The SJL/J T cell response to both spontaneous and transplantable syngeneic reticulum cell sarcoma is mediated predominantly by the V beta 17a+ T cell clonotype.

Previous studies have revealed that the reticulum cell sarcoma (RCS) of SJL/J (H-2s, IE-) mice express an "IE-like" stimulatory tumor-associated antigen, the expression of which is requisite for stimulating host T cells necessary for tumor growth. Herein, we present evidence that the predominant T cells raised in the syngeneic response to both spontaneous and transplantable RCS tumors are of the V beta 17a TCR clonotype. The V beta 17a+ clonotype of T cells has been shown to interact with IE allogeneic specificities. We demonstrate that all four characterized RCS-specific T cell hybridomas stained positively for the anti-V beta 17a mAb, KJ23a. Additionally, KJ23a, when added to cocultures of the T cell hybridomas and RCS tumors, inhibited the release of IL-2 by the hybridomas. Further, KJ23a was shown to markedly inhibit the proliferation of SJL/J T cells when cocultured with either spontaneous or transplantable RCS tumor cells. When analyzed by flow cytometry, the T cell blast population raised in response to both spontaneous and transplantable RCS were greater than 80% KJ23a+. These T cells were brightly stained by the anti-CD4 mAb, Gk1.5, and, therefore, represent class II-responsive T cells. In corroboration of the in vitro data, T cells derived from mesenteric lymph nodes of RCS tumor-bearing mice had likewise undergone a similar expansion of V beta 17a+, CD4+ T cells. Together, these results indicate that KJ23a+ T cells play an important and predominant role in the response of SJL/J mice to spontaneous RCS tumors and provide further suggestive evidence that the stimulatory antigen(s) on the RCS tumor is IE or an "IE-like" molecule. Significantly, the important role V beta 17a+ T cells play in the response to RCS suggests a potential therapeutic role for KJ23a mAb in the intervention and prevention of RCS tumors in SJL/J mice.

Treatment of hypercholesterolemia in the Watanabe rabbit using allogeneic hepatocellular transplantation under a regeneration stimulus.

Numerous studies have reported successful allotransplantation of hepatocytes. However, none have shown long-term correction of a liver-related metabolic defect. In this study, we used a method of regional hepatocyte transplantation and subsequent induction of transplanted cell proliferation by regeneration response in the transplant-bearing liver lobes. New Zealand White rabbits were used as cell donors and Watanabe heritable hyperlipidemic (WHHL) rabbits were used as cell recipients (2 x 10(8) cells/rabbit). All recipient rabbits were maintained on daily cyclosporine. Two weeks after baseline serum cholesterol determination, group I WHHL rabbits (n = 7) received an infusion of cells into the right lateral liver lobe, and a loose ligature was placed around the portal venous branch supplying the anterior lobe. After 1 week, to allow engraftment, the portal venous branch was ligated, which resulted in the atrophy of the affected liver parenchyma and induction of hyperplasia in the transplant-bearing liver tissue. Group II rabbits (n = 6) were transplanted with New Zealand White hepatocytes without portal branch ligation (PBL) and group III rabbits (n = 4) were subjected to sham transplantation (saline) and PBL. The experimental period extended to 150 days after transplantation. All WHHL rabbits transplanted with normal hepatocytes showed reduction in serum cholesterol and low-density lipoprotein (LDL) levels. Group I (PBL-stimulated) recipients demonstrated a more pronounced and sustained effect than group II animals (P < 0.05). Group III controls showed only a slight, typical for aging decrease in serum cholesterol. Group I recipient livers perfused with LDL labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate (DiI) showed much higher numbers of DiI-LDL-positive hepatocytes than those of group II recipients. In conclusion, a liver regeneration stimulus enhanced the population of transplanted hepatocytes and their functional effect in a large animal model of inborn error of liver metabolism.

Automated liver cell processing facilitates large scale isolation and purification of porcine hepatocytes.

