# Protocol to study in vivo organ-specific migration of apoptotic splenocytes in mice with tumor and immune checkpoint inhibitor-induced colitis

## TL;DR

This paper provides a detailed protocol to track the migration of ECP-treated immune cells in mice with tumor and colitis, helping understand how these cells affect immune responses.

## Contribution

A novel protocol for tracing organ-specific migration of apoptotic splenocytes in tumor-bearing mice with ICI-induced colitis.

## Key findings

- ECP-treated splenocytes can be tracked in vivo using fluorescence imaging and tissue digestion.
- The protocol allows analysis of phagocytic uptake and tolerogenic polarization of phagocytes.
- The method enables investigation of immune cell migration into target organs and lamina propria.

## Abstract

Extracorporeal photopheresis (ECP) reduces immune checkpoint inhibitor (ICI)-induced colitis without affecting anti-tumor immunity. Here, we provide a protocol to trace ECP-treated cells in vivo after transfer into tumor-bearing mice with ICI-induced colitis. We detail tumor and colitis induction, ICI therapy, and the labeling of ECP-treated splenocytes to trace their migration into target organs. Fluorescence imaging and tissue digestion enable the analysis of phagocytic uptake and the analysis of tolerogenic polarization of phagocytes based on congenic markers of donor and recipient mice.

For complete details on the use and execution of this protocol, please refer to Braun et al.1

•Study in vivo migration of fluorescently labeled cells into different target organs•Instructions for investigating phagocytic uptake of cells in vivo•Guidance on inducing cell death with extracorporeal photopheresis•Procedures for isolating immune cells from lamina propria and tumor tissue

Study in vivo migration of fluorescently labeled cells into different target organs

Instructions for investigating phagocytic uptake of cells in vivo

Guidance on inducing cell death with extracorporeal photopheresis

Procedures for isolating immune cells from lamina propria and tumor tissue

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Extracorporeal photopheresis (ECP) reduces immune checkpoint inhibitor (ICI)-induced colitis without affecting anti-tumor immunity. Here, we provide a protocol to trace ECP-treated cells in vivo after transfer into tumor-bearing mice with ICI-induced colitis. We detail tumor and colitis induction, ICI therapy, and the labeling of ECP-treated splenocytes to trace their migration into target organs. Fluorescence imaging and tissue digestion enable the analysis of phagocytic uptake and the analysis of tolerogenic polarization of phagocytes based on congenic markers of donor and recipient mice.