Abstract A008: Photochemical internalization: Light-induced enhancement of MHC Class I antigen presentation, giving strong enhancement of cytotoxic T-cell responses to vaccination

For cancer vaccination and immunotherapy it is essential to stimulate cytotoxic T-cells (CTLs) to recognize and kill the tumor cells. Priming of CTLs is generally mediated through MHC Class I antigen presentation by antigen presenting cells (APCs). Since the MHC class I presentation machinery is localised in the cytosol, MHC class I presentation typically requires cytosolic delivery of the antigen. Unfortunately, this is often difficult to achieve with exogenously added peptide or protein antigens, since such antigens are primarily taken up into endocytic vesicles, and then “by default” are routed for MHC Class II presentation. Photochemical internalisation (PCI) is a technology that can help solving this problem by inducing an illumination-mediated permeabilisation of the membranes of endocytic vesicles, thereby releasing endocytosed antigens into the cytosol. This is achieved by employing a photosensitising molecule that is designed to localise specifically in endocytic membranes. Upon illumination, the photosensitiser induces photochemical reactions that make the membranes leaky, thereby releasing endocytosed molecules into the cytosol. In vitro it has been shown that the use of PCI leads to strongly increases MHC Class I presentation APCs. In vivo PCI-mediated vaccination is performed by injecting a mixture of vaccine and photosensitiser intradermally, followed by illumination of the injection site; and with this regimen, PCI substantially enhances immune responses to various types of polypeptide- based antigens. Thus, with short peptide antigens enhancement of CD8+ T-cell responses of up to 100 times have been observed when PCI is used in combination with the poly(IC) adjuvant; with a strong synergy between PCI and the adjuvant. With an HPV long peptide and with several protein antigens in addition to the CD8+ T-cell response a significant stimulation of CD4+ T-cell responses can also be observed, and in some cases also an increase in antibody production. In vivo studies with therapeutic peptide antigen vaccination in a mouse model for HPV-induced cancer show that the use of PCI strongly enhances anti-tumor responses to the vaccine, both when the vaccination is performed intradermally and when intratumoral administration is employed. The TPCS 2a photosensitiser used in PCI is cheap to produce, withstands autoclavation and is stable for several years at ambient temperatures. TPCS 2a is currently in clinical development for enhancement of the effect of cytotoxic anti-cancer drugs, and it has been shown that TPCS 2a can be administered safely to patients in much higher doses than what is needed for the use in immunotherapy. In conclusion, PCI has a completely new mechanism of action as a vaccination enhancement technology, representing a new and potent tool for stimulation of CTL and in some cases also other types of immune responses. Preparations for a clinical study with PCI-mediated vaccination is on-going. Citation Format: Tone Otterhaug, Markus Haug, Gaute Brede, Monika Hakerud, Anne Grete Nedberg, Victoria Edwards, Pal Kristian Selbo, Pal Johansen, Oyvind Halaas, Anders Hogset. Photochemical internalization: Light-induced enhancement of MHC Class I antigen presentation, giving strong enhancement of cytotoxic T-cell responses to vaccination [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A008.