Adeno-associated virus serotype 2-mediated gene transfer to the parotid glands of nonhuman primates

Transduction of Salivary Gland Acinar Cells with a Novel AAV Vector 44.9

The loss of salivary gland function caused by radiation therapy of the head and neck or autoimmune disease such as Sjögren's syndrome is a serious condition that affects a patient's quality of life. Due to the combined exocrine and endocrine functions of the salivary gland, gene transfer to the salivary glands holds the potential for developing therapies for disorders of the salivary gland and the expression of therapeutic proteins via the exocrine pathway to the mouth, upper gastrointestinal tract, or endocrine pathway, systemically, into the blood. Recent clinical success with viral vector-mediated gene transfer for the treatment of irradiation-induced damage to the salivary glands has highlighted the need for the development of novel vectors with acinar cell tropism able to result in stable long-term transduction. Previous studies with adeno-associated virus (AAV) focused on the submandibular gland and reported mostly ductal cell transduction. In this study, we have screened AAV vectors for acinar cell tropism in the parotid gland utilizing membrane-tomato floxed membrane-GFP transgenic mice to screen CRE recombinase encoding AAV vectors of different clades to rapidly identify capsid isolates able to transduce salivary gland acinar cells. We determined that AAVRh10 and a novel isolate found as a contaminant of a laboratory stock of simian adenovirus SV15, AAV44.9, are both able to transduce parotid and sublingual acinar cells. Persistence and localization of transduction of these AAVs were tested using vectors encoding firefly luciferase, which was detected 6 months after vector administration. Most luciferase expression was localized to the salivary gland compared to that of distal organs. Transduction resulted in robust secretion of recombinant protein in both blood and saliva. Transduction was species specific, with AAVRh10 having stronger transduction activity in rats compared with AAV44.9 or AAV2 but weaker in human primary salivary gland cells. This work demonstrates efficient transduction of parotid acinar cells by AAV that resulted in secretion of recombinant protein in both serum and saliva.

Tetravalent dengue DNA vaccine is not immunogenic when delivered by retrograde infusion into salivary glands

Introduction and background

A tetravalent DNA vaccine for Dengue virus is under development but has not yet achieved optimal immunogenicity. Salivary glands vaccination has been reported efficacious in rodents and dogs. We report on a pilot study testing the salivary gland as a platform for a Dengue DNA vaccine in a non-human primate model.

Materials and methods

Four cynomolgus macaques were used in this study. Each macaque was pre-medicated with atropine and sedated with ketamine. Stensen’s duct papilla was cannulated with a P10 polyethylene tube, linked to a 500ul syringe. On the first two infusions, all macaques were infused with 300ul of TVDV mixed with 2 mg of zinc. For the 3rd infusion, to increase transfection into salivary tissue, two animals received 100uL TVDV mixed with 400uL polyethylenimine 1μg/ml (PEI) and the other two animals received 500uL TVDV with zinc. Antibody titers were assessed 4 weeks following the second and third infusion.

Results and conclusions

SGRI through Stensen’s duct is a well-tolerated, simple and easy to reproduce procedure. TVDV infused into macaques salivary glands elicited a significantly weaker antibody response than with different delivery methods.

Delivery of human erythropoietin gene with an adeno-associated virus vector through parotid glands to treat renal anaemia in a swine model

Anaemia is a common complication of chronic kidney disease, for which there is presently no adequate treatment. The delivery of human erythropoietin (hEPO) cDNA to salivary glands reportedly increases red blood cell counts, haematocrit (HCT) and haemoglobin concentration, representing a potential new method of renal anaemia treatment. However, no studies have examined the effects of this method in an animal model of renal anaemia. Here we established a miniature pig animal model of renal anaemia through continuous feeding with adenine. In these animals, we delivered the AAV2hEPO gene to the parotid glands through Stensen's duct. As a control, we transferred AAVLacZ. Enzyme-linked immunosorbent assay was used to detect hEPO in serum and saliva. Red blood counts and serum biochemistry were used to evaluate how hEPO gene administration affected renal anaemia. Compared with the control group, we found increased hEPO concentrations in parotid saliva and serum, respectively, at 2 and 6 weeks after AAV2hEPO administration to the anaemic animals. HCT and haemoglobin were also increased after AAV2hEPO was delivered; most serum indicators of renal damage were not changed over the time span of the experiment, suggesting the adenine-induced kidney damage had not been completely reversed. However, blood urea nitrogen and B2 microglobulin levels showed small but significant improvement. Overall, our present findings suggest that adeno-associated virus 2 (AAV2)-mediated gene transduction of hEPO via the parotid gland is a promising potential alternative therapy for renal anaemia.

