Dr. Clare Blackburn
Confirmed funding for a
BBSRC Case studentship, sponsored by Stem Cell Sciences UK.
T-cells are central
regulators of the adaptive immune system. They co-ordinate and effect the
cellular and humoral immune responses which are required to resolve microbial
and viral infections. The specialised organ, the thymus (1), is the principal
site of T-cell development, therefore, athymic individuals are profoundly
immunodeficient. The unique processes of T-cell differentation and T-cell
repertoire selection are dependent on interactions between developing T cells
and a number of highly specialised epithelial cell-types found only within the
thymus (2). These epithelial cell-types are thought to provide the molecular
niches required to support T-cells through the multiple stages of
differentiation, selection and maturation that ensure emergence into the
peripheral immune system of self-restricted, self-tolerant T-cells (3). T-cell
development therefore requires interactions with multiple epithelial
subpopulations.
The ability to generate
T-cells from haematopoietic progenitor cells in vitro would be highly
advantageous for many medical applications (4), particularly since it should be
possible to customise in vitro-derived T-cell repertoires to be tolerant to
defined MHC haplotypes. For instance, it would help reduce infection-related
morbidity in treatments requiring transplantation of T-cell depleted bone
marrow: in this case, patients could receive, at the same time as the
transplant itself, in vitro-generated T-cells tolerant to both the transplant donor
and recipient, thereby gaining an immediately functional adaptive immune system
rather waiting in excess of 9 months for immune reconstitution to occur.
However, the cellular complexity of the thymic epithelium has proved a
stumbling block for attempts to generate large T-cell repertoires in vitro, and
this is currently possible only in cultures based on limited amounts of ex
vivo-thymic tissue (5).
Recent work in my
laboratory has demonstrated that a population of cells in the thymic
primordium, identified by two monoclonal antibodies (6), can differentiate into
all thymic epithelial cell-types, attract lymphoid progenitors, support
thymocyte differentiation into mature CD4+ and CD8+ T-cells, and confer thymus
function on congenitally athymic nude mice. Neither other epithelial cell
populations in the thymic primordium, which include cells expressing markers
associated with mature cortical thymic epithelium, nor unfractionated
dissociated-and-reaggregated thymus primordium cells, can fulfil all of these functions
(7). These data indicate that our cell-population constitutes a thymic
epithelial progenitor cell-type (TEPC; 6; 7) sufficient to generate a
functional thymus in vivo. They provide the first functional evidence that all
subpopulations of thymic epithelial cell may arise from a common multipotent
progenitor, or stem, cell, and thus provide a model for understanding the
mechanisms underlying thymus organogenesis. Further to this, they present the
possibility of supporting T-cell differentiation in vitro and in vivo using a
single TEPC line: such lines could be propagated in their undifferentiated
state, but would differentiate into a functional thymus upon culture under
appropriate conditions.
Aims:
The aims of this PhD project are to derive human TEPC lines and to demonstrate
use of these lines to generate defined T-cell repertoires in vitro.
Further information is
available from Dr Clare Blackburn (c.blackburn@ed.ac.uk), Centre for Genome
Research/Institute of Cell, Animal and Population Biology, University of
Edinburgh, King's Buildings, West Mains Road, Edinburgh EH3 9JQ.
References for the
project:
1) Miller, J.F.A.P.,
Immunological function of the thymus. Lancet 2, 748 - 749 (1961).
2) Anderson, G., Moore, N.
C., Owen, J. J. T. & Jenkinson, E. J. (1996) Cellular interactions in
thymocyte development. Annu. Rev. Immunol. 14, 73 - 99.
3) Boyd, R. L., et al.
(1993) The thymic microenvironment. Immunol. Today 14, 445-459.
4) Markert, M. L., et al.
(1999) Transplantation of thymus tissue in complete DiGeorge Syndrome. N. Engl.
J. Med. 341, 1180-1189; Weissman, I.L., and Shizuru, J.A. (1999) Immune
Reconstitution. N Engl J Med 341 1227-1229; Reisner, Y. & Martelli, M. F.
(2000) Tolerance induction by 'megadose' transplants of CD34+ stem cells: a new
option for leukemia patients without an HLA-matched donor. Curr. Opinion.
Immunol. 12, 536-541; Slavin, S. (2000) New strategies for bone marrow
transplantation. Curr. Opinion. Immunol. 12 542-551.
5) Poznansky, M. C. et al.
(2000) Efficient generation of human T cells from a tissue-engineered thymic
organoid. Nature Biotech. 18, 729-734.
6) Blackburn, C.C., et al.
(1996) The nude gene acts cell-autonomously and is required for differentiation
of thymic epithelial progenitors. Proc. Natl. Acad. Sci. USA,. 93 5742-5746.
7) Bennett, A.R., Gordon,
J., Bennett, C.L., Boyd, R.L., and Blackburn, C.C. Identification and
characterization of progenitor cells for the thymic epithelium (submitted to
Nature Immunol.).
Recent publications:
Gordon, J., Bennett, A.R.,
Manley, N.R., and Blackburn, C.C. (2001) Gcm2 and Foxn1 mark parathyroid- and
thymus-specific domains in the developing third pharyngeal pouch (Mech. Dev. in
press).
Colledge, L., Sun, M-Y.,
Lin, W., Blackburn, C.C., and Reay, P.A. (2001) Characterization of the
processing requirements of several recombinant antigens for presentation by MHC
Class II (Immunol. in press)
Bennett, C.L., Misslitz,
A., Colledge, L., Aebischer, T., and Blackburn, C.C. (2001) Silent infection of
bone marrow-dendritic cells by Leishmania mexicana amastigotes. Eur. J.
Immunol. 31 876-883.
Blackburn, C.C., Grogan,
J., Augustine, C.L., Varigos, G., Miller, J.F.A.P., and Morahan, G. (2001)
Effect of Localised Cytokine Dysregulation: Accelerated Rejection of
IL-2-Expressing Skin Grafts. Immunol. Cell. Biol. 79 128-131.
Blackburn, C.C., Augustine,
C.L., Li, R., Harvey, R.P., Malin, M.A., Boyd, R.L., Miller, J.F.A.P., and
Morahan, G. (1996) The nude gene acts cell-autonomously and is required for
differentiation of thymic epithelial progenitors. Proc. Natl. Acad. Sci. USA,.
93 5742-5746.