A modified technique for experimental skin grafting

The new immunosuppressant PLNPK prolongs allograft survival in mice

The pentapeptide PLNPK (Pro-Leu-Asn-Pro-Lys) is extracted from the spleen. Preliminary studies have shown that PLNPK could inhibit T lymphocyte transformation and antibody production. In the present study, we detected the inhibitory effect of PLNPK on one-way mixed leukocyte reaction (MLR) in vitro and observed the effect of PLNPK on the duration of allograft survival in mouse models of skin or cardiac transplantation. Pathological damage and T cell infiltration of the grafts were also detected. Results showed that PLNPK could significantly inhibit T lymphocyte proliferation, with an optimized inhibition of 40%. Also PLNPK could significantly prolong the mean survival time of skin allograft and cardiac allograft, producing survival rates of 42% and 38.7%, respectively. PLNPK at a dose of 200 μg/kg/d or 100 μg/kg/d could significantly suppress ConA-induced T cell proliferation and T cell IL-2 secretion in transplant recipient mice, compared to the saline group (P<0.05). This information suggests that PLNPK can effectively antagonize transplant rejection, possibly by reducing IL-2 secretion by T cells and inhibiting T cell proliferation and activation.

Long-term pharmacologically regulated expression of erythropoietin in primates following AAV-mediated gene transfer

Gene therapy is a potential route for the delivery of secreted therapeutic proteins, but pharmacologic control of expression will generally be required for optimal safety and efficacy. Previous attempts to achieve regulated expression in largeanimal models have been thwarted by transient expression or immune responses to regulatory proteins. We evaluated the ability of the dimerizer-regulated gene expression system to achieve controlled, long-term production of erythropoietin (Epo) following intramuscular administration of adeno-associated virus (AAV) vectors to 16 primates. All animals showed dose-responsive and completely reversible elevation of Epo and hematocrit in response to the dimerizer rapamycin, or analogs with reduced immunosuppressive activity, administered intravenously or orally. Animals that received optimized dual vectors showed persistent regulated expression for the duration of the study, with no apparent immune response to Epo or the regulatory proteins. Similar results were obtained with single vectors incorporating both the Epo and regulatory genes, including those packaged into serotype 1 AAV vectors to allow use of lower viral doses. For the longest-studied animal, regulated expression has persisted for more than 6 years and 26 induction cycles. These data indicate that one-time or infrequent gene transfer followed by dimerizer regulation is a promising approach for delivery of therapeutic proteins.

Induction of Donor-Type Chimerism and Transplantation Tolerance Across Major Histocompatibility Barriers in Sublethally Irradiated Mice by Sca-1+Lin− Bone Marrow Progenitor Cells: Synergism With Non-Alloreactive (Host × Donor)F1 T Cells

Induction of transplantation tolerance by means of bone marrow (BM) transplantation could become a reality if it was possible to achieve engraftment of hematopoietic stem cells under nonlethal preparatory cytoreduction of the recipient. To that end, BM facilitating cells, veto cells, or other tolerance-inducing cells, have been extensively studied. In the present study, we show that BM cells within the Sca-1+Lin− cell fraction, previously shown to be enriched for early hematopoietic progenitors, are capable of reducing specifically antidonor CTL-p frequency in vitro and in vivo, and of inducing split chimerism in sublethally 7-Gy–irradiated recipient mice across major histocompatibility complex barriers. The immune tolerance induced by the Sca-1+Lin−cells was also associated with specific tolerance toward donor-type skin grafts. The minimal number of cells required to overcome the host immunity remaining after 7 Gy total body irradiation is very large and, therefore, it may be very difficult to harvest sufficient cells for patients. This challenge was further addressed in our study by demonstrating that non-alloreactive (host × donor)F1 T cells, previously shown to enhance T-cell–depleted BM allografts in lethally irradiated mice, synergize with Sca-1+Lin− cells in their capacity to overcome the major transplantation barrier presented by the sublethal mouse model.

