The present invention provides compositions for the production of an antibody or functional fragment thereof directed against Sialyl-Lewisa (sLea). The compositions of the invention include polynucleotides encoding a heavy chain and/or a light chain variable domain that binds to sLea. The invention also provides an isolated antibody or functional fragment thereof and methods of treating or preventing a disease, such as cancer or tumor formation, wherein the antibody or functional fragment includes a variable heavy chain domain and a variable light chain domain that has an amino acid sequence provided herein. The invention further provides a conjugate of an antibody or functional fragment thereof conjugated or recombinantly fused to a diagnostic agent, detectable agent or therapeutic agent, and methods of treating, preventing or diagnosing a disease in a subject in need thereof.