Title: Obesogenic microbial signatures and the development of obesity in childhood acute lymphoblastic leukemia.

Childhood acute lymphoblastic leukemia (ALL) is the most common childhood cancer with survival exceeding 90% for standard-risk groups. A debilitating side-effect of treatment is the development of overweight/obesity (OW/OB), which develops in approximately 40% of children by the end of treatment. The microbiome has been associated with the development of OW/OB. We examined fluctuations in the microbiome with the development of OW/OB during the first six months of treatment at diagnosis, and two subsequent timepoints (N = 62). Shotgun metagenomic sequencing was performed on Illumina Nextseq system, and taxa and functional pathways were extracted from sequences using kraken2 and humann2, respectively. An association of increased presence of several species (e.g., Klebsiella pneumoniae, Escherichia coli) was observed in children with OW/OB, while lean-promoting species (Veillonella, Haemophilus, and Akkermansia) were increased in children who maintained a normal weight. Pathway analysis revealed purine nucleotide biosynthesis, sugar nucleotide biosynthesis, and enzyme cofactor biosynthesis were positively correlated with Bacteroides spp. among children with OW/OB. We identified several taxa and functional pathways that may confer increased risk for the development of OW/OB. The associations observed in this pilot are preliminary and warrant further research in the microbiome and the development of OW/OB in childhood ALL.