Abstract 3289: Melanoma patients with high and low target expression can benefit from TCR-CD3 bispecifics through direct and indirect mechanisms of tumor control

Background: ImmTAC molecules are TCR-CD3 bispecific fusion proteins that can redirect and activate polyclonal T cells to kill tumors. Tebentafusp, which targets gp100, is the first ImmTAC to demonstrate an overall survival benefit and is approved for the treatment of HLA-A*02:01 adult patients with unresectable or metastatic uveal melanoma1. Clinical benefit was observed in patients with both high and low gp100 expression2, suggesting direct and indirect mechanisms of tumor control, which we explored using in vitro models.

Method: Uveal and cutaneous melanoma cell lines were pulsed with 0-1 µM peptide concentrations or were treated with supernatants from ImmTAC-activated PBMC, with or without blocking antibodies against IFNβ, IFNγ, TNFα, and IL6. Peptide-HLA (pHLA) molecules on tumor cell surface were quantified by microscopy. ImmTAC-redirected T cell activation and killing were measured by ELISPOT, MSD, and xCelligence assays. Antigen presentation machinery (APM) gene expression was measured by qPCR. Linear regression models were used to assess the influence of variables on ImmTAC-mediated T cell activation.

Results: Peptide-pulsing of tumor cells showed a dose response relationship between surface pHLA number and ImmTAC-mediated T cell killing (R2= 0.85), which was confirmed by ImmTAC redirected killing assays using tumor lines with differential endogenous expression of pHLA targets. Higher effector: target (E: T) and higher pHLA number are the key factors, by regression analyses, influencing ImmTAC mediated T cell activation. These account for 53% and 29% variability in IFNγ production (p<0.01), respectively. To assess the indirect impact of ImmTAC-activated T cells on tumor cells, cell lines were pre-treated with supernatants. ImmTAC-activated PBMC supernatants reduced tumor growth (2 to 25-fold) and increased tumor death (20 - 80%) in 5 of 8 cell lines tested. Blocking IFNγ restored tumor growth by over 40%, which was further enhanced by additional blocking of IFNβ, TNFα, and IL6. All cell lines significantly upregulated APM genes and became more susceptible to direct ImmTAC-mediated T cell killing (1.4 to 2-fold increase).

Conclusions: In vitro, ImmTAC bispecifics kill cancer cells by both direct and indirect mechanisms. Redirection of polyclonal T cells to kill melanoma cells is greatly influenced by surface pHLA number and E:T ratio. ImmTAC-induced cytokines inhibited tumor growth, increased tumor apoptosis and resulted in higher antigen presentation demonstrating the indirect effect of ImmTAC. These observations highlight how ImmTAC-treated melanoma patients could benefit through direct and indirect mechanisms of tumor control, and in part help to explain how patients with low gp100 expression can derive benefit from tebentafusp.

References:

1. Nathan, P. et al. NEJM 385, 1196-1206 (2021)

2. Leach E. et al. JITC 10.1136, 868 (2021)

Citation Format: Esra Güç, Anna Broomfield, Sang S. Seo, Aleksandra Raczka, Alex Greenshields-Watson, Laura Collins, Adel Benlahrech. Melanoma patients with high and low target expression can benefit from TCR-CD3 bispecifics through direct and indirect mechanisms of tumor control [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3289.

571 IL-2 combination with ImmTAC overcomes CD163+ TAM-like M2 macrophage inhibition of ImmTAC-mediated T cell killing of tumor cells

Background

ImmTAC molecules are bispecific fusion proteins consisting of an affinity-enhanced T cell receptor fused to an anti-CD3 effector that can redirect T cells to target cells. Tebentafusp, a gp100-directed ImmTAC, has demonstrated survival benefit in metastatic uveal melanoma [1]. We previously reported that a tumor microenvironment with a high immunosuppressive CD163+ tumor-associated macrophage (TAM): CD3 T cell ratio was associated with reduced benefit from tebentafusp [2]. Here, we explored whether IL-2 could potentiate T cells to overcome inhibition of ImmTAC-mediated killing by TAM-like M2 macrophages.

Methods

Tumor biopsies from a Phase 2 trial of metastatic uveal melanoma HLA-A*02:01+ patients treated with tebentafusp (NCT02570308) were used to quantify CD163+ TAMs and CD3+ T cells by immunohistochemistry (N=107) and to measure gene expression by bulk RNAseq (N=70). Pro-inflammatory M1 and TAM-like M2 macrophages were generated in vitro from healthy donors (N=5) and their effect on ImmTAC-mediated T cell activation and tumor killing was assessed against THP-1 tumor cells. T cells were untreated or pre-treated for 4 days with commercially sourced IL-2 or IL-15.

