ABO-incompatible (ABOi) transplantation is a method of allocation in

organ transplantation Organ transplantation is a medical procedure in which an organ is removed from one body and placed in the body of a recipient, to replace a damaged or missing organ. The donor and recipient may be at the same location, or organs may be transpor ...

that permits more efficient use of available organs regardless of

ABO blood type The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes. For human blood transfusions, it is the most important of the 43 different blood type (or group) classification syste ...

, which would otherwise be unavailable due to

hyperacute rejection Transplant rejection occurs when transplanted tissue is rejected by the recipient's immune system, which destroys the transplanted tissue. Transplant rejection can be lessened by determining the molecular similitude between donor and recipient ...

.West, L. J., Karamlou, T., Dipchand, A. I., Pollock-Barziv, S. M., Coles, J. G., & McCrindle, B. W. (2006). Impact on outcomes after listing and transplantation, of a strategy to accept ABO blood group-incompatible donor hearts for neonates and infants. The Journal of Thoracic and Cardiovascular Surgery, 131(2), 455–461. Schmoeckel, M., Däbritz, S. H., Kozlik-Feldmann, R., Wittmann, G., Christ, F., Kowalski, C., et al. (2005). Successful ABO-incompatible heart transplantation in two infants. Transplant International, 18(10), 1210–1214. Primarily in use in infants and young toddlers, research is ongoing to allow for increased use of this capability in adult transplants. Normal ABO-compatibility rules may be observed for all recipients. This means that anyone may receive a transplant of a type-O organ, and consequently, type-O recipients are one of the biggest beneficiaries of ABO-incompatible transplants. While focus has been on infant heart transplants, the principles generally apply to other forms of solid organ transplantation.ABO Incompatible Heart Transplantation in Young Infants. (2009, July 30). ABO Incompatible Heart Transplantation in Young Infants. American Society of Transplantation. Retrieved from __TOC__

ABO-incompatible transplantation in young children

Because very young children (generally under 12 months, but often as old as 24 months) do not have a well-developed

immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splint ...

,West, L. J., Pollock-Barziv, S. M., Dipchand, A. I., Lee, K.-J. J., Cardella, C. J., Benson, L. N., et al. (2001). ABO-incompatible (ABOi) heart transplantation in infants. New England Journal of Medicine, 344(11), 793–800. it is possible for them to receive organs from otherwise incompatible donors. This is known as ABO-incompatible (ABOi) transplantation. During the initial study period of 1996–2001, allowing for ABOi

heart transplant A heart transplant, or a cardiac transplant, is a surgical transplant procedure performed on patients with end-stage heart failure or severe coronary artery disease when other medical or surgical treatments have failed. , the most common procedu ...

ation reduced infant mortality from 58% to 7%. Graft survival and patient mortality is approximately the same between ABOi and ABOc recipients.Saczkowski, R., Dacey, C., & Bernier, P.-L. (2010). Does ABO-incompatible and ABO-compatible neonatal heart transplant have equivalent survival? Interactive cardiovascular and thoracic surgery, 10(6), 1026–1033. Stewart, Z. A., Locke, J. E., Montgomery, R. A., Singer, A. L., Cameron, A. M., & Segev, D. L. (2009). ABO-incompatible deceased donor liver transplantation in the United States: a national registry analysis. Liver transplantation : official publication of the American Association for the Study of Liver Diseases and the International Liver Transplantation Society, 15(8), 883–893. This was found to not only allow for better allocation of organs among donors, but improved graft ischemia by reducing the time required to transport organs to prospective patients. Children are more likely to be listed for ABOi transplantation if they are UNOS status 1A (i.e. the most critical category.)Almond, C. S. D., Gauvreau, K., Thiagarajan, R. R., Piercey, G. E., Blume, E. D., Smoot, L. B., et al. (2010). Impact of ABO-Incompatible Listing on Wait-List Outcomes Among Infants Listed for Heart Transplantation in the United States: A Propensity Analysis. Circulation, 121(17), 1926–1933. The most important factors are that the recipient not have produced isohemagglutinins, and that they have low levels of T cell-independent

antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune respons ...

