Retrospective analysis of cutaneous T-cell lymphoma (CTCL) biopsy samples for interleukin-2 receptor (IL2-R) subunit expression by immunohistochemistry (IHC) and real-time quantitative PCR (RT-PCR): Correlation to response to denileukin diftitox

Abstract

20080 Background: Denileukin diftitox, a chimeric diphtheria toxin-IL2 protein, exerts its cytotoxic effect on cells expressing high or intermediate affinity IL2-R. IL2-R is a complex of 3 distinct polypeptide chains: IL2-Rα (CD25), IL2-Rβ (CD122), and IL2-Rγ (CD132). IL2-R α/β/γ heterotrimer binds with high affinity, IL2-R β/γ with intermediate affinity, and IL2-R α/γ with low affinity. Denileukin diftitox is indicated for patients with persistent or recurrent CTCL whose malignant cells express IL2-Rα protein. There is no currently available methodology to measure expression of the high affinity receptor in patient samples. This study was initiated to discover a correlation between expression of IL2-R components (at the mRNA and protein levels) and clinical response to denileukin diftitox. Methods: Of 33 available frozen clinical CTCL biopsy samples, 27 (10 responders) were sufficient for IHC. IL2-Rβ staining intensity was assigned a value of 0 (no staining relative to background), 1+ (weak), 2+ (moderate), or 3+ (strong). 22 samples (8 responders) were sufficient for RT-PCR. mRNA levels of the 3 IL2-R chains were normalized to 36B4 mRNA or 18S rRNA. Correlation between clinical response and IL2-R chain expression was assessed using Spotfire Decision Site. Results: The population of samples tested was representative of the study population. 26 of 27 samples exhibited 2+, all exhibited 1+, and none 3+ IL2-Rβ staining. The percentage of cells stained varied from 20%–90% for 1+ and 10%–80% for 2+ with no correlation to response. Correlation of levels of individual IL2-R subunit mRNA expression with response could not be established. Conclusions: Neither the IL2-Rβ IHC nor the RT-PCR assay, at current sensitivity levels, appear to identify denileukin diftitox responders. Larger sample datasets from current studies, and further assay refinement, are ongoing to define the merits of these approaches. [Table: see text]