CD28 family and chronic rejection: "to belatacept...And beyond!"

Functional characterization of human T cell hyporesponsiveness induced by CTLA4-Ig

During activation, T cells integrate multiple signals from APCs and cytokine milieu. The blockade of these signals can have clinical benefits as exemplified by CTLA4-Ig, which blocks interaction of B7 co-stimulatory molecules on APCs with CD28 on T cells. Variants of CTLA4-Ig, abatacept and belatacept are FDA approved as immunosuppressive agents in arthritis and transplantation, yet murine studies suggested that CTLA4-Ig could be beneficial in a number of other diseases. However, detailed analysis of human CD4 cell hyporesponsivness induced by CTLA4-Ig has not been performed. Herein, we established a model to study the effect of CTLA4-Ig on the activation of human naïve T cells in a human mixed lymphocytes system. Comparison of human CD4 cells activated in the presence or absence of CTLA4-Ig showed that co-stimulation blockade during TCR activation does not affect NFAT signaling but results in decreased activation of NF-κB and AP-1 transcription factors followed by a profound decrease in proliferation and cytokine production. The resulting T cells become hyporesponsive to secondary activation and, although capable of receiving TCR signals, fail to proliferate or produce cytokines, demonstrating properties of anergic cells. However, unlike some models of T cell anergy, these cells did not possess increased levels of the TCR signaling inhibitor CBLB. Rather, the CTLA4-Ig-induced hyporesponsiveness was associated with an elevated level of p27kip1 cyclin-dependent kinase inhibitor.

Construction of CTLA-4-Ig Fusion Gene in pBudCE4.1 Expression Vector

BACKGROUND

CTLA-4 inhibitory signals prevent cell cycle progression and IL-2 production, leading to a halt on an ongoing immune response. CTLA4-Ig fusion proteins contain the extracellular domain of CTLA-4 and Fc fragment of human IgG antibody. In this study we aimed to fuse the ctla-4 gene encoding the extracellular domain of CTLA-4 molecule with igg1 gene encoding Fc region of human IgG.

METHODS

After primer design, PCR reaction was performed using pfu polymerase enzyme and specific primers. PCR amplified fragment was ligated into the vector containing the human igg1 gene. The resulting fusion fragment of ctla-4 and human igg1 genes was ligated to pBudCE4.1 expression vector.

RESULTS

Extracellular domain of ctla-4 gene was ligated to igg1 gene and then ctla4-ig fragment was cloned into pBudCE4.1 vector. Construction of the expression vector was confirmed by restriction pattern analysis and sequencing.

CONCLUSION

By confirming the construct, in the next step, the recombinant DNA will be used to produce CTLA4-Ig recombinant protein for the clinical uses.