Immunogenicity and Efficacy of TNX-1800, A Live Virus Recombinant Poxvirus Vaccine Candidate, against SARS-CoV-2 Challenge in Nonhuman Primates

TNX-1800 is a synthetically derived live recombinant chimeric horsepox virus (rcHPXV) vaccine candidate expressing Wuhan SARS-CoV-2 spike (S) protein. The primary objective of this study was to evaluate the immunogenicity and efficacy of TNX-1800 in two nonhuman primate species challenged with USA-WA1/2020 SARS-CoV-2. TNX-1800 vaccination was well tolerated with no serious adverse events or significant changes in clinical parameters. A single dose of TNX-1800 generated humoral responses in African Green Monkeys and Cynomolgus Macaques, as measured by the total binding of anti-SARS-CoV-2 S IgG and neutralizing antibody titers against the USA-WA1/2020 strain. In addition, a single dose of TNX-1800 induced an interferon-gamma (IFN-γ)-mediated T-cell response in Cynomolgus Macaques. Following challenge with SARS-CoV-2, African Green and Cynomolgus Macaques exhibited rapid clearance of virus in the upper and lower respiratory tract. Future studies will assess the efficacy of TNX-1800 against newly emerging variants and demonstrate its safety in humans.

TNX-1500, a crystallizable fragment-modified anti-CD154 antibody, prolongs nonhuman primate renal allograft survival

The blockade of the CD154-CD40 pathway with anti-CD154 monoclonal antibody has been a promising immunomodulatory approach to prevent allograft rejection. However, clinical trials of immunoglobulin G1 antibodies targeting this pathway revealed thrombogenic properties, which were subsequently shown to be mediated by crystallizable fragment (Fc)-gamma receptor IIa-dependent platelet activation. To prevent thromboembolic complications, an immunoglobulin G4 anti-CD154 monoclonal antibody, TNX-1500, which retains the fragment antigen binding region of ruplizumab (humanized 5c8, BG9588), was modified by protein engineering to decrease Fc binding to Fc-gamma receptor IIa while retaining certain other effector functions and pharmacokinetics comparable with natural antibodies. Here, we report that TNX-1500 treatment is not associated with platelet activation in vitro and consistently inhibits kidney allograft rejection in vivo without clinical or histologic evidence of prothrombotic phenomena. We conclude that TNX-1500 retains efficacy similar to that of 5c8 to prevent kidney allograft rejection while avoiding previously identified pathway-associated thromboembolic complications.

TNX-1500, a crystallizable fragment-modified anti-CD154 antibody, prolongs nonhuman primate cardiac allograft survival

Blockade of the CD40/CD154 T cell costimulation pathway is a promising approach to supplement or replace current clinical immunosuppression in solid organ transplantation. We evaluated the tolerability and activity of a novel humanized anti-CD154 monoclonal antibody, TNX-1500 (TNX), in a nonhuman primate heterotopic cardiac allogeneic (allo) transplant model. TNX-1500 contains a rupluzimab fragment antigen-binding region and an immunoglobin G4 crystallizable fragment region engineered to reduce binding to the crystallizable fragment gamma receptor IIa and associated risks of thrombosis. Recipients were treated for 6 months with standard-dose TNX (sTNX) monotherapy, low-dose TNX monotherapy (loTNX), or loTNX with mycophenolate mofetil (MMF) (loTNX + MMF). Results were compared with historical data using chimeric humanized 5c8 monotherapy dosed as for loTNX but discontinued at 3 months. Median survival time was similar for humanized 5c8 and both loTNX groups, but significantly longer with sTNX (>265 days) than with loTNX (99 days) or loTNX + MMF (88 days) (P < 0.05 for both comparisons against sTNX). Standard-dose TNX prevented antidonor alloantibody elaboration, inhibited chronic rejection, and was associated with a significantly reduced effector T cells/regulatory T cells ratio relative to loTNX with MMF. No thrombotic complications were observed. This study demonstrated that TNX was well tolerated, prolongs allograft survival, and prevents alloantibody production and cardiac allograft vasculopathy in a stringent preclinical nonhuman primate heart allotransplant model.

