Virus and Autoantigen-Specific CD4+ T Cells Are Key Effectors in a SCID Mouse Model of EBV-Associated Post-Transplant Lymphoproliferative Disorders

Abstract

Polyclonal Epstein-Barr virus (EBV)-infected B cell line (lymphoblastoid cell lines; LCL)-stimulated T-cell preparations have been successfully used to treat EBV-positive post-transplant lymphoproliferative disorders (PTLD) in transplant recipients, but function and specificity of the CD4+ component are still poorly defined. Here, we assessed the tumor-protective potential of different CD4+ T-cell specificities in a PTLD-SCID mouse model. Injection of different virus-specific CD4+ T-cell clones showed that single specificities were capable of prolonging mouse survival and that the degree of tumor protection directly correlated with recognition of target cells in vitro. Surprisingly, some CD4+ T-cell clones promoted tumor development, suggesting that besides antigen recognition, still elusive functional differences exist among virus-specific T cells. Of several EBV-specific CD4+ T-cell clones tested, those directed against virion antigens proved most tumor-protective. However, enriching these specificities in LCL-stimulated preparations conferred no additional survival benefit. Instead, CD4+ T cells specific for unknown, probably self-antigens were identified as principal antitumoral effectors in LCL-stimulated T-cell lines. These results indicate that virion and still unidentified cellular antigens are crucial targets of the CD4+ T-cell response in this preclinical PTLD-model and that enriching the corresponding T-cell specificities in therapeutic preparations may enhance their clinical efficacy. Moreover, the expression in several EBV-negative B-cell lymphoma cell lines implies that these putative autoantigen(s) might also qualify as targets for T-cell-based immunotherapy of virus-negative B cell malignancies.

Author Summary

The γ-herpesvirus Epstein-Barr virus (EBV) is associated with several human malignancies, including post-transplant lymphoproliferative disorders (PTLD) in immunocompromised patients. The successful treatment of EBV-positive PTLD by the infusion of EBV-specific T-cell lines has provided an important proof of principle for immunotherapy of EBV-associated tumors and for cancer immunotherapy in general. EBV-specific T-cell preparations for clinical application are generated by repeated stimulation with autologous LCL in vitro. These lines contain CD4+ and CD8+ components but the specificity of the infused CD4+ T cells is still poorly defined. Using a mouse model of PTLD, we assessed the antitumoral potential of single virus-specific CD4+ T-cell clones. While T cells specific for a virion antigen of the virus prolonged mouse survival, other virus-specific clones had no effect or, unexpectedly, even promoted tumor growth. Moreover, the principal antitumoral effectors in LCL-stimulated T-cell preparations were CD4+ T cells specific for non-virus antigens. The definition of virion- and potentially autoantigen-specific CD4+ T cells as key effectors against PTLD may contribute to the design of generic and standardized protocols for the generation of T-cell lines with improved clinical efficacy. In addition, the observed tumor-promoting propensity of some CD4+ T cells may have implications for adoptive T-cell therapy in general.