Pretreatment with PFT-β or KGF + PFT-β significantly improves primary and secondary immune responses against Lm after congenic BMT. Lethally irradiated B6 recipients of congenic (B6 Ly5.1⁺) BM were left untreated (BMT Control) or pretreated with KGF, PFT-β, or KGF + PFT-β and immunized at 4 weeks after BMT alongside unmanipulated age-/sex-matched B6 controls (non-BMT control). For primary immunization, 10⁶ CFU of an attenuated strain of Lm that express recombinant full-length chicken ovalbumin (ΔactA-Lm-OVA) was intravenously injected. (A) Absolute numbers of CD44⁺CD8⁺ K^b-OVA_257-64–specific T cells were quantified in peripheral blood of infected animals by FACS 8 days after primary infection. (B) Immunized mice were then rechallenged with 10⁵ CFU of the virulent parent strain, Lm-OVA, 5 weeks after primary infection. After 3 days, bacterial CFUs in (B) liver and (C) spleen were determined by plating of serial dilutions of organ homogenates onto BHI agar. (D-H) Immunofluorescence staining of spleen cryosections for B220⁺ B cells (green) and gp38⁺ FRCs (red) was used to assess the relative abundance of gp38⁺ FRCs in T-cell zones of (A) unmanipulated, age-/sex-matched B6 control (non-BMT Controls) or BM transplant recipients that were (B) left untreated (BMT control) or treated with (C) KGF, (D) PFT-β, or (E) KGF + PFT-β. A white, dashed line encircles the B220⁻ T-cell zones. Data are representative of 2 experiments, each with 4 mice per group; *P < .05 compared with BMT controls.