Bacteremia after hematopoietic stem cell transplantation: incidence and predictive value of surveillance cultures.

We studied 622 transplants undertaken between 1982 and 2001 to: (1) determine the incidence, timing and etiology of bacteremias, and (2) examine the ability of routine surveillance cultures to predict bacteremias. A total of 404 episodes (0.65 episode per patient) occurred in 248 patients, due to coagulase-negative staphylococci (n=171, 42%), Gram-negative bacteria (n=129, 32%), streptococci (n=48, 12%), other Gram-positive bacteria (n=33, 8%), anaerobes (n=9, 2%) and fungi (n=14, 3%). Bacteremias were more frequent in allogeneic (0.96 episode/patient) compared to autologous (0.44) transplants (P<0.0001). The overall incidence decreased from 0.92 episode/patient until 1990 to 0.66 in 1991-1996 and 0.55 in 1997-2001 (P<0.0001), but this was only observed in autologous transplants. Among them, 212 (53%) occurred before hospital discharge and 192 (47%) thereafter. This proportion was lower for coagulase-negative staphylococci, other Gram-positive bacteria and Gram-negative bacteria compared to other agents (P=0.001). In 50% of the cases, the agent responsible for the bacteremic episode was present in routine surveillance cultures previously. In conclusion: (1) bacteremias remain a frequent complication, particularly in allogeneic transplantation, even long after hospital discharge; (2) routine surveillance cultures can predict bacteremias in 50% of the cases, but the practical impact of this observation is limited in view of the costs

The haemopoietic growth factor, Flt3L, alters the immune response induced by transcutaneous immunization

Topical application of antigen induces antigen-specific humoral and cellular immune responses. In this study we examined whether expansion of dendritic cells (DC) by Flt3 ligand (Flt3L) treatment influences the induction of immune responses following transcutaneous immunization. Mice were treated intraperitoneally with Flt3L or phosphate-buffered saline (PBS) and immunized transcutaneously with hen egg lysozyme (HEL). Flt3L-treated mice developed lower HEL-specific cellular and humoral immune responses than PBS-treated mice. However, in the presence of cholera toxin (CT), a potent adjuvant for mucosal and transcutaneous immunization, Flt3L-treated mice developed significantly higher cellular and humoral immune responses to HEL when compared to PBS-treated mice. We assessed whether the immunomodulatory effects of CT were a result of activation of epidermal dendritic cells (Langerhans' cells; LC). Our results indicate that within 8–12 hr of topical application of CT, epidermal LC cells lose their dendritic morphology and become rounder in appearance. In addition, we observed enhanced expression of major histocompatibility complex (MHC) class II, and of adhesion molecules CD11c and intracellular adhesion molecule-1 (ICAM-1). Our observations support the concept that the state of activation of DC in the skin is central to the regulation of immune responses. This information is relevant to the design of effective transcutaneous vaccination strategies