Bidirectional recognition of donor- and recipient-derived immunocompetent cells has been proven to play a pivotal role for the induction of long-term unresponsiveness to allogeneic grafts. This study investigated the fate of heterotopic heart grafts with respect to the timing of subtherapeutic doses of FK-506 and with respect to the time point and type of donor antigen application, leaving space for mutual adaptation of alloreactive lymphocytes, designated as the 'WOFIE-concept' (window of opportunity for immunological engagement), originally described by R Calne.
Methods: Heterotropic heart transplantation was performed using male DA (RT1.a) donor and LEW (RT1.1) recipient rats in the following groups (n = 6). FK-506 was applied intramuscularly (i.m.) using doses of 2 mg/kg x body weight per day. Donor antigen application was performed either by DA blood transfusion, 2 ml intravenously (i.v.), or by i.v. transfusion of 5 x 10(7) DA splenocytes. (i) LEW --> LEW, untreated; (ii) DA --> LEW, untreated; (iii) DA --> LEW, FK-506 days 0, 4-7; (iv) DA --> LEW, FK-506 as group (iii) plus 2 ml of DA blood 6 h post-Tx; (v) same as group (iv) but DA blood transfusion 24 h post-Tx; (vi) DA --> LEW, FK-506 as group (iii) plus DA splenocytes 6 h post-Tx; (vii) same as group (vi) but DA splenocyte transfusion 24 h post-Tx; (viii) DA --> LEW, FK-506 days 0-4 and (ix) DA --> LEW, FK-506 as group (viii) plus DA blood 6 h post-Tx. Immunohistochemical stainings (APAAP-method) of the allografts and flow cytometric analysis of recipient spleens were performed electively 3, 7 and 14 days after organ reperfusion.
Results: The mean graft survival differed significantly between groups and comprised (mean +/- SD days): (i) >100, (ii) 6.5 +/- 1.0, (iii) 31.6 +/- 12.1, (iv) 44.8 +/- 10.1, (v) 29.8 +/- 14.2, (vi) 27.2 +/- 4.7, (vii) 14.6 +/- 4.2, 17.5 +/- 4.2, (viii) 17.5 +/- 4.2 and (ix) 18.8 +/- 2.8 days. Prolongation of graft survival and long-term unresponsiveness (group iv) revealed a substantially different pattern of graft infiltration.
Conclusions: Effective treatment with unspecific immunosuppressants like FK-506 can be substantially improved if (i) mutual antigen recognition between donor and recipient immunocompetent cells is warranted, (ii) donor-derived blood-borne antigens are given immediately after graft reperfusion, and (iii) the type of inoculated donor antigen has a strong impact on graft survival as splenocytes which contain a large population of professional antigen-presenting cells failed to prolong graft survival after interrupted FK-506 treatment.