{
  "abstract": "Background Pancreatic ductal adenocarcinoma (PDAC) is one of the most difficult-to-treat cancers. This therapeutic challenge is primarily driven by an immunosuppressive tumor microenvironment characterized by a dense stroma that limits T-cell infiltration and impairs anti-tumor T-cell activities. For example, mesothelin-targeted chimeric antigen receptor (MSLN-CAR) T cells demonstrated minimal efficacy in PDAC patients in early clinical trials, with stable disease being the best outcome observed. We recently showed that a tailored synthetic vaccine can specifically stimulate adoptively transferred tumor-targeting chimeric antigen receptor (CAR) T cells in vivo in the lymph node microenvironment, markedly enhancing CAR T cell fitness, tumor infiltration, and anti-tumor activity. 1–3 We hypothesize that a vaccine boost could reprogram MSLN-CAR T cells to enhance their infiltration and cytotoxicity against immunologically cold PDAC tumors, thereby achieving superior tumor control.Methods We employed a syngeneic mouse PDAC model and a murine MSLN-CAR. To enable synthetic vaccine boosting of MSLN-CAR T, we incorporated a FITC-targeting CAR into MSLN-CAR T as a vaccine receptor and boosted (FITC)MSLN-tandem CAR T using our synthetic FITC vaccine (e.g., amphiphile FITC, amph-FITC). As a control, we used amph-FITC vaccine to boost FITC-CAR T cells and CAR T cells without vaccine boosting.Results (FITC)MSLN-tandem CAR T potently regressed PDAC tumors when boosted with a single dose of amph-FITC vaccine. Unexpectedly, mice receiving tumor-ignorant FITC-CAR T cells and amph-FITC vaccine also exhibited a pronounced and immediate PDAC tumor control, with >70% reduction of tumor volume in the first 24 hours which lasts >7 days. This marked CAR antigen-independent early tumor control is completely lost in Rag1-knockout (no endogenous T cells) and BatF3-knockout (no antigen cross-presentation) recipient mice. Amph-FITC vaccine boosting through the FTIC-CAR induced rapid but non-toxic cytokine and chemokine release, including IFNγ, TNFα, IL-6, and CCL2. Notably, IFNγ blockade completely abolished this CAR antigen-independent early tumor control.Conclusions The potent early regression of PDAC tumors is independent of the target antigen specificity of the CAR but dependent on the CAR-specific vaccine boost, suggesting a previously unappreciated early anti-tumor bystander effect associated with vaccine boosting of CAR T cells. And this bystander effect is critically dependent on IFNγ and the pre-existing endogenous anti-tumor T cells. Therefore, synthetic vaccine boosting of tumor-agnostic CAR T cells likely offers a novel therapeutic strategy that can be used independently or in combination with other therapeutic modalities for treating PDAC tumors.Acknowledgements The current work is supported by IDF at Children’s Hospital of Philadelphia.References Ma L, Dichwalkar T, Chang JYH, Cossette B, Garafola D, Zhang AQ, Fichter M, Wang C, Liang S, Silva M, Kumari S, Mehta NK, Abraham W, Thai N, Li N, Wittrup KD, Irvine DJ. Enhanced CAR-T cell activity against solid tumors by vaccine boosting through the chimeric receptor. Science. 2019 Jul 12;365(6449):162-168. doi: 10.1126/science.aav8692. PMID: 31296767; PMCID: PMC6800571.Ma L, Hostetler A, Morgan DM, Maiorino L, Sulkaj I, Whittaker CA, Neeser A, Pires IS, Yousefpour P, Gregory J, Qureshi K, Dye J, Abraham W, Suh H, Li N, Love JC, Irvine DJ. Vaccine-boosted CAR T crosstalk with host immunity to reject tumors with antigen heterogeneity. Cell. 2023 Jul 20;186(15):3148–3165.e20. doi: 10.1016/j.cell.2023.06.002. Epub 2023 Jul 5. PMID: 37413990; PMCID: PMC10372881.Grzywa T, Mehta N, Cossette B, Romanov A, Paruzzo L, Ramasubramanian R, Cozzone A, Morgan D, Sukaj I, Bergaggio E, Tannir R, Kadauke S, Myers R, Yousefpour P, Ghilardi G, Schuster S, Neeser A, Frey N, Goncalves B, Zhang L, Abraham W, Suh H, Ruella M, Grupp S, Chiarle R, Wittrup KD, Ma L, Irvine DJ. Directed evolution-based discovery of ligands for in vivo restimulation of CAR-T cells. bioRxiv [Preprint]. 2024 Oct 1:2024.04.16.589780. doi: 10.1101/2024.04.16.589780. PMID: 38659938; PMCID: PMC11042270.",
  "authors": [
    {
      "affiliations": [
        "Children’s Hospital of Philadelphia, Philadelphia, PA, USA",
        "University of Pennsylvania, Philadelphila, PA, USA"
      ],
      "name": "Leyuan Ma"
    },
    {
      "affiliations": [
        "Children’s Hospital of Philadelphia, Philadelphia, PA, USA"
      ],
      "name": "Tomasz M Grzywa"
    }
  ],
  "title": "1015 Early bystander effect of vaccine boosting of CAR T cells reinvigorates endogenous anti-tumor T cell immunity to regress pancreatic cancer",
  "uid": "2ad7babd-5045-5647-aac9-f937f5d55870"
}