Therapeutic human polyclonal
antibodies (hpAbs) derived from pooled plasma from human donors are Food and Drug Administration approved biologics used in the treatment of a variety of human diseases. Powered by the natural diversity of immune response, hpAbs are effective in treating diseases caused by complex or quickly-evolving
antigens such as viruses. We previously showed that transchromosomic (Tc) cattle carrying a human artificial chromosome (HAC) comprising the entire unrearranged human
immunoglobulin heavy-chain (hIGH) and kappa-chain (hIGK) germline loci (named as κHAC) are capable of producing functional hpAbs when both of the bovine
immunoglobulin mu heavy-chains, bIGHM and bIGHML1, are homozygously inactivated (double knockouts or DKO). However, B lymphocyte development in these Tc cattle is compromised, and the overall production of hpAbs is low. Here, we report the construction of an improved HAC, designated as cKSL-HACΔ, by incorporating all of the human
immunoglobulin germline loci into the HAC. Furthermore, for avoiding the possible human-bovine interspecies incompatibility between the human
immunoglobulin mu chain protein (hIgM) and bovine transmembrane α and β
immunoglobulins (bIgα and bIgβ) in the
pre-B cell receptor (pre-BCR) complex, we partially replaced (bovinized) the hIgM constant domain with the counterpart of bovine
IgM (bIgM) that is involved in the interaction between bIgM and bIgα/Igβ; human
IgM bovinization would also improve the functionality of hIgM in supporting B cell activation and proliferation. We also report the successful production of DKO Tc cattle carrying the cKSL-HACΔ (cKSL-HACΔ/DKO), the dramatic improvement of B cell development in these cattle and the high level production of hpAbs (as measured for the human
IgG isotype) in the plasma. We further demonstrate that, upon immunization by
tumor immunogens, high titer
tumor immunogen-specific human
IgG (
hIgG) can be produced from such Tc cattle.