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Background: Many studies have compared real-world clinical outcomes of immunotherapy in patients with metastatic non-small cell lung cancer (NSCLC) with reported outcomes data from pivotal trials. However, any differences observed could be only limitedly explored further for causation because of the unavailability of individual patient data (IPD) from trial participants. The present study aims to explore the additional benefit of comparison with IPD. Methods: This study compares progression free survival (PFS) and overall survival (OS) of metastatic NSCLC patients treated with second line nivolumab in real-world clinical practice (n = 141) with IPD from participants in the Checkmate-057 clinical trial (n = 292). Univariate and multivariate Cox proportional hazards models were used to construct HRs for real-world practice versus clinical trial. Results: Real-world patients were older (64 vs. 61 years), had more often ECOG PS ≥ 2 (5 vs. 0%) and were less often treated with subsequent anti-cancer treatment (28.4 vs. 42.5%) compared to trial patients. The median PFS in real-world patients was longer (3.84 (95%CI: 3.19-5.49) vs 2.30 (2.20-3.50) months) and the OS shorter than in trial participants (8.25 (6.93-13.2) vs. 12.2 (9.90-15.1) months). Adjustment with available patient characteristics, led to a shift in the hazard ratio (HR) for OS, but not for PFS (HRs from 1.13 (0.88-1.44) to 1.07 (0.83-1.38), and from 0.82 (0.66-1.03) to 0.79 (0.63-1.00), respectively). Conclusions: This study is an example how IPD from both real-world and trial patients can be applied to search for factors that could explain an efficacy-effectiveness gap. Making IPD from clinical trials available to the international research community allows this. [ABSTRACT FROM AUTHOR]

Recent results of patients with advanced melanoma treated with first-line BRAF-MEK inhibitors in clinical trials showed 5-year survival in one-third of patients with a median overall survival (OS) of more than 2 years. This study aimed to investigate these patients' real-world survival and identify the characteristics of long-term survivors. The study population consisted of patients with advanced cutaneous melanoma with a BRAF-V600 mutated tumor who were treated with first-line BRAF-MEK inhibitors between 2013 and 2017. Long-term survival was defined as a minimum OS of 2 years from start therapy. The median progression-free survival (mPFS) and median OS (mOS) of real-world patients ( n  = 435) were respectively 8.0 (95% CI, 6.8-9.4) and 11.7 (95% CI, 10.3-13.5) months. Two-year survival was reached by 28% of the patients, 22% reached 3-year survival and 19% reached 4-year survival. Real-world patients often had brain metastases (41%), stage IV M1c disease (87%), ECOG PS ≥2 (21%), ≥3 organ sites (62%) and elevated LDH of ≥250 U/I (49%). Trial-eligible real-world patients had an mOS of 17.9 months. Patients surviving more than 2 years ( n  = 116) more often had an ECOG PS ≤1 (83%), normal LDH (60%), no brain metastases (60%), no liver metastases (63%) and <3 organ sites (60%). Long-term survival of real-world patients treated with first-line BRAF-MEK inhibitors is significantly lower than that of trial patients, which is probably explained by poorer baseline characteristics of patients treated in daily practice. Long-term survivors generally had more favorable characteristics with regard to age, LDH level and metastatic sites, compared to patients not reaching long-term survival., (Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc.)

