SGN-CD70A inhibits cell proliferation and induces apoptosis in CD70-expressing primary tumor cells from CTCL PDX mice. (A) CD70 expression levels by flow cytometry in primary malignant T cells harvested from spleens of CTCL PDX mice, PRS-1, PRS-2, and PRS-3. PRS-1 was generated from a patient with MF, and PRS-2 and -3 were generated from patients with Sézary syndrome, as described previously. (B) CD70 expression levels in T cells (CD3+CD4+) in the PBMC from 4 normal donors (Normal-1 through Normal-4). (C) Antiproliferative activity of SGN-CD70A in PRS-1, PRS-2, and PRS-3 primary tumor cells. The T-cell expansion was triggered by incubation with anti-CD2/CD3/CD28 beads in cell medium containing IL-2 (500 U/mL) and IL-7 (250 U/mL). Cell viability was determined at 24, 48, and 72 hours after treatment. (D) SGN-CD70A induces apoptosis in CD70-expressing primary tumor cells (PRS-1 and PRS-3) but not in tumor cells that do not express CD70 (PRS-2). The primary tumor cells harvested from spleens of PRS-1, PRS-2, and PRS-3 PDX mice were treated with various concentrations of SGN-CD70A, medium control (PBS), or IgG isotype control for 72 hours, and the apoptosis induction was analyzed by the annexin V/PI assay.