Upregulation of FcγRIIb on monocytes is necessary to promote the superagonist activity of TGN1412.
The anti-CD28 superagonist antibody TGN1412 caused life-threatening cytokine release syndrome (CRS) in healthy volunteers, which had not been predicted by preclinical testing. T cells in fresh peripheral blood mononuclear cells (PBMCs) do not respond to soluble TGN1412 but do respond following high-density (HD) preculture. We show for the first time that this response is dependent on crystallizable fragment gamma receptor IIb (FcγRIIb) expression on monocytes. This was unexpected because, unlike B cells, circulating monocytes express little or no FcγRIIb. However, FcγRIIb expression is logarithmically increased on monocytes during HD preculture, and this upregulation is necessary and sufficient to explain TGN1412 potency after HD preculture. B-cell FcγRIIb expression is unchanged by HD preculture, but B cells can support TGN1412-mediated T-cell proliferation when added at a frequency higher than that in PBMCs. Although low-density (LD) precultured PBMCs do not respond to TGN1412, T cells from LD preculture are fully responsive when cocultured with FcγRIIb-expressing monocytes from HD preculture, which shows that they are fully able to respond to TGN1412-mediated activation. Our novel findings demonstrate that cross-linking by FcγRIIb is critical for the superagonist activity of TGN1412 after HD preculture, and this may contribute to CRS in humans because of the close association of FcγRIIb-bearing cells with T cells in lymphoid tissues.
Antibody and Vaccine Group, Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom;
Khiyam
K
Hussain
Antibody and Vaccine Group, Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom;
Chantal E
CE
Hargreaves
Antibody and Vaccine Group, Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom;
Ali
A
Roghanian
Antibody and Vaccine Group, Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom;
Robert J
RJ
Oldham
Antibody and Vaccine Group, Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom;
H T Claude
HT
Chan
Antibody and Vaccine Group, Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom;
C Ian
CI
Mockridge
Antibody and Vaccine Group, Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom;
Ferdousi
F
Chowdhury
Preclinical Research, BioInvent International AB, Lund, Sweden;
Bjorn
B
Frendéus
Huntingdon Life Sciences Ltd, Woolley Road, Alconbury, Huntingdon, Cambridgeshire, United Kingdom; and.
Kirsty S
KS
Harper
Cancer Genomics Group, and.
Jonathan C
JC
Strefford
Antibody and Vaccine Group, Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom;
Mark S
MS
Cragg
Antibody and Vaccine Group, Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom;
Martin J
MJ
Glennie
Southampton Experimental Cancer Medicine Centre, Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom.
Anthony P
AP
Williams
Antibody and Vaccine Group, Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom;
Ruth R
RR
French
D000818:Animals; D061067:Antibodies, Monoclonal, Humanized / Q000737:chemistry*; D001402:B-Lymphocytes / Q000166:cytology; D018106:CD28 Antigens / Q000378:metabolism; D016466:CHO Cells; D049109:Cell Proliferation; D018920:Coculture Techniques; D006224:Cricetinae; D003412:Cricetulus; D016207:Cytokines / Q000378:metabolism; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000166:cytology; D009000:Monocytes / Q000166:cytology*; D017452:Receptors, IgG / Q000378:metabolism*; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology; D014162:Transfection; D015854:Up-Regulation
D061067:Antibodies, Monoclonal, Humanized; D018106:CD28 Antigens; D016207:Cytokines; C080571:Fc gamma receptor IIB; D017452:Receptors, IgG; C509303:TGN-1412