Human mesenchymal stromal cells deliver systemic oncolytic measles virus to treat acute lymphoblastic leukemia in the presence of humoral immunity

Clinical trials of oncolytic attenuated measles virus (MV) are ongoing, but successful systemic delivery in immune individuals remains a major challenge. We demonstrated high-titer anti-MV antibody in 16 adults with acute lymphoblastic leukemia (ALL) following treatments including numerous immunosuppressive drugs. To resolve this challenge, human bone marrow-derived mesenchymal stromal cells (BM-MSC) were used to efficiently deliver MV in a systemic xenograft model of precursor B-ALL. BM-MSCs were successfully loaded with MV ex-vivo, and MV was amplified intracellularly, without toxicity. Live-cell confocal imaging demonstrated viral hand-off between BM-MSC and ALL targets in the presence of antibody. In a murine model of disseminated ALL, successful MV treatment (judged by bioluminescence quantification and survival) was completely abrogated by passive immunization with high-titer human anti-MV antibody. Importantly, no such abrogation was seen in immunized mice receiving MV delivered by BM-MSCs. These data support the use of BM-MSCs as cellular carriers for MV in patients with ALL.