ABSTRACT
This study examined the survival of orthotopic, vascularized, osteochondral allografts,
following 12 weeks of immunosuppression and transfer into a naive, allograft host
up to 14 weeks later, and compared the results with those previously reported for
similar grafts in a heterotopic position. Knee-joint allografts between DA (donor)
and Lewis (recipient) rat strains were assessed by quantitative histology up to 6
months after transplantation, and graft microcirculation was examined by India-ink
infusion. Graft repopulation was assessed by re-transferring the graft to a naive,
non-suppressed allograft host 12 to 26 weeks after the initial transplantation. Isografts
survived for as long as grafts were examined (6 months) and showed good healing of
the graft/host bone junction, although long-term isografts showed some deterioration
of the growth plate. Non-suppressed allografts rejected within 2 weeks. Allografts
in hosts immunosuppressed for 12 weeks remained healthy and healed in a similar manner
to the isografts. Following cessation of immunosuppression, allografts progressively
deteriorated, with mononuclear cell infiltration apparent in graft bone marrow and
muscle in the later stages examined. Transfer to second non-suppressed hosts resulted
in rapid rejection of the allografts, indicating that, as shown previously in heterotopic,
osteochondral allografts, little or no graft repopulation by host-derived cells had
occurred during the protected period in the first host.
