Randy Taplitz

Memory T cells in latent Mycobacterium tuberculosis infection are directed against three antigenic islands and largely contained in a CXCR3+CCR6+ Th1 subset.

An understanding of the immunological footprint of Mycobacterium tuberculosis (MTB) CD4 T cell recognition is still incomplete. Here we report that human Th1 cells specific for MTB are largely contained in a CXCR3+CCR6+ memory subset and highly focused on three broadly immunodominant antigenic islands, all related to bacterial secretion systems. Our results refute the notion that secreted antigens act as a decoy, since both secreted proteins and proteins comprising the secretion system itself are targeted by a fully functional T cell response. In addition, several novel T cell antigens were identified which can be of potential diagnostic use, or as vaccine antigens. These results underline the power of a truly unbiased, genome-wide, analysis of CD4 MTB recognition based on the combined use of epitope predictions, high throughput ELISPOT, and T cell libraries using PBMCs from individuals latently infected with MTB.

Dissecting Mechanisms of Immunodominance to the Common Tuberculosis Antigens ESAT-6, CFP10, Rv2031c (hspX), Rv2654c (TB7.7), and Rv1038c (EsxJ)

Diagnosis of tuberculosis often relies on the ex vivo IFN-γ release assays QuantiFERON-TB Gold In-Tube and T-SPOT.TB. However, understanding of the immunological mechanisms underlying their diagnostic use is still incomplete. Accordingly, we investigated T cell responses for the TB Ags included in the these assays and other commonly studied Ags: early secreted antigenic target 6 kDa, culture filtrate protein 10 kDa, Rv2031c, Rv2654c, and Rv1038c. PBMC from latently infected individuals were tested in ex vivo ELISPOT assays with overlapping peptides spanning the entirety of these Ags. We found striking variations in prevalence and magnitude of ex vivo reactivity, with culture filtrate protein 10 kDa being most dominant, followed by early secreted antigenic target 6 kDa and Rv2654c being virtually inactive. Rv2031c and Rv1038c were associated with intermediate patterns of reactivity. Further studies showed that low reactivity was not due to lack of HLA binding peptides, and high reactivity was associated with recognition of a few discrete dominant antigenic regions. Different donors recognized the same core sequence in a given epitope. In some cases, the identified epitopes were restricted by a single specific common HLA molecule (selective restriction), whereas in other cases, promiscuous restriction of the same epitope by multiple HLA molecules was apparent. Definition of the specific restricting HLA allowed to produce tetrameric reagents and showed that epitope-specific T cells recognizing either selectively or promiscuously restricted epitopes were predominantly T effector memory. In conclusion, these results highlight the feasibility of more clearly defined TB diagnostic reagent.

Development and Use of Personalized Bacteriophage-Based Therapeutic Cocktails To Treat a Patient with a Disseminated Resistant Acinetobacter baumannii Infection

ABSTRACT Widespread antibiotic use in clinical medicine and the livestock industry has contributed to the global spread of multidrug-resistant (MDR) bacterial pathogens, including Acinetobacter baumannii. We report on a method used to produce a personalized bacteriophage-based therapeutic treatment for a 68-year-old diabetic patient with necrotizing pancreatitis complicated by an MDR A. baumannii infection. Despite multiple antibiotic courses and efforts at percutaneous drainage of a pancreatic pseudocyst, the patient deteriorated over a 4-month period. In the absence of effective antibiotics, two laboratories identified nine different bacteriophages with lytic activity for an A. baumannii isolate from the patient. Administration of these bacteriophages intravenously and percutaneously into the abscess cavities was associated with reversal of the patients downward clinical trajectory, clearance of the A. baumannii infection, and a return to health. The outcome of this case suggests that the methods described here for the production of bacteriophage therapeutics could be applied to similar cases and that more concerted efforts to investigate the use of therapeutic bacteriophages for MDR bacterial infections are warranted.

Managing bite wounds. Currently recommended antibiotics for treatment and prophylaxis.

PREVIEW About half of all persons in the United States will incur an animal or human bite sometime in their life. Not all bite wounds need medical attention, but severe bite wounds and those at high risk of infection are frequent reasons for emergency department visits. What steps are involved in the care of such wounds, and which antibiotics provide the most effective coverage? Dr Taplitz discusses the major epidemiologic factors of various types of bite wounds and outlines a systematic approach to wound care and infection control.

A Heterologous, High-Affinity RNA Ligand for Human Immunodeficiency Virus Gag Protein Has RNA Packaging Activity

ABSTRACT Retroviral RNA encapsidation depends on the specific binding of Gag proteins to packaging (ψ) signals in genomic RNA. We investigated whether an in vitro-selected, high-affinity RNA ligand for the nucleocapsid (NC) portion of the Gag protein from human immunodeficiency virus type 1 (HIV-1) could mediate packaging into HIV-1 virions. We find that this ligand can functionally substitute for one of the Gag-binding elements (termed SL3) in the HIV-1 ψ locus to support packaging and viral infectivity in cis. By contrast, this ligand, which fails to dimerize spontaneously in vitro, is unable to replace a different ψ element (termed SL1) which is required for both Gag binding and dimerization of the HIV-1 genome. A single point mutation within the ligand that eliminates high-affinity in vitro Gag binding also abolishes its packaging activity at the SL3 position. These results demonstrate that specific binding of Gag or NC protein is a critical determinant of genomic RNA packaging.

