Safety and immunogenicity of a mosquito saliva peptide-based vaccine: a randomised, placebo-controlled, double-blind, phase 1 trial.

BACKGROUND: In animal models, immunity to mosquito salivary proteins protects animals against mosquito-borne disease. These findings provide a rationale to vaccinate against mosquito saliva instead of the pathogen itself. To our knowledge, no vector salivary protein-based vaccine has been tested for safety and immunogenicity in humans. We aimed to assess the safety and immunogenicity of Anopheles gambiae saliva vaccine (AGS-v), a peptide-based vaccine derived from four A gambiae salivary proteins, in humans. METHODS: In this randomised, placebo-controlled, double-blind, phase 1 trial, participants were enrolled at the National Institutes of Health Clinical Center in Bethesda, MD, USA. Participants were eligible if they were healthy adults, aged 18-50 years with no history of severe allergic reactions to mosquito bites. Participants were randomly assigned (1:1:1), using block randomisation and a computer-generated randomisation sequence, to treatment with either 200 nmol of AGS-v vaccine alone, 200 nmol of AGS-v with adjuvant (Montanide ISA 51), or sterile water as placebo. Participants and clinicians were masked to treatment assignment. Participants were given a subcutaneous injection of their allocated treatment at day 0 and day 21, followed by exposure to feeding by an uninfected Aedes aegypti mosquito at day 42 to assess subsequent risk to mosquito bites in a controlled setting. The primary endpoints were safety and immunogenicity at day 42 after the first immunisation. Participants who were given at least one dose of assigned treatment were assessed for the primary endpoints and analysis was by intention to treat. The trial was registered with ClinicalTrials.gov, NCT03055000, and is closed for accrual. FINDINGS: Between Feb 15 and Sept 10, 2017, we enrolled and randomly assigned 49 healthy adult participants to the adjuvanted vaccine (n=17), vaccine alone (n=16), or placebo group (n=16). Five participants did not complete the two-injection regimen with mosquito feeding at day 42, but were included in the safety analyses. No systemic safety concerns were identified; however, one participant in the adjuvanted vaccine group developed a grade 3 erythematous rash at the injection site. Pain, swelling, erythema, and itching were the most commonly reported local symptoms and were significantly increased in the adjuvanted vaccine group compared with both other treatment groups (nine [53%] of 17 participants in the adjuvanted vaccine group, two [13%] of 16 in the vaccine only group, and one [6%] of 16 in the placebo group; p=0·004). By day 42, participants who were given the adjuvanted vaccine had a significant increase in vaccine-specific total IgG antibodies compared with at baseline than did participants who were give vaccine only (absolute difference of log10-fold change of 0·64 [95% CI 0·39 to 0·89]; p=0·0002) and who were given placebo (0·62 [0·34 to 0·91]; p=0·0001). We saw a significant increase in IFN-γ production by peripheral blood mononuclear cells at day 42 in the adjuvanted vaccine group compared with in the placebo group (absolute difference of log10 ratio of vaccine peptide-stimulated vs negative control 0·17 [95% CI 0·061 to 0·27]; p=0·009) but we saw no difference between the IFN-γ production in the vaccine only group compared with the placebo group (0·022 [-0·072 to 0·116]; p=0·63). INTERPRETATION: AGS-v was well tolerated, and, when adjuvanted, immunogenic. These findings suggest that vector-targeted vaccine administration in humans is safe and could be a viable option for the increasing burden of vector-borne disease. FUNDING: Office of the Director and the Division of Intramural Research at the National Institute of Allergy and Infectious Diseases, and National Institutes of Health.

Immunogenicity, Safety, and Efficacy of a Standalone Universal Influenza Vaccine, FLU-v, in Healthy Adults: A Randomized Clinical Trial.

