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Background: Immune checkpoint inhibitors (ICIs) with or without chemotherapy represent first-line standard of care for patients with advanced non-small cell lung cancer (NSCLC) without targetable driver mutations. The most appropriate second-line therapy after failing immunochemotherapy remains an open question. Nintedanib, an oral triple angiokinase inhibitor that targets the vascular endothelial growth factor receptor, fibroblast growth factor receptor, and, platelet-derived growth factor receptor, in combination with docetaxel, is approved for treatment of advanced NSCLC (adenocarcinoma histology) following progression on first-line chemotherapy., Methods: VARGADO (NCT02392455) is an ongoing, prospective, non-interventional study investigating the efficacy and safety of nintedanib plus docetaxel following first-line chemotherapy with or without ICIs in patients with locally advanced, metastatic, or locally recurrent NSCLC of adenocarcinoma histology. This analysis focuses on Cohort C, which enrolled patients who had received prior first line chemotherapy with ICIs. Patients received second-line docetaxel (75 mg/m 2 ) by intravenous infusion on Day 1, plus oral nintedanib (200 mg twice daily) on Days 2-21 of each 21-day cycle during routine clinical care. The primary endpoint is overall survival (OS) rate 1 year after the start of treatment with nintedanib plus docetaxel. Secondary endpoints include progression-free survival (PFS), OS, and disease control rate (DCR). Safety was also assessed., Results: Among 137 patients treated, the median age was 63 years (range, 37-84); 57 patients (41.6%) were female, most patients had Eastern Cooperative Oncology Group performance status of 0 (28.5%) or 1 (43.1%); 118 (86.1%) had stage IV NSCLC and 27 (19.7%) had brain metastases. Most (n=120, 87.6%) patients had received pembrolizumab/pemetrexed/platinum-based chemotherapy as first-line treatment. In 80 patients with available response data, the DCR was 72.5% (complete response: 1.3%; partial response: 36.3%; stable disease: 35.0%). Median progression-free survival was 4.8 months (95% confidence interval: 3.7-6.6). OS data were immature. Grade ≥3 treatment-emergent adverse events (TEAEs), serious TEAEs, and TEAEs leading to treatment discontinuation were reported in 62 (45.3%), 50 (36.5%), and 40 patients (29.2%), respectively., Conclusions: This analysis indicates that nintedanib plus docetaxel represents an effective second-line treatment option in patients with advanced adenocarcinoma NSCLC following progression on first-line immunochemotherapy. The safety profile was manageable with no unexpected signals., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tlcr.amegroups.com/article/view/10.21037/tlcr-21-1018/coif). CG reports consulting fees from Boehringer Ingelheim; payment or honoraria for lectures, presentations, speakers’ bureaus, manuscript writing or educational events from Boehringer Ingelheim; payment for expert testimony from Boehringer Ingelheim; support for attending meetings and/or travel from Boehringer Ingelheim; participation on a Data Safety Monitoring Board or Advisory Board for Boehringer Ingelheim; leadership or fiduciary role in other board, society, committee or advocacy group, paid or unpaid for DKG DGP. TW reports grants or contracts from Boehringer Ingelheim in support of an investigator-initiated trial (NCT04413201); consulting fees from AbbVie, AstraZeneca, Boehringer Ingelheim, Bristol-Myers Squibb, Merck Serono, Merck Sharp & Dohme, Pfizer, Roche/Genentech; payment or honoraria for lectures, presentations, speakers’ bureaus, manuscript writing or educational events from Boehringer Ingelheim, Bristol-Myers Squibb, Merck Sharp & Dohme, Roche/Genentech; payment for expert testimony from Takeda, Roche; support for attending meetings and/or travel from AstraZeneca, Boehringer Ingelheim, Celgene, Pfizer, Roche/Genentech; participation on a data safety monitoring or advisory board from Boehringer Ingelheim, Roche, AstraZeneca; research funding from AstraZeneca, Boehringer Ingelheim, Roche/Genentech. S Henschke reports provision of study data as part of the VARGADO study and review of the manuscript (no payment); grants or contracts from Amgen, AstraZeneca, Bristol-Myers Squibb, Boehringer Ingelheim, Chugai, Merck Sharp & Dohme, Roche; consulting fees from Amgen, AstraZeneca, Bristol-Myers Squibb, Boehringer Ingelheim, Chugai, Merck Sharp & Dohme, Roche; payment or honoraria for lectures, presentations, speakers’ bureaus, manuscript writing or educational events from Amgen, AstraZeneca, Bristol-Myers Squibb, Boehringer Ingelheim, Chugai, Merck Sharp & Dohme, Roche; support for attending meetings and/or travel from Amgen, AstraZeneca, Bristol-Myers Squibb, Boehringer Ingelheim, Chugai, Merck Sharp & Dohme, Roche; participating on an advisory board for Amgen, AstraZeneca, Bristol-Myers Squibb, Boehringer Ingelheim, Chugai, Merck Sharp & Dohme, Roche; equipment, materials, drugs, medical writing, gifts or other services from Boehringer Ingelheim in the context of participation in the VARGADO study. WS reports consulting fees from Boehringer Ingelheim (served in an advisory board and fees paid to the author); payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Boehringer Ingelheim (paid to the author). ID reports payment or honoraria for lectures, presentations, speakers’ bureaus, manuscript writing or educational events from Boehringer Ingelheim Pharma GmbH, Bristol-Myers Squibb GmbH & Co KgaA, Takeda Pharma GmbH, Novartis Pharma GmbH, Pfizer Pharma GmbH, AstraZeneca Pharma GmbH, Merck Sharp & Dohme GmbH; payment for expert testimony, support for attending meetings and/or travel, and participation on a data safety monitoring board or advisory board from Siehe Punkt 5. S Hammerschmidt reports consulting fees from Boehringer Ingelheim; payment or honoraria for lectures, presentations, speakers’ bureaus, manuscript writing or educational events from Boehringer Ingelheim. HMH reports research funding from Roche, Bristol-Myers Squibb, Boehringer Ingelheim, AstraZeneca; honoraria from Roche, Bristol-Myers Squibb, Boehringer Ingelheim, AstraZeneca, Merck Sharp & Dohme, Merck, Eisai, Janssen; consulting fees from Roche, Bristol-Myers Squibb, Boehringer Ingelheim, AstraZeneca, Merck Sharp & Dohme, Merck, Eisai, Janssen; travel support from AstraZeneca, Janssen. CS reports recruitment of patients and manuscript review and approval as support for the present manuscript; honoraria or presentations from AstraZeneca and Bristol-Myers Squibb to institution and to self. S Krüger reports support for the present manuscript from Boehringer Ingelheim; payment or honoraria for lectures, presentations, speakers’ bureaus, manuscript writing or educational events from Boehringer Ingelheim. JA reports employment with Boehringer Ingelheim. R Kaiser reports employment with Boehringer Ingelheim and patent (EP 2994125). TD has no conflicts of interest to declare., (2022 Translational Lung Cancer Research. All rights reserved.)

