The most potent risk factor for GvHD is disparity in HLA alleles between the recipient and donor. Some risk factors depend on demographics of the recipient and donor.

Risk factors for GvHD include:

• High degree of HLA disparity between host and donor cells^[1]
• Use of unrelated donors as the stem cell source^[1]
• Total body irradiation as the conditioning regimen prior to transplant^[1]
• Prior acute GvHD^[2]
• Use of peripheral blood stem cells^[2]
• Use of a T cell replete graft^[2]
• Viral infection, since this can contribute to immune activation^[2]
• Male host^[2]
• Multiparous female donor^[2]

Protective factors include:

• High degree of HLA concordance between the host and donor
• Use of umbilical cord blood as the donor source (given decreased number of donor T cells)