Background: FLU-v is a broad-spectrum influenza vaccine that induces antibodies and cell-mediated immunity. Objective: To compare the safety, immunogenicity, and exploratory efficacy of different formulations and dosing regimens of FLU-v versus placebo. Design: Randomized, double-blind, placebo-controlled, single-center phase 2b clinical trial. (ClinicalTrials.gov: NCT02962908; EudraCT: 2015-001932-38). Setting: The Netherlands. Participants: 175 healthy adults aged 18 to 60 years. Intervention: 0.5-mL subcutaneous injection of 500 µg of adjuvanted (1 dose) or nonadjuvanted (2 doses) FLU-v (A-FLU-v or NA-FLU-v) or adjuvanted or nonadjuvanted placebo (A-placebo or NA-placebo) (2:2:1:1 ratio). Measurements: Vaccine-specific cellular responses at days 0, 42, and 180 were assessed via flow cytometry and enzyme-linked immunosorbent assay. Solicited information on adverse events (AEs) was collected for 21 days after vaccination. Unsolicited information on AEs was collected throughout the study. Results: The AEs with the highest incidence were mild to moderate injection site reactions. The difference between A-FLU-v and A-placebo in the median fold increase in secreted interferon-γ (IFN-γ) was 38.2-fold (95% CI, 4.7- to 69.7-fold; P = 0.001) at day 42 and 25.0-fold (CI, 5.7- to 50.9-fold; P < 0.001) at day 180. The differences between A-FLU-v and A-placebo in median fold increase at day 42 were 4.5-fold (CI, 2.3- to 9.8-fold; P < 0.001) for IFN-γ-producing CD4+ T cells, 4.9-fold (CI, 1.3- to 40.0-fold; P < 0.001) for tumor necrosis factor-α (TNF-α), 7.0-fold (CI, 3.5- to 18.0-fold; P < 0.001) for interleukin-2 (IL-2), and 1.7-fold (CI, 0.1- to 4.0-fold; P = 0.004) for CD107a. At day 180, differences were 2.1-fold (CI, 0.0- to 6.0-fold; P = 0.030) for IFN-γ and 5.7-fold (CI, 2.0- to 15.0-fold; P < 0.001) for IL-2, with no difference for TNF-α or CD107a. No differences were seen between NA-FLU-v and NA-placebo. Limitation: The study was not powered to evaluate vaccine efficacy against influenza infection. Conclusion: Adjuvanted FLU-v is immunogenic and merits phase 3 development to explore efficacy. Primary Funding Source: SEEK and the European Commission Directorate-General for Research and Innovation, European Member States within the UNISEC (Universal Influenza Vaccines Secured) project.

Evaluation of the immunogenicity and safety of different doses and formulations of a broad spectrum influenza vaccine (FLU-v) developed by SEEK: study protocol for a single-center, randomized, double-blind and placebo-controlled clinical phase IIb trial.

BACKGROUND: Current influenza vaccines, based on antibodies against surface antigens, are unable to provide protection against newly emerging virus strains which differ from the vaccine strains. Therefore the population has to be re-vaccinated annually. It is thus important to develop vaccines which induce protective immunity to a broad spectrum of influenza viruses. This trial is designed to evaluate the immunogenicity and safety of FLU-v, a vaccine composed of four synthetic peptides with conserved epitopes from influenza A and B strains expected to elicit both cell mediated immunity (CMI) and humoral immunity providing protection against a broad spectrum of influenza viruses. METHODS: In a single-center, randomized, double-blind and placebo-controlled phase IIb trial, 222 healthy volunteers aged 18-60 years will be randomized (2:2:1:1) to receive two injections of a suspension of 500 µg FLU-v in saline (arm 1), one dose of emulsified 500 µg FLU-v in Montanide ISA-51 and water for injection (WFI) followed by one saline dose (arm 2), two saline doses (arm 3), or one dose of Montanide ISA-51 and WFI emulsion followed by one saline dose (arm 4). All injections will be given subcutaneously. Primary endpoints are safety and FLU-v induced CMI, evaluated by cytokine production by antigen specific T cell populations (flow-cytometry and ELISA). Secondary outcomes are measurements of antibody responses (ELISA and multiplex), whereas exploratory outcomes include clinical efficacy and additional CMI assays (ELISpot) to show cross-reactivity. DISCUSSION: Broadly protective influenza vaccines able to provide protection against multiple strains of influenza are urgently needed. FLU-v is a promising vaccine which has shown to trigger the cell-mediated immune response. The dosages and formulations tested in this current trial are also estimated to induce antibody response. Therefore, both cellular and humoral immune responses will be evaluated. TRIAL REGISTRATION: EudraCT number 2015-001932-38 ; retrospectively registered clinicaltrials.gov NCT02962908 (November 7th 2016).

Synthetic immunotherapy induces HIV virus specific Th1 cytotoxic response and death of an HIV-1 infected human cell line through classic complement activation.

