Distinguishing genetics and eugenics on the basis of fairness

There is concern that human applications of modern genetic technologies may lead inexorably to eugenic abuse. To prevent such abuse, it is essential to have clear, formal principles as well as algorithms for distinguishing genetics from eugenics. This work identifies essential distinctions between eugenics and genetics in the implied nature of the social contract and the importance ascribed to individual welfare relative to society. Rawls's construction of 'justice as fairness' is used as a model for how a formal systems of ethics can be used to proscribe eugenic practices. Rawls's synthesis can be applied to this problem if it is assumed that in the original condition all individuals are ignorant of their genetic constitution and unwilling to consent to social structures which may constrain their own potential. The principles of fairness applied to genetics requires that genetic interventions be directed at extending individual liberties and be applied to the greatest benefit of individuals with the least advantages. These principles are incompatible with negative eugenics which would further penalize those with genetic disadvantage. These principles limit positive eugenics to those practices which are designed to provide absolute benefit to those individuals with least advantage, are acceptable to its subjects, and further a system of basic equal liberties. This analysis also illustrates how simple deviations from first principles in Rawls's formulation could countenance eugenic applications of genetic technologies.

Overexpression of human methylmalonyl CoA mutase in mice after in vivo gene transfer with asialoglycoprotein/polylysine/DNA complexes

Methylmalonic acidemia resulting from genetic deficiency of methylmalonyl CoA mutase (MCM) is an often fatal metabolic disease. Somatic gene therapy for this disorder may require gene replacement in the liver. We describe overexpression of MCM in the liver of mice after in vivo gene delivery using asialoglycoprotein/polylysine/DNA (ASO/PL/DNA) targeted delivery to the liver of plasmids expressing recombinant MCM. After intravenous administration of the ASO/PL/DNA complex, the vector sequences are cleared from the blood with t1/2 = 2.5 min and > 95% of the vector is taken up by the liver. Vector sequences are cleared from the liver with t1/2 = 1.0-1.3 hr. MCM enzyme activity in the liver increases to levels 30-40% over baseline 6-24 hr after injection. No acute or chronic toxicity was observed. This net level of expression is likely to be therapeutic for MCM if the complex could be administered repetitively to treat acute episodes of life-threatening acidosis or establish a steady-state level of MCM activity. Repetitive administration of the ASO/PL/DNA complexes in mice was associated with formation of antibodies against asialo-orosomucoid and the asialo-orosomucoid complex but not against DNA.

Clustering of mutations in methylmalonyl CoA mutase associated with mut- methylmalonic acidemia

Mutations have been described in human methylmalonyl CoA mutase (MCM) that exhibit partial defects in enzyme activity, including cobalamin-dependent (i.e., mut-) or interallelic complementation. This work describes mutations in cells from four patients, three of whom exhibit a cobalamin-dependent phenotype and all four of whom exhibit interallelic complementation. Four novel mutations (R694W, G648D, G630E, and G626C) are identified that cluster near the carboxyl terminus of the protein, a region close to another mut- mutation (G717V). Each of these mutations was shown to express a phenotype congruent with that of the parental cell line, after transfection into mut0 fibroblasts, and each exhibits interallelic complementation in cotransfection assays with clones bearing a R93H mutation. The activity of mutant enzymes expressed in Saccharomyces cerevisiae parallels the residual activity of the parental cell lines and exhibits novel sensitivities to pH and salt. The clustering of these mutations identifies a region of MCM that most likely represents the cobalamin-binding domain. The location of this domain, as well as the pattern of sequence preservation between the homologous human and Probiono-bacterium shermanii enzymes, suggests a mechanism for interallelic complementation in which the cobalamin-binding defect is complemented in trans from the heterologous subunits of the dimer.

