Ultrastructural analysis of human natural killer cell activation

In this study we describe characteristic ultrastructural changes of CD3- large granular lymphocytes (LGL), ie, natural killer (NK) cells, following stimulation with recombinant (r) interleukin 2 (IL 2) or r- gamma interferon (r-gamma IFN) and after interaction with K562 target cells (TC) or Sepharose-bound anti-Fc gamma receptor (FcR) monoclonal antibody (MoAb). When compared to resting cells the cytolytic activity of r-IL 2- and r-gamma IFN-stimulated cells against K562 TC was enhanced. The r-IL 2-stimulated LGL were larger and consistently displayed the shape and cytoskeletal rearrangement characteristic of activated cells. The Golgi apparatus was expanded, and the number of electron-dense granules and vesicles was increased. The ultrastructural changes in r-gamma IFN-stimulated LGL were markedly different from those observed following r-IL 2 activation. Cells did not exhibit changes in size, shape, cytoskeletal organization, or in the structure of the Golgi apparatus. However, r-gamma IFN-stimulated cells exhibited distinctive changes in the structure and content of electron-dense granules with deaggregation of the matrix and parallel tubular arrays (PTAs). Within organelles apparently derived from the electron-dense granules, vesicular and tubular structures were noted that may be the morphological equivalent of cytotoxic factors produced by cytolytic effector cells. These ultrastructural observations indicate that r-IL 2 and r-gamma IFN enhance the lytic ability of NK cells by acting on distinct cell machineries. The cytolytic ability was decreased when LGL were pretreated with K562 TC or immobilized anti-FcR antibody. In both experimental conditions cells displayed ultrastructural features indicating activation as well as loss of cytoplasmic granules and other Golgi-derived organelles. Stimulation of r-gamma IFN- or r-IL 2- activated LGL with K562 TC or Sepharose-bound anti-FcR antibody decreased their cytolytic ability, with cells depleted of granules at the ultrastructural level. Intracytoplasmic fusion of granules and a massive release of the granule content were found in r-IL 2-stimulated cells, reminiscent of the mechanism of basophil degranulation. These observations suggest that multiple activation signals involving distinct surface membrane molecules induce release of cytolytic factors by both resting and activated NK cells.     

Imbalances within the peripheral blood T-helper (CD4+) and T-suppressor (CD8+) cell populations in the reconstitution phase after human bone marrow transplantation

Peripheral blood T cell subsets were evaluated in 11 patients during the reconstitution phase after allogeneic bone marrow transplantation and compared with 11 age-matched controls. The proportion of cells coexpressing Leu7 and CD11b (C3bi receptor) markers was determined within the CD4+ (T-helper) and the CD8+ (T-suppressor) subsets by two- color immunofluorescence analysis. CD4+ and CD8+ T cells reached normal or near-normal values within the first year posttransplant. In contrast to normal controls, however, most of the cells in both subsets coexpressed the Leu7 and CD11b markers. T cells with such phenotype display the morphological features of granular lymphocytes (GLs) and a functional inability to produce interleukin 2 (IL 2). These T cell imbalances were not related to graft v host disease (GvHD) or to clinically detectable virus infections and may account for some defects of cellular and humoral immunity that occur after bone marrow transplantation.     

Busulfan pharmacokinetics using a single daily high-dose regimen in children with acute leukemia

The pharmacokinetics of busulfan, given as a single daily dose (either 4 mg/kg or 150 mg/m2), was determined in 22 children undergoing bone marrow transplantation for acute leukemia. The single daily dose regimen showed similar pharmacokinetics to previously reported regimens of 4 x 1 mg/kg, except for fourfold higher mean peak plasma levels and negligible trough levels. Daily systemic exposure for single dose regimens based on weight (4 mg/kg) or surface area (150 mg/m2), respectively were very similar to regimens of (4 x 1 mg/kg) or (4 x 37.5 mg/m2). Dose (milligrams per kilogram), peak plasma level, and area under the curve (AUC) were all higher in 12 children treated with 150 mg/m2 busulfan than in 9 children treated with 4 mg/kg. AUC was age dependent for the 4 mg/kg dose but not for the 150 mg/m2 dose. The use of a 150 mg/m2 dose allows escalation of the dose above 4 mg/kg, eliminating the tendency for younger children to receive lower systemic exposure. Little toxicity was observed in this study. Clearance and distribution volume correlated negatively with age, and AUC correlated positively with dose (milligram per kilogram). Administration of busulfan as crushed rather than whole tablets reduced the delay time for appearance of busulfan in plasma but had no effect on absorption or other pharmacokinetic parameters.