It has been shown that inhalation exposure to copper oxide nanoparticles (CuO NPs) results in pulmonary inflammation. However, immunomodulatory consequences after CuO NP inhalation exposure have been less explored. We tested the effect of CuO NP aerosols on immune responses in healthy, house dust mite (HDM) asthmatic, or allergen immunotherapy (AIT)-treated asthmatic mice (BALB/c, females). The AIT consisted of a vaccine comprising HDM allergens and CpG-loaded nanoparticles (CpG NPs). AIT treatment involved mice being immunized (via subcutaneous (sc) injection; 2 doses) while concomitantly being exposed to CuO NP aerosols (over a 2 week period), starting on the day of the first vaccination. Mice were then sensitized twice by sc injection and subsequently challenged with HDM extract 10 times by intranasal instillation. The asthmatic model followed the same timeline except that no immunizations were administered. All mice were necropsied 24 h after the end of the HDM challenge. CuO NP-exposed healthy mice showed a significant decrease in T1 and T2 cells, and an elevation in T-bet Treg cells, even 40 days after the last exposure to CuO NPs. Similarly, the CuO NP-exposed HDM asthma model demonstrated decreased T2 responses and increased T-bet Treg cells. Conversely, CuO NP inhalation exposure to AIT-treated asthmatic mice resulted in an increase in T2 cells. In conclusion, immunomodulatory effects of inhalation exposure to CuO NPs are dependent on immune conditions prior to exposure.