Isodisomy of chromosome 6 in a newborn with methylmalonic acidemia and agenesis of pancreatic beta cells causing diabetes mellitus

Isodisomy (ID) is a genetic anomaly defined as the inheritance of two copies of the same genetic material from one parent. ID in an offspring is a rare cause of recessive genetic diseases via inheritance of two copies of a mutated gene from one carrier parent. We studied a newborn female with a mut(o) of methylmalonic acidemia and complete absence of insulin-producing beta cells in otherwise normal-appearing pancreatic islets, causing insulin-dependent diabetes mellitus. The patient died 2 wk after birth. Serotyping of the HLA antigens, DNA typing of HLA-B and HLA class II loci, study of polymorphic DNA markers of chromosome 6, and cytogenetic analysis demonstrated paternal ID, involving at least a 25-centiMorgan portion of the chromosome pair that encompasses the MHC. ID probably caused methylmalonic acidemia by duplication of a mutated allele of the corresponding gene on the chromosome 6 inherited from the father. It is also very likely that ID was etiologically related to the agenesis of beta cells and consequent insulin-dependent diabetes mellitus in our patient. We thus speculate on the existence of a gene on chromosome 6 involved in beta cell differentiation.

In vivo gene transfer into rabbit thyroid follicular cells by direct DNA injection

Direct injection of DNA expression vectors into muscle leads to expression of encoded recombinant gene products in mature muscle cells. This phenomenon is not shared by most other organs. We have surveyed various organs in the rabbit to identify other cell types that would express DNA vectors after direct injection. We observed that thyroid follicular cells were capable of acquiring plasmid DNA and expressing recombinant gene products after direct interstitial injection of plasmid vectors into the thyroid gland. The level of expression of a chloramphenicol acetyltransferase (CAT) reporter gene in thyroid tissue was similar to that seen in muscle tissue three days after injection in controlled experiments. Using a beta-galactosidase reporter gene, expression was localized to thyroid follicular cells. CAT activity decreased with first-order kinetics and a half-life t1/2 of 40 hr. DNA was identified in thyroid tissue by polymerase chain reaction (PCR) analysis and displayed first-order elimination kinetics with a half-life t1/2 of 10 hr. The persistence of the gene and gene product in the thyroid was significantly different from that observed after injection of DNA vectors into muscle or delivery of DNA vectors to the liver using asialoglycoprotein/polylysine/DNA complexes, suggesting that there are significant differences in the process of DNA uptake or compartmentalization in these experimental systems. These results introduce the possibility of developing the thyroid as a novel target for treating certain thyroid or systemic diseases using DNA vectors.

Multicompartment, numerical model of cellular events in the pharmacokinetics of gene therapies

DNA expression vectors may be administered to patients like conventional medicines to have a finite and controlled duration of action. The clinical application of these medicines will require a precise understanding of the kinetics of the administered gene, the mRNA transcript, and the gene product. The apparent kinetic properties of the therapeutic gene product, including the level and duration of action, will be determined by various intrinsic kinetic processes including: (i) distribution and biological fate of the DNA expression vector; (ii) rates of DNA uptake into cells and dynamics of intracellular trafficking; (iii) half-life of the DNA vector in the cell; (iv) transcription rate; (v) half-life of mRNA; (vi) translation rate; and (vii) post-translational processing, distribution, and fate of the gene product. To consider in a theoretical manner how the intrinsic kinetics of cellular processes may affect the apparent level of a therapeutic gene product over time, we have constructed a multicompartment, numerical model. The model has six compartments, designated MILIEU, ENDOSOME, CELL, RNA, PROTEIN, and PRODUCT. The apparent level and kinetics of the gene product over time are calculated with different values for the intrinsic t1/2 of DNA in the MILIEU, ENDOSOME, and CELL; the intrinsic t1/2 of mRNA; the intrinsic t1/2 of the gene product; endosomal stability; and transcription rate. The model demonstrates how first-order kinetics can result from the summation of complex kinetic processes and provides a theoretical basis for future pharmacokinetic studies. This theoretical model illustrates how the half-lives of DNA, RNA, and gene product each affect the level of the product and highlights strategies for enhancing the therapeutic profile of gene therapies.

