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Abstract: Background: Livers exposed to warm ischemia (WI) are increasingly used for transplantation. The molecular mechanisms activated by WI alone (prior to procurement and transplantation) are not understood. To elucidate the pathways involved, we used microarrays to investigate the gene expression in porcine livers exposed to WI. Methods: Porcine livers (n = 6 group) were randomly subjected to WI periods of 15, 30 or 45 minutes. mRNA was extracted and gene expression determined by microarray analysis. Using bioinformatics software, we identified differentially expressed genes and related molecular pathways. We used the corresponding human annotation of the porcine microarray for the functional analysis. Results: Between 0 and 15 minutes of WI, 3530 genes were altered with a 2-log-fold change of <−0.58 or >+0.58 and P < .05. Between 0 and 30 minutes of WI, 4141 genes were differentially expressed; and between 0 and 45 minutes of WI, 2814 genes. At each time point, ∼50% of genes were up-regulated, whereas 50% were down-regulated. After pathway mapping, we found that the same pathways were induced for observed clustering of in the three WI periods: cell death, proliferation, inflammation, and metabolism pathways. Among the top genes that were up-regulated after 15 minutes of WI, the majority started to return to but did not reach baseline expression with increasing WI. A similar pattern was observed for the top suppressed genes. Conclusions: WI causes rapid changes in gene expression that affect several molecular pathways. This phenomenon seems to plateau at 15 to 30 minutes of WI. These new insights in the timing and the nature of molecular pathways induced by WI alone may help to design specific interventions to alter these changes and improve the outcome of livers from cardiac death donors. [Copyright &y& Elsevier]

Abstract: In a porcine liver transplant model, a brief period of oxygenated hypothermic machine perfusion (HMP) at the end of simple cold storage (SCS) has been shown to improve the viability of damaged liver grafts. To test the clinical validity of this strategy, we randomized SCS-discarded human liver grafts to either 4 hours of HMP (n = 13) or an additional 4 hours of SCS (n = 14). All livers were then warm reperfused to mimic ischemia-reperfusion injury ex vivo. The settings for HMP were: portal vein: 3 mm Hg, 300 mL/min and hepatic artery: 20 mm Hg, po 2: 300 mm Hg. Perfusion used Kidney Machine Perfusion Solution at 4°C to 8°C. During warm reperfusion, aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) values were higher (P < .015) among the SCS versus HMP methods at all times. The AST slope was lower in HMP versus SCS (P = .01). The LDH slope tended to be lower for HMP versus SCS (P = .07). Morphological scores were not different between HMP and SCS. At the start of warm reperfusion, MAPK was lower in HMP versus SCS (P = .02). Endothelin-1 (EDN1) and ICAM-1 tended to be lower in HMP versus SCS (P = .1 and .07, respectively). No difference was noted in MAPK, EDN1, and ICAM-1 after 60 or 120 minutes of warm reperfusion. In conclusion, HMP down-regulated MAPK and tended to reduce EDN1 and ICAM-1 mRNA in human liver grafts. During warm reperfusion, HMP versus SCS livers showed reduced AST and LDH release but no morphological difference. Further optimization of liver HMP may require different timing/duration of perfusion and/or an higher perfusion temperature. [Copyright &y& Elsevier]

Abstract: Objective: Proton magnetic resonance spectroscopy (1H MRS) is a technique to identify and quantify the composition of biofluids. Hypothermic machine perfusion (HMP) is an organ preservation method that has the potential to evaluate organ viability prior to transplantation by analyzing the composition of the perfusate. The aim of this study was to use 1H MRS to examine the perfusate during HMP of porcine livers exposed to warm ischemia (WI) and to identify potential biomarkers of liver viability. Materials and Methods: Porcine livers underwent 4 hours of HMP using kidney perfusion solution-1 (KPS-1) as perfusate after exposure to in situ WI of 0 (n = 6) or 2 hours (n = 5). Samples of the perfusate were taken at the start/end of HMP. Lactate and aspartate aminotransferase (AST) in the samples were measured biochemically as surrogates of the WI-induced damage. MRS acquisition was conducted on a 9.4 Tesla (400 MHz) high-resolution system. Results: AST increased significantly during 4 hours of HMP within groups (P < .02) and discriminated WI injury significantly from the start to the end of HMP (P < .03). 1H MRS showed significantly elevated signal intensity of lactate, alanine, and histidine during HMP within both groups (P < .02). Furthermore, alanine and histidine were significantly higher in the WI group than in the control group at the end of HMP (P = .011 and P = .038, respectively). Conclusion: AST, alanine, and histidine in HMP perfusate discriminated WI injury on porcine liver grafts and might be potential biomarkers of liver viability. [Copyright &y& Elsevier]

