The dual-function hamster receptor for amphotropic murine leukemia virus (MuLV), 10A1 MuLV, and gibbon ape leukemia virus is a phosphate symporter

Previously, we showed that the amphotropic receptor homolog in hamster cells functions as a receptor not only for amphotropic murine leukemia viruses and 10A1 murine leukemia virus but also for gibbon ape leukemia virus (C.A. Wilson, K. B. Farrell, and M. V. Eiden, J. Virol. 68:7697-7703, 1994). Here, we demonstrate that this receptor functions as a sodium-dependent Pi transporter and that Na-Pi uptake can be specifically blocked following infection with either amphotropic murine leukemia virus, 10A1 murine leukemia virus, or gibbon ape leukemia virus.     

Gene transfer into human dendritic antigen-presenting cells by vaccinia virus and adenovirus vectors

In a search for means to deliver exogenous gene(s) into human dendritic cells (DCs) from the perspective of tumor-specific vaccination, we have evaluated two recombinant viruses, both of which carry a reporter gene which is namely a modified vaccinia virus Ankara (MVA) and an adenovirus, as possible expression vectors. The recombinant MVA-P11 LZ vector carries the Escherichia coli lacZ gene coding for the enzyme beta-galactosidase, and the recombinant Ad-MFG-AP vector carries a modified membrane-exposed alkaline phosphatase (AP) gene. DCs were generated ex vivo in the presence of tumor necrosis factor-alpha, granulocyte macrophage colony-stimulating factor, stem cell factor, and flk-2/flt-3 ligand taken from CD34+ hematopoietic progenitors that were mobilized into the peripheral blood of cancer patients treated with high-dose cyclophosphamide and filgrastim. The target cells used for gene delivery were either CD34+ cells that had been subsequently induced to differentiate into mature DCs or DCs transduced after ex vivo generation from CD34+ cells. The results showed that: (a) infection of CD34+ cell derived-DCs (mature DCs) with either viral vector resulted in the efficient synthesis of recombinant protein, and (b) CD34+ cells were permissive for the expression of the recombinant reporter gene after infection with Ad-MFG-AP but not after infection with MVA-P11 LZ. In conclusion, these results suggest that vaccinia and adenovirus vectors are candidate to act as vehicles in genetically engineering human DCs.     

Gene transfer of herpes simplex virus type I thymidine kinase gene as a drug sensitivity gene into human lung cancer cell lines using retroviral vectors

A number of packaging materials are being used not only to contain food during distribution but also to serve as the cooking container. The higher temperatures that these materials reach led the US Food and Drug Administration (FDA) to issue an intent to publish new regulations in 1989. The food and packaging industries responded by conducting extensive research and submitting the results to FDA. The methods used and results obtained are discussed. Most of the data were focused on microwave susceptors and the volatile compounds generated. One project showed that for a specific product, popcorn, there was no transfer into the food. Work is continuing to validate methods to test for non-volatile compounds. In addition to susceptors, various paper and plastic materials are used in dual ovenable (microwave and conventional ovens) applications. Most of the research on these materials has investigated the food contact temperatures on testing for migrants. An update on the current regulatory status of packaging materials intended for high temperature use in the US is discussed.     

Analysis of a multi-mutant herpes simplex virus type 1 for gene transfer into sympathetic preganglionic neurons and a comparison to adenovirus vectors

