No Harmful Impact of 90Yttrium-Ibritumomab Tiuxetan Combined with BEAM On Bone Marrow Microenvironment.

Recently, Yttrium-90 labeled anti-CD20 (⁹⁰Y-ibritumomab tiuxetan, Zevalin^®) has been introduced as a new therapeutic option in relapsed malignant B cell lymphoma. The results of adding 90Y-ibritumomab tiuxetan to high-dose BEAM with autologous stem-cell transplantation(auSCT) are promising. However, the toxic impact of radioimmunotherapy to the haematopoietic microenvironment, and its effects on stem cell homing and engraftment are largely unknown. Stromal Derived Factor-1 (SDF-1α) is a key regulator of stem cell engraftment. SDF-1α has been found to co-localize with hyaluronan (HA) on human bone marrow sinusoidal endothelium and endosteum, supporting transendothelial migration of human progenitor cells and their final anchorage within specific niches of the BM. External irradiation influences levels of SDF-1α and HA. Therefore, we studied the effect of 90Y-ibritumomab tiuxetan on in vivo SDF-1α and HA levels.

Patients with relapsed B cell NHL, treated with Zevalin-BEAM and autologous stem cell transplantation were included after obtaining their informed consent. At 3 different time points, bone marrow aspirates and peripheral blood samples of 9 consecutive patients were analysed: day -22 (before Z-BEAM), day -8 (7 days after Zevalin (0.4 mCi/kg, max. 32 mCi (n=8) or 64 mCi (n=1) (before BEAM)) and day 0 (after BEAM and before auSCT). SDF-1α and HA protein levels were determined in bone marrow and peripheral blood plasma using ELISA. Also, SDF-1α mRNA expression was quantified by real time PCR. Quality of bone marrow stroma was determined by investigating CFU-F after 1 and 2 weeks and the percentage of confluency in cultures after 1, 2 and 3 weeks. Also, in 5 patients dosimetry of Zevalin was performed.

In 5 patients dosimetry of Zevalin was performed, by using Zirconium-89 labelled Zevalin as surrogate for PET scanning at day 0, +3 and +6 after injection. Patients received 3.4.10 * 6/kg(mean, range 1,9-8,3) CD34+ cells, and all but one showed engraftment. ANC>0.5 10*9/l was reached at 12,8 days (range 11-15, n=9), platelets>50 10*9/l at 18 days (range 11-38, n=8) ), being comparable with retrospective data on BEAM transplantation. In the one patient not recovering, a second transplant did not result in platelet recovery. Zevalin alone did not affect bone marrow MNC count (23,3 vs 17,4 10*6/ml, p=0.40), CFU-F capacity (colonies > 50 cells: 2,4 vs 8,3, p=0.35) and stromal confluency (41,9 vs 62,1%, p=0.31). In addition, the levels of SDF-1α (4584 vs 5305 pg/ml, p=0.11) and HA (227 vs 247 mcg/ml, p=0.86) were not influenced. Following BEAM, production of SDF-1α (4584 vs 6166 pg/ml, p=0.01) and HA levels (227 vs 356 mcg/ml, p=0.03), significantly increased. A corresponding increase in SDF-1α mRNA copies was observed (0.16 vs 17.2 cps % GAPDH, p=0.02), indicating that induction of SDF-1α gene expression was involved. There was a trend in decreased quality of bone marrow stroma, as determined by MNC count, CFU-F capacity and confluency. Whereas Fibroblast Growth Factor increased the confluence of stromal culture before and after Zevalin, it didn't overcome the harmful effect of the BEAM chemotherapy.

90Y-ibritumomab tiuxetan alone did not effect the bone marrow environment as measured by SDF-1α and HA. As expected, significant changes were found after high dose chemotherapy. Engraftment and repopulation after Z-BEAM and auSCT was similar to standard BEAM followed by auSCT.

No relevant conflicts of interest to declare.