An automated method for large scale isolation and purification of porcine hepatocytes is described. Liver cells were harvested by a two-step portal vein perfusion with ethylenediaminetetraacetate and collagenase. Hepatocyte purification was carried out using either a standard manual processing method (Procedure A) or an automated processing method using a filtration chamber and a programmable cell washer (Procedure B). Both methods produced high cell yields (Procedure A: 1.30 +/- 0.55 x 10(10) viable hepatocytes/liver; Procedure B: 1.38 +/- 0.32 x 10(10) viable hepatocytes/liver) and viability (Procedure A: 89 +/- 6.5%; Procedure B: 92 +/- 3.9%). Hepatocyte purity was significantly greater after Procedure B than after Procedure A (93.1 +/- 3.1% versus 83.1 +/- 3%, p < 0.01). Isolated hepatocytes by either method were morphologically intact, as demonstrated by transmission electron microscopy showing integrity of plasma membranes and intracellular organelles. Cultured hepatocytes isolated by either method were functionally intact, although those isolated by Procedure A showed significantly lower activity of microsomal 7-ethoxycoumarin-O-deethylase activity (p < 0.05) and mitochondrial succinate dehydrogenase activity (p < 0.01). In conclusion, use of the automated hepatocyte processing method resulted in efficient large scale preparation of porcine hepatocytes, with higher purity and greater retention of differentiated liver metabolic functions, and was found to be less time consuming and less labor intensive.

Purification and characterization of cytolytic and noncytolytic human natural killer cell subsets.

Natural killer (NK) cells form three functionally distinct populations of effectors: competent cytolytic effectors able to bind and kill target cells and two subsets of nonlytic effectors, one able and the other unable to bind target cells. A flow cytometric method was developed, based on size and two-color fluorescence of NK cell-target conjugates, for the characterization and sorting of highly purified subpopulations--killer cells, nonkiller binder cells, and free cells. Ultrastructural examination revealed that granule content was reduced in the killer cells and absent in most of the binder cells. Quantitative differences in the expression level of HLA class I, CD11b (C3bi receptor), and CD16 (receptor for the Fc portion of IgG) antigens could differentiate the subsets. The killer phenotype was HLAlo, CD11bvery hi, and CD16very lo; the binder phenotype was CD11bhi and CD16lo; and the free-cell phenotype was CD11blo and CD16hi. Cell activation was not requisite for lytic function because no difference in either expression of activation markers or cell cycle could be established among the sorted subpopulations. Although recycling function was inhibited, retention of lytic activity was enriched 4-fold in the sorted killer cell population. These results represent characterization of a successful bulk isolation of competent killer, nonkiller binder, and free cells in human NK-cell populations and should aid our understanding of NK-cell development, lineage, and function.

Qualitative and quantitative analysis of subpopulations of cytotoxic effector cells by flow cytometry.

The heterogeneous nature of cytotoxic effector cells presents a difficult obstacle to the study of developmental, biochemical and molecular events governing cytotoxic T lymphocytes (CTL) and natural killer (NK) cell biology. In previous studies, there were no available methods, other than the single cell assay or micromanipulation techniques that could distinguish between lytic and non-lytic cells present in purified populations or clones. Further, there were no available means to isolate these subsets for further investigation. The studies presented here describe a novel approach to identify and isolate cells based on their functional characteristics. Thus, non-lytic free and conjugate forming cells as well as killer cells could be identified, quantified, and further purified by flow cytometric cell sorting for further investigations. Studies of several properties of isolated NK subpopulations (free, non-lytic binders, and killers) are presented.

Natural killer cell subsets: maturation, differentiation and regulation.

Studies of the maturation and differentiation of human peripheral blood-derived natural killer (NK) cells were examined on isolated three subsets of NK cells. These subsets were separated based on their ability to bind and/or kill the target cells. Flow cytometry and cell-sorting analyses enabled the separation of free, binder and killer cells. These three subsets were subjected to various phenotypic and functional analyses. The findings suggest that the three subsets belong to the same lineage of maturation and differentiation, e.g. free and binders can mature into killer cells. The killer cells are not terminally differentiated as they respond to IL-2 and targets and proliferate. The response of free cells to IL-2 and IFN-alpha proceeds by distinct pathways, namely IL-2-mediated activation and proliferation is under the control of endogenous TNF-alpha production but not IFN-alpha-mediated activation. Regulation of several surface markers' expression is associated with functional maturation. In addition to activation, the cells can also undergo inactivation or anergy following interaction with targets. The binder and killer cells are the predominant subsets that become inactivated for cytotoxicity and their response to IL-2 is inhibited. The studies also show that various events associated with activation of cytotoxicity are under different regulatory controls than those for proliferation and secretion. These studies suggest that biochemical and molecular events associated with signalling and differentiation are now possible to unravel using the NK subsets.

