Economic evaluation of latent tuberculosis infection screening among health care workers in Houston

Since interferon-gamma release assays (IGRAs) were introduced in the 2000's, tuberculin skin testing (TST) and IGRAs have been used in various latent tuberculosis infection (LTBI) screening settings. IGRAs are laboratory-based tests and are considered not to be affected by previous Bacille de Calmette et Guérin (BCG) vaccination; however, they are more costly when compared directly with TST, which does not require specimen processing in a laboratory. This study aimed to examine TST and two types of IGRAs, QuantiFERON-TB Gold in Tube (QFT-GIT) and T-SPOT. TB (TSPOT), from an economic viewpoint. Firstly, a systematic literature review was conducted to identify cost related analyses of LTBI screening. Secondly, specific cost information detailing each test's items and labor was collected from an LTBI screening program of health care workers in Houston, and the cost of each test was computed. Thirdly, using the computed cost estimate of each test, cost-effectiveness analyses were conducted to compare TST and IGRAs.^ A literature search showed that a limited number of studies have been conducted, but the IGRA's economic advantages were common among studies. Cost analyses showed that IGRAs were much more costly than TST. The results were consistent with previous studies. In cost-effectiveness analyses, where test cost and consequential TB-related cost were considered, IGRAs showed variable advantages over TST depending on the targeted population. When only non BCG-vaccinated people were considered, TST was the least costly option among the three tests. On the other hand, when only BCG-vaccinated people were considered, IGRAs were less costly options. These results were mostly consistent even with varying assumption parameters.^ IGRAs can be more costly than TST, but their economic disadvantages are alleviated when the target population was BCG-vaccinated. Based on current knowledge, IGRAs may be recommended in a population where the BCG history is mixed. Additional studies are needed to better understand IGRA's reliability among low-incidence and low-risk populations in which background TB prevalence is low.^

INDUCTION OF STRONGER AND LONG LASTING VACCINE IMMUNITY TO TUBERCULOSIS

Tuberculosis is a major cause of death due to an infection in mankind. BCG vaccine protects against childhood tuberculosis although, it fails to protect against adult tuberculosis. BCG vaccine localizes to immature phagosomes of macrophages, and avoids lysosomal fusion, which decreases peptide antigen production. Peptides are essential for macrophage-mediated priming of CD4 and CD8 T cells respectively through MHC-II and MHC-I pathways. Furthermore, BCG reduces the expression of MHC-II in macrophages of mice after infection, through Toll-like receptor-1/2 (TLR-1/2) mediated signaling. In my first aim, I hypothesized that BCG-induced reduction of MHC-II levels in macrophages can decrease CD4 T cell function, while activation of other surface Toll-like receptors (TLR) can enhance CD4 T cell function. An in vitro antigen presentation model was used where, TLR activated macrophages presented an epitope of Ag85B, a major immunogen of BCG to CD4 T cells, and T cell derived IL-2 was quantitated as a measure of antigen presentation. Macrophages with BCG were poor presenters of Ag85B while, TLR-7/9/5/4 and 1/2 activation led to an enhanced antigen presentation. Furthermore, TLR-7/9 activation was found to down-regulate the degradation of MHC-II through ubiquitin ligase MARCH1, and also stimulate MHC-II expression through activation of AP-1 and CREB transcription elements via p38 and ERK1/2 MAP kinases. I conclude from Aim-I studies that TLR-7/9 ligands can be used as more effective ‘adjuvants’ for BCG vaccine. In Aim-II, I evaluated the poor CD8 T cell function in BCG vaccinated mice thought to be due to a decreased leak of antigens into cytosol from immature phagosomes, which reduces the MHC-I mediated activation of CD8 T cells. I hypothesized that rapamycin co-treatment could boost CD8 T cell function since it was known to sort BCG vaccine into lysosomes increasing peptide generation, and it also enhanced the longevity of CD8 T cells. Since CD8 T cell function is a dynamic event better measurable in vivo, mice were given BCG vaccine with or without rapamycin injections and challenged with virulent Mycobacterium tuberculosis. Organs were analysed for tetramer or surface marker stained CD8 T cells using flow cytometry, and bacterial counts of organisms for evaluation of BCG-induced protection. Co-administration of rapamycin with BCG significantly increased the numbers of CD8 T cells in mice which developed into both short living effector- SLEC type of CD8 T cells, and memory precursor effector-MPEC type of longer-living CD8 T cells. Increased levels of tetramer specific-CD8 T cells correlated with a better protection against tuberculosis in rapamycin-BCG group compared to BCG vaccinated mice. When rapamycin-BCG mice were rested and re-challenged with M.tuberculosis, MPECs underwent stronger recall expansion and protected better against re-infection than mice vaccinated with BCG alone. Since BCG induced immunity wanes with time in humans, we made two novel observations in this study that adjuvant activation of BCG vaccine and rapamycin co-treatment both lead to a stronger and longer vaccine-mediated immunity to tuberculosis.

