Poster Presentation 36th Lorne Cancer Conference 2024

Aptamer-Based Targeting of PD-L1-Positive sEVs: Enhancing Therapeutic Strategies for Immune Cell Tolerance (#139)

Satendra Jaysawal 1 2 , Rocky Chowdhury 1 2 , Rajindra Napit 1 2 , Jasmine Catague 1 2 , Haben Melke 1 2 , Cuong Pham 3 , Lingxue Kong 4 , Wei Duan 1 2
  1. School of Medicine, Deakin University , Geelong, VIC, Australia
  2. Institute of Mental and Physical Health and Clinical Translation (IMPACT), Deakin University , Geelong, VIC, Australia
  3. Molecular Imaging and Theransotics Laboratory, Baker Heart and Diabetes, Melbourne, VIC, Australia
  4. Institute for Frontier Materials, Deakin University, Geelong, VIC, Australia

PD-L1, also known as Programmed Death Ligand-1, is a protein that plays a crucial role in immune cell tolerance. It acts as an immune checkpoint ligand for the co-inhibitory receptor Programmed cell death protein 1 (PD-1), which is found on T-cells. However, when PD-L1 binds to PD-1, it inhibits the growth and proliferation of T-cells, ultimately promoting the growth of tumor cells. As a therapeutic approach, multiple anti-PD-L1 antibodies have been used to target the PD-L1 protein, thereby reducing immune cell tolerance. Notably, these tumor cells produce small extracellular vesicles (sEVs) that express PD-L1 on their surface, which further masks the anti-PD-L1 antibodies, leading to a reduction in their effectiveness. Therefore, a quantitative detection system is necessary to identify and capture PD-L1-positive sEVs. The primary objective of this project is to create an aptamer that specifically targets PD-L1-positive sEVs.

In this study, candidate aptamers obtained from SELEX were screened against recombinant PD-L1 protein. The most promising aptamers that bound to the recombinant PD-L1 protein were selected and characterized using ELASA and flow cytometry.

Through SELEX, twenty-nine candidate aptamers were obtained. Aptamers PD-L1-24-apt and PD-L1-29-apt showed promising binding to the recombinant PD-L1 protein. Using ELASA, the affinities of PD-L1-24-apt and PD-L1-29-apt were determined to be 310 nM and 286 nM against 90 nM of recombinant PD-L1 protein, respectively. Moreover, these aptamers have shown substantial selective binding to the native structure of PD-L1 protein anchored on the cell surface.

These aptamers will undergo further engineering and development to enhance their binding affinity and specificity. The final selected aptamers should exhibit a rapid on-rate and a slow off-rate, enabling the establishment of an aptamer-based capture system for PD-L1 positive sEVs through liquid biopsy. However, additional verification is needed to confirm the efficacy of these aptamers.

  1. Chen, Gang, et al. "Exosomal PD-L1 contributes to immunosuppression and is associated with anti-PD-1 response." Nature 560.7718 (2018): 382-386.‚Äč
  2. Ye, Lingxiao, et al. "The Importance of Exosomal PD-L1 in Cancer Progression and Its Potential as a Therapeutic Target." Cells 10.11 (2021): 3247.
  3. Alba-Bernal, Alfonso, et al. "Challenges and achievements of liquid biopsy technologies employed in early breast cancer." EBioMedicine 62 (2020): 103100.