halfmatching

Halfmatching, or half-matching, is a term used in genetics and medicine to describe partial genetic compatibility between two individuals. In practice, it denotes sharing one of the two parental haplotypes, resulting in a partial match across many loci. The concept is especially relevant to human leukocyte antigen (HLA) matching in hematopoietic stem cell transplantation and, less commonly, in solid organ transplantation.

In hematopoietic stem cell transplantation, a half-match typically refers to a haploidentical donor who shares one haplotype with the recipient. Such donors are often a biological parent or child, providing a readily available source when a fully matched donor cannot be found. Full compatibility is usually described as 8/8 or 10/10 at key HLA loci, depending on the matching panel used; a half-match falls short of these criteria.

Clinical considerations include the balance between donor availability and transplant-related risks. Half-matched transplants can carry higher risks of graft-versus-host disease (GVHD), graft failure, and infectious complications due to immunosuppressive therapies. Contemporary strategies, such as post-transplant cyclophosphamide, targeted T cell depletion, and refined donor selection, aim to mitigate these risks and expand the pool of usable donors.

Outside hematopoietic stem cell transplantation, half-matching concepts can influence solid organ allocation and immunogenicity assessments when exact matches are unavailable. Overall, halfmatching describes a pragmatic compromise that enables access to therapy while recognizing elevated immunological risk relative to full matching.

See also: HLA matching, haploidentical transplantation.