Tapping CD4 T cells for cancer immunotherapy
Sébastien Wälchli1, Marit R. Myhre1, Nadia Mensali1, Anne Fåne1, Kari Lislerud1, Gunnar Kvalheim1, Gustav Gaudernack2, Else M Inderberg1T-cell based immunotherapy is an attractive treatment for advanced cancer.
Whereas cellular immune responses against tumour have typically been attributed to CD8 T cells, CD4 T cells play a critical role in tumour elimination and the priming and maintenance of CD8 T-cell responses. Recent findings have highlighted new opportunities for CD4 T cells in cancer immunotherapy.
From patients that clinically benefitted from treatment with cancer vaccines targeting antigens such as hTERT, survivin and frequent neoantigens such as frameshift mutated TGFβRII we have isolated CD4+ T cells reactive against tumour antigens.
Strong T-cell responses against the vaccine or unrelated cancer antigens suggesting epitope spreading correlated to enhanced survival and/or tumour regression in late stage cancer patients.
These HLA class II restricted T-cell clones recognised target cells loaded with long peptides or protein and for some CD4+ T cell clones we could also show direct tumour recognition.
TCRs were expressed in expanded third-party T cells by mRNA electroporation or retroviral transduction and tested for functionality. Both CD8+ and CD4+ T cells expressing the TCRs produced TNF-α, IFN-γ and had the capacity to kill following co-incubation with their targets.
Selecting highly functional CD4+ T-cell clones reactive against tumour-associated or -specific antigens from patients with clinical responses after immunotherapy treatment is a successful method for identifying highly functional HLA class II restricted TCRs for adoptive immunotherapy.
The use of HLA class II-restricted TCRs may be of therapeutic value both in haematopoietic malignancies and in melanoma where tumour cells often express HLA class II.
Furthermore, combining HLA class I- and class II-restricted TCRs for T-cell redirection may provide a more potent therapeutic effect in adoptive T cell therapy.
Csk overexpression makes T cell dummy
Else M. Inderberg, Nadia Mensali, Bitte Stenvik, Morten Oksvold, Cinzia Progida, Oddmund Bakke, Lars-Egil Fallang, Gunnar Kvalheim, June H. Myklebust, Sébastien Wälchli
TCR signaling is tightly modulated by positive and negative regulators in order to guarantee proper signal transduction upon cognate peptide MHC complex recognition. The same type of regulation occurs when a therapeutic TCR is expressed in a patient T cell during adoptive transfer. To enhance positive signal is an idea that has recently been proposed to improve TCR efficacy. Indeed efficient adoptive T cell therapy depends on the fitness of the redirected cells.
Interestingly, negative modulators of signaling could also be exploited. Indeed, a main concern using therapeutic TCRs is their safety in terms of off target toxicity. A safe way to validate them could be to use a cell exactly similar to the therapeutic one, but lacking the ability to get activated. We tested the impact of over-expressing c-src kinase (CSK), a negative regulator of TCR signalling. We confirmed previous reports showing that CSK was able to completely inhibit TCR signaling thus blocking the cells. In contrast, CSK over-expression did not affect the capability of the TCR to bind the cognate peptide/MHC complex or exert cellular features such as membrane exchange, known as trogocytosis. CSK presence interfered with both early and late events in the TCR signaling cascade. As a consequence the effector functions of the TCR-engineered T cells were shut down. We named these gene-modified T cells “Dummy T cells” because although they were able to bind their target cells they had lost the capability to kill. We therefore propose that the “Dummy T cells” could be used as a prospective tool for in vivo monitoring of the homing, selectivity and antigen specificity of therapeutic TCR redirected T cells for adoptive T cell therapy.