Introduction: Regulatory decisions on paediatric investigation plans (PIPs) aim at making effective and safe medicines timely available for children with high unmet medical need. At the same time, scientific knowledge progresses continuously leading frequently to the identification of new molecular targets in the therapeutic area of oncology. This, together with further efforts to optimise next generation medicines, results in novel innovative products in development pipelines. In the context of global regulatory development requirements for these growing pipelines of innovative products (e.g. US RACE for children Act), it is an increasing challenge to complete development efforts in paediatric oncology, a therapeutic area of rare and life-threatening diseases with high unmet needs., Objective: Regulators recognise feasibility challenges of the regulatory obligations in this context. Here, we explain the EU regulatory decision making strategy applied to paediatric oncology, which aims fostering evidence generation to support developments based on needs and robust science. Because there is a plethora of products under development within given classes of or within cancer types, priorities need to be identified and updated as evidence evolves. This also includes identifying the need for third or fourth generation products to secure focused and accelerated drug development., Conclusion: An agreed PIP, as a plan, is a living document which can be modified in light of new evidence. For this to be successful, input from the various relevant stakeholders, i.e. patients/parents, clinicians and investigators is required. To efficiently obtain this input, the EMA is co-organising with ACCELERATE oncology stakeholder engagement platform meetings., Competing Interests: Conflict of interest statement The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Background: The Dutch Institute for Clinical Auditing (DICA) Medicines Program was set up in September 2018 to evaluate expensive medicine use in daily practice in terms of real-world effectiveness using only existing data sources., Objective: The aim of this study is to describe the potential of the addition of declaration data to quality registries to provide participating centers with benchmark information about the use of medicines and outcomes among patients., Methods: A total of 3 national population-based registries were linked to clinical and financial data from the hospital pharmacy, the Dutch diagnosis treatment combinations information system including in-hospital activities, and survival data from health care insurers. The first results of the real-world data (RWD) linkage are presented using descriptive statistics to assess patient, tumor, and treatment characteristics. Time-to-next-treatment (TTNT) and overall survival (OS) were estimated using the Kaplan-Meier method., Results: A total of 21 Dutch hospitals participated in the DICA Medicines Program, which included 7412 patients with colorectal cancer, 1981 patients with metastasized colon cancer, 3860 patients with lung cancer, 1253 patients with metastasized breast cancer, and 7564 patients with rheumatic disease. The data were used for hospital benchmarking to gain insights into medication use in specific patient populations, treatment information, clinical outcomes, and costs. Detailed treatment information (duration and treatment steps) led to insights into differences between hospitals in daily clinical practices. Furthermore, exploratory analyses on clinical outcomes (TTNT and OS) were possible., Conclusions: The DICA Medicines Program shows that it is possible to gather and link RWD about medicines to 4 disease-specific population-based registries. Since these RWD became available with minimal registration burden and effort for hospitals, this method can be explored in other population-based registries to evaluate real-world efficacy., (©Rawa Kamaran Ismail, Jesper van Breeschoten, Silvia van der Flier, Caspar van Loosen, Anna Maria Gerdina Pasmooij, Maaike van Dartel, Alfons van den Eertwegh, Anthonius de Boer, Michel Wouters, Doranne Hilarius. Originally published in the Journal of Medical Internet Research (https://www.jmir.org), 23.06.2022.)

