Phage therapy and the microbiome in hematologic malignancies: opportunities, mechanisms, and early evidence.

Hematologic malignancies remain among the most difficult cancers to treat, challenged by profound heterogeneity, treatment-induced immune dysfunction, and the frequent emergence of drug resistance. Beyond tumor-intrinsic mechanisms, dysbiosis of the gut microbiome is increasingly recognized as a critical determinant of therapeutic outcomes, shaping hematopoiesis, immune responses, and drug metabolism. Bacteriophage (phage) therapy has re-emerged as a precision tool capable of selectively eradicating pathogenic taxa while preserving commensal short-chain fatty acid-producing communities. Preclinical and early human studies demonstrate that phages can recalibrate microbial ecosystems, disrupt antibiotic-tolerant biofilms, and enrich metabolites such as butyrate that support mucosal integrity and immune balance. Mechanistically, phage DNA enriched with CpG motifs engages Toll-like receptor 9, activating dendritic cells and enhancing cytotoxic T lymphocyte responses, suggesting dual benefits in infection control and anti-tumor immunity. Emerging applications extend further, with engineered phages serving as vectors for CRISPR-Cas gene editing, targeted cytokine delivery, and nanocarrier platforms for leukemia therapy. Despite translational promise, major hurdles persist, including immunogenicity, horizontal gene transfer, resistance evolution, and regulatory uncertainty. Addressing these challenges through GMP-compliant manufacturing, metagenomics-guided personalization, and AI-optimized cocktail design could establish phage therapy as a microbiome-informed adjunct to overcome drug resistance in blood cancers. However, direct clinical evidence of phage therapy efficacy in hematologic malignancies remains limited, and current data are largely derived from preclinical and compassionate-use contexts.