Modification of Dendritic Cells for the Induction of Tolerance
Author(s)
Khan, Adnan
Type
Thesis
Abstract
Allogeneic T cell stimulation requires not only antigen-specific signals but also
costimulatory signals, most importantly between CD80/86 on the antigen presenting cell
and CD28 or CTLA4 on the T cell. Engagement of the T cell receptor without
costimulation can lead to anergy and the subsequent induction of regulatory T cells
(Tregs). T cell activation is also controlled by dendritic cell (DC) expression of the
tryptophan-catabolising, immunomodulatory enzyme indoleamine 2,3-dioxygenase
(IDO). Depletion of this essential amino acid, and/or the production of tryptophan
metabolites (kynurenines) inhibits T cell proliferation.
With the aim of generating tolerogenic DCs for the induction of donor-specific
transplantation tolerance, lentiviral vectors were used in this study for gene transfer into
murine DCs. Firstly, an intracellular approach that prevents costimulation was
developed: A fusion protein- CTLA4-KDEL- consisting of the extracellular domain of
CTLA4 and the KDEL peptide [an endoplasmic reticulum (ER) retention signal] was
expressed in DCs and prevented surface CD80/86 expression due to ER retention. A
second approach used in the study involved the lentiviral gene transfer of IDO into DCs.
The induction of donor-specific tolerance (mediated by Tregs with direct and indirect
pathway allospecificity) was demonstrated, both in vitro and in vivo, using
CTLA4-KDEL-expressing DCs. Linked suppression was observed and mediated by
donor-specific Tregs. Although IDO-expressing DCs did not induce and/or sustain
allogeneic T cell proliferation, this anergy lacked donor specificity. It was demonstrated
that IDO+CD80/86+ DCs fail to induce and/or expand FoxP3+CTLA4+ Treg
populations. Furthermore, IDO+CD80/86- DCs failed to sustain pre-induced populations
of FoxP3+CTLA4+ Tregs (associated with a high rate of cell death). The capacity of
CTLA4-KDEL- and IDO-expressing DCs to induce tolerance to allografts was
investigated using a murine corneal allograft model, and administration of
CTLA4-KDEL-expressing DCs prevented allograft rejection. The study demonstrates
the clinical potential of CTLA4-KDEL-expressing DCs to induce Treg-mediated,
donor-specific transplantation tolerance.
costimulatory signals, most importantly between CD80/86 on the antigen presenting cell
and CD28 or CTLA4 on the T cell. Engagement of the T cell receptor without
costimulation can lead to anergy and the subsequent induction of regulatory T cells
(Tregs). T cell activation is also controlled by dendritic cell (DC) expression of the
tryptophan-catabolising, immunomodulatory enzyme indoleamine 2,3-dioxygenase
(IDO). Depletion of this essential amino acid, and/or the production of tryptophan
metabolites (kynurenines) inhibits T cell proliferation.
With the aim of generating tolerogenic DCs for the induction of donor-specific
transplantation tolerance, lentiviral vectors were used in this study for gene transfer into
murine DCs. Firstly, an intracellular approach that prevents costimulation was
developed: A fusion protein- CTLA4-KDEL- consisting of the extracellular domain of
CTLA4 and the KDEL peptide [an endoplasmic reticulum (ER) retention signal] was
expressed in DCs and prevented surface CD80/86 expression due to ER retention. A
second approach used in the study involved the lentiviral gene transfer of IDO into DCs.
The induction of donor-specific tolerance (mediated by Tregs with direct and indirect
pathway allospecificity) was demonstrated, both in vitro and in vivo, using
CTLA4-KDEL-expressing DCs. Linked suppression was observed and mediated by
donor-specific Tregs. Although IDO-expressing DCs did not induce and/or sustain
allogeneic T cell proliferation, this anergy lacked donor specificity. It was demonstrated
that IDO+CD80/86+ DCs fail to induce and/or expand FoxP3+CTLA4+ Treg
populations. Furthermore, IDO+CD80/86- DCs failed to sustain pre-induced populations
of FoxP3+CTLA4+ Tregs (associated with a high rate of cell death). The capacity of
CTLA4-KDEL- and IDO-expressing DCs to induce tolerance to allografts was
investigated using a murine corneal allograft model, and administration of
CTLA4-KDEL-expressing DCs prevented allograft rejection. The study demonstrates
the clinical potential of CTLA4-KDEL-expressing DCs to induce Treg-mediated,
donor-specific transplantation tolerance.
Date Issued
2009-06
Date Awarded
2009-07
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
George, Andrew
Lombardi, Giovanna
Sponsor
Roche Organ Transplantation Research Foundation (ROTRF)
Creator
Khan, Adnan
Publisher Department
Immunology
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)