Lentiviral Gene Transfer to the Nonhuman Primate Brain Jeffrey H. Kordower,* Jocelyne Bloch,² Shuang Y. Ma,*Yaping Chu,* Ste ´ phane Palfi,* Ben Zion Roitberg,* , ‡ Marina Emborg,* Philippe Hantraye,§ Nicole De ´ glon,² and Patrick Aebischer² *Departments of Neurological Sciences and Research Center for Brain Repair, Rush Presbyterian-St. Luke’s Medical Center, Chicago, Illinois 60612; ‡Department of Neurosurgery, University of Illinois Medical Center, Chicago, Illinois 60612; §CEA CNRS URA 2210 Service Hospitalier Frederic Joliot, CEA, DSV, DRM, Orsay cedex, France; and ²Division of Surgical Research and Gene Therapy Center, Lausanne University Medical School, Switzerland Received April 16, 1999; accepted June 28, 1999 Lentiviral vectors infect quiescent cells and allow for the delivery of genes to discrete brain regions. The present study assessed whether stable lentiviral gene transduction can be achieved in the monkey nigrostria- tal system. Three young adult Rhesus monkeys re- ceived injections of a lentiviral vector encoding for the marker gene b galatosidase (bGal). On one side of the brain, each monkey received multiple lentivirus injec- tions into the caudate and putamen. On the opposite side, each animal received a single injection aimed at the substantia nigra. The first two monkeys were sacrificed 1 month postinjection, while the third mon- key was sacrificed 3 months postinjection. Robust incorporation of the bGal gene was seen in the stria- tum of all three monkeys. Stereological counts re- vealed that 930,218; 1,192,359; and 1,501,217 cells in the striatum were bGal positive in monkeys 1 (n 5 2) and 3 (n 5 1) months later, respectively. Only the third mon- key had an injection placed directly into the substan- tia nigra and 187,308 bGal-positive cells were identi- fied in this animal. The injections induced only minor perivascular cuffing and there was no apparent inflam- matory response resulting from the lentivirus injec- tions. Double label experiments revealed that between 80 and 87% of the bGal-positive cells were neurons. These data indicate that robust transduction of stria- tal and nigral cells can occur in the nonhuman primate brain for up to 3 months. Studies are now ongoing testing the ability of lentivirus encoding for dopamin- ergic trophic factors to augment the nigrostriatal sys- tem in nonhuman primate models of Parkinson’s disease. r 1999 Academic Press INTRODUCTION The transfer of genes into postmitotic cells in vivo can have far reaching implications for understanding basic functions of specific systems within the central nervous system as well as potentially delivering therapeutic molecules to brain regions vulnerable to neurodegener- ative diseases (See 30, for review). Currently, a number of vector delivery systems exist that can be applied toward these goals. In this regard, recombinant and defective herpes simplex virus, as well as adenovirus, display moderate-to-high rates of transduction effi- ciency. However, these gene transfer technologies may also be toxic and immunogenic. Although less immuno- genic, adenoassociated has lower transduction effi- ciency compared to herpes simplex virus and adenovi- rus. Recently a new HIV-based vector system has begun to be evaluated. This lentivirus integrates into the genome of nonproliferating brain cells (4, 23, 24, 25, 27). Recent studies have demonstrated stable long- term expression of the reporter gene b galactosidase (bGal) following lentivirus injections into multiple re- gions across the rodent neuraxis (4, 24, 25). Lentiviral- mediated gene transfer has been demonstrated to have potent biologic properties as injections of lentivirus encoding for the antiapoptotic gene Bcl-xL as well as nerve growth factor prevents the experimental degen- eration of cholinergic basal forebrain (5). Furthermore, lentiviral delivery of glial-derived neurotrophic factor (GDNF; 10) prevents the loss of axotomized dopaminer- gic nigrostriatal neurons. For in vivo gene therapy strategies to be of value to humans, safety and efficacy need to be established in the best animal models available. For Parkinson’s disease, the best animal model is the MPTP-treated monkey. However, at present, studies examining the safety and the efficiency of in vivo gene transfer proce- dures in nonhuman primates are limited. Davidson and coworkers (9) initially demonstrated short-term (7-day) gene transfer using adenovirus in Rhesus monkeys. Bohn and coworkers (6) attempted in vivo gene delivery to African green monkeys. Successful transduction was highly variable and accompanied by significant immu- nogenicity and cytotoxicity using adenoviral vectors. Finally Bankiewicz and colleagues (1, 2) have success- fully achieved bGal and tyrosine hydroxylase expres- sion in rhesus monkeys for up to 3 months postinjec- Experimental Neurology 160, 1–16 (1999) Article ID exnr.1999.7178, available online at http://www.idealibrary.com on 1 0014-4886/99 $30.00 Copyright r 1999 by Academic Press All rights of reproduction in any form reserved.