Killer cell recruitment and renewal capacity of purified cytolytic and noncytolytic human peripheral blood natural killer cell subsets.

The inability to isolate NK precursors at different stages of development has impeded understanding of the processes involved in NK maturation. The present studies utilize a flow cytometric technique that enables the isolation of operationally defined cell subsets, lytic (killers) and nonlytic conjugate-forming (binders), and nonconjugate-forming (free) cells, within NK-enriched preparations to test whether these might represent cells in different stages of NK development. To characterize both the steps involved in NK maturation and the cells responsible for IL-2 induced proliferation, these purified subsets were analyzed for their killer cell recruitment and renewal capacity. After a 2-h exposure to IFN-alpha or IL-2, induction of lytic function was developed only in the binder subset as detected in the single cell assay. Neither enhancement of killer cell recycling nor induction of binding function among the subsets was observed. However, after an 18-h culture period, with or without rIL-2, killer cells preferentially expressed activation Ag CD69 (Leu-23) and the IL-2R alpha-chain, TAC (CD25). In addition, all cells in contact with K562 targets displayed enhanced expression of these Ag. Killer cells also showed an enhanced capacity to proliferate in response to rIL-2 in a 6-day [3H]TdR incorporation assay. Additional irradiated K562 targets enhanced the proliferative capacity of all the subsets, with only a marginal effect on sorted free cells. Nevertheless, sorted free cells, in addition to binders, developed potent binding and lytic function when tested in the single-cell assay after 4 days of IL-2 culture. The lytic activity of killers was reduced, as compared with freshly isolated killers. The results are consistent with a two-step model for NK maturation, involving the acquisition of lytic function before proliferative capacity, and specific triggering of killer cells through interaction with target cells for induction of a proliferative competent state.

The in vivo depletion of V beta 17a+ T cells results in the inhibition of reticulum cell sarcoma growth in SJL/J mice. Evidence for the use of anticlonotypic antibody therapy in the control of malignancy.

Previous findings revealed that reticulum cell sarcoma (RCS) of SJL/J mice growth and survival depended on its ability to stimulate a potent host T cell response, by the means of a tumor-associated class II MHC molecule with IE-like specificities. Previously we presented evidence that the V beta 17a TCR+ clonotype of T cell was the predominant T cell involved in the host response to the tumor. We undertook our study to examine whether the depletion of the V beta 17a+ T cells, by the use of the anticlonotypic antibody, KJ23a, resulted in the inhibition of RCS tumor growth in vivo. We present evidence herein that supports this hypothesis. KJ23a-treated mice exhibited a complete reduction in T cells bearing the V beta 17a TCR. These mice exhibited a dramatic reduction in the in vitro proliferative response to RCS. Furthermore, the pretreatment of SJL/J mice with KJ23a mAb resulted in the complete loss in their ability to harbor RCS tumor. When tumor-bearing mice were treated with a single inoculum of KJ23a mAb within the first 7 days after the passage of tumor, the mice showed long term survival with diminishing tumor burden. These results demonstrated that the V beta 17a clonotype of T cells is required for the growth and maintenance of RCS tumor. Within the first 6 wk after tumor inoculation KJ23a-treated mice were capable of transferring tumor to naive syngeneic recipient mice despite the obvious lack of tumor growth in the treated donor animal. These results suggested that RCS tumors in the absence of V beta 17a+ T cells can persist for up to 6 wk in a state of "tumor dormancy." The predominant usage of the V beta 17a gene in RCS-specific T cells suggests that these T cells play an important role in the pathogenesis of RCS tumor. Furthermore, the positive therapeutic course taken by tumor-bearing mice upon the treatment with KJ23a mAb, demonstrates the enormous potential in anticlonotypic antibody therapy in the treatment of T cell-dependent tumors and diseases.

Mechanism of cell-mediated cytotoxicity at the single cell level. VI. Direct assessment of the cytotoxic potential of human peripheral blood non-lytic effector-target cell conjugates.