Background: This study aimed to provide insights into the real-world use of palbociclib, dose reductions, and drug effectiveness in (older) patients with advanced breast cancer (BC)., Patients and Methods: Patients with advanced BC treated with palbociclib from 2017 to 2020 were included. The Kaplan-Meier method was used to calculate time to next treatment (TTNT) and overall survival (OS) for patients with or without dose reductions. These clinical outcomes were also compared in subgroup analyses for older patients (≥70 years) and younger patients (<70 years) and for patients discontinuing palbociclib early (<4 administrations)., Results: A total of 598 patients with advanced BC were included, with a median age of 64 years. Palbociclib dose reductions occurred in 33% of all patients. Early discontinuation of palbociclib without dose reductions occurred in 23% of the patients. Patients who required a palbociclib dose reduction were older (median age 67 years vs. 63 years). Patients with dose reductions had a significantly higher TTNT of 16.9 vs. 11.4 months (p < 0.001) and median OS of 29.7 vs. 21.9 months (p = 0.003) compared to patients without dose reductions. The TTNT in older patients was significantly longer (16.9 vs. 11.6 months, p = 0.013) than younger patients, but OS was similar (20.7 vs. 26.7 months, p = 0.051)., Conclusion: Palbociclib dose reductions occurred in real-world practice similarly to the PALOMA-3 trial. Patients with dose reductions had no poorer outcomes compared to patients not requiring a dose reduction. Older patients treated with palbociclib had more frequent dose reductions, but this did not appear to affect OS., Competing Interests: Declaration of competing interest The authors declare that they have no competing interests., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: Little is known about outcomes of adjuvant-treated melanoma patients beyond the clinical trial setting. Since 2019, adjuvant-treated melanoma patients have been registered in the DMTR, a population-based registry to monitor the quality and safety of melanoma care in the Netherlands. This study aims to describe treatment patterns, relapse, and toxicity rates of adjuvant-treated melanoma patients beyond the clinical trial setting., Methods: Analyses were performed on adjuvant-treated melanoma patients included in the DMTR. Descriptive statistics were used to analyse patient-, and treatment characteristics. A baseline registration completeness analysis was performed, and an analysis on trial eligibility in clinical practice patients. Recurrence-free survival (RFS) at 12-months was estimated with the Kaplan-Meier method., Results: A total of 641 patients were treated with adjuvant anti-PD-1 therapy. RFS at 12-months was 70.6% (95% CI, 66.9-74.6) with a median follow-up of 12.8 months. Sex, stage of disease and Breslow thickness were associated with a higher hazard for RFS. Eighteen per cent of the anti-PD-1-treated patients developed grade ≥3 toxicity. Sixty-one per cent of patients prematurely discontinued anti-PD-1 therapy., Conclusion: Adjuvant anti-PD-1 treatment of resected stage III/IV melanoma in daily practice showed slightly higher toxicity rates and more frequent premature discontinuation but similar RFS rates compared to trials., Competing Interests: Conflict of interest statement AvdE has advisory relationships with Amgen, Bristol Myers Squibb, Roche, Novartis, MSD, Pierre Fabre, Sanofi, Pfizer, Ipsen, Merck and has received research study grants not related to this paper from Sanofi, Roche, Bristol Myers Squibb, Idera and TEVA and has received travel expenses from MSD Oncology, Roche, Pfizer and Sanofi and has received speaker honoraria from BMS and Novartis. MBS has consultancy/advisory relationships with Pierre Fabre, MSD and Novartis. JdG has consultancy/advisory relationships with Bristol Myers Squibb, Pierre Fabre, Servier, MSD, Novartis. GH consultancy/advisory relationships with Amgen, Bristol Myers Squibb, Roche, MSD, Pfizer, Novartis, Pierre Fabre and has received research grants not related to this paper from Bristol Myers Squibb, Seerave. EK has consultancy/advisory relationships with BristolMyers Squibb, Novartis, Merck, Pierre Fabre, and received research grants not related to this paper from Bristol Myers Squibb. KS has advisory relationships with Bristol Myers Squibb, Novartis, MSD, Pierre Fabre, Abbvie and received honoraria from Novartis, MSD and Roche. AvdV has consultancy relationships with Bristol Myers Squibb, MSD, Roche, Novartis, Pierre Fabre, Pfizer, Sanofi, Ipsen, Eisai, Merck. JH has advisory relationships with Achilles Therapeutics, Bristol Myers Squibb, BioNTech, Immunocore, Ipsen, MSD, Merck Serono, Molecular Partners, Novartis, Neogene Therapeutics, PokeAcel, Pfizer, Roche/Genentech, Sanofi, T-Knife, Third Rock Ventures, and has received research grants not related to this paper from Amgen, Bristol Myers Squibb, MSD, BioNTech, Neogene Therapeutics and Novartis. All grants were paid to the institutions. The funders had no role in the writing of this article or decision to submit it for publication. AvA has advisory board/consultancy honoraria from Amgen, Bristol Myers Squibb, Novartis, MSD-Merck, Merck-Pfizer, Pierre Fabre, Sanofi, Sirius Medical, 4SC. Research grants from Amgen, Merck-Pfizer. All outside of current work and all paid to institute. MA has advisory board/consultancy honoraria from Amgen, Bristol Myers Squibb, Novartis, MSD-Merck, Merck-Pfizer, Pierre Fabre, Sanofi, Astellas, Bayer. Research grants Merck-Pfizer. Not related to current work and paid to institute. HMW has received travel expenses from Ipsen and Astellas and has received honoraria from Roche and Astellas. RvR has received expert meeting fees from Roche and advisory board fees from Pfizer. EE has received speaker honoraria from BMS, Pierre Fabre, Kyowa Kirin, and travel/conference expenses from MSD. All remaining authors have declared no conflicts of interest., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Postapproval trials and patient registries have their pros and cons in the generation of postapproval data. No direct comparison between clinical outcomes of these data sources currently exists for advanced melanoma patients. We aimed to investigate whether a patient registry can complement or even replace postapproval trials. Postapproval single-arm clinical trial data from the Medicines Evaluation Board and real-world data from the Dutch Melanoma Treatment Registry were used. The study population consisted of advanced melanoma patients with brain metastases treated with targeted therapies (BRAF- or BRAF-MEK inhibitors) in the first line. A Cox hazard regression model and a propensity score matching (PSM) model were used to compare the two patient populations. Compared to patients treated in postapproval trials (n = 467), real-world patients (n = 602) had significantly higher age, higher ECOG performance status, more often ≥3 organ involvement and more symptomatic brain metastases. Lactate dehydrogenase levels were similar between both groups. The unadjusted median overall survival (mOS) in postapproval clinical trial patients was 8.7 (95% CI, 8.1-10.4) months compared to 7.2 (95% CI, 6.5-7.7) months (P < 0.01) in real-world patients. With the Cox hazard regression model, survival was adjusted for prognostic factors, which led to a statistically insignificant difference in mOS for trial and real-world patients of 8.7 (95% CI, 7.9-10.4) months compared to 7.3 (95% CI, 6.3-7.9) months, respectively. The PSM model resulted in 310 matched patients with similar survival (P = 0.9). Clinical outcomes of both data sources were similar. Registries could be a complementary data source to postapproval clinical trials to establish information on clinical outcomes in specific subpopulations., (Copyright © 2020 The Author(s). Published by Wolters Kluwer Health, Inc.)