Results

In vitro, ImmTAC-mediated T cell killing of tumor cells was reduced by 85±5% in the presence of TAM-like M2 but not M1 macrophages. Consistent with this finding, below median CD163:CD3 ratio was associated with greater tumor shrinkage (TS) (odds ratio OR=2.9, p=0.014) and longer overall survival (OS) (hazard ratio HR=0.4, p=0.001) in tebentafusp-treated patients. We next explored in vitro whether the T cell activating cytokines IL-2 and IL-15 could overcome TAM-mediated inhibition of T cell redirection by ImmTAC. At clinically relevant doses, IL-2 but not IL-15 treatment resulted in dose dependent restoration of ImmTAC-mediated T cell killing of tumor cells in the presence of TAM-like M2 macrophages—60% and 83% restoration of killing at 50 and 150 U/ml of IL-2, respectively. Consistent with this observation, increased expression of IL2RB (HR 0.3, p<0.001) and IL2RG (HR 0.4, p=0.002), but not IL2RA (HR 0.8, p=0.5) in tumors was associated with longer OS on tebentafusp.

Conclusions

Low CD163+ TAM to CD3 T cell ratio and high IL2RB/G expression in tumors at baseline were associated with longer OS and greater TS in tebentafusp-treated metastatic uveal melanoma patients in a Phase 2 trial. In vitro, TAM-like M2 macrophages suppressed ImmTAC-mediated T cell killing of tumor cells, an effect abrogated by IL-2. These observations provide strong rationale for combining IL-2 biased to IL2RB/G with ImmTAC molecules to enhance benefit in tumors with high levels of TAMs.

Trial Registration

NCT02570308

References

Piperno-Neumann S, Hassel JC, Rutkowski P et al. Abstract CT002: Phase 3 randomized trial comparing tebentafusp with investigator’s choice in first line metastatic uveal melanoma. Cancer Res. 2021; 81 (13 Supplement) CT002.

Hassel JC, Benlahrech A, Stanhope S, et al. Abstract 1673: Uveal melanoma study patients with low CD163:CD3 ratio in tumor biopsy and low serum IL-6 showed enhanced tumor shrinkage (TS) and overall survival (OS) on tebentafusp. Cancer Res. 2021; 81 (13 Supplement) 1673.

Ethics Approval

The Oxford A REC approved protocol 13/SC/0226 was used to obtain written consent for all blood donations and was fully approved by the National Research Ethics Committee South Central.

Redefining macrophage and neutrophil biology in the metastatic cascade

Tumor cells metastasize to distant organs through a complex series of events that are driven by tumor intrinsic and extrinsic factors. In particular, non-malignant stromal cells, including immune cells, modify tumor metastatic behavior. Of these cells, tumor-associated innate immune cells, particularly macrophages and neutrophils, suppress the cytotoxic activity of innate and adaptive killer cells and interact with tumor cells to promote their growth and malignancy. These findings in mouse cancer models suggest that targeting these sub-populations of immune cells holds therapeutic promise in treating metastatic disease. In this review, we describe the origin and role of the macrophages, neutrophils, and their progenitors in the metastatic cascade and suggest strategies that might enhance cancer therapy.

Glioblastomas acquire myeloid-affiliated transcriptional programs via epigenetic immunoediting to elicit immune evasion

Glioblastoma multiforme (GBM) is an aggressive brain tumor for which current immunotherapy approaches have been unsuccessful. Here, we explore the mechanisms underlying immune evasion in GBM. By serially transplanting GBM stem cells (GSCs) into immunocompetent hosts, we uncover an acquired capability of GSCs to escape immune clearance by establishing an enhanced immunosuppressive tumor microenvironment. Mechanistically, this is not elicited via genetic selection of tumor subclones, but through an epigenetic immunoediting process wherein stable transcriptional and epigenetic changes in GSCs are enforced following immune attack. These changes launch a myeloid-affiliated transcriptional program, which leads to increased recruitment of tumor-associated macrophages. Furthermore, we identify similar epigenetic and transcriptional signatures in human mesenchymal subtype GSCs. We conclude that epigenetic immunoediting may drive an acquired immune evasion program in the most aggressive mesenchymal GBM subtype by reshaping the tumor immune microenvironment.