Abstract: Objective: Hypothermic machine perfusion (HMP) is superior to simple cold storage for kidney preservation. We previous observed in a porcine liver transplantation model increased tumor necrosis factor–α (TNF-α) production eventually leading to poor recipient survival after HMP using standard kidney perfusion solution (KPS-1) compared with simple cold storage. We compared two solutions for HMP preservation of the liver: enriched KPS-1 (EKPS-1) and Aqix RS-I. Methods: Pig livers were obtained after cold flushing with histidine-tryptophan-ketoglutarate solution. Subsequently, the livers were subjected to dual-vessel perfusion with two preservation solutions: EKPS-1 (n = 6) and Aqix RS-I (n = 3). After HMP preservation and transplantation, graft and recipient survival, hepatocellular damage (aspartate aminotransferase concentration), TNF-α production, and endothelial cell damage (hyaluronic acid clearance) were recorded. Results: No primary graft nonfunction was observed. Recipient survival at postoperative day 3 was similar in both groups (33%). Aspartate aminotransferase concentration measured in serum samples after reperfusion was similar in both groups. After reperfusion, TNF-α concentration was higher and hyaluronic acid clearance was lower in the EKPS-1 group vs the Aqix RS-I group at 60, 120, and 180 minutes (all P < .05). Conclusion: Hypothermic machine perfusion provided adequate longer term graft survival. After reperfusion, TNF-α production seems to be reduced, and endothelial cell dysfunction remains pronounced with Aqix RS-1 solution compared with EKPS-1 solution. [Copyright &y& Elsevier]

Abstract: In renal transplantation, hypothermic machine perfusion optimizes preservation of marginal grafts, assesses their quality prior to transplantation, improves outcome, and may contribute to an increased number of transplantations. Recently, hypothermic machine perfusion has become increasingly popular given the organ shortage and the “obligatory” utilization of marginal organs. Increasing mortality on the liver transplantation waiting list makes it urgent to develop machine perfusion systems for livers, trying to better preserve marginal livers and perhaps to recover currently discarded livers are for clinical transplantation without an increased risk of graft nonfunction. However, data on machine perfusion of livers and perfusion parameters capable of predicting viability are scarce. The aim of this study was to determine the baseline hemodynamic and metabolic profiles and morphology of livers during hypothermic machine perfusion in a porcine model. We used protocol similar to hypothermic machine perfusion of kidneys. Hemodynamic analysis revealed higher vascular resistance in the hepatic artery versus the portal vein. The arterial resistance gradually decreased during perfusion (similar to kidneys), suggesting progressive relaxation of the arterial vasculature, and perhaps better penetration of the microcirculation by the perfusion solution. During hypothermic machine perfusion, transaminases were gradually (but modestly) released, and livers displayed unequivocal signs of aerobic and anaerobic metabolism. After 24 hours, livers appeared morphologically well preserved. In conclusion, this study showed that hypothermic machine perfusion was feasible. During hypothermic machine perfusion, was easily assessed hemodynamic, biochemical, and morphological parameters. [Copyright &y& Elsevier]

Abstract: Introduction: In contrast with kidneys, data on hypothermic machine perfusion (HMP) of livers remain scarce. Optimal liver HMP is poorly defined. Superiority of liver HMP over simple cold storage (SCS), the current standard preservation, must be proven before HMP is applied clinically. In this study, morphology and adenosine triphosphate (ATP) contents of HMP livers at different flows and with versus without O2 studied in a porcine ex vivo model were compared to SCS. Methods: Pig livers were procured, flushed with HTK and preserved via SCS or HMP at 3 HMP settings: high flow (HF); low flow (LF); low flow + O2 (300 mm Hg) (LFO). HMP livers were perfused via the hepatic artery (HA) and portal vein (PV) with KPS-1 TM at 4°C to 6°C for 24 hours with HF: PV: 3 to 5 mm Hg, 1 mL/g liver/min for HA and 25 mm Hg; LF: PV: 3 to 5 mm Hg, 0.5 ml/g liver/min with HA: 20 mm Hg. Morphology and ATP levels were measured in preserved liver tissues. Results: Throughout the SCS preservation, livers remained intact. In HMP livers, vacuoles appeared after 4 hours of preservation in the HF group and after 12 hours in the LF livers. LFO livers remained intact with limited vacuoles. Compared to SCS, HMP livers showed dilated sinusoids, particularly in the HF group. ATP remained relatively constant or even increased during HMP, particularly in the LF group, whereas ATP decreased after SCS. Conclusion: Among the various HMP settings, HMP with LFO was superior. ATP levels were the highest in LF. In contrast with all HMP groups, SCS showed the lowest ATP levels, indicating that HMP has the potential to better preserve energy stores. [Copyright &y& Elsevier]