Induction of Donor-Type Chimerism and Transplantation Tolerance Across Major Histocompatibility Barriers in Sublethally Irradiated Mice by Sca-1+Lin− Bone Marrow Progenitor Cells: Synergism With Non-Alloreactive (Host × Donor)F1 T Cells

Induction of transplantation tolerance by means of bone marrow (BM) transplantation could become a reality if it was possible to achieve engraftment of hematopoietic stem cells under nonlethal preparatory cytoreduction of the recipient. To that end, BM facilitating cells, veto cells, or other tolerance-inducing cells, have been extensively studied. In the present study, we show that BM cells within the Sca-1+Lin− cell fraction, previously shown to be enriched for early hematopoietic progenitors, are capable of reducing specifically antidonor CTL-p frequency in vitro and in vivo, and of inducing split chimerism in sublethally 7-Gy–irradiated recipient mice across major histocompatibility complex barriers. The immune tolerance induced by the Sca-1+Lin−cells was also associated with specific tolerance toward donor-type skin grafts. The minimal number of cells required to overcome the host immunity remaining after 7 Gy total body irradiation is very large and, therefore, it may be very difficult to harvest sufficient cells for patients. This challenge was further addressed in our study by demonstrating that non-alloreactive (host × donor)F1 T cells, previously shown to enhance T-cell–depleted BM allografts in lethally irradiated mice, synergize with Sca-1+Lin− cells in their capacity to overcome the major transplantation barrier presented by the sublethal mouse model.

Prolongation of rat skin and cardiac allograft survival by low molecular weight heparin

BACKGROUND

We have previously reported that very low doses of low molecular weight heparin compounds (LMWH) inhibit a variety of T-cell-mediated reactions by down-regulation of TNF-alpha production. This study tested the efficacy of LMWH in organ transplantation.

METHODS

Skin and heterotopic heart transplantations were performed between recipient Wistar rats and donor BN rats. Two doses of LMWH were given sc, 1 and 20 micrograms, each in three protocols, with day of grafting as Day 0: (A) Daily: -1, 0, 1 ellipsis, (B) Late Weekly: -1, 6, 13 ellipsis, and (C) Early Weekly: -7, 0, 7 ellipsis. Doses and schedules were selected based on efficacy in autoimmune models. Skin graft rejection was defined by complete separation of the graft, and heart transplant rejection was defined as cessation of heartbeat.

RESULTS

Treatment with 1 microgram (26.8 +/- 2.0 days) and 20 micrograms (24.5 +/- 2.3 days) of LMWH using the Early Weekly protocol significantly prolonged skin allograft survival compared to controls (17.8 +/- 4.4 days), P < 0.001 for both, whereas other protocols did not. Compared to controls (8.3 +/- 1.4 days), treatment with both 1 and 20 micrograms of LMWH using all three protocols significantly prolonged cardiac allograft survival. The efficacy, however, varied considerably. Increase in graft survival ranged from 18% (1 microgram, Daily, 9.8 +/- 0.7 days, P = 0.02) to more than twofold (20 micrograms, Early Weekly, 20.8 +/- 5.5 days, P < 0.001) according to the dose and schedule of LMWH.

CONCLUSIONS

Treatment with very low doses of nonanticoagulant LMWH preparations having anti-TNF-alpha activity significantly prolongs rat skin and cardiac allograft survival in a dose- and schedule-dependent manner.

