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Summary Background PD-1 and PD-L1 inhibitors are active in metastatic urothelial carcinoma, but positive randomised data supporting their use as a first-line treatment are lacking. In this study we assessed outcomes with first-line pembrolizumab alone or combined with chemotherapy versus chemotherapy for patients with previously untreated advanced urothelial carcinoma. Methods KEYNOTE-361 is a randomised, open-label, phase 3 trial of patients aged at least 18 years, with untreated, locally advanced, unresectable, or metastatic urothelial carcinoma, with an Eastern Cooperative Oncology Group performance status of up to 2. Eligible patients were enrolled from 201 medical centres in 21 countries and randomly allocated (1:1:1) via an interactive voice-web response system to intravenous pembrolizumab 200 mg every 3 weeks for a maximum of 35 cycles plus intravenous chemotherapy (gemcitabine [1000 mg/m2] on days 1 and 8 and investigator's choice of cisplatin [70 mg/m2] or carboplatin [area under the curve 5] on day 1 of every 3-week cycle) for a maximum of six cycles, pembrolizumab alone, or chemotherapy alone, stratified by choice of platinum therapy and PD-L1 combined positive score (CPS). Neither patients nor investigators were masked to the treatment assignment or CPS. At protocol-specified final analysis, sequential hypothesis testing began with superiority of pembrolizumab plus chemotherapy versus chemotherapy alone in the total population (all patients randomly allocated to a treatment) for the dual primary endpoints of progression-free survival (p value boundary 0·0019), assessed by masked, independent central review, and overall survival (p value boundary 0·0142), followed by non-inferiority and superiority of overall survival for pembrolizumab versus chemotherapy in the patient population with CPS of at least 10 and in the total population (also a primary endpoint). Safety was assessed in the as-treated population (all patients who received at least one dose of study treatment). This study is completed and is no longer enrolling patients, and is registered at ClinicalTrials.gov , number NCT02853305 . Findings Between Oct 19, 2016 and June 29, 2018, 1010 patients were enrolled and allocated to receive pembrolizumab plus chemotherapy (n=351), pembrolizumab monotherapy (n=307), or chemotherapy alone (n=352). Median follow-up was 31·7 months (IQR 27·7–36·0). Pembrolizumab plus chemotherapy versus chemotherapy did not significantly improve progression-free survival, with a median progression-free survival of 8·3 months (95% CI 7·5–8·5) in the pembrolizumab plus chemotherapy group versus 7·1 months (6·4–7·9) in the chemotherapy group (hazard ratio [HR] 0·78, 95% CI 0·65–0·93; p=0·0033), or overall survival, with a median overall survival of 17·0 months (14·5–19·5) in the pembrolizumab plus chemotherapy group versus 14·3 months (12·3–16·7) in the chemotherapy group (0·86, 0·72–1·02; p=0·0407). No further formal statistical hypothesis testing was done. In analyses of overall survival with pembrolizumab versus chemotherapy (now exploratory based on hierarchical statistical testing), overall survival was similar between these treatment groups, both in the total population (15·6 months [95% CI 12·1–17·9] with pembrolizumab vs 14·3 months [12·3–16·7] with chemotherapy; HR 0·92, 95% CI 0·77–1·11) and the population with CPS of at least 10 (16·1 months [13·6–19·9] with pembrolizumab vs 15·2 months [11·6–23·3] with chemotherapy; 1·01, 0·77–1·32). The most common grade 3 or 4 adverse event attributed to study treatment was anaemia with pembrolizumab plus chemotherapy (104 [30%] of 349 patients) or chemotherapy alone (112 [33%] of 342 patients), and diarrhoea, fatigue, and hyponatraemia (each affecting four [1%] of 302 patients) with pembrolizumab alone. Six (1%) of 1010 patients died due to an adverse event attributed to study treatment; two patients in each treatment group. One each occurred due to cardiac arrest and device-related sepsis in the pembrolizumab plus chemotherapy group, one each due to cardiac failure and malignant neoplasm progression in the pembrolizumab group, and one each due to myocardial infarction and ischaemic colitis in the chemotherapy group. Interpretation The addition of pembrolizumab to first-line platinum-based chemotherapy did not significantly improve efficacy and should not be widely adopted for treatment of advanced urothelial carcinoma. Funding Merck Sharp and Dohme, a subsidiary of Merck, Kenilworth, NJ, USA.

