Modification of tumor cells by a low dose of Newcastle disease virus

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Abstract
Augmented tumor-specific T cell responses were observed against the high metastatic murine lymphoma variant ESb when using as immunogen ESb tumor cells that had been modified by infection with a low dose of Newcastle disease virus (NDV). Such virus-modified inactivated tumor cells (ESb-NDV) were potent tumor vaccines when applied postoperatively for active specific immunotherapy of ESb metastases. We demonstrate here that immune spleen cells from mice immunized with ESb-NDV contain enhanced immune capacity in both the CD4+, CD8− and the CD4−, CD8+ T cell compartments to mount a secondary-tumor-specific cytotoxic T cell response in comparison with immune cells from mice immunized with ESb. ESb-NDV immune CD4+, CD8− helper T cells also produced more interleukin 2 after antigen stimulation than the corresponding ESb immune cells. There was no participation of either CD4+ or CD8+ virus-specific cells in the augmented response. The specificity of the T cells for the tumor-associated antigen remaind unchanged. Thus, there is the paradox that the virus-mediated augmentation of the tumor-specific T cell response in this system involves increased T helper activity but does not involve the recognition of viral epitopes as potential new helper determinants.