An Endogenous Retrovirus Vaccine Encoding an Envelope with a Mutated Immunosuppressive Domain in Combination with Anti-PD1 Treatment Eradicates Established Tumours in Mice

Abstract

Endogenous retroviruses (ERVs) account for 8% of our genome, and, although they are usually silent in healthy tissues, they become reactivated and expressed in pathological conditions such as cancer. Several studies support a functional role of ERVs in tumour development and progression, specifically through their envelope (Env) protein, which contains a region described as an immunosuppressive domain (ISD). We have previously shown that targeting of the murine ERV (MelARV) Env using virus-like vaccine (VLV) technology, consisting of an adenoviral vector encoding virus-like particles (VLPs), induces protection against small tumours in mice. Here, we investigate the potency and efficacy of a novel MelARV VLV with a mutated ISD (ISDmut) that can modify the properties of the adenoviral vaccine-encoded Env protein. We show that the modification of the vaccine’s ISD significantly enhanced T-cell immunogenicity in both prime and prime-boost vaccination regimens. The modified VLV in combination with an α-PD1 checkpoint inhibitor (CPI) exhibited excellent curative efficacy against large established colorectal CT26 tumours in mice. Furthermore, only ISDmut-vaccinated mice that survived CT26 challenge were additionally protected against rechallenge with a triple-negative breast cancer cell line (4T1), showing that our modified VLV provides cross-protection against different tumour types expressing ERV-derived antigens. We envision that translating these findings and technology into human ERVs (HERVs) could provide new treatment opportunities for cancer patients with unmet medical needs.

The Insertion of an Evolutionary Lost Four-Amino-Acid Cytoplasmic Tail Peptide into a Syncytin-1 Vaccine Increases T- and B-Cell Responses in Mice

“…Previously, we observed the association of vaccine immunogenicity with differences in the expression of activation markers on the surfaces of matured murine bone marrow-derived dendritic cells (BMDCs) [ 18 , 25 ]. In this study, we measured the surface expression of Syncytin-1 (from here on HERV-W Env) 24 h after transduction with either HERV-W WT or HERV-W LQMV and compared it to a lack of transduction (Neg.…”

“…Still, we could break the immunological tolerance to MelARV through the use of viral vectors [ 39 ]. Additionally, via the delivery of a vaccine with immunogenic replication-deficient adenoviral vectors in a prime-boost regimen, in combination with relief of the immunosuppressive activity of the intrinsic Env immunosuppressive domain (ISD) via two point-mutations, we achieved considerably stronger T-cell responses of up to 10% of the CD8 + T-cells [ 25 ]. These data illustrate that gradually augmenting immunogenicity by improving the delivery vehicle and antigen used allows for an intrinsically tolerant antigen to induce responses of the magnitudes that are typically associated with live viral infections.…”

“…These data illustrate that gradually augmenting immunogenicity by improving the delivery vehicle and antigen used allows for an intrinsically tolerant antigen to induce responses of the magnitudes that are typically associated with live viral infections. Furthermore, the MelARV study showed that the adenovirus-vectored vaccine encoding the MelARV Gag and the mutated Env, in combination with the immune checkpoint inhibitor, anti-PD-1 antibody, could eradicate established colorectal tumours in mice [ 25 ].…”

“…The hAd19a/64 vaccines were produced by Sirion Biotech, following the procedure described in [ 25 ]. In brief, after the cloning of the HERV-W antigens into the hAd19a/64 backbone in BAC cells, the DNA was purified, linearized, and then transfected into a modified HEK293 production cell line.…”

“…Following 24 h of incubation, the cells were fixed with 2% glutaraldehyde in a 0.05 M sodium phosphate buffer (pH 7.2). As a control, T24 cells were transfected with a plasmid encoding a copGFP sequence and incubated for 48 h. TEM was performed by the Core Facility for Integrated Microscopy at the University of Copenhagen (see detailed description in [ 18 , 25 ]).…”