PURPOSE Pembrolizumab, a programmed death 1 inhibitor, demonstrated promising single-agent activity in untreated patients with various cancer types. The phase II KEYNOTE-427 study evaluated efficacy and safety of single-agent pembrolizumab in treatment-naive patients with advanced clear cell renal cell carcinoma (ccRCC; cohort A) and advanced non-ccRCC (cohort B). Results of cohort A are reported. METHODS In this open-label, single-arm phase II study, patients with advanced ccRCC received pembrolizumab 200 mg every 3 weeks for ≤ 24 months. The primary end point was objective response rate by RECIST, version 1.1. RESULTS In the total population (N = 110), median time from enrollment to data cutoff was 35.9 (range, 29.5-40.3) months. Objective response rate was 36.4% with four (3.6%) complete responses and 36 (32.7%) partial responses; disease control rate was 58.2% (95% CI, 48.4 to 67.5). Most patients (68.2%) had a decrease in target lesions, including 30.9% with a reduction ≥ 60%. Median duration of response was 18.9 (range, 2.3-37.6+) months; 64.1% of responders had a response ≥ 12 months (Kaplan-Meier). Median progression-free survival was 7.1 months (95% CI, 5.6 to 11.0). Median overall survival was not reached; 12-month and 24-month overall survival rates were 88.2% and 70.8%, respectively. Durable responses were observed across all International Metastatic RCC Database Consortium categories. Grade 3-5 treatment-related adverse events were reported in 30.0% of patients, of which colitis and diarrhea were most frequent. CONCLUSION Single-agent pembrolizumab showed promising antitumor activity as a first-line treatment in patients with advanced ccRCC, with durable responses across International Metastatic RCC Database Consortium categories. Safety and tolerability profile of pembrolizumab monotherapy was comparable to what has been previously described in other tumor types.

PURPOSE Patients with advanced endometrial carcinoma have limited treatment options. We report final primary efficacy analysis results for a patient cohort with advanced endometrial carcinoma receiving lenvatinib plus pembrolizumab in an ongoing phase Ib/II study of selected solid tumors. METHODS Patients took lenvatinib 20 mg once daily orally plus pembrolizumab 200 mg intravenously once every 3 weeks, in 3-week cycles. The primary end point was objective response rate (ORR) at 24 weeks (ORRWk24); secondary efficacy end points included duration of response (DOR), progression-free survival (PFS), and overall survival (OS). Tumor assessments were evaluated by investigators per immune-related RECIST. RESULTS At data cutoff, 108 patients with previously treated endometrial carcinoma were enrolled, with a median follow-up of 18.7 months. The ORRWk24 was 38.0% (95% CI, 28.8% to 47.8%). Among subgroups, the ORRWk24 (95% CI) was 63.6% (30.8% to 89.1%) in patients with microsatellite instability (MSI)–high tumors (n = 11) and 36.2% (26.5% to 46.7%) in patients with microsatellite-stable tumors (n = 94). For previously treated patients, regardless of tumor MSI status, the median DOR was 21.2 months (95% CI, 7.6 months to not estimable), median PFS was 7.4 months (95% CI, 5.3 to 8.7 months), and median OS was 16.7 months (15.0 months to not estimable). Grade 3 or 4 treatment-related adverse events occurred in 83/124 (66.9%) patients. CONCLUSION Lenvatinib plus pembrolizumab showed promising antitumor activity in patients with advanced endometrial carcinoma who have experienced disease progression after prior systemic therapy, regardless of tumor MSI status. The combination therapy had a manageable toxicity profile.

