Bone Marrow Cell Allografts Research Articles

Pharmacological profiles of mycophenolate mofetil (CellCept), a new immunosuppressive agent

Mycophenolate mofetil (MMF, CellCept), a semisynthetic derivative of mycophenolic acid (MPA) produced by a fungus, is an inhibitor of the inosine monophosphate dehydrogenase (IMPDH) enzyme (IC50 = 25 nM) that catalyzes the synthesis of guanosine monophosphate (GMP) from inosine. GMP is an essential nucleoside for purine synthesis during cell division. As T and B-lymphocytes almost exclusively use the de novo pathway of purine synthesis, these cells are particularly sensitive to the inhibitory action of MMF. It has a mechanism of action distinct from cyclosporine and tacrolimus. Although MMF does not affect cytokine production, by inhibiting the rate-limiting enzyme IMPDH in the de novo synthesis of purines, it inhibits the proliferation of T and B-lymphocytes, the production of antibodies, and the generation of cytotoxic T lymphocytes. Reversal of acute allograft rejection and increased survival of kidney, heart and bone marrow cell allograft has been shown in several animal studies. Moreover, it was suggested that MMF combined with CsA prevented the acute rejection, and approximately half of the animals became long-term survivors. The Ministry of Health and Welfare approved MMF in 1999 for use for rejection treatment in renal transplantation based on several prospective, randomized and blind efficacy trials.

Synergistic effects of in vivo depletion of Ly-49A and Ly-49G2 natural killer cell subsets in the rejection of H2b bone marrow cell allografts

Subsets of murine natural killer (NK) cells exist that express the Ly-49 family of molecules that recognize different major histocompatibility complex (MHC) determinants. Bone marrow transplantation studies were performed to examine the in vivo functions of 2 of these subsets. Subsets of Ly-49A and Ly-49G2 NK share specificity for the same MHC class 1 ligand, D(d), binding of which results in an inhibitory signal to the NK cell but allows them to lyse H2(b) targets in vitro. We therefore examined the ability of these subsets to reject H2(b) bone marrow cell allografts in lethally irradiated mice. Surprisingly, depletion of Ly-49A(+) NK cells in BALB/c or B10.D2 mice (both H2(d)) had no effect on the rejection of H2(b) BMC. However, Ly-49A depletion did partially abrogate the ability of B10.BR (H2(k)) mice to reject H2(b) allografts. Although depletion of either Ly-49A(+) or Ly-49G2(+) NK cells alone had no effect on the ability of B10.D2 mice to reject H2(b) BMC, depletion of both subsets dramatically and synergistically abrogated rejection. Studies with various B10 congenic mice and their F(1) hybrids indicate that this synergy between Ly49A and Ly4G2 depletion occurs in every instance. Thus, Ly-49A(+) NK cells appear to play a role in the rejection H2(b) bone marrow allografts, but, in most strains of mice studied, Ly-49G2(+) NK cells must also be eliminated. The putative roles of these NK cell subsets in clinical transplantation remains to be elucidated. (Blood. 2000;95:3840-3844)

Synergistic effects of in vivo depletion of Ly-49A and Ly-49G2 natural killer cell subsets in the rejection of H2b bone marrow cell allografts

AbstractSubsets of murine natural killer (NK) cells exist that express the Ly-49 family of molecules that recognize different major histocompatibility complex (MHC) determinants. Bone marrow transplantation studies were performed to examine the in vivo functions of 2 of these subsets. Subsets of Ly-49A and Ly-49G2 NK share specificity for the same MHC class 1 ligand, Dd, binding of which results in an inhibitory signal to the NK cell but allows them to lyse H2b targets in vitro. We therefore examined the ability of these subsets to reject H2b bone marrow cell allografts in lethally irradiated mice. Surprisingly, depletion of Ly-49A+ NK cells in BALB/c or B10.D2 mice (both H2d) had no effect on the rejection of H2b BMC. However, Ly-49A depletion did partially abrogate the ability of B10.BR (H2k) mice to reject H2ballografts. Although depletion of either Ly-49A+ or Ly-49G2+ NK cells alone had no effect on the ability of B10.D2 mice to reject H2b BMC, depletion of both subsets dramatically and synergistically abrogated rejection. Studies with various B10 congenic mice and their F1 hybrids indicate that this synergy between Ly49A and Ly4G2 depletion occurs in every instance. Thus, Ly-49A+ NK cells appear to play a role in the rejection H2b bone marrow allografts, but, in most strains of mice studied, Ly-49G2+ NK cells must also be eliminated. The putative roles of these NK cell subsets in clinical transplantation remains to be elucidated.

Positive Recognition of MHC Class I Molecules by the Ly49D Receptor of Murine NK Cells

Members of the murine Ly49 family of receptors have been shown to inhibit and activate NK cell function. Subsets of Ly49-expressing NK cells mediate the rejection of bone marrow cell allografts and the lysis of allogeneic lymphoblasts. In this report we have studied Ly49-mediated positive and negative signaling in an in vitro cytotoxicity assay using sorted NK cell subsets as effectors and a panel of 51Cr-labeled Con A lymphoblasts as targets in the presence or the absence of Abs to Ly49 and/or class I molecules. Our results demonstrate that the activating receptor Ly49D delivers stimulatory signals for target cell lysis upon interacting with H2-Dd, Dr, and Dsp2, but not H2b or H2k class I Ags. On the other hand, the inhibitory receptor Ly49G2 delivers negative signals for target cell lysis upon interacting with Dd, Dr, and H2k, but not H2b or Dsp2, class I Ags. Furthermore, Ly49-mediated negative signaling dominates Ly49D-mediated positive signaling. Thus, lysis of class I MHC-bearing targets by NK cells is not merely the consequence of the absence of an Ly49-mediated negative signal, but also requires positive recognition of class I molecules by certain Ly49 receptors. Activation of NK cells by nonself class I molecules was not predicted by the missing self hypothesis.

