Be. Bax et al., In vitro and in vivo studies with human carrier erythrocytes loaded with polyethylene glycol-conjugated and native adenosine deaminase, BR J HAEM, 109(3), 2000, pp. 549-554
Polyethylene glycol-conjugated adenosine deaminase (pegademase) is used for
enzyme replacement therapy for patients with severe combined immunodeficie
ncy caused by adenosine deaminase deficiency. The entrapment of pegademase
within human energy-replete carrier erythrocytes using a hypo-osmotic dialy
sis procedure was investigated with the objective of prolonging the in vivo
circulatory half-life of the enzyme and maintaining therapeutic blood leve
ls, Native unmodified adenosine deaminase (ADA) was similarly studied. The
efficiency of pegademase entrapment was low (9%) whereas the entrapment of
native unmodified ADA was substantial (50%), suggesting that the polyethyle
ne glycol side-chains were impeding intracellular entrapment. The biochemic
al characteristics and the osmotic fragility of these carrier erythrocytes
were not adversely affected by the entrapment of either pegademase or nativ
e ADA. In vivo survival studies of pegademase-loaded Cr-51- labelled carrie
r erythrocytes in an ADA-deficient adult patient showed a mean cell half-li
fe of 16 d. Carrier erythrocyte-entrapped pegademase and native ADA had in
vivo half-lives of 20 and 12.5 d, respectively demonstrating that entrapmen
t prolongs the half-life over that of plasma pegademase, which has a circul
ating half-life of 3-6 d. These results provide the basis for a more extens
ive clinical evaluation of carrier erythrocyte-entrapped native adenosine d
eaminase therapy.