The aim of this open, non-randomised, 2-stage feasibility study was to determine whether radical prostatectomy (RP) was safe and could provide cure for good prognosis patients with clinical T3 prostate cancer, in a multicentre setting. Cure was defined as a 3 months post-operative of undetectable serum PSA in combination with the presence of pathologically negative margins in the surgical specimen. Forty patients were enrolled of whom 38 were eligible. Six patients (5 pN+ and 1 pNx) did not meet the inclusion criteria and were excluded leaving 32 evaluable pN0 patients of whom 19 (59.4%, SE=4.26) achieved a complete response (CR) and in whom only two serious toxic events (STEs) were observed. The results of the first phase of the study passed the toxicity criteria (<3 STE's) but failed on the cure rate (>20 CRs). This resulted in discontinuation of the study after the first stage. The main reason for failure was the incidence of positive margins in the resected specimen. Although the study was stopped after the first phase, 28 of the 32 pN0 patients (87.5%) had undetectable serum PSA at 3 months. We continue to believe that RP with extensive resection can be beneficial as monotherapy for T3aN0M0 prostate cancer. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this open, non-randomised, 2-stage feasibility study was to determine whether radical prostatectomy (RP) was safe and could provide cure for good prognosis patients with clinical T3 prostate cancer, in a multicentre setting. Cure was defined as a 3 months post-operative of undetectable serum PSA in combination with the presence of pathologically negative margins in the surgical specimen. Forty patients were enrolled of whom 38 were eligible. Six patients (5 pN+ and 1 pNx) did not meet the inclusion criteria and were excluded leaving 32 evaluable pN0 patients of whom 19 (59.4%, SE=4.26) achieved a complete response (CR) and in whom only two serious toxic events (STEs) were observed. The results of the first phase of the study passed the toxicity criteria (<3 STE’s) but failed on the cure rate (>20 CRs). This resulted in discontinuation of the study after the first stage. The main reason for failure was the incidence of positive margins in the resected specimen. Although the study was stopped after the first phase, 28 of the 32 pN0 patients (87.5%) had undetectable serum PSA at 3 months. We continue to believe that RP with extensive resection can be beneficial as monotherapy for T3aN0M0 prostate cancer. [Copyright &y& Elsevier]

Abstract: Background: Wider use of donors after circulatory death (DCD) could reduce mortality on the liver transplantation waiting list. We previously reported that pig livers exposed to ≥30 minutes of warm ischemia followed by 4 hours of cold ischemia are at high risk of primary graft nonfunction. We sought to determine how prolonged cold ischemia, after a short, normally well-tolerated period of warm ischemia affects graft function and recipient survival using a porcine model of liver transplantation. Materials and Methods: Livers were transplanted after exposure to no warm plus 4 hours cold ischemia (group 1); 15 minutes of warm and 4 hours of cold ischemia (group 2); no warm and 8 hours of cold ischemia (group 3); or 15 minutes of warm and 8 hours of cold ischemia (group 4). Recipient survival, graft dysfunction incidence, liver function (prothrombin time), hepatocellular damage (aspartate aminotransferase), sinusoidal cell function (hyaluronic acid), and inflammation (tumor necrosis factor-α) were recorded after transplantation. Biopsies were scored for ischemia–reperfusion injury. Results: Day 4 survival in group 4 was 0% versus 100%, 83%, and 100% in groups 1, 2, and 3, respectively. Recipients in group 4 exposed to short warm but prolonged cold ischemia displayed severe graft dysfunction, the highest peak transaminase, the greatest inflammatory response, more sinusoidal endothelial cell dysfunction and, the worst histologic score for ischemia–reperfusion injury. Conclusions: Liver grafts from DCD donors, even when exposed to short periods of warm ischemia, did not tolerate prolonged cold ischemia well and should be transplanted without delay. [Copyright &y& Elsevier]

