Experimental evidence that infections promote pB-ALL development comes from a new pB-ALL mouse model that was presented in a special session on mouse models (see also section Experimental Findings): Transgenic Sca1-ETV6-RUNX1 mice only developed pB-ALL when exposed to common pathogens (conventional facility, CF conditions) but not when kept in a specific pathogen-free (SPF) environment (54). The gene discussed is RUNX1; the disease is acute lymphoblastic leukemia.