Promising Gene Therapeutics for Salivary Gland Radiotoxicity

More than 0.5 million new cases of head and neck cancer are diagnosed worldwide each year, and approximately 75% of them are treated with radiation alone or in combination with other cancer treatments. A majority of patients treated with radiotherapy develop significant oral off-target effects because of the unavoidable irradiation of normal tissues. Salivary glands that lie within treatment fields are often irreparably damaged and a decline in function manifests as dry mouth or xerostomia. Limited ability of the salivary glands to regenerate lost acinar cells makes radiation-induced loss of function a chronic problem that affects the quality of life of the patients well beyond the completion of radiotherapy. The restoration of saliva production after irradiation has been a daunting challenge, and this review provides an overview of promising gene therapeutics that either improve the gland’s ability to survive radiation insult, or alternately, restore fluid flow after radiation. The salient features and shortcomings of each approach are discussed.

Advances in salivary gland gene therapy - oral and systemic implications

INTRODUCTION

Much research demonstrates the feasibility and efficacy of gene transfer to salivary glands. Recently, the first clinical trial targeting a salivary gland was completed, yielding positive safety and efficacy results.

AREAS COVERED

There are two major disorders affecting salivary glands: radiation damage following treatment for head and neck cancers and Sjögren's syndrome (SS). Salivary gland gene transfer has also been employed in preclinical studies using transgenic secretory proteins for exocrine (upper gastrointestinal tract) and endocrine (systemic) applications.

EXPERT OPINION

Salivary gland gene transfer is safe and can be beneficial in humans. Applications to treat and prevent radiation damage show considerable promise. A first-in-human clinical trial for the former was recently successfully completed. Studies on SS suffer from an inadequate understanding of its etiology. Proof of concept in animal models has been shown for exocrine and endocrine disorders. Currently, the most promising exocrine application is for the management of obesity. Endocrine applications are limited, as it is currently impossible to predict if systemically required transgenic proteins will be efficiently secreted into the bloodstream. This results from not understanding how secretory proteins are sorted. Future studies will likely employ ultrasound-assisted and pseudotyped adeno-associated viral vector-mediated gene transfer.

Adult stem cells and tissue engineering strategies for salivary gland regeneration: a review

Saliva is an important compound produced by the salivary glands and performs numerous functions. Hyposalivation (dry mouth syndrome) is a deleterious condition often resulting from radiotherapy for patients with head and neck cancer, Sjogren's Syndrome, or as a side effect of certain medications. Hyposalivation negatively affects speaking, mastication, and swallowing in afflicted patients, greatly reducing their quality of life. Current treatments for this pathology include modifying lifestyle, synthetic saliva supplementation, and the utilization of salivary gland stimulants and sialagogues. However, many of these treatments do not address the underlying issues and others are pervaded by numerous side effects. In order to address the shortcomings related to current treatment modalities, many groups have diverted their attention to utilizing tissue engineering and regenerative medicine approaches. Tissue engineering is defined as the application of life sciences and materials engineering toward the development of tissue substitutes that are capable of mimicking the structure and function of their natural analogues within the body. The general underlying strategy behind the development of tissue engineered organ substitutes is the utilization of a combination of cells, biomaterials, and biochemical cues intended to recreate the natural organ environment. The purpose of this review is to highlight current bioengineering approaches for salivary gland tissue engineering and the adult stem cell sources used for this purpose. Additionally, future considerations in regard to salivary gland tissue engineering strategies are discussed.

