of the Max - MDC

Molecular Immunology
and Gene Therapy
Thomas Blankenstein
M
ost of the current experimental cancer models do not reflect the pathophysiology of real-life
cancer. Cancer usually occurs sporadically and is clonal in origin. Between tumor initiation and
progression clinically unapparent pre-malignant cells may persist for years or decades in humans.
More recently, mouse models of sporadic cancer have been developed. The mouse germ-line can be
engineered with high precision so that defined genes can be switched on and off in the adult organism,
ideally in a locally and timely controlled fashion. However, analysis of the immune response
against sporadic tumors requires the knowledge of a tumor antigen.
The adaptive immune response to sporadic cancer
Ideally, a silent oncogene, for which the mice are not tolerant,
is stochastically activated in individual cells. This offers
the opportunity to analyze the adaptive immune response
throughout the long process of malignant transformation
and most closely resembles cancer in humans. In such a
model with the highly immunogenic SV40 large T as dormant
oncogene we showed, by generating a mouse model of
sporadic cancer based on rare spontaneous activation of a
dormant oncogene, that immunogenic tumors do not escape
their recognition but induce tolerance. In this model,
tumors derive from single cells and express a tumor-specific
transplantation rejection antigen. Whereas vaccinated mice
remain tumor-free throughout their lifetime, naive mice
develop a progressively growing tumor after a usually very
long lacency. We also showed that despite specific recognition
by T cells, the tumors do not lose their intrinsic
immunogenicity and are rejected after transplantation in T
cell-competent recipients. Furthermore, in the primary host
tumor-induced tolerance is associated with the expansion of
non-functional T cells. More recently, we discovered that
sporadic cancer is recognized by the adaptive immune system
at the pre-malignant stage, concomitant with the
induction of tumor antigen-specific tolerance. These results
demonstrated that even highly immunogenic sporadic
tumors are unable to induce functional cytotoxic T lymphocytes.
Based on this model we conclude that immunosurveillance
plays little or no role against sporadic cancer and that
tumors must not escape immune recognition or destruction.
Designer T cells by T cell receptor replacement
T cell receptor (TCR) gene transfer is a convenient method
to produce antigen-specific T cells for adoptive therapy.
However, the expression of two TCR in T cells could impair
their function or cause unwanted effects by mixed TCR heterodimers.
With five different TCR and four different T cells,
either mouse or human, we show that some TCR are strong –
in terms of cell surface expression – and replace weak TCR
on the cell surface resulting in exchange of antigen specificity.
Two strong TCR are co-expressed. A mouse TCR
replaces human TCR on human T cells. Even though it is still
poorly understood why some TCR alpha/beta combinations
are preferentially expressed on T cells, our data suggest
that, in the future, designer T cells with exclusive tumor
reactivity can be generated by T cell engineering.
Dual T cell receptor expressing CD8 + T cells with
tumor- and self- specificity can inhibit tumor
growth without causing severe autoimmunity
The engineering of antigen-specific T cells by expression of
TCR genes is a convenient method for adoptive T cell
immunotherapy. A potential problem is the TCR gene transfer
into self-reactive T cells that survived tolerance mechanisms.
We have developed an experimental system with T
cells that express two TCRs with defined antigen-specificities,
one recognizing a tumor-specific antigen (LCMV-gp 33 ),
the other recognizing a self-antigen in the pancreas (OVA).
By using tumor cells expressing high and low amount of
antigen and mice expressing high and low level of self-antigen
in the pancreas (RIP-OVA-Hi and RIP-OVA-Lo), we show
that i) tumor rejection requires high amount of tumor-antigen,
ii) severe autoimmunity requires high amount of selfantigen,
and iii) if antigen expression on tumor cells is sufficient
and low in the pancreas, successful adoptive T cell
therapy can be obtained in the absence of severe autoimmunity.
These results are shown with T cells from dual TCR
transgenic mice or T cells that were redirected by TCR gene
transfer. Our data demonstrate that the approach of adop-
Cancer Research 135