ABSTRACTS – ORAL PRESENTATIONS - AMCA, spol. s r.o.

(EXBIO, clone MEM-63). The immunophenotype of the leukemic cells were identified at
diagnosis by 5-color panels. The MRD detection at day 15 was carried out according to
the ALL IC-BFM 2009 flow cytometric MRD protocol. In the control bone marrows the
precursor B-cells were gated by their CD19, CD45, CD10, FSC and SSC parameters.
Using the median CD58 MEFL values of the leukemic population the 3 groups of samples
were compared by Mann-Whitney U test and ROC analysis was performed.
In agreement with previous studies we found significant difference (in average 6.3 times
overexpression) between diagnostic samples (mean MEFL= 7109) and control bone
marrows (mean MEFL=1127). However in the day 15 samples we found a decrease
compared to the diagnostic values in most (16 of 17) cases (mean MEFL=3494). The
relative intensity decreased in 11 of 17 cases below 50% of the original value. We tried
to define cut-off values to separate CD58 overexpressed samples. The best cut-off value
for the day 15 samples was 1367 but with significantly lower specificity (81.8%) and
sensitivity (70.6%) compared to the excellent cut-off value (MEFL=2741, specificity: 100%
and sensitivity: 95.2%) of the diagnostic samples. When applying the higher original cutoff
to the day 15 samples the results show no overexpression of CD58 in more than half
of the patients.
In contrast with previous studies we found a remarkable decrease in the CD58 expression
during the induction phase of the ALL IC-BFM 2009 treatment protocol at day 15. In conclusion,
due to its downregulation, CD58 should be treated with caution as an MRD marker to
avoid underestimation of residual leukemic cells in day 15 p-B-ALL bone marrow samples.
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