The effect of a PD-1/CTLA-4 tandem scFv on T cell cytokine response under immunosuppressive conditions
Forough Maleki, Farhoodeh Ghaedrahmati, Nafiseh Esmaeil, Ali N. Kamali, Vajihe AkbariBackground and purpose:
Immune checkpoint blockade targeting PD-1 and CTLA-4 has shown promise in cancer immunotherapy; however, limitations such as immune resistance and toxicity from combined full-length antibodies remain. Tandem single-chain variable fragments (scFvs) offer a novel bispecific approach with potentially improved tissue penetration and reduced systemic effects. This study aimed to evaluate the effect of a bispecific tandem scFv targeting PD-1 and CTLA-4 on cytokine secretion of human peripheral blood mononuclear cells (PBMCs) under immunosuppressive conditions.
Experimental approach:
PBMCs were isolated from healthy donors, activated with concanavalin A (ConA), and treated with various concentrations of the bispecific tandem scFv (0.2-200 nM). Cells were also exposed to soluble CD86, PD-L1, or co-cultured with mitomycin C-treated MDA-MB-231 tumor cells. IFN-γ and IL-2 levels were quantified using ELISA.
Findings/Results:
The tandem scFv increased IFN-γ and IL-2 secretion from ConA-activated PBMCs, especially at 20 nM. Furthermore, the bispecific tandem scFv significantly enhanced IL-2 secretion in the presence of inhibitory ligands, CD86 and PD-L1. However, the bispecific tandem scFv could reverse the inhibitory effect of CD86 on IFN-γ secretion but not PD-L1. Under co-culture with tumor cells, the modest effect of the bispecific tandem scFv on restoration of IL-2 secretion was observed.
Conclusion and implications:
Dual CTLA-4/PD-1 blockade using bispecific antibodies such as the bispecific tandem scFv used in the current study could restore the immunosuppressive effect of the tumor microenvironment. However, more