Maternal inflammation leads to different mTORC1 activity varied by anatomic locations in mouse placenta†

Maternal inflammation (MI) is associated with many adverse perinatal outcomes. The placenta plays a vital role in mediating maternal-fetal resource allocation. Studies have shown that MI contributes to placental dysfunction, which then leads to adverse birth outcomes and high health risks throughout childhood. Placental mammalian target of rapamycin complex 1 (mTORC1) signaling pathway links maternal nutrient availability to fetal growth; however, the impact of MI on mTORC1 signaling in the placenta remains unclear. In this study, we sought to explore the changes of mTORC1 signaling in the mouse placenta at late gestation by using two models of MI employing lipopolysaccharide (LPS) and interleukin-1β (IL-1β) to mimic acute (aMI) and sub-chronic (cMI) inflammatory states, respectively. We determined placental mTORC1 activity by measuring the activity of mTORC1 downstream molecules, including S6k, 4Ebp1, and rpS6. In the aMI model, we found that mTORC1 activity was significantly decreased in the placental decidual and junctional zone at 2 and 6 h after LPS surgery, respectively; however, mTORC1 activity was significantly increased in the placental labyrinth zone at 2, 6, and 24 h after LPS treatment, respectively. In the cMI model, we observed that mTORC1 activity was increased only in the placental labyrinth zone after consecutive IL-1β exposure. Our study reveals that different parts of the mouse placenta react differently to MI, leading to variable mTORC1 activity throughout the placenta. This suggests that different downstream molecules of mTORC1 from different parts of the mouse placenta may be used in clinical research to monitor the fetal well-being during MI.

Mouse Bone Marrow-Derived Mesenchymal Stem Cells Alleviate Perinatal Brain Injury Via a CD8+ T Cell Mechanism in a Model of Intrauterine Inflammation

The objective of this study was to determine if mouse bone marrow-derived mesenchymal stem cells (BMMSCs) ameliorate preterm birth and perinatal brain injury induced by intrauterine inflammation (IUI). A mouse model of IUI-induced perinatal brain injury at embryonic (E) day 17 was utilized. BMMSCs were derived from GFP-transgenic mice and phenotypically confirmed to be CD44⁺, Sca-1⁺, CD45^-, CD34^-, CD11b^-, and CD11c^- by flow cytometry and sorted by fluorescence-activated cell sorting (FACS). Dams were assigned to four groups: phosphate-buffered saline (PBS) + PBS, PBS + BMMSCs, lipopolysaccharide (LPS) + PBS, and LPS + BMMSCs. Following maternal IUI, there was a significant increase in CD8⁺ T cells in the placentas. Maternally administered BMMSCs trafficked to the fetal side of the placenta and resulted in significantly decreased placental CD8⁺ T cells. Furthermore, fetal trafficking of maternally administered BMMSCs correlated with an improved performance on offspring neurobehavioral testing in LPS + BMMSC group compared with LPS + PBS group. Our data support that maternal administration of BMMSCs can alleviate perinatal inflammation-induced brain injury and improve neurobehavioral outcomes in the offspring via CD8⁺ T cell immunomodulation at the feto-placental interface.

Melatonin for prevention of placental malperfusion and fetal compromise associated with intrauterine inflammation-induced oxidative stress in a mouse model

Melatonin has been shown to reduce oxidative stress and mitigate hypercoagulability. We hypothesized that maternally administered melatonin may reduce placental oxidative stress and hypercoagulability associated with exposure to intrauterine inflammation (IUI) and consequently improve fetoplacental blood flow and fetal sequelae. Mice were randomized to the following groups: control (C), melatonin (M), lipopolysaccharide (LPS; a model of IUI) (L), and LPS with melatonin (ML). The expression of antioxidant mediators in the placenta was significantly decreased, while that of pro-inflammatory mediators was significantly increased in L compared to C and ML. The systolic/diastolic ratio, resistance index, and pulsatility index in uterine artery (UtA) and umbilical artery (UA) were significantly increased in L compared with other groups when analyzed by Doppler ultrasonography. The expression of antioxidant mediators in the placenta was significantly decreased, while that of pro-inflammatory mediators was significantly increased in L compared to C and ML. Vascular endothelial damage and thrombi formation, as evidenced by fibrin deposits, were similarly increased in L compared to other groups. Maternal pretreatment with melatonin appears to modulate maternal placental malperfusion, fetal cardiovascular compromise, and fetal neuroinflammation induced by IUI through its antioxidant properties.