The aim was to provide evidence on systemically treated patients with advanced melanoma not represented in phase III trials to support clinical decision-making. Analysis were performed on advanced melanoma patients diagnosed between 2014 and 2017 in the Netherlands, treated with immune- or targeted therapy, who met ≥1 trial exclusion criteria. These criteria were derived from the KEYNOTE-006 and CHECKMATE-067/-066 phase III trials. Prognostic importance of factors associated with overall survival (OS) was assessed with the Kaplan-Meier method, Cox models, predicted OS probabilities of prognostic subgroups and a conditional inference survival tree (CIST). A nationwide population-based registry was used as data source. Of 2536 systemically treated patients with advanced melanoma, 1004 (40%) patients were ineligible for phase IIII trials. Ineligible patients had a poorer median OS (mOS) compared to eligible patients (8.8 vs 23 months). Eligibility criteria strongly associated with OS in systemically treated ineligible patients were Eastern Cooperative Oncology Group Performance Score (ECOG PS) ≥2, brain metastases (BM) and lactate dehydrogenase (LDH) of >500 U/L. Patients with ECOG PS of ≥2 with or without symptomatic BM had a predicted mOS of 6.5 and 11.3 months and a 3-year survival probability of 9.3% and 23.6%, respectively. The CIST showed the strongest prognostic covariate for survival was LDH, followed by ECOG PS. The prognosis of patients with LDH of >500 U/L is poor, but long-term survival is possible. The prognosis of ineligible patients with advanced melanoma in real-world was very heterogeneous and highly dependent on LDH value, ECOG PS and symptomatic BM., (© 2020 The Authors. International Journal of Cancer published by John Wiley & Sons Ltd on behalf of UICC.)

Timely and successful drug development for rare cancer populations, such as pediatric oncology, requires consolidated efforts in the spirit of shared responsibility. In order to advance tailored development efforts, the concept of multistakeholder Strategy Forum involving industry, academia, patient organizations, and regulators has been developed. In this study, we review the first five pediatric oncology Strategy Forums co-organized by the European Medicines Agency between 2017 and 2020, reflecting on the outcomes and the evolution of the concept over time and providing an outline of how a "safe space" for multistakeholder engagement facilitated by regulators could be of potential value beyond pediatric oncology drug development., (© 2020 The Authors Clinical Pharmacology & Therapeutics © 2020 American Society for Clinical Pharmacology and Therapeutics.)

On 13 July 2011 the European Commission issued a marketing authorisation valid throughout the European Union (EU) for ipilimumab for the treatment of advanced (unresectable or metastatic) melanoma in adults who have received prior therapy. Ipilimumab is a monoclonal antibody that specifically blocks the inhibitory signal of cytotoxic T lymphocyte antigen 4 (CTLA-4), resulting in T cell activation, proliferation and lymphocyte infiltration into tumours, leading to tumour cell death. The recommended induction regimen of ipilimumab is 3mg/kg administered intravenously over a 90 min period every 3 weeks for a total of four doses. In a phase 3 trial in patients with advanced melanoma, median overall survival for ipilimumab was 10 months versus 6 months for gp100, an experimental melanoma vaccine (Hazard ratio (HR) 0.66; 95% confidence interval (CI): 0.51, 0.87; p = 0.0026). Ipilimumab was most commonly associated with adverse reactions resulting from increased or excessive immune activity. Most of these, including severe reactions, resolved following initiation of appropriate medical therapy or withdrawal of ipilimumab. The most common side-effects (affecting more than 10% of patients) were diarrhoea, rash, pruritus, fatigue, nausea, vomiting, decreased appetite and abdominal pain. The objective of this paper is to summarise the scientific review of the application leading to approval in the EU. The detailed scientific assessment report and product information, including the summary of product characteristics (SmPC), are available on the European Medicines Agency (EMA) website (www.ema.europa.eu)., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

