Manhui Pang

Combined host-conditioning with CTLA4-Ig, tacrolimus, anti-lymphocyte serum, and low-dose radiation leads to stable mixed hematopoietic chimerism

The toxic dose of irradiation required to achieve stable mixed hematopoietic chimerism is the major limitation to its clinical application in transplantation and other nonmalignant conditions such as hemoglobinopathies. This study examines the additive effect of costimulatory blockage, to our previously described tacrolimus-based conditioning regimen, in further reducing the dose of total-body irradiation to achieve stable mixed chimerism in rats. Fully mismatched, 4- to 6-week-old ACI and Wistar Furth rats were used as donors and recipients, respectively. Recipients were administered CTLA4-Ig 2mg/kg/day (alternate days) in combination with tacrolimus 1 mg/kg/day (daily) from day 0 through day +10, anti-lymphocyte serum 10 mg at day +10 (single dose), and total-body irradiation ranging from 100-600 cGy, prior to bone marrow transplantation (day 0) with 100 x 10(6) of T-cell-depleted bone marrow cells. Levels of donor chimerism were determined over a period of 12 months. The short course of CTLA4-Ig, tacrolimus, and ALS led to dramatic engraftments at reduced doses of irradiation: 100% (5/5) and 93% (13/14) of the animals developed mixed chimerism at 400 cGy and 300 cGy, respectively. At 300 cGy, recipients exhibited durable, multilineage mixed chimerism at 365 days with donor cells ranging from 19-42% (mean 23.4%) with no evidence of graft-vs-host disease. These mixed chimeras exhibited in vitro (mixed lymphocyte reaction) and in vivo (skin grafts) donor-specific tolerance. This study suggests that addition of costimulatory blockade to a tacrolimus-based conditioning regimen reduces the dose of irradiation required to achieve stable multilineage chimerism in rats.

A clinically relevant CTLA4-Ig-based regimen induces chimerism and tolerance to heart grafts

BACKGROUND We determined whether a nontoxic CTLA4-Ig-based conditioning regimen effected mixed chimerism and donor-specific tolerance when heart and bone marrow were transplanted simultaneously. METHODS Fully mismatched rat strain combinations were used. Recipients received total-body irradiation (300 centigrays), bone marrow (10(8) cells), and cardiac transplants from the donor on day 0. Subsequently, recipient animals received CTLA4-Ig (2 mg/kg, every other day, x 5 doses), tacrolimus (1 mg/kg/day; days 0 to 9), and one dose (10 mg) of antilymphocyte serum on day 10. RESULTS All bone marrow recipients (n = 7) developed mixed chimerism (mean = 25% +/- 9% at 1 year) and accepted cardiac allografts permanently (> 375 +/- 32 days). Recipients that received conditioning regimen but no bone marrow (n = 5) rejected donor hearts within 51 +/- 13 days (p < 0.01). Recipients that accepted heart grafts also permanently accepted (> 180 days) donor-specific skin grafts, but rapidly rejected (< 10 days) third-party skin grafts. CONCLUSIONS A nontoxic CTLA4-Ig-based conditioning regimen effects mixed chimerism and donor-specific tolerance when heart and bone marrow are transplanted simultaneously. This regimen may have clinical application.

FK409, a Spontaneous Nitric Oxide Releaser, Attenuates Allograft Vasculopathy in a Rat Aortic Transplant Model

Although systemic administration of NO donors has been shown to attenuate the development of neointimal hyperplasia in the balloon injury model, this strategy has not been tested in a model of allograft vasculopathy. In this study, we investigated the effect of FK409, a spontaneous NO releaser, on the development of allograft vasculopathy, using a rat aortic transplant model. Thoracic aortas from ACI rats were transplanted heterotopically into the abdominal aorta of Wistar-Furth rats. Postoperatively, recipients received FK409 orally every 8 hours from the day of transplantation to the time of euthanization. Morphometric and immunohistochemical analyses were performed on the aortic grafts 8 weeks after transplantation. Control allografts showed severe neointimal hyperplasia, which consists mainly of alpha-actin-containing vascular smooth muscle cells. The FK409-treated allografts showed a dose-dependent reduction (statistically significant compared with the control) in the neointimal thickness as the dose increased from 1 to 10 mg/kg (thrice per day). However, there was no significant difference in the neointimal thickness between groups treated with 10 and with 20 mg/kg. FK409 treatment (10 mg/kg) caused a significant decrease in DNA synthesis (5-bromo-2-deoxyuridine [BrdU] uptake), an increase in DNA fragmentation (terminal deoxynucleotidyltransferase-mediated uridine nick-end labeling [TUNEL]), and upregulation of Fas expression, in the neointimal vascular smooth muscle cells. These data suggest that FK409 attenuates the allograft vasculopathy in a rat aortic transplant model.

Aging and transplant arteriosclerosis in absence of alloreactivity and immunosuppressive drugs in a rat aortic model: recipient age's contribution.

Background. Almost half of all transplanted vascularized organ grafts will be lost to transplant arteriosclerosis sometime posttransplantation. Organ shortage for primary transplants and retransplants has led to donor-pool expansion to include elderly donors, knowing that aging per se promotes arteriosclerosis. The current understanding that donor age negatively affects organ and/or patient survival outcome is undermined by variables such as the use of immunosuppressive drugs, their toxicity to the graft, degree of donor-recipient histocompatibility, and the resulting chronic rejection. The purpose of this study was to determine whether the donor’s age or recipient’s age matters the most in transplant arteriosclerosis in the absence of such variables. Methods. A syngeneic combination was used where young (2-month-old) and old (22-month-old) donor aortas were injured to initiate neointimal thickening, then transplanted into age-mismatched recipients for 14, 60, and 90 days and then assessed for neointimal thickening. Base level injury response due ischemia and surgery was evaluated in age-matched and noninjured aortic grafts, respectively. Results. Young aortas invariably developed thicker neointima when transplanted into old recipients than when transplanted into young ones. Correspondingly, old aortas transplanted in young recipients consistently developed less neointimal thickening than when transplanted into old recipients. Conclusions. Our findings strongly suggest that the severity of age-related neointima formation is primarily determined by the recipient’s age rather than the donor’s age. Therefore, in addition to focusing on donor-specific tolerance induction, strategies aiming at increasing the lifespan of vascularized organ grafts also have to take into consideration the recipient’s aging milieu.