High-density preculture of PBMCs restores defective sensitivity of circulating CD8 T cells to virus- and tumor-derived antigens.

Peripheral blood mononuclear cells (PBMCs) are the only source of human lymphoid cells routinely available for immunomonitoring of T-cell responses to microbial and tumor-associated antigens. However, previous work in mice and humans had indicated that CD4 T cells transiently lose antigen sensitivity when cellular contacts are lost (eg, by entering the circulation). Using the simple and robust protocol for resetting T cells to original reactivity (RESTORE; ie, preculturing PBMCs for 2 days at a high cell density before initiation of antigenic stimulation), we show that CD8 T-cell responses to viral and tumor-associated antigens are greatly underestimated in blood, and sometimes even remain undetected, if conventional, unprocessed PBMC cultures are used. The latter finding is particularly striking with regard to the appearance of Wilms tumor 1 protein-specific CD8 T-cell responses in leukemia patients after allogeneic bone marrow transplantation. The dramatic increase in antigen sensitivity of "restored" CD8 T cells is associated with phosphorylation of proximal T-cell receptor signaling components, and with the upregulation of genes involved in aerobic glycolysis, thereby increasing T-cell functionality. The RESTORE protocol permits a more meaningful monitoring of CD8 memory T-cell responses to viral infections and tumors and vaccination success. Furthermore, when generating T-cell lines for adoptive T-cell therapy, it avoids the loss of those clones, which strictly depend on the primed status conferred by cellular interactions in the tissue context for their initial reactivation by antigen. The data reported in this article have been deposited in the Gene Expression Omnibus database (accession number GSE63430).

From TGN1412 to TAB08: the return of CD28 superagonist therapy to clinical development for the treatment of rheumatoid arthritis.

CD28 superagonists (CD28SA) are CD28-specific monoclonal antibodies which are able to activate T-cells without overt TCR engagement. In rodents, CD28SA efficiently activate regulatory T-cells and are therapeutically effective in multiple models of autoimmunity, inflammation and transplantation. However, a phase I study of the human CD28SA TGN1412 in 2006 resulted in a life-threatening cytokine storm. This brief review summarises preclinical work before and since the failed phase I trial with an emphasis on understanding the reasons why there had been no warning of toxicity, and how a novel assay paved the way for a new phase I, phase Ib (both completed), and an ongoing phase II study.

Cell contact-dependent priming and Fc interaction with CD32+ immune cells contribute to the TGN1412-triggered cytokine response.

Following inconspicuous preclinical testing, the superagonistic anti-CD28 mAb TGN1412 was applied to six study participants who all developed a devastating cytokine storm. We verified that TGN1412 treatment of fresh PBMCs induced only moderate responses, whereas restoration of tissue-like conditions by high-density preculture (HDC) allowed vigorous cytokine production. TGN1412 treatment of T cells isolated from HDC-PBMCs induced moderate cytokine responses, which upon additional anti-IgG crosslinking were significantly boosted. Moreover, coincubation of TGN1412-treated T cells with B cells expressing the intermediate affinity Fcγ receptor IIB (CD32B), or coincubation with CD32B(+) transfectants, resulted in robust T cell activation. This was surprising because TGN1412 was expressed as an Ig of the subclass 4 (IgG4), which was shown before to exhibit only minor affinity to FcγRs. Transcriptome analysis of TGN1412-treated T cells revealed that similar gene signatures were induced irrespective of whether T cells derived from fresh or HDC-PBMCs were studied. Collectively, these data indicate that HDC-PBMCs and HDC-PBMC-derived T cells mount rapid TGN1412 responses, which are massively boosted by FcγR crosslinking, in particular by CD32-expressing B cells. These results qualify HDC-PBMCs as a valuable in vitro test system for the analysis of complex mAb functions.