Hill, T. F. | Search bioRxiv

bioRxiv2025

Humanized mice enable in vivo evaluation of engineered plasma cell biology and therapeutic function

Engineered plasma cells (ePCs) offer a durable strategy for in vivo delivery of therapeutic antibodies, but standard immunodeficient mouse models lack human immune factors critical for plasma cell survival and function. We utilized a humanized mouse model in which NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice were engrafted with human CD34+ stem cells as recipients for infusions with autologous ePCs. In this setting, ePCs localized to plasma cell niches and stably secreted antibodies for over three months. To improve the selection of antibodies for secretion, we developed a B cell receptor surface display screen that identified candidate antibody sequences with high secretion potential. An anti-SARS-CoV-2 antibody (clone 297) selected by this method showed robust secretion both in vitro and vivo, and serum from ePC-engrafted mice potently neutralized SARS-CoV-2 pseudovirus. Together, these findings establish a physiologically relevant model for testing human ePCs, and offer a generalizable strategy for optimizing antibody selection to support long-term therapeutic delivery.

molecular biology↗

bioRxiv2023

Human plasma cells engineered to secrete bispecifics drive effective in vivo leukemia killing

Bispecific antibodies are an important tool for the management and treatment of acute leukemias. Advances in genome-engineering have enabled the generation of human plasma cells that secrete therapeutic proteins and are capable of long-term in vivo engraftment in humanized mouse models. As a next step towards clinical translation of engineered plasma cells (ePCs) towards cancer therapy, here we describe approaches for the expression and secretion of bispecific antibodies by human plasma cells. We show that human ePCs expressing either fragment crystallizable domain deficient anti-CD19 x anti-CD3 (blinatumomab) or anti-CD33 x anti-CD3 bispecific antibodies mediate T cell activation and direct T cell killing of specific primary human cell subsets and B-acute lymphoblastic leukemia or acute myeloid leukemia cell lines in vitro. We demonstrate that knockout of the self-expressed antigen, CD19, boosts anti-CD19 bispecific secretion by ePCs and prevents self-targeting. Further, anti-CD19 bispecific-ePCs elicited tumor eradication in vivo following local delivery in flank-implanted Raji lymphoma cells. Finally, immunodeficient mice engrafted with anti-CD19 bispecific-ePCs and autologous T cells potently prevented in vivo growth of CD19+ acute lymphoblastic leukemia in patient-derived xenografts. Collectively, these findings support further development of ePCs for use as a durable, local delivery system for the treatment of acute leukemias, and potentially other cancers. Key pointsO_LIUsing gene editing, we engineered human plasma cells that secrete functional bispecifics to target leukemia cells expressing CD19 or CD33 C_LIO_LIEngineered plasma cells secreting bispecifics suppress patient-derived leukemia in immunodeficient mice C_LI

bioengineering↗