Keri Tate

Altered T cell receptor ligands trigger a subset of early T cell signals.

TCR ligands are complexes of peptides and MHC proteins on the surfaces of APCs. Some of these ligands cause T cell proliferation (agonists), while others block it (antagonists). We compared the acid release, calcium flux, and proliferation response of helper T cells to a variety of ligands. We found that all agonist ligands but not most antagonist ligands trigger acid release, a general indicator of early cellular activation. Only a subset of ligands triggering acid release cause sustained calcium flux, and only a subset of these ligands cause T cell proliferation. Antagonist ligands and anti-CD4 antibodies both effectively block T cell proliferation. However, significantly greater antagonist ligand or antibody concentrations are required to block acid release and initial calcium influx. These data demonstrate a hierarchy of early T cell signaling steps and show that altered TCR ligands can initiate some steps while blocking the completion of others.

Dielectrophoretic studies of the activation of human T lymphocytes using a newly developed cell profiling system

Human T lymphocytes were stimulated using phorbol myristate acetate and ionomycin. Twenty‐four hours post‐activation the cells were harvested for DNA content and for measurements using a newly developed cell profiling system employing dielectrophoresis. This system provides individual cell size and dielectrophoresis data for statistically relevant numbers of control and activated cells. From this it was determined that the mean membrane specific capacitance decreased from 13.49 (± 4.72) mF/m2 to 10.62 (± 5.13) mF/m2. This can be related to a 21.3% reduction in the effective membrane surface area associated with membrane topography (e.g. reduction of membrane associated microvilli, blebs and folding), or to other changes of membrane architecture, following cell activation. From cytometric determinations of DNA content, it was concluded that these effects were related to a 3.0‐fold decrease of cells in S‐phase, and a 1.5‐fold increase in G1 cells. This work demonstrates the powerful potential of using dielectrophoresis as a noninvasive tool to follow physiological changes that accompany transmembrane signaling events.

Infusion of donor-derived CD8+ memory T cells for relapse following allogeneic hematopoietic cell transplantation

Murine models showed that CD8+CD44hi memory T (TM) cells could eradicate malignant cells without inducing graft-versus-host disease (GVHD). We evaluated the feasibility and safety of infusing freshly isolated and purified donor-derived phenotypic CD8+ TM cells into adults with disease relapse after allogeneic hematopoietic cell transplantation (HCT). Phenotypic CD8 TM cells were isolated after unmobilized donor apheresis using a tandem immunomagnetic selection strategy of CD45RA depletion followed by CD8+ enrichment. Fifteen patients received CD8+ TM cells at escalating doses (1 × 106, 5 × 106, or 10 × 106 cells per kg). Thirteen received cytoreduction before CD8+ TM cell infusion, and 9 had active disease at the time of infusion. Mean yield and purity of the CD8+ TM infusion were 38.1% and 92.8%, respectively; >90% had CD8+ T effector memory phenotype, cytokine expression, and secretion profile. No adverse infusional events or dose-limiting toxicities occurred; GVHD developed in 1 patient (grade 2 liver). Ten patients (67%) maintained or achieved response (7 complete response, 1 partial response, 2 stable disease) for at least 3 months after infusion; 4 of the responders had active disease at the time of infusion. With a median follow-up from infusion of 328 days (range, 118-1328 days), median event-free survival and overall survival were 4.9 months (95% confidence interval [CI], 1-19.3 months) and 19.6 months (95% CI, 5.6 months to not reached), respectively. Collection and enrichment of phenotypic CD8+ TM cells is feasible, well tolerated, and associated with a low incidence of GVHD when administered as a manipulated infusion of donor lymphocytes in patients who have relapsed after HCT. This trial was registered at www.clinicaltrials.gov as #NCT01523223.