| Summary: | TCR gene therapy allows redirection of the antigen specificity of T cells by the introduction of novel TCR α and β chains by retroviral transduction. These TCR gene modified T cells can be adoptively transferred to target defined tumour antigens. The majority of TCR gene therapy studies has focused on the adoptive transfer of CD8+ T cells but there is increasing recognition of a central role for CD4+ T cells in effective immunotherapy protocols. The use of CD4+ T cells has been limited by the lack of well defined class II restricted TCR and also because the majority of tumours don’t express class II MHC. As a result research has focused on introducing class I restricted TCR into CD4+ T cells. Initial work has demonstrated that class I restricted CD4+ T cells often have reduced functional avidity compared to the parental CD8+ T cell. In particular, CD4+ T cells transduced with CD8 dependent TCRs are often of much lower functional avidity when introduced in the absence of a CD8 co-receptor. In order to improve the functional avidity of class I restricted CD4+ T cells, murine CD4+ T cells were co-transduced with F5 TCR (specific for influenza peptide, NP, in the context of H2-Kb) and additional CD3 molecules. The amount of CD3 within in a cell is rate limiting for the expression of introduced TCR and thus when cells are transduced with additional CD3 it removes this rate limiting step and thus enhances the surface expression of the TCR. TCR surface expression is one of the key determinants of T cell functional avidity. CD4+ T cells co-transduced with F5- TCR and CD3 had increased surface expression of F5-TCR and increased pentamer binding. This translated in vitro into increased functional avidity compared to CD4+ T cells transduced with F5-TCR only. When adoptively transferred in vivo into irradiated tumour bearing syngeneic recipients, F5- TCR + CD3 CD4+ T cells had greater expansion and persistence and trafficked to the tumour site at higher and faster rates than F5-TCR only CD4+ T cells. In addition, F5-CD3 CD4+ T cells demonstrated superior control of tumour growth. Unexpectedly mice that received adoptive transfer of F5-TCR + CD3 CD4+ T cells developed marked lethal toxicity. Further experiments to try to determine the nature of this toxicity suggest a multifactorial cause including mispairing of the introduced TCR α and β chains with the endogenous TCR and development of autoreactive T cells in the presence of additional CD3 mediated either by upregulation of the introduced TCR or the endogenous TCR.
|
|---|
