Cells were plated on gelatin-coated coverslips, fixed in 4% paraformaldehyde (Sigma-Aldrich, St. Louis, MO), incubated in blocking buffer (1% bovine serum albumin, 0.3% Triton X-100 (ThermoFisher, Waltham, MA) in PBS), stained with mouse anti-human Tert antibody incubated overnight at 4C (ab5181, Abcam, Cambridge, MA) at 1:25 dilution, followed by PE-conjugated anti-mouse IgM antibody for 2 hours at room temperature (1:250 dilution) (clone eB121-15F9, eBioscience/ThermoFisher, Waltham, MA). Coverslips were mounted on slides with VectaSheild with DAPI (H-1200, Vector Laboratories, Burlingame, CA) and cells imaged at 63x on a Zeiss spinning disk confocal microscope.