Recovery of radiation-induced dry eye and corneal damage by pretreatment with adenoviral vector-mediated transfer of erythropoietin to the salivary glands in mice

Therapeutic doses of radiation (RTx) causes dry eye syndrome (DES), dry mouth, and as in other sicca syndromes, they are incurable. The aims of this work are as follows: (a) to evaluate a mouse model of DES induced by clinically relevant doses of radiation, and (b) to evaluate the protective effect of erythropoietin (Epo) in preventing DES. C3H female mice were subjected to five sessions of RTx, with or without pre-RTx retroductal administration of the AdLTR2EF1a-hEPO (AdEpo) vector in the salivary glands (SG), and compared with naïve controls at Day 10 (10d) (8 Gy fractions) and 56 days (56d) (6 Gy fractions) after RTx treatment. Mice were tested for changes in lacrimal glands (LG), tear secretion (phenol red thread), weight, hematocrit (Hct), and markers of inflammation, as well as microvessels and oxidative damage. Tear secretion was reduced in both RTx groups, compared to controls, by 10d. This was also seen at 56d in RTx but not AdEpo+RTx group. Hct was significantly higher in all AdEpo+RTx mice at 10d and 56d. Corneal epithelium was significantly thinner at 10d in the RTx group compared with AdEpo+RTx or the control mice. There was a significant reduction at 10d in vascular endothelial growth factor (VEGF)-R2 in LG in the RTx group that was prevented in the AdEpo+RTx group. In conclusion, RTx is able to induce DES in mice. AdEpo administration protected corneal epithelia and resulted in some recovery of LG function, supporting the value of further studies using gene therapy for extraglandular diseases.

Gene therapy using IL-27 ameliorates Sjögren's syndrome-like autoimmune exocrinopathy

Introduction

Sjögren's syndrome (SjS) is a systemic autoimmune disease characterized by decreased salivary and lacrimal gland secretions, resulting in severe dry mouth and dry eyes. Recent studies have suggested that T_H17 cells and its signature cytokine IL-17 are involved in the underlying pathogenic mechanisms leading to destructive inflammation and autoimmunity. In the present study, we examined whether IL-27, a natural inhibitor of T_H17 activity, could down-regulate or reverse SjS in C57BL/6.NOD-Aec1Aec2 mice, a model of primary-SjS.

Methods

Recombinant serotype 2 adeno-associated viral (AAV2) vectors expressing either IL-27 (rAAV2-IL27) or LacZ (rAAV2-LacZ) were injected into 6 or 14 week-old C57BL/6.NOD-Aec1Aec2 mice. Changes in IL-27, IL-17, and IL-10 cytokine levels in peripheral blood were determined by ELISAs, while flow cytometry analyses were used to quantify cytokine-positive splenocytes. Histological assessment of salivary glands, anti-nuclear autoantibody (ANA) staining, and stimulated saliva flow rates were used to profile SjS disease severity.

Results

Mice systemically treated with intravenous rAAV2-IL27 injections at either 6 or 14 weeks of age exhibited long-term elevated levels of serum IL-27 with concomitantly reduced levels of IL-17 compared with sera from mice injected with rAAV2-LacZ or saline out to 20 weeks post-inoculation. Most importantly, disease profiles revealed that rAAV2-IL27 treatment had little effect on lymphocytic focus (LF) scores, but resulted in structural changes in LF, lower titers of ANAs with changes in staining patterns, and a less severe clinical disease as determined by saliva flow rates.

Conclusions

These data support the concept that IL-27, when provided exogenously, can induce a suppressive effect on SjS development and thus may be an effective therapeutic agent for regulating T_H17 pro-inflammatory activity in autoimmune diseases where the T_H17 system has been shown to play an important role in their pathogenesis.

A novel hybrid adenoretroviral vector with more extensive E3 deletion extends transgene expression in submandibular glands

Salivary glands are an attractive target for gene transfer. Salivary epithelial cells are considered to be highly differentiated and have low rates of cell division (~6 months), affording the opportunity to obtain relatively long-term transgene expression in the absence of genomic integration. Here, we report a novel modified hybrid adenoretroviral vector, which provides stable transgene expression in salivary epithelial cells in vivo for up to 6 months in the absence of genomic integration. This modified hybrid vector, Ad(ΔE1/3)LTR(2)EF1α-hEPO, encodes human erythropoietin (hEPO) and differs from a previously developed hybrid vector, AdLTR(2)EF1α-hEPO, by having more extensive E3 gene deletion. Following direct salivary gland gene transfer by retroductal cannulation, rats transduced with Ad(ΔE1/3)LTR(2)EF1α-hEPO had sustained, elevated serum hEPO levels and hematocrits for 6 months (length of experiment), as compared with ~2 months for animals administered the AdLTR(2)EF1α-hEPO vector. Immunohistochemistry demonstrated that this novel vector could transduce both acinar and ductal cells. Interestingly, the Ad(ΔE1/3)LTR(2)EF1α-hEPO vector evoked much weaker local (salivary gland) immune responses than seen after AdLTR(2)EF1α-hEPO vector delivery, which likely permits its significantly lengthened transgene expression in this tissue.