We summarize and briefly discuss recent findings with respect to the amplification and overexpression of candidate oncogenes in 17p11.2 ~p12 in high-grade osteosarcomas. Amplification of this region occurs in about 25% of cases. The amplification profiles are often complex and suggest the involvement of more than one oncogene. The 17p11.2 ~ p12 region harbors many low-copy repeats (LCRs). We propose LCR-mediated repeated duplication by mitotic nonallelic homologous recombination as mechanism for the generation of the amplifications in this region. Genes PMP22 and COPS3 and three expressed sequence tags from within 17p11.2 ~ p12 have been found to be frequently overexpressed and consistently overexpressed after amplification, which identifies them as candidate oncogenes in this region. Overexpression of COPS3 has been linked to TP53 protein degradation and, being equivalent to TP53 mutation, the induction of genomic instability, which frequently occurs in high-grade osteosarcoma. These findings may serve as a framework for future work aimed to identify the causative oncogenes in 17p11.2 ~p12, to clarify the mechanism of their amplification, and to determine their importance in osteosarcoma tumorigenesis.

The peripheral myelin protein (PMP22) gene is highly expressed in peripheral Schwann cells and encodes an important constituent of the myelin sheath. It is also expressed at lower levels in other normal tissues in which the protein is supposed to be involved in cell growth regulation. We recently reported frequent amplification and overexpression of PMP22 in high-grade osteosarcoma. Here, we analyzed PMP22 expression in five osteosarcoma tumors and three osteosarcoma cell lines. In normal Schwann cells, transcription of PMP22 starts at three promoters, P1A, P1B, and P2, which results in the synthesis of three alternatively spliced transcripts that all code for the same protein. We found a comparable expression pattern in normal osteoblasts. However, promoter P1A-driven transcripts were absent in all investigated tumors and cell lines and, compared to normal osteoblasts, the P1B/P2 transcript ratio was found to be increased in two of three cases with PMP22 overexpression and decreased in all five cases without overexpression. In normal Schwann cells and in NIH3T3 cells, PMP22 expression increases upon serum starvation-induced growth arrest. In contrast to this, serum withdrawal caused a considerable decrease of PMP22 expression in the osteosarcoma cell lines. We conclude that the different PMP22 expression in osteosarcoma may result in alternative availability of the PMP22 protein during the cell cycle and aberrant regulation of cell growth control in osteosarcoma tumorigenesis.

Osteosarcomas are malignant tumors of the bone that are characterized by complex genetic changes, including loss and amplification of chromosome regions. Region 17p11.2 approximately p12 is frequently found to be amplified in this tumor, suggesting the presence of an oncogene (or oncogenes) important in osteosarcoma tumorigenesis. We had previously determined amplification profiles for this region. Reasoning that amplification of a causative oncogene in a tumor should result in increased expression of that gene, we have now determined the expression status of genes and expressed sequence tags (ESTs) in 17p11.2 approximately p12. We constructed a 17p11.2 approximately p12-specific macroarray containing 40 genes and 21 ESTs from this region, which was used for expression profiling of 11 osteosarcoma samples (9 tumors and 2 cell lines) and of normal human osteoblasts. Compared to normal osteoblasts, genes with at least threefold increased expression were considered to be overexpressed in the tumor. Genes PMP22 and COPS3, EST AA126939 (encoding part of the hypothetical protein FLJ20343), and two anonymous ESTs (AA918483 and R02360) were found to be most consistently overexpressed after amplification. By real-time reverse transcriptase polymerase chain reaction, we could confirm the overexpression status of PMP22 and COPS3 but not of FLJ20343. We conclude that PMP22 and COPS3, and possibly also the three ESTs, are candidate amplification targets in 17p11.2 approximately p12 in osteosarcoma.

We reported previously the amplification of DNA markers in 17p12 in 3 of 60 high-grade gliomas. To detect additional cases, we screened in total 104 gliomas of various types and grades by Southern blot analysis using marker 745R, which is within the commonly amplified region. However, no other caseswith significant amplification (amplification level > 4) were found. To investigate in detail the extent of the amplifications in the three tumors, which were all glioblastomas, we determined 17p11.2 approximately p12 amplification profiles by semiquantitative polymerase chain reaction using 15 microsatellite markers and seven candidate genes. Distinct and high-level amplifications, with maximum levels ranging from 15 to 38, were found in these tumors. The 0.8 Mb-region between D17S1525 and MAP2K4 in 17p12 proved to be commonly amplified in these tumors. In one tumor, a heterogeneous distribution of the amplification in 17p12 was found, suggesting that it is a late event during glioma tumorigenesis. Another tumor showed additional high-level amplification of PMP22 and D17S1843 in 17p11.2. From the high-level amplifications we conclude that at least one, but possibly more, putative oncogenes are present in 17p11.2 approximately p12 whose amplifications and/or overexpressions contribute to glioma tumorigenesis.

