Effective vaccines inducing lifelong protection against many important infections such as respiratory syncytial virus (RSV), human immunodeficiency virus (HIV), influenza and Epstein-Barr virus (EBV) are not yet available despite decades of research. As an alternative to a protective vaccine we developed a genetic engineering strategy in which CRISPR/Cas9 was utilized to replace endogenously-encoded antibodies with antibodies protective against RSV, HIV, influenza or EBV in primary human or murine B cells. The engineered antibodies were expressed in up to 59% of primary B cells under the control of endogenous regulatory elements, which maintained normal antibody expression and secretion.Importantly, a single transfer of murine B cells engineered to express an antibody protective against RSV resulted in potent and durable protection against RSV infection in immunocompromised hosts.This approach offers the opportunity to achieve sterilizing immunity against pathogens for which traditional vaccination has failed to induce or maintain protective antibody responses.