OBJECTIVES/GOALS: Re-administration of inhaled gene therapies has the potential to overcome low correction efficiencies and limiting immune responses observed in previous trials of gene therapy for Cystic Fibrosis. We therefore tested the hypothesis that pre-treatment with a B-cell depleting α ± CD20 antibody would permit vector re-administration. METHODS/STUDY POPULATION: We first selected Adenoviral (Ad) vectors to study initially due to their well-known ability to elicit potent immune responses. Mice were dosed with a depleting α ± CD20 antibody or isotype control 2 days prior to delivery of Ad-Luc. 4 weeks later, mice were euthanized to assess the development of anti-vector immune responses. Flow cytometry and single-cell RNA sequencing were used to evaluate the development of lung-resident memory cells. Serum and airway antibody responses were assessed by ELISA. After 4 weeks, mice were dosed with Ad-LacZ and euthanized 3 days later to assess efficiency of second-round gene transfer by β-galactosidase activity assay. Similar methods were used in a pilot experiment with Adeno-associated virus vector (AAV), but with euthanasia 3 weeks after secondary gene transfer. RESULTS/ANTICIPATED RESULTS: Delivery of Ad vectors leads to the development of lung-resident memory B and T-cells. The depletion of B-cells prior to first-round vector delivery attenuated airway T-cell infiltration and serum IgG production, abrogated mucosal IgG and IgA production, and completely rescued secondary gene transfer. Genetically modified mouse models suggest secreted antibodies are critical in prevention of vector redosing. AAV vectors were found to be less immunogenic than Ad vectors, with only partial reduction of second-round gene transfer. However, anti-CD20 provided no benefit for AAV redelivery. DISCUSSION/SIGNIFICANCE: Mucosal humoral immunity is critical in preventing re-administration of Adenoviral vectors. Impairment of B-cell responses by α ± CD20 treatment prior to vector delivery allows re-administration and may help overcome low efficiencies of CF gene therapy. AAV vectors may be less susceptible to neutralization by pre-existing immunity.