A non-replicating triple-mutant herpes simplex virus (14H delta 3vhsZ) expressing the bacterial marker enzyme beta-galactosidase, was assessed for neurotropism and cytopathic effects as a vector for gene transfer into differentiated phaeochromocytoma 12 cells in vitro and into spinal sympathetic neurons in vivo. In the in vivo study, the 14H delta 3vhsZ was injected into the adrenal gland of hamsters. For comparison, an evaluation of two adenovirus vectors, AdCA17lacZ and AdCA36lacZ, was performed. Infection of the differentiated phaeochromocytoma 12 cells by 14H delta 3vhsZ resulted in intense beta-galactosidase staining in 80-90% of the cells without changes in cell morphology, detected by light microscopy, after a period of four days. No cytoskeletal disruption was detected by immunocytochemistry for the neurofilament protein and no apoptosis was demonstrated by the Hoescht stain for nuclear chromatin in virus-infected cells in comparison to mock-infected control cells. Twoto three days after adrenal inoculation with 14H delta 3vhsZ, beta-galactosidase was detected in 240 preganglionic neurons per hamster (n = 8), a number equal to about 25% of the population of targeted neurons. The beta-galactosidase reaction product extended throughout the normal kite-shaped neuronal somata and extensive dendritic arbour. The number decreased to 120 by five days (n = 3) and to two by eight days (n = 4). This decrease was presumably due to loss of expression of the marker gene and not to cell death because, at eight days, the number of sympathetic pregnanglionic neurons in the nucleus intermediolateralis, pars principalis, that were immunoreactive for the neurotransmitter enzyme choline acetyltransferase, and demonstrated nicotinamide adenine dinucleotide phosphate-diaphorase activity, were the same on the infected left side of the cord as on the uninfected right side. Inflammatory cells surrounded some of the infected neurons at five days but by eight days the infiltrate was reduced. Infection of differentiated phaeochromocytoma 12 cells by AdCA17lacZ and AdCA36lacZ also resulted in marker gene expression in a large proportion of the cells (80-90%) in the absence of cytopathic effects. In contrast, four days after adrenal injection of AdCA17lacZ or AdCA36lacZ (n = 5 for each) only an average of three preganglionic neurons per hamster expressed beta-galactosidase activity, despite clear adrenal infection. AdCA17lacZ and AdCA36lacZ both produced light patches of staining confined to the neuronal soma. These neurons had normal morphology but sometimes were surrounded by an inflammatory infiltrate. In conclusion, the non-replicating herpes simplex virus, 14H delta 3vhsZ, had minimal cytotoxic effects in neurons, in vitro or in vivo, and was efficiently transported from the adrenal gland to infect many sympathoadrenal pregnanglionic neurons. In contrast, very few neurons demonstrated beta-galactosidase activity after injection into the adrenal gland of AdCA17lacZ and AdCA36lacZ. Therefore, 14H delta 3vhsZ is a more suitable vector than either of the adenovirus vectors tested for eliciting short-term changes in preganglionic neuron gene expression.     

Efficient gene transfer into primary and immortalized human fetal glial cells using adeno-associated virus vectors: establishment of a glial cell line with a functional CD4 receptor

Adeno associated virus (AAV) is a non-pathogenic dependent parvovirus with a broad host range, capable of high levels of transduction and stable integration into the host cell genome. We have investigated the potential for using AAV as a vector for gene transfer into glial cells of the human fetal nervous system. Recombinant AAV vectors expression either the reporter gene beta-galactosidase or a human CD4 receptor were able to transduce both primary glial cells of the human fetal nervous system and an SV40 immortalized human fetal glial cell line (SVG). No difference in transduction efficiency was observed between the primary cells and the cell line which in both cases was as high as 95%. Stable transfectants of the glial cell line expressing the CD4 receptor were selected. An SVG/CD4 expressing line was then established. The presence of the CD4 receptor was confirmed by immunohistochemistry, Westerm immuno-blotting and flow cytometric analysis. The CD4 receptor was shown to be functional by infection of the SVG/CD4 cell line with the human immunodeficiency virus (HIV). Upon infection, the SVG/CD4 cells produced 20-fold higher levels of the HIV intracellular core antigen P24 than the CD4 negative parental cells and in addition formed syncytia. The use of AAV vectors should prove useful in biological investigations of human glial cells and offers promise as a means of ex vivo and in vivo gene delivery.     

In utero gene therapy: transfer and long-term expression of the bacterial neo(r) gene in sheep after direct injection of retroviral vectors into preimmune fetuses

We investigated whether directly injecting retroviral vectors into preimmune fetuses could result in the transfer and long-term expression of exogenous genes. Twenty-nine preimmune sheep fetuses were injected with helper-free retroviral vector preparations. Twenty-two fetuses survived to term, 4 of which were sacrificed at birth. Of the remaining 18 animals, 3 were controls and 15 had received vector preparations. Twelve of these 15 animals demonstrated transduction of hematopoietic cells when blood and marrow were analyzed by neo(r)-specific PCR. Eight experimental sheep have been followed for 5 years, during which time we have consistently observed proviral DNA and G418-resistant hematopoetic progenitors. The G418-resistant colonies were positive when analyzed by neo(r)-specific PCR. neo(r) gene expression was also demonstrated using several immunological and biochemical methods. The transduction of hematopoietic stem cells was confirmed when lambs transplanted with bone marrow from in utero-transduced sheep exhibited neo(r) activity in marrow and blood. Vector distribution was widespread in primary animals without pathology. PCR analysis indicates that the germ line was not altered. These studies demonstrate that direct injection of an engineered retrovirus is a feasible means of safely delivering a foreign gene to a developing fetus and achieving long-term expression without modifying the germ line of the recipient.     