Single cell cytotoxicity assays reveal that a large percentage of lymphocytes are unable to kill attached targets in a 4- to 18-hr assay. Additional signals (in the form of lectin or anti-target antibody) delivered to target-bound lymphocytes enable these previously non-lytic lymphocytes to kill attached target cells. This finding was obtained by using a modification of the single cell assay, in which lectin or target cell antibody is incorporated into agarose with preformed lymphocyte-target conjugates. Human peripheral blood lymphocytes (PBL) or Percoll density gradient-enriched large granular lymphocytes (LGL) were used as effector cells in natural killer (NK), antibody-dependent cellular cytotoxicity (LDCC) assay systems. The targets used were NK-sensitive K562 and Molt-4 and NK-insensitive Raji. Several findings were made in the modified single cell assay, namely a) the frequency of cytotoxic NK or ADCC effector cells was not augmented, suggesting that the initial trigger was sufficient for lytic expression in these instances. Furthermore, these results showed that the NK-sensitive targets used do not bind nonspecifically to the LDCC effector cells. K562 coated with Con A, however, serve as LDCC targets. b) The frequency of two target conjugate lysis by NK/K effectors was not augmented by Con A. These results suggest that Con A does not potentiate the killing of multiple targets bound to a single cytotoxic lymphocyte. c) Although conjugates formed between LGL or PBL and NK-insensitive Raji are non-lethal, significant lysis was observed when these conjugates were suspended in Con A or antibody agarose. These results demonstrate that Raji bind to cytotoxic NK, K, and LDCC effector cells, but are lysed only when the appropriate trigger is provided. d) The cytotoxic potential of non-lytic conjugates appears to lie within the low density Percoll fraction, although the high density lymphocytes are able to nonlethally bind to targets. Altogether the results demonstrate that target recognition and/or binding by the effector cells is a distinct event from the trigger or lytic process. The implications of these findings are discussed.

Mechanism of defective NK cell activity in patients with acquired immunodeficiency syndrome (AIDS) and AIDS-related complex. II. Normal antibody-dependent cellular cytotoxicity (ADCC) mediated by effector cells defective in natural killer (NK) cytotoxicity.

Our studies and other investigations have shown that NK effector cells can also mediate antibody-dependent cellular cytotoxicity (ADCC) through the use of the Fc gamma receptor on the NK cell membrane. Peripheral blood lymphocytes (PBL) derived from patients with acquired immunodeficiency syndrome (AIDS) and AIDS-related complex exhibit a poor NK activity due to a defective "trigger" required for activation in the lethal hit stage of the NK lytic pathway. Consequently, it was important to delineate whether the defect in AIDS NK cells affected the ADCC function. By using the 51Cr-release assay, the ADCC cytotoxic activity of AIDS PBL was found to be within the normal range, despite the absence of significant NK activity. Several experiments corroborated that the same effector cells mediate both NK CMC and ADCC. Depletion of Fc gamma R-bearing cells resulted in elimination of both the ADCC and NK cytotoxic functions. Single cell analyses, using one- and two-target cell conjugates, revealed that the frequency of ADCC effector:target conjugates and the frequency of killer cells from AIDS PBL were comparable to the frequencies seen in the normal controls. However, when mixtures of NK and ADCC targets were used to form mixed two-target conjugates, the AIDS effector cells lysed only the bound ADCC target, whereas the normal effector cells lysed both the bound NK and ADCC targets. These results demonstrate clearly that the same NK/K effector cells from AIDS PBL, defective in NK activity, are not impaired in mediating ADCC activity. These findings were supported by the demonstration that AIDS PBL stimulated with ADCC targets, but not with NK targets, released NK cytotoxic factors, postulated mediators of the NK CMC reaction. These findings indicate that the NK/K cells in AIDS are triggered normally for ADCC activity but are not triggered for NK activity. Furthermore, the results indicate that the lytic machinery is not impaired in the AIDS NK/K cells.

Analysis of lymphocyte-target conjugates by flow cytometry. I. Discrimination between killer and non-killer lymphocytes bound to targets and sorting of conjugates containing one or multiple lymphocytes.