Administration of melatonin for prevention of preterm birth and fetal brain injury associated with premature birth in a mouse model

PROBLEM

Maternal inflammation leads to preterm birth and perinatal brain injury. Melatonin, through its anti-inflammatory effects, has been shown to be protective against inflammation-induced perinatal adverse effects. However, the immunomodulatory effects of melatonin on preterm birth and prematurity-related morbidity remain unknown. We wanted to investigate the effects of maternally administered melatonin on preterm birth and perinatal brain injury in a mouse model of maternal inflammation.

METHOD OF STUDY

A model of maternal inflammation employing lipopolysaccharide (LPS) was used to mimic the most common clinical scenario of preterm birth, that of maternal inflammation. Mice were randomly divided into the following groups: control, LPS, and LPS with melatonin pre-treatment. Doppler ultrasonography was used to obtain fetal and maternal hemodynamic measurements in utero. Placenta and fetal brains were harvested and analyzed for proinflammatory markers and signs of perinatal brain injury, respectively. Surviving offspring were assessed for neuromotor outcomes.

RESULTS

Melatonin pre-treatment lowered the level of proinflammatory cytokines in the uterus and the placenta, significantly improved LPS-induced acute fetal neuroinflammation and perinatal brain injury, as well as significantly upregulated the SIRT1/Nrf2 signaling pathway to reduce LPS-induced inflammation. Melatonin also prevented adverse neuromotor outcomes in offspring exposed to maternal inflammation.

CONCLUSION

Maternally administered melatonin modulated immune responses to maternal inflammation and decreased preterm birth and perinatal brain injury. These results suggest that melatonin, a safe treatment during pregnancy, may be used as an experimental therapeutic in clinical trials.

Placental malperfusion in response to intrauterine inflammation and its connection to fetal sequelae

Exposure to intrauterine inflammation (IUI) is associated with short- and long-term adverse perinatal outcomes. However, little data exist on utilizing placenta to prognosticate fetal injury in this scenario. Our study aimed to utilize imaging modalities to evaluate mechanisms contributing to placental injury following IUI exposure and correlated it to concomitant fetal brain injury. CD1 pregnant dams underwent laparotomies and received intrauterine injections of either lipopolysaccharide (LPS; a model of IUI) or phosphate-buffered saline (PBS). In utero ultrasound Doppler velocimetry of uterine and umbilical arteries and magnetic resonance imaging (MRI) of placental volumes with confirmatory immunohistochemical (vimentin) and histochemistry (fibrin) analyses were performed. ELISA for thrombosis markers, fibrinogen and fibrin was performed to analyze thrombi in placenta. Fetal brain immunohistochemistry was performed to detect microglial activation (ionized calcium-binding adaptor molecule 1, Iba1). On ultrasound, LPS group demonstrated elevated resistance indices, pulsatility indices and a greater occurrence of absent end-diastolic flow in the umbilical and uterine arteries. In the fetus, there was an increased cardiac Tei indices in the LPS group. MRI revealed decreased volume of placenta in the LPS group associated with placental thinning and placental endothelial damage on immunohistochemistry. Decreased fibrinogen content and more thrombi staining in placenta exposed to maternal LPS indicated the hypercoagulability. Furthermore, the expression of Iba1was significantly associated with placental thickness (r = -0.7890, Pearson correlation coefficient). Our data indicate that IUI can trigger events leading to maternal placental malperfusion and fetal vessel resistance, as well as predispose the developing fetus to cardiac dysfunction and brain damage. Furthermore, our data suggest that prenatal ultrasound can be a real-time clinical tool for assessing fetal risk for adverse neurologic outcomes following the potential IUI exposure.

