Adaptation of an in vitro generated human skin model for tick feeding to study Borrelia burgdorferi transmission and colonization

Abstract
The Lyme Disease pathogen Borrelia burgdorferi is estimated to cause nearly half a million human
infections in the U.S. every year. Transmitted by the blacklegged deer tick (Ixodes scpaularis), B.
burgdorferi is passed between rodents, ticks and large mammals to complete its complex enzootic cycle.
Humans get infected as an incidental host, usually in the springtime by nymph-stage ticks. In this
proposal we adapt an established lab-generated in vitro organotypic stratified keratinocyte skin model
to induce attachment and feeding of ticks. In Aim 1, we continue to modify the skin to increase tick
feeding efficiency and demonstrate transmission and acquisition of B. burgdorferi by nymph-stage ticks.
In Aim 2, we characterize the kinetics of bacterial growth and spread within organotypic skin following
direct injection and validate that B. burgdorferi responds to environmental cues of the bloodmeal (pH,
temperature) to increase expression of mammalian stage virulence factors. This novel organotypic
human skin model is highly adaptable and can accommodate introduction of other cell types. For
instance, in Aim 1 we introduce endothelial cells, macrophages and extracellular matrix factors into the
skin to induce vascularization and provide a biologically-relevant blood delivery system. This is the first
demonstration of arthropod feeding on in vitro organotypic human skin, and its development will enable
new avenues of research not only for Lyme Disease research, but also for other tick-borne diseases. We
expect this model will reduce the need for animals in Lyme Disease research and will provide a system
to answer long-standing questions in tick-pathogen biology, such as the role of resident immune cells in
containing infection and the contribution of specific bacterial virulence factors to skin colonization and
dissemination into the bloodstream. Given the scalable and reproducible nature of this model, we can
use it as a platform to screen therapies that could prevent pathogen colonization following a tick bite or
prophylactics that would prevent tick feeding.

Grant Number: 1R21AI185574-01A1
NIH Institute/Center: NIH
Principal Investigator: Amanda Brinkworth