CD200 expression suppresses natural killer cell function and directly inhibits patient anti-tumor response in acute myeloid leukemia.

Upregulation of the immunosuppressive cell surface glycoprotein, CD200, is a common feature of acute myeloid leukemia (AML) and is associated with poor patient outcome. We investigated whether CD200 overexpression on AML cells could specifically compromise patient natural killer (NK) cell anti-tumor responses. We found that CD200(hi) patients showed a 50% reduction in the frequency of activated NK cells (CD56(dim)CD16(+)) compared with CD200(lo) patients. Additionally, NK receptor expression (NKp44 and NKp46) on these cells was also significantly downregulated in CD200(hi) patients. To assess whether NK cell activity was directly influenced by CD200 expression, we examined the effect of ectopic expression of CD200. These assays revealed that both NK cell cytolytic activity and interferon-γ response were significantly reduced toward CD200(+) leukemic targets and that these targets showed increased survival compared with CD200(-) cells. Similarly, NK cells isolated from AML patients were less functionally active toward CD200(hi) autologous blasts from both cytolytic and immunoregulatory perspectives. Finally, blocking CD200 alone was sufficient to recover a significant proportion of NK cell cytolytic activity. Together, these findings provide the first evidence that CD200 has a direct and significant suppressive influence on NK cell activity in AML patients and may contribute to the increased relapse rate in CD200(+) patients.

Sustained TL1A expression modulates effector and regulatory T-cell responses and drives intestinal goblet cell hyperplasia.

The tumor necrosis factor (TNF) superfamily protein TNF-like 1A (TL1A) is the ligand for death receptor 3 (DR3). TL1A is induced on activated dendritic cells (DCs) and its expression has been linked to human inflammatory bowel disease. To address how TL1A might influence intestinal inflammation, we generated transgenic mice that constitutively express TL1A on DCs. TL1A transgenic mice developed striking goblet cell hyperplasia in the ileum that was associated with elevated interleukin (IL)-13 levels in the small intestine. IL-13- and IL-17-producing small intestinal lamina propria T cells were increased in TL1A transgenic mice. TL1A also enhanced regulatory T (Treg) cell turnover in vivo and directly stimulated Treg cell proliferation in vitro. The presence of TL1A attenuated the ability of Treg cells to suppress conventional T cells, an effect that required DR3 signaling in either conventional T cells or Treg cells. Our findings identify mechanisms by which chronic DR3 signaling could promote pathogenesis in inflammatory bowel disease.

Cytomegalovirus destruction of focal adhesions revealed in a high-throughput Western blot analysis of cellular protein expression.

Human cytomegalovirus (HCMV) systematically manages the expression of cellular functions, rather than exerting the global shutoff of host cell protein synthesis commonly observed with other herpesviruses during the lytic cycle. While microarray technology has provided remarkable insights into viral control of the cellular transcriptome, HCMV is known to encode multiple mechanisms for posttranscriptional and post-translation regulation of cellular gene expression. High-throughput Western blotting (BD Biosciences Powerblot technology) with 1,009 characterized antibodies was therefore used to analyze and compare the effects of infection with attenuated high-passage strain AD169 and virulent low-passage strain Toledo at 72 hpi across gels run in triplicate for each sample. Six hundred ninety-four proteins gave a positive signal in the screen, of which 68 from strain AD169 and 71 from strain Toledo were defined as being either positively or negatively regulated by infection with the highest level of confidence (BD parameters). In follow-up analyses, a subset of proteins was selected on the basis of the magnitude of the observed effect or their potential to contribute to defense against immune recognition. In analyses performed at 24, 72, and 144 hpi, connexin 43 was efficiently downregulated during HCMV infection, implying a breakdown of intercellular communication. Mitosis-associated protein Eg-5 was found to be differentially upregulated in the AD169 and Toledo strains of HCMV. Focal adhesions link the actin cytoskeleton to the extracellular matrix and have key roles in initiating signaling pathways and substrate adhesion and regulating cell migration. HCMV suppressed expression of the focal-adhesion-associated proteins Hic-5, paxillin, and alpha-actinin. Focal adhesions were clearly disrupted in HCMV-infected fibroblasts, with their associated intracellular and extracellular proteins being dispersed. Powerblot shows potential for rapid screening of the cellular proteome during HCMV infection.

T cell responses to vaccines in infants: defective IFNgamma production after oral polio vaccination.

The immaturity of the neonatal immune system is associated with an increased susceptibility to infections. Studies in mice indicate that neonatal immune responses are biased towards the T helper 2 type, but little is known about helper T cell responses in human newborns. In this study, the oral polio vaccine was used as a model of early immunization to investigate the capacity of young infants to develop cellular immune responses. We show that neonatal immunization with oral polio vaccine induces the production of high titres of neutralizing antibodies but reduced proliferative and IFNgamma responses to polio antigens compared to immune adults. These data suggest that specific strategies will be required to immunize newborns against pathogens controlled by Th1 type immune responses.