e16542 Background: Immune checkpoint inhibitors (ICIs) are commonly used as first-line treatment for pts with advanced RCC. In the recent phase 3 CLEAR trial, LEN + PEMBRO showed improved objective response rate (ORR), progression-free survival (PFS), and overall survival (OS) vs sunitinib in first-line treatment of advanced RCC (Motzer R et al. NEJM. 2021). Additional treatment options are needed for pts with disease progression on ICIs. A phase 1b trial of LEN + PEMBRO was performed in multiple tumor types and included an expansion part into a phase 2 cohort of ICI-pretreated, treatment-naïve, or previously treated ICI-naïve pts with metastatic RCC (NCT02501096). We report the final results of the RCC cohort with an extended follow-up. Methods: Eligible pts were ≥18 years old and had measurable disease. Efficacy analyses were conducted by prior therapy grouping. The primary endpoint was ORR at week 24 (ORRwk24) per immune-related (ir) RECIST by investigator assessment. Secondary endpoints included ORR, duration of response (DOR), PFS, OS, and safety. Exploratory endpoints included tumor response assessed per RECIST v1.1 by independent review committee (IRC). Subgroup analyses of the ICI-pretreated group will be included in the poster. Results: The recommended doses determined in phase 1b were LEN 20 mg daily + PEMBRO 200 mg once every 3 weeks (Taylor M et al. JCO. 2020). The study enrolled 145 pts (efficacy analysis, n=143; safety analysis, n=145). At data cutoff (August 18, 2020), the median follow-up time was 19.8 months. The ORRwk24 was 55.8% (95% CI 45.7–65.5) for ICI-pretreated pts (n=104), 72.7% (95% CI 49.8–89.3) for treatment-naïve pts (n=22), and 41.2% (95% CI 18.4–67.1) for previously treated ICI-naïve pts (n=17). The median OS for the previously treated ICI-naïve pts was 30.3 months and was not reached in the other groups. Additional efficacy analyses are shown in the table. Treatment-related adverse events occurred in 99.3% of pts; the most common were fatigue (58.6%), diarrhea (55.2%), and hypertension (40.0%). Most pts (69%) maintained the LEN starting dose or were reduced to LEN 14 mg daily (dose level −1). Conclusions: LEN + PEMBRO demonstrated promising antitumor activity with a manageable safety profile in pts with metastatic RCC, including pts who were ICI-pretreated. Clinical trial information: NCT02501096. [Table: see text]

6083 Background: As part of an ongoing phase Ib/II study (NCT02501096) in patients (pts) with selected solid tumors, LEN (20 mg PO QD) + PEMBRO (200 mg IV Q3W) displayed substantial and durable antitumor activity in advanced EC. In previously treated EC that was not microsatellite instability high (MSI-H) or mismatch repair deficient (dMMR; n=94 pts), the objective response rate (ORR) by independent imaging review (IIR) per RECIST 1.1 was 38.3% (95% CI 28.5–48.9). In this post hoc analysis, we assessed 2 subgroups of pts with previously treated, advanced, non MSI-H or dMMR EC who received LEN + PEMBRO in an early-treatment setting. Methods: Pts were examined in 2 subgroups: (1) Pts with only 1 prior line of cytotoxic therapy regardless of surgical stage or setting (adjuvant treatment for local-regional disease or treatment for metastatic disease); and (2) pts from subgroup 1 with local-regional disease at diagnosis who received only adjuvant cytotoxic therapy. There were no restrictions on prior hormonal or chemoradiation therapies in either subgroup. Tumor responses were assessed by IIR per RECIST 1.1. Results: Subgroup 1 included 63 pts and subgroup 2 had 21 pts. ORR (95% CI) was 41.3% (29.0–54.4) for subgroup 1 and 57.1% (34.0–78.2) for subgroup 2. Additional efficacy outcomes are summarized in the table. In subgroup 1, treatment-related adverse events (TRAEs) occurred in 62 (98%) pts (42 [67%] ≥ grade 3). TRAEs led to study-drug interruption of one or both drugs in 43 (68%) pts and dose reductions of LEN in 42 (67%) pts; 12 (19%) pts discontinued one or both drugs due to a TRAE. Serious TRAEs occurred in 18 (29%) pts and 2 (3%) pts died from a TRAE. The safety profile for subgroup 2 was generally similar to the profile for subgroup 1. Conclusions: The efficacy of LEN + PEMBRO for early-line treatment of advanced non MSI-H or dMMR EC appears promising. No new safety signals have emerged. A phase III study of LEN + PEMBRO vs paclitaxel + carboplatin for first-line treatment in advanced or recurrent EC is underway. Clinical trial information: NCT02501096. [Table: see text]