Single Dose of Recombinant Chimeric Horsepox Virus (TNX-801) Vaccination Protects Macaques from Lethal Monkeypox Challenge

The ongoing global Monkeypox outbreak that started in the spring of 2022 has reinforced the importance of protecting the population using live virus vaccines based on the vaccinia virus (VACV). Smallpox also remains a biothreat and although some U.S. military personnel are immunized with VACV, safety concerns limit its use in other vulnerable groups. Consequently, there is a need for an effective and safer, single dose, live replicating vaccine against both viruses. One potential approach is to use the horsepox virus (HPXV) as a vaccine. Contemporary VACV shares a common ancestor with HPXV, which from the time of Edward Jenner and through the 19th century, was extensively used to vaccinate against smallpox. However, it is unknown if early HPXV-based vaccines exhibited different safety and efficacy profiles compared to modern VACV. A deeper understanding of HPXV as a vaccine platform may allow the construction of safer and more effective vaccines against the poxvirus family. In a proof-of-concept study, we vaccinated cynomolgus macaques with TNX-801, a recombinant chimeric horsepox virus (rcHPXV), and showed that the vaccine elicited protective immune responses against a lethal challenge with monkeypox virus (MPXV), strain Zaire. The vaccine was well tolerated and protected animals from the development of lesions and severe disease. These encouraging data support the further development of TNX-801.

Scintillation light detection in the 6-m drift-length ProtoDUNE Dual Phase liquid argon TPC

DUNE is a dual-site experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. ProtoDUNE Dual Phase (DP) is a 6  ×  6  ×  6 m 3 liquid argon time-projection-chamber (LArTPC) that recorded cosmic-muon data at the CERN Neutrino Platform in 2019-2020 as a prototype of the DUNE Far Detector. Charged particles propagating through the LArTPC produce ionization and scintillation light. The scintillation light signal in these detectors can provide the trigger for non-beam events. In addition, it adds precise timing capabilities and improves the calorimetry measurements. In ProtoDUNE-DP, scintillation and electroluminescence light produced by cosmic muons in the LArTPC is collected by photomultiplier tubes placed up to 7 m away from the ionizing track. In this paper, the ProtoDUNE-DP photon detection system performance is evaluated with a particular focus on the different wavelength shifters, such as PEN and TPB, and the use of Xe-doped LAr, considering its future use in giant LArTPCs. The scintillation light production and propagation processes are analyzed and a comparison of simulation to data is performed, improving understanding of the liquid argon properties.

Maternal mental health and partner delivered massage: a pilot study

Background

Mental health problems place a significant burden on the health system and are an important public health issue. Many pregnant women experience anxiety and depression, which can negatively impact health outcomes for both mother and baby. Partner-delivered massage may provide a cost effective and accessible approach to support the mental wellbeing of pregnant women.

Methods

A feasibility randomised controlled trial was conducted to compare partner-delivered relaxation massage (intervention) with a self-directed stress management program (control), for pregnant women with mild anxiety. Women attended an initial workshop at 28-32 weeks gestation, followed by the completion of either the self-directed massage or stress management program. Qualitative feasibility and acceptability data (primary outcomes) were collected via online participant diaries and post-birth interviews. Anxiety, depression and stress symptoms (secondary outcomes) were assessed using the Depression and Anxiety Stress Scale (DASS-21).

Results

14 women/partner dyads attended the partner- delivered massage group and 13 women attended the self-directed stress management group. Participants from both groups reported the programs were feasible and acceptable. Mean scores on all DASS-21 subscales significantly decreased over time in both the intervention and the control group.

Conclusions

The partner-delivered massage program was feasible and acceptable. Both programs decreased women's symptoms of anxiety, depression and stress, with no significant between-group differences identified. An adequately powered, experimental study is needed to determine the effectiveness of partner-delivered relaxation massage.

Key messages

Many women experience anxiety and depression during pregnancy and this can have a negative impact on both mother and baby. Partner-delivered relaxation massage, at least once a week in the third trimester, may help reduce women’s symptoms of anxiety, depression and stress.

The effectiveness of massage for reducing pregnant women's anxiety and depression; systematic review and meta-analysis

OBJECTIVE

To critically appraise and synthesize the best available evidence on the effectiveness of massage to reduce antenatal women's anxiety and/ or depression.

DESIGN

Systematic review with meta-analysis PARTICIPANTS, INTERVENTIONS: Pregnant women over the age of 18 years who receive massage interventions.

MEASUREMENTS AND FINDINGS

Eight studies were included in the review; seven were randomized controlled trials. Data were collected via pregnant women's self-reported ratings of anxiety or depression using validated tools. Meta-analysis of four studies revealed a moderate effect of massage therapy on women's depressive symptoms as measured by the Center for Epidemiologic Studies Depression Scale (CES-D) (MD = -5.95, 95%CI = -8.11 to -3.80, I² = 0%) compared with usual care. A moderate effect of massage interventions on women's anxiety were also found based on five studies using various measures (SMD = -0.59, 95%CI = -1.06 to -0.12, I² = 75%) when compared with usual care. However, none of the trials had a low risk of bias.

