T Cells enhance Natural Killer Cell antibody dependent cellular cytotoxicity
Creators: name: Arora, Jyoti
Publisher: name: University of Iowa
Year: 2024
Subjects: Antibody dependent cellular cytotoxicity (ADCC)
Bispecific antibody
Humanized mouse model
Monoclonal antibody
NK cell
T cell
Toxicology

description: Monoclonal antibodies (mAbs) that directly target cancer cells have been clinically effective for over two decades. However, some patients either do not respond or develop resistance over time. The mechanisms behind response or resistance to mAbs are not fully understood. Evidence suggests that antibody-dependent cellular cytotoxicity (ADCC), mediated by natural killer (NK) cells, is a key mechanism of action for many mAbs, including anti-CD20 mAb rituximab (RTX). Previous in vitro studies from our lab suggested a potential mechanism of resistance for mAbs, associated with reduced NK cell-mediated ADCC in the absence of T cells. Studies showed that T cells play an essential role in maintaining the viability and cytotoxicity of NK cells activated by RTX-coated cancer cells. This support is largely dependent on CD4+ T cells, involves direct contact between T cells and NK cells and is mediated in large part by interleukin-2 (IL-2). Therefore, resistance to mAb therapy can result from inadequate T cell help in the tumor microenvironment (TME). Based on this, we hypothesized that T cell help plays a central role in supporting NK cell-mediated ADCC by anti-cancer mAbs. Furthermore, we propose that anti-CD3-based bispecific antibodies (bsAbs) can enhance T cell help within the TME, thereby boosting NK cell-mediated ADCC and improving the efficacy of mAb-based therapies. Additional in vitro studies indicated that activating a small number of T cells using bsAbs targeting CD3 and cancer cells increases IL-2 production, thereby enhancing T cell-mediated support for NK cell viability and ADCC. However all this previous work was conducted in vitro, and whether this mechanism holds true in vivo or can be expanded to other antibodies and cancer models needed further testing.
description: In this thesis, we used a combination of preclinical mouse models and clinical approaches to further detail the impact of T cells on NK cell-mediated ADCC in vivo. Syngeneic mouse models are of limited value for studying this hypothesis in vivo due to biological differences in NK cell biology and the mechanisms of mAb action between mice and humans. Therefore, a humanized mouse model was developed that allows for control of immune cells, including T cells and NK cells in the TME. This model involves mixing Raji lymphoma cells with consistent numbers of NK cells, but varying number of T cells obtained from normal donor human PBMCs and inoculating this mixture into immunodeficient mice. In this model, NK-cell viability, and the expression of CD16 (Fc receptor) and CD25 (IL-2 receptor) dropped after RTX treatment in the absence of T cells but increased in the presence of T cells. RTX therapy was more effective when T cells were present and was ineffective when NK cells were depleted. To enhance T cell support for RTX-mediated NK cell ADCC, we utilized the bsAb epcoritamab (EPCOR), which specifically binds to CD3 and CD20 to activate T cells in the TME. Results showed that a low dose of EPCOR (0.1 μg/mouse) effectively activated intratumoral T cells, specifically CD4+ T cells, to produce a variety of cytokines including IL-2, which in turn enhanced NK cell viability and cytotoxicity. The combination of this low dose EPCOR with RTX was more effective than either treatment alone. However, higher doses of EPCOR (1 μg/mouse or 10 μg/mouse) proved toxic and intolerable for the mice.
description: In indolent lymphoma patients, fine needle aspirates taken before and after RTX-containing treatment revealed a strong correlation between pretherapy CD4+ T cell levels in the tumor microenvironment and increased NK cell CD16 and CD25 expression posttherapy, suggesting that the hypothesis is applicable in clinical settings. The effect of combining RTX with EPCOR in patients remains to be explored.
description: Additionally, we extended these hypotheses to other cancers and mAbs— in vitro studies showed that in myeloma model combining bsAb anti-CD3/anti-BCMA elranatamab (ELRA) with anti-CD38 daratumumab (DARA) enhanced NK cell viability and cytotoxicity, especially with low T cell numbers. Other monoclonal antibody combinations, including anti-SLAMF7 (elotuzumab) and ELRA in myeloma, RTX and anti-CD3/anti-CD20 bsAb (mosunetuzumab) in lymphoma, and anti-EGFR (cetuximab) and anti-CD3/anti-EGFR bsAb (rEGFRBi) in head and neck cancer also showed similar results. Short-term bsAb (ELRA) exposure at the start of a seven-day anti-CD38 DARA treatment course significantly increased NK cell activity, but this benefit was lost if bsAb was given later. Primary cells obtained from myeloma patients’ bone marrow immunosuppressive TME also showed improved NK cell viability and cytotoxicity with concurrent ELRA and DARA treatment. This suggests that the proposed mechanism of overcoming resistance to antibody therapy by providing T cell help is not limited to anti-CD20 treatment in lymphoma but could also enhance antibody therapy across various malignancies.
description: Overall, findings in this thesis provide in vivo evidence that T cell help enhances NK cell-mediated ADCC and anti-tumor activity by RTX. A low-dose anti-CD3-based bsAb (EPCOR) effectively activates T cells in the TME to improve mAb therapy. Additionally, this work can be extended to other cancers and mAbs that mediate its effects via NK cell ADCC. This work offers insights into mAbs resistance mechanism due to low intratumoral T cells and new therapeutic strategies for enhancing established mAb-based treatments.