{
  "abstract": "Background Programmed death-ligand 1 (PD-L1) is an immune checkpoint antigen that limits T-cell activation and contributes to immunosuppression. Preferentially expressed Antigen in Melanoma (PRAME) is a cancer-testis antigen that plays important roles in carcinogenesis. The tumor growth inhibition effect of a dual-antigen cancer vaccine (PD-PR) co-targeting PD-L1 and PRAME against hepatocellular carcinoma and melanoma have been demonstrated by our group. It is believed that protein fusion with built-in adjuvants may improve vaccine efficacy. In the present study, built-in adjuvants with different immunogenic mechanisms were utilized to optimize the PD-PR design and the vaccine efficacy was studied in terms of immune response induction, tumor growth inhibition, and protection against tumor rechallenge.Methods Two novel protein vaccines (TAT-PD-PR and DTT-PD-PR) with transactivator of transcription peptide (TAT) or diphtheria toxin T domain (DTT) fused to the N-terminus of PD-PR were synthesized. The protein vaccines (30 microgram/dose) were formulated with CpG oligodeoxynucleotide (30 microgram/dose) and Alhydrogel (300 microgram/dose) for subcutaneous vaccination four times before serum and splenocyte collection for ELISA antibody response study and ELISpot T-cell response study, respectively. To study tumor growth inhibition, C57BL/6 mice (n=10/group) were vaccinated twice before PRAME-positive lung cancer cell implantation, followed by two booster doses. At the end of the tumor growth study, some tumor-free mice (n = 2/group) were kept for three months to monitor recurrence and then subjected to tumor rechallenge. Immune responses were also assessed in the tumor growth inhibition study and the tumor rechallenge study.Results Vaccination with PD-PR and TAT-PD-PR showed more than 95% tumor growth inhibition compared to the control group ( p<0.01) and 90% of mice were tumor-free at the end of the study. Vaccination with DTT-PD-PR also exhibited 85% tumor growth inhibition (p<0.01) with 70% tumor-free mice. There was no recurrence in the tumor-free mice and the cancer vaccines were sufficient to protect the mice against tumor rechallenge. Regarding the immune enhancement effect by built-in adjuvant fusion, immune response study revealed that fusion of TAT to PD-PR significantly enhanced the T-cell response against PD-L1 (p < 0.05) and PRAME (p<0.01) and the highest anti-PDL1 antibody response was also found in the TAT-PD-PR group, while there was no significant immune response improvement by DTT fusion.Conclusions The results of this preclinical study further support the potential of co-targeting PD-L1 and PRAME by vaccination in cancer immunotherapy and reveal a novel optimized cancer vaccine design (TAT-PD-PR) for future development.Ethics Approval This study was approved by the Animal Committee of the Southern Model IACUC; approval number 2022-0049.",
  "authors": [
    {
      "affiliations": [
        "CK Life Sciences Limited, Hong Kong, Hong Kong"
      ],
      "name": "Kin-Tak Chan"
    },
    {
      "affiliations": [
        "CK Life Sciences Limited, Hong Kong, Hong Kong"
      ],
      "name": "Tristan Zhang"
    },
    {
      "affiliations": [
        "CK Life Sciences Limited, Hong Kong, Hong Kong"
      ],
      "name": "Melvin Toh"
    }
  ],
  "title": "1157 Novel cancer vaccines co-targeting PD-L1 and PRAME induce antigen-specific immune responses and inhibit tumor growth in a syngeneic mouse lung cancer model",
  "uid": "9e429471-70db-566a-9568-ae557c7c49a6"
}