Differences in Phage Recognition and Immunogenicity Contribute to Divergent Human Immune Responses to <i>Escherichia coli</i> and <i>Klebsiella pneumoniae</i> Phages

Bacteriophages (phages) are emerging as a viable adjunct to antibiotics for the treatment of multidrug-resistant (MDR) bacterial infections. While intravenous phage therapy has proven successful in many cases, clinical outcomes remain uncertain due to a limited understanding of host response to phages. In this study, we conducted a comprehensive examination of the interaction between clinical-grade phages used to treat MDR Escherichia coli and Klebsiella pneumoniae infections, and human peripheral blood immune cells. Using whole transcriptome as well as proteomic approaches, we identified a strong inflammatory response to E. coli phage vB_EcoM-JIPh_Ec70 (herein, JIPh_Ec70) that was absent upon exposure to K. pneumoniae phage JIPh_Kp127. We confirmed that JIPh_Ec70's DNA recognition by the STING pathway was principally responsible for the activation of NF-kB and the subsequent inflammatory response. We further show that monocytes and neutrophils play a dominant role in phage uptake, primarily through complement-mediated phagocytosis. Significant differences in complement-mediated phagocytosis of JIPh_Kp127 and JIPh_Ec70 were observed, suggesting that reduced recognition, phagocytosis, and immunogenicity all contribute to the significantly decreased response to JIPh_Kp127. Our findings contribute to the progress of our understanding of the innate immune response to therapeutic phages and offer potential insights into how to improve the safety and effectiveness of phage therapy.