Transgenic mice carrying the diphtheria toxin A chain gene under the control of the granzyme A promoter: expected depletion of cytotoxic cells and unexpected depletion of CD8 T cells

Absence of major histocompatibility complex class I on neural stem cells does not permit natural killer cell killing and prevents recognition by alloreactive cytotoxic T lymphocytes in vitro

Potential applications of neural stem cells (NSCs) for transplantation requires understanding myosin heavy chain (MHC) expression and the ability of T cells and natural killer (NK) cells to recognize this progenitor population. Cells from the cortices of day-13 embryonic (E13) B6 (H-2(b)) mice were explanted and cultured to expand NSCs. Analysis of P2-P17-cultured cells using anti-MHC class I/II monoclonal antibodies (mAbs) showed marginal expression of both products. Although recombinant murine interferon-gamma (rmIFN gamma) exposure did not alter the multipotential capacity of these stem cells, titration of mrIFN gamma NSC cultures demonstrated that MHC molecules could be strongly upregulated after addition of 3 ng/ml rmIFN gamma for 60 hours. To assess the susceptibility of NSCs with low or absent versus high levels of MHC expression to lysis by cytotoxic T lymphocyte (CTL) and NK populations, untreated and rmIFN gamma-treated NSC target cells were examined. Untreated NSCs were not recognized by BALB/c (H-2(d)) allospecific anti-H-2(b) CTL, consistent with the mAb findings; however, upregulation of MHC products on both early and later passaged NSCs resulted in their efficient lysis by CTL. NK cells were prepared from syngeneic B6 or allogeneic BALB/c mice. Although NK cells effectively killed control YAC-1 target cells, these effectors did not kill MHC-deficient (or expressing) NSC targets. Thus, similar to hematopoietic, embryonic, and mesenchymal stem cell populations, unmanipulated NSCs are not readily killed by T and NK cells. These findings suggest that following transplant into syngeneic or allogeneic recipients, NSCs may exhibit diminished susceptibility to clearance by host T- and NK-cell populations.

Antigen-primed CD8+ T cells can mediate resistance, preventing allogeneic marrow engraftment in the simultaneous absence of perforin-, CD95L-, TNFR1-, and TRAIL-dependent killing

Engraftment failure following allogeneic bone marrow (BM) transplantation is of clinical concern particularly involving T-cell-depleted inoculum and transplantations for aplastic anemia. Immune resistance by lymphoid and natural killer (NK) populations with "barrier" function is well established. Major histocompatibility complex (MHC)-identical marrow allografts were examined to investigate effector pathways in non-NK-mediated resistance. Barrier function was examined in cytotoxic normal and deficient B6 (H-2(b)) recipients primed to donor minor histocompatibility antigen (MiHA) prior to BM transplantation. Host resistance was sensitively evaluated by colony-forming unit (CFU) assays to directly assess for donor progenitor cell (PC) and peripheral chimerism. B6 host CD8(+) T cells but not CD4(+) or NK1.1(+) cells effected rejection of primitive (CFU-HPP [high-proliferative potential]) and lineage-committed (CFU-IL3/GM [interleukin 3/granulocyte macrophage]) allogeneic donor progenitors. To address complementation by the cytotoxic pathways existing in singly deficient (perforin or FasL) recipients, cytotoxically double (perforin plus FasL) deficient (cdd) recipients were used. Resistance in B6-cdd recipients was comparable to that of wild-type B6 recipients and was also dependent on CD8(+) T cells. A "triple" cytotoxic deficient model, involving transplantation of TNFR1(-/-) (tumor necrosis factor receptor 1) progenitor grafts did not diminish the ability of B6-cdd recipients to reject allografts. Finally, injection of anti-TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) monoclonal antibody (mAb) in B6-cdd recipients also failed to inhibit rejection of TNFR1(-/-) marrow grafts. In total, these studies demonstrate that CD8(+) host T cells can effectively resist MHC-matched MiHA-mismatched donor PCs via alternative effector pathway(s) independent of perforin-, FasL-, TNFR-1-, and TRAIL-dependent cytotoxicity. Therefore, inhibition of these effector pathways in sensitized recipients is unlikely to result in stem cell engraftment following PC allografts.

In vivo natural killer cell activities revealed by natural killer cell-deficient mice

Studies of natural killer (NK) cell function in vivo have been challenging primarily due to the lack of animal models in which NK cells are genetically and selectively deficient. Here, we describe a transgenic mouse with defective natural killing and selective deficiency in NK1.1(+) CD3(-) cells. Despite functionally normal B, T, and NK/T cells, transgenic mice displayed impaired acute in vivo rejection of tumor cells. Adoptive transfer experiments confirmed that NK1.1(+) CD3(-) cells were responsible for acute tumor rejection, establishing the relationship of NK1.1(+) CD3(-) cells to NK cells. Additional studies provided evidence that (i) NK cells play an important role in suppressing tumor metastasis and outgrowth; (ii) NK cells are major producers of IFNgamma in response to bacterial endotoxin but not to interleukin-12, and; (iii) NK cells are not essential for humoral responses to T cell-independent type 2 antigen or the generalized Shwartzman reaction, both of which were previously proposed to involve NK cells.

CD8+TCR+ and CD8+TCR- cells in whole bone marrow facilitate the engraftment of hematopoietic stem cells across allogeneic barriers

Although purified hematopoietic stem cells (HSC) are sufficient to engraft irradiated allogeneic recipients, bone marrow (BM) contains other cells that facilitate engraftment. Here, several candidate facilitators were tested by cotransplantation with HSC. Both TCR+ and TCR- CD8alpha+ BM subpopulations have facilitative potential. CD8+TCR+ cells are typical T lymphocytes. CD8+TCR- facilitators are CD3 , not CD3+, have a granular morphology, and are CD8beta- and CD11c+; they share phenotypic characteristics with CD8(alpha)alpha lymphoid dendritic cells and veto cells. We also demonstrate that lytic function is nqt necessary for facilitation and that the CD8alpha molecule is either important for facilitation or in the development of facilitators.

From stem cells to lymphocytes: biology and transplantation

We review the development of the hematopoietic system, focusing on the transition from hematopoietic stem cells (HSCs) to T cells. This includes the isolation of HSCs, and recent progress in understanding their ontogeny, homing properties, and differentiation. HSC transplantation is reviewed, including the kinetics of reconstitution, engraftment across histocompatibility barriers, the facilitation of allogeneic engraftment, and the mechanisms of graft rejection. We describe progress in understanding T-cell development in the bone marrow and thymus as well as the establishment of lymph nodes. Finally, the role of bcl-2 in regulating homeostasis in the hematopoietic system is discussed.