Topographical analysis of immune cell interactions reveals a biomechanical signature for immune cytolysis

Immune cells live intensely physical lifestyles characterized by structural plasticity, mechanosensitivity, and force exertion. Whether specific immune functions require stereotyped patterns of mechanical output, however, is largely unknown. To address this question, we used super-resolution traction force microscopy to compare cytotoxic T cell immune synapses with contacts formed by other T cell subsets and macrophages. T cell synapses were globally and locally protrusive, which was fundamentally different from the coupled pinching and pulling of macrophage phagocytosis. By spectrally decomposing the force exertion patterns of each cell type, we associated cytotoxicity with compressive strength, local protrusiveness, and the induction of complex, asymmetric interfacial topographies. These features were further validated as cytotoxic drivers by genetic disruption of cytoskeletal regulators, direct imaging of synaptic secretory events, and in silico analysis of interfacial distortion. We conclude that T cell-mediated killing and, by implication, other effector responses are supported by specialized patterns of efferent force.

TCR signal strength defines distinct mechanisms of T cell dysfunction and cancer evasion

T cell receptor (TCR) signal strength is a key determinant of T cell responses. We developed a cancer mouse model in which tumor-specific CD8 T cells (TST cells) encounter tumor antigens with varying TCR signal strength. High-signal-strength interactions caused TST cells to up-regulate inhibitory receptors (IRs), lose effector function, and establish a dysfunction-associated molecular program. TST cells undergoing low-signal-strength interactions also up-regulated IRs, including PD1, but retained a cell-intrinsic functional state. Surprisingly, neither high- nor low-signal-strength interactions led to tumor control in vivo, revealing two distinct mechanisms by which PD1hi TST cells permit tumor escape; high signal strength drives dysfunction, while low signal strength results in functional inertness, where the signal strength is too low to mediate effective cancer cell killing by functional TST cells. CRISPR-Cas9-mediated fine-tuning of signal strength to an intermediate range improved anti-tumor activity in vivo. Our study defines the role of TCR signal strength in TST cell function, with important implications for T cell-based cancer immunotherapies.

HLA-independent T cell receptors for targeting tumors with low antigen density

Chimeric antigen receptors (CARs) are receptors for antigen that direct potent immune responses. Tumor escape associated with low target antigen expression is emerging as one potential limitation of their efficacy. Here we edit the TRAC locus in human peripheral blood T cells to engage cell-surface targets through their T cell receptor-CD3 complex reconfigured to utilize the same immunoglobulin heavy and light chains as a matched CAR. We demonstrate that these HLA-independent T cell receptors (HIT receptors) consistently afford high antigen sensitivity and mediate tumor recognition beyond what CD28-based CARs, the most sensitive design to date, can provide. We demonstrate that the functional persistence of HIT T cells can be augmented by constitutive coexpression of CD80 and 4-1BBL. Finally, we validate the increased antigen sensitivity afforded by HIT receptors in xenograft mouse models of B cell leukemia and acute myeloid leukemia, targeting CD19 and CD70, respectively. Overall, HIT receptors are well suited for targeting cell surface antigens of low abundance.

132 HLA-independent T cell receptors effectively target low abundance antigens

Background

Chimeric antigen receptors (CARs) engage antigen independently of HLA and enable sustained T cell proliferation when they are endowed with both activating and costimulatory functions. While remission rates have been noticeably elevated in numerous clinical trials targeting CD19, CD22 or BCMA, relapses are common. One of the several underlying relapse mechanisms is antigen escape, which refers to a relapsing tumor that is either negative for the targeted antigen or expresses the latter at a low level. Failure to eliminate antigen-low tumors raises questions about the sensitivity of CARs and the minimum antigen density that is required for effective tumor eradication. Unlike CARs, TCRs engage antigen in an HLA-dependent manner, and they do so with high sensitivity. We hypothesized that a TCR/CD3 complex containing the same heavy and light immunoglobulin chains as a CAR will display increased sensitivity to the target antigen.

Methods

We edited the TRAC locus in human primary T cells to establish a novel antigen receptor structure, termed HLA-independent TCR or HIT receptor, by incorporating into the TCR/CD3 complex the same heavy and light chains as those of a corresponding CAR. We assessed their antigen sensitivity against a panel of cell lines expressing different antigen levels, analyzing their cytotoxicity, cytokine secretion, signaling response and degranulation activity. HIT and CAR T cells were further evaluated for their anti-tumor response using established ALL and AML mouse models.

