Imaging CAR T-cell kinetics in solid tumors: Translational implications

Our plain-English summary of Imaging CAR T-cell kinetics in solid tumors: Translational implications, by M.S. Skovgard, H.R. Hocine, J.K. Saini, et al (Molecular Therapy Oncolytics, 2021).

The study

• Authors: M.S. Skovgard, H.R. Hocine, J.K. Saini, M. Moroz, R.Y. Bellis, S. Banerjee, A. Morello, V. Ponomarev, J. Villena-Vargas, P.S. Adusumilli
• Journal: Molecular Therapy Oncolytics
• Published: 2021;22:355-367
• Cited by: 45 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Success in solid tumor chimeric antigen receptor (CAR) T-cell therapy requires overcoming several barriers, including lung sequestration, inefficient accumulation within the tumor, and target-antigen heterogeneity. Understanding CAR T-cell kinetics can assist in the interpretation of therapy response and limitations and thereby facilitate developing successful strategies to treat solid tumors. As T-cell therapy response varies across metastatic sites, the assessment of CAR T-cell kinetics by peripheral blood analysis or a single-site tumor biopsy is inadequate for interpretation of therapy response. The use of tumor imaging alone has also proven to be insufficient to interpret response to therapy. To address these limitations, we conducted dual tumor and T-cell imaging by use of a bioluminescent reporter and positron emission tomography in clinically relevant mouse models of pleural mesothelioma and non-small cell lung cancer. We observed that the mode of delivery of T cells (systemic versus regional), T-cell activation status (presence or absence of antigen-expressing tumor), and tumor-antigen expression heterogeneity influence T-cell kinetics. The observations from our study underscore the need to identify and develop a T-cell reporter-in addition to standard parameters of tumor imaging and antitumor efficacy-that can be used for repeat imaging without compromising the efficacy of CAR T cells in vivo.

© 2021 The Authors.

