Abstract 2059: Long-term survival of mice with relapsed ALL treated by oncolytic measles virus is terminated by expansion of persistently infected virus-resistant blasts
Authors: Goß Annika V. , Dorneburg Carmen , Mulaw Medhanie , Xu Chun , Landthaler Christine , Jeremias Irmela , Wei Jiwu , Debatin Klaus-Michael , Beltinger Christian 
Published: August 2019

Abstract
Background: The prognosis of patients with relapsed and refractory ALL is poor. Oncolytic virotherapy is a promising treatment modality combining cancer cell lysis with immunomodulation.
Aims: To determine whether clinical-grade attenuated measles virus (MV) controls relapsed and refractory ALL in vitro and in vivo, to assess resistance mechanisms and to outline targets for immunotherapy in resistant cells.
Methods: The clinical-grade MV-NIS strain was used. ALL cell lines insensitive to chemotherapy and ALL xenografts derived from patients that had died from their disease were investigated. In vitro, cells were treated with MV-NIS and viability was determined. NSG mice were transplanted with a relapsed ALL PDX. Treatment was started when the leukemic load was high, i.e. when 20-30% blasts were present in the peripheral blood, and when the disease had heavily infiltrated spleen, liver, bone marrow and CNS. One dose of i.v. MV-NIS was given. Peripheral blast counts and survival of mice were determined. At time of death the presence of MV in leukemic infiltrates was determined by immunohistochemistry and qRT-PCR, MV was isolated from blasts and serum, and infectivity of isolated MV was tested on Vero indicator cells. mRNA from the blasts, including the genome of the MV they were infected with (MV is a mRNA virus), was subjected to mRNA sequencing. Gene set enrichment and mutation analyses were performed.
Results: In vitro, MV-NIS effectively killed ALL cell lines insensitive to chemotherapy and cells from relapsed patient ALL. In NSG mice with a high and disseminated load of relapsed patient ALL cells, one injection of i.v. MV-NIS sufficed to rapidly decrease leukemic load leading to long-term survival of the mice. Survival was terminated by late disease exacerbation due to expansion of virus-resistant leukemic cells persistently infected with infectious MV. Genome-wide mRNA sequencing revealed strong enrichment of antiviral pathways in the resistant cells, without mutations in the viral genome that could explain the resistance of the blasts.
Conclusions: MV-NIS is preclinically effective against relapsed and refractory ALL in vitro and, initially, in vivo. Late expansion of virus-resistant cancer cells persistently infected with MV is a phenomenon hitherto not described. The viral and antiviral proteins strongly expressed in these cells, which include cell surface proteins, can serve as targets for subsequent immunotherapy.
Citation Format: Annika V. Goß, Carmen Dorneburg, Medhanie Mulaw, Chun Xu, Christine Landthaler, Irmela Jeremias, Jiwu Wei, Klaus-Michael Debatin, Christian Beltinger. Long-term survival of mice with relapsed ALL treated by oncolytic measles virus is terminated by expansion of persistently infected virus-resistant blasts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2059.