MONITORING OF CHIMERISM AFTER ALLOGENEIC BONE-MARROW TRANSPLANTATION WITH UNMANIPULATED MARROW BY USE OF DNA POLYMORPHISMS

Highly polymorphic tandemly repetitive DNA sequences provide powerful genetic markers for the identification of individuals by restriction f ragment length polymorphisms (RFLP) even in close relatives. Over a th ree-year period, 61 consecutive patients from a single institution und ergoing allogeneic bone marrow transplantation (BMT) for various hemat ological diseases were grafted with unmanipulated marrow and followed for the development of hematopoietic chimerism. Three synthetic oligon ucleotide probes homologous to the so-called minisatellite or variable number of tandem repeat (VNTR) sequences were evaluated in the clinic al setting of BMT for their usefullness: (i) to document marrow engraf tment or rejection; (ii) to elucidate the kinetics of mixed chimerism; and (iii) in providing a sensitive tool for early detection of relaps e. In addition, in patients with CML karyotyping and analysis of bcr/a bl gene rearrangement was performed. Using this panel of three oligonu cleotide probes, informative markers specific for donor or recipient R FLP could be demonstrated in all cases. Engraftment could be documente d in all patients surviving beyond day + 14 after BMT. Mixed chimerism was detected in 14% of the patients in the early phase (day + 14 to d ay + 78) after BMT but only one patient turned out to become a long-te rm stable mixed chimera. These results support the hypothesis that lym phocytes of recipient origin surviving the conditioning regimen may co nsiderably contribute to mixed chimerism early after BMT. Long-term st able mixed chimerism is a rare event after BMT with unmanipulated marr ow. Simultaneous analysis of chimerism after BMT by VNTR-RFLP, karyoty ping, and detection of bcr/abl rearrangement in patients with CML show ed corresponding results in nine out of 12 patients. In three patients either one of the methods failed to detect residual recipient cells i n the early phase after BMT. Therefore different methods for assessmen t of mixed chimerism seem to complement rather than to exclude each ot her. Eleven patients who all exhibited complete chimerism early after BMT relapsed from their underlying disease. In seven of these patients grafted for acute leukemia, analysis of DNA-RFLP had been performed s hortly before clinical relapse (30-86 days) and failed to herald relap se. As the sensitivity for the detection of the minor cell population by analysis of DNA-RFLPs is almost-equal-to 1%, these data may indicat e that relapse of acute leukemia after BMT is characterized by a sudde n increase in the percentage of recipient blast cells not detectable e ven by frequent RFLP analyses