Chart showing HLA allele duplication and type of match between donor and recipient: an allele match (0201 and 0401 for both donor and recipient); a mismatch (0201 for both donor and recipient and 0201 for donor, 0401 for recipient) shown by an arrow pointing in a direction that promotes GVHD (GVH-O); a mismatch (0201 for both donor and recipient and 0401 for donor, 0201 for recipient) shown by an arrow pointing in a direction that promotes rejection (R-O); and a bidirectional mismatch (0201 for donor, 0301 for recipient, and 0401 for both  donor and recipient) shown by arrows pointing in two directions, a direction that promotes rejection (R-O) and a direction that promotes GVHD (GVH-O).
Figure 2. HLA allele duplication in a donor or recipient results in a “half” match and a mismatch that will either occur in a direction that promotes GVHD (GVH-O) or a direction that promotes rejection (R-O).