Mj. Quinones et al., AVOIDANCE OF IMMUNE-RESPONSE PROLONGS EXPRESSION OF GENES DELIVERED TO THE ADULT-RAT MYOCARDIUM BY REPLICATION-DEFECTIVE ADENOVIRUS, Circulation, 94(6), 1996, pp. 1394-1401
Background Gene delivery is a rapidly expanding field with potential a
pplications to every human organ system. Recently. adenoviruses have b
een used as efficient nt vectors for in vivo gene transfer into the my
ocardium. These methods, however, have shown a sharp decline of gene e
xpression after week. To test the hypothesis that an immune-effector m
echanism is involved in this decline, we compared the results after in
jection of adenovirus-5 carrying the beta-galactosidase gene (Ad beta-
gal) into the left ventricular myocardium of athymic nude rats (NDRs)
versus immunocompetent Sprague-Dawley rats (SDRs). Methods and Results
Ad beta-gal (5.0x10(9) PFU/mL) was injected into the left ventricle o
f NDRs (n = 16) and SDRs (n = 22). Hearts were harvested, embedded in
paraffin, and sectioned and stained for beta-gal activity, hematoxylin
and eosin and picrosirius red at 4, 21, 35, 85, and 120 days. Represe
ntative samples were immunostained with antibodies directed at inflamm
atory markers. beta-gal activity was quantified by digital planimetry
and expressed as area of staining (%+/-SEM). Peak beta-gal activity wa
s highest at 4 days, with NDRs displaying significantly greater staini
ng (83+/-3.0% versus 54+/-8.0% P=.03). SDRs sustained a rapid drop in
activity, such that at 35 (1+/-0.19%) and 85 (1+/-0.4%) days, only occ
asional cells stained positive and by 120 days (0.3+/-0.0%), activity
had been extinguished. NDRs continued to show transgene expression at
all time periods (35 and 85 days, 25+/-7.1% and 7.4+/-2.7%, respective
ly) and was still readily detected at 120 days. An inflammatory respon
se was limited in NDRs compared with SDRs, in which there was intense
mono-nuclear cell infiltration, with collagen deposition and scar form
ation. Immunostaining identified the majority of these inflammatory ce
lls as not being of lymphocyte lineage, although small numbers of lymp
hocytes and phagocytic and activated plasma cells were identified. Con
clusions Our data suggest that immune-effector mechanisms can severely
affect the expression of gents delivered by adenovirus. The present m
odel provides efficient gene expression for at least 120 days without
significant inflammatory reaction.