ABO-incompatible renal transplant at ease

Balaji Kirushnan

Consultant Nephrologist, Kauvery Hospital, Chennai, India

Background

The shortfall between organ donors and kidney transplant recipients is ever-growing. The number of patients waiting on a deceased donor renal transplant program is increasing every year according to the UNOS data. To overcome this deficit, strategies like ABO-incompatible renal transplantation, paired kidney exchange program, SWAP transplants are performed at various centres. ABO-incompatible transplants have been performed worldwide since 1982 in countries like Japan, Belgium, and United States. It increases the chance of organ donation by 30%. It has been in practice for more than three decades now. The overall outcomes for ABO-incompatible renal transplantation have been reported to be equal to that of ABO compatible renal transplants. Recent meta-analysis reports however report an increased incidence of acute cellular rejection in them. Recipients require preoperative desensitization with B cell depleting therapies, antibody removal, and potent immunosuppression. This involves the risk of emergence of opportunistic infections to the recipient

Case Presentation

A 19-year-old male patient had a history of knocked knees which was detected by March 2020. On evaluation, he was found to have severe renal failure and contracted bilateral kidneys. In view of severe azotaemia, he was initiated on hemodialysis through a right-side perm catheter. He was evaluated for renal transplant with his mother as a prospective donor. He was B positive by blood group. Mother was AB positive. The Ant A titre preoperatively was 1:4 IgG and 1:2 IgM. The blood group subtype for the mother was A2B positive. HLA match was 6/6. CDC was negative. The patient received 2 doses of Inj Rituximab 200mg IV 2 weeks and 1 week before the date of transplant. He was started on triple immunosuppression namely Prednisolone 0.5 mg/kg, Tacrolimus 0.05 mg/Kg/dose, Mycophenolate Moeftil 500 mg twice a day. Plasmapharesis was not done as he had negligible titres. The patient underwent renal transplantation on 21/12/2021. He had a normal renal function and good urine output in the immediate post-transplant period. He was discharged 5 days after the transplant.

Discussion

Normal ABO-incompatible renal transplant patients need to be on a desensitization regimen to remove the existing Anti A or Anti B antibodies. This is achieved by plasmapheresis or Immunoadsoprtion which removes the pre-existing antibodies and Rituximab to prevent further antibody production. The patients are immunosuppressed even before the transplant due to the above medication posing them at risk of acquiring secondary infection. In this patient, we did not do plasmapharesis as the baseline anti-A titres itself was 1:4 only. This was a boon to the patient requiring only Rituximab and standard transplant medications. Later in the post-transplant scenario, the donor kidney will be expressing A2B and A2 is less antigenic than A1. Hence there is less chance of antibody rebound with A2 as compared to the A1 blood group.

This patient had a 100 percent HLA match with his mother on tissue typing. Tissue typing is a test that identifies a genetic background of an individual. There are 2 sets of 3 antigens (A, B, and DR) and each set is derived from one parent. HLA A, B, and DR are the most frequently typed HLA antigens as they are highly polymorphic. The child will have 3 antigens (A, B, and DR) and each set is derived from one parent. This patient had all 6 antigens match. The child matches to only 3 antigens of the parent, which is the normal scenario and there will be 3 antigens that are different between child and parent. The father and the mother of the patient were close relatives and they shared 3 common antigens. So, the boy had 100% HLA tissue typing match due to his parents having the phenomenon of consanguinity. 100% HLA Matching is also the situation seen in Identical twins or monozygotic twins. Monozygotic/identical twins do not require long-term immunosuppression due to 0 HLA mismatches. But in our patient although HLA matched 100%, non-HLA antigens may still trigger transplant rejection, hence he was maintained on triple immunosuppression at the lowest possible dose.

Dr. Balaji Kirushnan

Consultant Nephrologist

ABO-incompatible renal transplant at ease