BACKGROUND: This manuscript describes the development of a novel synthetic immunotherapy (HIV-v) composed of four multi-epitope polypeptides targeting conserved regions in the Nef, Rev, Vif and Vpr viral proteins. Immunogenicity and cytotoxicity of HIV-v are discussed. METHODS: Short conserved T-cell multi-epitope regions were identified in silico in the HIV proteome. The immunogenicity of the identified HIV-v polypeptides was assessed in vivo by immunisation of C57BLK6 mice transgenic for HLA-A*0201. Splenocytes from immunised animals were exposed in vitro to soluble HIV-v polypeptides or to syngeneic (T1) or allogeneic (Jurkat) cells transfected with these polypeptides. Specific T-cell reactivity was assessed by cell-based IFN-γ ELISA. Virus specific CD3 + CD8+ IFN-γ+ recall responses were also determined by flow cytometry following in vitro exposure of splenocytes from immunised mice to syngeneic (T1) and allogeneic (H9) cells infected with HIV-1 strain IIIB. HIV-v specific antibodies were quantified by ELISA whilst antibody mediated anti-viral immunotherapeutic effect on T1 cells infected with a laboratory adapted and a primary isolate of the HIV-1 virus was assessed in a LDH-based complement mediated lysis assay. RESULTS: HIV-v elicited antigen-specific IgG and IFN-γ responses against the synthetic polypeptides in the formulation. HIV-v specific T cells recognised polypeptides presented either as soluble antigen or complexed to HLA-A*0201 following natural processing and presentation by syngeneic human T1 cells. Moreover, the CD3 + CD8+ component of the response recognised syngeneic T1 cells naturally infected with HIV-1 in a virus-specific and MHC restricted-manner. The HIV-v specific IgG response was also able to recognise human T1 cells naturally infected with HIV-1 and induce cell death through classic activation of complement. CONCLUSIONS: HIV-v induces a vaccine-specific type I immune response characterised by activation of effector CD8+ T cell and antibody responses that recognise and kill human cell lines naturally infected with a laboratory adapted and a primary isolate of the HIV-1 virus. The data supports the hypothesis that alternative HIV protein targets can be effectively used to prime both cellular and antibody immune responses of clinical value in the prevention and treatment of HIV infection.

FLU-v, a Broad-Spectrum Influenza Vaccine, Induces Cross-Reactive Cellular Immune Responses in Humans Measured by Dual IFN-γ and Granzyme B ELISpot Assay.

Previous reports demonstrated that FLU-v, a peptide-based broad-spectrum influenza vaccine candidate, induced antibody and cellular immune responses in humans. Here, we evaluate cellular effector functions and cross-reactivity. PBMC sampled pre- (day 0) and post-vaccination (days 42 and 180) from vaccine (n = 58) and placebo (n = 27) recipients were tested in vitro for responses to FLU-v and inactivated influenza strains (A/H3N2, A/H1N1, A/H5N1, A/H7N9, B/Yamagata) using IFN-γ and granzyme B ELISpot. FLU-v induced a significant increase in the number of IFN-γ- and granzyme-B-secreting cells responding to the vaccine antigens from pre-vaccination (medians: 5 SFU/106 cells for both markers) to day 42 (125 and 40 SFU/106 cells, p < 0.0001 for both) and day 180 (75 and 20 SFU/106 cells, p < 0.0001 and p = 0.0047). The fold increase from pre-vaccination to day 42 for IFN-γ-, granzyme-B-, and double-positive-secreting cells responding to FLU-v was significantly elevated compared to placebo (medians: 16.3-fold vs. 1.0-fold, p < 0.0001; 3.5-fold vs. 1.0-fold, p < 0.0001; 3.0-fold vs. 1.0-fold, p = 0.0012, respectively). Stimulation of PBMC with inactivated influenza strains showed significantly higher fold increases from pre-vaccination to day 42 in the vaccine group compared to placebo for IFN-γ-secreting cells reacting to H1N1 (medians: 2.3-fold vs. 0.8-fold, p = 0.0083), H3N2 (1.7-fold vs. 0.8-fold, p = 0.0178), and H5N1 (1.7-fold vs. 1.0-fold, p = 0.0441); for granzyme B secreting cells reacting to H1N1 (3.5-fold vs. 1.0-fold, p = 0.0075); and for double positive cells reacting to H1N1 (2.9-fold vs. 1.0-fold, p = 0.0219), H3N2 (1.7-fold vs. 0.9-fold, p = 0.0136), and the B strain (2.0-fold vs. 0.8-fold, p = 0.0227). The correlation observed between number of cells secreting IFN-γ or granzyme B in response to FLU-v and to the influenza strains supported vaccine-induced cross-reactivity. In conclusion, adjuvanted FLU-v vaccination induced cross-reactive cellular responses with cytotoxic capacity, further supporting the development of FLU-v as a broad-spectrum influenza vaccine.