An AAV2/5 vector enhances safety of gene transfer to the mouse salivary gland

This study was designed to improve AAV-mediated gene transfer to the murine submandibular salivary glands. Our first aim was to utilize AAV pseudotype vectors, containing the genetic elements of the canonical AAV2, packaged within capsids of AAV serotypes 5, 8, and 9. Having determined that this pseudotyping increased the efficiency of gene transfer to the glands by several orders of magnitude, we next asked whether we could reduce the gene transfer inoculum of the pseudotype while still achieving gene transfer comparable with that achieved with high-dose AAV2. Having achieved gene transfer comparable with that of AAV2 using a pseudotype vector (AAV2/5) at a 100-fold lower dose, our final objective was to evaluate the implications of this lower dose on two pre-clinical parameters of vector safety. To evaluate systemic toxicity, we measured AAV vector sequestration in the liver using qPCR, and found that the 100-fold lower dose reduced the vector recovered from the liver by 300-fold. To evaluate salivary gland function, we undertook whole-proteome profiling of salivary gland lysates two weeks after vector administration and found that high-dose (5 × 10⁹) AAV altered the expression level of ~32% of the entire salivary gland proteome, and that the lower dose (5 × 10⁷) reduced this effect to ~7%.

Transduction, tropism, and biodistribution of AAV vectors in the lacrimal gland

PURPOSE

The lacrimal gland (LG) delivers defensive and metabolic factors to the ocular surface. These functions may be disrupted in several diseases, and for most of them there is no cure. The aim of this study is to investigate conditions and limitations for using adeno-associated virus (AAV) vectors as gene transfer agents to LG.

METHODS

Eight-week-old Balb/c mice were used to investigate route, gene expression, and time course of AAV gene vector transfer to LG. AAV vectors encoding firefly luciferase were administered to the LG and luciferase expression was evaluated in vivo by immunohistochemistry. Ocular surface and neutralizing antibodies were also evaluated.

RESULTS

The present work revealed that AAV vectors are able to delivery DNA to the LGs of mice. Direct injection had the highest level of transduction, and topical ocular drops the lowest. Overall, the AAV strain with highest transduction activity as measured by both luminescence and immunohistochemistry was AAV9, followed by AAV 5w8 and AAV5. Transduction was not different between sexes, could be detected as soon as 24 hours after injection, and lasted for at least 30 days (study termination). No tissue damage was observed when compared with controls. All vectors with detectable LG transduction induced neutralizing antibodies.

CONCLUSIONS

LG gene delivery by AAV vectors appears to be both safe and well tolerated. The choice of vector influences both the overall transduction activity, as well as the spread of vector to other organs. This work supports the use of AAV-mediated gene therapy for dry eye.

Gene delivery in salivary glands: from the bench to the clinic

In vivo gene delivery has long been seen as providing opportunities for the development of novel treatments for disorders refractory to existing therapies. Over the last two decades, salivary glands have proven to be a useful, if somewhat unconventional, target tissue for studying several potential clinical applications of therapeutic gene delivery. Herein, we follow the progress, address some problems and assess the outlook for clinical applications of salivary gland gene delivery. Our experience with these tissues provides a roadmap for the process of moving an idea from the laboratory bench to patients.

Assessment of the safety and biodistribution of a regulated AAV2 gene transfer vector after delivery to murine submandibular glands

Clinical gene transfer holds promise for the treatment of many inherited and acquired disorders. A key consideration for all clinical gene transfer applications is the tight control of transgene expression. We have examined the safety and biodistribution of a serotype 2, recombinant adeno-associated viral (AAV2) vector that encodes a rapamycin-responsive chimeric transcription factor, which regulates the expression of a therapeutic transgene (human erythropoietin [hEpo]). The vector, AAV2-TF2.3w-hEpo (2.5 × 10(7)-2.5 × 10(10) particles), was administered once to a single submandibular gland of male and female mice and mediated hEpo expression in vivo following a rapamycin injection but not in its absence. Control (saline treated) and vector-treated animals maintained their weight, and consumed food and water, similarly. Vector delivery led to no significant toxicological effects as judged by hematology, clinical chemistry, and gross and microscopic pathology evaluations. On day 3 after vector delivery, vector copies were not only abundant in the targeted right submandibular gland but also detected in multiple other tissues. Vector was cleared from the targeted gland much more rapidly in female mice than in male mice. Overall, our results are consistent with the notion that administration of the AAV2-TF2.3w-hEpo vector to salivary glands posed no significant risk in mice.

