Development of Vesiculovirus-based Therapeutics for Acute Leukemia

Abstract

Outcomes for most patients with acute leukemia remain dismal. In-vitro, vesiculovirus members induced rapid apoptosis of acute leukemia cells. Intravenous injection of lymphoblastic leukemia cells infected ex-vivo with attenuated Vesicular Stomatitis Virus or Maraba Virus followed by gamma-irradiation, controlled leukemic progression in murine recipients. Essential properties of this autologous vaccine [immunotherapy by Leukemia-Oncotropic Virus (iLOV)] and the host’s immune system were characterized. iLOV durability was restricted to the leukemia used to manufacture the vaccine. At administration, virion cell-entry was required but vesiculovirus lifecycle completion was not essential. Apoptotic or necrotic leukemia cells, with/without co-injection of virus, were ineffective vaccines. Similarly ineffective were leukemia cells activated by, or injected with, Toll-like receptor agonists. Naïve recipients of adoptive splenocyte transfer from vaccine-treated immunocompetent donors were protected from leukemic challenge. Efficacy was notably diminished following matched allogeneic bone marrow transplantation; this correlated with isolated depletion of cytotoxic T-cells. iLOV was ineffective in athymic mice. Taken together, iLOV therapy relies on immediate spaciotemporal interactions between infected-dead/dying leukemia cells and the immune system; this promotes adaptive anti-tumor responses. Clinical translation could target patients in remission to control relapse. During the above I discovered that under specific conditions, live vesiculovirus exposed to a precise window of UV fluence reproducibly generates unique “non-replicating rhabdovirus-derived particles” (NRRPs) that maintain cell-entry and cytopathic properties. A gamut of leukemia cells, including multidrug-resistant blasts, underwent rapid NRRPs-induced apoptosis. Normal cell lines and healthy bone marrow mononuclear cells were resistant, in part through interferon-mediated signaling responses. Administering NRRPs intravenously was curative in a murine acute leukemia model, versus uniform disease progression using maximal tolerated dose of replicating virus. Serum levels of an array of immunomodulatory cytokines were significantly elevated after injection of NRRPs. iLOV prepared with NRRPs protected recipients from otherwise lethal leukemia. Intracranial administration of NRRPs proved nonlethal as opposed to neurotoxic live vesiculovirus. Following treatment, neutralizing antibodies were diminished with NRRPs compared to replicating virus. Together, NRRPs exhibit enhanced therapeutic index over replication-competent vesiculovirus. Leukemocidal activity of NRRPs is exerted through a plurality of immune-related and direct cytotoxic effects. This novel approach now extends vesiculovirus-based therapeutics into upfront treatment for acute leukemia.