Safety and immunogenicity of AGS-v PLUS, a mosquito saliva peptide vaccine against arboviral diseases: A randomized, double-blind, placebo-controlled Phase 1 trial.

BACKGROUND: Immunity to mosquito salivary proteins could provide protection against multiple mosquito-borne diseases and significantly impact public health. We evaluated the safety and immunogenicity of AGS-v PLUS, a mosquito salivary peptide vaccine, in healthy adults 18-50 years old. METHODS: We conducted a randomized, double-blind, placebo-controlled Phase 1 study of AGS-v PLUS administered subcutaneously on Days 1 and 22 at the Center for Vaccine Development and Global Health, Baltimore, MD, USA. Participants were block randomized 1:1:1:1:1 to two doses saline placebo, two doses AGS-v PLUS, AGS-v PLUS/ISA-51 and saline placebo, two doses AGS-v PLUS/ISA-51, or two doses AGS-v PLUS/Alhydrogel. Primary endpoints were safety (all participants receiving ≥1 injection) and antibody and cytokine responses (all participants with day 43 samples), analysed by intention to treat. FINDINGS: Between 26 August 2019 and 25 February 2020, 51 participants were enrolled and randomized, 11 into the single dose AGS-v PLUS/ISA-51 group and ten in other groups. Due to COVID-19, 15 participants did not return for day 43 samplings. Participants experienced no treatment-emergent or serious adverse events. All solicited symptoms in 2/10 placebo recipients and 22/41 AGS-v PLUS recipients after dose one and 1/10 placebo recipients and 22/41 AGS-v PLUS recipients after dose two were mild/moderate except for one severe fever the day after vaccination (placebo group). Only injection site pain was more common in vaccine groups (15/51 after dose 1 and 11/51 after dose 2) versus placebo. Compared to placebo, all vaccine groups had significantly greater fold change in anti-AGS-v PLUS IgG and IFN-É£ from baseline. INTERPRETATION: AGS-v PLUS had favourable safety profile and induced robust immune responses. Next steps will determine if findings translate into clinical efficacy against mosquito-borne diseases. FUNDING: UK Department of Health and Social Care.

Efficacy of FLU-v, a broad-spectrum influenza vaccine, in a randomized phase IIb human influenza challenge study.

FLU-v, developed by PepTcell (SEEK), is a peptide vaccine aiming to provide a broadly protective cellular immune response against influenza A and B. A randomized, double-blind, placebo-controlled, single-center, phase IIb efficacy and safety trial was conducted. One hundred and fifty-three healthy individuals 18-55 years of age were randomized to receive one or two doses of adjuvanted FLU-v or adjuvanted placebo subcutaneously on days -43 and -22, prior to intranasal challenge on day 0 with the A/California/04/2009/H1N1 human influenza A challenge virus. The primary objective of the study was to identify a reduction in mild to moderate influenza disease (MMID) defined as the presence of viral shedding and clinical influenza symptoms. Single-dose adjuvanted FLU-v recipients (n = 40) were significantly less likely to develop MMID after challenge vs placebo (n = 42) (32.5% vs 54.8% p = 0.035). FLU-v should continue to be evaluated and cellular immunity explored further as a possible important correlate of protection against influenza.

Meta-Analysis and Potential Role of Preexisting Heterosubtypic Cellular Immunity Based on Variations in Disease Severity Outcomes for Influenza Live Viral Challenges in Humans.