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Experimental Neurology 160, 1–16 (1999)Article ID exnr.1999.7178, available online at http://www.idealibrary.com on
Lentiviral Gene Transfer to the Nonhuman Primate Brain
Jeffrey H. Kordower,* Jocelyne Bloch,† Shuang Y. Ma,* Yaping Chu,* Stephane Palfi,* Ben Zion Roitberg,*,‡Marina Emborg,* Philippe Hantraye,§ Nicole Deglon,† and Patrick Aebischer†
*Departments of Neurological Sciences and Research Center for Brain Repair, Rush Presbyterian-St. Luke’s Medical Center,Chicago, Illinois 60612; ‡Department of Neurosurgery, University of Illinois Medical Center, Chicago, Illinois 60612;
§CEA CNRS URA 2210 Service Hospitalier Frederic Joliot, CEA, DSV, DRM, Orsay cedex, France;and †Division of Surgical Research and Gene Therapy Center, Lausanne University Medical School, Switzerland
Received April 16, 1999; accepted June 28, 1999
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Lentiviral vectors infect quiescent cells and allowor the delivery of genes to discrete brain regions. Theresent study assessed whether stable lentiviral generansduction can be achieved in the monkey nigrostria-al system. Three young adult Rhesus monkeys re-eived injections of a lentiviral vector encoding for thearker gene b galatosidase (bGal). On one side of the
rain, each monkey received multiple lentivirus injec-ions into the caudate and putamen. On the oppositeide, each animal received a single injection aimed athe substantia nigra. The first two monkeys wereacrificed 1 month postinjection, while the third mon-ey was sacrificed 3 months postinjection. Robust
ncorporation of the bGal gene was seen in the stria-um of all three monkeys. Stereological counts re-ealed that 930,218; 1,192,359; and 1,501,217 cells in thetriatum were bGal positive in monkeys 1 (n 5 2) and 3n 5 1) months later, respectively. Only the third mon-ey had an injection placed directly into the substan-ia nigra and 187,308 bGal-positive cells were identi-ed in this animal. The injections induced only minorerivascular cuffing and there was no apparent inflam-atory response resulting from the lentivirus injec-
ions. Double label experiments revealed that between0 and 87% of the bGal-positive cells were neurons.hese data indicate that robust transduction of stria-
al and nigral cells can occur in the nonhuman primaterain for up to 3 months. Studies are now ongoingesting the ability of lentivirus encoding for dopamin-rgic trophic factors to augment the nigrostriatal sys-em in nonhuman primate models of Parkinson’sisease. r 1999 Academic Press
INTRODUCTION
The transfer of genes into postmitotic cells in vivo canave far reaching implications for understanding basicunctions of specific systems within the central nervousystem as well as potentially delivering therapeutic
olecules to brain regions vulnerable to neurodegener- s
1
tive diseases (See 30, for review). Currently, a numberf vector delivery systems exist that can be appliedoward these goals. In this regard, recombinant andefective herpes simplex virus, as well as adenovirus,isplay moderate-to-high rates of transduction effi-iency. However, these gene transfer technologies maylso be toxic and immunogenic. Although less immuno-enic, adenoassociated has lower transduction effi-iency compared to herpes simplex virus and adenovi-us. Recently a new HIV-based vector system hasegun to be evaluated. This lentivirus integrates intohe genome of nonproliferating brain cells (4, 23, 24, 25,7). Recent studies have demonstrated stable long-erm expression of the reporter gene b galactosidasebGal) following lentivirus injections into multiple re-ions across the rodent neuraxis (4, 24, 25). Lentiviral-ediated gene transfer has been demonstrated to have
otent biologic properties as injections of lentivirusncoding for the antiapoptotic gene Bcl-xL as well aserve growth factor prevents the experimental degen-ration of cholinergic basal forebrain (5). Furthermore,entiviral delivery of glial-derived neurotrophic factorGDNF; 10) prevents the loss of axotomized dopaminer-ic nigrostriatal neurons.For in vivo gene therapy strategies to be of value to
umans, safety and efficacy need to be established inhe best animal models available. For Parkinson’sisease, the best animal model is the MPTP-treatedonkey. However, at present, studies examining the
afety and the efficiency of in vivo gene transfer proce-ures in nonhuman primates are limited. Davidson andoworkers (9) initially demonstrated short-term (7-day)ene transfer using adenovirus in Rhesus monkeys.ohn and coworkers (6) attempted in vivo gene delivery
o African green monkeys. Successful transduction wasighly variable and accompanied by significant immu-ogenicity and cytotoxicity using adenoviral vectors.inally Bankiewicz and colleagues (1, 2) have success-
ully achieved bGal and tyrosine hydroxylase expres-
ion in rhesus monkeys for up to 3 months postinjec-
0014-4886/99 $30.00Copyright r 1999 by Academic Press
All rights of reproduction in any form reserved.