Cloning and expression of mutations demonstrating intragenic complementation in mut0 methylmalonic aciduria

The mut0 mutation resulting in methylmalonyl CoA mutase (MCM) apoenzyme deficiency and methylmalonic aciduria is characterized by undetectable enzyme activity in cell extracts and low incorporation of propionate into cultured cells which is not stimulated by hydroxycobalamin. A mut0 fibroblast cell line (WG1681) from an African-American male infant complemented another mut0 cell line (WG 1130). Cloning and sequencing of cDNA from WG 1681 demonstrated compound heterozygosity for two novel changes at highly conserved sites: G623R and G703R. In addition, two previously described homozygous polymorphisms, H532R and V671I, were found. Hybridization of allele-specific oligonucleotides to PCR amplified MCM exons from the proband and family members identified a clinically normal mother, half-sister, and half-brother as carriers of the G703R change in cis with both polymorphisms. Transfection of each change into a mut0 cell line with very low MCM mRNA (GM1673) demonstrated a lack of stimulation of propionate uptake in the absence and presence of hydroxycobalamin. Cotransfection of each mutation with the previously identified R93H mutation of WG 1130 stimulated propionate uptake, indicating that G623R and G703R are independently capable of complementing the R93H mutation.

Genomic structure of murine methylmalonyl-CoA mutase: evidence for genetic and epigenetic mechanisms determining enzyme activity

Methylmalonyl-CoA mutase (MCM) is a nuclear-encoded mitochondrial matrix enzyme. We have reported characterization of murine MCM and cloning of a murine MCM cDNA and now describe the murine Mut locus, its promoter and evidence for tissue-specific variation in MCM mRNA, enzyme and holo-enzyme levels. The Mut locus spans 30 kb and contains 13 exons constituting a unique transcription unit. A B1 repeat element was found in the 3' untranslated region (exon 13). The transcription initiation site was identified and upstream sequences were shown to direct expression of a reporter gene in cultured cells. The promoter contains sequence motifs characteristic of: (1) TATA-less housekeeping promoters; (2) enhancer elements purportedly involved in co-ordinating expression of nuclear-encoded mitochondrial proteins; and (3) regulatory elements including CCAAT boxes, cyclic AMP-response elements and potential AP-2-binding sites. Northern blots demonstrate a greater than 10-fold variation in steady-state mRNA levels, which correlate with tissue levels of enzyme activity. However, the ratio of holoenzyme to total enzyme varies among different tissues, and there is no correlation between steady-state mRNA levels and holoenzyme activity. These results suggest that, although there may be regulation of MCM activity at the level of mRNA, the significance of genetic regulation is unclear owning to the presence of epigenetic regulation of holoenzyme formation.

Somatic gene therapy in otolaryngology-head and neck surgery

The initial clinical trials of somatic gene therapy have demonstrated that gene transfer can be performed safely in a clinical setting and with public acceptance. These trials have focused attention on the broad applications of this technology in routine medical and surgical practice. This article reviews the reasons why somatic gene therapy could lead to significant improvements in clinical practice as well as specific therapies in otolaryngology-head and neck surgery. Early applications include the treatment of inherited diseases such as cystic fibrosis, new approaches for treating malignancies, new methods for enhancing tissue repair, and regeneration after plastic and reconstructive surgery, and the potential for using the thyroid as a target for somatic gene therapy. The following review will illustrate how somatic gene therapy may have a significant impact not only on the treatment of rare genetic diseases but on managing the common problems encountered by physicians and patients in daily practice.

Expression of recombinant human methylmalonyl-CoA mutase: in primary mut fibroblasts and Saccharomyces cerevisiae

Methylmalonyl-CoA mutase is an adenosylcobalamin-dependent enzyme which catalyzes isomerization of methylmalonyl-CoA to succinyl-CoA. Previous reports have described cloning and sequencing of a cDNA for human methylmalonyl-CoA mutase. This clone does not express an active apoenzyme after gene transfer into primary MCM-deficient fibroblasts and contains several sequences which differ from the consensus sequence of other cDNA clones. We describe reconstruction of a functional MCM cDNA and expression of recombinant enzyme activity in primary fibroblasts and Saccharomyces cerevisiae. This consensus human MCM cDNA is capable of complementing the inherited defect in mut MMA and overexpressing an enzyme in yeast with kinetic properties indistinguishable from the enzyme in murine or human tissues.