Results

CD19-TRAC-HIT and CD19-TRAC-CAR T cells lysed wild-type NALM6 (~27,000 CD19 molecules) and NALM6 variants with 100-fold less CD19. As CD19 levels decreased further, CAR T cells no longer killed their target, in contrast to HIT T cells. HIT T cells showed increased expression of IFN-gamma, IL-2 and TNF-alpha upon exposure to NALM6 cells expressing ~20 CD19 molecules per cell, compared to CAR T cells. This increased sensitivity of HIT receptors correlated to their greater signaling response, upon exposure to the low-antigen-density NALM6. Phospho-proteomic analyses further confirmed this increased response of HIT T cells to low antigen levels. Altogether, these results confirm that HIT receptors endow T cells with greater antigen sensitivity than canonical CARs. We further showed that HIT T cells have higher in vivo anti-tumor activity compared to CAR T cells in mice bearing low-antigen-density ALL or AML.

Conclusions

HIT receptors consistently afford high antigen sensitivity and mediate tumor recognition beyond what current CARs can provide. HIT receptors open new prospects for targeting cell surface antigens of low abundance.

Ethics Approval

Eight- to 12-week-old NOD/SCID/IL-2Rgamma-null (NSG) male mice (Jackson Laboratory) were used under a protocol approved by the MSKCC Institutional Animal Care and Use Committee.

Interfacial actin protrusions mechanically enhance killing by cytotoxic T cells

Cytotoxic T lymphocytes (CTLs) kill by forming immunological synapses with target cells and secreting toxic proteases and the pore-forming protein perforin into the intercellular space. Immunological synapses are highly dynamic structures that boost perforin activity by applying mechanical force against the target cell. Here, we used high-resolution imaging and microfabrication to investigate how CTLs exert synaptic forces and coordinate their mechanical output with perforin secretion. Using micropatterned stimulatory substrates that enable synapse growth in three dimensions, we found that perforin release occurs at the base of actin-rich protrusions that extend from central and intermediate locations within the synapse. These protrusions, which depended on the cytoskeletal regulator WASP and the Arp2/3 actin nucleation complex, were required for synaptic force exertion and efficient killing. They also mediated physical deformation of the target cell surface during CTL-target cell interactions. Our results reveal the mechanical basis of cellular cytotoxicity and highlight the functional importance of dynamic, three-dimensional architecture in immune cell-cell interfaces.

Abstract B190: WASP-dependent actin protrusions mechanically potentiate killing by cytotoxic T-cells

Cytotoxic T Lymphocytes (CTLs) play a central role in immune responses against intracellular pathogens and cancer. Cytotoxic responses are induced by the formation of the immunologic synapse after the recognition of the peptide-major histocompatibility complex by the T-cell receptor. Synapse formation is associated dramatic reorganization of both microtubules and filamentous actin (F-actin) within the T-cell. This promotes the directional secretion of toxic perforin and granzymes into the intercellular space, enhancing both the potency and the specificity of targeT-cell killing. We have previously demonstrated that force exertion by CTLs at the immunologic synapse was strongly correlated with the cytotoxic potential. Indeed, force exertion enhances cytotoxicity by increasing membrane tension on the target cell, which in turn promotes the pore-forming activity of secreted perforin. This correlation between applied force and biochemical responses, which we referr to as mechanopotentiation, raised the prospect that CTLs might use three-dimensional structures at the immunologic synapse to coordinate force exertion and lytic granules secretion. In the present study, we investigated the mechanisms underlying mechanopotentiation in CTLs using a combination of three-dimensional micropatterned stimulatory substrates and high-resolution imaging. Our results revealed that CTLs couple lytic granule release with the formation of highly dynamic F-actin rich protrusions. These protrusions, which are generated by the Wiskott-Aldrich Syndrome protein (WASP) and the Arp2/3 actin nucleation complex, are required for coordinating force exertion with cytolytic secretion allowing efficient killing. Our results provide insight into how cells organize mechanical output and emphasize the importance of studying complex, communicative interfaces in three dimensions.

Citation Format: Fella Tamzalit, Mitchell S. Wang, Weiyang Jin, Vitaly Boyko, John M. Heddleston, Charles T. Black, Lance C. Kam, Morgan Huse. WASP-dependent actin protrusions mechanically potentiate killing by cytotoxic T-cells [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B190.

