Initiation of primary T cell-B cell interactions and extrafollicular antibody responses in an organized...

Antibody production is central to protection against new pathogens and cancers, as well as to certain forms of autoimmunity. Antibodies often originate in the lymph node (LN), specifically at the extrafollicular border of B cell follicles, where T and B lymphocytes physically interact to drive B cell maturation into antibody-secreting plasmablasts. In vitro models of this process are sorely needed to predict aspects of the human immune response. Microphysiological systems (MPSs) offer the opportunity to approximate the lymphoid environment, but so far have focused primarily on memory recall responses to antigens previously encountered by donor cells. To date, no 3D culture system has replicated the engagement between T cells and B cells (T-B interaction) that leads to antibody production when starting with naïve cells. Here, we developed a LN-MPS to model early T-B interactions at the extrafollicular border built from primary, naïve human lymphocytes encapsulated within a collagen-based 3D matrix. Within the MPS, naïve T cells exhibited CCL21-dependent chemotaxis and chemokinesis as predicted. Naïve T and B cells were successfully skewed on chip to an early T follicular helper (pre-Tfh) and activated state, respectively, and co-culture of the latter cells led to CD38+ plasmablast cells and T cell dependent production of IgM. These responses required differentiation of the T cells into pre-Tfhs, physical cell-cell contact, and were sensitive to the ratio at which pre-Tfh and activated B cells were seeded on-chip. Dependence on T cell engagement was greatest at a 1:5 T:B ratio, while cell proliferation and CD38+ signal was greatest at a 1:1 T:B ratio. Furthermore, plasmablast formation was established starting from naïve T and B cells on-chip. We envision that this MPS model of primary lymphocyte physiology will enable new mechanistic analyses of human humoral immunity in vitro.