Engineering high-affinity PD-1 variants for optimized immunotherapy and immuno-PET imaging.

Area of Science:

• Immunology
• Oncology
• Biotechnology

Background:

• Immune checkpoint protein programmed cell death protein-1 (PD-1) signaling promotes tumor growth by suppressing anti-tumor immune responses.
• Monoclonal antibodies targeting the PD-1/programmed cell death ligand-1 (PD-L1) axis are effective cancer treatments but have limitations like poor tumor penetration and T-cell depletion.

Purpose of the Study:

• To engineer a high-affinity, non-antibody PD-1 antagonist for improved cancer immunotherapy.
• To evaluate the therapeutic efficacy and pharmacokinetic properties of the engineered PD-1 antagonist compared to anti-PD-L1 antibodies.
• To assess the potential of the engineered PD-1 as a PET imaging tracer for PD-L1-positive tumors.

Main Methods:

• Directed evolution using yeast-surface display to engineer the PD-1 ectodomain.
• In vitro and in vivo evaluation of high-affinity PD-1 antagonist in CT26 tumor models.
• Radiolabeling of high-affinity PD-1 for PET imaging studies in mice.

Main Results:

• Engineered PD-1 achieved high-affinity (110 pM) competitive antagonism of PD-L1.
• High-affinity PD-1 demonstrated superior tumor penetration and did not deplete peripheral T cells, unlike anti-PD-L1 antibodies.
• High-affinity PD-1 effectively treated both small and large tumors, whereas anti-PD-L1 antibodies were ineffective against large tumors.
• Radiolabeled high-affinity PD-1 successfully distinguished PD-L1-positive from PD-L1-negative tumors in vivo.

Conclusions:

• Small, non-antibody therapeutics targeting the PD-1/PD-L1 axis offer advantages over monoclonal antibodies for cancer immunotherapy.
• Engineered PD-1 exhibits favorable pharmacology, enhanced efficacy against larger tumors, and potential for non-invasive immune diagnostics.