A Spontaneously Arising Pancreatic Tumor Does Not Promote the Differentiation of Naive CD8+ T Lymphocytes into Effector CTL

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Abstract
In this report, we address whether a growing tumor provides sufficient inflammatory signals to promote activation, clonal expansion, and acquisition of effector functions by naive tumor-specific CD8+ T lymphocytes. CD8+ T lymphocytes obtained from hemagglutinin (HA)-specific clone 4 TCR-transgenic mice were injected into recipient mice that spontaneously develop pancreatic tumors expressing HA as a tumor-associated Ag (RIP-Tag2-HA mice). When 3 × 106 clone 4 CD8+ T cells were transferred into tumor-bearing mice, the cells became activated in the pancreatic lymph nodes where they proliferated and acquired effector functions such as cytolytic activity and IFN-γ production. Surprisingly, reducing the number of adoptively transferred CD8+ T cells led to a parallel reduction in the proportion of the activated cells that exhibited effector functions, suggesting that CTL differentiation was induced by the large numbers of activated CD8+ T cells and not the tumor environment. Provision of tumor-specific CD4+ helper cells provided the signals required to promote both the development of CTL effector functions and increased clonal expansion, resulting in tumor eradication. Considering that only small numbers of tumor-specific CD8+ T cells would be present in a conventional T cell repertoire, these data suggest that tumor growth alone may not provide the inflammatory signals necessary to support the development of CD8+ T cell effector functions.

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