Therapeutic KRASG12C inhibition drives effective interferon-mediated antitumor immunity in immunogenic lung cancers

Recently developed KRASG12C inhibitory drugs are beneficial to lung cancer patients harboring KRASG12C mutations, but drug resistance frequently develops. Because of the immunosuppressive nature of the signaling network controlled by oncogenic KRAS, these drugs can indirectly affect antitumor immunity, providing a rationale for their combination with immune checkpoint blockade. In this study, we have characterized how KRASG12C inhibition reverses immunosuppression driven by oncogenic KRAS in a number of preclinical lung cancer models with varying levels of immunogenicity. Mechanistically, KRASG12C inhibition up-regulates interferon signaling via Myc inhibition, leading to reduced tumor infiltration by immunosuppressive cells, enhanced infiltration and activation of cytotoxic T cells, and increased antigen presentation. However, the combination of KRASG12C inhibitors with immune checkpoint blockade only provides synergistic benefit in the most immunogenic tumor model. KRASG12C inhibition fails to sensitize cold tumors to immunotherapy, with implications for the design of clinical trials combining KRASG12C inhibitors with anti-PD1 drugs.

Adenosine 2A receptor and TIM3 suppress cytolytic killing of tumor cells via cytoskeletal polarization

Tumors generate an immune-suppressive environment that prevents effective killing of tumor cells by CD8⁺ cytotoxic T cells (CTL). It remains largely unclear upon which cell type and at which stage of the anti-tumor response mediators of suppression act. We have combined an in vivo tumor model with a matching in vitro reconstruction of the tumor microenvironment based on tumor spheroids to identify suppressors of anti-tumor immunity that directly act on interaction between CTL and tumor cells and to determine mechanisms of action. An adenosine 2A receptor antagonist, as enhanced by blockade of TIM3, slowed tumor growth in vivo. Engagement of the adenosine 2A receptor and TIM3 reduced tumor cell killing in spheroids, impaired CTL cytoskeletal polarization ex vivo and in vitro and inhibited CTL infiltration into tumors and spheroids. With this role in CTL killing, blocking A_2AR and TIM3 may complement therapies that enhance T cell priming, e.g. anti-PD-1 and anti-CTLA-4.

PD-1 suppresses the maintenance of cell couples between cytotoxic T cells and target tumor cells within the tumor

The killing of tumor cells by CD8⁺ T cells is suppressed by the tumor microenvironment, and increased expression of inhibitory receptors, including programmed cell death protein-1 (PD-1), is associated with tumor-mediated suppression of T cells. To find cellular defects triggered by tumor exposure and associated PD-1 signaling, we established an ex vivo imaging approach to investigate the response of antigen-specific, activated effector CD8⁺ tumor-infiltrating lymphocytes (TILs) after interaction with target tumor cells. Although TIL-tumor cell couples readily formed, couple stability deteriorated within minutes. This was associated with impaired F-actin clearing from the center of the cellular interface, reduced Ca²⁺ signaling, increased TIL locomotion, and impaired tumor cell killing. The interaction of CD8⁺ T lymphocytes with tumor cell spheroids in vitro induced a similar phenotype, supporting a critical role of direct T cell-tumor cell contact. Diminished engagement of PD-1 within the tumor, but not acute ex vivo blockade, partially restored cell couple maintenance and killing. PD-1 thus contributes to the suppression of TIL function by inducing a state of impaired subcellular organization.

Systems Imaging of the Immune Synapse

Three-dimensional live cell imaging of the interaction of T cells with antigen-presenting cells (APCs) visualizes the subcellular distributions of signaling intermediates during T cell activation at thousands of resolved positions within a cell. These information-rich maps of local protein concentrations are a valuable resource in understanding T cell signaling. Here, we describe a protocol for the efficient acquisition of such imaging data and their computational processing to create four-dimensional maps of local concentrations. This protocol allows quantitative analysis of T cell signaling as it occurs inside live cells with resolution in time and space across thousands of cells.

PKCθ links proximal T cell and Notch signaling through localized regulation of the actin cytoskeleton

Notch is a critical regulator of T cell differentiation and is activated through proteolytic cleavage in response to ligand engagement. Using murine myelin-reactive CD4 T cells, we demonstrate that proximal T cell signaling modulates Notch activation by a spatiotemporally constrained mechanism. The protein kinase PKCθ is a critical mediator of signaling by the T cell antigen receptor and the principal costimulatory receptor CD28. PKCθ selectively inactivates the negative regulator of F-actin generation, Coronin 1A, at the center of the T cell interface with the antigen presenting cell (APC). This allows for effective generation of the large actin-based lamellum required for recruitment of the Notch-processing membrane metalloproteinase ADAM10. Such enhancement of Notch activation is critical for efficient T cell proliferation and Th17 differentiation. We reveal a novel mechanism that, through modulation of the cytoskeleton, controls Notch activation at the T cell:APC interface thereby linking T cell receptor and Notch signaling pathways.

