Rationalse: TPI ASM8 contains two modified phosphorothioate antisense oligonucleotides, designed to inhibit allergic inflammation by down-regulating human CCR3 and the common beta chain (_c) of IL-3, IL-5, and GM-CSF receptors. This study examined the effects of inhaled TPI ASM8 on sputum cellular influx, CCR3 and _c mRNA and protein levels and the airway physiological response after inhaled allergen. Methods: Seventeen subjects with mild atopic asthma were randomized in a crossover study to inhale 1500 mcg TPI ASM8 or placebo by nebulizer, once daily for 4 days. On Day 3, subjects underwent allergen inhalation challenge. Sputum samples were collected before and after allergen. CCR3 and _c protein levels were measured by flow cytometry, mRNA was measured using real time quantitative PCR and the FEV₁ was measured over 7 hours after challenge. Results: Compared to placebo, TPI ASM8 inhibited sputum eosinophil influx by 46 % (p=0.02) and blunted the increase in total cells (63%) after allergen challenge. TPI ASM8 significantly reduced the EAR (p= 0.03) with a trend for the LAR (p= 0.08). The allergen-induced (Day 2 to Day 3) levels of _c mRNA and CCR3 mRNA in sputum-derived cells was inhibited by TPI ASM8 (p=0.039 and p=0.055, respectively) with no significant effects on the cell surface protein expression of CCR3 and _c (p>0.05). No serious adverse events were reported. Conclusions: TPI ASM8 attenuates the allergen-induced increase in target gene mRNA and airway responses in subjects with mild asthma. Clinical Trials Registry Information: ID# NCT00264966 registered at www.clinicaltrials.gov