Background LEN is a multikinase inhibitor of VEGFR 1–3, FGFR 1–4, PDGFRα, RET, and KIT. PEMBRO is an anti-PD-1 antibody. We report final results of a cohort of patients (pts) with metastatic EC (data cutoff, Jan. 10, 2019) as part of an ongoing phase 1b/2 study evaluating LEN + PEMBRO in pts with selected solid tumours. Methods In this cohort of a multicenter, open-label study, pts with histologically confirmed metastatic EC and measurable disease who received ≤2 prior chemotherapies (unless discussed with the sponsor) were administered LEN (20 mg PO QD) plus PEMBRO (200 mg IV Q3W). Tumour assessments for the primary phase 2 endpoint (objective response rate at 24 weeks [ORRWK24]) and secondary endpoints were evaluated by investigators per immune-related (ir)RECIST. Secondary endpoints included ORR, progression-free survival, overall survival, and duration of response. Tumour responses were also assessed by independent imaging reviewers per irRECIST, RECIST 1.1, and modified RECIST 1.1, and by investigators per mRECIST 1.1. Results At data cutoff, 108 pts with previously treated (1 regimen: 53%; >1 regimen: 47%) EC (endometrioid: 51%; serous: 32%; FIGO grade 3: 70%) were enrolled and had a median follow-up of 18.7 months. 13% of pts had high microsatellite instability (MSI-H) or mismatch-repair deficient (dMMR) status. Efficacy outcomes are summarized in the table. Treatment-related adverse events (TRAEs) occurred in 105 (97%) pts (97 [90%] ≤ grade 3, 8 [7%] ≥ grade 4). TRAEs led to study-drug interruption of one or both drugs in 78 (72%) pts and dose reductions of LEN in 70 (65%) pts; 20 (19%) pts discontinued one or both drugs due to a TRAE. The most common ≥ grade 3 TRAEs were hypertension (32%), fatigue (8%), and diarrhea (7%). Conclusions The LEN + PEMBRO combination showed promising antitumor activity in metastatic EC regardless of MSI/MMR status. Treatment was generally well tolerated, and no new safety signals emerged. A phase 3 study in advanced EC is underway (NCT03517449). Table: 994O . Investigator assessment per irRECIST Previously treated EC Total (N = 108) Not MSI-H or dMMR (n = 94) MSI-H/dMMR (n = 11) ORRWK24, n (%) 95% CI 41 (38.0) 28.8–47.8 34 (36.2) 26.5–46.7 7 (63.6) 30.8–89.1 ORR, n (%) (95% CI) Complete response Partial response 42 (38.9) 29.7–48.7 8 (7.4) 34 (31.5) 35 (37.2) 27.5–47.8 7 (7.4) 28 (29.8) 7 (63.6) 30.8–89.1 1 (9.1) 6 (54.5) Median duration of response, months (95% CI) 21.2 (7.6–NR) NE (7.4–NR) 21.2 (7.3–NR) Kaplan-Meier estimate of duration of response ≥6 months, a n Probability (95% CI) 32 0.87 (0.72–0.95) 25 0.85 (0.67–0.93) 7 1.00 (NR–NR) Median progression-free survival, months (95% CI) 7.4 (5.3–8.7) 7.4 (5.0–7.6) 18.9 (4.0–NR) Median overall survival, months (95% CI) 16.7 (15.0–NR) 16.4 (13.5–25.9) NR (7.4–NR) Time to response (months), mean (SD) 2.6 (1.6) 2.5 (1.5) 2.9 (1.8) a Probabilities of patients achieving a duration of response ≥6 months were calculated using the Kaplan-Meier product-limit method and Greenwood formula. CI, confidence interval; dMMR, mismatch repair deficient; NR, not reached; SD, standard deviation. Clinical trial identification NCT02501096. Editorial acknowledgement Jeffrey K. Bratz, PhD of Oxford PharmaGenesis, Newtown, PA was funded by Eisai Inc. Legal entity responsible for the study Eisai Inc. Funding Eisai Inc. and Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA. Disclosure V. Makker: Non-remunerated activity/ies: AstraZeneca; Honoraria (self), Non-remunerated activity/ies: Eisai; Honoraria (self), Non-remunerated activity/ies: Merck; Non-remunerated activity/ies: Lilly; Honoraria (self), Non-remunerated activity/ies: Karyopharm; Honoraria (self), Non-remunerated activity/ies: Takeda; Non-remunerated activity/ies: Genentech. M.H. Taylor: Research