Somatic gene therapy. Methods for the present and future

Somatic gene therapy involves the introduction of novel genetic material into somatic cells to express therapeutic gene products. This emerging technology holds great promise for the treatment of both inherited and acquired diseases. This review summarizes the principles of gene therapy and approaches that are being investigated in experimental animals and clinical trials. These include the construction of recombinant viruses capable of carrying genes into cells by the process of infection as well as the use of DNA molecules that are capable of being used like conventional medicines. Some methods for gene therapy lead to permanent insertion of genes into targeted cells, while others are designed to express a therapeutic product with a defined half-life and duration of action. The goal is to establish site-specific and regulated expression of therapeutic products. The demonstrated safety and public acceptance of initial clinical trials will lead to widespread investigation of applications in both medicine and surgery in the near future.

DNA- and viral-mediated gene transfer in follicular cells: progress toward gene therapy of the thyroid

The authors investigate the in vitro component of an ex situ strategy for gene transfer into the thyroid gland using DNA complex and retroviral vectors. Canine follicular cells harvested by unilateral lobectomy and grown in low-serum media proliferated in culture and retained their differentiated state as evidenced by morphology and thyroglobulin expression. Transient and "stable" gene transfer in thyroid cells were evaluated by comparing DNA and retroviral transduction techniques. Effective gene transfer and expression was demonstrated by histochemical staining for the marker gene product beta-galactosidase. The efficiency of transduction was assessed using an amphotropic retroviral vector carrying the neomycin resistance gene and semiquantitative polymerase chain reaction (PCR) identification of integrated proviral sequences. This analysis demonstrated a proviral frequency in transduced cultures of 10% to 30%. Transduced cells showed no change in morphology or growth patterns and maintained differentiated function as assessed by antibody staining for thyroglobulin. The thyroid gland is an attractive target for somatic gene therapy because of its large protein-synthetic capacity, sensitivity to hormonal regulation, and proportionately high blood flow. Follicular cell gene therapy may be useful not only for treating congenital or acquired diseases of the thyroid, but also disorders of circulating proteins such as hypopituitarism, hemophilia, and diabetes.

Prenatal application of somatic gene therapy

Somatic gene therapy in the fetus or neonate represents an exciting new approach for the management of some congenital or inherited diseases. It is likely that clinical trials of these methods will take place in the future. In contrast, despite the potential for manipulation of embryos and inherited genetic material, the clinical applicability of these methods is uncertain.

Factors influencing the interests, career paths, and research activities of recent graduates from an academic, pediatric residency program

OBJECTIVE

This study was undertaken to characterize the professional activity of a cohort of young pediatricians who completed an academically oriented residency program, to analyze factors which influenced their interests, career choices, and research activity, and to understand what steps might be effective in attracting more young physicians into academic and research career paths.

METHOD

We studied by questionnaire a cohort of 150 pediatric residents from the Children's Hospital in Boston who completed residency training between 1976 and 1981.

RESULTS

Questionnaires were returned by 117 (78%) of 150 individuals. Of these, 73% were in academic medicine and 37% were in clinical practice. Individuals were engaged in various activities with a mean of 47% effort in clinical care, 25% effort in administration and teaching, and 28% effort in basic or clinical research. The majority of respondents (71 [61%] of 117) reported at least 10% effort in all three activities. Only 9 (8%) of 117 reported no clinical activity, 8 (7%) of 117 reported no teaching or administrative activity, and 35 (30%) of 117 reported no research activity. Few individuals dedicated more than 50% of their time to research, and none reported a 100% commitment to research. Clinical sources provided 71% of all salary support, research grants 17%, government salaries 7%, and other sources 5%. For most respondents, interest in clinical practice predated medical school, whereas interest in research increased during preclinical training, particularly among those who engaged in research activities. Respondents identified previous research experience as the principle factor enhancing their decision and ability to do research. Factors that adversely influenced their decision or ability to do research included salary expectancy, funding, the perceived competitiveness of academic life, administrative duties, and family responsibilities.