Adjuvant-free immunization with infective filarial larvae as lymphatic homing antigen carriers

Controlled infection with intestinal nematodes has therapeutic potential for preventing the symptoms of allergic and autoimmune diseases. Here, we engineered larvae of the filarial nematode Litomosoides sigmodontis as a vaccine strategy to induce adaptive immunity against a foreign, crosslinked protein, chicken egg ovalbumin (OVA), in the absence of an external adjuvant. The acylation of filarial proteins with fluorescent probes or biotin was not immediately detrimental to larval movement and survival, which died 3 to 5 days later. At least some of the labeled and skin-inoculated filariae migrated through lymphatic vessels to draining lymph nodes. The immunization potential of OVA-biotin-filariae was compared to that of an OVA-bound nanoparticulate carrier co-delivered with a CpG adjuvant in a typical vaccination scheme. Production of IFNγ and TNFα by restimulated CD4+ cells but not CD8+ confirmed the specific ability of filariae to stimulate CD4+ T cells. This alternative method of immunization exploits the intrinsic adjuvancy of the attenuated nematode carrier and has the potential to shift the vaccination immune response towards cellular immunity.

Generation of mouse bone marrow-derived macrophages using tumor coculture assays to mimic the tumor microenvironment

Macrophages are one of the key immune cells within the tumor microenvironment that encourage the growth of tumors at the primary site as well as contributing to all parts of the metastatic cascade. Although it is possible to isolate macrophages directly from the tumor, this can be a laborious process and due to their plasticity, it is not possible to maintain their in vivo phenotype in vitro. For this reason, differentiating macrophages from bone marrow is an attractive alternative. Here we present robust methods to study in vitro derived macrophages including (i) the isolation and generation of macrophages from bone marrow, (ii) differentiation/characterization of classically activated, alternatively activated and tumor-conditioned macrophages, as well as (iii) in vitro co-culturing assays for tumor cell-macrophage interaction/transmigration.

Dampening the fire to prevent surgery- and chemotherapy-induced metastasis

In this issue of the JCI, Panigrahy et al. demonstrate that preoperative administration of the antiinflammatory drug ketorolac or specialized proresolving mediators (SPM) called resolvins increases disease-free survival rates and prevents metastasis after surgery and chemotherapy in mouse models of cancer. The antitumor response was partially mediated by tumor-specific T cell immunity and immunological memory.

Characterization of a B16-F10 melanoma model locally implanted into the ear pinnae of C57BL/6 mice

The common experimental use of B16-F10 melanoma cells focuses on exploring their metastatic potential following intravenous injection into mice. In this study, B16-F10 cells are used to develop a primary tumor model by implanting them directly into the ears of C57BL/6J mice. The model represents a reproducible and easily traceable tool for local tumor growth and for making additional in vivo observations, due to the localization of the tumors. This model is relatively simple and involves (i) surgical opening of the ear skin, (ii) removal of a square-piece of cartilage followed by (iii) the implantation of tumor cells with fibrin gel. The remodeling of the fibrin gel within the cartilage chamber, accompanying tumor proliferation, results in the formation of blood vessels, lymphatics and tissue matrix that can be readily distinguished from the pre-existing skin structures. Moreover, this method avoids the injection-enforced artificial spread of cells into the pre-existing lymphatic vessels. The tumors have a highly reproducible exponential growth pattern with a tumor doubling time of around 1.8 days, reaching an average volume of 85mm³ 16 days after implantation. The melanomas are densely cellular with proliferative indices of between 60 and 80%. The induced angiogenesis and lymphangiogenesis resulted in the development of well-vascularized tumors. Different populations of immunologically active cells were also present in the tumor; the population of macrophages decreases with time while the population of T cells remained quasi constant. The B16-F10 tumors in the ear frequently metastasized to the cervical lymph nodes, reaching an incidence of 75% by day 16. This newly introduced B16-F10 melanoma model in the ear is a powerful tool that provides a new opportunity to study the local tumor growth and metastasis, the associated angiogenesis, lymphangiogenesis and tumor immune responses. It could potentially be used to test different treatment strategies.

