article and how Dr. Merril and Dr. Murray concluded that they were identical. They performed a full-thickness skin graft on the recipient and 31 days later a histological examination of the skin graft indicated no rejection and these observations among other clinical findings lead the investigators to conclude that they were monozygous twins and rejection would be unlikely. No HLA typing existed at that time. Surgery was successful and Mr. Herrick lived for 9 years after the transplant without receiving any maintenance immunosuppression. He later died secondary to a myocardial infarction. The side effects of immunosuppression (IS) is a constant battle for nephrologists and finding a sweet spot on maintaining adequate IS to prolong graft survival and avoiding side effects is almost impossible to achieve.
A few days ago we took care of a 72 year-old female that underwent living donor kidney transplantation from her identical twin. Prior to surgery there was a discussion whether the recipient should get any induction and maintenance IS. She was a 0/6 HLA mismatch and genetic testing using PCR-based Short Tandem Repeats (STR) analysis indicated they were identical for the 16 different polymorphic gene loci that were evaluated and because she was elderly and highly functional she was at a low immunological risk.
Monozygous twins come from a single ovum fertilized by one sperm, and recent studies have shown that monozygous twins are not genetically-related due to the phenomenon of somatic variation, which can arise from three different mechanisms: somatic mosaicism, chimerism and epigenetic drift.
Somatic mosaicism occurs in early embryo development and results in tissues having varying genetic expression arising from a single zygote (think about the Rubik’s cube) through numerous mechanisms such as heteroplasmy (unequal division of mitochondrial DNA within the cellular cytoplasm) and uniparental disonomy (where both copies of a chromosome or genomic region are inherited from a single parent) Chimerism arises when new genetic material is introduced from an exogenous source such as maternal cells entering fetal circulation or between two embryos in multiple pregnancies. Epigenetic drift is the result of genetic alterations that have been accumulated throughout life as a result of the interaction of genes and environment (early in utero and lifestyle).
So, should monozygous twins receive any induction or maintenance IS? First of all, there are no randomized controlled trials addressing this question and there have been only a few reports where patients received minimal or no immunosuppression. In this article, the authors reported 194 probable identical twin transplants. Seventy percent of the cases received steroids as induction and 71% were discharged with some form of IS therapy. At one year post-transplant, 21% of recipients were receiving calcineurin inhibitors and 27% were on steroids. By one year post-transplant, 66% percent of recipients were not on any form of IS. Recipients off IS, tended to be younger, White, and had a cold ischemia time of less than 12 hours.
In regards to rejection rates in kidney transplantation in identical twins in the US and United Kingdom during 1988 and 2004, the authors reported 120 cases in the US and 12 cases in the UK and they concluded that there was no significant difference in graft survival between recipients that are received IS and those who did not. In addition, they also reported no differences on cases that had maintenance IS for possible recurrence disease in comparison to those recipients at low risk for recurrence disease.
In another series of 5 cases in a single center between 1969 and 2013 in Spain of kidney transplantation between monozygotic twins, the investigators reported good outcomes at one and five years. Recipients received only a single dose of high dose steroids intraoperatively and no maintenance IS. Of this five cases, two recipients died (from cardiovascular disease and melanoma) after 16 and 22.5 years post-transplant, respectively. One patient was lost to follow up and the two remaining were still alive.
DAMPs (damage-associated molecular patterns), among other chemokines, are released during ischemia-reperfusion injury and cellular stress during organ recovery which may modify gene expression after transplant, so using high dose perioperative steroids as induction therapy to suppress this response is a good approach. The somatic variation phenomena described in monozygotic twins should also be considered since they are not strictly identical. In conclusion, once the immune system has been adequately suppressed after the initial inflammatory response related to kidney transplantation surgery, the next step would be to attempt reducing or withdrawing maintenance IS very cautiously considering postoperative course, primary disease and pathological graft findings. Our patient received only high dose steroids as induction IS.
Image from Bioinfoworld