Abstract: Purpose: Using magnetic resonance imaging, the apparent diffusion coefficient (ADC) is an indicator to assess cerebral ischemia. The aim of this porcine study was to evaluate whether ADC assessed hepatic ischemia during ex vivo hypothermic machine perfusion (HMP) as well as in vivo. Methods: Ex vivo: ADC of normal versus warm ischemic (WI) livers was assessed during HMP and subsequent rewarming to mimic ischemia-reperfusion injury. As the preservation solution, we used either an acellular solution or diluted blood. WI was induced in the left lobe or in the whole liver and compared 2-hour WI and non-WI. In vivo: One liver was scanned with the left lobe vessels occluded for 2-hour WI and subsequently for 3 hour reperfusion to compare with the right lobe without WI. Aspartate aminotransferase (AST) in the perfusate and morphology were used as surrogates of WI. Results: In all WI livers, AST reached high levels and histology showed severe injury. Ex vivo ADC during acellular perfusion showed negligible differences between the livers with versus without WI, namely, 0.75 × 10−3 or 0.88 × 10−3 mm2/s during HMP. Ex vivo ADC using sanguineous perfusion showed 1.11 × 10−3 or 0.83 × 10−3 mm2/s during HMP in regions with versus without WI, respectively, a difference that remained stable during the whole experiment. ADC in vivo decreased from the physiological level of 1.07 × 10−3 mm2/s to 0.75 × 10−3 mm2/s in the first 30 minutes of WI, whereas ADC in the non-WI liver remained constant. Conclusion: ADC in vivo decreased during hepatic ischemia, as previously seen in cerebral ischemia. However, the effect of WI on ADC was less clear during ex vivo HMP. [Copyright &y& Elsevier]

The hepatotropism and intrahepatic distribution of adenoviral vectors may be species dependent. Hepatocyte transduction was evaluated in three rabbit strains after transfer with E1E3E4-deleted adenoviral vectors containing a hepatocyte specific α1-antitrypsin promoter-driven expression cassette (AdAT4). Intravenous administration of 4×1012 particles/kg of AdAT4 induced human apo A-I levels above 40 mg/dl in Dutch Belt, but below 1 mg/dl in New Zealand White and Fauve de Bourgogne rabbits. Diameters of sinusoidal fenestrae were significantly (P=0.0014) larger in Dutch Belt (124±3.4 nm) than in New Zealand White (108±1.3 nm) and Fauve de Bourgogne (105±2.6 nm) rabbits, suggesting that a smaller size constitutes a barrier for hepatocyte transduction. Indeed, intraportal transfer preceded by intraportal injection of sodium decanoate, which increases the diameter of sinusoidal fenestrae to 123±3.4 nm (P<0.01) in New Zealand White rabbits, increased human apo A-I levels 32- and 120-fold in New Zealand White and Fauve de Bourgogne rabbits, respectively, but did not affect expression in Dutch Belt rabbits. In conclusion, size of sinusoidal fenestrae appears to be a critical determinant of hepatocyte transduction after adenoviral transfer. [ABSTRACT FROM AUTHOR]

Summary Investigating rare cellular events is facilitated by studying thick sections with confocal laser scanning microscopy (CLSM). Localization of cells in tissue sections can be done by immunolabelling or by fluorescent labelling of cells prior to intravenous administration. Immunolabelling is technically complicated because of the preservation of antigens during fixation and the problems associated with the penetration of the antibodies. In this study, an alternative and simple approach for the labelling of cells in vitro with the fluorescent probe DiO and its subsequent application in vivo will be outlined. The method was applied to trace DiO-labelled colon carcinoma cells (CC531s) in 100 µm thick liver sections. In vitro and in vivo experiments revealed that DiO-labelling of CC531s cells had no cytotoxic or antiproliferative effect and the cells preserved their susceptibility towards hepatic NK cells or Kupffer cells. In addition, DiO remained stable for at least 72 h in the living cell. DiO-labelled CC531s cells could be traced all over the tissue depth and anti-metastatic events such as phagocytosis of tumour cells by Kupffer cells could be easily observed. In situ staining with propidium iodide (nucleic acids) or rhodamine-phalloidin (filamentous actin) resulted in additional tissue information. The data presented improved the understanding of the possible effects of the vital fluorescent probe DiO on cell function and provided a limit of confidence for CLSM imaging of DiO-labelled cells in tissue sections. [ABSTRACT FROM AUTHOR]

