The invention provides methods for generating high titers of high-affinity antibodies from hybridoma cells produced by fusing myeloma cells with in vitro immunized donor cells. The hybridoma cells or mammalian expression cells with cloned antibody genes from the hybridomas producing the high-affinity antibodies may be mismatch repair defective due to defects of endogenous mismatch repair subunits of through expression of a dominant negative allele of a mismatch repair gene which allows the hybridoma cell to be hypermutable, may be rendered hypermutable by chemical means, or may be naturally mismatch repair deficient. High-affinity antibodies and high titer producer cells producing antibodies may be prepared by the methods of the invention.