CONCLUSIONS

Efforts to encourage more young physicians to enter academic careers should focus on providing research experience during preclinical training and providing long-term support for research which enables physician scientists to maintain their interest and involvement in clinical medicine.

Feasibility of hepatocellular transplantation via the umbilical vein in prenatal and perinatal lambs

Hepatocellular transplantation has previously been performed in experimental animals by infusion of hepatocyte suspensions into the spleen or portal venous system. Cells injected into these sites flow to the liver and engraft within the hepatic parenchyma. We designed this study to evaluate the feasibility of hepatocellular transplantation through the umbilical vein in the prenatal or perinatal periods. Allogeneic sheep hepatocytes were harvested, stained with the vital fluorescent dye DiI, and injected into the umbilical vein of fetal lambs at 85% gestation and term. Hemodynamic studies performed to assess the physiological impact of transplantation on the recipient animal demonstrated that the procedure was well tolerated. No significant short-term complications were encountered and no lesions were found by conventional histological examination at necropsy 1-17 days after transplantation. Engrafted cells were identified within the liver by fluorescent microscopy and flow cytometry in 4/7 animals constituting 1.2-5% of the hepatocyte population. Fluorescent cellular material with the morphology of hepatocytes, noncellular material, and fluorescent phagocytic cells were seen occasionally in other organs including lung, brain, adrenal, and placenta. These studies demonstrate the feasibility of performing hepatocellular transplantation in the fetus via the umbilical vein in experimental animals.

Retrovirus-mediated gene transfer into canine thyroid using an ex vivo strategy

We describe studies in a canine model aimed at establishing methods for ex vivo gene delivery to thyroid follicular cells. Canine follicular cells were harvested from tissue obtained by unilateral lobectomy, grown in thyrotropin-containing media, and transduced with amphotropic retroviral vectors carrying Escherichia coli beta-galactosidase or Tn7 neomycin-resistance genes. Up to 30% of cells were transduced with retroviral vectors containing the neomycin resistance gene, and transduced cells could be selected with G418. Significantly, transduced and selected cells exhibited the morphology of thyroid follicular cells and continued to express thyroglobulin. To assess the viability of cultivated and transduced cells for transplantation, cells were stained with the vital fluorescent dye DiI, recovered by trypsinization, and transplanted into the contralateral thyroid lobe of autologous animals. Engraftment was demonstrated by fluorescence microscopy and identification of proviral sequences 7-10 days after transplantation. Proviral transcripts were evident using coupled reverse transcription and the polymerase chain reaction using total RNA from transplanted glands. Thyroid follicular cells may represent an attractive target for gene therapy due to their proliferative potential, their large protein synthetic and secretory capacity, and their susceptibility to regulation. The thyroid might be a target for therapy of congenital or acquired thyroid diseases as well as disorders requiring regulated expression of proteins in the circulation. This work demonstrates the feasibility of ex vivo gene delivery to thyroid follicular cells that may be used in future investigations.

Development of a clinical protocol for hepatic gene transfer: lessons learned in preclinical studies