Differential Effects of the Rejection of Bone Marrow Allografts by the Depletion of Activating Versus Inhibiting Ly-49 Natural Killer Cell Subsets

Natural killer cells mediate the specific rejection of bone marrow cell (BMC) allografts in lethally irradiated mice. The Ly-49 family of molecules present on subsets of murine NK cells appears capable of binding class I MHC molecules, resulting in transmission of an inhibitory signal to the NK cell. These Ly-49 family members have been shown to have an immunoreceptor tyrosine-based inhibitory motif that is responsible for the inhibitory signal. However, a new Ly-49 family member was found that lacks this motif, Ly-49D, and evidence suggests that this may be an activating receptor. We therefore compared the role of the activating Ly-49 member with NK cells bearing inhibitory Ly-49 receptors in BMC rejection. Depletion of Ly-49D+ NK cells in H-2b mice abrogated their ability to reject H-2d BMC allografts. Similarly, Ly-49C+ NK cells also were shown to mediate the specific rejection of H-2d BMC. When both subsets were depleted, an additive enhancement of BMC engraftment was observed, indicating that both subsets play a role in the rejection of allogeneic H-2-homozygous H-2d BMC. However, rejection of H-2(b x d) or D8 (H-2b, Dd transgene) BMC allografts was unaffected by Ly-49C+ NK cell depletion in H-2b mice. In marked contrast, depletion of Ly-49D+ NK cells in H-2b mice totally abrogated the rejection of H-2(b x d) heterozygous BMC in support of in vitro data suggesting that Ly-49D+ NK cells receive activating signals. Therefore, NK subsets demonstrate a differential ability to reject H-2 homozygous and heterozygous BMC.

Rejection of bone marrow cell allografts by natural killer cell subsets: 5E6+ cell specificity for Hh‐1 determinant 2 shared by H‐2d and H‐2f

The 5E6 antigen, defined by anti-5E6 mAb, is expressed on one-half of murine natural killer (NK) cells, and we have previously demonstrated (C. L. Sentman et al., J. Exp. Med. 1989. 170: 1991) that 5E6+ NK cells are necessary for the rejection of BALB/c (Hh-1d) but not C567BL/6 (Hh-1b) bone marrow cells (BMC). In experiments described here, we have characterized the specificity of 5E6+ and 5E6- NK cell subsets for hemopoietic histocompatibility-1 (Hh-1) antigens. Prospective recipient mice were treated with anti-5E6 mAb and challenged with BMC from a variety of donors. In addition, H-2d/Hh-1d C.B-17 scid 5E6+ or 5E6- NK cells were adoptively transferred into irradiated, NK cell-depleted hosts and challenged with H-2b/Hh-1b BMC. The data indicate that the 5E6+ NK cells are necessary for the rejection of only those BMC that express the Hh-1 determinant 2 shared by H-2d and H-2f haplotypes of strains BALB/c (d), A.Ca (f), and B10.M (f). No reactivity to other Hh-1 antigens resides in the 5E6+ population. In contrast, the ability of NK cells to lyse H-2d or H-2b tumor cells was independent of 5E6 expression. These results suggest that the 5E6 molecule is likely to be important in the specific recognition and rejection of BMC that express Hh-1 determinant 2, and is probably not involved in recognition of "tumor target cell structures".

Homozygosity at the major histocompatibility complex is required for optimal immunogenicity of bone marrow cell allografts in irradiated rats

Hemopoietic histocompatibility (Hh) Genes associated with the H-2 region control the antigenicity of hemopoietic cell grafts in the mouse. We have tested for similar genes in rats. Wistar Furth (WF, RTlu) or Lewis (LEW RTl1) bone marrow cell grafts did not proliferate in spleens of lethally irradiated (WFxLEW) F1 hybrid rats as assessed by measuring the incorporation of 5-iodo-2' deoxyuridine - 125I (IUdR) into recipient spleens 5 days after transplantation. In contrast, (WFxLEW) F1 hybrid marrow cells grew well in both WF and LEW parental strain hosts. (WFxLEW) F1 or (WFxLEW) F1 hybrid rats were backcrossed to WF parental strain rats to produce progeny, either homozygous, or heterozygous for the MHC. The RTl type of 46 individual backcross progeny was determined using a 5 day mixed-lymphocyte reaction (MLR). Correlation between RTl type and growth of marrow grafts of individual backcross rats were determined by using each rat as a bone marrow donor for irradiated LEW hosts. Marrow grafts from rats heterozygous for RTl were accepted in all 25 cases, whereas, grafts from 19 to 21 homozygous donors were rejected by the LEW hosts. Thus, homozygosity, for Hh determinants in or near the RTl region appears to be necessary for optimal immunogenicity of bone marrow allografts.