Emergence of daptomycin non-susceptibility in colonizing vancomycin-resistant Enterococcus faecium isolates during daptomycin therapy

Infections due to vancomycin-resistant enterococci (VRE) are of significant importance in high-risk populations, and daptomycin is a bactericidal antibiotic to treat multidrug-resistant VRE in these patients. The emergence of daptomycin non-susceptibility invasive VRE during daptomycin therapy is a major clinical issue. Here the hypothesis was tested that systemic daptomycin therapy also induces the emergence of daptomycin non-susceptible (DNS-) isolates in colonizing VRE populations. 11 vancomycin-resistant Enterococcus faecium strain pairs recovered from rectal swabs were available for analysis. All initial isolates exhibited daptomycin MICs within the wild type MIC distribution of E. faecium (MIC≤4 mg/L). In follow-up isolates from five patients a 4-16-fold daptomycin MIC increase was detected. All patients carrying DNS-VRE received daptomycin (14-28 days) at 4 mg/kg body weight, while two patients in whom no DNS-VRE emerged were only treated with daptomycin for 1 and 4 days, respectively. Comparative whole genome sequencing identified DNS-VRE-specific single nucleotide polymorphisms (SNP), including mutations in cardiolipin synthase (Cls), and additional SNPs in independent genes potentially relevant for the DNS phenotype. Mutations within cls were also identified in three additional, colonizing DNS-VRE. Of these, at least one strain was transmitted within the hospital. In none of the VRE isolates tested, pre-existing or de novo mutations in the liaFSR operon were detected. This is the first report documenting the emergence of DNS-VRE in colonizing strains during daptomycin treatment, putting the patient at risk for subsequent DNS-VRE infections and priming the spread of DNS-VRE within the hospital environment.

Serum albumin level predicts survival of patients with gastrointestinal acute graft-versus-host disease after allogeneic stem cell transplantation

In a retrospective single-centre study, we analysed the prognostic impact of factors identifiable at initial diagnosis of acute GVHD (aGVHD). We retrospectively analysed 495 adult patients of whom 308 (62 %) developed acute GVHD (I-IV) and were included in further analysis. Gut aGVHD was diagnosed in 163/308 cases (53 %). Conditioning was myeloablative conditioning (MAC) in 123 (39.9 %) and reduced intensity (RIC) in 185 (60.1 %) patients. Median serum albumin level at diagnosis of aGVHD was 34 g/l, which was used as cut-off for low vs. normal albumin levels. In patients with gut aGVHD, low albumin level at the time of diagnosis of aGVHD was associated with poorer overall survival (OS) which was 52 vs. 67 % at 1 year and 40 vs. 61 % at 3 years, p = 0.015. In patients with only skin aGVHD, 1- and 3-year OS of patients with low vs. normal albumin levels were 72 vs. 72 % and 59 vs. 57 %, respectively, p = 0.69. In multivariate analysis of patients with gut aGVHD, low serum albumin level ≤34 g/l (relative risk (RR) 2.13, p = 0.003), gut aGVHD grades 3-4 (RR 2.70, p = 0.001), RIC (RR 1.84, p = 0.024), matched unrelated donor (RR 1.86, p = 0.18) and mismatched unrelated donor (RR 2.76, p = 0.03) retained negative impact on OS. Subgroup analysis revealed that impact of albumin was restricted to patients with gut aGVHD after RIC. Low serum albumin levels are associated with poorer OS in patients with gut but not skin aGVHD after RIC but not MAC allogeneic stem cell transplantation.

Donor choice according to age for allo-SCT for AML in complete remission

In a retrospective study of 168 patients with AML in CR who underwent allo-SCT, we compare the impact of young unrelated donors (UD) vs older matched related donors (MRD) on 5-year OS (5-yr OS). Median follow-up was 59 months and median donor age was 39 years, which was used as cutoff for young vs older donors. Kaplan-Meier-estimated 5-yr OS was better with UD ≤39 years vs MRD >39 years (66% vs 34%, P=0.001). In multivariate analysis, only donor age and cytogenetic risk impacted 5-yr OS. Compared with UD ≤39 years, both MRD >39 years (relative risk (RR): 4.31, P=0.001) and UD >39 years (RR: 2.14, P=0.03) were associated with poorer 5-yr OS. Standard-risk cytogenetics was associated with better 5-yr OS compared with bad-risk cytogenetics, (RR: 0.53, P=0.02). Subgroup analyses of patients ≥50 years (n=76) revealed similar results, with 5-yr OS of 62% for UD ≤39 yrs and 26% for MRD >39 yrs (P=0.022). In patients undergoing allo-HSCT for AML, young UD may improve outcome as compared with older MRD.