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ion. To date, there are no data evaluating the safetynd efficiency of lentiviral gene transfer to the nonhu-an primate brain. One of our ultimate goals is to
etermine whether lentiviral delivery of GDNF canrevent parkinsonism in nonhuman primate models ofarkinson’s disease. As a prelude to functional andtructural studies using MPTP-treated monkeys, theresent report describes the robust lentiviral transferf the bGal gene to the striatum and substantia nigra ofhesus monkeys.
METHODS
Subjects. Three young adult male (4–6 kg) Rhesusonkeys served as subjects. These animals were housed
ingly with food and water available ad libitum. Allxperimentation was performed according to NIH guide-ines.
Surgery. Coordinates for stereotaxic injection wereased upon MRI guidance. For the caudate nucleus, theore rostral injection was targeted to the head of the
audate nucleus at its largest extent. The secondaudate injection was targeted 4 mm more caudally athe level of the body of the caudate nucleus. Thiseposit was at a level just caudal to the decussation ofhe anterior commissure. The first two putaminalnjections were at the same rostrocaudal levels as thewo caudate injection. The final putaminal injectionas placed 4 mm caudally at the level of the lateraleniculate nucleus. Prior to surgery, monkeys werenesthetized with an intramuscular injection of Ket-mine (10 mg/kg) and Xylazine (2 mg/kg). Once in annesthetic plane, the monkeys were placed in a spe-ially designed MRI compatible stereotaxic unit mod-led after a Kopf primate stereotaxic apparatus. Thengle of the head was established by measuring theeight of the incisor tooth using a standard microma-ipulator and a modified electrode holder. Then theonkey was transferred to the 1.5 Tesla MRI unit,
verlapping T1 and T2 images, where 4-mm imagesere obtained using standard procedures. The coordi-ates for injection sites into the caudate, putamen, andubstantia nigra were then ascertained using the MRI’somputer software.On the day of surgery, monkeys were tranquilizedith Ketamine (10 mg/kg, im). The monkeys were then
ntubated, anesthetized with isoflurane (1–3%), andeplaced in the same stereotaxic unit. The angle of theead was reestablished to be the same as when thenimal received his MRI scan. Under sterile conditions,
sagittal incision was made. On the left side, araniotomy was made over the striatum. On the rightide, a burr hole was made over the substantia nigra.ach monkey then received six lentiviral injections.ive injections were made in the left striatum. Two of
hese injections were made in the caudate nucleus (5 µl i
ostral and 10 µl 4 mm caudal) and three were placed inhe putamen (10 µl rostral, 10 µl mid, and 5 µl caudal;ll injections separated by 4 mm in a rostrocaudallane). In addition, a single 5-µl injection was placednto the right substantia nigra. The viral particlesnjected can be deduced from the titer, which is 2 3 108U/ml (transducing unit per milliliter). Thus, each 5-µl
njection corresponds to 1 3 106 TU and each 10-µlnjection corresponds to 2 3 106 TU. All injections wereerformed manually through a 10-µl Hamilton syringet a rate of 0.5 µl per minute. The needle was left in situor an additional 3 min to allow the virus to diffuse fromhe needle tip. The craniotomy and burr hole were filledith Gelfoam. The subcutaneous tissues were closedith 4-0 Coated Vicryl and the skin was closed with 4-0thilon. The monkeys were sacrificed either 1 month
n 5 2) or 3 months (n 5 1) postinjection.Construction of the lentiviral vector. The cDNA cod-
ng for the b-galactosidase (LacZ) containing a nuclearocalization signal was cloned in the SIN-W-PGK trans-er vector. A 400-bp fragment (EcoRV–PvuII) of the U3egion of the 38-LTR was deleted to obtain the self-nactivating vector (SIN; 34). This plasmid was further
odified by insertion of the posttranscriptional cis-cting regulatory element of the woodchuck hepatitisirus (WHV; a 587-bp fragment: position 1093–1684 ofhe WHV complete genome: GenBank Accession No.04514; 35). This element significantly increases trans-ene expression in a variety of contexts, apparentlyhrough a combination of stabilization of nascent RNAranscripts and facilitation of their cytoplasmic export7, 11, 12). The mouse phosphoglycerate kinase (PGK) 1romoter was used as internal promoter. The packag-ng construct and the VSV-G envelope used in thistudy were the pCMVDR-8.91 and the pMD.G plasmidsescribed previously (33). High-titer stocks were ob-ained by ultracentrifugation. The batch of virus wasested for the absence of replication-competent viralectors (25). The titer of 2 3 108 TU/ml was determinedn 293T cells. The cells were plated at a density of 2 305 cells per well on six-well tissue culture dishesCostar). Serial dilutions of the viral stock were addednd the number of LacZ-infected cells was analyzed8 h later.Histology. All monkeys were tranquilized with Ket-
mine (10 mg/kg, im), intubated, and anesthetized withembutal (25 mg/kg, iv). Monkeys were then sequen-
ially perfused with warm (100 ml) and ice cold (100 ml)aline, followed by fixation with a 4% Zamboni’s solu-ion (500 ml). The brains were removed from thealvaria and placed in a 30% sucrose/phosphate-uffered saline (PBS) solution until fully immersed.rozen (40 µm) thick sections were then cut in theoronal plane on a sliding knife microtome and stored
n a cryoprotectant solution.
