Xenograft tumor studies

A431 epidermoid carcinoma tumor cells (CRL-1555, ATCC) were implanted subcutaneously in SIRPA^h/h TPO^h/m Rag2^−/− Il2rg^−/− mice that were engrafted with fetal liver CD34⁺ cells. Mice were segregated into four groups to have similar distribution of fetal liver donors, human immune cell engraftment frequency, and sex. Mice were dosed by intraperitoneal injection twice per week starting on the day of implant (day 0) with isotype control, EGFRxCD28 (5 mg/kg), anti–PD-1 (10 mg/kg), or combination. Antibody injections were then administered every 2 to 3 days through the experiment. Tumors were measured two-dimensionally (length by width), and tumor volume was calculated (length × width² × 0.5). Mice were euthanized when the tumor reached a designated tumor end point (tumor volume >2000 mm³ or tumor ulceration).