A radiolabeled VISTA antibody for imaging VISTA expression

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Burvenich et al. Targeting of immune checkpoint regulator V-domain Ig suppressor of T-cell activation (VISTA) with ⁸⁹Zr-labelled CI-8993, European Journal of Nuclear Medicine and Molecular Imaging, 2024

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Radiolabeling (zirconium-89) of an anti-VISTA monoclonal antibody that was tested in clinical trials (CI-8993) was performed to analyze the biodistribution of the therapeutic antibody and of VISTA-expressing cells, and to help understand the patient’s response to treatment. In vivo imaging of the distribution of [⁸⁹Zr]-CI-8993 and hVISTA was performed thanks to the development of the humanized VISTA mouse model by genOway.

Combining antibodies and PET imaging for cancer therapy and monitoring

Positron emission tomography (PET) scanning is a powerful, non-invasive technique to analyze the progression of cancers and their response to therapy, and has become a popular tool to validate the specificity of new therapies or examine the distribution and dynamics of biomarkers¹. Consequently, numerous researchers are now developing new radiolabeled antibodies that can be tracked by PET imaging. The immune checkpoint VISTA (V-domain immunoglobulin suppressor of T-cell activation) has been reported to be highly expressed on tumor-infiltrating myeloid cells, and to have a role in tumor evasion², making it a promising target for immune checkpoint inhibitor (ICI) therapies. Furthermore, recent anti-VISTA antibodies have been developed, showing promising outcomes and moving to clinical trials^3–5.

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[⁸⁹Zr]-CI-8993 can be used to tracking VISTA-expressing cells

In order to study the biodistribution and pharmacokinetics of the CI-8993 antibody, which was tested in clinical trials, Burvenich and colleagues radiolabeled the antibody and observed that this did not affect the binding of CI-8993 to VISTA⁶. In vivo validation of the construct was performed using a humanized VISTA (hVISTA) model developed by genOway. This model displays a physiological expression of hVISTA on immune cells, and allows for the binding of the human-specific CI-8993 while maintaining the intracellular function of VISTA in mouse cells. PET and magnetic resonance imaging revealed a high [⁸⁹Zr]-CI-8993 uptake in organs containing myeloid cells, such as the spleen, as well as the accumulation of [⁸⁹Zr]-CI-8993 in the MC38 tumor (see figure below), validating this construct as a useful tool to trace VISTA-expressing cells. Although MC38 tumors do not express VISTA, they are highly immunogenic and therefore elicit an immune response. Importantly, hVISTA expression was confirmed by FACS in tumor-infiltrating lymphocytes, the spleen, and on myeloid cells. This validates the hVISTA mouse model as both a valuable tool for syngeneic studies and to analyze the biodistribution of hVISTA-expressing cells, as well as the specificity of the [⁸⁹Zr]-CI-8993 construct.

To validate the construct in the context of a VISTA-expressing human tumor, the authors used an immunodeficient mouse strain implanted with a Capan-2 tumor. Once more, PET imaging revealed a specific uptake in the spleen and in the tumor of these mice, further confirming the specificity of the antibody.

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Radiolabeled monoclonal antibodies have a wide range of useful applications

This study shows that the radiolabeled CI-8993 is suitable for targeting and imaging VISTA expression, which could help to monitor patients receiving therapy, as well as screen patients eligible for ICI treatment, based on the presence or absence of VISTA-expressing cells in the tumor microenvironment. The combination of radiolabeling the construct with the use of PET imaging also allowed the precisely monitoring of the accumulation of the anti-VISTA antibody in the tumors, confirming the effectiveness of this anti-cancer therapy. Additionally, this study shows that the humanized VISTA mouse model has a wide range of applications, from PK and biodistribution to enabling the development of new tools and biomarkers, and preclinical eval of hVISTA therapies^3,7,8.

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Figure 2 in the paper: PET/MRI imaging of [ ⁸⁹Zr]Zr-Df-CI-8993 in MB49-tumor-bearing hVISTA Knock-in mice. B) From left to right, each panel shows a representative whole body MR image (MRI, surface rendered), a maximum intensity projection PET image, and a fused PET/MRI images of MB49 tumor-bearing hVISTA Knock-in mice or control C57BL/6 mice on day 3 post-injection. Mice were injected with 1 mg/kg [⁸⁹Zr]Zr-Df-CI-8993, 1 mg/kg [89Zr]Zr-Df-CI-8993 with 30 mg/kg unlabeled CI-8993, or [⁸⁹Zr]Zr-Df-IgG1 control. Adapted from Burvenich et al., 2024⁶.

A hVISTA mouse model is available off the shelf at genOway, designer and provider of multiple preclinical models in several research areas, including immuno-oncology, metabolism, cardiovascular diseases and neuroscience.

References

1. Bai, J.-W., Qiu, S.-Q. & Zhang, G.-J. Molecular and functional imaging in cancer-targeted therapy: current applications and future directions. Signal Transduct. Target. Ther. 8, 89 (2023).
2. Le Mercier, I. et al. VISTA Regulates the Development of Protective Antitumor Immunity. Cancer Res. 74, 1933–1944 (2014).
3. Thisted, T. et al. VISTA checkpoint inhibition by pH-selective antibody SNS-101 with optimized safety and pharmacokinetic profiles enhances PD-1 response. Nat. Commun. 15, 2917 (2024).
4. Scott, F. et al. 324 Preclinical evaluation of anti-VISTA antibody CI-8993 in a syngeneic huVISTA-KI model. J. Immunother. Cancer 9, A349 (2021).
5. Noelle, R. J. et al. Clinical and research updates on the VISTA immune checkpoint: immuno-oncology themes and highlights. Front. Oncol. 13, 1225081 (2023).
6. Burvenich, I. J. G. et al. Targeting of immune checkpoint regulator V-domain Ig suppressor of T-cell activation (VISTA) with 89Zr-labelled CI-8993. Eur. J. Nucl. Med. Mol. Imaging (2024) doi:10.1007/s00259-024-06854-z.
7. Iadonato, S. et al. A highly potent anti-VISTA antibody KVA12123 - a new immune checkpoint inhibitor and a promising therapy against poorly immunogenic tumors. Front. Immunol. 14, 1311658 (2023).
8. Johnston, R. J. et al. VISTA is an acidic pH-selective ligand for PSGL-1. Nature 574, 565–570 (2019).