Influenza live viral challenges in humans are valuable models for testing the efficacy of vaccines and antiviral agents. Volunteers are treated with an investigational agent, and their clinical outcomes postchallenge are compared to those of placebo-treated volunteers. Despite using a common protocol, similar recruitment criteria, and similar doses of the same challenge strain, we noticed differences in disease severity outcomes between the placebo groups from different studies. We investigated whether these differences were significant and, if so, whether any pattern and its possible causes could be identified. We compared the clinical outcomes postchallenge in placebo groups from five clinical studies carried out between 2008 and 2013. Correlations between the prechallenge heterosubtypic cellular response (gamma interferon [IFN-γ]) and postchallenge clinical outcomes were also investigated in one study. Placebo groups from studies carried out between 2009 and 2010 attained significantly reduced (P < 0.05) symptom scores postchallenge compared to those of placebo groups from studies carried out in either 2008 or 2013. Also, in a 2010 study, the frequency of high-influenza heterosubtypic cellular responders prevaccination was significantly lower in the test group (FLU-v) than that in the placebo group (P = 0.04). Moreover, the increased preexisting heterosubtypic cellular response of the placebo group correlated with reductions in symptom score and viral shedding postchallenge (P ≤ 0.023). Only postvaccination did the test group display an equivalent correlation. The last influenza pandemic coincided with a significant reduction in disease severity outcomes. This reduction also appears to correlate with increased preexisting influenza heterosubtypic cellular responses. (This study is registered at ClinicalTrials.gov under registration number NCT01226758.).

A Synthetic Influenza Virus Vaccine Induces a Cellular Immune Response That Correlates with Reduction in Symptomatology and Virus Shedding in a Randomized Phase Ib Live-Virus Challenge in Humans.

Current influenza vaccines elicit primarily antibody-based immunity. They require yearly revaccination and cannot be manufactured until the identification of the circulating viral strain(s). These issues remain to be addressed. Here we report a phase Ib trial of a vaccine candidate (FLU-v) eliciting cellular immunity. Thirty-two males seronegative for the challenge virus by hemagglutination inhibition assay participated in this single-center, randomized, double-blind study. Volunteers received one dose of either the adjuvant alone (placebo, n = 16) or FLU-v (500 µg) and the adjuvant (n = 16), both in saline. Twenty-one days later, FLU-v (n = 15) and placebo (n = 13) volunteers were challenged with influenza virus A/Wisconsin/67/2005 (H3N2) and monitored for 7 days. Safety, tolerability, and cellular responses were assessed pre- and postvaccination. Virus shedding and clinical signs were assessed postchallenge. FLU-v was safe and well tolerated. No difference in the prevaccination FLU-v-specific gamma interferon (IFN-γ) response was seen between groups (average ± the standard error of the mean [SEM] for the placebo and FLU-v, respectively, 1.4-fold ± 0.2-fold and 1.6-fold ± 0.5-fold higher than the negative-control value). Nineteen days postvaccination, the FLU-v group, but not the placebo group, developed FLU-v-specific IFN-γ responses (8.2-fold ± 3.9-fold versus 1.3-fold ± 0.1-fold higher than the negative-control value [average ± SEM] for FLU-v versus the placebo [P = 0.0005]). FLU-v-specific cellular responses also correlated with reductions in both viral titers (P = 0.01) and symptom scores (P = 0.02) postchallenge. Increased cellular immunity specific to FLU-v correlates with reductions in both symptom scores and virus loads. (This study has been registered at ClinicalTrials.gov under registration no. NCT01226758 and at hra.nhs.uk under EudraCT no. 2009-014716-35.).

Adrenomedullin signals through NF-kappaB in epithelial cells.

Adrenomedullin is a peptide found in a variety of cells and tissues and involved in a multitude of biological processes. Recently, adrenomedullin has been identified as a host defense peptide and as such it plays a role in the inflammatory response. The transcription factor NF-kappaB is a major regulator of genes involved in the inflammatory response and the aim of this study was to determine whether NF-kappaB played a role in the inflammatory process triggered by adrenomedullin. Skin epithelial cells (HaCaTs) were used as our model in vitro. Western blot analysis from adrenomedullin-stimulated HaCaT cells revealed a rapid degradation of NF-kappaB inhibitor alpha and beta followed by the translocation of free NF-kappaB to the nucleus, where it was detected by Texas Red immunostaining after incubation with adrenomedullin for 15 min. Electromobility shift assay showed that NF-kappaB present in the nucleus was active, since it bound to a probe containing an NF-kappaB binding site. Supershift assays indicated that p50 and p65, members of the NF-kappaB family, were both part of the NF-kappaB dimmers involved in adrenomedullin cell signaling. HaCaTs secreted interleukin-6 in response to AM, which was significantly attenuated by the NF-kappaB inhibitor SN-50. Taken together, the data lend support for an immunoregulatory role for AM.

Safety, immunogenicity and efficacy assessment of HIV immunotherapy in a multi-centre, double-blind, randomised, Placebo-controlled Phase Ib human trial.

