PD-1/PD-L1 Checkpoint Inhibitors Are Active in the Chicken Embryo Model and Show Antitumor Efficacy In Ovo

Area of Science:

• Immunology
• Oncology
• Drug Development

Background:

• Immuno-oncology (IO) drug development relies on effective in vivo models.
• Programmed cell death protein-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) inhibitors are crucial in cancer therapy.
• Alternative in vivo models are needed for efficient IO drug discovery.

Purpose of the Study:

• To evaluate the chicken embryo (in ovo) model as an alternative in vivo system for IO drug development.
• To assess the efficacy of PD-1/PD-L1 immune checkpoint inhibitors using this model.
• To investigate immune cell presence and function within the chicken embryo model.

Main Methods:

• Immunophenotyping of chicken peripheral blood mononuclear cells (PBMCs) and in ovo tumor-infiltrating lymphocytes using FACS and IHC.
• Verification of pembrolizumab cross-reactivity with chicken PD-1.
• In vitro cytotoxicity assays to assess PD-1/PD-L1 blockade effects.
• Chorioallantoic Membrane (CAM) assay to evaluate anti-tumor performance and immune cell infiltration in vivo.
• Testing of multiple PD-1/PD-L1 inhibitors (pembrolizumab, nivolumab, atezolizumab, avelumab).

Main Results:

• Presence of CD3+, CD4+, CD8+ T lymphocytes and monocytes confirmed in the chicken model.
• Pembrolizumab demonstrated cross-reactivity with chicken lymphocytes, restoring T-cell cytotoxicity against human lung cancer cells.
• In ovo, pembrolizumab inhibited tumor growth and increased immune cell infiltration.
• Other PD-1/PD-L1 inhibitors also showed tumor growth inhibition in the CAM assay.

Conclusions:

• The chicken embryo provides a physiologically relevant, immune-reactive in vivo environment for IO research.
• This model allows observation of anti-tumor immune responses and immune escape mechanisms.
• The chicken embryo model is a promising, fast, and reliable alternative for IO drug discovery.