Control of an Outbreak of Human Parainfluenza Virus 3 in Hematopoietic Stem Cell Transplant Recipients

Human parainfluenza virus 3 (HPIV3) infection can cause significant morbidity and mortality in patients undergoing hematopoietic stem cell transplantation (HSCT). There are no standard guidelines for the prevention and control of HPIV3 in the outpatient setting. After 2 HSCT inpatients diagnosed with HPIV3 were noted to have had multiple recent HSCT outpatient clinic (OPC) visits, an investigation of policy and procedures in the HSCT OPC was undertaken, and active surveillance for respiratory viral illness was instituted in the at-risk HSCT population. Between July 19 and August 30, 2005, 13 patients were diagnosed with HPIV3 infection. Morbidity in affected patients was significant, and mortality was high (38.5%) and not affected by antiviral therapy. Molecular typing identified several genetically distinct groups of the hemagglutinin-neuraminidase gene of the 11 available isolates. Based on sequence relatedness among the isolates and the demographic and exposure history of the patients, in many of these cases HPIV3 infection likely was acquired in the HSCT OPC. The major infection control interventions were introduced between August 20 and August 24. An epidemic curve revealed that HPIV3 infection frequency peaked between August 17 and August 26, with no cases identified after August 30. Prompt attention and focus on infection control interventions were associated with a rapid decrease in the number of incident cases. Policies and procedures regarding patients with respiratory viral illnesses in HSCT OPC populations should be formulated and universally reinforced with HSCT clinic staff to prevent the spread of these infections.

Hospital-Onset Clostridium difficile Infection Rates in Persons with Cancer or Hematopoietic Stem Cell Transplant: A C3IC Network Report

A multicenter survey of 11 cancer centers was performed to determine the rate of hospital-onset Clostridium difficile infection (HO-CDI) and surveillance practices. Pooled rates of HO-CDI in patients with cancer were twice the rates reported for all US patients (15.8 vs 7.4 per 10,000 patient-days). Rates were elevated regardless of diagnostic test used.

Novel H1N1 Influenza in Hematopoietic Stem Cell Transplantation Recipients: Two Centers’ Experiences

Respiratory virus infections, such as influenza A, cause significant morbidity in hematopoietic stem cell transplantation (HSCT) recipients. The clinical characteristics and impact of infection with the novel H1N1 virus in this patient population is not yet well defined, however. HSCT recipients diagnosed with proven or probable H1N1 during the 2009 pandemic were identified and charts were retrospectively reviewed with analysis of clinical descriptions, risk factors, diagnosis, treatments, and outcomes. Twenty-seven patients from two medical centers were identified. Fever and cough were the most common presenting symptoms. The incidence of influenza lower respiratory tract infection (LRTI) was 52% (14/27). Compared with patients with LRTI, those with influenza upper respiratory tract infection (URTI) were more likely to have a classic influenza-like syndrome. Compared to patients with URTI, those with LRTI were started on antiviral therapy significantly later after symptom onset (3.0 days vs 6.58 days after onset of symptoms; P = .03; 95% confidence interval [CI], 0.29-6.8). Overall influenza-related 30-day mortality was 22% (6/27), and that in patients with LRTI was 43% (6/14). Chronic steroid use (≥20 mg/day of prednisone equivalent) at the time of presentation was associated with LRTI (P = .006) and mortality (P = .003) on univariate analysis. Five cases were hospital-acquired. In this first season of the novel H1N1 pandemic, infection in HSCT often presented as an atypical severe illness with a high incidence of LRTI and high mortality.

Extensive Geographical Mixing of 2009 Human H1N1 Influenza A Virus in a Single University Community

ABSTRACT Despite growing interest in the molecular epidemiology of influenza virus, the pattern of viral spread within individual communities remains poorly understood. To determine the phylogeography of influenza virus in a single population, we examined the spatial diffusion of H1N1/09 influenza A virus within the student body of the University of California, San Diego (UCSD), sampling for a 1-month period between October and November 2009. Despite the highly focused nature of our study, an analysis of complete viral genome sequences revealed between 24 and 33 independent introductions of H1N1/09 into the UCSD community, comprising much of the global genetic diversity in this virus. These data were also characterized by a relatively low level of on-campus transmission as well as extensive spatial mixing, such that there was little geographical clustering by either student residence or city ZIP code. Most notably, students experiencing illness on the same day and residing in the same dorm possessed phylogenetically distinct lineages. H1N1/09 influenza A virus is therefore characterized by a remarkable spatial fluidity, which is likely to impede community-based methods for its control, including class cancellations, quarantine, and chemoprophylaxis.

Risk factors associated with linezolid-nonsusceptible enterococcal infections

Linezolid is one of few treatment options available for vancomycin-resistant enterococci. The present study investigated risk factors for linezolid-nonsusceptible enterococci using a case-control study of 15 cases and 60 control patients. Previous hospitalization, admission to a medical service, comorbidity, and linezolid and sulfonamide therapy were identified as risk factors.