Aims: To evaluate the efficacy and safety of nintedanib plus docetaxel in patients with advanced adenocarcinoma non-small cell lung cancer (NSCLC) who progressed after chemotherapy and immune checkpoint inhibitor (ICI) therapy., Materials and Methods: VARGADO (NCT02392455) is an ongoing, prospective, non-interventional, real-world study of nintedanib plus docetaxel after first-line chemotherapy in the routine clinical treatment of patients with locally advanced, metastatic or locally recurrent adenocarcinoma NSCLC. Data were collected during routine visits. We report the results from cohort B (n = 80), who received third-line nintedanib plus docetaxel after first-line chemotherapy and second-line ICI therapy., Results: The median duration of follow-up was 12.4 months. Median progression-free survival from initiation of third-line nintedanib plus docetaxel was 6.4 months (95% confidence interval 4.8, 7.3); median overall survival was 12.1 months (95% confidence interval 9.4, 13.5). The 1-year overall survival rate after initiation of third-line nintedanib plus docetaxel treatment (primary end point) was 52% (95% confidence interval 38.0%, 64.4%). Among 64 patients with a documented response, the objective response rate was 50% (n = 32; one complete response and 31 partial responses) and the disease control rate was 86% (n = 55). There were no new safety signals or unexpected toxicities. Among all treated patients, 74% (n = 59) experienced drug-related adverse events, most commonly (nintedanib-related/docetaxel-related) diarrhoea (34%/24%), a decreased white blood cell count (11%/19%) and nausea (13%/16%)., Conclusions: Nintedanib plus docetaxel demonstrated a high response rate and disease stabilisation in the third-line setting after failure of prior chemotherapy and ICI treatment, with a manageable safety profile. These results suggest that nintedanib plus docetaxel represents an efficient treatment option after failure of prior ICIs. The ongoing VARGADO study provides valuable real-world data to inform clinical decision-making regarding treatment sequencing after chemotherapy and ICI failure in patients with adenocarcinoma NSCLC., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Aim: This real-world analysis evaluated docetaxel plus nintedanib in patients with advanced pulmonary adenocarcinoma after chemotherapy and immune checkpoint inhibitor failure, for whom treatment options are limited. Methods: Data were sourced retrospectively from seven German centers. Results: Of 93 patients, overall response rate was 41.4% (disease control rate: 75.9%). Of 57 patients given third-line docetaxel plus nintedanib, overall response rate was 50.0% (disease control rate: 82.7%). Median overall survival following third-line docetaxel plus nintedanib was 8.4 months. Adverse events were consistent with the known safety profile of docetaxel plus nintedanib. Conclusion: To date, this was the largest retrospective, real-world analysis of docetaxel plus nintedanib after chemotherapy-immunotherapy failure, indicating that docetaxel plus nintedanib offers meaningful clinical benefits in this setting.