Gene therapy for chronic myelogenous leukemia (CML): a retroviral vector that renders hematopoietic progenitors methotrexate-resistant and CML progenitors functionally normal and nontumorigenic in vivo

Chronic myelogenous leukemia (CML) is a malignant disease of the human hematopoietic stem cell caused by the BCR/ABL gene rearrangement. The only curative therapy is allogeneic transplantation. Although autologous transplants may prolong survival, most patients relapse because of disease persisting in the host and in the graft. Continued administration of chemotherapy after transplant could reduce the incidence of relapse provided that the autograft can be protected by transfer of a drug-resistance gene. However, CML autografts will almost certainly contain malignant stem cells that will also be rendered drug-resistant. The presence of the BCR/ABL oncoprotein is necessary and sufficient for malignant transformation seen in CML. We thus hypothesized that transfer of a vector that combines a drug-resistance gene with anti-BCR/ABL antisense (AS) sequences may allow for posttransplant chemotherapy to decrease persistent disease while rendering inadvertently transduced CML stem and progenitor cells functionally normal. We constructed a retroviral vector, LasBD, that combines the methotrexate (MTX)-resistant tyrosine-22 dihydrofolate-reductase (tyr22-DHFR) gene and AS sequences directed at the b3a2 BCR/ABL breakpoint. b3a2 BCR/ABL containing 32D and MO7e cells were transduced with LasBD and selected in MTX for 14 days. Expression of the AS sequences reduced BCR/ABL mRNA and p210(BCR/ABL) protein levels by 6- to 10-fold in most cells. This subsequently led to the restoration of normal function of BCR/ABL cDNA+ cells: they grew significantly slower in the presence of interleukin-3 (IL-3); they underwent apoptotic cell death when cultured without IL-3; and they had restored expression and function of adhesion receptors. These effects were specific, because LasBD-containing AS sequences directed at the b3a2 BCR/ABL breakpoint did not affect p190(BCR/ABL)-containing cells. LasBD also rendered 20% to 30% of primary Ph- and Ph+ CD34(+) cells MTX-resistant and decreased BCR/ABL mRNA levels in MTX resistant Ph+ CD34(+) cells by 10-fold. Expression of the MTX-resistant DHFR gene and the AS sequences has been stable for at least 1 year in vitro and for more than 70 days in vivo. Finally, LasBD decreased tumorigenicity of 32DBCR/ABL cells in vivo by 3 to 4 logs. In conclusion, the tyr22-DHFR gene in the LasBD vector can protect normal hematopoietic cells from MTX-mediated toxicity, whereas the AS sequences in LasBD can suppress expression of the BCR/ABL gene and restore normal function of BCR/ABL cDNA-containing cells. The LasBD vector may therefore prove to be an extremely useful adjunct in autologous transplantation for CML.     

Lactate-dehydrogenase activity in the rat testis: a comparison between fluorometric assay of freeze-dried sections and histochemical localization with phenazine methosulphate

The activity of lactate dehydrogenase (LDH) in freeze-dried sections of rat testes was determined by using a fluorometric assay method and found to be 4.47 +/- 0.23 moles/Kg dry weight/hr (MKDH +/- S.E.M.) in whole sections, 3.31 +/- 0.16 in tubules and 12.0 +/- 1.9 in interstitial tissue. The activities and regional variation are similar to those measured in nervous tissue and are well correlated with the histochemical localization of LDH activity when phenazine methosulphate (PMS) is not used as an electron carrier. LDH and lipoamide dehydrogenase activity have the same histochemical distribution and there is no nonspecific staining with either method. The use of PMS results in reduced dependence on substrate and coenzyme and does not indicate higher interstitial activity but may provide an indication of developing lactate metabolism in maturing sperm. It is recomended that methods with and without PMS be used in studies of LDH activity in the testis.     