Human parathyroid hormone is secreted primarily into the bloodstream after rat parotid gland gene transfer

Hypoparathyroidism is a hormone deficiency syndrome that leads to low blood calcium levels and for which current replacement therapy is inadequate. Gene transfer to salivary glands leads to safe and abundant secretion of therapeutic protein into either saliva or the bloodstream. We previously reported the successful transduction of rat submandibular glands with an adenoviral vector encoding human parathyroid hormone (Ad.hPTH), but unfortunately most of the hPTH was secreted into saliva. Because submandibular and parotid glands are morphologically and functionally different, we hypothesized that hPTH sorting might be different in parotid glands. After 2 days, the pattern of hPTH secretion from transduced parotid glands of intact rats was reversed from that of transduced submandibular glands, that is, most transgenic hPTH was detected in serum (5 × 10(10) viral particles per gland; the saliva-to-serum ratio of total hPTH secreted was 0.04). Vector copies were localized to the targeted parotid glands, with none detected in liver or spleen. Ad.hPTH next was administered to parotid glands of parathyroidectomized rats. Two days after delivery no hPTH was detectable in saliva, but high levels were found in serum, leading to normalization of serum calcium and a significant increase in the urinary phosphorus-to-creatinine ratio. This study demonstrates for the first time differential sorting of transgenic hPTH between submandibular and parotid glands, suggesting that hPTH may be a valuable model protein for understanding the molecular basis of transgenic secretory protein sorting in these exocrine glands. We also show the clinical potential of salivary gland hPTH gene therapy for patients with hypoparathyroidism.

AAV2-mediated transfer of the human aquaporin-1 cDNA restores fluid secretion from irradiated miniature pig parotid glands

Previously (Shan et al, 2005), we reported that adenoviral vector-mediated transfer of the human aquaporin-1 (hAQP1) cDNA to minipig parotid glands following irradiation (IRti) transiently restored salivary flow to near normal levels. This study evaluated a serotype 2, adeno-associated viral (AAV2) vector for extended correction of IR (single dose; 20 Gy)-induced, parotid salivary hypofunction in minipigs. Sixteen weeks following IR, parotid salivary flow decreased by 85-90%. AAV2hAQP1 administration at week 17 transduced only duct cells and resulted in a dose-dependent increase in salivary flow to ∼35% of pre-IR levels (to ∼1ml/10min) after 8 weeks (peak response). Administration of a control AAV2 vector or saline, was without effect. Little change was observed in clinical chemistry and hematology values after AAV2hAQP1 delivery. Vector treated animals generated high anti-AAV2 neutralizing antibody titers by week 4 (∼1:1600) and significant elevations in salivary (∼15%), but not serum, GM-CSF levels. Following vector administration, salivary [Na⁺] was dramatically increased, from ∼10mM to ∼55 (at 4 weeks) and 39 mM (8 weeks). The findings demonstrate that localized delivery of AAV2hAQP1 to IR-damaged parotid glands leads to increased fluid secretion from surviving duct cells, and may be useful in providing extended relief of salivary hypofunction in previously irradiated patients.

Evaluation of a rapamycin-regulated serotype 2 adeno-associated viral vector in macaque parotid glands

OBJECTIVES

Salivary glands are useful target organs for local and systemic gene therapeutics. For such applications, the regulation of transgene expression is important. Previous studies by us in murine submandibular glands showed that a rapamycin transcriptional regulation system in a single serotype 2, adeno-associated viral (AAV2) vector was effective for this purpose. This study evaluated if such a vector was similarly useful in rhesus macaque parotid glands.

