On the feasibility of inducing tolerance in man: a study in the cynomolgus monkey

Fetal and adult hematopoietic stem cells give rise to distinct T cell lineages in humans

Although the mammalian immune system is generally thought to develop in a linear fashion, findings in avian and murine species argue instead for the developmentally ordered appearance (or "layering") of distinct hematopoietic stem cells (HSCs) that give rise to distinct lymphocyte lineages at different stages of development. Here we provide evidence of an analogous layered immune system in humans. Our results suggest that fetal and adult T cells are distinct populations that arise from different populations of HSCs that are present at different stages of development. We also provide evidence that the fetal T cell lineage is biased toward immune tolerance. These observations offer a mechanistic explanation for the tolerogenic properties of the developing fetus and for variable degrees of immune responsiveness at birth.

Fetal stem-cell transplantation

Fetal stem-cell transplantation is an attractive approach to the treatment of a variety of hematological, metabolic and immunological diseases before birth. The possibility of delivering a large number of cells in an early stage of life, and of taking advantage of normal fetal stem-cell migration and development, is promising. During fetal life, the capacity to mount an immune response to allogeneic cells is impaired compared with adult life. This provides an opportunity to induce tolerance to alloantigens without the need for myeloablation, although there are possible immune barriers to foreign cells in the fetus.

The use of CD 34(+) mobilized peripheral blood as a donor cell source does not improve chimerism after in utero hematopoietic stem cell transplantation in non-human primates

In utero hematopoietic stem cell transplantation is a therapeutic procedure that could potentially cure many developmental diseases affecting the immune and hematopoietic systems. In most clinical and experimental settings of fetal hematopoietic transplantation the level of donor cell engraftment has been low, suggesting that even in the fetus there are significant barriers to donor cell engraftment. In postnatal hematopoietic transplantation donor cells obtained from mobilized peripheral blood engraft more rapidly than cells derived from marrow. We tested the hypothesis that use of donor hematopoietic/stem cells obtained from mobilized peripheral blood would improve engraftment and the level of chimerism after in utero transplantation in non-human primates. Despite the potential competitive advantage from the use of CD 34(+) from mobilized peripheral blood, the level of chimerism was not appreciably different from a group of animals receiving marrow-derived CD 34(+) donor cells. Based on these results, it is unlikely that this single change in cell source will influence the clinical outcome of fetal hematopoietic transplantation.

Fetal Immune Suppression as Adjunctive Therapy for In Utero Hematopoietic Stem Cell Transplantation in Nonhuman Primates

In utero hematopoietic stem cell transplantation could potentially be used to treat many genetic diseases but rarely has been successful except in severe immunodeficiency syndromes. We explored two ways to potentially increase chimerism in a nonhuman primate model: (a) fetal immune suppression at the time of transplantation and (b) postnatal donor stem cell infusion. Fetal Macaca nemestrina treated with a combination of the corticosteroid betamethasone (0.9 mg/kg) and rabbit thymoglobulin (ATG; 50 mg/kg) were given haploidentical, marrow-derived, CD34+ -enriched donor cells. Animals treated postnatally received either donor-derived T cell-depleted or CD34+ -enriched marrow cells. Chimerism was determined by traditional and real-time polymerase chain reaction from marrow, marrow progenitors, peripheral blood, and mature peripheral blood progeny. After birth, the level of chimerism in the progenitor population was higher in the immune-suppressed animals relative to controls (11.3% +/- 2.7% and 5.1% +/- 1.5%, respectively; p = .057). Chimerism remained significantly elevated in both marrow (p = .02) and fluorescence-activated cell sorted and purified CD34+ cells (p = .01) relative to control animals at > or = 14 months of age. Peripheral blood chimerism, both at birth and long term, was similar in immune-suppressed and control animals. In the animals receiving postnatal donor cell infusions, there was an initial increase in progenitor chimerism; however, at 6-month follow-up, the level of chimerism was unchanged from the preinfusion values. Although fetal immune suppression was associated with an increase in the level of progenitor and marrow chimerism, the total contribution to marrow and the levels of mature donor progeny in the peripheral blood remained low. The level of long-term chimerism also was not improved with postnatal donor cell infusion.

In utero hematopoietic stem cell transplantation in nonhuman primates: the role of T cells

In utero transplantation of hematopoietic stem cells is a promising treatment for immune and hematologic diseases of fetuses and newborns. Unfortunately, there are limited data from nonhuman primates and humans describing optimal transplantation conditions. The purpose of this investigation was to determine the effect of T-cell number on engraftment and the level of chimerism after in utero transplantation in nonhuman primates. CD34(+) allogeneic adult bone marrow cells, obtained from the sire after G-CSF and stem cell factor administration, were transplanted into female fetal recipients. The average CD34(+) cell dose was 3.0 x 10(9)/kg (range, 9.9 x 10(8) to 4.4 x 10(9)) and the T-cell dose ranged from 2.6 x 10(5) to 1.1 x 10(8)/kg. Chimerism was determined in peripheral blood subsets (CD2, CD13, and CD20) and in progenitor cell populations by using polymerase chain reaction. Chimerism was noted in seven of eight live-born animals. The level of chimerism in the progenitor population was related to the fetal T-cell dose (r = 0.64, p < 0.02). At the lowest T-cell dose (2.6 x 10(5)/kg), no chimerism was detected. As the T-cell dose increased to 10(6-7)/kg, the level of chimerism increased. Adjusting the T-cell dose to 1.1 x 10(8)/kg resulted in fatal graft-versus-host disease (GVHD). The results of this study emphasize the importance of T cells in facilitating donor cell engraftment and in producing GVHD in fetal nonhuman primates. Some animals achieved levels of chimerism in the marrow hematopoietic progenitor cell population that would likely have clinical relevance. However, the levels of chimerism in peripheral blood were too low for therapeutic benefit. Further studies are needed to test methods that are likely to enhance donor cell engraftment and peripheral blood levels of donor cells.

Fetal hematopoietic stem cell transplantation: a challenge for the twenty-first century

Successful in utero hematopoietic stem cell transplantation will likely represent a major step forward in the management of patients with congenital hematological, metabolic, and immunological disorders. We review the naturally occurring models of hematopoietic chimerism in animals and humans, as well as available experimental animal data and human clinical attempts of fetal transplantation. Data available from naturally occurring models and experimental models of fetal transplantation suggest that this technique should be translatable to the human fetus. However, to date, the success of human fetal hematopoietic stem cell therapy has been limited to fetuses with severe immunologic defects. Evaluation of successful attempts of human transplantation, the ontogeny of fetal immune development, and data available from animals provide insights into innovative approaches to fetal therapy that may bring the reality of successful fetal transplantation closer.

Fetal target organs of graft-versus-host reaction induced in utero by injection of maternal cells in a pig model

The target organs of graft-versus-host reaction (GVHR) in adult or neonates are the site of multifocal lymphocytic infiltrates. GVHR can also be acquired in utero by maternal cells crossing the placenta, but the fetal target organs are unknown. The aim of this study was to determine these target fetal organs. The distribution pathway of infused labeled lymphocytes within cryostat sections of fetal organs was analyzed, and fetal target organs of infused lymphocytes were investigated in both isogenic and semiallogenic situations. Isogenic cells were observed in less organs and semiallogenic cells were localized in a more restricted number of organs than isogenic cells. Furthermore, the liver, the thyroid, and the spleen were the fetal target organs in the two studied gestations. GALT, thymus, and kidney were also lymphocyte targets in isogenic gestation. In conclusion, isogenic cells induced GVHR in more fetal organs than semiallogenic cells.