Emergence of NK Cell Hyporesponsiveness after Two IL-15 Stimulation Cycles

IL-15 is a cytokine playing a crucial role in the function of immune cells, including NK and CD8 T cells. In this study, we demonstrated that in vivo, in mice, IL-15-prestimulated NK cells were no longer able to respond to a second cycle of IL-15 stimulation. This was illustrated by defects in cell maturation, proliferation, and activation, seemingly linked to the environment surrounding NK cells but not related to the presence of CD4 regulatory T cells, TGF-β, or IL-10. Moreover, NK cells from immunodeficient mice could respond to two cycles of IL-15 stimulation, whereas an adoptive transfer of CD44⁺CD8⁺ cells impaired their responsiveness to the second cycle. Conversely, in immunocompetent mice, NK cell responsiveness to a second IL-15 stimulation was restored by the depletion of CD8⁺ cells. These biological findings refine our understanding of the complex mode of action of NK cells in vivo, and they should be taken into consideration for IL-15-based therapy.

Abstract A070: The role of the centrosome in cytotoxic T cell function

Cytotoxic T lymphocytes (CTLs) are essential for productive immune responses and recent studies have demonstrated their strong clinical potential as immunotherapeutic agents against established tumors. Cytotoxic responses in CTLs are induced by the T cell receptor, which recognizes cognate peptide-major histocompatibility complex molecules on the surfaces of infected or transformed cells, which induces the formation the immunological synapse. Synapse formation is accompanied by a series of actin and microtubule remodeling events, the most striking of which is the dramatic reorientation of the centrosome to a position just beneath the center of the contact site. It has been proposed that lytic granules containing perforin and granzyme cluster around the centrosome in activated CTLs. This polarization toward the synapse promotes the selective fusion of these granules with the synaptic membrane, leading to directional release of their contents toward the target cell.

In order to study more precisely how the centrosome influences secretory responses and how these contributions affect CTL activity, we have developed an approach using OT-I mice bearing a conditional allele of both p53 (p53flox) as well as SAS4 (SAS4flox), a scaffolding protein that is absolutely required for the formation and maintenance of the centrosome. OT-I SAS4−/−p53−/− cells were generated by transducing SAS4flox/floxp53flox/flox cells with a retrovirus expressing Cre. Using gamma-tubulin and pericentrin staining, we were able to show that SAS4 deletion effectively eliminates interphase centrosomes in CTLs. OT-I SAS4−/− p53−/− cells exhibited a marked defect in target cell killing after 24h, implying a crucial role of the centrosome in cytotoxic responses. This killing defect was accompanied by a decrease in both granzyme B and perforin production. IFN-gamma production and secretion were not altered by the loss of the centrosome. Importantly, TCR induced signaling was normal in these cells.

In summary, we were able to show that centrosome deletion impairs target cell killing without altering their overall magnitude. Given the importance of centrosome polarization for lytic granules delivery, we can assume that the centrosome ablation selectively alters cytotoxic efficiency by disrupting the directional synaptic secretion.

Citation Format: Fella Tamzalit, Ariella Kepecs, Hisham Bazzi, Kathryn Anderson, Morgan Huse. The role of the centrosome in cytotoxic T cell function [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A070.

Presence of B cells in tertiary lymphoid structures is associated with a protective immunity in patients with lung cancer

RATIONALE

It is now well established that immune responses can take place outside of primary and secondary lymphoid organs. We previously described the presence of tertiary lymphoid structures (TLS) in patients with non-small cell lung cancer (NSCLC) characterized by clusters of mature dendritic cells (DCs) and T cells surrounded by B-cell follicles. We demonstrated that the density of these mature DCs was associated with favorable clinical outcome.

OBJECTIVES

To study the role of follicular B cells in TLS and the potential link with a local humoral immune response in patients with NSCLC.

METHODS

The cellular composition of TLS was investigated by immunohistochemistry. Characterization of B-cell subsets was performed by flow cytometry. A retrospective study was conducted in two independent cohorts of patients. Antibody specificity was analyzed by ELISA.

MEASUREMENTS AND MAIN RESULTS

Consistent with TLS organization, all stages of B-cell differentiation were detectable in most tumors. Germinal center somatic hypermutation and class switch recombination machineries were activated, associated with the generation of plasma cells. Approximately half of the patients showed antibody reactivity against up to 7 out of the 33 tumor antigens tested. A high density of follicular B cells correlated with long-term survival, both in patients with early-stage NSCLC and with advanced-stage NSCLC treated with chemotherapy. The combination of follicular B cell and mature DC densities allowed the identification of patients with the best clinical outcome.

CONCLUSIONS

B-cell density represents a new prognostic biomarker for NSCLC patient survival, and makes the link between TLS and a protective B cell-mediated immunity.