A new humanized mouse mounting mature class-switched, hypermutated and neutralizing antibody responses: estrogen power

Existing humanized mice have shown significant limitations in immune functions, particularly in the maturation of antibody responses. We have constructed a new humanized (THX) mouse by intracardiac grafting of non-gamma-irradiated, genetically myeloablated NBSGW and NSGW41 immunodeficient mouse neonates with human umbilical cord CD34+ hematopoietic stem cells (HSCs), followed by hormonal conditioning with estradiol, the most potent and abundant estrogen, to promote immune cell differentiation. THX mice reconstitute an immune system with human CD45+ cells accounting for virtually all lymphoid and myeloid cells, including human TFH cells and neutrophils. They develop a thymus that includes human epithelial cells and human B cells and show well-developed lymph nodes and spleen. Using expressed human BCR and TCR cell repertoires, THX mice mount mature antibody responses to T-dependent and T-independent conjugated haptens, entailing SHM/CSR, germinal center formation, plasma cell differentiation and generation of memory B cells. Upon vaccination with flagellin and Pfizer COVID-19 mRNA, they mount mature neutralizing antibody responses to Salmonella Typhimurium and SARS-CoV-2 Spike S1 RBD, as accompanied by human APRIL, BAFF, TGF-beta, IFN-gamma and other antibody response-related cytokines at physiological human concentrations. Finally, THX mice develop lupus autoimmunity after one pristane injection. In addition to providing a new and advanced platform for potential development of human vaccines and immune therapeutics, they reveal and leverage a critical activity of estradiol to promote human immune cell differentiation and maturation of antibody responses.