grant / Funding (institution): BioAlta; Honoraria (self), Advisory / Consultancy, Speaker Bureau / Expert testimony, Travel / Accommodation / Expenses: Bristol-Myers Squibb; Honoraria (self), Advisory / Consultancy, Travel / Accommodation / Expenses: Array Biopharma; Honoraria (self), Advisory / Consultancy, Speaker Bureau / Expert testimony, Travel / Accommodation / Expenses: Eisai; Honoraria (self), Travel / Accommodation / Expenses: Bayer; Honoraria (self), Advisory / Consultancy, Travel / Accommodation / Expenses: LOXO; Honoraria (self), Advisory / Consultancy, Travel / Accommodation / Expenses: Blueprint; Honoraria (self), Advisory / Consultancy: Arquele; Honoraria (self), Advisory / Consultancy: Novartis. C. Aghajanian: Advisory / Consultancy: Tesaro; Advisory / Consultancy: Immunogen; Advisory / Consultancy, Research grant / Funding (self): Clovis; Honoraria (self): Mateon Therapeutics; Advisory / Consultancy: Cerulean Pharma; Research grant / Funding (self): Genentech. A. Oaknin: Travel / Accommodation / Expenses: Roche; Travel / Accommodation / Expenses: AstraZeneca; Research grant / Funding (institution), Travel / Accommodation / Expenses: PharmaMar; Research grant / Funding (institution), Travel / Accommodation / Expenses: Clovis Oncology; Honoraria (self), Research grant / Funding (institution): Tesaro; Honoraria (self), Research grant / Funding (institution): Immunogen; Research grant / Funding (institution): Eisai Ltd.; Research grant / Funding (institution): Merck Sharp & Dohme de Espana SA; Honoraria (self): Genmab; Research grant / Funding (institution): AbbVie Deutschland; Research grant / Funding (institution): Millennium Pharma; Research grant / Funding (institution): Regeneron Pharmaceuticals; Research grant / Funding (institution): Ability Pharmaceuticals; Research grant / Funding (institution): Advaxis Inc; Research grant / Funding (institution): Aeterna Zentaris; Research grant / Funding (institution): Amgen SA; Research grant / Funding (institution): Aprea Therapeutics AB; Research grant / Funding (institution): F. Hoffman - La Roche Ltd. M. Romeo Marin: Advisory / Consultancy: Tesoro; Advisory / Consultancy, Non-remunerated activity/ies: Roche; Speaker Bureau / Expert testimony: AstraZeneca. M.S. Brose: Honoraria (self): Eisai. D.E. Stepan: Full / Part-time employment: Formerly of Eisai Inc. C.E. Dutcus: Leadership role, Full / Part-time employment: Eisai Inc. J. Wu: Full / Part-time employment: Eisai Inc. E.V. Schmidt: Full / Part-time employment: Merck & Co Inc. R.J. Orlowski: Full / Part-time employment: Merck & Co Inc. P. Sachdev: Full / Part-time employment: Eisai Inc. R. Shumaker: Full / Part-time employment: Eisai Inc. A. Casado Herraez: Research grant / Funding (institution), Travel / Accommodation / Expenses: PharmaMar. All other authors have declared no conflicts of interest.

16 Background: Lenvatinib (LEN) is a multikinase inhibitor of VEGFR 1−3, FGFR 1−4, PDGFRα, RET, and KIT. Pembrolizumab (PEM), an anti-PD-1 antibody, is an approved monotherapy for previously treated patients (pts) with PD-L1 (+) (tumor proportion score ≥1%) metastatic non-small cell lung cancer (mNSCLC; objective response rate [ORR] 18%). We report interim results of an ongoing phase 1b/2 trial of LEN + PEM in pts with solid tumors, focusing on the mNSCLC cohort. Methods: In this multicenter, open-label study (NCT02501096), pts with measurable, confirmed mNSCLC, ECOG PS ≤1, ≤ 2 prior systemic therapies (phase 2 only) received oral LEN (20 mg/day) and PEM (200 mg Q3W, IV). Pts were not preselected by PD-L1 status. The phase 2 primary end point was ORR at 24 weeks (ORRWK24) by investigator-assessed immune-related RECIST (irRECIST). Secondary end points included ORR, progression-free survival (PFS) and duration of response (DOR). Results: At data cutoff (March 1, 2018), 21 pts were enrolled: 9 (43%) PD-L1(+), 5 (24%) PD-L1(-), and 7 (33%) not tested. Pts were treatment-naïve (14%); or had 1 (33%), 2 (48%), or ≥3 (5%) prior lines of systemic therapy. ORRWK24 was 33.3% (95% CI, 14.6–57.0); other efficacy outcomes are summarized in the table. Grade 3 and 4 treatment-related adverse events (TRAEs) occurred in 48% and 5% (increased aspartate aminotransferase) of pts. There was 1 fatal TRAE (exsanguination; “possibly related” to study treatment). The most common grade 3 TRAEs were hypertension (24%), fatigue (14%), diarrhea (14%), proteinuria (10%), and arthralgia (10%). Conclusions: LEN + PEM showed promising clinical activity and a manageable safety profile in previously treated pts with mNSCLC who were not preselected for PD-L1 status. Further study is warranted.[Table: see text]