Allograft and xenograft rejection in C3H/SCID mice. A new model for the study of non-T cell graft rejection mechanisms

Comparative cell transfer experiments have revealed that, despite their equal immune deficiency, C3H/SCID mice were markedly inferior compared with C.B-17/SCID mice in their ability to accept allogeneic and xenogeneic grafts. Allogeneic C.B-17/SCID bone marrow cells were engrafted poorly compared with syngeneic C3H/SCID when transplanted into C3H/SCID recipients, whereas cells of both strains were equally well engrafted into C.B-17/SCID mice. C.B-17/SCID mice were much more permissive for outgrowth of human Burkitt lymphoma (Raji), as well as for Epstein-Barr virus lymphoma development after transplantation of human peripheral blood lymphocytes. Human skin grafts were accepted by the C.B-17/SCID mice but were promptly rejected by the C3H/SCID mice. The resistance to human RaJi cells could be adoptively transferred by infusion of C3H/SCID splenocytes into C.B-17/SCID mice. Because the C.B-17/SCID and C3H/SCID mice equally lack both T and B lymphocytes, the latter may provide a relevant model for studies of non-T mechanisms of allograft or xenograft rejection.

Prolongation of survival of rat cardiac allografts by T cell vaccination

Administration of attenuated, activated autoimmune T lymphocytes to syngeneic mice and rats has been shown to prevent or induce remission of experimental autoimmune diseases specific for the autoimmune T cells. The process has been termed "T cell vaccination." In a recent study, T cell vaccination was done using T cells sensitized to rat alloantigens. The procedure produced a significant reduction of the mixed lymphocyte reaction (MLR) against allogeneic cells. The reduction in MLR was not specific: Vaccination with T cells specific for stimulator cells of one allotype led to a reduced MLR stimulated by cells of another allotype. The present study was undertaken to examine whether T cell vaccination can induce tolerance to transplantation antigens in vivo. We used the model of heterotopic cardiac transplantation in rats. We now report that vaccinating rats with syngeneic, activated, alloantigen-primed T lymphocytes significantly prolonged survival of rat cardiac allografts. The effect of T cell vaccination was most evident when the T cells had been obtained from rats specifically sensitized against the donor rats: Brown-Norway (BN) allografts in control Wistar rats survived 8.5 +/- 0.4 d while BN allografts survived 29.2 +/- 7.1 d in Wistar rats that had been vaccinated with Wistar anti-BN cells. Vaccination of Wistar rats with Wistar anti-hooded T cells prolonged survival of BN heart allografts to a lesser but significant degree (13.0 +/- 1.1 d). Thus, T cell vaccination of recipients can prolong survival of allografts.

Suppression of experimental autoimmune diseases and prolongation of allograft survival by treatment of animals with low doses of heparins

The ability of activated T lymphocytes to penetrate the extracellular matrix and migrate to target tissues was found to be related to expression of a heparanase enzyme (Naparstek, Y., I. R. Cohen, Z. Fuks, and I. Vlodavsky. 1984. Nature (Lond.). 310:241-243; Savion, N., Z. Fuks, and I. Vlodavsky. 1984. J. Cell. Physiol. 118:169-176; Fridman, R., O. Lider, Y. Naparstek, Z. Fuks, I. Vlodavsky, and I. R. Cohen. 1987. J. Cell. Physiol. 130:85-92; Lider, O., J. Mekori, I. Vlodavsky, E. Baharav, Y. Naparstek, and I. R. Cohen, manuscript submitted for publication). We found previously that heparin molecules inhibited expression of T lymphocyte heparanase activity in vitro and in vivo, and administration of a low dose of heparin in mice inhibited lymphocyte traffic and delayed-type hypersensitivity reactions (Lider, O., J. Mekori, I. Vlodavsky, E. Baharav, Y. Naparstek, and I. R. Cohen, manuscript submitted for publication). We now report that treatment with commercial or chemically modified heparins at relatively low doses once daily (5 micrograms for mice and 20 micrograms for rats) led to inhibition of allograft rejection and the experimental autoimmune diseases adjuvant arthritis and experimental autoimmune encephalomyelitis. Higher doses of the heparins were less effective. The ability of chemically modified heparins to inhibit these immune reactions was associated with their ability to inhibit expression of T lymphocyte heparanase. There was no relationship to anticoagulant activity. Thus heparins devoid of anticoagulant activity can be effective in regulating immune reactions when used at appropriate doses.