KEY CONCLUSIONS

Non-pharmacologic treatments for mental health symptoms are an important option for women to use during pregnancy. As shown in meta-analysed data, massage therapy might be more effective in reducing pregnant women's anxiety and depression than usual care, although the current results may be prone to bias. Further high-quality research is required to fully evaluate the impact of massage therapy on pregnant women's mental health symptoms in the immediate and also longer term.

IMPLICATIONS FOR PRACTICE

Massage therapy may be an acceptable and feasible approach for pregnant women to employ to reduce their anxiety and depressive symptoms. More research evidence examining the safety and effectiveness of massage is required before practice recommendations can be made.

Personality-dependent dispersal: characterization, ontogeny and consequences for spatially structured populations

Dispersal is one of the most fundamental components of ecology, and affects processes as diverse as population growth, metapopulation dynamics, gene flow and adaptation. Although the act of moving from one habitat to another entails major costs to the disperser, empirical and theoretical studies suggest that these costs can be reduced by having morphological, physiological or behavioural specializations for dispersal. A few recent studies on different systems showed that individuals exhibit personality-dependent dispersal, meaning that dispersal tendency is associated with boldness, sociability or aggressiveness. Indeed, in several species, dispersers not only develop behavioural differences at the onset of dispersal, but display these behavioural characteristics through their life cycle. While personality-dependent dispersal has been demonstrated in only a few species, we believe that it is a widespread phenomenon with important ecological consequences. Here, we review the evidence for behavioural differences between dispersers and residents, to what extent they constitute personalities. We also examine how a link between personality traits and dispersal behaviours can be produced and how personality-dependent dispersal affects the dynamics of metapopulations and biological invasions. Finally, we suggest future research directions for population biologists, behavioural ecologists and conservation biologists such as how the direction and the strength of the relationship between personality traits and dispersal vary with ecological contexts.

Development of protein kinase activators: AMPK as a target in metabolic disorders and cancer

AMP-activated protein kinase (AMPK) is a cellular energy sensor activated by metabolic stresses that either inhibit ATP synthesis or accelerate ATP consumption. Activation of AMPK in response to an increase in the cellular AMP:ATP ratio results in inhibition of ATP-consuming processes such as gluconeogenesis and fatty acid synthesis, while stimulating ATP-generating processes, including fatty acid oxidation. These alterations in lipid and glucose metabolism would be expected to ameliorate the pathogenesis of obesity, type 2 diabetes and other metabolic disorders. Recently, AMPK has also been identified as a potential target for cancer prevention and/or treatment. Cell growth and proliferation are energetically demanding, and AMPK may act as an "energy checkpoint" that permits growth and proliferation only when energy reserves are sufficient. Thus, activators of AMPK could have potential as novel therapeutics both for metabolic disorders and for cancer, which together constitute two of the most prevalent groups of diseases worldwide.

Effect of increasing intraperitoneal infusion rates on bupropion hydrochloride-induced seizures in mice

BACKGROUND

It is not known if there is a relationship between input rate and incidence of bupropion-induced seizures. This is important, since different controlled release formulations of bupropion release the active drug at different rates.

METHODS

We investigated the effect of varying the intraperitoneal infusion rates of bupropion HCl 120 mg/kg, a known convulsive dose 50 (CD50), on the incidence and severity of bupropion-induced convulsions in the Swiss albino mice. A total of 69 mice, approximately 7 weeks of age, and weighing 21.0 to 29.1 g were randomly assigned to bupropion HCl 120 mg/kg treatment by intraperitoneal (IP) administration in 7 groups (9 to 10 animals per group). Bupropion HCl was infused through a surgically implanted IP dosing catheter with infusions in each group of 0 min, 15 min, 30 min, 60 min, 90 min, 120 min, and 240 min. The number, time of onset, duration and the intensity of the convulsions or absence of convulsions were recorded.

RESULTS

The results showed that IP administration of bupropion HCl 120 mg/kg by bolus injection induced convulsions in 6 out of 10 mice (60% of convulsing mice) in group 1. Logistic regression analysis revealed that infusion time was significant (p = 0.0004; odds ratio = 0.974) and increasing the IP infusion time of bupropion HCl 120 mg/kg was associated with a 91% reduced odds of convulsions at infusion times of 15 to 90 min compared to bolus injection. Further increase in infusion time resulted in further reduction in the odds of convulsions to 99.8% reduction at 240 min.