IL-1 receptor antagonist therapy mitigates placental dysfunction and perinatal injury following Zika virus infection

Zika virus (ZIKV) infection during pregnancy causes significant adverse sequelae in the developing fetus, and results in long-term structural and neurologic defects. Most preventive and therapeutic efforts have focused on the development of vaccines, antivirals, and antibodies. The placental immunologic response to ZIKV, however, has been largely overlooked as a target for therapeutic intervention. The placental inflammatory response, specifically IL-1β secretion and signaling, is induced by ZIKV infection and represents an environmental factor that is known to increase the risk of perinatal developmental abnormalities. We show in a mouse model that maternally administrated IL-1 receptor antagonist (IRA; Kineret, or anakinra), following ZIKV exposure, can preserve placental function (by improving trophoblast invasion and placental vasculature), increase fetal viability, and reduce neurobehavioral deficits in the offspring. We further demonstrate that while ZIKV RNA is highly detectable in placentas, it is not correlated with fetal viability. Beyond its effects in the placenta, we show that IL-1 blockade may also directly decrease fetal neuroinflammation by mitigating fetal microglial activation in a dose-dependent manner. Our studies distinguish the role of placental inflammation during ZIKV-infected pregnancies, and demonstrate that maternal IRA may attenuate fetal neuroinflammation and improve perinatal outcomes.

Maternal Supplementation of Low Dose Fluoride Alleviates Adverse Perinatal Outcomes Following Exposure to Intrauterine Inflammation

Maternal periodontal disease has been linked to adverse pregnancy sequelae, including preterm birth (PTB); yet, root planing and scaling in pregnancy has not been associated with improved perinatal outcomes. Fluoride, a cariostatic agent, has been added to drinking water and dental products to prevent caries and improve dental health. The objective of this study was to explore the effects of fluoride supplementation using a mouse model of preterm birth and perinatal sequalae. Pregnant mice were fed low dose fluoride (LF^-) or high dose fluoride (HF^-) and given intrauterine injections of lipopolysaccharide (LPS) or phosphate-buffered saline (PBS). We found that LPS + LF^- significantly increased livebirths, pup survival, and litter size compared to LPS alone. Moreover, offspring from the LPS + LF^- group exhibited significantly improved neuromotor performance and more neurons compared to those from the LPS group. Additionally, LF^- treatment on human umbilical vein endothelial cells (HUVECs) increased cell viability and decreased oxidative stress after treatment with LPS. Collectively, our data demonstrates that maternal LF^- supplementation during pregnancy postpones the onset of PTB, acts to increase the liveborn rate and survival time of newborns, and reduces perinatal brain injury in cases of intrauterine inflammation.

Increased placental T cell trafficking results in adverse neurobehavioral outcomes in offspring exposed to sub-chronic maternal inflammation

Interleukin-1 beta (IL-1β) is a cytokine mediator of perinatal brain injury. The effect of sub-chronic systemic IL-1β exposure in perinatal and offspring outcomes is unclear. The aim of this study was to examine the effects of maternal IL-1β exposure on pregnancy and offspring outcomes. At E15, CD1 dams were allocated to receive intraperitoneal injection of phosphate buffered saline or mouse recombinant IL-1β (1 mcg) for four consecutive days. We analyzed pup survivaland neurobehavioral status. At E18, placental H&E staining and fetal brain Nissl staining was performed. Placental gene expression was analyzed by qPCR and T cell infiltration was analyzed by flow cytometry. Effects of inflammation on feto-placental blood flow were analyzed by Doppler ultrasonography. IL-1β decreased pup survival (P < .0001) and adversely affected offspring performance on neurodevelopmental tests (P < .05). Placentas of exposed dams exhibited significant thinning of maternal and fetal sides, and fetal brain exhibited cortical thinning. Placental qPCR analysis revealed significant upregulation of NFκB2 (P = .0021) and CXCL11 (P = .0401). While maternal IL-1β exposure did not affect feto-placental blood flow, placental flow cytometry showed an increase in placental infiltration of CD4⁺ T cells at 24 h post-injection (hpi, P < .0001) and CD8⁺ T cells at 72 hpi (P = .0217). Maternal sub-chronic, systemic inflammation with IL-1β decreased pup survival and played a key role in perinatal brain injury. The mechanisms behind these outcomes may involve immune system activation and alterations in placental T cell trafficking.

