Israel Medical Association Journal

Quantitative chimerism testing has become an indispensable tool for following the course and success of allogeneic hematopoietic stem cell transplants. In this paper, we describe the current laboratory approach to quantitative chimerism testing based on an analysis of short tandem repeats, and explain why performing this analysis longitudinally is important and feasible. Longitudinal analysis focuses on relative changes appearing in the course of sequential samples, and as such exploits the ultimate potential of this intrinsically semi-quantitative platform. Such an analysis is more informative than single static values, less likely to be confused with platform artifacts, and is individualized to the particular patient. It is particularly useful with non-myeloablative conditioning, where mixed chimerism is common. When longitudinal chimerism analysis is performed on lineage-specific subpopulations, the sensitivity, specificity and mechanistic implications of the data are augmented. Importantly, longitudinal monitoring is a routinely feasible laboratory option because multiplex STR-PCR[1] kits are available commercially, and modern software can be used to perform computation, reliability testing, and longitudinal tracking in a rapid, easy to use format. The ChimerTrack© application, a shareware program developed in our laboratory for this purpose, produces a report that automatically summarizes and illustrates the quantitative temporal course of the patient’s chimeric status. Such a longitudinal perspective enhances the value of quantitative chimerism monitoring for decisions regarding immunomodulatory post-transplant therapy. This information also provides unique insights into the biological dynamics of engraftment underlying the fluctuations in the temporal course of a patient’s chimeric status.

Background: Recent advances in immunosuppressive therapy have led to a substantial improvement in the outcome of kidney transplantation. Living unrelated donors may become a source of additional organs for patients on the kidney waiting list.

Objectives: To study the impact of combination of calcineurin inhibitors and mycophenolate-mofetile, together with steroids, on outcomes of living related and unrelated transplants. 

Methods: Between September 1997 and January 2000, 129 patients underwent living related (n=80) or unrelated (n=49) kidney transplant. The mean follow-up was 28.2 months. Immunosuppressive protocols consisted of MMF[1] with cyclosporine (41%) or tacrolimus (59%), plus steroids. Patient and graft survival data, rejection rate, and graft functional parameters were compared between the groups.

Results: LUD[2] recipients were older (47.8 vs. 33.6 years) with higher number of re-transplants (24.5% vs. 11.2% in LRD[3] recipients, P < 0.05). Human leukocyte antigen matching was higher in LRD recipients (P < 0.001). Acute rejection developed in 28.6% of LUD and 27.5% of LRD transplants (P = NS). Creatinine levels at 1, 2 and 3 years post-transplant were 1.6, 1.7 and 1.7 mg/dl for LRD patients and 1.5, 1.5 and 1.3 mg/dl for LUD recipients (P = NS). There was no difference in patient survival rates between the groups. One, 2 and 3 year graft survival rates were similar in LRD (91.3%, 90% and 87.5%) and LUD (89.8%, 87.8% and 87.8%) recipients.

Conclusions: Despite HLA[4] disparity, rejection and survival rates of living unrelated transplants under current immunosuppressive protocols are comparable to those of living related transplants.