Insulin stimulation of lactate accumulation in isolated human granulosa-luteal cells: a comparison between normal and polycystic ovaries

Polycystic ovary syndrome (PCOS) is often associated with hyperinsulinaemia and peripheral insulin resistance. Whether the ovary is resistant to insulin is a matter of controversy. The aim was therefore to study the effect of insulin on lactate accumulation, an indicator of glucose metabolism, in granulosa-luteal cells from women with PCOS and from women with normal ovarian function. The cells were obtained from women undergoing clinical in-vitro fertilization-embryo transfer, either from patients with normal ovarian function and tubal or male infertility, or from women with PCOS, with or without tubal factor. The patients were down-regulated with buserelin and stimulated with urofollitrophin and human chorionic gonadotrophin (HCG). Follicle aspiration was performed under ultrasound guidance. Following oocyte recovery the granulosa-luteal cells were isolated, washed and cultured (2-3 x 10(4) viable cells/well) in serum-free Eagle's minimal essential medium for 48 h. After washing, the cells were then cultured in medium containing HCG (0.1-10 IU/ml) or insulin (0.05-0.5 microg/ml) for 24-48 h. Lactate accumulation in the media and cellular protein were analysed. Basal lactate accumulation did not differ in granulosa-luteal cells obtained from normal or PCOS ovaries, and averaged 46 and 49 nmol/g protein/24 h, respectively. A significant stimulation (40-60%) was obtained by HCG in both groups. Insulin caused a dose-dependent increase in lactate in granulosa-luteal cells obtained from normal ovaries (control: 45.5 +/- 6.3; insulin 0.5 microg/ml: 77 +/- 10 nmol/microg protein). Lactate accumulation in granulosa-luteal cells from PCOS ovaries was not altered in the presence of insulin. These results suggest that granulosa-luteal cell glucose metabolism is resistant to insulin in PCOS.     

Treatment of Ph1-positive chronic myelogenous leukemia in children: comparison between allogeneic bone marrow transplantation and conventional chemotherapy. Spanish Working Party for BMT in Children (GETMON)

BACKGROUND AND OBJECTIVE: To compare the estimated survival and disease-free survival between children with Ph1-positive chronic myeloid leukemia treated with allogeneic bone marrow transplantation or conventional chemotherapy. DESIGN AND METHODS: In this retrospective study we compared the results obtained in a group of 14 children who received allogeneic bone marrow transplantation (BMT) between 1983 and 1993, and another group of 27 children treated with busulfan, hydroxyurea or alpha-interferon during the same time period. Patients were transplanted at a median of 7 months from diagnosis and all except one were in their first chronic phase. Conditioning consisted in total body irradiation and cyclophosphamide in 12 cases, and busulfan was added in two. RESULTS: Of the 14 patients treated with BMT, two died of transplant-related complications and two relapsed 18 and 48 months after the BMT. Ten children remain alive and disease free at a median follow up of 60 months. The probability of DFS at 5 years is 70%. Of the 27 patients treated with chemotherapy, 22 have died at a median of 36 months from diagnosis. The probability of survival at 5 years is 5% versus 83% for the BMT group (p = 0.001). INTERPRETATION AND CONCLUSIONS: Allogeneic BMT is a safe and very effective treatment for Ph-positive CML in children. Patients who have an HLA-identical sibling donor must receive a transplant as soon as possible after being diagnosed.     

2-CDA in treatment of hairy cell leukemia: a comparison between intravenous and subcutaneous administration. Swiss Study Group of Applied Cancer Research

2-chlorodeoxyadenosine (2-CDA) is very effective in the treatment of patients with hairy-cell leukaemia, with an overall response rate of 80-95%. The standard treatment is a continuous intravenous infusion for 7 days. The bioavailability of 2-CDA after subcutaneous injection is 100%, but the concentration-time profile is completely different compared to continuous intravenous administration. In the present study we compared the intravenous standard treatment (group 1, n = 22; 0.1 mg/kg/d for 7 days, civ.) with subcutaneous administration of 2-CDA (group 2, n = 62; 0.14 mg/kg/d for 5 days, s.c.) in patients with hairy-cell leukaemia. In group 1, 96% (21/22) of patients responded to 2-CDA (complete remission 73%, partial remission 23%) and in the second group 97% were responsive (complete response 76%, 47/62; partial remission 21%, 13/62). The percentage for moderate and severe infections in the trial with intravenous and subcutaneous treatment was 14% and 26% respectively (p = 0.37). We conclude that subcutaneous administration of 2-CDA in patients with hairy-cell leukaemia is feasible and economical and results in comparable responses and toxicity compared to the intravenous standard treatment.     

