Transplantation of ABO A2 kidneys into O recipients: do IgM anti‐A1 titers matter?

Abstract

Our data show a high incidence of early acute rejection or thrombotic microangiopathy in A2 to O kidney transplants with high recipient anti-A IgM titers despite low IgG titers. Steps to lower anti-IgM pre-transplant may reduce the risk of early allograft dysfunction in A2 to O or B kidney transplants. Attention should be paid to IgM titers in establishing individual center selection criteria for A2 to B kidney transplants under the new UNOS kidney allocation system.

Kidney transplantation across minor ABO incompatibility: the use of A2 to B transplants

“…patients with high titer IgM, one had acute cellular rejection and two others had findings consistent with antibody-mediated rejection (thrombotic microangiopathy with c4d positivity). This compared with only a single patient who demonstrated rejection among the low IgM group [18]. It is worth noting that this study did have an unusually high rate of rejection (four of seven total patients) and was exclusively in blood group O recipients, so many centers doing A2 to B transplants still primarily rely on IgG titers.…”

“…The early MTN experience reported, however, that it was IgG titers rather than IgM titers that were predictive of outcomes [29,30]. However, some centers have restricted patients with higher IgM titers as well [16,18]. In the most recent report, outcomes of a seven patient case series were reported and analyzed with respect to pretransplant IgG and IgM titers.…”

“…The use of measuring anti-A 1 vs. anti-A 2 titers in potential recipients for determining eligibility for A 2 to B transplantation has been an ongoing question. Early studies, which considered the A 2 phenotype to be primarily defined by decreased expression of a common A antigen used A 1 titers for determining eligibility [15][16][17][18][19][20]. Others, considering the A 2 antigen to be qualitatively different (based on its different selection of core chains), have used A 2 titers for their patients [20][21][22][23][24].…”

A2/A2B to B kidney transplantation outcomes: A single center 7‐year experience

“…24 Our lab has chosen to measure anti-A1 titers. 8,13 From a clinical perspective, we know that the A1 antigen is more immunogenic than the other A, non-A1 antigens, since the A, non-A1 subtypes have a lower density of N-acetylgalactosamine, the immunodominant A antigen sugar. We also know there is a divergent group of molecules assigned to the "A2" or A, non-A1 subtype, so measuring just anti-A2 titers does not represent all the minor A subtypes.…”

“…7 However, early studies showed there is a correlation between high pre-transplant anti-A titers and allograft loss. [8][9][10][11][12] The addition of preferential allocation of A2/A2B donor kidneys to B recipients in the kidney allocation system (KAS) instituted by the United Network for Organ Sharing (UNOS) in 2014 was meant to improve organ access and reduce wait time for B recipients, the majority of whom are minorities. We previously published our center's three-year experience with A2/A2B kidney transplants.…”