Immunohistochemical Application of Mutant IDH1 Antibody in Evaluation of Acute Myeloid Leukemia.
Mu Su, Dinesh Rakheja, Jack M Raisanen, Michael Gallegos, Nitin J Karandikar, Weina Chen. UT Southwestern Medical Center, Dallas, TX
Background: Somatic mutations of IDH1 and IDH2 have recently been described in acute myeloid leukemia (AML) with an incidence of 10-20%. An antibody suitable for immunohistochemistry (IHC) of paraffin-embedded specimens specifically detecting mutant IDHR132H protein (mIDHR132H, clone H09) has recently been generated and characterized in gliomas. This antibody has not yet been studied in AML and is the focus of our study.
Design: IHC stain for mutant IDH1 (H09, DIANOVA) was performed on tissue microarray sections of 65 AML cases that encompass heterogeneous subtypes of AML except AML with t(15;17). In 5 cases, DNA extraction was successful for IDH1 and IDH2 exon 4 sequencing. The immunophenotype in the corresponding blood/bone marrow specimens was analyzed by 4-color flow cytometry (FC).
Results: There were 32 females and 33 males, aged 19 to 78 years (median 52 years). Two cases (2/65, 3.1%) had uniform moderate to strong cytoplasmic staining for mutant IDH1. These 2 cases did not yield sufficient DNA for mutation analysis. Of 5 cases in which DNA was available for mutation analysis (all with negative staining for mutant IDH1), 3 cases revealed IDH2 mutations while 2 cases were wild-type for IDH1 and IDH2. The morphologic, immunophenotypic, and cytogenetic features of 2 IHC-IDH1 mutant positive cases were similar to 3 IDH2-mutated cases. These features included AML without maturation and with cup-like nuclei, normal karyotype, and lack of CD34 and HLD-DR.
Conclusions: The morphologic, immunophenotypic, and cytogenetic similarity between the 2 IHC-IDH1 mutant positive cases and 3 IDH2-mutated cases suggests that the IDH1 mutant antibody (H09) may identify mutant IDH1 and does not cross-react with mutant IDH2. Our study is limited by small sample size and difficulty in extraction of good quality DNA from paraffin-embedded tissues. Further studies are in progress to validate these preliminary observations.
Wednesday, March 2, 2011 9:30 AM
Poster Session V # 180, Wednesday Morning