Amplification of region 17p11.2 approximately p12 has been found in 13%-29% of high-grade osteosarcomas, suggesting the presence of an oncogene or oncogenes that may contribute to their development. To determine the location of these putative oncogenes, we established 17p11.2 approximately p12 amplification profiles by semiquantitative PCR, using 15 microsatellite markers and seven candidate genes in 19 high-grade osteosarcomas. Most of the tumors displayed complex amplification profiles, with frequent involvement of marker D17S2041 in 17p12 and TOP3A in 17p11.2 and, in some cases, very high-level amplification of PMP22 and MAPK7 in 17p11.2. Our findings suggest that multiple amplification targets, including PMP22, TOP3A, and MAPK7 or genes close to these candidate oncogenes, may be present in 17p11.2 approximately p12 and thus contribute to osteosarcoma tumorigenesis.

Serial analysis of gene expression (SAGE) was used to identify a gene named GOA (gene overexpressed in astrocytoma), which codes for a novel Ring finger B-box coiled-coil (RBCC) protein. Northern blot hybridization showed overexpression of GOA in 9 of 10 astrocytomas. Except for kidney, in which high expression was found, expression levels in normal tissues were low and comparable to normal brain. Immunohistochemistry demonstrated presence of GOA, with prominent nuclear staining, in astrocytoma tumor cells and astrocytes of fetal brain, but virtual absence in mature astrocytes. Overexpression was not due to amplification, since amplification of GOA was only found in one of 65 astrocytomas. GOA was localized to 17q24-25, a region that is frequently gained or amplified in a number of other tumor types. GOA contains two LXXLL motifs, which are thought to be important for nuclear receptor binding. Our data suggest an important role of GOA in the process of dedifferentiation that is associated with astrocytoma tumorigenesis and possibly with that of other tumor types as well.

Direct cell/cell communication occurs through gap junctions (GJ). We mapped GJ expression in secondary lymphoid organs and found, for the first time, a high density of connexin43 (Cx43) GJ in follicular dendritic cells (FDC) in close association with lymphocytes (Krenacs T. and Rosendaal M., J. Histochem. Cytochem. 1995. 43: 1125-1137). In this work, we used a combination of ultrastructural, immunocytochemical, molecular methods, and functional dye transfer experiments to study which germinal center cells are involved in direct cell/ cell communication and how GJ expression is regulated during antigen responses. One week after injecting the footpad of mice with 50 micrograms lysozyme, Cx43 GJ were detected on elongated cells in the paracortex of their popliteal lymph nodes. Repeated challenge led to the formation of secondary follicles with enlarged FDC meshwork full of Cx43 GJ. This positive correlation may reflect an importance for GJ in the pattern formation of FDC and lymphoid follicles. In human tonsil, the density of GJ and FDC was highest in the light zone of germinal centers where the fate of B cells is thought to be decided. Cx43 colocalized with CD21 and CD35 antigens in the vicinity of desmosomal junctions on FDC embracing lymphocytes. Freeze-fracture hallmarks of GJ of 200-400 nm were also found on FDC in the vicinity of desmosomal plaques. Furthermore, Northern blot analysis showed the consistent presence of Cx43 mRNA in human tonsil and spleen. Most Cx43 message was localized in situ to cells with FDC morphology and some to a few germinal center lymphocytes. To investigate functional cell coupling, we set up FDC/B cell cultures from the low density cell fractions of human tonsils. Cx43 plaques associated with lymphocytes were detected both on elongated FDC processes in early cultures (up to 4 h) and in established FDC/B cell clusters (between 4 and 24 h). In early cultures, we injected FDC with Lucifer Yellow, a fluorescent dye which passes through GJ: the dye spread into adjacent FDC and occasionally from FDC into CD19+ B cells. Based on these results, we propose that direct cell/cell communication through Cx43 GJ is involved in FDC/FDC and in FDC/B cell interactions. The functionally coupled FDC meshwork may serve as a communication channel synchronizing germinal center events. FDC may also deliver crucial direct signals through GJ involved in the rescue of high-affinity B cell clones from apoptotic cell death.