Costimulation blockade promotes the apoptotic death of graft-infiltrating T cells and prolongs survival of hepatic allografts from FLT3L-treated donors.
BACKGROUND
Mouse liver grafts are accepted across major histocompatibility complex (MHC) barriers and induce donor-specific tolerance without immunosuppressive therapy. By contrast, hepatic allografts from donors treated with the hematopoietic growth factor fms-like tyrosine kinase 3 ligand (FL), which dramatically increases hepatic interstitial dendritic cells (DC), are rejected acutely (median survival time 5 days). This switch from tolerance to rejection is associated with a marked reduction in apoptotic activity of graft-infiltrating T cells. We hypothesized that T-cell costimulation, provided by markedly enhanced numbers of donor antigen presenting cells (APCs), might inhibit apoptosis, promote expansion of T helper 1 cells and play a key role in acute liver rejection.


METHODS
C3H (H2k) recipients of orthotopic liver grafts from FL-treated B10 (H2b) donors were given cytotoxic T-lymphocyte antigen 4: immunoglobulin (CTLA4Ig), a chimeric fusion protein that blocks the B7-CD28 costimulatory pathway, or control human immunoglobulin (200 microg) on the day of transplantation (day 0). Livers and spleens were removed on day 4. Cryostat sections were stained for interleukin (IL)-12 or by terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL). Expression of mRNA encoding interferon (IFN)-gamma and IL-10 was determined by RNase protection assay. Suspensions of graft-infiltrating cells (GICs) and spleen cells were analyzed for apoptotic (TUNEL+) T-cell subsets by flow cytometry. CTL activity of GICs and circulating alloantibody levels were determined by cytotoxicity assays.


RESULTS
Survival of liver grafts from FL donors was markedly prolonged by CTLA4Ig administration. This effect was associated with reductions in IFN-gamma and IL-10 gene transcripts within the GIC population, and with decreases in donor-specific CTL and NK cell activities and circulating anti-donor alloantibody levels. At the same time, there were marked increases in TUNEL+ CD4+ and especially CD8+ cells, both within the grafts and in the spleens of CTLA4Ig-treated mice.


CONCLUSIONS
Signaling via the B7-CD28 pathway appears to play a key role in the switch from tolerance to rejection that is precipitated by markedly enhanced numbers of donor DCs. Inhibition of acute liver allograft rejection by CTLA4Ig, linked to restoration of apoptotic activity of graft-infiltrating T cells, further suggests that deletion of these cells may be critical for promotion of long-term allograft survival.
Li
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Thomas E. Starzl Transplantation Institute and Department of Surgery, University of Pittsburgh Medical Center, E1540 Biomedical Science Tower, 200 Lothrop Street, Pittsburgh, Pennsylvania, 15213, USA.
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Wang
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Wang
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Fung
J J
JJ
Thomson
A W
AW
Qian
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S
D000069594:Abatacept; D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000494:pharmacology; D017209:Apoptosis; D018122:B7-1 Antigen / Q000502:physiology*; D018106:CD28 Antigens / Q000502:physiology*; D060908:CTLA-4 Antigen; D016207:Cytokines / Q000096:biosynthesis; D006085:Graft Survival; D018796:Immunoconjugates; D007518:Isoantibodies / Q000096:biosynthesis; D016031:Liver Transplantation; D008213:Lymphocyte Activation; D008297:Male; D008565:Membrane Proteins / Q000494:pharmacology*; D051379:Mice; D008815:Mice, Inbred Strains; D013601:T-Lymphocytes / Q000502:physiology*; D014184:Transplantation, Homologous
D015703:Antigens, CD; D000943:Antigens, Differentiation; D018122:B7-1 Antigen; D018106:CD28 Antigens; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; C556707:Ctla4 protein, mouse; D016207:Cytokines; D018796:Immunoconjugates; D007518:Isoantibodies; D008565:Membrane Proteins; C084881:flt3 ligand protein; D000069594:Abatacept