[Adenovirus-mediated CTLA4-FasL gene transfer induces long-term survival of cardiac allograft in rats]

Abstract

Objective: To investigate the potential of exogenously expressed CTLA4-FasL in inducing transplantation tolerance using rat cardiac graft model and its related mechanisms.

Methods: The heart allograft of DA rat was placed in the abdomen of LEW rat, and adenoviruses containing CTLA4-FasL gene (AdCTLA4-FasL) adenovirus containing CTLA4Ig, and AdEGPP were infused at a dose of 5 x 10(9) pfu/ml via portal vein in different recipients respectively immediately after the operation. DA-->LEW cardiac graft controls and syngeneic LEW-LEW cardiac graft controls were used. The survival of cardiac allografts was monitored by daily palpation. The total cessation of beating was defined as rejection and was confirmed by histology. The serum level of CTLA4-FasL was measured via ELISA. The tolerance mechanisms were investigated with adoptive transfer, mixed lymphocyte reaction (MLR), IL-2 reverse experiment, determinations of frequencies of HTLp and CTLp, and analysis of the polarization of TH1/TH2 type cytokines using RT-PCR.

Results: The survival of DA allografts were prolonged significantly in LEW recipients receiving AdCTLA4-FasL with a mean survival time of 71.0 +/- 23.7 d (n = 6), significantly longer than those of the untreated recipients (5.7 +/- 0.5 d, n = 6), AdEGFP-treated recipients (5.2 +/- 0.4 d, n = 6) and AdCTLA4Ig-treated recipients (45.7 +/- 12.4 d, n = 6) (call P < 0.05). Prolonged expression of serum CTLA4-FasL was shown in AdCTLA4-FasL-treated rats. Splenocytes of LEW recipients with long-term surviving cardiac allograft displayed donor-specific hyporesponsiveness, which could not be reversed in the presence of exogenous added IL-2 in MLR. Frequencies of HTLp and CTLp were significantly reduced. The polarization of TH1/TH2 type cytokines was not shown.

Conclusion: Adenovirus-mediated CTLA4-FasL gene transfer renders prolonged therapeutic expression of CTLA4-FasL in LEW recipient rats, leading to long-term survival of cardiac allografts. The induced tolerance is donor-specific, and may result from regulatory T cells and the deletion of alloreactive T cells. However, T cell anergy and the deviation of TH1/TH2 type cytokines may not be the involved mechanism, at least when tested.