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3LENTIVIRAL GENE TRANSFER TO NONHUMAN PRIMATE BRAIN
X-galactosidase (x-Gal) histochemistry. One seriesf sections from each brain was treated with detergent2 mM MgCl2, 0.01% sodium deoxycholate, 10% Noni-et P-40 in PBS, pH 7.2) for 10 min and then incubatedor 4 h at room temperature in the X-Gal substrateolution, which consisted of 5 mM K3Fe(CN)6, 5 mM4Fe(CN)63H2O, 2 mM MgCl2, and X-Gal (1 mg/ml inBS, pH 7.2). Sections were mounted on gelatin-coatedlides, dehydrated through graded alcohols (50, 70, 95,nd 99%), cleared in xylenes, and coverslipped withermount.Immunohistochemistry. Sections were also stained
or X-Gal immunofluorescence, GFAP, and NeuN usingtandard procedures. After the cryoprotectant wasashed from the sections, incubating the sections in a
ackground staining. Sections were then incubated for8 h at room temperature in the polyclonal bGal (58–38;:1000), polyclonal GFAP (Dakopatz; 1:2000), monoclo-al TH (Chemicon; 1:20,000), or monoclonal NeuNChemicon; 1:1000) antibodies. Some sections wererocessed for fluorescence visualization. Sections pro-essed for fluorescence (bGal or TH) were then sequen-ially incubated in the biotinylated goat antirabbit ororse antimouse IgG (1:200) for 1 h and streptavidinonjugated to Cy2 (1:1000) for 1 h at room temperature.ections processed using immunoperoxidase methods
GFAP and NeuN) were incubated in either the biotinyl-ted goat antirabbit (GFAP) or horse antimouse (NeuN)gG for 1 h following by a 75-min incubation in the EliteBC substrate (1:500; Vector Labs). The sections wereeacted in a chromogen solution containing 0.05% 383iaminobenzidine and 0.005% hydrogen peroxide. Allections were then mounted, dehydrated, and cover-lipped with DPX. For each experiment, control sec-ions were processed in an identical manner except therimary antibody solvent or an irrelevant IgG matchedor protein concentration were substituted for the pri-ary antibody. While no staining was observed under
hese conditions, caution is still required since theossibility of the antibody reacting with structurallyelated proteins cannot be eliminated. The term immu-oreactivity in this study refers to ‘‘like immunoreactiv-
ty.’’Double labeling immunofluorescence procedure. In
rder to identify the cell types infected with the lentivi-al vector, an indirect immunofluorescence double-labelechnique was employed to label bGal-positive cellsith a neuronal and glial markers. In the striatum, bal immunofluorescence was codetected with NeuN, aeuronal marker, or GFAP, a glial marker. In theubstantia nigra, identical colocalization studies wereerformed with the addition of experiments colocaliz-ng bGal with tyrosine hydroxylase. For each experi-
ent, background staining was inhibited with a 1-h a
ncubation in a blocking solution (5% normal goaterum, 2% bovine serum albumin [BSA], and 0.3%riton X-100 in TBS, pH 7.4) at room temperature.ections were then incubated in primary rabbit poly-lonal antibody to b-gal (1:500) overnight at 4°C. Afterashes, the sections were incubated in the secondaryoat anti-rabbit IgG coupled to the fluorescent markerexas Red (1:200) for 1 h. Following completion of theeaction, the sections were blocked again in a blockingolution (5% normal horse serum, 2% BSA, and 0.3%riton X-100 in TBS, pH 7.4), and incubated in one ofhe following the primary antibodies: mouse monoclo-al anti-NeuN (Chemicon; 1:500), mouse monoclonalnti-GFAP (Sigma; 1:500), or mouse monoclonal anti-THIncstar 1:10000) for 24 h at 4°C. After incubation in theecondary antibody (biotinylated horse anti-mouse IgG:200) for 1 h at room temperature, the sections werelaced in fluorolink Cy 2-labeled streptavidin (1:1000)or 1 h at room temperature. Following several washes,ections were mounted on gelatin-coated slides, dehy-rated through graded alcohols (50, 70, 95, and 99%),leared in xylenes, and coverslipped with DPX. Forontrol, the first or second primary antibodies wereeleted. All fluorescence images were analyzed with thelympus Confocal Fluoroview microscope equippedith argon and krypton lasers.Stereological analysis b-Gal-positive neurons. The
otal number of lentivirus-positive neurons within theaudate nucleus, putamen, and substantia nigra wasetermined using the optical fractionator procedure13, 17, 22, 29). The optical fractionator, a design-basedtereological method for estimating total number oftructures, is optically disected using a high mag-ification objective with a high numerical aperture (1,) in a known fraction of a defined reference spaceithout affected by tissue shrinkage (13, 17, 22, 29).riefly, the optical fractionator system consisted of aomputer-assisted image analysis system including anlympus BX-60 microscope hard-coupled to a Prior128 computer-controlled x-y-z motorized stage, aigh-sensitivity Hitachi 3CCD video camera system
