Background: Infections caused by multidrug-resistant bacteria and inadequate vaccine coverage against opportunistic pathogens highlight the need for interventions that broadly and durably enhance host defense beyond antigen-specific adaptive immunity. Trained immunity, driven by metabolic and epigenetic reprogramming of innate immune cells, has been predominantly characterized using Bacille Calmette–Guérin and β-glucan, whereas its induction by Gram-negative bacteria remains poorly defined. To address this gap, we aimed to determine whether heat-killed Klebsiella pneumoniae (HK Kp) induces trained immunity through metabolic and hematopoietic reprogramming to confer heterologous antibacterial protection. Methods: HK Kp-trained murine bone marrow-derived macrophages and HK Kp-immunized C57BL/6 mice were employed to interrogate functional, metabolic, and transcriptomic reprogramming in vitro, hematopoietic progenitor remodeling in vivo, and protective efficacy against systemic Salmonella Typhimurium and Staphylococcus aureus infection. Results: HK Kp-trained macrophages showed markedly enhanced IL-1β secretion across all restimulation conditions, stimulus-dependent amplification of TNF-α responses, increased phagocytosis, and improved intracellular control of S. typhimurium, together with sustained upregulation of the glycolytic enzymes-encoding genes Hk2 and Pfkfb3. Transcriptomic profiling revealed extensive reprogramming enriched in glycolysis/gluconeogenesis and hematopoietic cell lineage pathways. In vivo, HK Kp immunization shifted bone marrow stem/progenitor compartments toward a myeloid-biased state. HK Kp-trained mice challenged with lethal S. typhimurium or S. aureus exhibited less weight loss, improved survival rates, and reduced bacterial burdens. Conclusions: Inactivated K. pneumoniae orchestrates metabolic and hematopoietic reprogramming to establish enhanced innate immune responsiveness and confer heterologous protection in murine S. typhimurium and S. aureus sepsis models, supporting its potential as a potent inducer of trained immunity. These findings establish HK Kp-based trained immunity as a promising strategy for combating multidrug-resistant and vaccine-evading pathogens.
Cheng et al. (Fri,) studied this question.