Study Description:
This study aims to develop a model for acquired tick resistance in humans, characterize the acquisition of tick-associated skin immunity, and monitor the innate and adaptive immune response of Ixodes scapularis tick bites. The study will be a prospective, non-randomized, single-center study performed at the National Institutes of Health (NIH) Clinical Center. It will be performed under Investigational Device Exemption (IDE) G210153, and will be monitored as per National Institute of Allergy and Infectious Diseases (NIAID) and NIH regulations. Participants (35 adult healthy volunteers) will undergo up to 3 tick feeding placements, 2 to 8 weeks
apart. One to two punch skin biopsies (2-3 mm) from the tick bite sites will be collected at 1 day (early) and 2-4 days (late) after the first tick placement procedure. Skin biopsies of an unaffected site will be performed as a control. One to two punch skin biopsies (2-3 mm) from the tick bite sites will be collected at day 2-3 after the 2nd and 3rd tick placement procedures. Additionally, blood will be collected to evaluate systemic immune response to tick salivary proteins. Ticks will also be collected at each timepoint and gene expression will be analyzed to determine the effect of the human skin response on ticks.
Changes in resistance to tick bites can be evaluated by:
* Local reaction to the tick bite
* pruritus
* site reactions
* Blood flow index as measured by laser speckle contrast imaging
* Number of fed ticks
Changes in the immune response and cellular recruitment in the skin can be evaluated using:
Differential expression of immune transcripts and other skin associated transcripts using RNAseq or other high-throughput profiling of cells
Conventional histology and immunohistochemistry
Digital Spatial Profiling to determine cell type and other immune markers using a high-plex platform
Changes in the systemic immune response will be evaluated by:
Measurement of antibodies against tick salivary proteins will be assessed by enzyme-linked immunosorbent assay (ELISA) and
western blot
Novel state-of-the-art high resolution technologies to deeply characterize the immune response to tick bites over time, both phenotypically and functionally.
Changes in tick transcriptomic profile will be assessed by:
RNAseq: Ribonucleic acid (RNA) will be isolated from tick after they have been removed from subjects and unexposed ticks.
Differential expression profile will be performed and validated by NanoString
Objectives:
Primary Objectives:
1. Develop a model of acquired tick resistance in humans
2. Continue to assess the safety of tick feeding using laboratory-reared Ixodes scapularis larva in humans
Exploratory Objectives:
1. Comparison of the early and late immune response in the skin site of the bite of Ixodes scapularis after a single tick exposure.
2. Determine the effects of repeated tick feeding on the immune response at the tick bite site in human skin and development of tick resistance.
3. Analyze the evolution of the systemic immune response to tick bite in participants after multiple tick exposures and validate development of reliable biomarkers of tick exposure.
4. Analyze gene expression of Ixodes scapularis larvae feeding on humans and determine the effects of immune response of subjects
repeatedly bitten on larvae gene expression.
Endpoints:
Primary Endpoints:
1. Pruritus at the site of tick attachment in the first 24 hours of tick placement over the three placements as measured by a positive slope
over the three placements of the numerical rating score. The slope of other pruritus scores at 24 hours and at Day 2-4, and the number of attached ticks collected from participants over the three placements will also be measured.
2. Monitor safety adverse events (AEs) using reporting tools and Sponsor safety monitors.
Exploratory Endpoints:
1. Compare the results from the skin biopsies acquired with the first tick placement. Our hypothesis is that there will be differential phenotypic, transcriptomic, and immunohistochemical differences between:
* Exposed (bitten skin at day 1) and unexposed (unbitten skin)
* Exposed (bitten skin at day 2-4) and unexposed (unbitten skin)
* Exposed (bitten skin at day 1) and exposed (bitten skin at day 2-4)
Measurement of changes will be assessed by:
* Differential expression of immune transcripts and other skin associated transcripts using RNAseq
* Conventional histology and immunohistochemistry
* Digital Spatial Profiling to determine cell type and other immune markers using a high-plex platform
2. Compare the changes in the local immune response and cellular recruitment between the 1st, 2nd and the 3rd tick exposures and correlate with measures of itching, blood flow index and number of attached ticks and the feeding status.
We postulate that differences between the timepoints will become more marked with multiple exposures. We hypothesize that there will be differential phenotypic and transcriptomic differences between:
Exposed (bitten skin at day 2-3, exposure 2) and exposed (bitten skin at day 2-3, exposure 3)
Correlate these changes with measures of resistance to tick feeding (itching, number and level of feeding of attached ticks, blood flow index).
3. Compare the development of antibody responses against Ixodes scapularis salivary protein antigens between the 1st, 2nd, and the 3rd tick exposures and correlate antibodies against tick salivary proteins with measures of resistance (itching, erythema, blood flow index, number of fed ticks).
Explore the development of the host response in blood using high resolution technologies such as immunophenotyping, proteomics and
transcriptomics and compare the responses between the 1st, 2nd, and the 3rd tick exposures.
4. Using RNAseq technology, measure changes in gene expression of ticks fed at early timepoint (1 day) vs late timepoint (2-4 days) vs unfed ticks and of ticks fed at 1st, 2nd, and 3rd placements. Correlation of pruritus and changes in tick gene expression.
