Engineering Adaptive Immunity in 3D: A Patient‐Specific Lymphoid Model Using Stromal Networks and Peripheral Blood Mononuclear Cells

Abstract Tertiary lymphoid organs (TLOs) are non‐encapsulated immune structures that emerge in response to chronic inflammation, orchestrating local adaptive immune responses. However, recapitulating their complexity in vitro remains challenging due to the difficulty in generating physiologically relevant stromal‐immune interactions. Here, a 3D lymphoid tissue model is presented, engineered using human adipose‐derived stem cells (ADSCs) differentiated into fibroblastic reticular cell (FRC)‐like populations within collagen matrices. Differentiation is induced using TNF‐α and LT‐α, with or without IL‐4, generating two stromal phenotypes: FRC _P1 and FRC _P2 . These subsets exhibit matrix remodeling, distinct transcriptional signatures, and surface markers consistent with lymph node‐resident T cell reticular and follicular dendritic cell subsets. Upon co‐culture with peripheral blood mononuclear cells (PBMCs) and SARS‐CoV‐2 S1‐primed mature dendritic cells, the model supports antigen‐specific B cell activation and cytokine environments indicative of Th1 or Th2 polarization. FRC _P1 favors B cell support and IgM secretion, whereas FRC _P2 promotes dendritic cell activation and Th1‐type chemokine expression. This platform demonstrates the functional diversification of stem cell‐derived FRC‐like subsets and their role in orchestrating immune microenvironments. It enables investigation of lymphoid tissue remodeling, stromal‐immune crosstalk, and antibody generation using total PBMCs, providing a scalable, customizable system for personalized vaccine screening, autoimmune modeling, and therapeutic development.