Blood, 15 August 2000, Vol. 96, No. 4, pp. 1608-1609
CORRESPONDENCE
To the Editor:
In utero fetal liver hematopoietic stem cell transplantation:
is there a role for alloreactive T lymphocytes?
The use of hematopoietic stem cells for in utero transplantation
to create permanent hematochimerism represents a new concept in fetal
therapy, although this approach has provided quite heterogeneous results. Flake and Zanjani have provided an excellent updated review of
the current knowledge of in utero stem cell transplantation and have
formulated diverse possible reasons for its poor clinical success.1 In fact, the only clear success, or claims of
success, has been obtained in fetuses affected by immunodeficiency
syndromes such as severe combined immunodeficiency (SCID) or bare
lymphocyte syndrome. Flake and Zanjani strongly support the
possibility that in such immunodeficiency disorders there is a
selective advantage for donor cells, which then overcome a
biological barrier to engraftment in fetuses. To date, the nature of
this biological barrier remains unknown.
Alternatively, or perhaps additionally, we have raised the possibility
that the fetus may develop an allogeneic immune response that
ultimately accounts for graft failure. Accordingly, it has been
reported that fetal liver stem cells are capable of engraftment in a
syngeneic, nonallogeneic host,2 and that successful
allogeneic in utero transplantation of fetal stem cells in sheeps and
monkeys occurs if both the donor and the recipient fetuses are in a
preimmune condition.3 Finally, we have reported a case in
which in utero fetus-to-fetus transplantation performed at the 19th
week of gestation resulted in neither engraftment nor tolerance
induction; rather, 2 years after birth, the recipient had developed a
highly increased cytotoxic T-lymphocyte precursor (CTLp) frequency
against donor cells.4
Toward this possibility, we have recently undertaken molecular,
phenotypic, and functional studies aimed at identifying the presence of
fully competent T lymphocytes in samples of fetal livers and cord
blood. We have found the presence of mature VDJ TCR
chain
transcripts in fetal liver and cord blood cells taken from 7 to 16 weeks of gestation. T-cell clones obtained from fetal liver cells
showed a mature TCR 
+, CD8+ phenotype and
displayed strong alloreactivity against allogeneic HLA class I
molecules.5 The very low yield of such clones from fetal
liver-derived T lymphocytes strongly supports the view that their
frequency is rather low and we have estimated it at around 0.2/106 cells. Similar low, yet significant alloreactive
response has been found within CD8+ T lymphocytes taken
from cord blood.6
Based on our results, as well as experimental data from the literature,
we favor the possibility that the presence of alloreactive T
lymphocytes may explain the failure to engraft in fetuses older than 13 to 16 weeks. Overall, our results may provide useful
informations on the stages of fetal T-cell development and can help in
devising new strategies and planning further clinical trials in
intrauterine transplantation.
Maria Concetta Renda, Emanuela Fecarotta, and Aurelio Maggio
Servizio Talassemia Unità di Ricerca "Piera
Cutino" AOV Cervello Palermo, Italy
Francesco Dieli, Guido Sireci, and Alfredo Salerno
Dipartimento di Biopatologia e Metodologie Biomediche
Università di Palermo Palermo Italy
Lola Markling
Department of Clinical Immunology Huddinge Hospital
Stockholm, Sweden
Magnus Westgren
Department of Obstetrics and Gynecology Huddinge
Hospital Stockholm, Sweden
Gianfranca Damiani, Cristina Jakil, and Francesco Picciotto
Servizio Diagnosiu Prnatale AOV Cervello Palermo, Italy
References
1.
Flake AW, Zanjani ED.
In utero hematopoietic stem cell transplantation: ontogenic opportunities and biological barriers.
Blood.
1999;94:2179-2191[Free Full Text].
2.
Gaines BA, Colson YL, Kaufman CL, Ildstad S.
Facilitating cells enable engraftment of purified fetal liver stem cells in allogeneic recipients.
Exp Hematol.
1996;24:902-913[Medline]
[Order article via Infotrieve].
3.
Zanjani ED, Ascensao JL, Flake AW, Harrison MR, Tavassoli M.
The fetus as an optimal donor and recipient of hemopoietic stem cells.
Bone Marrow Transplant.
1992;10:107-110.
4.
Orlandi F, Giambona A, Messana F, et al.
Evidence of induced non-tolerance in HLA-identical twins with hemoglobinopathy after in utero fetal transplantation.
Bone Marrow Transplant.
1996;18:637-639[Medline]
[Order article via Infotrieve].