DOI:http://dx.doi.org/10.7554/eLife.20003.001

The body’s immune system recognizes and responds to foreign agents such as bacteria and viruses. Immune cells known as T cells recognize foreign substances through a protein on their surface called the T cell receptor. Specifically, the T cell receptor binds to fragments of foreign proteins displayed on the surface of other cells, which sets in motion a chain of events that leads to the T cell becoming activated. An activated T cell divides to form new cells that develop into “effector” T cells, which can mount an effective immune response.

The T cell engages with the cell displaying the foreign proteins via an interface referred to as the immunological synapse. This zone of contact brings together the signaling machinery of the T cell. Like many other cells, T cells contain an internal skeleton-like structure made up of actin filaments. These filaments are crucial for the formation of the immunological synapse, in part because they help to transport the T cell receptor and other signaling proteins to the immunological synapse.

Recent research suggests that a signaling protein called Notch plays an important role in instructing activated T cells to develop into effector cells. Notch is found on the surface of many cells, including T cells, and it becomes activated when it is cut by a specific enzyme. However, it was not entirely clear how T cell signaling drives the activation of the Notch protein.

Britton et al. have now investigated the mechanism that leads to Notch activation in T cells from mice. The results show that a protein found inside the T cell, called PKCθ, is a major contributor to Notch activation when T cells become activated. So how does the PKCθ protein control the activation of Notch? Britton et al. observed that PKCθ inactivates a protein that normally inhibits actin filaments from forming, and does so specifically at the center of the immunological synapse. This inhibition promotes the generation of a large actin-rich structure known as the lamellal actin network. This structure is required to recruit the Notch-cutting enzyme to the immunological synapse. Further analysis revealed that Notch gets cut and activated during the first few minutes of T cell activation leading to cell division and the development of effector T cells.

Following on from this work, the next challenge will be to explore if altering signaling from the T cell receptor – for example, using drugs or small molecules – can modify the activation of Notch. If so, it will be important to explore if the chemicals could potentially be used to treat diseases that develop when T cells go awry, such as rheumatoid arthritis, psoriasis and Crohn’s disease.

DOI:http://dx.doi.org/10.7554/eLife.20003.002

Computational spatiotemporal analysis identifies WAVE2 and cofilin as joint regulators of costimulation-mediated T cell actin dynamics

Fluorescence microscopy is one of the most important tools in cell biology research because it provides spatial and temporal information to investigate regulatory systems inside cells. This technique can generate data in the form of signal intensities at thousands of positions resolved inside individual live cells. However, given extensive cell-to-cell variation, these data cannot be readily assembled into three- or four-dimensional maps of protein concentration that can be compared across different cells and conditions. We have developed a method to enable comparison of imaging data from many cells and applied it to investigate actin dynamics in T cell activation. Antigen recognition in T cells by the T cell receptor (TCR) is amplified by engagement of the costimulatory receptor CD28. We imaged actin and eight core actin regulators to generate over a thousand movies of T cells under conditions in which CD28 was either engaged or blocked in the context of a strong TCR signal. Our computational analysis showed that the primary effect of costimulation blockade was to decrease recruitment of the activator of actin nucleation WAVE2 (Wiskott-Aldrich syndrome protein family verprolin-homologous protein 2) and the actin-severing protein cofilin to F-actin. Reconstitution of WAVE2 and cofilin activity restored the defect in actin signaling dynamics caused by costimulation blockade. Thus, we have developed and validated an approach to quantify protein distributions in time and space for the analysis of complex regulatory systems.

Ultrasound monitoring of diaphragm activity in bilateral diaphragmatic paralysis

Recovery of diaphragm activity after bilateral diaphragmatic paralysis was monitored in a term infant using a mechanical sector scanner fitted with a 5 MHz transducer. The ratio of diaphragmatic excursion during spontaneous breathing and ventilator assistance was used an objective measure for comparison of diaphragmatic activity during recovery. Ultrasound assessment of diaphragm contraction may be used to study progress in diaphragmatic paralysis.