Abstract Book 2010 - CIMT Annual Meeting

058 Echchannaoui | Cellular therapy
Evaluation of the safety of p53 TCR gene transfer in a
humanized mouse model
Hakim Echchannaoui 1 , Edite Antunes 1 , Carina Lotz 2 , Simone Thomas 1 , Ralf-Holger Voss 1
and Matthias Theobald 1
1 Department of Hematology & Oncology, University Medical Center, Mainz, Germany
2 Actelion Pharmaceuticals Ltd, Allschwil, Switzerland
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Adoptive cell therapy with T cells retrovirally trans-
duced with tumor-associated antigen (TAA) specific
TCRs is a promising approach for immunotherapy
in patients with haematological malignancies. The
TAA p53 is over-expressed in approximately 50% of
human tumors. We have reported that HLA-A*0201
(A2.1) transgenic mice can be used to circumvent
self-tolerance to universal human TAA and to generate
efficient tumor-reactive CTL. We used A2.1
transgenic mice, in which the mouse CD8 molecule
cannot efficiently interact with A2.1 to generate a
high-affinity, CD8-independent p53(264-272) specific
TCR. Retroviral expression of CD8-independent
p53-specific TCR into T cells, allowed CD8+ T lymphocytes
to acquire a broad tumor-specific CTL activity
but also redirected CD4+ T cells into potent
tumor-reactive, p53-specific T helper cells. However
a particular safety concern with TCR gene transfer,
is the formation of mixed TCR heterodimers
between the introduced TCR α and β chains with
the endogenous TCR chains, resulting in the potential
generation of autoreactive T cells. To reduce
the formation of TCR mixed dimers an additional
inter-chain disulfide bond between the TCR α and β
chain constant domains was introduced. We further
improved the expression level of p53 TCR transgene
using codon-optimization of the TCR sequence.
Mouse T cells transduced with cysteine-modified
(Cys) and codon-optimized (Opt) p53(264-272)A2.1
TCR showed higher expression levels of the introduced
TCR as compared to p53(264-272)-specific
WT TCR. Importantly, p53(264-272)A2.1-Opt.Cys
TCR transduced CTL recognized and killed a wide
variety of malignant A2.1 tumor cells with altered
p53 expression, but not p53-deficient A2.1 cells
more efficiently as compared to CTL transduced
with the WT p53(264-272)-specific TCR.
However, when p53(264-272)A2.1-Opt.Cys TCR
transduced mouse T cells are adoptively transferred
into p53-deficient partially humanized (A2Kb)
mice, under conditioning-induced lymphopenia,
expansion of infused T cells following high dose
IL-2 administration is associated with the development
of lethal autoimmunity similarly to mice
receiving p53(264-272)-specific WT TCR transduced
T cells due to the formation of self-reactive
TCRs. The so called off-target toxicity observed in
our preclinical mouse model highlights the need
for further improvement of TCR gene therapy to
prevent TCR mispairing-induced autoimmunity. To
address this concern, a novel single chain p53TCR
construct was engineered and is currently under
investigation.