Chimerism does not influence graft-versus-myeloma and graft-versus-host disease in reduced intensity setting

In this study we serially evaluated the chimerism status in 20 multiple myeloma patients allotransplanted with a reduced intensity regimen. All patients engrafted, with total 75% overall responses and 35% of CRs. After a median follow-up of 35 months, seven patients (35%) died, three of them due to disease progression. Four patients died before day +100, with a TRM of 20%. Nine patients (45%) developed aGVHD and six (40%) had cGVHD. Twenty-five percent of patients achieved full donor chimerism (FDC) before day +100, 42% before day +200 and 75% 24 months after graft. In our series, level of chimerism did not correlate with either the quality of response or aGVHD. No significant differences were found between bone marrow and peripheral blood samples. Analogously, even if donor DNA percentage often resulted higher in the PMN fraction than in the mononuclear one, these differences were not significant after statistical analysis. On the other hand, cGVHD was associated with increased rates of FDC, with 6/6 cases showing a full donor pattern in concomitance of the cGVHD versus 5/9 cases presenting a FDC in the group of patients without cGVHD (p=0.057). The Kaplan-Meier estimates of OS and PFS at 2 years were 59% and 58%, respectively; chimerism pattern did not impact in the predicting clinical outcome. In summary, our study shows that a stable engraftment and high frequency of donor chimerism are achievable after a reduced intensity conditioning regimen. Moreover, even as result of a single center experience, we suggest that chimerism, graft-versus-myeloma and GVHD would represent distinct entities that require larger immunological studies for further clarification.