Strategies for hepatic gene therapy have been proposed that involve isolation of primary hepatocytes and introduction of recombinant genes into these cells in culture, followed by autologous hepatocellular transplantation (HCT). Consideration of clinical applications requires data suggesting that HCT can be performed safely in human subjects in addition to data indicating that recombinant gene expression can reverse a disease process. This report describes preclinical studies that underlie a clinical trial of HCT in which hepatocytes would be labeled with a marker gene to facilitate assessment of engraftment in the recipient. Human hepatocytes were harvested from liver segments preserved in Belzar's solution and transduced with an amphotropic retroviral vector carrying a recombinant marker gene (neomycin phosphotransferase II). Human hepatocytes were recovered from monolayer culture, stained with the fluorescent dye 1,1'-dioctadecyl-3,3,3,3'-tetra-methylindo-carbocyanine perchlorate (DiI) and transplanted into severe combined immunodeficient mice by splenic injection. Engrafted hepatocytes were identified in the liver and spleen of severe combined immunodeficient mice but not immunocompetent controls. Two large animal models of HCT are described. In a dog model, neomycin phosphotransferase II-containing hepatocytes were identified in the liver 7 wk after transplantation. In a baboon model, autologous HCT with DiI-stained cells demonstrated that transplanted cells assume a normal morphology and constitute up to 5% of hepatocytes. These data demonstrate transduction and transplantation of human hepatocytes and the feasibility of HCT in large animals. On the basis of these studies, the proposed clinical trial for gene transfer and transplantation in human subjects has been approved by the National Institutes of Health and the Food and Drug Administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Propionate metabolism in cultured human cells after overexpression of recombinant methylmalonyl CoA mutase: implications for somatic gene therapy

Strategies for somatic gene therapy must consider the metabolic consequences of expressing the recombinant gene product in addition to methods for gene transfer and expression. We describe studies of propionate metabolism in cultured cells transfected with methylmalonyl CoA mutase (MCM), the enzyme deficient in mut methylmalonic acidemia. Transfection of MCM into mut fibroblasts restores propionate metabolism to normal levels in a dose-dependent manner. Overexpression of MCM, or the addition of excess propionate, carnitine, or cobalamin, does not increase propionate metabolism in normal human fibroblasts, lymphoblasts, or hepatoma cells, although hepatic cells exhibit > 10-fold higher levels of propionate metabolism. Significantly, the restoration of propionate metabolism in mut fibroblasts is disproportionately greater than the efficiency of transfection, suggesting the presence of a cooperative phenomenon between cells. Intercellular participation in propionate metabolism is evident in cocultures of MCM-deficient and propionyl CoA carboxylase-deficient cells. We conclude that the liver is the preferred target for gene therapy of MCM deficiency because of its greater capacity for propionate metabolism and that cooperation between cells could enhance the biological effect of a subpopulation of cells transformed with recombinant MCM.

Varying neurological phenotypes among muto and mut- patients with methylmalonylCoA mutase deficiency

MethylmalonylCoA mutase (MCM) is a mitochondrial homodimer responsible for the isomerization of methylmalonylCoA to succinylCoA. Apomutase defects are traditionally divided into muto and mut- classes on the basis of residual mutase activity. Clinical findings were reviewed in 20 patients with methylmalonic aciduria secondary to MCM deficiency. All 11 muto patients had an early neonatal presentation; 6 of these patients died in infancy and 3 of 5 survivors had a poor neurological outcome as evidenced by severe delay or spastic quadriparesis with dystonia. The 2 other survivors include a 27-month-old child with a mild delay in verbal and fine motor skills and an adolescent with low normal intelligence. Of the 9 mut- patients, 7 became symptomatic in late infancy or childhood and 2 were picked up on screening. Two of the 9 patients have never had an episode of metabolic decompensation yet both are neurologically compromised; one severely retarded and autistic, the other mildly delayed. Four mut- patients have had episodic acidosis and are neurologically moderately affected, while 3 have had episodic acidosis and are neurologically intact. These results confirm phenotypic pleomorphism without a consistent pattern of neurological injury and suggest some broad correlation between mutase class and phenotype. Survival with good outcome is possible among muto patients as is significant morbidity among mut- patients. Acidosis and metabolic imbalance are not necessary preconditions for significant morbidity.