The use of flow cytometric analysis and sorting techniques for the enumeration and purification of lymphocyte-target conjugates was investigated. Murine cytotoxic T-lymphocytes (CTL) with killer effector function were identified and quantitated during a 3-hour cell-mediated cytotoxicity reaction using multiparameter analysis. Resolution of conjugates containing single and multiple lymphocytes was achieved by two-color fluorescence, and individual conjugate subpopulations were subsequently sorted for further analysis. To measure total and cytotoxic conjugate frequencies, CTL were labelled with FITC-conjugated Thy 1.2 antibody and dead target cells were stained with propidium iodide (PI). Size difference between the CTL and P815 tumor target cells, as measured by Coulter volume and axial light loss, facilitated detection of conjugates which were identified as both large and Thy 1.2-positive. Conjugates containing dead target cells possessed red fluorescence due to PI uptake. The frequency of conjugates containing cytotoxic activity increased with time during the cytotoxicity period and correlated with frequencies obtained in single-cell assays. Analysis of the distribution of single and multiple lymphocyte-bound conjugates was done by co-centrifugation of Hoechst-stained CTL and FITC-labeled P815 target cells. Analysis by two-color fluorescence effectively resolved conjugate populations containing different numbers of CTL and allowed their purification by cell sorting. The purity of the separate populations was confirmed by fluorescence microscopic inspection. The results of these studies demonstrate that flow cytometry can resolve target-bound and free CTL, measure cytolytic efficiency and specifically sort out cytometrically defined subgroups within the effector cell population.

Teleost fish islets: a potential source of endocrine tissue for the treatment of diabetes.

Anatomical separation of pancreatic islets in some teleost fish makes them a useful source of pancreatic endocrine tissue. Islets were harvested from tropical Tilapia fish (Oreochromis nilotica) and cultured for 24 hr at 37 degrees C. Eight athymic nude mice were rendered diabetic by streptozotocin (STZ) and transplanted under the kidney capsule with fish islets. After transplantation (Tx), nonfasting blood glucose (n-FBG), which was in all recipients > 450 mg/dl, decreased to < 100 mg/dl. At 4 and 7 weeks post-Tx, the intraperitoneal (ip) glucose tolerance test was performed in the normoglycemic Tx mice and in six normal controls. In controls, K value (percentage of decline in blood glucose/min) was 1.076 +/- 0.383 and in Tx mice it was 0.956 +/- 0.336 and 0.869 +/- 0.483 at 4 and 7 weeks, respectively (P = n.s.). Nephrectomy raised the n-FBG to pre-Tx levels. On immunohistochemistry, recipient's pancreata showed atrophic islets with no beta-cell granules, while the islet-bearing kidneys had distinct beta-cells under their capsules. Alginate-embedded fish islets were encapsulated in permselective (25-kDa) cellulose membranes and implanted ip in six STZ-diabetic nude mice. On the following day, all recipients became normoglycemic and their n-FBG remained normal for 7 days. In one animal, the n-FBG was < 200 mg/dl for 14 days and subsequent removal of the capsule raised the n-FBG to the pre-Tx level. Finally, it was found that fish islets can be cultured at 37 degrees C for extended periods of time.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential secretion of TNF-alpha and IFN-gamma by human peripheral blood-derived NK subsets and association with functional maturation.

Natural killer cells can be separated into three major subsets (free, binder, and killer) based on their ability to bind and kill sensitive target cells. The nonbinder, nonkiller free cells are the most immature and can be activated to become binders and killers. Natural killer (NK) cells synthesize and secrete several cytokines that are intimately involved in NK activation. This study investigated the secretion of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) by purified NK cells and NK subsets following activation by various stimuli. K562 target cells stimulated secretion of both TNF-alpha and IFN-gamma by both the binder and the killer subsets but not by the free subset. IFN-alpha activated the secretion of IFN-gamma only, whereas IL-2 activated the secretion of both TNF-alpha and IFN-gamma by the binder and killer subsets and secretion was augmented by the addition of K562 to the cultures. Phorbol myristate acetate (PMA) and ionophore stimulated TNF-alpha and IFN-gamma secretion in both the binder and the killer subsets, though IFN-gamma secretion was more pronounced in the binder subset. Activation of TNF-alpha and IFN-gamma secretion was dependent on de novo protein synthesis. Analysis at the single-cell level demonstrated that the binder subset had the highest frequency of cells secreting IFN-gamma. These results demonstrate that both the binder and the killer subsets can be activated to secrete TNF-alpha and IFN-gamma, whereas the free NK subset secretes little or no TNF-alpha and IFN-gamma following activation. These data suggest that the ability of NK cells to secrete TNF-alpha and IFN-gamma following activation correlates with the functional stage of maturation of NK cells.