Maternal CD8+ T-cell depletion alleviates intrauterine inflammation-induced perinatal brain injury

We investigated the mechanisms by which CD8⁺ T-cell trafficking in placenta contributes to perinatal brain injury by studying effects of maternal CD8⁺ T-cell depletion (DEP) in a mouse model of intrauterine inflammation (IUI). Maternal CD8⁺ T cells were depleted with anti-CD8⁺ antibodies. IUI was induced with lipopolysaccharide (LPS). DEP was confirmed using flow cytometry. Preterm birth rate was evaluated. Offspring neurologic sequelae were assessed by Nissl staining, immune arrays, confirmatory individual TaqMan^® gene assays, and neurobehavioral tests. DEP did not significantly prevent LPS-induced preterm birth but improved neurobehavioral performance (P < .001) and increased cortical neuronal density (P < .05) in LPS-exposed pups compared to controls. These changes were associated with decreased CCL3 and CXCL10 and increased CCL5 in DEP LPS-exposed mice. We demonstrate that DEP reduces perinatal brain injury following IUI. This supports a role for maternal CD8⁺ T-cell trafficking in placenta in mediating perinatal brain injury separate from preterm birth mechanisms.

Abstract 4251: Paclitaxel is necessary for improved survival in epithelial ovarian cancers with somatic homologous recombination gene mutations

The impact of somatic mutations and genomic alterations in determining the clinical outcome of sporadic epithelial ovarian cancer (EOC) remains uncertain. Our goal was to identify molecular markers of optimal cytoreduction, chemotherapeutic response, and survival. We focused on genes in the homologous recombination (HR) DNA repair pathway, as germline mutations in these genes confer improved survival, and data suggest that somatic mutations may similarly predict improved survival and chemosensitivity. One hundred fifty-eight patients were included with diagnoses of serous, endometrioid, or clear cell EOC and underwent primary cytoreduction followed by platinum-based chemotherapy. We performed targeted massively parallel sequencing of 53 genes in known genes from pathways such as HR and checkpoint inhibition in primary surgical samples. Patients were treated with platinum and cyclophosphamide (n = 24) or platinum and paclitaxel (n = 67). We detected 226 deleterious variants in 35 distinct genes. TP53 mutations were found in tumors from 90 subjects (56%) and deleterious mutations in HR genes in 45 (28%). Twenty-three patient tumors (15%) were found to have homozygous copy number loss of genes in the HR pathway. We did not detect an overall survival (OS) benefit in advanced stage patients treated with platinum whose tumors had HR mutations/loss as compared to those without HR defects. However, OS was significantly different between patients (p = 0.0028) whose tumors had HR mutations/loss if they received cyclophosphamide (median 24.1 months) as compared to paclitaxel (median 50.4 months). Furthermore, in patients with both TP53 and HR gene mutations or deletions, median OS improved to 76.6 months in the platinum and paclitaxel treated cohort (p = 0.0001). In this analysis by chemotherapy regimen and mutation status, the patients with TP53 and HR mutation/loss demonstrated worse median OS than those without such defects when treated with platinum and cyclophosphamide (24.1 months vs. 32.7 months respectively), but improved survival over patients without TP53 and HR defects when treated with platinum and paclitaxel (76.6 months vs. 44.4 months respectively, p = 0.0100). We also found that a somatic HR mutation was significantly associated with suboptimal debulking status (p = 0.012). Chances for optimal debulking and early stage were significantly increased in patients with PTEN mutations (p = 0.042), leading to OS benefit. The survival benefit attributed to platinum agents in HR deficient ovarian cancers may depend upon the use of paclitaxel in addition to platinum. This merits elucidation of the mechanism, and may be due to the mitosis cell cycle specificity of paclitaxel, and ensuing inhibition of HR deficient genomically unstable tumor subclones.

Citation Format: Stephanie Jean, Bradley Wubbenhorst, Jiaqi Li, Kara N. Maxwell, Lauren Fishbein, Michael W. McLane, Nandita Mitra, Lin Zhang, Katherine L. Nathanson, Janos L. Tanyi. Paclitaxel is necessary for improved survival in epithelial ovarian cancers with somatic homologous recombination gene mutations. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4251. doi:10.1158/1538-7445.AM2015-4251

Identifying the serotonin transporter signal in Western blot studies of the neurotoxic potential of MDMA and related drugs

A number of published studies have questioned the serotonin neurotoxic potential of 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") and related drugs (fenfluramine, p-chloroamphetamine) based upon results from Western blot studies using a custom synthesized serotonin transporter (SERT) antibody that found no reduction in the abundance of a 50kDa protein after substituted amphetamine treatment. The purpose of this study was to collect Western blot data using the same SERT antibody used in those studies, but with positive and negative controls to identify the SERT protein signal. A 63-68 kDa band that had the regional distribution expected of rat brain SERT, was decreased by 5,7-DHT, and was absent in SERT KO animals was identified as the SERT protein. Significant, lasting decreases in the abundance of the 63-68 kDa band were evident in the rat brain after treatment with MDMA and related drugs (FEN, PCA). Thus, when the band corresponding to the SERT protein is identified in Western blots through the use of positive and negative controls, reduced abundance of the SERT protein can be readily demonstrated after substituted amphetamine treatment. These data provide further evidence of lasting loss of the SERT protein after exposure to MDMA and other substituted amphetamines.