EBV reactivation and post transplant lymphoproliferative disorders following allogeneic SCT

Fatal problems encountered in allogeneic stem cell transplantation include EBV reactivation and post transplant lymphoproliferative disorders (PTLDs) with high mortality rates. We performed a retrospective analysis in all consecutive adult and pediatric EBV reactivations and PTLD during a period of 8.5 years. There were 26 patients with EBV reactivation/PTLD out of a total of 854 transplantations giving an overall incidence of 3.0%. Specifically, the incidence of EBV-PTLD was 1.3%, whereas that of EBV reactivation was 1.8%. Median age was 46.0 and 11.0 years in the adult and pediatric patients, respectively. There were high rates (54%) of concomitant bacterial, viral, fungal and parasitic infections at the time of EBV manifestation. Variable treatment regimens were applied including in most cases an anti-CD20 regimen often in combination with virustatic compounds, polychemotherapy or donor lymphocytes. The mortality rates were 9 of 11 (82%) in patients with EBV-PTLD and 10 of 15 (67%) in patients with reactivation. Only 7 of 26 patients (27%) are alive after a median follow-up of 758 days (range 24-2751). The high mortality rates of EBV reactivation and of EBV-PTLD irrespective of multimodal treatment approaches emphasize standardization and optimization of post transplant surveillance and treatment strategies to improve control of these often fatal complications.

Reconstitution of mRNA editing in yeast using a Gal4-apoB-Gal80 fusion transcript as the selectable marker

We describe a fusion transcript of Gal4 linked to its specific inhibitor protein Gal80 by 276 nucleotides of apolipoprotein (apo) B sequence as a selectable marker for mRNA editing. Editing of apoB mRNA is catalyzed by an editing enzyme complex that introduces a stop codon by deamination of C to U. The catalytic subunit APOBEC-1 is a cytidine deaminase and requires a second essential component recently cloned and termed APOBEC-1 complementing factor (ACF) or APOBEC-1-stimulating protein (ASP). The aim of this study was to demonstrate that APOBEC-1 plus ACF/ASP comprise all that is required for editing of apoB mRNA in vivo. Expression of APOBEC-1 and Gal4 fused to its inhibitor Gal80 by an intervening unedited apoB sequence (Gal4-apoB(C)-Gal80) did not result in the Gal4-dependent expression of HIS3 and beta-galactosidase in the yeast strain CG1945. Co-expression of APOBEC-1 and ACF/ASP induced editing of the apoB site in up to 13% of the Gal4-apoB(C)-Gal80 transcripts and enabled selection of yeast cells for robust expression of HIS3 and beta-galactosidase. Additional expression of the alternative splicing regulatory protein KSRP increased the editing of the apoB site by APOBEC-1 and ACF/ASP to 21%. Thus, APOBEC-1 and ACF/ASP represent the core apoB mRNA editing enzyme in vivo. This study demonstrates for the first time the successful use of a selectable marker for mRNA editing. The Gal4-Gal80 system is analogous to the two-hybrid assay and may have broader applications for the study of other mRNA processing reactions.