Aim: To assess outcomes in patients with advanced adenocarcinoma non-small-cell lung cancer who received nintedanib plus docetaxel after progression on prior chemotherapy followed by immune checkpoint inhibitor (ICI) therapy. Patients & methods: VARGADO is a prospective, noninterventional study. We describe initial data from a cohort of 22 patients who received nintedanib plus docetaxel after chemotherapy and ICI therapy. Results: Median progression-free survival with nintedanib plus docetaxel was 5.5 months (95% CI: 1.9-8.7 months). The objective response rate was 7/12 (58%) and the disease control rate was 10/12 (83%). Data for overall survival rate 12 months after the start of treatment (primary end point) are not yet mature and are not reported. Of 22 patients, 73% experienced drug-related adverse events; adverse events led to treatment discontinuation in 32% of patients. Conclusion: These data highlight the potential clinical benefit of nintedanib plus docetaxel in patients who failed prior ICI therapy. Trial registration number: NCT02392455.

Background: Patients with gastric cancer benefit from perioperative chemotherapy, however, treatment is toxic and many patients will relapse. The trifunctional antibody catumaxomab targets EpCAM on tumor cells, CD3 on T cells, and the Fcγ-receptor of antigen-presenting cells. While in Europe catumaxomab is approved for treating malignant ascites, it has not been investigated in the perioperative setting and its exact immunological mode of action is unclear., Methods: In our study, gastric cancer patients received neoadjuvant platinum-based chemotherapy, one intraoperative application of catumaxomab, and 4 postoperative doses of intraperitoneal catumaxomab. Immunomonitoring was performed in 6 patients before surgery, after completion of catumaxomab treatment, and one month later., Results: Intraperitoneal application of catumaxomab caused an increased expression of activation markers on the patients' T cells. This was accompanied by a transient decrease in numbers of CXCR3(+) effector T cells with a T-helper (Th)-1 phenotype in the peripheral blood. All patients evidenced pre-existing EpCAM-specific CD4(+) and/or CD8(+) T cells. While these cells transiently disappeared from the blood stream after intraperitoneal application of catumaxomab, we detected increased numbers of peripheral EpCAM-specific cells and a modified EpCAM-specific T-cell repertoire 4 weeks after completion of treatment. Finally, catumaxomab also amplified humoral immunity to tumor antigens other than EpCAM., Conclusions: Our findings suggest that catumaxomab exerts its clinical effects by (1) activating peripheral T cells, (2) redistributing effector T cells from the blood into peripheral tissues, (3) expanding and shaping of the pre-existing EpCAM-specific T-cell repertoire, and (4) spreading of anti-tumor immunity to different tumor antigens.

