination of CD19-4-1BBL and the ADCC-enhanced Type II CD20 antibody obinutuzumab induces complete tumor remissions in WSU-DLCL2 tumor-bearing HSC-NSG mice, confirming effective 4-1BB co-stimulation on NK cells. Taken together, tumor-targeted cross-linking of 4-1BB mediated by CD19-4-1BBL provides safe and efficient co-stimulation of T cells that are pre-activated by a TCB, or of NK cells pre-activated by an ADCC mediating antibody. This novel and effective combination immunotherapy warrants clinical investigation and offers possible “chemo-free” treatment of B cell malignancies.

Citation Format: Wei Xu, Johannes Sam, Mario Perro, John Challier, Christina Claus, Stanford Chen, Claudia Ferrara Koller, Michael Mølhøj, Stella Tournaviti, Marina Bacac, Tom Moore, Christian Klein, Pablo Umana. Design of CD19-4-1BBL, a novel CD19-targeted 4-1BB ligand for combination therapy with CD20 T-cell bispecific antibodies and CD20 antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 957.

Adenosine and cAMP signalling skew human dendritic cell differentiation towards a tolerogenic phenotype with defective CD8(+) T-cell priming capacity

Multiple endogenous mechanisms that regulate immune and inflammatory processes contribute to the maintenance of peripheral tolerance and prevent chronic inflammation in mammals. Yet pathogens and tumours are able to exploit these homeostatic pathways to foster immunosuppressive microenvironments and evade immune surveillance. The release of adenosine in the extracellular space contributes to these phenomena by exerting a broad range of immunomodulatory effects. Here we document the influence of adenosine receptor triggering on human dendritic cell differentiation and functions. We show that the expression of several immunomodulatory proteins and myeloid/monocytic lineage markers was affected by adenosine receptors and the cAMP pathway. These changes were reminiscent of the phenotype associated with tolerogenic dendritic cells and, functionally, translated into a defective capacity to prime CD8(+) T-cells with a common tumour antigen in vitro. These results establish a novel mechanism by which adenosine hampers CD8(+) T-cell immunity via dendritic cells that may contribute to peripheral tolerance as well as to the establishment of immunosuppressive microenvironments relevant to tumour biology.

Placental leptin receptor isoforms in normal and pathological pregnancies

Alternate mRNA splicing of human leptin receptor generates four membrane isoforms with different C-terminal sequences. They differ by the length of their intracellular domain which include specific motifs crucial for the specificity of leptin signalling. As a step towards functional studies, we have characterized leptin receptors in human placenta from normal pregnancies and pregnancies associated with diabetes and pre-eclampsia. Leptin and leptin receptors were visualized by immunohistochemistry of placentas obtained from first and third trimester pregnancies. Antibodies against N and C-terminal epitopes showed signals in the apical membrane of the syncytiotrophoblast in early and term placental villi as well as in JAr and BeWo derived trophoblast cells. In addition, a distinct isoform recognized by its extracellular juxtamembrane epitope was exclusively localized in cytotrophoblast cells and likely stains the soluble receptor. At contrast with the transmembrane receptors, the expression of this isoform is increased in placentas of pre-eclamptic and diabetic women which synthesize more leptin than placenta from uncomplicated pregnancy. These data demonstrate that short and long transmembrane leptin receptors are expressed in the trophoblast and indicate that leptin synthetized within the placenta can act locally through both receptor isoforms. Being also accessible to leptin from maternal origin, these transmembrane receptors may signal differently in pregnancy with normal and increased leptin production. The co-localization of leptin and the soluble receptor isoform suggests that this isoform serves for modulating maternal free leptin levels through modification of leptin binding capacities.