CONCLUSION

In conclusion, the demonstration of an inverse relationship between infusion time of a fixed and convulsive dose of bupropion and the risk of convulsions in a prospective study is novel.

Convulsive liability of bupropion hydrochloride metabolites in Swiss albino mice

BACKGROUND

It is known that following chronic dosing with bupropion HCl active metabolites are present in plasma at levels that are several times higher than that of the parent drug, but the possible convulsive effects of the major metabolites are not known.

METHODS

We investigated the convulsive liability and dose-response of the three major bupropion metabolites following intraperitoneal administration of single doses in female Swiss albino mice, namely erythrohydrobupropion HCl, threohydrobupropion HCl, and hydroxybupropion HCl. We compared these to bupropion HCl. The actual doses of the metabolites administered to mice (n = 120; 10 per dose group) were equimolar equivalents of bupropion HCl 25, 50 and 75 mg/kg. Post treatment, all animals were observed continuously for 2 h during which the number, time of onset, duration and intensity of convulsions were recorded. The primary outcome variable was the percentage of mice in each group who had a convulsion at each dose. Other outcome measures were the time to onset of convulsions, mean convulsions per mouse, and the duration and intensity of convulsions.

RESULTS

All metabolites were associated with a greater percentage of seizures compared to bupropion, but the percentage of convulsions differed between metabolites. Hydroxybupropion HCl treatment induced the largest percentage of convulsing mice (100% at both 50 and 75 mg/kg) followed by threohydrobupropion HCl (50% and 100%), and then erythrohydrobupropion HCl (10% and 90%), compared to bupropion HCl (0% and 10%). Probit analysis also revealed the dose-response curves were significantly different (p < 0.0001) with CD50 values of 35, 50, 61 and 82 mg/kg, respectively for the four different treatments. Cox proportional hazards model results showed that bupropion HCl, erythrohydrobupropion HCl, and threohydrobupropion HCl were significantly less likely to induce convulsions within the 2-h post treatment observation period compared to hydroxybupropion HCl. The mean convulsions per mouse also showed the same dose-dependent and metabolite-dependent trends.

CONCLUSION

The demonstration of the dose-dependent and metabolite-dependent convulsive effects of bupropion metabolites is a novelty.

Alcohol significantly lowers the seizure threshold in mice when co-administered with bupropion hydrochloride

BACKGROUND

Bupropion HCl is a widely used antidepressant that is known to cause seizures in a dose-dependent manner. Many patients taking antidepressants will consume alcohol, even when advised not to. Previous studies have not shown any interactions between bupropion HCl and alcohol. However, there have been no previous studies examining possible changes in seizure threshold induced by a combination of alcohol and bupropion HCl.

METHODS

Experimentally naïve female Swiss albino mice (10 per group) received either single doses of bupropion HCl (ranging from 100 mg/kg to 120 mg/kg) or vehicle (0.9% NaCl) by intraperitoneal (IP) injection in a dose volume of 10 ml/kg, and single-dose ethanol alone (2.5 g/kg), or vehicle, 5 min prior to bupropion dosing. The presence or absence of seizures, the number of seizures, the onset, duration and the intensity of seizures were all recorded for 5 h following the administration of ethanol.

RESULTS

The results show that administration of IP bupropion HCl alone induced seizures in mice in a dose-dependent manner, with the 120 mg/kg dose having the largest effect. The percentage of convulsing mice were 0%, 20%, 30% and 60% in the 0 (vehicle), 100, 110, and 120 mg/kg dose groups, respectively. Pretreatment with ethanol produced a larger bupropion HCl-induced convulsive effect at all the doses (70% each at 100, 110 and 120 mg/kg) and a 10% effect in the ethanol + vehicle only group. The convulsive dose of bupropion HCl required to induce seizures in 50% of mice (CD50), was 116.72 mg/kg for bupropion HCl alone (CI: 107.95, 126.20) and 89.40 mg/kg for ethanol/bupropion HCl (CI: 64.92, 123.10).

CONCLUSION

These results show that in mice alcohol lowers the seizure threshold for bupropion-induced seizures. Clinical implications are firstly that there may be an increased risk of seizures in patients consuming alcohol, and secondly that formulations that can release bupropion more readily in alcohol may present additional risks to patients.

