Cancer Research in Switzerland - Krebsliga Schweiz

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Renner Christoph | Selective inhibition of intratumoral
regulatory T cells by antibody-GITR ligand fusion
proteins (OCS 02119­08­2007)
Cancer patients possess tumour­reactive T cells, but these
are suppressed by naturally occurring regulatory T cells
(Treg cells). Activation or support of these tumour­reactive
T cells is therefore a major objective in cancer immunotherapy.
Stimulation of glucocorticoid­induced tumour
necrosis factor­related receptor (GITR) represents a promising
approach, since this receptor is expressed on both
CD4 + and CD8 + effector T cells as well as on CD4 + 25 +
Treg cells.
Triggering of murine GITR with its natural ligand (GITRL) or
anti­GITR agonistic antibodies enhances T cell responses,
inhibits Treg mediated suppression and thereby induces
tumour immunity in a variety of murine tumour models.
However, systemic administration of costimulatory agents
can lead to global T cell activation and autoimmunity.
Therefore, we proposed to specifically manipulate the
T cell compartment in the tumour microenvironment by
using a bispecific fusion protein combining mGITRL and a
single chain antibody that targets fibroblast activation
protein (FAP). Accumulation of antiFAP­mGITRL in the
tumour microenvironment can be mediated through binding
to FAP, which is specifically expressed on sarcomas
and on cancer­associated fibroblasts (CAFs) found in the
stroma of epithelial cancers.
The antiFAP­mGITRL fusion protein generated in this
study formed dimers and bound to murine GITR with
an affinity of 1.2 μM and to murine FAP with an affinity
of 4.5 nM. In vitro cell assays with murine splenocytes
showed that our antiFAP­mGITRL fusion protein can stimulate
CD8 + and CD4 + effector T cells, as shown by their
increased proliferation and production of IFN­g and IL­2.
This costimulatory effect was enhanced when the fusion
protein was presented by a FAP­positive cell line mimicking
FAP + CAFs or FAP + tumours. Presumably, the membrane­bound
antiFAP­mGITRL allows for cross­linking of
multiple GITR molecules on T cells, thus leading to increased
signalling and enhanced costimulation. In vitro,
Treg cells inhibit the expansion and function of CD8 +
T cells. Addition of our antiFAP­mGITRL to the Treg: CD8 +
T cell coculture could restore proliferation and IFN­g production
of CD8 + T cells. Furthermore, cell membranebound
antiFAP­mGITRL was 100­fold more effective in
overcoming Treg­mediated suppression compared to unbound
fusion protein.
To translate the in vitro results in a preclinical model, we
established syngeneic murine cancer models to either target
the tumour stroma or the tumour cells directly. Immunotherapeutic
antiFAP­mGITRL treatment of a colon carcinoma
provoked no delay in tumour growth due to weak
stroma formation. However, therapy of a FAP + osteosarcoma
led to enhanced survival of mice treated with anti­
FAP­mGITRL. The antibody­directed delivery of GITRL
opens a new path to positively act on the local T cell environment
in the tumour. Targeted delivery and thereby
enhanced immunomodulatory effects of antiFAP­mGITRL
represent a promising approach in antibody­based tumour
immunotherapy.
Project coordinator
Prof. Dr. Christoph Renner
Klinik und Poliklinik für Onkologie
Medizinbereich Innere Medizin–Onkologie
UniversitätsSpital Zürich
Rämistrasse 100
CH­8091 Zurich
Phone +41 (0)44 255 21 54
christoph.renner@usz.ch
Romero Pedro | Impact of lentiviral cancer vaccines on
the anti-tumour response in vivo (OCS 2011­02­2007)
The incidence of malignant melanoma continues to increase
in our country in people of all ages. Except for early
detection and surgical excision, the currently available
treatments fail to cure this disease. Thus, new effective
therapies for metastatic melanoma are urgently needed.
The development of cancer vaccines is a promising approach,
and recent results in this field are encouraging. To
optimize them, it is necessary not only to enhance their
ability to induce specific immunity but also to prove their
ability to control or even reject established tumours.
We have recently reported the development of recombinant
lentivectors carrying tumour specific antigens as vaccines.
Results with lentiviral immunization in mice demonstrate
their ability to induce strong and long­lived specific
T cell responses, even with a single injection. Typically, the
peak of specific T cell responses is attained during the
third week post immunization, and stable levels of immune
memory can be detected as long as six months later.
Importantly, this response is sufficient to protect from
melanoma tumour challenge, even when this is performed
six months after a single immunization. However, the key
quality expected from vaccination against cancer is its
ability to control established large tumours rather than to
confer a prophylactic protection. In this regard, we observed
that the therapeutic vaccination failed to exert any
detectable control of tumour growth. A detailed analysis
of this vaccine failure revealed that while effector CD8
T cells are able to home to the tumour sites, they are compromised
in their ability to function normally. Indeed, vaccine
induced T cells are inactivated by many immunosuppressive
factors active in the tumour microenvironment.
We identified the selective overexpression on specific
T cells of the inhibitory receptor PD­1 as one of the pathways
leading to T cell dysfunction. We therefore tested
combination therapies, whereby vaccination was either
preceded by chemotherapy (single injection of cyclophosphamide)
or followed by administration of antibodies
blocking both PD­1 and its main ligand PD­L1. In both
cases we clearly observed a stronger effect on retardation
of tumour growth and increase of mouse survival. These
results indicate that the combination therapies can synergize
in affording protection.