s.Burch, M., & Aurora, P. (2004). Current status of paediatric heart, lung, and heart-lung transplantation. Archives of Disease in Childhood, 89(4), 386–389. Studies have shown that the period under which a recipient may undergo ABOi transplantation may be prolonged by exposure to nonself A and B antigens.Fan, X., Ang, A., Pollock-Barziv, S. M., Dipchand, A. I., Ruiz, P., Wilson, G., et al. (2004). Donor-specific B-cell tolerance after ABO-incompatible infant heart transplantation. Nature medicine, 10(11), 1227–1233. Furthermore, should the recipient (for example, type B-positive with a type AB-positive graft) require eventual retransplantation, the recipient may be medically capable of receiving a new organ of either blood type. In the United States, UNOS policies allow for ABOi transplantation in children under two years of age if isohemagglutinin titers are 1:4 or below,Urschel, S., Larsen, I. M., Kirk, R., Flett, J., Burch, M., Shaw, N. L., et al. (2013). ABO-incompatible heart transplantation in early childhood An international multicenter study of clinical experiences and limits. The Journal of Heart and Lung Transplantation, 32(3), 285–292. United Network for Organ Sharing. (2013, January 31). OPTN Policy 3.7 - Allocation of Thoracic Organs. Retrieved from and if there is no matching ABO-compatible (ABOc) recipient, UNOS is considering relaxation of the infant heart transplantation policy such that ABO matching is not a consideration for children under 1 year of age, and if titers are 1:16 or below for children up to age 2.Ghimire, V. (2013, March 7). Proposal to Change Pediatric Heart Allocation Policy. United Network for Organ Sharing. Retrieved from Canadian centers have a heart transplantation policy matching the proposed policy in the United States. Intentional ABOi heart transplantation in infants was conceived in the 1960s by

Adrian Kantrowitz Adrian Kantrowitz (October 4, 1918 – November 14, 2008) was an American cardiac surgeon whose team performed the world's second heart transplant attempt (after Christiaan Barnard) at Maimonides Medical Center in Brooklyn, New York on December ...

,McRae, Donald (2007-08-07). Every Second Counts: The Race to Transplant the First Human Heart (p. 25). Penguin Group. Kindle Edition. with clinical evidence first being shown by Leonard L. Bailey's team in the mid-1980s, which he termed " immunologic privilege."Bailey, L. L., Assaad, A. N., Trimm, R. F., Nehlsen-Cannarella, S. L., Kanakriyeh, M. S., Haas, G. S., & Jacobson, J. G. (1988). Orthotopic transplantation during early infancy as therapy for incurable congenital heart disease. Annals of Surgery, 208(3), 279. It was first conducted in practice in 1996 by a team led by Dr. Lori J. WestKlein, A. A., Lewis, C. J., & Madsen, J. C. (2011). Organ Transplantation: A Clinical Guide. p.116. Cambridge University Press. at the Hospital for Sick Children in

Toronto Toronto ( ; or ) is the capital city of the Canadian province of Ontario. With a recorded population of 2,794,356 in 2021, it is the most populous city in Canada and the fourth most populous city in North America. The city is the anch ...

, and published in a seminal 2001 study.Everitt, M. D., Donaldson, A. E., Casper, T. C., Stehlik, J., Hawkins, J. A., Tani, L. Y., et al. (2009). Effect of ABO-incompatible listing on infant heart transplant waitlist outcomes: analysis of the United Network for Organ Sharing (UNOS) database. The Journal of Heart and Lung Transplantation, 28(12), 1254–1260. In the United Kingdom, policy since 2000 is that ABOi heart transplantation is ''de rigueur'' for infants, and is considered for children under age 4, though proactive measures are often taken to lower titer levels.Roche, S. L., Burch, M., O'Sullivan, J., Wallis, J., Parry, G., Kirk, R., et al. (2007). Multicenter Experience of ABO-Incompatible Pediatric Cardiac Transplantation. American Journal of Transplantation, 0(0), 071117175452003–???

ABO-incompatible transplantation in older children and adults

Limited success has been achieved in ABOi heart transplantation in adults,Tydén, G., Hagerman, I., Grinnemo, K.-H., Svenarud, P., van der Linden, J., Kumlien, G., & Wernerson, A. (2012). Intentional ABO-incompatible heart transplantation: a case report of 2 adult patients. The Journal of Heart and Lung Transplantation, 31(12), 1307–1310. though this requires that the adult recipients have low levels of anti-A or anti-B antibodies. Some organs are more conducive to adult ABOi transplant than others, such as

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

and

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...

.Montgomery, J. R., Berger, J. C., Warren, D. S., James, N. T., Montgomery, R. A., & Segev, D. L. (2012). Outcomes of ABO-incompatible kidney transplantation in the United States. Transplantation, 93(6), 603–609. Adults are significantly likely to suffer from hyperacute rejection,

thrombosis Thrombosis (from Ancient Greek "clotting") is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (t ...

, or

death Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain ...

, but could be considered to be an acceptable risk if the alternative is otherwise death. In the case of ABOi renal transplantation, aggressive antibody removal is required, along with supplemental medication, with the resulting condition being termed "accommodation." While such recipients are more likely to require re-transplantation early on, long-term graft survival is similar to recipients who receive ABOc kidneys.

References

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