Pharmacodynamics and T-cell mitogen responses after therapy with visilizumab.

(A) Skin biopsies from a representative patient with cutaneous GVHD documenting clearance of CD8⁺ dermal T-cell infiltrates (black dots) following a single dose of visilizumab on day 1. Original magnification × 100, immunoperoxidase staining. (B) Flow cytometric analysis of peripheral blood leukocytes from the same patient, before and after visilizumab. Details of antibody staining are described in “Patients and methods.” Lymphocytes were identified (left panels) by their characteristic forward and light scatter (R2). Thus set, the R2 gate contained more than 95% of the CD5 bright events in R1 (T cells). The right panels show T-cell surface CD3 molecules bound by visilizumab in vivo (dotted line) and total surface CD3 (solid line). The middle panels show free CD3 (solid line) or free CD3 blocked by exogenous visilizumab (dotted line). The relative amounts of free, bound, and total CD3 before and after administration of visilizumab are indicated by the respective histogram plots of peak fluorescence intensities of gated CD5⁺ T cells. (C) Patient T cells were frozen on study days 0, 21, and 42 when the peripheral blood T-cell counts were, respectively, 57/μL (range, 28-877/μL), 13/μL (range, 1-38/μL), and 32/μL (range, 22-1291/μL). Thawed T cells were compared to fresh healthy control T cells. Individual sample and median (—) mitogen responses to PHA, anti-CD3, and anti-CD3 + anti-CD28 as described in “Patients and methods” are shown. T-cell mitogen response is not significantly reduced by visilizumab therapy.