BACKGROUND: Combination antiretroviral therapy (cART) is the main therapeutic management tool for HIV/AIDS. Despite its success in controlling viral load and disease progression, cART is expensive, associated with a range of significant side effects and depends for its efficacy on the patient's life-long commitment to high levels of treatment adherence. Immunotherapeutic agents can provide potential solutions to these shortcomings. Here we describe a Phase Ib trial of HIV-v, a synthetic immunotherapy that elicits T- and B-cell effector responses against HIV infected cells. METHODS: Fifty-nine cART-naive HIV-infected males aged 18-50 years with viral load of 5000-500,000 copies/ml and CD4 counts >350/µl were recruited for this multi-centre, randomised, double blind study. Volunteers received one low (250 µg) or high (500 µg) dose of HIV-v, either alone or adjuvanted (ISA-51). Safety, immunogenicity, CD4 count and viral load were monitored over 168 Days. RESULTS: HIV-v was well tolerated and the adjuvanted formulations elicited IgG responses in up to 75% of volunteers. The high adjuvanted dose also elicited cellular responses in 45% of tested volunteers. In these responding subjects viral loads were reduced by over 1 log (p=0.04) compared to Placebo and non-responders. No changes in CD4 count were observed. CONCLUSIONS: HIV-v is safe and can elicit T- and B-cell responses in ART-naive HIV patients that significantly reduce viral load. Improved dosing regimens and further research on long term efficacy are required, but HIV-v appears to have potential as an immunotherapeutic anti-viral agent. Trial registered as EudraCT-2009-010593-37 (ClinicalTrials.gov Identifier: NCT01071031).

Synthetic Influenza vaccine (FLU-v) stimulates cell mediated immunity in a double-blind, randomised, placebo-controlled Phase I trial.

OBJECTIVES: Current Influenza vaccines elicit antibody mediated prophylactic immunity targeted to viral capsid antigens. Despite their global use these vaccines must be administered yearly to the population, cannot be manufactured until the circulating viral strain(s) have been identified and have limited efficacy. A need remains for Influenza vaccines addressing these issues and here we report the results of a Phase Ib trial of a novel synthetic Influenza vaccine (FLU-v) targeting T cell responses to NP, M1 and M2. METHODS: Forty-eight healthy males aged 18-40 were recruited for this single-centre, randomised, double blind study. Volunteers received one single low (250 µg) or high (500 µg) dose of FLU-v, either alone or adjuvanted. Safety, tolerability and basic immunogenicity (IgG and IFN-γ responses) parameters were assessed pre-vaccination and for 21 days post-vaccination. RESULTS: FLU-v was found to be safe and well tolerated with no vaccine associated severe adverse events. Dose-dependent IFN-γ responses >2-fold the pre-vaccination level were detected in 80% and 100% of volunteers receiving, respectively, the low and high dose adjuvanted FLU-v formulations. No formulation tested induced any significant FLU-v antibody response. CONCLUSION: FLU-v is safe and induces a vaccine-specific cellular immunity. Cellular immune responses are historically known to control and mitigate infection and illness during natural infection.

Identification of a novel cathelicidin gene in the rainbow trout, Oncorhynchus mykiss.

We report the cloning of a novel antimicrobial peptide gene, termed rtCATH_1, found in the rainbow trout, Oncorhynchus mykiss. The predicted 216-residue rtCATH_1 prepropeptide consists of three domains: a 22-residue signal peptide, a 128-residue cathelin-like region containing two identifiable cathelicidin family signatures, and a predicted 66-residue C-terminal cationic antimicrobial peptide. This predicted mature peptide was unique in possessing features of different known (mammalian) cathelicidin subgroups, such as the cysteine-bridged family and the specific amino-acid-rich family. The rtCATH_1 gene comprises four exons, as seen in all known mammalian cathelicidin genes, and several transcription factor binding sites known to be of relevance to host defenses were identified in the 5' flanking region. By Northern blot analysis, the expression of rtCATH_1 was detected in gill, head kidney, and spleen of bacterially challenged fish. Primary cultures of head kidney leukocytes from rainbow trout stimulated with lipopolysaccharide or poly(I x C) also expressed rtCATH_1. A 36-residue peptide corresponding to the core part of the fish cathelicidin was chemically synthesized and shown to exhibit potent antimicrobial activity and a low hemolytic effect. Thus, rtCATH_1 represents a novel antimicrobial peptide gene belonging to the cathelicidin family and may play an important role in the innate immunity of rainbow trout.