Epitope Preservation Methods for Tissue Microarrays: Longitudinal Prospective Study

Abstract

Objectives: We sought to test recent guidelines for preserving immunoreactivity of precut slides, to quantify loss of immunoreactivity, and to determine potential for preservation by altering storage conditions.

Methods: Precut slides from tissue microarrays were stored under one of several conditions: exposed to ambient air at room temperature, 4°C, or -20°C or in a vacuum-sealed container at room temperature, -20°C, -80°C, or with paraffin coating. At multiple intervals over 1 year, slides were stained with antibodies against p53, isocitrate dehydrogenase 1, Ki-67, synaptophysin, and androgen receptor and evaluated.

Results: Compared with time 0, the overall median percentage immunoreactivity was 66% at 6 months and 51% at 1 year. During the experiment, this was as low as 55% for precut slides stored in paraffin coating and up to 87% for those stored at -20°C. Vacuum sealing was an effective preservative for some antibody targets and detrimental for others. Storage at -80°C did not have added value.

Conclusions: For precut slides, there is a time, storage condition, and antibody-dependent loss of immunoreactivity that could compromise analysis of prognostic, predictive, and diagnostic markers. Our findings support previous recommendations and suggest that the best storage conditions are at -20°C, without paraffin coating or vacuum sealing.

Keywords: Antibody; Antigenicity; Epitope; Immunoreactivity; Storage; Tissue microarray.