METHODS

A recombinant AAV2 vector (AAV-TF-RhEpo-2.3w), encoding rhesus erythropoietin (RhEpo) and a rapamycin-inducible promoter, was constructed. The vector was administered to macaques at either of two doses [1.5 x 10(11) (low dose) or 1.5 x 10(12) (high dose) vector genomes] via cannulation of Stensen's duct. Animals were followed up for 12-14 weeks and treated at intervals with rapamycin (0.1 or 0.5 mg kg(-1)) to induce gene expression. Serum chemistry, hematology, and RhEpo levels were measured at interval.

RESULTS

AAV-TF-RhEpo-2.3w administration led to low levels of rapamycin-inducible RhEpo expression in the serum of most macaques. In five animals, no significant changes were seen in serum chemistry and hematology values over the study. One macaque, however, developed pneumonia, became anemic and subsequently required euthanasia. After the onset of anemia, a single administration of rapamycin led to significant RhEpo production in this animal.

CONCLUSION

Administration of AAV-TF-RhEpo-2.3w to macaque parotid glands was generally safe, but led only to low levels of serum RhEpo in healthy animals following rapamycin treatment.

Salivary epithelial cells: an unassuming target site for gene therapeutics

Salivary glands are classical exocrine glands whose external secretions result in the production of saliva. However, in addition to the secretion of exocrine proteins, salivary epithelial cells are also capable of secreting proteins internally, into the bloodstream. This brief review examines the potential for using salivary epithelial cells as a target site for in situ gene transfer, with an ultimate goal of producing therapeutic proteins for treating both systemic and upper gastrointestinal tract disorders. The review discusses the protein secretory pathways reported to be present in salivary epithelial cells, the viral gene transfer vectors shown useful for transducing these cells, model transgenic secretory proteins examined, and some clinical conditions that might benefit from such salivary gland gene transfer.

Development of a gene transfer-based treatment for radiation-induced salivary hypofunction

A significant long-term side effect of radiation therapy for head and neck cancers is xerostomia, a dry mouth, due to salivary gland damage. Despite continuing efforts to eliminate this problem, many patients continue to suffer. This brief review describes our efforts to develop a gene transfer approach, employing the aquaporin-1 cDNA, to treat patients with existing radiation-induced salivary hypofunction. A Phase I/II clinical trial, using a recombinant adenoviral vector to mediate gene transfer, is currently underway.

AAV5-mediated gene transfer to the parotid glands of non-human primates

Salivary glands are potentially useful target sites for multiple clinical applications of gene transfer. Previously, we have shown that serotype 2 adeno-associated viral (AAV2) vectors lead to stable gene transfer in the parotid glands of rhesus macaques. As AAV5 vectors result in considerably greater transgene expression in murine salivary glands than do AAV2 vectors, herein we have examined the use of AAV5 vectors in macaques at two different doses (n = 3 per group; 10(10) or 3 x 10(11) particles per gland). AAV5 vector delivery, as with AAV2 vectors, led to no untoward clinical, hematological or serum chemistry responses in macaques. The extent of AAV5-mediated expression of rhesus erythropoietin (RhEpo) was dose-dependent and similar to that seen with an AAV2 vector. However, unlike results with the AAV2 vector, AAV5 vector-mediated RhEpo expression was transient. Maximal expression peaked at day 56, was reduced by approximately 80% on day 84 and thereafter remained near background levels until day 182 (end of experiment). Quantitative PCR studies of high-dose vector biodistribution at this last time point showed much lower AAV5 copy numbers in the targeted parotid gland (approximately 1.7%) than found with the same AAV2 vector dose. Molecular analysis of the conformation of vector DNA indicated a markedly lower level of concatamerization for the AAV5 vector compared with that of a similar AAV2 vector. In addition, cellular immunological studies suggest that host response differences may occur with AAV2 and AAV5 vector delivery at this mucosal site. The aggregate data indicate that results with AAV5 vectors in murine salivary glands apparently do not extend to macaque glands.