Introduction: In patients, a transient decrease in peripheral blood lymphocyte counts was observed following intraperitoneal administration of the trifunctional monoclonal antibody catumaxomab (anti-human EpCAM x anti-human CD3). The aim of this study was to clarify the observed effect in a preclinical mouse model and to analyse the related mechanism of action in vitro., Materials and Methods: A related antibody, BiLu (antihuman EpCAM x anti-mouse CD3), was administered to mice and blood leukocytes were analysed. In vitro studies measured activation and cytokine secretion from human peripheral blood mononuclear cells (PBMC). For the analysis of T cell adhesion, PBMC were preincubated with catumaxomab and then co-cultured with human endothelial cells (HUVEC); T cell adhesion was assessed in the presence or absence of endothelial cell preactivation by TNFα. Adherent T cells were determined by flow cytometry., Results: Treatment of mice with BiLu resulted in a dosedependent transient decrease in CD3+ T cells (both CD4+ and CD8+) that returned to the normal range within 48 h. Catumaxomab physiologically activated T cells in vitro (increased CD69 expression) and induced cytokine release (TNFα, IFNγ). TNFα increased expression of adhesion molecules CD54 and CD62E on endothelial cells. Furthermore, catumaxomab dose-dependently enhanced adhesion of T cells to endothelial cells. Adhesion was further increased when endothelial cells were preactivated with TNFα., Conclusions: Catumaxomab increases adhesion of T cells to endothelial cells due to antibody-mediated activation of T cells and production of T cell cytokines that up-regulate endothelial cell adhesion molecules. These results provide a mechanistic rationale for the transient, reversible decrease in lymphocyte counts observed following catumaxomab administration in patients, which is likely to be due to redistribution of lymphocytes.

BACKGROUND Trifunctional antibodies, such as catumaxomab (anti-EpCAM×anti-CD3) and ertumaxomab (anti- HER-2/neu×anti-CD3), transiently link immune effector cells to tumour cells, which results in cellular cytotoxicity towards the tumour cells. A functional immune system is therefore essential for effective anti-tumour activity. However, the commonly observed haematotoxicity of chemotherapeutics and radiation therapy may be associated with some degree of immunosuppression. Combining chemotherapy and trifunctional antibodies in cancer treatment requires understanding of the impact of chemotherapeutics on immune cell function and, thus, on the activity of trifunctional antibodies. METHODS The effect of chemotherapeutic treatment on trifunctional antibody-mediated anti-tumour activity was assessed in vitro. Blood samples were collected from 12 head and neck squamous cell carcinoma patients after chemotherapy (5-fluorouracil, cisplatin) and radiotherapy, and from one healthy control donor. The immune cell status was analysed and mononuclear cells (MNC) were isolated. The potency of catumaxomab and ertumaxomab was assessed in a cytotoxicity assay using MNC isolated from each patient sample in co-culture with a tumour target cell line. The release of infl ammatory cytokines was also monitored in the cell culture supernatant. RESULTS Most patients included in this study had decreased immune cell counts during the course of chemotherapy. Nonetheless, an effective and concentration-dependent anti- tumour activity mediated by trifunctional antibodies was demonstrated using these patient immune effector cells. The immune response activity of the patient immune cells was not impaired one week after cisplatin administration or even three days after the last 5-fluorouracil treatment. CONCLUSION This study shows for the first time that immune effector cells from cancer patients undergoing standard chemotherapy and radiotherapy can be activated by trifunctional antibodies for efficient killing of tumour cells.

Monoclonal antibodies such as rituximab and alemtuzumab show considerable therapeutic efficacy in chronic lymphocytic leukaemia (CLL). Aiming to further improve antineoplastic efficacy, the trifunctional bispecific antibody FBTA05 was developed. FBTA05 is thought to function by simultaneously binding B cells and T cells by its variable regions and by recruiting FcγR-positive accessory immune cells by its intact Fc region. As it was previously shown that this antibody shows considerable cytotoxicity towards a spectrum of B-cell lymphoma cell lines, we here tested its potential efficacy ex vivo against malignant B-CLL cells. Therefore, we assessed the capacity of increasing concentrations of FBTA05 to bind to neoplastic cells, to induce cytotoxicity (comparing it with rituximab and alemtuzumab) and cytokine release. We evaluated the results with respect to the extent of CD20 expression, the effector:target cell ratio as well as with the patients' overall effector cell status. Thus, we show that, although FBTA05-elicited cytotoxicity was comparable with that induced by alemtuzumab, it considerably exceeded the antineoplastic effects of rituximab. Noteworthy, FBTA05 shows effective elimination of malignant B cells even if CD20 surface expression is low. Importantly, a high grade of cytotoxicity was associated with the induction of T-cell proliferation and the concomittant release of interferon-γ and interleukin-6, thus overcoming the detrimental effects of an unfavourable effector:target cell ratio. In conclusion, we here present novel evidence for the therapeutic efficacy of the trifunctional, bispecific antibody FBTA05 in CLL and provide evidence for the importance of immune-mediated mechanisms conveying the cytotoxic effects against malignant B lymphocytes.

