Immunological Shift On Day 15 of Remission Induction in Children with CD10-Positive B-Cell Precursor ALL Treated by ALL-MB 2008 Protocol.
Authors: Popov Alexander , Verzhbitskaya Tatiana , Tsaur Grigory , Shorikov Egor , Saveliev Leonid , Fechina Larisa 
Published: October 2019

Abstract
Abstract 2650
Poster Board II-626

Statement.
Flow cytometric (FC) minimal residual disease (MRD) monitoring during remission induction is a strong tool for prediction of outcome in children with acute lymphoblastic leukemia (ALL) of B-cell precursor (BCP) origin. Antigens' expression changes during treatment. Immunological shift can significantly complicate MRD detection. Immunophenotypical changes could vary during antileukemic treatment.

Aim.
To compare CD19, CD10, CD34, CD20, CD45 and CD58 expression at diagnosis and on day 15 of remission induction of currently applied ALL-MB 2008 treatment protocol and to evaluate significance of this changes for FC MRD monitoring.

Patients and methods.
Since November 2008 till July 2009 38 cases of childhood ALL were enrolled onto ALL-MB 2008 trial in Pediatric Oncology and Hematology Center in Ekaterinburg. Among them 22 patients were selected for present study as they fulfilled following criteria: had CD10-positive BCP-ALL and were MRD-positive ≥ 10−4 on day 15. MRD detection in bone marrow was performed by 9-color FC. We compared mean fluorescence intensity (MFI) values at diagnosis and on day 15. We also analyzed changes in CD19, CD20, CD45 and CD58 expression by normal B-lymphocytes on day 15 because at this time-point B-lineage regeneration is absent in bone marrow and MRD has to be discriminated only from mature B-cells. Coefficient of variation (CV) of fluorescence intensity and percentage of positive cells were used for evaluation of cells' distribution changes.

Results.
At diagnosis we found significant differences in antigen expression between tumor cells and B-lymphocytes. CD10, CD34, CD58 overexpression and CD19, CD20, CD45 underexpression by leukemic blasts were noted. On day 15 CD10, CD34 and CD58 were downmodulated (p = 0,0030, p = 0,0007 and p = 0,0017 respectively) while CD19, CD20 and CD45 were upmodulated (p = 0,0033, p = 0,0273 and p = 0,0001 respectively). At the same time CD20, CD45 and CD58 expression by mature B-lymphocytes decreased (p = 0,0013, p = 0,0130 and p = 0,0067 respectively) while CD19 was stable (p = 0,1060). Hence malignant and normal cells became closer on dot plots. On day 15 significant differences in CD10, CD34, CD20, CD45 and CD58 between blasts and lymphocytes were still presented. CD19 expression by leukemic cells on day 15 became higher than by mature B-cells (median MFI = 20284, range1587-34505 and median MFI = 15823, range 811–30882, p = 0,0196). Cells' distribution by CD10 and CD34 became more heterogeneous (p = 0,0364 and p = 0,0008 respectively), CD45 expression became more homogeneous (p = 0,0003) while CD20 and CD58 expression CV didn't change significantly (p = 0,1913 and p = 0,3443 respectively). CD20- and CD45-positive cells' percentage increased (p = 0,0015 and p = 0,0002 respectively) and CD34-positive cells' percentages decreased (p = 0,0003).

Discussion.
Changes in antigens' expression could complicate MRD detection so far as they decrease immunophenotypical differences between tumor blasts and mature B-lymphocytes. Interestingly, disparity of our results and previously shown data was found. Differences in immunological shift could be partially explained by differences in induction intensity of ALL-MB 2008 and international protocols.

Conclusion.
Significant immunological shift occurred on day 15 of ALL-MB 2008 remission induction. These antigens' expression changes have to be taken into account by the researcher for the successful FC MRD monitoring.

Disclosures:
No relevant conflicts of interest to declare.