430. MVhGCSF Is Therapeutic In-Vivo B Cell Malignancies With Neutrophils (PMNs) Playing Different Roles

Abstract

Measles virus (MV) has been shown to be oncolytic in various tumor models and is being evaluated in various Phase I clinical trials. The mechanisms by which MV kills cancer cells still remain obscure. We aimed to enhance the therapeutic efficacy of MV by expressing the human granulocyte colony stimulating factor (hGCSF), as an additional transcription unit of MV. We showed that MVhGCSF is therapeutic in two different in-vivo subcutaneous model of B cell malignancy, Raji (Burkitt's lymphoma) and Nalm-6 (acute lymphoblastic leukemia). In the Raji model, MVhGCSF treatment generated a highly significantly superior (p=0.0001) anti tumor effect by comparison to MVNSe and the MVhGCSF treated mice survived significantly longer than MVNSe treated mice (p=0.0098). In the Nalm-6 model, both MVhGCSF and MVNSe resulted in complete regression of the tumors in both groups with no survival advantage to MVhGCSF therapy. We then determined therapeutic efficacy of MVhGCSF in disseminated Nalm-6 xenografts as our previous data showed that approx. 60% of mice have complete regression of the tumors with IV delivered MV, offering a greater potential to observe any therapeutic benefit to MVhGCSF. Nalm-6 tumor cells expressing luciferase were used, in order to enable in-vivo imaging of disease progression by imaging. Mice were treated with MVNSe, MVhGCSF, or UV-MV control and an additional control of hGCSF alone, using pegylated hGCSF. Mice treated with the controls alone succumbed to leukemia the most quickly; in the group treated with GCSF alone, the median survival was 50 days compared to 75 days in the UV-MV treated group (p=0.012). As expected, 75% of the mice treated with MVNSe responded well and were alive at the end of the experiment. Surprisingly, mice receiving treatment with MVhGCSF had a median survival of 78.5 days compared to the MVNSe treated cohort where the median was not reached by the end of the experiment (p=0.0149). At humane end point, the spleen sizes and cellularity were similar across all the groups. hGCSF was detected at comparable levels in the serum of the hGCSF and MVhGCSF treated cohorts. Flow cytometric analysis of CD11b, Ly6G6C, NK and Mac3 cells did not show any difference in the PMN, macrophage and NK cell percentages between the different groups. Finally, to be certain that the less good outcome of mice treated with MVhGCSF did not also result from toxicity of high GCSF levels, IfnarKO * CD46Ge mice were injected IV with either MVNSe or MVhGCSF. They were monitored for 35 days after which spleen size, differential cell count (NK, macrophage, PMN percentages) and serum hGCSF levels were determined. There was no difference between the groups. The mice treated with MVhGCSF showed 200-800pg/ml of hGCSF in the serum at Day 35, but there was no toxicity. Taken together these data in the disseminated Nalm-6 model, suggests that any adverse effect of expressing hGCSF as an additional transcription unit in tumor bearing mice relates solely to promotion of tumor growth and not to toxicity of GCSF production.Our data suggest that a “one-size fits all” model of immune response to viral oncolysis is not appropriate and each tumor target will need full characterization for the potential of both direct and indirect, innate immune responses to generate benefit.