Therapy with donor-derived MR-DCs regulates the antidonor response and prolongs allograft survival in mice. (A) Survival of BALB/c hearts transplanted into B6 mice nontreated or injected intravenously 7 days before transplantation with (1) 5 × 10⁶ donor (BALB/c)-derived MR-DCs, (2) 5 × 10⁶ donor (BALB/c)-derived immature (not MR) DCs, (3) 5 × 10⁶ recipient (B6)-derived MR-DCs, or (4) 5 × 10⁶ third-party (C3H)-derived MR-DCs. (B) Representative images of sections of BALB/c heart grafts, 7 days after transplantation in B6 recipients nontreated or injected intravenously (7 days before transplantation) with donor-derived MR-DCs. The arrow indicates an area with leukocyte infiltration and edema. Hematoxylin and eosin (original magnification ×200). (C) Microscopic analysis and quantification of graft-infiltrating CD4⁺ and CD8⁺ T lymphocytes (as average number of cells per 10 low-powered fields [LPF]) on sections of BALB/c hearts collected 7 days after transplantation in B6 recipients. *Tissue areas detailed in insets. Fluorescence microscopy (original magnifications ×200 and ×400). (D) Assessment of the direct and indirect pathway T-cell responses by IFN-γ ELISPOT assay, 7 days after transplantation, using as responders purified T cells from spleens of naive B6 mice or B6 recipients of BALB/c hearts pretreated (or not) with BALB/c MR-DCs. Data represent 2 or more independent experiments with 3 or more animals per group (mean ± SD shown; values shown for direct pathway).