5.
Renda MC, Fecarotta E, Dieli F, et al.
Evidence of alloreactive T lymphocytes in fetal liver: implications for fetal hematopoietic stem cell transplantation.
Bone Marrow Transplant.
2000;25:135-141[Medline]
[Order article via Infotrieve].
6.
Barbey C, Irion O, Helg C, et al.
Characterisation of the cytotoxic alloresponse of cord blood.
Bone Marrow Transplant.
1998;22:26-30.
Response:
Role of the alloimmune response after in utero hematopoietic
stem cell transplantation
We appreciate Renda et al's comments regarding their important
investigations into the presence of alloreactivity in the early gestational human fetus. We agree that the immune response likely plays
an important role in the barrier to engraftment following in utero
transplantation, particularly after the appearance of phenotypically
mature T lymphocytes in the peripheral circulation. The question is not
whether the immune system presents a barrier to
engraftment but, rather, when the human immune response becomes an important consideration and what components of the immune response play an important role. It is clear from animal studies in
sheep1,2 and mice3 that engraftment can occur
across full allogeneic or xenogeneic4 barriers if
transplantation is performed early enough in gestation. In
studies that we have presented (manuscripts in preparation or
submission),5,6 it is also clear that tolerance in the
mouse model of in utero hematopoietic stem cell (HSC)
transplantation can be achieved across full major histocompatibility
complex (MHC) barriers and involves deletion of
host-against-donor-reactive T cells, as well as
donor-against-host-reactive T cells, and can be mediated by either
direct or indirect antigen presentation, by donor- or
host-derived antigen-presenting cells, respectively. Thus if the
transplant is performed early enough in gestation and there is adequate
antigen presentation in the thymus, it appears that T-cell mediated
alloreactivity is not prohibitive to engraftment.
The natural immune system may also play a role in fetal immune
response. NK cells are present early in gestation, but their function
is poorly understood. We are in the process of investigating the effect
of prenatal transplantation on the inhibitory receptor profile of host-
and donor-derived NK populations.7 Until better studies are
performed in defined animal models, the importance of the immune
response and the parameters required for tolerance or immune
sensitization will remain conjectural. There is a strong need for
further direct studies, as Renda et al are pursuing, to define the
immune response of the early gestational human fetus. These studies
will allow informed extrapolation of findings in animal models to
the human fetus for optimization of clinical in utero HSC transplantation.
Alan W. Flake
Department of Surgery and the Center for Fetal Diagnosis and
Therapy Children's Hospital of Philadelphia, University of
Pennsylvania Philadelphia, PA
Esmail D. Zanjani
Department of Medicine Veterans Administration Medical
Center, University of Nevada Reno, NV
References
1.
Flake AW, Harrison MR, Adzick NS, Zanjani ED.
Transplantation of fetal hematopoietic stem cells in utero: the creation of hematopoietic chimeras.
Science.
1986;233:776-778[Abstract/Free Full Text].
2.
Flake AW, Zanjani ED.
In utero hematopoietic stem cell transplantation: ontologic opportunities and biologic barriers.
Blood.
1999;94:2179-2191.
3.
Shaaban AF, Milner R, Kim HB, Flake AW.
Fetal liver is a superior donor source for the engraftment of prenatally transplanted allogeneic hematopoietic stem cells [abstract].
Exp Hematol.
1999;27(suppl 1):121a.
4.
Zanjani ED, Flake AW, Rice H, Hedrick M, Tavassoli M.
Long-term repopulating ability of xenogeneic transplanted human fetal liver hematopoietic stem cells in sheep.
J Clin Invest.
1994;93:1051-1055.
5.
Shaaban AF, Milner R, Kim HB, Fichter C, Flake AW.
Donor T-cell education in stable high-level hematopoietic chimeric mice after prenatal MHC-disparate hematopoietic stem cell transplantation [abstract].
Transplantation.
1999;67:605a.
6.
Shaaban AF, Milner R, Kim HB, Flake AW.
High-level allogeneic hematopoietic chimerism following prenatal stem cell transplantation requires negative selection of donor thymocytes mediated by host antigen presentation cells [abstract].
Exp Hematol.
1999;27(suppl 1):347a.
7.
Shaaban AF, Milner R, Kim HB, Fichter C, Flake AW.
Donor natural killer cell Ly49 inhibitory profile is altered by development in an MHC mismatched recipient environment following in utero hematopoietic stem cell transplantation [abstract].
Transplantation.
1999;67:573a
