Israel Medical Association Journal

Myelodysplastic syndrome (MDS) is frequently associated with clinical manifestations of autoimmune disorders (AD) and inflammatory responses of the immune system. The biological linkage between MDS clones and the occurrence of autoimmune manifestations is mirrored by the response of the latter to MDS modifying therapeutic approaches [1]. We encountered a rare case of MDS coexisting with antiphospholipid syndrome (APS), which was effectively treated with a hypomethylating agent followed by allogenic bone marrow transplantation.

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.

In recent years, umbilical cord blood has emerged as an alternative source of hematopoietic progenitors (CD34+) for allogeneic stem cell transplantation, mainly in patients who lack an human leukocyte antigen-matched marrow donor. Since 1998, about 2,500 patients have received UCB[1] transplants for a variety of malignant and non-malignant diseases. The vast majority of recipients were children with an average weight of 20 kg, however more than 500 UCB transplantations have already been performed in adults. The “naive” nature of UCB lymphocytes may explain the lower incidence and severity of graft versus host disease encountered in UCBT[2] compared to the allogeneic transplant setting. Furthermore, UCB is rich in primitive CD16^-CD56⁺⁺ natural killer cells, which possess significant proliferative and cytotoxic capacities and can be expanded using interleukin-12 or 15, so as to mount a substantial graft versus leukemia effect. The major disadvantage of UCB is the low yield of stem cells, resulting in higher graft failure rates and slower time to engraftment compared to bone marrow transplantation. A rational approach thus involves ex vivo expansion of UCB-derived hematopoietic precursors.