** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THE HORSE-BREEDING INDUSTRY IS AN ECONOMICALLY IMPORTANT AGRICULTURAL ENTITY IN TEXAS AND OTHER STATES. PNEUMONIA IN FOALS CAUSED BY INHALING THE BACTERIUM RHODOCOCCUS EQUI (R. EQUI) INTO THEIR LUNGS IS A LEADING CAUSE OF DISEASE AND DEATH AT HORSE-BREEDING FARMS THAT RESULTS IN LARGE ECONOMIC COSTS AND WELFARE CONCERNS FOR THE INDUSTRY. A HIGHLY EFFECTIVE METHOD FOR PREVENTING THIS DISEASE IS LACKING. WE HYPOTHESIZE THAT AEROSOLIZING FOALS WITH MESSENGER RNA (MRNA) THAT INSTRUCTS THE FOALS LUNG CELLS TO MAKE MONOCLONAL ANTIBODIES TARGETING R. EQUI WILL BE AN EFFECTIVE WAY TO PREVENT RHODOCOCCAL PNEUMONIA. OUR OBJECTIVES ARE: 1) TO DEMONSTRATE THAT MRNA-ENCODED ANTIBODIES RECOGNIZE AND MEDIATE KILLING OF R. EQUI IN CELL-CULTURES; 2) TO OPTIMIZE THE DOSE AND FORMULATION OF THE MRNA ENCODING ANTIBODIES FOR AEROSOL DELIVER TO THE LUNGS OF FOALS; 3) TO DEMONSTRATE THAT AEROSOLIZING AN MRNA CAN ENABLE FOALS TO MAKE ANTIBODIES THAT RECOGNIZE AND MEDIATE KILLING OF R. EQUI IN THEIR LUNGS; AND, 4) TO DEMONSTRATE THAT AEROSOLIZING FOALS WITH MRNA ENCODING ANTIBODIES TARGETING R. EQUI CAN PREVENT FOALS FROM DEVELOPING MRNA. THE IMPACT OF THIS PROJECT WILL BE TO LEAD TO A MORE EFFECTIVE, FASTER, AND SAFER WAY TO PROTECT FOALS AGAINST RHODOCOCCAL PNEUMONIA. MOREOVER, THE APPROACH OF USING MRNA TO PROTECT AGAINST RESPIRATORY TRACT INFECTIONS WILL HAVE APPLICATIONS TO MICROBES OTHER THAN R. EQUI AND TO SPECIES OF AGRICULTURAL ANIMALS OTHER THAN HORSES.