Correlation of tuberculosis and human immunodeficiency virus in Harris County, Texas from 2009 through 2010 using Geographic Information Systems

A population based ecological study was conducted to identify areas with a high number of TB and HIV new diagnoses in Harris County, Texas from 2009 through 2010 by applying Geographic Information Systems to determine whether distinguished spatial patterns exist at the census tract level through the use of exploratory mapping. As of 2010, Texas has the fourth highest occurrence of new diagnoses of HIV/AIDS and TB.[31] The Texas Department of State Health Services (DSHS) has identified HIV infected persons as a high risk population for TB in Harris County.[29] In order to explore this relationship further, GIS was utilized to identify spatial trends. ^ The specific aims were to map TB and HIV new diagnoses rates and spatially identify hotspots and high value clusters at the census tract level. The potential association between HIV and TB was analyzed using spatial autocorrelation and linear regression analysis. The spatial statistics used were ArcGIS 9.3 Hotspot Analysis and Cluster and Outlier Analysis. Spatial autocorrelation was determined through Global Moran's I and linear regression analysis. ^ Hotspots and clusters of TB and HIV are located within the same spatial areas of Harris County. The areas with high value clusters and hotspots for each infection are located within the central downtown area of the city of Houston. There is an additional hotspot area of TB located directly north of I-10 and a hotspot area of HIV northeast of Interstate 610. ^ The Moran's I Index of 0.17 (Z score = 3.6 standard deviations, p-value = 0.01) suggests that TB is statistically clustered with a less than 1% chance that this pattern is due to random chance. However, there were a high number of features with no neighbors which may invalidate the statistical properties of the test. Linear regression analysis indicated that HIV new diagnoses rates (β=−0.006, SE=0.147, p=0.970) and census tracts (β=0.000, SE=0.000, p=0.866) were not significant predictors of TB new diagnoses rates. ^ Mapping products indicate that census tracts with overlapping hotspots and high value clusters of TB and HIV should be a targeted focus for prevention efforts, most particularly within central Harris County. While the statistical association was not confirmed, evidence suggests that there is a relationship between HIV and TB within this two year period.^

Human complement component C3 -binding proteins of Mycobacterium tuberculosis

Mycobacterium tuberculosis, the causative agent of tuberculosis, is a facultative intracellular pathogen that uses the host mononuclear phagocyte as a niche for survival and replication during infection. Complement component C3 has previously been shown to enhance the binding of M. tuberculosis to mononuclear phagocytes. Using a C3 ligand affinity blot protocol, we identified a 30 kDa C3-binding protein in M. tuberculosis as heparin-binding hemagglutinin (HbhA). HbhA was found to be a hydrophobic protein that localized to the cell membrane/cell wall fraction of M. tuberculosis, and this protein has previously been shown by others to be located on the surface of M. tuberculosis. The C3-binding activity of HbhA was localized to the C-terminus of the protein, which consists of lysine-alanine repeats. Full-length recombinant HbhA coated onto latex beads was shown to mediate the adherence of the beads to murine macrophage-like cells in both a C3-dependent and a C3-independent manner. An in-frame 576 by deletion in the hbhA gene was created in a virulent strain of M. tuberculosis using a PCR technique known as gene splicing by overlap extension (SOEing). Using the ΔhbhA mutant, HbhA was found not to be necessary for growth of M. tuberculosis in laboratory media or in macrophage-like cells, nor is HbhA required for adherence of M. tuberculosis to macrophage-like cells. HbhA is, however, required for infectivity of M. tuberculosis in mice. Mice infected with the ΔhbhA mutant show decreased growth in the lungs, liver, and spleen compared to mice infected with the wild-type strain. Using the ΔhbhA mutant strain, we were able to purify and identify a second 30-kDa C3-binding protein, HupB. These data demonstrate that HbhA is required for the in vivo but not the in vitro survival of M. tuberculosis and that HbhA is not necessary for the adherence of M. tuberculosis to the macrophage-like cells used in these studies. The expression of two proteins that bind human C3 may aid in the efficient binding of M. tuberculosis to complement receptors for uptake into mononuclear cells, or may influence other aspects of the host-parasite interaction. ^