Hitachi, Japan), and a Macintosh 8500 computer. Allnalyses were performed using NeuroZoom software,ustom-designed morphology and stereology softwareeveloped in collaboration between Mount Sinai Schoolf Medicine and the Scripps Research Institute (31)y an observer blinded to the survival time of eachnimal. Prior to each series of measurements, thenstrument was calibrated. The region of lentivirus-ositive neurons in the caudate, putamen, or substan-ia nigra was outlined at low magnification (1.253bjective) and at least 15% of the outlined region waseasured with a systematic random design of disector
ounting frames (9890 µm2) using a 1003 planapo oilmmersion objective with a 1.4 numerical aperture. The
verage thickness of the sections was empirically mea-
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ured at 30 µm but neurons were only counted within a0-µm height of tissue, with guard heights of 5 µm athe top and 5 µm at the bottom of each section. Between0 and 58 sections through the striatum of each mon-ey were evaluated. Thirteen sections through theubstantia nigra were analyzed in the one monkeyeceiving an accurate lentivirus injection. The totalumber of lentivirus positive neurons (N) within theaudate nucleus, putamen, and substantia nigra wasstimated using the following formula N 5 Q t/h l/asf/ssf, where Q is the total disector number of lentivirus-ositive neurons actually counted by optical scanningsing uniform, systematic, and random design proce-ures in each disector for all measurements. The height
FIG. 1. Low power photomicrograph through the caudate nuistochemically stained) cells from two lentivirus injections. For orie000 µm.
h) of the disector is known relative to the thickness of (
he section (t). The areal sampling fraction (asf) is theercentage (15%) of the section-sampling fraction (ssf,he area containing lentivirus positive neurons; 13, 17,2, 29).The percentage of bGal-positive cells that double
abeled for the neuronal marker NeuN and the astro-ytic marker GFAP were determined using stereologi-al principals. Random but systematically chosen micro-copic fields through areas of positive labeling from aull series of sections were evaluated using an Olympusnverted confocal microscope and Fluoroview software.n separate experiments, bGal-immunofluorescent cellsere colocalized with either NeuN or GFAP. Withinach field, the number of cells stained singly for bGal
s of a monkey illustrating the area of bGal transduced (X-Galtion, the asterisk denotes the lateral ventricle. Scale bar represents
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7LENTIVIRAL GENE TRANSFER TO NONHUMAN PRIMATE BRAIN
FIG. 4. (A) Low and (B) high power photomicrographs of laser-cohis transgene seen in perikarya, processes and spinelike structures.
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ere double labeled for bGal and either NeuN or GFAPyellow in the merged image) were quantified.
RESULTS
Lentiviral injections into striatum. All monkeys tol-rated the surgery and lentivirus injections withoutoticeable complications. Both bGal histochemistrynd immunofluorescence revealed robust gene expres-ion within the striatum of all three monkeys (Figs. 1nd 2). Numerous bGal-positive cells were scatteredhroughout both the caudate nucleus and putamen onhe side of the injection (Figs. 1 and 2). Sectionsncubated in a solution lacking the lacZ substrate didot display positive staining. Additionally, bGal label-
ng was never observed in the uninjected contralateraltriatum. bGal-positive cells were identified up to 1.8nd 1.9 cm from the needle tract in the caudate nucleusnd putamen, respectively. In both monkeys humanelyilled at 1 month postinjection, the bGal reactionroduct was localized principally to striatal perikaryaFig. 3A), although reaction product could be observedithin a number of striatal processes as well (Fig. 3B).
n the monkey sacrificed 3 months postinjection, areater number of striatal cells displayed extensiveabeling of processes (Figs. 3C and 3D). In some cells,pine-like structures appear to be labeled (Figs. 4A andB). The presence of bGal within nonnuclear cellularompartments was observed to a similar degree inections processed for x-Gal histochemistry and bGal-mmunohistochemistry. In contrast to labeled neuronsn the striatum, there were no bGal-positive cellsithin the substantia nigra on the side ipsilateral to
he striatal injection, indicating that the lentivirus wasot retrogradely transported.Stereological counts of bGal-positive cells in the
triatum were performed on sections stained for x-Galistochemistry (Table 1). Robust and consistent generansfer was observed. For the two animals sacrificed 1onth postinjection, 930,218 and 1,192,359 bGal-
ositive cells were counted. For the monkey sacrificed 3onths postinjection, 1,501,217 bGal-positive cells were
bserved.Confocal microscopy and double immunofluorescenceas employed to assess the cell types expressing bGal.
