Allograft

An allograft is a transplant of tissue between genetically non-identical members of the same species. It contrasts with autografts (tissue from the same individual), isografts (genetically identical individuals, such as identical twins), and xenografts (between different species). Allografts are used in a variety of settings, including organ transplantation, bone and tendon grafting, skin grafts, and corneal transplantation. Donor tissue can come from cadaveric sources or living donors, including related or unrelated individuals.

Immune response and rejection are central to allografts. Because donor and recipient differ at major histocompatibility complex antigens, the recipient’s immune system may reject the graft. Rejection can be hyperacute, acute, or chronic, reflecting different immune mechanisms. Management relies on immunosuppression to suppress T-cell– and antibody-mediated responses. Common strategies include calcineurin inhibitors (such as cyclosporine and tacrolimus), antiproliferatives, steroids, and targeted biologics. Pre-transplant testing, including HLA typing and crossmatching, reduces risk and helps guide donor selection.

Outcomes and considerations vary by tissue type and degree of mismatch. Corneal and some skin allografts can have favorable outcomes, while solid organ and bone allografts typically require lifelong immunosuppression and monitoring for infection, malignancy, and drug toxicity. Ethical, logistical, and donor-recipient compatibility factors influence the availability and success of allografts in clinical practice.