Introduction:
Heated-tobacco-products (HTPs) are electronic devices that ?heat? a processed tobacco/chemical mixture to ~250-350ºC to produce inhalable emissions. They are advertised as a reduced-risk alternative to cigarette smoking. The aim of our research was to assess these claims with unbiased scientific data.

Methods:
Primary human airway epithelial cells (n=9, from adolescents aged 11-21yrs) were grown at Air-Liquid Interface for 28-days allowing for mucociliary differentiation. These cultures were then exposed for 1 hour to the emissions from three HTPs (Philip Morris International IQOS3 Duo, British American Tobacco glo and Japan Tobacco International Ploom S) according to a standardised protocol. Air and conventional cigarette smoke were used as controls. Emission physico-chemical characteristics were analysed and health impacts including viability, airway barrier integrity and inflammatory mediator release were assessed.

Results:
HTP emissions contained a range of toxic chemicals, some at higher concentrations than in cigarette smoke. Particle size spectra showed smaller average particle size but also fewer particles overall for HTPs. Ploom and glo led to the most direct cellular damage, with decreased viability, increased necrotic cell death and decreased barrier integrity compared to Air controls. Cigarette smoke caused the greatest increase in mediator response. Conversely, exposure to all HTP emissions instead decreased mediator response (compared with Air control), suggesting immune suppression.

Conclusion:
HTPs are not a reduced-risk alternative to cigarettes but a different risk alternative.

Support: Wal-Yan Respiratory Research Centre, Australian Respiratory Council