Abstract A40: CD44 expression in T-cell acute lymphoblastic leukemia and acute myeloid leukemia associated with RAS mutations

Abstract

Abstract CD44 is an adhesion glycoprotein which helps with the homing of hematopoietic precursor cells. In acute myeloid leukemia (AML), CD44 has been investigated as a stem cell marker, and expression of its variant proteins has been associated with poor prognosis. Only in murine T-cell acute lymphoblastic leukemia (T-ALL) models, CD44 expression was associated with tumor progression, organ infiltration, and influencing survival. In early T-cell precursor-ALL (ETP-ALL, a T-ALL subset) several similarities were observed with AML genomic aberrations. Taking the CD44 gene that is a target of the RAS pathway, which promotes its alternative splicing, throughout a positive feedback loop, we have investigated whether the cellular expression of CD44 in different maturational subtypes of pediatric T-ALL and AML would predict RAS mutations. We have tested if the cellular CD44 status would be associated with patient's clinical characteristics. Methods: A series of 193 T-ALL and 28 AML patients (≤ 21 years) was tested by multiparameter flow cytometry with a panel of monoclonal antibodies combined as CD4FITC/CD7PE/CD45PercPCy5.5/CD8Pe-Cy7/CD44APC (T-ALL), and CD117PE/ CD45PercPCy5.5/HLA-DR PE-Cy7/CD44APC (AML). CD44 expression was evaluated by median fluorescence intensity (MFI) in blast cells and the value of the MFI in the 75th percentile was used as a cutoff to discriminate between high or low expression of CD44. Sanger sequencing was used to detect mutation in codons 12 and 13 of N/KRAS genes, after DNA extraction, amplification through polymerase chain reaction and product purification. Fisher´s exact test or chi-square test was used to evaluate the distribution of categorical variables, whereas Mann-Whitney (two groups) or Kruskal Wallis (more than two groups) tests were used to evaluate the distribution of non-parametric continuous variables; t-test and one-way ANOVA were used for parametric variables; p values of < 0.05 were considered statistically significant. Results: Only two cases were negative for CD44 (<20% positive blasts). There was no association between high expression of CD44 and organomegaly in T-ALL while for chloroma in AML the evaluation was impaired due to small series. There was no association between the expression of CD44 and T-ALL subtypes. AML patients have a higher cellular expression of CD44 (MFI: 18890 [1019-44720]) than T-ALL (MFI: 1211 [68-8325]) (p<0,0001). The CD44 expression in ETP-ALL were lower than in AML (MFI: 1504 [855-3296], p<0,0001). The frequency of N/KRAS mutations in T-ALL cases was 11,7% (12/102), whereas in AML cases it was 16.7%. There was no significant difference in CD44 expression between cases with N/KRAS mutations (MFI: 1715 [365-8325]) and without mutation (MFI: 1179 [68-5544]) in T-ALL, whereas in AML, N/KRAS mutated cases had a lower CD44 expression (MFI: 10979 [7650-18810]) than the cases without mutation (MFI: 21720 [1019-44720]) (p=0,032). Conclusions: CD44 cellular status was not relevant for T-ALL tumoral profile and its expression was not associated with T-ALL subtype. CD44 is underexpressed in T-ALL and ETP-ALL when compared with AML. N/KRAS mutation does not seems be associated with different expression of CD44 in pediatric T-ALL whereas further investigation is required in AML subsets. Citation Format: Luisa V. C. Marques, Elda P. Noronha, Franciane G. Andrade, Eugenia T. G. Pina, Maria S. Pombo-de-Oliveira. CD44 expression in T-cell acute lymphoblastic leukemia and acute myeloid leukemia associated with RAS mutations [abstract]. In: Proceedings of the AACR International Conference held in cooperation with the Latin American Cooperative Oncology Group (LACOG) on Translational Cancer Medicine; May 4-6, 2017; São Paulo, Brazil. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(1_Suppl):Abstract nr A40.