Abstract: Reduced glutathione (GSH), an important radical scavenger, has been added to various organ preservation solutions. Because GSH oxidizes into oxidized glutathione (GSSG) and only GSH has scavenging capacity, only GSH in the solution at the time of clinical use is relevant. The concentrations of GSH (GSHconc) and GSSGconc were determined in 2 static preservation solutions—University of Wisconsin (UW) and Celsior—and in 1 machine preservation solution—Kidney Preservation Solution 1 (KPS-1). We determined the half-life (T1/2) of freshly added GSH. The GSHconc in UW and KPS-1 was 0.006 ± 0.0018 mmol/L and 0.13 ± 0.30 mmol/L, respectively. The GSHconc in Celsior was 2.7 ± 0.17 mmol/L. The manufacturers of these solutions reported 3 mmol/L GSH. GSSGconc in UW, KPS-1, and Celsior was 1.58 ± 0.61 mmol/L, 1.13 ± 0.16 mmol/L, and 0.24 ± 0.01 mmol/L, respectively. T1/2 of GSH in UW, KPS-1, and Celsior was 18 days, 86 days, and 83 days, respectively. The actual GSHconc in UW and KPS-1 at the time of clinical use was substantially lower than reported by the manufacturer, owing to the relatively short T1/2 of GSH. For Celsior, the GSHconc was maintained. Therefore, addition of fresh GSH to UW and KPS-1 before clinical use is recommended. [Copyright &y& Elsevier]

Abstract: Background: Hypothermic machine perfusion (HMP) is superior to simple cold storage (SCS) for the preservation of kidney grafts. Whether HMP is superior to SCS for liver preservation is not known. Before a HMP system can be used clinically for the liver, its superiority to SCS needs to be demonstrated in an in vivo large animal transplant model. Objective: The aim was to compare outcomes after liver transplantation (LT) following preservation by SCS or HMP using technology/perfusion conditions similar to those for kidney HMP. Methods: Pig livers were perfused via the hepatic artery and portal vein for 4 hours with nonoxygenated 4°C University of Wisconsin machine perfusion solution. In the SCS group, flushed livers were stored in histidine-tryptophan-ketoglutarate solution. After preservation by SCS (n = 6) or HMP (n = 8) and LT, we assessed graft and recipient survivals, pH and lactate, hepatocellular damage [aspartate aminotransferase (AST)], Kupffer cell activation (β-galactosidase), tumor necrosis factor (TNF) α production, endothelial cell function (hyaluronic acid), and expression of Krüppel-like factor (KLF) 2 and 4, which are mediators of the flow-dependent vasoprotective endothelial phenotype. Results: No primary graft nonfunction was observed; livers recovered equally well from the postanhepatic metabolic acidosis in both groups. Pig survival was 5/6 (83%) in the SCS versus 2/8 (12.5%) in the HMP group (P = .04). Livers from both groups recovered equally well from the postanhepatic metabolic acidosis. AST in liver rinse-out samples obtained before LT were lower in the HMP than in the SCS group (P < .05). After reperfusion, AST and β-galactosidase were equally increased in both groups (P = .13 and 0.962, respectively); TNF-α and hyaluronic acid levels were higher after HMP versus SCS (P = .001 and 0.043, respectively). KLF-2 and -4 expressions were equally up-regulated after reperfusion in the SCS and HMP groups. Conclusions: In this in vivo model, liver HMP with subsequent transplantation was feasible. However, we did not demonstrate an advantage of HMP, using perfusion conditions shown to be effective for the kidney, over SCS. Despite similar immediate graft function, TNF-α generation, and endothelial cell dysfunction were more pronounced after HMP. [Copyright &y& Elsevier]

