EμB29-Btk-LV therapy restores splenic follicular morphology. Frozen sections from secondary transplantation mice were stained for IgM (blue), IgD (green), and MOMA (red) and then imaged using fluorescence microscopy. Slides were analyzed for the presence of follicles, indicated by IgM^loIgD^hi follicular B cells (green) separated from IgM^hiIgD^lo marginal zone B cells (blue) by a ring of MOMA⁺ marginal zone macrophages (red). Images show representative spleen sections from a WT control mouse (A) and recipients of WT mock (B), KO mock (C-D), and LV MOI 15- to 25-treated BM (E-F).