An approach towards genetically engineered cell fate mapping in maize using the Lc gene as a visible marker: transactivation capacity of Lc vectors in differentiated maize cells and microinjection of Lc vectors into somatic embryos and shoot apical meristems

To establish a system for genetically engineered cell fate mapping, different vectors carrying the Lc gene, a member of the R gene family, were delivered into embryonic and meristematic cells of maize by the microinjection technique. Vectors in which the Lc cDNA is driven either by a constitutive promoter (CaMV 35S), with or without the Adh1 intron 1 of maize, or a tissue-specific promoter (phosphoenolpyruvate carboxylase, PEPC) as well as self-replicating wheat dwarf virus (WDV) vectors carrying a Lc-expression-cassette, have been tested. The ability of these vectors to transactivate was evaluated in mesophyll-derived protoplasts of the maize genotype appropriate for these microinjection experiments. The expression product of the introduced Lc gene can substitute for mutated R and B loci, resulting in anthocyanin production. Analogous results were obtained by microinjection into organized tissues, where transactivation of anthocyanin biosynthesis resulted in pigmented sectors in somatic embryos (B79) and in the leaves of plants regenerated from the cultivated shoot apical meristems (K55, r-g, b). The tissue-specific appearance of pigmented sectors in leaves, using the mesophyll-specific PEPC promoter suggests the possibility of using this approach for layer-specific cell fate studies. The presence of the introduced plasmids in leaves showing red sectors 20-30 days after injection was proven by PCR analysis.     

Improving the intracellular delivery and molecular efficacy of antisense oligonucleotides in chronic myeloid leukemia cells: a comparison of streptolysin-O permeabilization, electroporation, and lipophilic conjugation

The hybrid gene BCR-ABL that typifies chronic myeloid leukemia (CML) represents an attractive target for therapy with antisense oligodeoxyribonucleotides (ODN). A central obstacle in the therapeutic application of ODN is their poor cellular uptake. Adding various lipophilic conjugates to the ODN backbone has been reported to improve uptake, and electroporation of target cells has also been shown to enhance intracellular ODN delivery. We have shown that (1) BCR-ABL-directed ODN will specifically decrease the level of BCR-ABL mRNA, provided that cells are first permeabilized with Streptolysin-O (SL-O), and (2) chimeric methylphosphonodiester:phosphodiester ODN directed against 9 bases either side of the BCR-ABL junction are more efficient ODN effectors than structures composed solely of phosphodiester or phosphorothioate linkages. In this study, we compared the efficacy of lipophilic conjugation, SL-O permeabilization and electroporation on the intracellular delivery and molecular effect of BCR-ABL-directed ODN. b2a2- and b3a2-directed chimeric ODN were synthesized either unmodified or with one of the following groups at the 5' end: cholesterol, vitamin E, polyethylene glycol of average molecular weight 2,000 or 5,000, N-octyl-oligo-oxyethylene, or dodecanol. ODN associated with Lipofectin was also studied. Comparison was made in untreated, electroporated, and SL-O permeabilized KYO1 cells. Uptake was examined by fluorescence microscopy and flow cytometry, using ODN structures that were 3' labeled with fluorescein. The effect on target BCR-ABL mRNA expression was analyzed by Northern blotting. Several conjugated structures associated avidly with the cell membrane without achieving significant intracellular uptake or molecular effect. Similarly, ODN:Lipofectin complexes moderately increased cell association, without enhancing intracellular levels of ODN or inducing detectable molecular effect. In SL-O permeabilized or electroporated cells, uptake was approximately 1 to 2 logs greater than in untreated cells, and rapid nuclear localization was seen, especially with unmodified chimeric ODN. In SL-O permeabilized cells treated with ODN directed to the b2a2 and b3a2 junctions respectively, b2a2 BCR-ABL mRNA levels at 4 hours were reduced to 2. 6% +/- 2.1% and 38.4% +/- 1.3% of control values. In cells permeabilized by electroporation, BCR-ABL mRNA levels were decreased to 4.0% +/- 1.4% of control levels by b2a2 directed ODN, although very little nontargeted suppression was seen with b3a2-targeted ODN (93.4% +/- 4.2% of control). Greater cell to cell variation in ODN uptake was seen for SL-O permeabilized cells when compared with electroporated cells, suggesting that, after SL-O permeabilization, relatively unpermeabilized and overpermeabilized populations may coexist. No structure had any effect on the level of irrelevant (p53, MYC, and GADPH) mRNA levels. We conclude that the conjugation of chimeric ODN with one of the above-mentioned lipophilic groups or the complexing of ODN with Liopfectin does not improve either intracellular delivery of ODN or the molecular effect. In contrast, both electroporation and SL-O permeabilization (1) considerably enhanced uptake of chimeric ODN (even for structures without a conjugate group) and (2) achieved significant suppression of target mRNA levels.     