Heating induces aggregation and decreases detection of serotonin transporter protein on western blots

In recent years, there has been growing interest in the use of Western blot analysis to monitor changes in the abundance of the serotonin transporter (SERT) protein. In the Western blot procedure, heat denaturation is a common, early step. We now report that heating samples to 90 degrees C decreases the abundance of the SERT protein band and causes dispersion of a majority of the SERT signal to a high molecular weight smear. These observations are in keeping with the fact that heating can influence the electrophoretic behavior of some proteins. By omitting the heat denaturation step in the Western blot procedure, better detection of the SERT protein is achieved.

Loss of serotonin transporter protein after MDMA and other ring-substituted amphetamines

We studied in vivo expression of the serotonin transporter (SERT) protein after 3,4-methylenedioxymethamphetamine (MDMA), p-chloroamphetamine (PCA), or fenfluramine (FEN) treatments, and compared the effects of substituted amphetamines to those of 5,7-dihydroxytryptamine (5,7-DHT), an established serotonin (5-HT) neurotoxin. All drug treatments produced lasting reductions in 5-HT, 5-HIAA, and [(3)H]paroxetine binding, but no significant change in the density of a 70 kDa band initially thought to correspond to the SERT protein. Additional Western blot studies, however, showed that the 70 kDa band did not correspond to the SERT protein, and that a diffuse band at 63-68 kDa, one that had the anticipated regional brain distribution of SERT protein (midbrain>striatum>neocortex>cerebellum), was reduced after 5,7-DHT and was absent in SERT-null animals, was decreased after MDMA, PCA, or FEN treatments. In situ immunocytochemical (ICC) studies with the same two SERT antisera used in Western blot studies showed loss of SERT-immunoreactive (IR) axons after 5,7-DHT and MDMA treatments. In the same animals, tryptophan hydroxylase (TPH)-IR axon density was comparably reduced, indicating that serotonergic deficits after substituted amphetamines differ from those in SERT-null animals, which have normal TPH levels but, in the absence of SERT, develop apparent neuroadaptive changes in 5-HT metabolism. Together, these results suggest that lasting serotonergic deficits after MDMA and related drugs are unlikely to represent neuroadaptive metabolic responses to changes in SERT trafficking, and favor the view that substituted amphetamines have the potential to produce a distal axotomy of brain 5-HT neurons.

The cloned neurotensin receptor mediates cyclic GMP formation when coexpressed with nitric oxide synthase cDNA

Rat neurotensin (NT) receptor (NTR) cDNA was subcloned into the pRC-CMV expression vector and transfected into 293 cells, and cellular clones that stably expressed the NTR were isolated and characterized. [3H]NT binding to membranes prepared from the NTR cDNA-transfected cells displayed specificity and saturability, with an apparent Kd of 1.25 nM and a Bmax of 43.4 pmol/mg of protein (approximately 3.5 x 10(6) binding sites/cell). NT stimulated an increase in [3H]inositol phosphate levels in the NTR-expressing cells up to 2500% of basal levels. The response was time and dose dependent, with an EC50 of 10.4 nM. NT also stimulated cAMP formation in these cells, with an EC50 of 27.0 nM. In addition, NT evoked an increase in the level of intracellular calcium. Approximately 60% of the calcium rise was attributable to the release of intracellular stores and 40% was attributable to calcium influx. Although NTR occupancy has been shown to stimulate cGMP formation in several brain preparations and cell lines, NT was unable to mediate cGMP synthesis in the NTR-expressing 293 cells. We found that 293 cells have guanylate cyclase activity but have undetectable levels of nitric oxide synthase (NOS) activity. Because it was possible that the production of nitric oxide is required as the mediator of NT-induced cGMP synthesis, we subcloned NOS cDNA into the pCEP4 expression vector and transiently expressed it in the NTR cells. We report that NT increased cGMP levels up to 375% of basal levels when NOS cDNA was coexpressed and that the increase was completely inhibited by the NOS inhibitor N omega-nitro-L-arginine. NT-induced cGMP accumulation was time and dose dependent, with an EC50 of 1.7 nM. To our knowledge, this is the first report of NT mediating cGMP formation with a cloned receptor and the first evidence that NT-induced cGMP accumulation requires the production of nitric oxide.