Expression of recombinant human glutathione reductase in eukaryotic cells after DNA-mediated gene transfer

Glutathione reductase (EC 1.6.4.2) protects tissues from oxidant stress by catalyzing the NADPH-mediated reduction of glutathione disulfide to glutathione. We describe construction of a vector for DNA-mediated gene transfer and successful transient overexpression of human glutathione reductase cDNA in CHO cells. No expression was observed when the same vector was transiently transfected into NIH3T3 or LA4 cells or stably integrated in CHO cells. These results demonstrate the ability to constitute recombinant glutathione reductase expression in eukaryotic cells but suggest that this expression may be toxic.

Are contemporary methods for somatic gene therapy suitable for clinical applications?

Clinical trials involving the introduction of recombinant genes into human subjects began in 1989 after a decade of earnest debate concerning the technical, social, and ethical implications of somatic gene therapy. The initial trials involved the introduction of recombinant genes into peripheral blood lymphocytes to study the characteristics of tumor infiltrating lymphocytes, enhance immunotherapy for cancer, and treat severe combined immunodeficiency due to adenosine deaminase deficiency. Additional clinical trials involving the introduction of genes into bone marrow, hepatocytes, and tumor cells are underway. Are these clinical trials premature? This article reviews basic methods for somatic gene therapy and the clinical trials which have been proposed or performed to date. This clinical experience suggests that gene therapy can be performed in select clinical trials safely and with public acceptance. Clinical trials have provided essential data concerning the feasibility and safety of gene transfer in human subjects. These trials have also brought a clinical focus to the assessment of technologies currently being used in experimental models. While there will certainly be significant advances in somatic gene therapy in the future, existing methods may be employed fairly in clinical trials.

Cloning of functional alpha propionyl CoA carboxylase and correction of enzyme deficiency in pccA fibroblasts

Propionyl CoA carboxylase (PPC) is a heteromeric enzyme composed of alpha subunits (PCCA) and beta (PCCB) subunits. We describe cDNA clones expressing human PCCA and complementation of the genetic defect in pccA fibroblasts by DNA-mediated gene transfer. Two cDNA clones were constructed. The first corresponds to the previously reported, putatively full-length, open reading frame. The second encodes a chimera composed of the mitochondrial leader sequence of human methylmalonyl CoA mutase and the mature PCCA protein. Both clones reconstitute propionate flux to normal levels in fibroblasts from patients genetically deficient in PCCA (pccA). The maximal level of propionate flux approached, but never exceeded, the levels seen in control plates of normal cells. In contrast, the maximal level of PPC holoenzyme activity reached only 10%-20% that of normal controls, which corresponded roughly to the fraction of cells actually transformed with the recombinant gene. These data suggest that the level of PCCA expression in fibroblasts does not normally limit PCC holoenzyme activity or propionate flux. The fact that a small fraction of cells reconstitutes propionate flux to normal levels suggests that metabolic cooperation between cells is capable of increasing the metabolic capacity of recombinant enzyme in a subpopulation of cells. These factors may have important implications for the rational design of somatic gene therapy for PCCA deficiency.

Autologous, orthotopic thyroid follicular cell transplantation: a surgical component of ex vivo somatic gene therapy

Ex vivo strategies for somatic gene therapy involve the harvest of primary cells from patients, the transfer of novel genetic material into these cells in cell culture, and reimplantation of the genetically engineered cells back into patients. In consideration of methods for targeting somatic gene therapy to the thyroid, we have studied the autologous, orthotopic transplantation of thyroid follicular cells in a canine model. Using the fluorescent dye Dil, we were able to stain follicular cells in vitro before transplantation and then follow the pattern of engraftment through histologic sectioning and microscopy up to 14 days after transplantation. The transplantations involved the direct injection of intact and disrupted follicles into a remaining thyroid lobe after cell harvest from the contralateral lobe. We also demonstrated engraftment of individual follicular cells recovered from primary monolayer cultures. Histologic studies revealed the presence of transplanted cells and follicles as well as focal regions of granulomatous reaction in close relation to the engrafted material. These studies demonstrate the feasibility of autologous, orthotopic transplantation of thyroid follicular cells. This method is an essential component of ex vivo strategies for targeting somatic gene therapy to the thyroid gland.