Abstract: Background: Intrahepatic air embolism can occur during liver transplantation, jeopardizing the posttransplant outcome. Until now, the role of the procurement in the origin of intrahepatic air remains unclear; it might be underestimated. In this pilot study using magnetic resonance imaging (MRI), we observed a substantial amount of air trapped in porcine livers during multiorgan procurement. We quantified the amount of air, examining whether it could be reduced by avoiding direct contact of air with the lumen of the hepatic vasculature during procurement and back-table preparation. Methods: Five livers (control group) were procured according to standard techniques for comparison with 6 livers (modified group) where air could not enter into the livers due to clamping of the vasculature. MRI was performed during continuous machine perfusion (MP) preservation there after. We counted the number of black signal voids on T2*-weighted images, which were indicative of air bubbles within the hepatic contour. Additionally, an MRI contrast agent (gadolinium–diethylene triamine pentaacetic acid [Gd-DTPA]) was injected into the hepatic artery and circulated by MP. Insufficiently perfused areas with less contrast enhancement were analyzed quantitatively in T1-weighted images and expressed as the percentage of total liver volume. Results: The images of the control livers showed more air bubbles compared with the modified group (45 ± 27 vs 6 ± 3; P = .004). The percentage of insufficiently perfused areas was higher among the control compared with the modified group (28.0 ± 15.8% vs 2.6 ± 4.6%; P = .047) on first-pass postcontrast T1-weighted images. After recirculating the contrast agent, insufficiently perfused areas showed similar localizations and contours within every liver. Conclusion: These data suggested that a substantial amount of air enters into the hepatic microcirculation through direct contact of air with the hepatic vasculature during standard procurement and back-table preparation. Avoiding opening the hepatic vessels to air substantially reduced this phenomenon. [Copyright &y& Elsevier]

Satraplatin is a novel oral platinum (IV) complex that shows activity against hormone-refractory prostate cancer (HRPC) in cisplatin-resistant human tumor lines in phase I and phase II trials [1]. A randomized multicenter phase III trial with a target sample size of 380 patients was initiated in men with HRPC. After 50 randomized patients, the trial was closed to further accrual by the sponsoring company. An ad hoc analysis of all available data is reported here. Eligibility criteria included pathological proof of prostate cancer, documented progression despite prior hormonal manipulation, WHO PS 0–2, and no daily intake of narcotic analgesics. Patients were randomized between satraplatin 100 mg/m2 for 5 days plus prednisone 10 mg orally BID or prednisone alone. Compliance was excellent. 48/50 patients have progressed and 42 have died, mostly due to prostate cancer. Median overall survival was 14.9 months (95% CI: 13.7–28.4) on the satraplatin plus prednisone arm and 11.9 months (95% CI: 8.4–23.1) on prednisone alone (hazard ratio, HR = 0.84, 95% CI: 0.46–1.55). A >50% decrease in prostrate specific antigen (PSA) was seen in 9/27 (33.3%) in the satraplatin plus prednisone arm vs. 2/23 (8.7%) on the prednisone alone arm. Progression-free survival was 5.2 months (95% CI: 2.8–13.7) on the satraplatin plus prednisone arm as compared to 2.5 months (95% CI: 2.1– 4.7) on the prednisone alone arm (HR = 0.50, 95% CI: 0.28–0.92). This difference is statistically significant (p = 0.023). Toxicity was generally minimal in both arms. This randomized comparison of a combination of satraplatin and prednisone versus prednisone alone supports the antitumor activity of the combination. Its role in the treatment of HPRC remains to be elucidated in an appropriate phase III setting. Copyright © 2005 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Summary Prolactin (PRL) shares structural and functional features with haemopoietic factors and cytokine peptides. Dendritic cells (DC) are involved in both initiating the primary and boosting the secondary host immune response and can be differentiated in vitro from precursors under the effect of granulocyte–macrophage colony‐stimulating factor (GM‐CSF) plus other factors. Because PRL has been shown to functionally interact with GM‐CSF, we have addressed its role on GM‐CSF‐driven differentiation of DC. Monocytic DC precursors from peripheral blood mononuclear cells (PBMC) were enriched either by adhesion to a plastic surface or CD14‐positive selection and cultured for 7 days in serum‐free medium containing GM‐CSF, interleukin (IL)‐4 and PRL, alone or in combination. Cells with large, veiled cytoplasm, expressing major histocompatibility complex (MHC) class II and the costimulatory molecules CD80, CD86 and CD40 and lacking the monocyte marker CD14, were considered as having the phenotype of cytokine‐generated DC. Functional maturation was assessed by proliferation and interferon‐γ (IFN‐γ) release of allogeneic T lymphocytes. Physiological (10–20 ng/ml) concentrations of PRL interacted synergistically with GM‐CSF and the effect was similar to that induced by IL‐4 on GM‐CSF‐driven DC maturation. When used alone, the physiological concentrations of PRL were inhibitory, whereas higher concentrations (80 ng/ml) were stimulatory. The synergistic effect of PRL may in part be caused by its ability to counteract the down‐modulation of the GM‐CSF receptor observed in serum‐free conditions. These data provide further evidence of the significance of PRL in the process of T lymphocyte activation. [ABSTRACT FROM AUTHOR]