In plain English

This was a preclinical mouse imaging study of mesothelin (MSLN)-targeted CAR T cells (M28z) carrying imaging reporter genes. Human pleural mesothelioma (MSTO-211H) and non-small cell lung cancer (A549) cells were implanted in immunodeficient NSG mice, and donor human T cells were transduced with the CAR plus enhanced firefly luciferase (bioluminescence) or HSVtk (PET-CT with 18F-FEAU). After intravenous injection into tumor-free mice, signal peaked in the lungs at 4 hours and T cells remained sequestered up to 70 hours; with an antigen-positive flank tumor, signal rose in the tumor by day 6. In lung tumors with high MSLN expression, tumors were eradicated by day 8, while low- and heterogeneous-antigen tumors relapsed. In mice with established orthotopic mesothelioma given a single low dose, intrapleurally delivered CAR T cells proliferated within the pleural cavity (6-fold signal increase at 2 days), whereas systemically delivered cells did not accumulate in pleural tumors within 5 days; without tumor, regional cells persisted in the pleural space 5 days without proliferation. The authors concluded that T-cell imaging, alongside tumor imaging, is needed to interpret CAR T-cell kinetics and therapy response.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Preclinical animal (mouse) experiment using in vitro and in vivo reporter-gene imaging (bioluminescence and PET-CT) of CAR T cells and tumors
• Who was studied: Female NSG (NOD/SCID/gamma-null) immunodeficient mice, 6-10 weeks old, bearing human pleural mesothelioma (MSTO-211H) or human non-small cell lung cancer (A549) xenografts; T cells came from 5 healthy human volunteer donors; group sizes of 2-7 mice per dose or treatment arm
• Exposure: Human T cells transduced with a second-generation mesothelin-targeted CAR (M28z) plus a reporter gene (enhanced firefly luciferase or HSVtk), given intravenously (systemic) or intrapleurally (regional) at doses from 5 x 10^4 to 2 x 10^6 cells; control non-MSLN-targeted (prostate-specific membrane antigen) CAR T cells
• Main results:
  • In tumor-free mice given CAR T cells intravenously, bioluminescence peaked in the lungs at 4 hours, decreased up to 24 hours, and T cells remained in the lungs up to 70 hours
  • In mice with an antigen-expressing (MSLN+) subcutaneous mesothelioma flank tumor, intravenous CAR T cells first accumulated in the lungs and then increased in the flank tumor by day 6
  • In the lung adenocarcinoma model, tumors with high MSLN expression were eradicated 8 days after CAR T-cell administration, while regression of low-antigen tumors began only at day 4
  • Tumors with low and with heterogeneous antigen expression relapsed
  • Control (non-MSLN-targeted) CAR T cells did not accumulate within the tumor
  • Regionally (intrapleurally) delivered CAR T cells in mice without pleural tumor stayed in the pleural space for 5 days with no imaging evidence of proliferation or egress until day 6, at any dose tested
  • In mice with established orthotopic mesothelioma treated with a single low dose (n = 5 mice per group), intrapleurally administered T cells proliferated within the pleural cavity while systemically administered CAR T cells did not accumulate in the tumor
  • Regionally delivered CAR T cells showed a 6-fold rise in imaging intensity 2 days after delivery, whereas systemically delivered cells did not accumulate in pleural tumors within 5 days
  • With HSVtk-transduced CAR T cells imaged by PET-CT and ffLuc tumor bioluminescence, tumor regression tracked with CAR T-cell accumulation
  • HSVtk-transduced CAR T cells were less effective than M28z CAR T cells alone, per the authors' supplementary data
  • Transduction efficiency across experiments: 45%-60% for M28z (GFP) and 10%-30% for effLuc (Thy1.1)
• The authors' conclusion: The authors concluded that T-cell imaging, combined with tumor imaging, is needed to understand how tumor site, T-cell activation status, delivery route and antigen heterogeneity affect CAR T-cell kinetics, and that a non-immunogenic reporter detectable in deep organs that does not reduce antitumor efficacy must be identified
• Limitations the authors state:
  • Immunodeficient mouse models were used, so a complete tumor immune microenvironment and immunosuppressive mechanisms were not represented
  • Only one CAR target (MSLN) was studied, so kinetics may not apply to other antigen targets
  • The luciferase reporter used is not translatable to humans, and a single reporter cannot quantify tumor and T cells at the same time
  • Repeat imaging compromised CAR T-cell efficacy, so efficacy and T-cell kinetics had to be studied in separate experiments
  • The reporters tested are limited to preclinical use

Topics

Medical terms in this study, explained in our Lexicon: Biopsy, Pleural Mesothelioma, Non-Small Cell Lung Cancer.

Related studies

• Mesothelin-Targeted CARs: Driving T Cells to Solid Tumors — A. Morello, M. Sadelain, et al. (2016)
• Mesothelin-specific chimeric antigen receptor mRNA-engineered T cells induce anti-tumor activity in solid malignancies — G.L. Beatty, A.R. Haas, et al. (2014)
• Assessing Tumor-Infiltrating Lymphocytes in Solid Tumors: A Practical Review for Pathologists and Proposal for a Standardized Method from the International Immuno-Oncology Biomarkers Working Group: Part 2: TILs in Melanoma, Gastrointestinal Tract Carcinomas, Non-Small Cell Lung Carcinoma and Mesothelioma, Endometrial and Ovarian Carcinomas, Squamous Cell Carcinoma of the Head and Neck, Genitourinary Carcinomas, and Primary Brain Tumors — S. Hendry, R. Salgado, et al. (2017)
• Mesothelin-targeted CAR-T cell therapy for solid tumors — A. Klampatsa, V. Dimou, et al. (2021)
• Targeting the effector site with IFN-alphabeta-inducing TLR ligands reactivates tumor-resident CD8 T cell responses to eradicate established solid tumors — A.J. Currie, R.G. van der Most, et al. (2008)
• Development of Highly Effective Anti-Mesothelin hYP218 Chimeric Antigen Receptor T Cells With Increased Tumor Infiltration and Persistence for Treating Solid Tumors — S. Tomar, J. Zhang, et al. (2022)

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