(A) Mice bearing KLM-1 tumors were treated with vehicle or tofacitinib at t = –48 and –24 hours. At t = 0, mice were injected with LMB-100 and blood was harvested at t = 0, 15, 30, 45, and 60 minutes. Circulating LMB-100 was detected by ELISA and normalized to a standard curve for purified LMB-100. The half-life and area under the curve were calculated from best-fit regression analysis. Results are averaged from 2 biological replicates. (B) Naive mice were treated with vehicle or tofacitinib at t = –48 and –24 hours. At t = 0, mice were injected with LMB-100 and blood was harvested at t = 0, 15, 30, 45, and 60 minutes. Circulating LMB-100 was detected by ELISA and normalized to a standard curve for purified LMB-100. The half-life and area under the curve were calculated from best-fit regression analysis. Results are averaged from 4 biological replicates. (C) Mice bearing KLM-1 xenografts were pretreated with either vehicle or tofacitinib, then administered 50 μg LMB-100–A647 for 3 hours. Dissociated tumors were scored for the presence of LMB-100–A647 in malignant cells and inflammatory populations. Tumor cells were identified by staining with anti-huEGFR, and tumor-associated inflammatory cell populations were identified by staining with anti-mCD11b. The percentage of huEGFR or mCD11b cells containing immunotoxin in vehicle or tofacitinib-treated mice is shown. n = 4 biological replicates. (D) CD11b⁺ cells containing LMB-100–A647 were further discriminated into CD68⁺ (macrophage) or LY6G⁺ (neutrophil) populations. The percentage of tumor-associated LMB-100–A647⁺ cells displaying each cell marker is shown. n = 4 biological replicates. *P < 0.05; **P < 0.01; ***P < 0.001 by unpaired 2-tailed t test (A–D). ns, not significant.