11 Background: Pembrolizumab (PEM), an anti-PD-1 antibody, is approved for advanced urothelial cancer in the second-line setting (objective response rate [ORR] 21%) and in the first-line setting for patients (pts) ineligible for cisplatin with combined positive score ≥10 or ineligible for platinum-based chemotherapy (ORR 29%). Tyrosine kinase inhibitors such as lenvatinib (LEN; a multikinase inhibitor of VEGFR 1-3, FGFR 1-3, PDGFRα, RET and KIT) have demonstrated activity in urothelial cancer and may reverse the immunosuppressive environment that leads to immuno-oncology (IO) failure. We present a phase 1b/2 trial of LEN + PEM in advanced urothelial cancer. Methods: In this multicenter, open-label study, pts with confirmed metastatic urothelial cancer and ECOG PS of 0 or 1 received oral LEN 20 mg/day + PEM (200 mg Q3W, IV). Pts were not preselected for PD-L1 status. The phase 2 primary end point was investigator-assessed ORR at week 24 (ORRwk24) per immune-related RECIST (irRECIST). Secondary end points included ORR, duration of response (DOR), and progression-free survival (PFS). Results: At data cutoff (March 1, 2018), 20 pts were enrolled: 9 (45%) PD-L1(+), 5 (25%) PD-L1(-); 6 (30%) not tested. 4 Pts (20%) were treatment-naïve; 11 (55%) and 5 (25%) pts had had 1 and 2 lines of prior anticancer therapies, respectively. No pt had received prior IO. ORRwk24 was 25% (95% CI: 8.7–49.1). 18 (90%) pts had ≥1 treatment-related adverse event (TRAE). Grade 3 and 4 TRAEs occurred in 5 (25%) and 5 (25%) pts, respectively. There was 1 fatal TRAE (gastrointestinal hemorrhage). The most common any-grade TRAEs were proteinuria (45%), diarrhea (40%), fatigue (30%), hypertension (30%), and hypothyroidism (30%). Conclusions: LEN + PEM demonstrated activity in this study of pts with advanced urothelial cancer, which included pts receiving later-line treatment, and deserves further investigation. Clinical trial information: NCT02501096. [Table: see text]

Recent studies of viral entry proteins from influenza, measles, human immunodeficiency virus, type 1 (HIV-1), and Ebola virus have shown, first with molecular modeling, and then X-ray crystallographic or other biophysical studies, that these disparate viruses share a coiled-coil type of entry protein. Structural models of the transmembrane glycoproteins (GP-2) of the Arenaviruses, lymphochoriomeningitis virus (LCMV) and Lassa fever virus, are presented, based on consistent structural propensities despite variation in the amino acid sequence. The principal features of the model, a hydrophobic amino terminus, and two antiparallel helices separated by a glycosylated, antigenic apex, are common to a number of otherwise disparate families of enveloped RNA viruses. Within the first amphipathic helix, demonstrable by circular dichroism of a peptide fragment, there is a highly conserved heptad repeat pattern proposed to mediate multimerization by coiled-coil interactions. The amino terminal 18 amino acids are 28% identical and 50% highly similar to the corresponding region of Ebola, a member of the Filovirus family. Within the second, charged helix just prior to membrane insertion there is also high similarity over the central 18 amino acids in corresponding regions of Lassa and Ebola, which may be further related to the similar region of HIV-1 defining a potent antiviral peptide analogue. These findings indicate a common pattern of structure and function among viral transmembrane fusion proteins from a number of virus families. Such a pattern may define a viral transmembrane superfamily that evolved from a common precursor eons ago.