Purification and molecular cloning of a novel essential component of the apolipoprotein B mRNA editing enzyme-complex

Editing of apolipoprotein B (apoB) mRNA requires the catalytic component APOBEC-1 together with "auxiliary" proteins that have not been conclusively characterized so far. Here we report the purification of these additional components of the apoB mRNA editing enzyme-complex from rat liver and the cDNA cloning of the novel APOBEC-1-stimulating protein (ASP). Two proteins copurified into the final active fraction and were characterized by peptide sequencing and mass spectrometry: KSRP, a 75-kDa protein originally described as a splicing regulating factor, and ASP, a hitherto unknown 65-kDa protein. Separation of these two proteins resulted in a reduction of APOBEC-1-stimulating activity. ASP represents a novel type of RNA-binding protein and contains three single-stranded RNA-binding domains in the amino-terminal half and a putative double-stranded RNA-binding domain at the carboxyl terminus. Purified recombinant glutathione S-transferase (GST)-ASP, but not recombinant GST-KSRP, stimulated recombinant GST-APOBEC-1 to edit apoB RNA in vitro. These data demonstrate that ASP is the second essential component of the apoB mRNA editing enzyme-complex. In rat liver, ASP is apparently associated with KSRP, which may confer stability to the editing enzyme-complex with its substrate apoB RNA serving as an additional auxiliary component.

Absence of APOBEC-1 mediated mRNA editing in human carcinomas

The transgene expression of the catalytic subunit APOBEC-1 of the apo B mRNA editing enzyme-complex can cause hepatocellular carcinoma in mice and rabbits. It has been proposed that aberrant editing of mRNA may represent a novel oncogenic principle. This investigation aimed to define whether such aberrant hyperediting mediated by APOBEC-1 occurs in human carcinomas. Editing and hyperediting of apo B, NAT1 or NF1 mRNA was not identified in any of 28 resected tumor specimens, including hepatocellular, bile duct, gastric, colorectal, pancreatic adeno- and neuroendocrine, lung adeno-, medullary thyroid and breast carcinoma, soft tissue sarcoma and neuroblastoma. In most types of carcinoma, significant levels for full-length APOBEC-1 mRNA could not be detected. Low level expression of APOBEC-1 was found in colorectal and gastric carcinoma where most of the APOBEC-1 mRNA is inactivated by alternate splicing. The 'auxiliary' components of the apo B mRNA editing enzyme-complex are missing in many tumors including colorectal and gastric carcinoma, but are highly expressed in hepatocellular, lung adeno- and breast carcinoma all of which lack APOBEC-1. Taken together, either APOBEC-1 or the 'auxiliary' components of the apo B mRNA editing enzyme-complex or both are missing in human carcinomas resulting in the absence of mRNA editing. Currently, there is no evidence that aberrant editing mediated by APOBEC-1 contributes to the tumorigenesis of natural human carcinomas.

Inhibition of the apolipoprotein B mRNA editing enzyme-complex by hnRNP C1 protein and 40S hnRNP complexes

The apolipoprotein (apo) B mRNA can be modified by a posttranscriptional base change from cytidine to uridine at nucleotide position 6666. This editing of apo B mRNA is mediated by a specific enzyme-complex of which only the catalytic subunit APOBEC-1 (apo B mRNA editing enzyme component 1) has been cloned and extensively characterized. In this study, two-hybrid selection in yeast identified hnRNP C1 protein to interact with APOBEC-1. Recombinant hnRNP C1 protein inhibited partially purified apo B mRNA editing activity from rat small intestine and bound specifically to apo B sense RNA around the editing site. The inhibition of apo B mRNA editing by hnRNP C1 protein was not due to masking of the RNA substrate as the mutant protein M104 spanning the RNA-binding domain of hnRNP C1 protein bound strongly to the apo B RNA, but did not inhibit the editing reaction. The apo B mRNA editing enzyme-complex of rat liver nuclear extracts sedimented in sucrose density gradients around 22-27S, but did not contain hnRNP C1 protein that was found exclusively within 40S hnRNP complexes. The removal of 40S hnRNP complexes increased the activity of the 22-27S editing enzyme-complex. Adding back 40S hnRNP complexes with hnRNP C1 protein resulted in an inhibition of the 22-27S apo B mRNA editing enzyme-complex, while addition of 18S fractions had no effect. In conclusion, hnRNP C1 protein identified by two-hybrid selection in yeast is a potent inhibitor of the apo B mRNA editing enzyme-complex. The abundant hnRNP C1 protein, which is contiguously deposited on nascent pre-mRNA during transcription and is involved in spliceosome assembly and mRNA splicing, is a likely regulator of the editing of apo B mRNA which restricts the activity of APOBEC-1 to limited and specific editing events.