n all monkeys, both NeuN-immunoreactive neuronsnd GFAP-immunoreactive astrocytes colocalized thearker gene bGal. Qualitatively, it appeared thatGal-immunofluorescent cells were colocalized princi-ally in cells that were labeled by the neuronal markereuN (Fig. 5), while fewer bGal-immunofluorescent
ells colocalized with the astrocytic marker GFAP (Fig.). Quantitative analyses in all three monkeys sup-orted these qualitative assessments. Stereological as-essments of double label-immunostained sections re-ealed that the range of bGal/NeuN double-labeledeurons was between 80.53 and 87.54% (Table 2). Inupport of these data, bGal/GFAP double label experi-ents revealed a range of bGal/GFAP double-labeled
strocytes in the range of 14.79–20.73% (Table 2).Nissl and NeuN-immunostained sections were em-
loyed to evaluate potential cytotoxicity of the lentivi-al injection. Nissl-stained sections revealed a minimalnflammatory response in the striatum (Fig. 7). Thisesponse was similar in animals sacrificed at oneonth to the monkey sacrificed at three months postin-
ection. In the areas directly adjacent to the needleract, there was minor perivascular cuffing aroundome blood vessels (Fig. 7B). The maximum distancerom a needle tract to a cuffed vessel was 240 and 960m in the monkeys sacrificed at 1 month postlentivirus
njection and 240 µm in the monkey sacrificed 3 monthsostinjection. This phenomenon was not observed inessels slightly more distal to the injection site (Fig.A). We assessed between 45–52 Nissl-stained sectionshrough the striatum in these three animals. The totalumber of ‘‘cuffed’’ vessels observed in these sectionsas 191 and 215, for the monkeys sacrificed at 1 monthostlentivirus injection, and 22, for the monkey sacri-ced at 3 months postinjection. Both Nissl (Figs. 7And 7C) and NeuN (Fig. 7D) immunoreacted sectionsevealed normal striatal cytoarchitecture bilaterallyithout any obvious loss of striatal neurons or exten-
ive reactive gliosis on the side of the injection.Lentiviral injections into the substantia nigra. Len-
iviral injections aimed for the substantia nigra in thewo monkeys sacrificed 1 month postinjection wereocalized to the underlying crux cerebri. Only scatteredGal-positive cells were observed within the whiteatter tracts of these animals (data not shown). The
entivirus injection for the monkey sacrificed 3 monthsostsurgery was accurately placed in the ventral mesen-ephalon. In this animal, numerous cells scatteredhroughout the nigra proper and within the supra-igral region exhibited extensive bGal labeling (Fig.A). bGal labeling in this region was principally nuclear,lthough the reaction product was also seen within theytoplasm and proximal dendrites of a few cells (Fig.B). Labeled cells were observed up to 1.8 cm from theeedle tract. Quantification of bGal-positive cells was
nly performed within the nigra for the monkey with
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9LENTIVIRAL GENE TRANSFER TO NONHUMAN PRIMATE BRAIN
n accurate injection placement. For this animal,87,305 bGal-positive cells were quantified (Table 1).ouble label experiments revealed that most bGal-ositive cells within the nigra colocalized with NeuNnd few colocalized GFAP. Some of the bGal-positiveells colocalized with TH.The lentivirus injection did not cause significant
eurotoxicity within the ventral midbrain (Fig. 9).H-immunostained sections revealed robust stainingf dopaminergic cells with an apparently normal collec-ion of TH-ir neurons on the side of the injection (Fig.A). Nissl-stained sections revealed healthy appearingeurons with normal morphological features through-ut the substantia nigra, even in regions directlydjacent to the needle tract (Figs. 9B and 9C). Signifi-ant perivascular cuffing was not observed within theubstantia nigra. In this monkey, only 2 ‘‘cuffed’’ vesselsere seen in the 12 Nissl-stained sections that werenalyzed. These were seen approximately 240 µm fromhe needle tract.