Background: Catumaxomab is an antibody that binds with one arm epithelial cell adhesion molecule (EpCAM) positive tumors and with the other arm CD3+ T cells. Intravenous application of therapeutic antibodies may result in intravascular cytokine release., Aim: In this pilot trial we assessed whether cytokine release can be controlled by ex vivo cell opsonization and cytokine wash-out before administration of catumaxomab, preserving its anti-cancer activity. In addition, preliminary data on safety of and clinical response to catumaxomab coated autologous immune cells were acquired., Methods: Peripheral blood mononuclear cells (PBMNC) of four patients with recurrent head and neck carcinoma were collected by leukapheresis, incubated ex vivo with catumaxomab for 24 h and cleared from released cytokines. Each patient received an escalated number of antibody-coated PBMNC equivalent to 1 x 10(4), 1 x 10(5), 1 x 10(6) and 1 x 10(7) CD3(+) cells/kgBW intravenously at bi-weekly intervals., Results: After opsonization, PBMNC released substantial amounts of interferon gamma (IFNgamma) and tumor necrosis factor alpha (TNFalpha) in vitro, which were removed before administration. Catumaxomab up-regulated CD25, CD69, and CD83 on PBMNC, and catumaxomab loaded PBMNC released IFNgamma and granzyme B when coincubated with EpCAM(+) BHY cells, suggesting cell activation and target directed biological activity. During the study period, one patient died of aspiration pneumonia and one patient needed a tracheotomy. Treatment related adverse events (AE) occurred at the highest cell dose in two patients, whereas 1 x 10(6) loaded CD3(+) cells/kgBW were well tolerated by all patients. One patient showed stable disease for 6 months and one patient is in complete remission for 27 months., Conclusion: Ex vivo opsonization of PBMNC with catumaxomab provided biologically active, tumor targeting cells. Extracorporeal PBMNC coating may be an option to control intravascular cytokine release induced by therapeutic antibodies.

Epithelial cell adhesion molecule EpCAM is a transmembrane glycoprotein that is frequently overexpressed in a variety of carcinomas. This pan-carcinoma antigen has served as the target for a plethora of immunotherapies. Innovative therapeutic approaches include the use of trifunctional antibodies (trAbs) that recruit and activate different types of immune effector cells at the tumour site. The trAb catumaxomab has dual specificity for EpCAM and CD3. In patients with malignant ascites, catumaxomab significantly increased the paracentesis-free interval, corroborating the high efficacy of this therapeutic antibody. Here, we characterised the monoclonal antibody (mAb) HO-3, that is, the EpCAM-binding arm of catumaxomab. Peptide mapping indicated that HO-3 recognises a discontinuous epitope, having three binding sites in the extracellular region of EpCAM. Studies with glycosylation-deficient mutants showed that mAb HO-3 recognised EpCAM independently of its glycosylation status. High-affinity binding was not only detected for mAb HO-3, but also for the monovalent EpCAM-binding arm of catumaxomab with an excellent K(D) of 5.6 x 10(-10) M. Furthermore, trAb catumaxomab was at least a 1000-fold more effective in eliciting the eradication of tumour cells by effector peripheral blood mononuclear cells compared with mAb HO-3. These findings suggest the great therapeutic potential of trAbs and clearly speak in favour of EpCAM-directed cancer immunotherapies.

Mutations that affect the oligomerization domain (OD) of the p53 tumor suppressor may be of particular interest because of the remarkable contradiction between the conservation of the OD and its relative functional resistance to amino acid substitutions, and because of recent hints that cellular protein factors may interact with the OD. Both point to the possibility that this domain fulfills tasks beyond oligomerization. We report that the tumor-associated mutants 330H, 334V, and 337C are defective for homo-oligomerization by three criteria. Accordingly, 330H and 337C failed to bind to a p53 recognition motif in gel-shift assays and to stimulate reporter genes efficiently in transient transfections. 334V retained some activity in both assays despite being oligomerization-defective. The ability of the mutants to induce apoptosis correlated with their performance in the DNA binding and transactivation assays. However, mutants 330H and 337C were able to provoke cell death when overexpressed, which in combination with their failure to transactivate genes suggests competence for the induction of transactivation-independent apoptosis at high protein levels. Although 334V and 337C failed to homo-oligomerize, they were able to hetero-oligomerize with a p53 with wild-type OD, and 334V was able to interfere with transactivation by wt p53. All mutants showed a reduced reactivity with antibody PAb421 and a distinct calpain cleavage pattern indicative of conformational alterations. In conclusion, tumor-associated OD mutants of p53 can be functionally competent to different degrees despite of being oligomerization defective., (Copyright 2000 Wiley-Liss, Inc.)

