The adoptive transfer of antigen-specific T cells that have been expanded ex vivo is being actively pursued to treat infections and malignancy in humans. The T cell populations that are available for adoptive immunotherapy include both effector memory and central memory cells, and these differ in phenotype, function, and homing. The efficacy of adoptive immunotherapy requires that transferred T cells persist in vivo, but identifying T cells that can reproducibly survive in vivo after they have been numerically expanded by in vitro culture has proven difficult. Here we show that in macaques, antigen-specific CD8 + T cell clones derived from central memory T cells, but not effector memory T cells, persisted long-term in vivo, reacquired phenotypic and functional properties of memory T cells, and occupied memory T cell niches. These results demonstrate that clonally derived CD8 + T cells isolated from central memory T cells are distinct from those derived from effector memory T cells and retain an intrinsic capacity that enables them to survive after adoptive transfer and revert to the memory cell pool. These results could have significant implications for the selection of T cells to expand or to engineer for adoptive immunotherapy of human infections or malignancy.

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 × × 10 9 /kg (range, 9.9 × × 10 8 to 4.4 × × 10 9 ) and the T-cell dose ranged from 2.6 × × 10 5 to 1.1 × × 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 × × 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 × × 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.

We used a primate model of autologous peripheral blood progenitor cell (PBPC) transplantation to study the effect of in vitro expansion on committed progenitor cell engraftment and marrow recovery after transplantation. Four groups of baboons were transplanted with enriched autologous CD34 + PBPC collected by apheresis after five days of G-CSF administration (100 µg/kg/day). Groups I and III were transplanted with cryopreserved CD34 + PBPC and Groups II and IV were transplanted with CD34 + PBPC that had been cultured for 10 days in Amgen-defined (serum free) medium and stimulated with G-CSF, megakaryocyte growth and development factor (MGDF), and stem cell factor each at 100 ηg/ml. Group III and IV animals were administered G-CSF (100 µg/kg/day) and MGDF (25 µg/kg/day) after transplant, while animals in Groups I and II were not. For the cultured CD34 + PBPC from groups II and IV, the total cell numbers expanded 14.4 ± 8.3 and 4.0 ± 0.7-fold, respectively, and CFU-GM expanded 7.2 ± 0.3 and 8.0 ± 0.4-fold, respectively. All animals engrafted. If no growth factor support was given after transplant (Groups II and I), the recovery of WBC and platelet production after transplant was prolonged if cells had been cultured prior to transplant (Group II). Administration of post-transplant G-CSF and MGDF shortened the period of neutropenia (ANC < 500/µL) from 13 ± 4 (Group I) to 10 ± 4 (Group III) days for animals transplanted with non-expanded CD34 + PBPC. For animals transplanted with ex vivoexpanded CD34 + PBPC, post-transplant administration of G-CSF and MGDF shortened the duration of neutropenia from 14 ± 2 (Group II) to 3 ± 4 (Group IV) days. Recovery of platelet production was slower in all animals transplanted with expanded CD34 + PBPC regardless of post-transplant growth factor administration. Progenitor cells generated in vitro can contribute to early engraftment and mitigate neutropenia when growth factor support is administered posttransplant. Thrombocytopenia was not decreased despite evidence of expansion of megakaryocytes in cultured CD34 + populations.

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.