Role of thymic- and graft-dependent mechanisms in tolerance induction to rat kidney transplant by donor PBMC infusion.

We previously demonstrated the presence of regulatory T cells (Tregs) in lymph nodes (LNs) from rats made tolerant to a kidney allograft by donor peripheral blood mononuclear cell (PBMC) infusion. Here, we investigated the origin of Treg and characterized their phenotype and mechanisms underlying their suppressive effect. At different points after PBMC infusion, thymus, LN, and graft-infiltrating -lymphocyte's (GIL) alloreactivity was evaluated in mixed lymphocyte reaction (MLR), coculture, and transwell experiments. GIL phenotype (by fluorescence-activated cell sorting and immunohistochemistry) and cytokines mRNA expression were analyzed. Before transplantation, CD4(+) thymocytes and LN cells from donor PBMC-infused rats showed a reduced anti-donor but a normal anti-third-party proliferation. Anti-donor hyporesponsiveness was reverted by interleukin (IL)-2. CD4(+) thymocytes had no regulatory activity on a naïve MLR. Treg appeared in LN at 60 days post-transplant. CD4(+)-GIL isolated early (5 days) and late post-transplant (days 60-80) were hyporesponsive and suppressed a naïve MLR. IL-10 mRNA was upregulated in GIL and an anti-IL-10 monoclonal antibody reverted their inhibitory effect. Cell-to-cell contact potentiated the suppressive activity of CD4(+)-GIL. We suppose that allograft tolerance in this model is mediated by pretransplant generation of anergic cells in the thymus, which may have a permissive role to prevent early graft disruption. The healed graft is a source of donor antigens, which led to early selection of Treg. In the late phase, tolerance is maintained by appearance of Treg in LN.

Peripheral donor leukocytes prolong survival of rat renal allografts.

BACKGROUND: The development of strategies to enhance the survival of transplanted organs and to potentially lower or even discontinue immunosuppressive therapy would represent a significant advancement in post-transplant patient care. METHODS: We studied the effect of pretransplant infusion of donor leukocytes alone or in combination with a short course of cyclosporine on the long-term outcome of a rat model of kidney allograft. RESULTS: A single intravenous infusion of donor peripheral blood leukocytes (100x10(6) cells) from Brown-Norway (BN) rats into major histocompatibility complex (MHC) incompatible Lewis recipients largely failed to prolong kidney allograft viability from the same donor transplanted 60, 40, or 30 days after cell infusion. A short course of cyclosporine (per se, unable to prolong graft survival) was started at the same day of donor leukocyte infusion, but instead was able to prolong the survival of the BN kidney transplant-performed 40 days later-but not of a Wistar Furth (WF) third party, with some animals even developing tolerance. A mixed lymphocyte reaction of host cells from long-term surviving rats to BN stimulator cells was significantly reduced as compared with controls. Donor BN DNA was detected in the peripheral blood of Lewis rats until day 40 after BN leukocyte infusion. Microchimerism persisted (60 to 70 days post-transplant) in most long-term graft recipients. Reducing the time interval between donor leukocyte infusion and subsequent kidney transplant to 10 days still prolonged graft survival. Donor peripheral blood mononuclear cells, but not polymorphonuclear cells, in the leukocyte preparation contributed to prolong kidney allograft survival. CONCLUSIONS: Pretransplant donor leukocyte infusion under the appropriate conditions can tip the immune balance toward improved graft acceptance. This result could be relevant to the achievement of donor-specific tolerance of the graft with the maintenance of an intact response to third-party antigens.

Chronic allograft nephropathy in the rat is improved by angiotensin II receptor blockade but not by calcium channel antagonism.

Functional and structural changes of chronic renal allograft failure share similarities with other chronic nephropathies with low nephron number. In models of reduced nephron number, angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers prevented proteinuria and retarded renal lesions. This study investigates whether blockade of angiotensin II activity prevented chronic allograft injury in the Fisher 344 --> Lewis rat kidney transplant model, and compares its effect with that of calcium channel blockers, the main antihypertensive agents used in transplant patients to control BP. Transplanted rats received either no treatment (control), the type 1 angiotensin II receptor antagonist losartan, or the calcium channel blocker lacidipine. Rats received cyclosporine for the first 10 d posttransplant to prevent acute rejection. Doses of antihypertensive drugs were adjusted to achieve a comparable level of BP control throughout the study. Awake systolic BP was comparable in animals given losartan or lacidipine during the 6-mo observation period. Daily treatment with losartan but not lacidipine resulted in a significant decrease in the amount of proteinuria, preserved glomerular and tubulointerstitial structure, and improved graft survival compared with corresponding parameters in control untreated rats. GFR, measured as inulin and p-aminohippurate clearances, respectively, in rats surviving the 6-mo follow-up, was numerically but not significantly higher in losartan-treated animals than in all other groups. Thus, at comparable levels of BP control, losartan but not lacidipine effectively protects animals from chronic allograft injury and allows long-term survival.