The Epstein-Barr virus-encoded nuclear antigens EBNA2 and EBNA3C both interact with the cellular transcription factor RBP-Jkappa and modulate the expression of several shared target genes, suggesting a tight cooperation in latently infected cells. In a survey for additional cellular factors that bind to EBNA2 as well as EBNA3C, we have isolated and characterized DP103, a novel human member of the DEAD box family of putative ATP-dependent RNA helicases. The interaction with DP103 is mediated by amino acids (aa) 121-213 of EBNA2 and aa 534-778 of EBNA3C, regions that are not involved in binding of the viral proteins to RBP-Jkappa. The DP103-cDNA encodes a protein of 824 aa that harbors all of the common DEAD box motifs. Monoclonal antibodies raised against DP103 detect a protein of 103 kDa in mammalian cells that resides in high molecular weight complexes in vivo. We have detected an ATPase activity intrinsic to or closely associated with DP103. By subcellular fractionation, we find DP103 in both a soluble nuclear fraction as well as in the insoluble skeletal fraction. Whereas the protein and its mRNA are uniformly expressed in all tested cell lines, we observed differential expression of the mRNA in normal human tissues.

p53-mediated programmed cell death (PMCD) often requires an intact transactivation domain of the p53 tumor suppressor and is therefore usually interpreted to rely upon the transactivation of genes. As a notable exception, murine GHFT1 cells have been documented to perish in a p53-dependent manner even in the presence of transcription inhibitor actinomycin D (Act D) and have since served as one model system for transactivation-independent apoptosis. We report here that p53 transactivation domain mutant Q22,S23 nonetheless fails to mediate apoptosis in these cells as efficiently as wild-type p53. This suggests that some function of the NH2-terminal domain other than the transactivation of genes supports PMCD of GHFT1 cells. To substantiate this suggestion, we employed a p53 whose transactivation domain had been replaced with the one of VP16, which acts through the same elements of the basal transcription machinery. Although the hybrid was fully competent for transactivation, it was impaired for the mediation of apoptosis to the same extent as mutant Q22,S23. Thus, a function of the transactivation domain other than the binding to the transcription co-activators hTAF(II)31 and 70 is required for the efficient induction of apoptosis in GHFT1 cells.

Our objectives were to describe the ultrastructural morphogenesis of pulmonary lesions induced by 3-methylindole in 30- to 45-day-old Holstein calves and to determine whether toxic exposure to 3-methylindole exacerbates pulmonary lesions induced by bovine respiratory syncytial virus. Administration of 3-methylindole (0.25 g/kg) to calves resulted in interstitial edema and ultrastructural swelling of type-I alveolar epithelial cells and nonciliated bronchiolar epithelial cells as early as 4 to 6 hours after intraruminal administration. More severe alveolar edema containing protein was associated with swelling of capillary endothelial cells at 2 days after administration. Proliferation of type-II alveolar epithelial cells was first observed at 2 days after 3-methylindole administration, and marked hyperplasia of type-II epithelial cells and nonciliated bronchiolar epithelial cells was evident by 4 days after administration. Pulmonary cytochrome P-450 monooxygenase concentrations decreased significantly (P less than 0.001) by 12 hours after administration and did not increase significantly again by 8 days after administration. Calves were inoculated with bovine respiratory syncytial virus 3 days after administration of 3-methylindole, and pulmonary lesions were assessed 5 days after viral inoculation. Viral replication was demonstrated by fluorescence microscopy for viral antigen or by transmission electron microscopy in ciliated and nonciliated airway epithelial cells. Viral antigen was identified infrequently in alveolar macrophages and in type-II alveolar epithelial cells. 3-Methylindole exposure in calves did not result in more widespread distribution of viral antigen in alveolar tissue of respiratory syncytial virus-inoculated calves or in significant enhancement of viral pneumonia.(ABSTRACT TRUNCATED AT 250 WORDS)