DISCUSSION
The present experiment was a feasibility study exam-ning whether extensive lentiviral gene transfer couldccur in the monkey brain without apparent cytotoxic-ty. The present data revealed the lentiviral constructesults in a robust transfer of the marker gene bgalacto-idase to the nonhuman primate nervous system. Aumber of important features of the present datahould be emphasized. Between 930,218–1,501,217ells within the striatum were bGal positive. This levelf transduction is greater than any previously reportedest of in vivo gene delivery in the central nervousystem. Most (between 80 and 87%) of these trans-ected cells were neurons. This percentage of generansduction into neurons is similar to what has beeneported in rodents as 88.7% of cells successfully trans-ected with lenti-bGal in rats are neurons (4). It needso be noted, however, that this feasibility study was
TABLE 2
Relative Levels of Lentiviral Gene Transfer to Neuronsand Glia in the Nonhuman Primate Striatum
erformed in a small number of monkeys. The consis- r
ent results obtained across the three monkeys lead uso complete the present feasibility study and initiateunctional studies, preventing the addition of moreonkeys into this experiment. Thus although the mon-
ey sacrificed at 3 months displayed the most robustene transfer, one cannot, at present, draw meaningfulonclusions regarding the sustained expression of theentiviral delivered transgene in the monkey brain.
In the substantia nigra, 187,305 bGal-positive cellsere identified in the monkey sacrificed 3 monthsostinjection. While this number is less than what waseen in the striatum, it needs to be noted that the nigralnjection was in a 5-µl volume, while the striatalnjections were made in a 40-µl volume. Indeed, extrapo-ating for volumetric differences, the number of infectedells in the midbrain of this animal is remarkablyimilar to the number of bGal-positive cells identifiedn the striatum. Only this monkey had an accuratelacement of lentivirus into the ventral midbrain withhe other two having injections placed into the underly-ng crux cerebri resulting in poor gene delivery. Theseatter injections illustrate the point that even with MRIuidance, misplaced delivery into white matter bundlesan severely compromise the rate of gene transfection.A critical aspect of the present data is the consistent
evel of gene transfer across the three monkeys. Mostther studies in nonhuman primates using in vivo generansfer approaches have found high variability inransgene expression. Although the numbers of mon-eys employed in this feasibility study was relativelymall by design, it is still notable that the monkeyisplaying the largest number of transfected cells washe one that had the longest postinjection survival. Theaveats associated with small sample sizes are notedbove. Further experiments will be needed to supporthe notion that long-term gene expression may bechievable using the lentiviral vector system. The usef self-inactivating lentiviral vectors containing post-ranscriptional regulatory elements such as the onerom the woodchuck hepatitis virus may be responsibleor the sustained gene expression. The consistent levelf gene transfer across the three subjects employed inhe present study strengthens the concept that thisene delivery method might be advantageous for deliv-ring therapeutic genes of interest to the human brain.An interesting aspect of the present data is the
resence of bGal-immunoreactivity within the cyto-lasm and processes of some transfected cells despitehe fact that the gene is a marker gene for the nucleusf the cell. The fact that similar results were observedith X-gal histochemistry and bGal-immunofluores-
ence indicates that this finding is not artifactual.ndeed, others have seen bGal within nonnuclear com-artments under similar in vivo gene delivery condi-ions (6; Bohn, personal communication) and this may
eflect the diffusion of the bGal to other cellular compart-
atn
10 KORDOWER ET AL.
FIG. 5. Laser confocal microscopic images through a series of focal planes through the caudate nucleus stained for (A) b Gal, (B) NeuN,nd (C) the composite image. Note the yellow appearing cells in C (arrows), denoting those cells that coexpress bGal and NeuN, indicating thathe lentivirus has infected these neurons. In contrast, cells with only red reaction product (arrowheads) represent gene transfer into
onneuronal cells. Scale bar in C represents 35 µm in all panels.
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11LENTIVIRAL GENE TRANSFER TO NONHUMAN PRIMATE BRAIN
FIG. 6. Laser confocal microscopic images of a field through the caudate nucleus stained for (A) b Gal, (B) GFAP, and (C) the compositemage. Note in C the few yellow-appearing cells, denoting that the bGal only infected a few astrocytes arrows. In contrast, cells with only redeaction product represent gene transfer into nonastrocytes (arrowheads). Scale bar in C represents 50 µm in all panels.
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12 KORDOWER ET AL.
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13LENTIVIRAL GENE TRANSFER TO NONHUMAN PRIMATE BRAIN
ents over time. The fact that bGal was most exten-ively seen within neurites in the monkey sacrificed 3onths postinjection supports this hypothesis.Other groups have evaluated other in vivo gene
elivery systems in the primate brain. Davidson andoworkers found bGal-positive cells in the Rhesusonkey following adenovirus delivery 1 week following
njection (9). Using an adenovirus harboring the herpesimplex viral thymidine kinase. Goodman et al. (15)sed PCR to localize the vector DNA for up to 6 weeksollowing delivery. Bohn and colleagues performed theost detailed study of adenoviral expression in theonhuman primate (6). These experiments resulted in
FIG. 8. (A) Low and (B) high power photomicrographs through thmonths following an intranigral injection. Sections were stained h
erimeter of the substantia nigra. Scale bar in A represents the follow
nferior and more inconsistent gene transfer. Using o
ultiple titers and volumes of adenovirus, they foundhousands of bGal positive cells in two of three Africanreen monkeys sacrificed 1 week following injection.ignificant variability in bGal gene expression wasbserved in these monkeys between 1 and 3 monthsostinjection. As many as 292,448 positive bGal-ositive cells were identified in one monkey 1 monthollowing adenoviral injection. However, in the monkeyhat survived for 3 months postinjection, only 156 and4 bGal-positive cells were identified at the two injec-ion sites, respectively.
