A DNA telomerase vaccine for canine cancer immunotherapy.

Telomerase reverse transcriptase (TERT) is highly expressed in more than 90% of canine cancer cells and low to absent in normal cells. Given that immune tolerance to telomerase is easily broken both naturally and experimentally, telomerase is an attractive tumor associated antigen for cancer immunotherapy. Indeed, therapeutic trials using human telomerase peptides have been performed. We have developed an immunogenic yet catalytically inactive human telomerase DNA construct that is in clinical trials with patients presenting solid tumors. Paralleling this human construct, we have developed a canine telomerase DNA vaccine, called pDUV5. When administered intradermally to mice combined with electrogene transfer, pDUV5 induced canine TERT specific cytotoxic T-cells as measured by IFN-γ ELISpot assay. Intradermal vaccination of healthy dogs with 400 µg of pDUV5 generated strong, broad and long lasting TERT specific cellular immune responses. In vitro immunization with cTERT peptides revealed the maintenance of cTERT specific T-cells in PBMCs from tumor bearing dogs showing that this repertoire was not depleted. This study highlights the potential of pDUV5 as a cancer vaccine and supports its evaluation for the treatment of spontaneous canine tumors.

Strong antigen-specific T-cell immunity induced by a recombinant human TERT measles virus vaccine and amplified by a DNA/viral vector prime boost in IFNAR/CD46 mice.

Cancer immunotherapy is seeing an increasing focus on vaccination with tumor-associated antigens (TAAs). Human telomerase (hTERT) is a TAA expressed by most tumors to overcome telomere shortening. Tolerance to hTERT can be easily broken both naturally and experimentally and hTERT DNA vaccine candidates have been introduced in clinical trials. DNA prime/boost strategies have been widely developed to immunize efficiently against infectious diseases. We explored the use of a recombinant measles virus (MV) hTERT vector to boost DNA priming as recombinant live attenuated measles virus has an impressive safety and efficacy record. Here, we show that a MV-TERT vector can rapidly and strongly boost DNA hTERT priming in MV susceptible IFNAR/CD46 mouse models. The cellular immune responses were Th1 polarized. No humoral responses were elicited. The 4 kb hTERT transgene did not impact MV replication or induction of cell-mediated responses. These findings validate the MV-TERT vector to boost cell-mediated responses following DNA priming in humans.

Anticancer DNA vaccine based on human telomerase reverse transcriptase generates a strong and specific T cell immune response.

Human telomerase reverse transcriptase (hTERT) is overexpressed in more than 85% of human cancers regardless of their cellular origin. As immunological tolerance to hTERT can be overcome not only spontaneously but also by vaccination, it represents a relevant universal tumor associated antigen (TAA). Indeed, hTERT specific cytotoxic T lymphocyte (CTL) precursors are present within the peripheral T-cell repertoire. Consequently, hTERT vaccine represents an attractive candidate for antitumor immunotherapy. Here, an optimized DNA plasmid encoding an inactivated form of hTERT, named INVAC-1, was designed in order to trigger cellular immunity against tumors. Intradermal injection of INVAC-1 followed by electrogene transfer (EGT) in a variety of mouse models elicited broad hTERT specific cellular immune responses including high CD4+ Th1 effector and memory CD8+ T­cells. Furthermore, therapeutic INVAC­1 immunization in a HLA-A2 spontaneous and aggressive mouse sarcoma model slows tumor growth and increases survival rate of 50% of tumor-bearing mice. These results emphasize that INVAC-1 based immunotherapy represents a relevant cancer vaccine candidate.

Long-term maintenance of skin immune system in a NOD-Scid IL2rγ(null) mouse model transplanted with human skin.

We developed a NOD-Scid IL2rγ(null) mouse model transplanted with human skin that brings fundamental insight on in vivo cellular mechanisms of intradermal immunization and antigen presentation by dermal dendritic and epidermal Langerhans cells for skin T-cell immunity. Indeed, T-cell immunity is a crucial checkpoint for the induction of in vivo rapid control of skin infection. With the long-term preservation of a complete human skin immune system, this model offers the unique opportunity not only to better understand mechanisms of skin immune response but also to test new compounds and devices for cutaneous routes of vaccination, as well as new therapeutics approach for skin diseases, allergies or infections.

Antigen stored in dendritic cells after macropinocytosis is released unprocessed from late endosomes to target B cells.

B lymphocytes can be triggered in lymph nodes by nonopsonized antigens (Ag), potentially in their native form. However, the mechanisms that promote encounter of B lymphocytes with unprocessed antigens in lymph nodes are still elusive. We show here that antigens are detected in B cells in the draining lymph nodes of mice injected with live, but not fixed, dendritic cells (DCs) loaded with antigens. This highlights active processes in DCs to promote Ag transfer to B lymphocytes. In addition, antigen-loaded DCs found in the draining lymph node were CD103+. Using 3 different model Ag, we then show that immature DCs efficiently take up Ag by macropinocytosis and store the internalized material in late endocytic compartments. We find that DCs have a unique ability to release antigens from these compartments in the extracellular medium, which is controlled by Rab27. B cells take up the regurgitated Ag and the chemokine CXCL13, essential to attract B cells in lymph nodes, enhances this transfer. Our results reveal a unique property of DCs to regurgitate unprocessed Ag that could play an important role in B-cell activation.