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Blood, 1 April 2006, Vol. 107, No. 7, pp. 2619-2626.
Prepublished online as a Blood First Edition Paper on December 1, 2005; DOI 10.1182/blood-2005-03-0989.
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Submitted March 11, 2005
Accepted November 8, 2005
Intravascular survival of red cells coated with a mutated human anti-D antibody engineered to lack destructive activity
Kathryn L Armour, David R Parry-Jones, Nigel Beharry, James R Ballinger, Rosey Mushens, R K Williams, Cynthia Beatty, Simon Stanworth, Paul Lloyd-Evans, Marion Scott, Michael R Clark, A M Peters, and Lorna M Williamson*
Department of Pathology, University of Cambridge, Cambridge, United Kingdom
Department of Nuclear Medicine, Addenbrooke's Hospital, Cambridge, United Kingdom; Department of Radiology, University of Cambridge, Cambridge, United Kingdom
Cambridge National Blood Service, Bristol, United Kingdom
Clinical Biotechnology Centre, National Blood Service, Bristol, United Kingdom
National Blood Service, Cambridge, United Kingdom
National Blood Service, Cambridge, United Kingdom; Department of Haematology, University of Cambridge, Cambridge, United Kingdom
* Corresponding author; email: lorna.williamson{at}nbs.nhs.uk.
Alloimmune feto-maternal destruction of blood cells is thought to be mediated by binding of alloantibodies to Fc receptors on effector cells. Blocking the antigen using inert antibodies might prolong cell survival. We have performed a 'proof of principle' study in volunteers to measure the intravascular survival of autologous red cells coated with human recombinant IgG antibody containing a novel constant region, G1 nab, devoid of in vitro cytotoxic activity. RhD-positive RBC, labelled with chromium-51 or technetium-99m, were separately coated to equal levels with wildtype IgG1 or G1 nab anti-D antibody (Fog-1). After reinjection, there was complete, irreversible clearance of IgG1-coated RBC by 200 min, concomitant with appearance of radiolabel in plasma. Gamma camera imaging revealed accumulation in spleen and, at higher coating levels, in liver. In contrast, clearance of G1 nab-coated cells was slower, incomplete and transient, with whole blood counts falling to 7 - 38% injected dose by about 200 min before increasing to 12 - 67% thereafter. There was no appearance of plasma radiolabel and no hepatic accumulation. These findings suggest that G1 nab-coated RBC were not haemolysed but temporarily sequestered in the spleen and that our approach merits investigation in larger studies.

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