In vivo experiments
Six- to 8-week-old female SCID mice were purchased from Charles River Laboratories (Calco, Italy) and housed in our specific pathogen-free animal facility. Procedures involving animals and their care were in conformity with institutional guidelines (D.L. 116/92 and subsequent complementing circulars), and all experimental protocols were approved by the local ethical committee of Padova University (CEASA).
A total of 80–100 × 106 cells from every cell line were injected i.p., while 20–25 × 106 cells were used for s.c. injection. Four days later, the subcutaneous masses were recovered, mechanically disaggregated, and used for immunophenotyping. Similarly, i.p. injected cells were recovered by peritoneal washing and used for the flow cytometry analyses. A high number of cells were required for the initial injection to provide the recovery of sufficient cells for subsequent staining and in vitro culture.
In vitro and in vivo treatment with epigenetic drugs
Tumor cells explanted ex vivo were cultured in vitro with different epigenetic drugs (trichostatin A and decitabine, also known as 2′-deoxy-5-azacytidine) that had already proven to be effective in vitro [
3,
4] or in vivo [
1]. Cells were plated at 5 × 10
5 cells/well in 24-well plate in complete medium (control) or medium added with trichostatin A (50, 250, and 500 nM, Sigma) or decitabine (1 μM, Pharmachemie B.V., Haarlem, Holland), for up to 72 h. For in vivo experiments, mice were treated with trichostatin A (1 mg/kg once a day, days 0–3, Sigma [
5]), decitabine (0.25 mg/kg once at day 0, then twice a day, days 1–3 [
1]), suberoylanilide hydroxamic acid (SAHA, 1.25 mg/mouse, once a day, days 1–3, Alexis Biochemicals, Lausen, Switzerland [
6]), valproic acid (5 mg/mouse, once a day, days 1–3, modified from [
7], Sigma), and Interferon-γ (50,000 IU/mouse, once, 6 h before cells recovery, modified from [
1], PeproTech, Rocky Hill, NJ). On day 4, cells were recovered by peritoneal washing and used for the flow cytometry analyses.
Flow cytometry analysis
Human cancer cells recovered ex vivo were initially gated according to their forward- and side-scatter profiles and then specifically identified for their human origin with antibodies to CD5 (for the MOLT-3 cell line; clone MEM-32, ImmunoTools, Friesoythe, Germany), CD19 (for all the B cell lines; clone 89B, Coulter, Milano, Italy), CD45 (for all the T cell lines, but MOLT-3; clone MEM-28, ImmunoTools), and CD44 antibody (for all the epithelial cancer cell lines; clone J-173, Immunotech Coulter, Milano, Italy). The gated populations always confirmed to be 100% positive for the respective markers.
Further stainings were performed with antibodies to β2-microglobulin (clone 2M2, BioLegend, Cambridge, UK), HLA-I (HLA-A, HLA-B, and HLA-C loci, clone W6/32, BioLegend), HLA-A2 (clone BB7.2, BioLegend), HLA-II (clone Tü39, BD, Erembodegem, Belgium), HLA-DR (clone L243, BD; clone LN3, eBiosciences, San Diego, California, USA), HLA-DQ (clone HLADQ1, BioLegend; clone Tu169, BD), and PAN-Ig (Goat polyclonal anti-human IgG, IgA, and IgM (H+L), AbD Serotec, Oxford, UK). Control stainings were performed using the appropriate isotypes (mouse IgG1 for β2-microglobulin and HLA-DQ, BD; goat IgG for PAN-Ig, AbD Serotec; mouse IgG2a for all the other antibodies, BD).
To avoid potential bias in recognizing the implanted human cell lines, all antibodies were tested for cross-reactivity with mouse splenocytes and found negative.
After staining, red blood cells were lysed and cells were analyzed using FACSCalibur (BD) instrument and FlowJo software (TreeStar Inc., Olten, Switzerland).
Percentage of positivity was calculated as the difference between the positivity percentage of each marker and that of the corresponding isotype control.