Dorsal Ear Skin Window for Intravital Imaging and Functional Analysis of Lymphangiogenesis

Postdevelopmental lymphangiogenesis occurs in chronic inflammation and wound healing, and here we describe a window preparation in the mouse ear in which lymphangiogenesis can be observed and manipulated. This model has many advantages, including access for intravital immunostaining and imaging to assess morphological features and regeneration kinetics, as well as functional assays such as lymphatic clearance. We describe five procedures: (1) the creation of a collagen-fibrin-filled window in the mouse ear as a model for regenerative lymphangiogenesis, (2) intravital immunostaining for live analysis of morphology and structure, (3) lymphatic clearance assay for functional quantification, (4) whole-mount imaging with tissue clearing for confocal imaging, and (5) postmortem lymphangiography. These procedures allow for identification of morphological and functional abnormalities in both preexisting and newly formed lymphatic vessels.

Transcellular Pathways in Lymphatic Endothelial Cells Regulate Changes in Solute Transport by Fluid Stress

Rationale:

The transport of interstitial fluid and solutes into lymphatic vessels is important for maintaining interstitial homeostasis and delivering antigens and soluble factors to the lymph node for immune surveillance. Transendothelial transport across lymphatic endothelial cells (LECs) is commonly considered to occur paracellularly, or between cell–cell junctions, and driven by local pressure and concentration gradients. However, emerging evidence suggests that LECs also play active roles in regulating interstitial solute balance and can scavenge and store antigens, raising the possibility that vesicular or transcellular pathways may be important in lymphatic solute transport.

Objective:

The aim of this study was to determine the relative importance of transcellular (vesicular) versus paracellular transport pathways by LECs and how mechanical stress (ie, fluid flow conditioning) alters either pathway.

Methods and Results:

We demonstrate that transcellular transport mechanisms substantially contribute to lymphatic solute transport and that solute uptake occurs in both caveolae- and clathrin-coated vesicles. In vivo, intracelluar uptake of fluorescently labeled albumin after intradermal injection by LECs was similar to that of dermal dendritic cells. In vitro, we developed a method to differentially quantify intracellular solute uptake versus transendothelial transport by LECs. LECs preconditioned to 1 µm/s transmural flow demonstrated increased uptake and basal-to-apical solute transport, which could be substantially reversed by blocking dynamin-dependent vesicle formation.

Conclusions:

These findings reveal the importance of intracellular transport in steady-state lymph formation and suggest that LECs use transcellular mechanisms in parallel to the well-described paracellular route to modulate solute transport from the interstitium according to biomechanical cues.

Perivascular Macrophages Limit Permeability

OBJECTIVE

Perivascular cells, including pericytes, macrophages, smooth muscle cells, and other specialized cell types, like podocytes, participate in various aspects of vascular function. However, aside from the well-established roles of smooth muscle cells and pericytes, the contributions of other vascular-associated cells are poorly understood. Our goal was to ascertain the function of perivascular macrophages in adult tissues under nonpathological conditions.

APPROACH AND RESULTS

We combined confocal microscopy, in vivo cell depletion, and in vitro assays to investigate the contribution of perivascular macrophages to vascular function. We found that resident perivascular macrophages are associated with capillaries at a frequency similar to that of pericytes. Macrophage depletion using either clodronate liposomes or antibodies unexpectedly resulted in hyperpermeability. This effect could be rescued when M2-like macrophages, but not M1-like macrophages or dendritic cells, were reconstituted in vivo, suggesting subtype-specific roles for macrophages in the regulation of vascular permeability. Furthermore, we found that permeability-promoting agents elicit motility and eventual dissociation of macrophages from the vasculature. Finally, in vitro assays showed that M2-like macrophages attenuate the phosphorylation of VE-cadherin upon exposure to permeability-promoting agents.

CONCLUSIONS

This study points to a direct contribution of macrophages to vessel barrier integrity and provides evidence that heterotypic cell interactions with the endothelium, in addition to those of pericytes, control vascular permeability.

The dual role of tumor lymphatic vessels in dissemination of metastases and immune response development

Lymphatic vasculature plays a crucial role in the immune response, enabling transport of dendritic cells (DCs) and antigens (Ags) into the lymph nodes. Unfortunately, the lymphatic system has also a negative role in the progression of cancer diseases, by facilitating the metastatic spread of many carcinomas to the draining lymph nodes. The lymphatics can promote antitumor immune response as well as tumor tolerance. Here, we review the role of lymphatic endothelial cells (LECs) in tumor progression and immunity and mechanism of action in the newest anti-lymphatic therapies, including photodynamic therapy (PDT).

