Minor histocompatibility antigen peptide–major histocompatibility complex complex (MiHA–MHC complex)

Minor histocompatibility antigen peptide–major histocompatibility complex complexes are molecular assemblies formed when short peptide fragments (typically 9–12 amino acids) derived from polymorphic cellular proteins (MiHAs) are bound and presented by major histocompatibility complex (MHC, or HLA in humans) class I or II molecules on the cell surface. These complexes are recognized by T cells as foreign when there are peptide sequence differences between donor and recipient, even if the major HLA alleles are matched, leading to immunological events such as graft rejection, GVHD, or beneficial GVL effects in allogeneic transplantation. Individual MiHA peptides result from DNA polymorphisms (SNPs, indels, etc.) that alter peptides processed and presented, often conferring unique immunogenicity between participants in transplantation. While primarily of clinical significance in hematopoietic cell transplantation, minor histocompatibility antigens are also implicated in other cellular therapy settings and recurrent miscarriage. Therapeutically, these complexes present a double-edged sword: they can be targeted for beneficial anti-leukemic responses but are responsible for off-target immune-mediated tissue damage if not properly controlled.

Other names

Minor histocompatibility antigen–MHC complexminor H antigen–HLA complexmHAg–MHC complexMiHA–HLA complexminor H antigenmHAgMiHA

Cytotoxic T-cell (CD8+) recognition and lysis of recipient/donor cells expressing non-self MiHA peptides in the context of MHC Induction of targeted adaptive immune response against specific MiHA-derived peptides Exploitation in immunotherapeutic settings to selectively attack malignant hematopoietic cells while sparing non-hematopoietic tissues when suitably tissue-restricted minor H antigens are present