Fulminant hepatic failure in rats: survival and effect on blood chemistry and liver regeneration.

A reproducible experimental animal model of fulminant hepatic failure (FHF) resembling the clinical condition is needed. We have developed such a model in the rat by combining resection of the two anterior liver lobes (68% liver mass) with ligation of the right lobes pedicle (24% liver mass), resulting in liver necrosis; the remaining two omental lobes (8% liver mass) are left intact. Adult Sprague-Dawley rats (250-300 g) were used. Survival time was determined in 60 rats. Because maintenance of body temperature at 37 degrees C shortened survival time by half, FHF rats were not warmed during the postinduction period and were allowed to gradually enter a state of mild to moderate hypothermia (29-32 degrees C). Additionally, 42 FHF rats were killed in batches of six rats each 2, 6, 12, 18, 24, 30, and 36 hours postoperatively to evaluate changes in blood chemistry (glucose, lactate, liver function tests, prothrombin time) and to assess liver regenerative response in the residual omental liver lobes (weight, protein content, incorporation of bromodeoxyuridine [BrdU], expression of proliferation cell nuclear antigen [PCNA], mitotic activity), plasma levels of hepatocyte growth factor (HGF) and transforming growth factor beta (TGF-beta1), and tissue expression of the HGF and it's receptor c-met. Rats undergoing partial hepatectomy of 68% (PH; n = 42) and a sham operation (SO; n = 42) served as controls. All SO and PH controls survived. PH rats showed only transient decreases in body temperature, signs of modest early hepatic dysfunction (hyperlactemia, hyperammonemia, prolonged PT time), and normal restitution of liver mass. All FHF rats became comatose by 24 hours postoperatively. Most animals (90%) died within 24-48 hours postoperatively (mean, 39 +/- 11 hours). Changes in blood chemistry reflected rapid development of liver failure. Plasma HGF levels were markedly elevated and at all time points were higher than in PH controls (P < .05). At the same time, expression of HGF and c-met messenger RNA in the remnant liver was delayed. Plasma TGF-beta1 levels increased early (18 hours) and remained twofold to threefold higher than that of PH and SO controls (P < .05). There was only a 20% increase in the weight of the remnant liver lobes due to swelling. No hepatocytes stained positively for BrdU and PCNA, and none showed mitotic figures. In contrast, all PH controls showed vigorous liver regeneration. In conclusion, we have developed and characterized a novel model of FHF in rats that has a number of physiological and biochemical features seen clinically in FHF, including severely impaired ability of the residual liver tissue to regenerate.

Ultrastructure, enzymatic, and transport properties of the PICM-19 bipotent liver cell line.

The pig epiblast-derived PICM-19 cell line was previously shown to spontaneously differentiate into liver-like cells and structures and to secrete serum proteins. A study was undertaken to further define the liver-like characteristics of the PICM-19 cell line. PICM-19 cells displayed in vitro ultrastructure, enzymatic, and transport characteristics similar to those of parenchymal hepatocytes and bile duct epithelium. The PICM-19 cells contained large oval nuclei, numerous oval to elongate mitochondria with flat cristae, extensive rough and smooth endoplasmic reticulum, Golgi complexes, lipid vacuoles, and glycogen granules. Biliary canaliculi with intraluminal projecting microvilli were delimited by the junctional apparatuses between adjacent PICM-19 cells. The PICM-19 cells rapidly transported fluorescein into their biliary canaliculi from the extracellular environment. PICM-19 cells that had differentiated into multicellular ductal structures had high gamma-glutamyltranspeptidase (GGT) activity at their apical surfaces as shown by histochemical staining. PICM-19 total GGT activity was at least 19 times higher than that found in porcine hepatocytes. Metyrapone induced cytochrome P-450 content of PICM-19 cells was at least one-fourth of that found in porcine hepatocytes. PICM-19 P-450 activity induced by 7-ethoxycoumarin was nearly equivalent to that of primary cultures of pig hepatocytes. The data support the proposal that differentiated PICM-19 cells resembled hepatocytes, or bile duct epithelium cells, and, therefore, the PICM-19 cell line behaved like early embryonic liver progenitor cells.