Interference of CD40L-Mediated Tumor Immunotherapy by Oncolytic Vesicular Stomatitis Virus

Abstract

Oncolytic virotherapy can be achieved in two ways: (1) by exploiting an innate ability of certain viruses to selectively replicate in tumor tissues, and (2) by using viruses to deliver toxic or immunostimulatory genes to tumors. Vesicular stomatitis virus (VSV) selectively replicates in tumors lacking adequate type I interferon response. The efficacy of oncolytic virotherapy using VSV against B16 melanomas in C57BL=6 mice is dependent on CD8 þ T and natural killer cells. Because immunotherapies that prime specific CD8 þ T cells against melanocyte= melanoma antigens can generate significant therapeutic responses, we hypothesized that engineering VSV to express the potent T cell costimulatory molecule CD40 ligand (VSV-CD40L) would enhance virotherapy with concomitant priming of melanoma-specific T cells. However, we observed no difference in antitumor efficacy between the parental VSV-GFP and VSV-CD40L. In contrast, intratumoral injection of a replication-defective adenovirus expressing CD40L (Ad-CD40L) consistently produced significantly greater therapy than either replication-competent VSV-GFP or VSV-CD40L. The Ad-CD40L-mediated tumor regressions were associated with specific T cell responses against tumor-associated antigens (TAAs), which took several days to develop, whereas VSV-CD40L rapidly induced high levels of T cell activation without specificity for TAAs. These data suggest that the high levels of VSV-associated immunogenicity distracted immune responses away from priming of tumor-specific T cells, even in the presence of potent costimulatory signals. In contrast, a replication-defective Ad-CD40L allowed significant priming of T cells directed against TAAs. These observations suggest that an efficiently primed antitumor T cell response can produce similar, if not better, therapy against an established melanoma compared with intratumoral injection of a replication-competent oncolytic virus.

Molecular Pathways: Multimodal Cancer-Killing Mechanisms Employed by Oncolytic Vesiculoviruses

“…For several reasons, however, this approach has proven more challenging, including the facts that (1) real self-tumor antigens are relatively weak as the host is tolerized towards them and contains very few T-cell precursors (39); (2) the selective pressure applied by immune therapies towards a single tumor antigen can lead to escape variants (44), and (3) OVs are extremely immunogenic themselves and may distract the immune system from the tumor (34,45). To address aspects of these barriers, two innovative approaches have recently been developed.…”

Vesicular Stomatitis Virus Oncolytic Treatment Interferes with Tumor-Associated Dendritic Cell Functions and Abrogates Tumor Antigen Presentation

“…Early studies demonstrated the presence of tumor-specific CD8 T cells following VSV treatment and a reduction of the therapeutic effect after CD8 T cell depletion (15). However, subsequent studies indicated that tumor-specific CD8 T cells either were not detected in the tumor, spleen, or draining lymph nodes following VSV treatment (35) or were detected at low levels that were not statistically significant (9,10,17,37). It was also suggested that tumor regression in CD8 T cell depletion experiments was the result of nonspecific CD8 T cell activation induced by VSV rather than a tumor-specific response (17, 35).…”

Expressing human interleukin-15 from oncolytic vesicular stomatitis virus improves survival in a murine metastatic colon adenocarcinoma model through the enhancement of anti-tumor immunity

“…Transgenes have been added to oncolytic VSV vectors in an attempt to improve on efficacy through modulation of the immune response, with varying impacts on therapeutic outcome. 9,[31][32][33][34] A number of groups have added cytokines, including IL-4, IL-12 and IL-23, into VSV in an effort to polarize the adaptive immune response to improve on anti-tumor immune responses. Although there was some improvement over parental control viruses, the immune responses were either not measured in these studies or showed no, or only very minor, increases to immune responses, leaving room for further improvement.…”

“…[31][32][33][34] Alternatively, co-stimulatory molecules have been expressed from the OV VSV vector again with no improvement over control viruses in survival or induction of immune responses. 9 To improve on the oncolytic efficacy of VSV, we have added a highly secreted form of human IL-15 to our oncolytic VSV vector for its immuno-stimulatory effects on innate and acquired immunity. 12,15,16,35 The addition of the hIL-15 transgene did not impair viral replication in vitro and led to high levels of secretion of hIL-15 from virally infected cells both in vitro and in vivo.…”

“…6,8 Therefore, normal cells will be protected from infection, while the hypo-responsive tumor cells will still remain susceptible. VSV, when delivered systemically, has been shown to improve survival of mice in various tumor models; [9][10][11] however, it has been difficult to achieve high proportions of longterm survivors with VSV alone. The improvements observed in some cases have been associated with a requirement of adaptive immune responses following oncolytic therapy.…”