In B-cell acute lymphoblastic leukemia (B-ALL), a measurable residual disease (MRD) level of <0.01% after remission induction therapy is an important prognostic factor. Regardless of the timing of measurement, the lower the MRD, the better the prognosis; however, the risk of relapse can vary due to multiple factors, such as immune phenotype, chromosomal analysis findings, and genetic mutations. In addition, there are various measurement methods, each with its own advantages and disadvantages. One of these methods, multicolor flow cytometry (MCFCM), although somewhat less sensitive than others, is relatively inexpensive, quick, and can be utilized even in the absence of specific genetic abnormalities, making it applicable to a wide range of cases. In recent years, it has been reported that the prognosis may differ based on the presence of CD antigens. We therefore analyzed pre-transplant MCFCM in adult patients with B-ALL and identified factors related to prognosis.

The present study included 39 consecutive patients with B-ALL who underwent allogeneic hematopoietic stem cell transplantation at Osaka Metropolitan University Hospital between January 2014 and December 2019. Pre-transplant bone marrow samples were subjected to MCFCM using a Gallios® flow cytometer (3 laser, 10 color; BECKMAN COULTER) to evaluate the MRD with two panels. The antibodies used were CD45-APC-A700, CD19-ECD, CD10-APC-A750, CD34-APC, CD13-PC7, CD33-PC5.5, CD65-FITC, CD66c-PE, CD21-PB, CD56-BV510, CD58-PE, CD11c-PC7, CD20-FITC, CD3-PB, and CD38-BV510. Leukemia-associated immunophenotypes and different-from-normal approaches were used to identify leukemia cells, and antigen expression ratings were evaluated according to the AIEOP-BFM consensus guidelines.

The median patient age was 44 (range, 19–66) years old. The analysis included 39 cases, with a 5-year overall survival (OS) of 55.4% (36.9%-70.6%), a 5-year relapse-free survival (RFS) of 30.6% (17.0%-45.2%), a 5-year cumulative incidence of relapse (CIR) of 54.1% (36.9%-68.5%), and a 5-year non-relapse mortality (NRM) of 15.4% (6.1%-28.5%). In the hematological complete remission (CR) cases (31 cases), when classified by MRD levels of <0.1%, 0.1%-1%, and >1%, the group with >1% (2 cases) experienced relapse or death within 1 year. For the groups with <0.1% (18 cases) and 0.1%-1% (11 cases), the 5-year OS rates were 70.5% (42.8%-86.6%) and 68.2% (28.6%-88.9%), respectively, while the 5-year RFS rates were 44.4% (21.6%-65.1%) and 36.4% (11.2%-62.7%), respectively, and the 5-year CIRs were 33.3% (12.9%-55.5%) and 54.5% (20.3%-79.4%), respectively. In addition, an examination of the relationship between MRD levels and CD66c revealed that the median MRD level was 0.972% for CD66c-positive patients and 0.101% for CD66c-negative patients (p = 0.0127). The 1-year CIRs were 50.0%(2.3%-88.1%) for CD66c-positive patients and 17.6%(4.1%-39.0%) for CD66c-negative patients (p = 0.0186).These results indicate that in B-ALL, even in CR, the presence of ≥1% leukemia cells was associated with a poor prognosis almost equivalent to that in non-CR cases. In terms of prognostic differences based on CD expression profiles, CD66c-positive B-ALL patients showed a significantly higher MRD level and exhibited higher CIR than CD66c-negative B-ALL patients, suggesting that the expression of CD66c may be a negative prognostic factor. CD66c expression was observed in 4 out of 21 (19%) CR patients with MRD ≥0.01%, and in 6 out of 8 (75%) non-CR patients (data not shown). The CD66c, carcinoembryonic antigen-related cell adhesion molecule 6(CEACAM6) has been found to be associated with the SRC/FAK/PI3K/AKT pathways in various cancer types and may be associated with chemoresistance in CD66c-positive B-ALL. Using MCFCM, MRD levels can be evaluated at each stage of treatment, allowing prognosis prediction based on MRD depth. Although the present study was conducted just before transplantation, the surface marker CD66c was identified as a poor prognostic factor and was associated with increased CIR. We believe that B-ALL patients with CD66c expression should undergo more aggressive chemotherapy or antibody therapy to reduce the number of leukemia cells at an early stage.

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2025
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