Effects of site-specific acetylation on omega-conotoxin GVIA binding and function

Chemical modification of omega-conotoxin GVIA (omega-CgTXGVIA) was performed using nonsaturating concentrations of acetic anhydride to generate seven distinct derivatives. Following separation of these peptides using reverse-phase HPLC (RP-HPLC), their individual molecular weights were determined using fast bombardment mass spectrometry (FAB-MS). Three peptides contained a single acetylated amino group, three possessed two acetylated amino groups, and the last contained three acetylations. For each peptide, the specific site of acetylation was confirmed using a scheme of tryptic digestion, under nonreducing conditions, followed by RP-HPLC and FAB-MS. Biological profiles for each peptide were obtained by analyzing their capacity to displace native 125I-omega-CgTx GVIA binding to rat hippocampal membranes and to block K(+)-stimulated 45Ca2+ influx into chick brain synaptosomes. The data indicate that successive additions of acetyl moieties to omega-CgTx GVIA lead to a loss of both binding affinity and Ca2+ influx inhibitory potency. Within the monoacetylated series, acetylation of the amino terminal of Cys-1, as compared to the epsilon-amino group of either Lys-2 or Lys-24, leads to the greatest shift in potency. In summary, these results indicate that basic (i.e., primary amino) groups, which are brought into close proximity as a result of disulfide bridging, are important in the functional blockade of neuronal Ca2+ channels by omega-CgTx GVIA.

A growth factor-inducible nuclear protein with a novel cysteine/histidine repetitive sequence

Growth factors rapidly induce transcription of a set of genes that encode regulatory proteins, many of which have been identified by cDNA cloning. Here we report the analysis of a cDNA corresponding to a gene induced in mouse 3T3 cells by growth factors and a variety of other extracellular signaling agents. The cDNA encodes a proline-, serine-, and glycine-rich nuclear protein designated Nup475 of 319 amino acids that contains two tandemly repeated cysteine- and histidine-containing sequences (CX8CX5CX3H) suggestive of a novel heavy metal-binding domain. Nup475 produced in Escherichia coli binds zinc. Its mRNA is present in a number of mouse tissues and cell lines, being especially abundant in intestine, thymus, and regenerating liver and in a macrophage cell line stimulated by gamma-interferon. We hypothesize that Nup475 is a regulatory protein with a novel zinc finger structure.

Transfection with the isolated herpes simplex virus thymidine kinase genes. II. Evidence for amplification of viral and adjacent cellular DNA sequences

We have previously described several series of biochemical transformation experiments in which small defined portions of herpes simplex virus (HSV-1 and HSV-2) DNA encompassing the thymidine kinase (TK) gene were introduced into Ltk- cells by the calcium transfection procedure. The presence of authentic virus TK enzyme in several subcloned cell lines derived from these experiments was confirmed by either the specific incorporation of [125I]iododeoxycytidine into their nuclei or the inhibition of cell growth by the antiviral drug arabinosyl thymine. A panel of 24 independent Ltk+ cell lines receiving either isolated virus DNA fragments or cleaved plasmid DNAs was examined by blot hybridization for both the presence and copy number of virus TK DNA sequences. Most cell lines contained a single virus DNA fragment covalently joined to host (or carrier Ltk-) mouse DNA sequences, but several contained multiple copies of the TK gene. Examination of the structural arrangement of the virus DNA in two early passage multicopy cell lines indicated that the TK gene had integrated into Ltk- cell DNA and then subsequently both viral and flanking cellular sequences were amplified to create up to 20 tandem duplications. In one case, mapping of the adjacent cellular sequences has revealed that the total repeat unit is greater that 23 kilobases (kb) in size. On subsequent passaging, even in HAT medium, the amplified repeat units were not stable and fell to only three to four copies per haploid cell genome. These cell lines should prove useful for additional studies to examine the expression of co-selected non-TK virus sequences and the influence of adjacent cellular DNA sequences on transcription and retransfection of the resident TK gene.