Bone marrow relapse in high-risk pediatric patients with acute lymphoblastic leukemia: a comparison of relapse times and initial clinical features of patients on different protocols. Children''s Cancer and Leukemia Study group (CCLSG)

Alpha adrenergic blocker has become the first choice in the medical treatment of benign prostatic hyperplasia (BPH). The efficacy of alpha adrenergic blocker has been suggested to be related to the prostatic tissue components, and to be ineffective in treating the clinical symptoms caused by BPH in some cases. The efficacy and prostate reduction of an anti-androgenic agent, chlormadinone acetate, combined with alpha adrenergic blocker, tamsulosin hydrochloride, were evaluated using 40-BPH patients insufficiently treated with tamsulosin hydrochloride alone. Fifty mg of chlormadinone acetate and 0.2 mg of tamsulosin hydrochloride were administered orally once a day for 16 weeks to patients with a prostate subjective symptoms score, I-PSS, of greater than 13 or a peak flow rate of less than 12 ml/s, even after the treatment with 0.2 mg of tamsulosin hydrochloride alone for more than four weeks. Total I-PSS decreased significantly after four weeks. The total irritative symptom score did not change for 16 weeks, but the total obstructive symptom score decreased significantly, as did the total I-PSS. In objective data, the estimated volume of both total prostate and the transition zone on transrectal ultrasonogram decreased significantly at the end of the treatment, and the peak flow rate decreased significantly after 12 weeks. These findings suggest that the addition of chlormadinone acetate may be a reasonable alternative in the treatment of BPH patients responding insufficiently to tamsulosin hydrochloride alone, and that combination therapy using chlormadinone acetate and tamsulosin hydrochloride may be useful for BPH patients with serious obstructive symptoms.     

Correlation between oral drug absorption in humans, and apparent drug permeability in TC-7 cells, a human epithelial intestinal cell line: comparison with the parental Caco-2 cell line

PURPOSE: To determine and compare the relationship between in vivo oral absorption in humans and the apparent permeability coefficients (Papp) obtained in vitro on two human intestinal epithelial cell lines, the parental Caco-2 and the TC-7 clone. METHODS: Both cell lines were grown for 5-35 days on tissue culture-treated inserts. Cell monolayers were analysed for their morphology by transmission electron micrography, and for their integrity with respect to transepithelial electrical resistance, mannitol and PEG-4000 transport, and cyclosporin efflux. Papp were determined for 20 compounds exhibiting large differences in chemical structure, molecular weight, transport mechanisms, and percentage of absorption in humans. RESULTS: The TC-7 clone exhibits morphological characteristics similar to those of the parental Caco-2 cell line, concerning apical brush border, microvilli, tight junctions and polarisation of the cell line. The TC-7 clone however appeared more homogenous in terms of cell size. Both cell lines achieved a similar monolayer integrity towards mannitol and PEG-4000. Monolayer integrity was achieved earlier for the TC-7 clone, mainly due to its shorter doubling time, i.e. 26 versus 30 hours for parental Caco-2 cells. When using cyclosporin A as a P-glycoprotein substrate, active efflux was lower in the TC-7 clone than in the parental Caco-2 cells. The Papp and mechanisms of transport (paracellular or transcellular routes, passive diffusion and active transport) were determined for 20 drugs. A relationship was established between the in vivo oral absorption in humans and Papp values, allowing to determine a threshold value for Papp of 2 10(-6) cm/sec, above for which a 100% oral absorption could be expected in humans. Both correlation curves obtained with the two cell types, were almost completely superimposable. These studies also confirmed that the dipeptide transporter is underexpressed in both cell lines. CONCLUSIONS: On the basis of morphological parameters, biochemical activity and drug transport characteristics, the TC-7 clone appeared to be a valuable alternative to the use of parental Caco-2 cells for drug absorption studies.