Long-term intravital immunofluorescence imaging of tissue matrix components with epifluorescence and two-photon microscopy

Besides being a physical scaffold to maintain tissue morphology, the extracellular matrix (ECM) is actively involved in regulating cell and tissue function during development and organ homeostasis. It does so by acting via biochemical, biomechanical, and biophysical signaling pathways, such as through the release of bioactive ECM protein fragments, regulating tissue tension, and providing pathways for cell migration. The extracellular matrix of the tumor microenvironment undergoes substantial remodeling, characterized by the degradation, deposition and organization of fibrillar and non-fibrillar matrix proteins. Stromal stiffening of the tumor microenvironment can promote tumor growth and invasion, and cause remodeling of blood and lymphatic vessels. Live imaging of matrix proteins, however, to this point is limited to fibrillar collagens that can be detected by second harmonic generation using multi-photon microscopy, leaving the majority of matrix components largely invisible. Here we describe procedures for tumor inoculation in the thin dorsal ear skin, immunolabeling of extracellular matrix proteins and intravital imaging of the exposed tissue in live mice using epifluorescence and two-photon microscopy. Our intravital imaging method allows for the direct detection of both fibrillar and non-fibrillar matrix proteins in the context of a growing dermal tumor. We show examples of vessel remodeling caused by local matrix contraction. We also found that fibrillar matrix of the tumor detected with the second harmonic generation is spatially distinct from newly deposited matrix components such as tenascin C. We also showed long-term (12 hours) imaging of T-cell interaction with tumor cells and tumor cells migration along the collagen IV of basement membrane. Taken together, this method uniquely allows for the simultaneous detection of tumor cells, their physical microenvironment and the endogenous tissue immune response over time, which may provide important insights into the mechanisms underlying tumor progression and ultimate success or resistance to therapy.

Growth factors engineered for super-affinity to the extracellular matrix enhance tissue healing

Growth factors (GFs) are critical in tissue repair, but their translation to clinical use has been modest. Physiologically, GF interactions with extracellular matrix (ECM) components facilitate localized and spatially regulated signaling; therefore, we reasoned that the lack of ECM binding in their clinically used forms could underlie the limited translation. We discovered that a domain in placenta growth factor-2 (PlGF-2(123-144)) binds exceptionally strongly and promiscuously to ECM proteins. By fusing this domain to the GFs vascular endothelial growth factor-A, platelet-derived growth factor-BB, and bone morphogenetic protein-2, we generated engineered GF variants with super-affinity to the ECM. These ECM super-affinity GFs induced repair in rodent models of chronic wounds and bone defects that was greatly enhanced as compared to treatment with the wild-type GFs, demonstrating that this approach may be useful in several regenerative medicine applications.

Intravital immunofluorescence for visualizing the microcirculatory and immune microenvironments in the mouse ear dermis

Visualizing the dynamic behaviors of immune cells in living tissue has dramatically increased our understanding of how cells interact with their surroundings, contributing important insights into mechanisms of leukocyte trafficking, tumor cell invasion, and T cell education by dendritic cells, among others. Despite substantial advances with various intravital imaging techniques including two-photon microscopy and the generation of multitudes of reporter mice, there is a growing need to assess cell interactions in the context of specific extracellular matrix composition and microvascular functions, and as well, simpler and more widely accessible methods are needed to image cell behaviors in the context of living tissue physiology. Here we present an antibody-based method for intravital imaging of cell interactions with the blood, lymphatic, and the extracellular matrix compartments of the living dermis while simultaneously assessing capillary permeability and lymphatic drainage function. Using the exposed dorsal ear of the anesthetized mouse and a fluorescence stereomicroscope, such events can be imaged in the context of specific extracellular matrix proteins, or matrix-bound chemokine stores. We developed and optimized the method to minimize tissue damage to the ear, rapidly immunostain for multiple extracellular or cell surface receptors of interest, minimize immunotoxicity with pre-blocking Fcγ receptors and phototoxicity with extracellular antioxidants, and highlight the major dermal tissue structures with basement membrane markers. We demonstrate differential migration behaviors of bone marrow-derived dendritic cells, blood-circulating leukocytes, and dermal dendritic cells, with the latter entering sparse CCL21-positive areas of pre-collecting lymphatic vessels. This new method allows simultaneous imaging of cells and tissue structures, microvascular function, and extracellular microenvironment in multiple skin locations for 12 hours or more, with the flexibility of immunolabeling in addition to genetic-based fluorescent reporters.