Sorting of transgenic secretory proteins in rhesus macaque parotid glands after adenovirus-mediated gene transfer

We have previously used viral vectors encoding either human growth hormone (hGH) or erythropoietin (hEPO) to study the sorting of transgenic proteins in mouse and minipig salivary glands. Whereas hGH (a regulated secretory pathway [RSP] protein) is secreted predominantly into saliva in both species, hEPO (a constitutive secretory pathway [CSP] protein) is found primarily in the bloodstream with mice, but overwhelmingly in saliva with minipigs. In view of the hEPO sorting difference, we have conducted a similar study in nonhuman primates. Specifically, we examined hGH and hEPO sorting after adenoviral (Ad) vector-mediated gene transfer to parotid glands of rhesus macaques, another large and important animal model. Two groups (n = 2 per dose group; total n = 8) of male macaques received either 10(10) particles per gland (low-dose group) or 10(11) particles per gland (high-dose group) of adenoviral (Ad) vectors encoding either hGH (AdhGH) or hEPO (Ad-hEPO) via intraoral cannulation of both parotid glands. All macaques tolerated administration of Ad vectors well, with no clinically significant changes observed in any hematological and serum chemistry parameters. In AdhGH-treated animals, hGH was secreted exclusively into saliva. In contrast, after AdhEPO delivery, hEPO was secreted both in serum and saliva, at levels intermediate between mice and minipigs. We conclude that RSP proteins are faithfully secreted into saliva in all model species tested, whereas patterns of CSP protein secretion are variable.

Long-term transduction of miniature pig parotid glands using serotype 2 adeno-associated viral vectors

BACKGROUND

Previously, using an adenoviral vector, we showed that miniature pigs could provide a valuable and affordable large animal model for pre-clinical gene therapy studies to correct parotid gland radiation damage. However, adenoviral vectors lead to short-term transgene expression and, ideally, a more stable correction is required. In the present study, we examined the suitability of using a serotype 2 adeno-associated viral (AAV2) vector to mediate more stable gene transfer in the parotid glands of these animals.

METHODS

Heparan sulfate proteoglycan was detected by immunohistochemistry. beta-galactosidase expression was determined histochemically. An AAV2 vector encoding human erythropoietin (hEpo) was administered via Stensen's duct. Salivary and serum hEpo levels were measured using an enzyme-linked immunosorbent assay. Serum chemistry and hematological analyses were performed and serum antibodies to hEpo were measured throughout the study. Vector distribution was determined by a quantitative polymerase chain reaction.

RESULTS

Transgene expression was vector dose-dependent, with high levels of hEpo being detected for up to 32 weeks (i.e. the longest time studied). hEpo reached maximal levels during weeks 4-8, but declined to approximately 25% of these values by week 32. Haematocrits were elevated from week 2. Transduced animals exhibited low serum anti-hEpo antibodies (1 : 8-1 : 16). Vector biodistribution at animal sacrifice revealed that most copies were in the targeted parotid gland, with few being detected elsewhere. No consistent adverse changes in serum chemistry or hematology parameters were seen.

CONCLUSIONS

AAV2 vectors mediate extended gene transfer to miniature pig parotid glands and should be useful for testing pre-clinical gene therapy strategies aiming to correct salivary gland radiation damage.

Current status of the development of an artificial salivary gland

Salivary glands (SGs) secrete more than half a liter of saliva daily. Saliva has many functions in maintaining the normal homeostasis of the oral cavity. Several causes underlie salivary impairment, where irradiation therapy to head and neck cancer patients is one of the most debilitating causes leading to considerable decrease in the patients' quality of life. In the last decade, others and we have focused on implementing tissue engineering principles combined with gene transfer and stem cell methodologies to develop an artificial SG device. This manuscript provides an overview of the current status of engineering an artificial SG.

Gene therapy: some history, applications, problems, and prospects

The concept of transferring genes to tissues for clinical applications has been discussed for nearly half a century, but our ability to manipulate genetic material via recombinant DNA technology has brought this goal to reality. While originally conceived as a way to treat life-threatening disorders (inborn errors, cancers) refractory to conventional treatment, gene therapy now is considered for many non-life-threatening conditions, including those adversely affecting a patient's quality of life. The lack of suitable treatment has become a rational basis for extending the scope of gene therapy. This manuscript reviews the general methods by which genes are transferred as well as diverse examples of clinical applications (acquired tissue damage, upper gastrointestinal tract infection, autoimmune disease, systemic protein deficiency). Despite some well-publicized problems, gene therapy has made substantive progress, including tangible success, albeit much slower than was initially predicted. Although gene therapy is still at a fairly primitive stage, it is firmly science based. There is justifiable optimism that with increased pathobiological understanding and biotechnological improvements, gene therapy will become a standard part of clinical practice within 20 years.