Concomitant with excellent and sustained gene ex-ression in the present study was the apparent absence
idbrain of RH6075, illustrating the breath of lentiviral gene transferologically for bGal. CP, cerebral peduncle. Dashed lines delimit themagnifications: A, 500 µm; B, 65 µm.
e misting
f a significant cytotoxic or immune response to the
ctf
FIG. 9. (A) TH-immunofluorescence through the substantia nigra of a monkey receiving a lentiviral-bGal injection. Note the normalytoarchitectonic appearance of this region. (B) Low and (C) high power photomicrographs of Nissl-stained sections through the nigral needleract (curved arrows) illustrate the presence of normal appearing nigral cells adjacent to the lentivirus injection. Scale bar in C represents the
ollowing magnifications: A, 325 µm; B, 165 µm; C, 65 µm; and D, 500 µm.
14
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15LENTIVIRAL GENE TRANSFER TO NONHUMAN PRIMATE BRAIN
entivirus injection. Both Nissl- and NeuN-stainedections revealed that the lentiviral injections did notnduce notable cytotoxicity in either the striatum or theubstantia nigra. Further, only minor perivascularuffing was observed within the striatum of thesenimals and the perivascular cuffing that was observedas principally limited to the regions of the injection
ract. In contrast, no perivascular cuffing was observedn striatal or midbrain regions slightly distal to thenjection site. This lack of toxicity is dissimilar to whatas been seen in monkeys previously using other inivo delivery systems. In this regard, adenoviral injec-ions into the monkey striatum results in extensiveerivascular cuffing and a mild to moderate immuneesponse in monkeys with reasonable bGal expressionnd an intense immune response in monkeys withnsuccessful transduction (6). This group concludedhat the degree of immune response engendered bydenoviral limits transgene expression. The robust andonsistent data gene delivery seen in the present study,n the absence of obvious neurotoxicity and immunoge-icity, support the use of lentiviral gene transfer meth-ds in the primate nervous system.With the feasibility of using lentiviral gene transferethods in nonhuman primates now established, itsse for the delivery of therapeutic genes can be investi-ated. In rodents, biologically relevant lentiviral geneelivery has been demonstrated in two systems; theholinergic basal forebrain systems and the dopaminer-ic nigrostriatal system. In this regards, Blomer andolleagues (5) demonstrated that lentiviral delivery oferve growth factor can prevent the degeneration ofholinergic neurons within the septodiagonal bandegion that normally would occur following transectionf the fimbria–fornix transection. This model systemodels, in some respects mimics, the degeneration of
holinergic basal forebrain neurons seen in Alzheimer’sisease and has been applied previously to nonhumanrimates (14, 20, 28). Furthermore, aged monkeysisplay cognitive deficits that are reversed with pharma-ological augmentation of the cholinergic basal fore-rain system (for review, see 3). Determining whetherge-related cognitive deficits displayed by nonhumanrimates can be reversed by lentiviral delivery ofrophic factors would seem to be an important andationale approach toward determining whether thispproach can impact neurological problems.Perhaps a more straightforward application of the
entiviral gene delivery system involves studies theelivery of the glial derived neurotrophic factor (GDNF)n animal models of Parkinson’s disease. Using theame gene transfer system employed in the presenttudy, Deglon and colleagues (10) recently demon-trated that dopaminergic nigral neurons destined toie following axotomy could be rescued by supranigral
entiviral delivery of GDNF. For many reasons, the best
nimal model of Parkinson’s disease is the MPTP-reated monkey. The present study demonstrates thatobust and consistent lentiviral gene delivery can bechieved in the nigra and striatum in nonhumanrimates. Animal studies have consistently demon-trated that GDNF can provide functional and struc-ural protection and regeneration to dopaminergic nigro-triatal neurons (for reviews, see 17 and 21). However,recent case report indicated the lack of anatomical
nd clinical changes following infusions of the GDNFrotein into the lateral ventricle of a patient with PD19, 26). We argued in that study that the lack of anyffect of GDNF in the PD patient was principally due tohe method and location of GDNF delivery and not dueo the absence of GDNF potency. We believe thatite-specific delivery of GDNF will be necessary toxploit the trophic effects of this potent molecule inatients and that site-specific delivery of lentiviralene vectors might be an optimal delivery vehicle.tudies testing this hypothesis, in addition to examin-
ng potential peripheral nervous system toxicity, inonhuman primate models of PD are underway. Shouldhey be successful, then careful consideration for these of this technology in a clinical trial for PD patientsay be warranted.
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