Mechanisms underlying the metabolic actions of galegine that contribute to weight loss in mice

BACKGROUND AND PURPOSE

Galegine and guanidine, originally isolated from Galega officinalis, led to the development of the biguanides. The weight-reducing effects of galegine have not previously been studied and the present investigation was undertaken to determine its mechanism(s) of action.

EXPERIMENTAL APPROACH

Body weight and food intake were examined in mice. Glucose uptake and acetyl-CoA carboxylase activity were studied in 3T3-L1 adipocytes and L6 myotubes and AMP activated protein kinase (AMPK) activity was examined in cell lines. The gene expression of some enzymes involved in fat metabolism was examined in 3T3-L1 adipocytes.

KEY RESULTS

Galegine administered in the diet reduced body weight in mice. Pair-feeding indicated that at least part of this effect was independent of reduced food intake. In 3T3-L1 adipocytes and L6 myotubes, galegine (50 microM-3 mM) stimulated glucose uptake. Galegine (1-300 microM) also reduced isoprenaline-mediated lipolysis in 3T3-L1 adipocytes and inhibited acetyl-CoA carboxylase activity in 3T3-L1 adipocytes and L6 myotubes. Galegine (500 microM) down-regulated genes concerned with fatty acid synthesis, including fatty acid synthase and its upstream regulator SREBP. Galegine (10 microM and above) produced a concentration-dependent activation of AMP activated protein kinase (AMPK) in H4IIE rat hepatoma, HEK293 human kidney cells, 3T3-L1 adipocytes and L6 myotubes.

CONCLUSIONS AND IMPLICATIONS

Activation of AMPK can explain many of the effects of galegine, including enhanced glucose uptake and inhibition of acetyl-CoA carboxylase. Inhibition of acetyl-CoA carboxylase both inhibits fatty acid synthesis and stimulates fatty acid oxidation, and this may to contribute to the in vivo effect of galegine on body weight.

A Penetrating Inferior Vena Caval Filter…

INTRODUCTION

The concept of vena caval interruption was first described by Armand Trousseau in 1865 [HANN CL. STREIFF MB. The role of vena caval filters in the management of venous thromboembolism. Blood Rev 2005;19(4):179-202]. Methods described have included surgical ligation of the inferior vena cava (IVC) to the development of percutaneous inferior vena caval filters which have been, up until recently, permanently placed in the vessel. These devices are not without risk. We describe a case of penetration of the duodenum by a standard stainless steel Greenfield vena caval filter.

REPORT

An 83 year old woman presented with vague epigastric discomfort. She was noted to have intermittent globally deranged liver function tests and was investigated accordingly. Investigations included an endoscopic retrograde cholangio-pancreatography (ERCP) which revealed an inferior vena cava filter penetrating the wall of the small bowel.

CONCLUSION

We describe this unique presentation of a penetrating vena caval filter and suggest that a clinician may be inclined to consider a simple endoscopy on occasions when this complication/diagnosis is considered.

Soluble fibrin augments platelet/tumor cell adherence in vitro and in vivo, and enhances experimental metastasis

There is considerable evidence for a relationship between hemostasis and malignancy. Since platelet adhesion to tumor cells has been implicated in the metastatic process and plasma levels of fibrinogen (Fg) and soluble fibrin (sFn) monomer are increased in cancer, we hypothesized that these molecules might enhance tumor-platelet interaction. We therefore studied binding of sFn monomer to tumor cells in a static microplate adhesion assay and determined the effect of pre-treating tumor cells with sFn on tumor cell-induced thrombocytopenia and experimental metastasis. Soluble fibrin (produced by adding thrombin to FXIII- and plasminogen-free Fg in the presence of Gly-Pro-Arg-Pro-amide (GPRP-NH2) significantly increased platelet adherence to tumor cells. This effect was primarily mediated by the integrins alphaIIb beta3 on the platelet and CD 54 (ICAM-1) on the tumor cells. Platelets adhered to untreated A375 cells (28 +/- 8 platelets/tumor cell) and this was not significantly affected by pre-treatment of the tumor cells with fibrinogen or GPRP-NH2. Although thrombin treatment increased adherence, pre-incubation of the tumor cells with sFn resulted in a further increase in platelet binding to tumor cells. In contrast to untreated tumor cells, intravenous injection of sFn-treated A 375 cells reduced the platelet count in anticoagulated mice, supporting the in vitro finding that sFn enhanced tumor cell-platelet adherence. In a more aggressive model of experimental metastasis, treating tumor cells with sFn enhanced lung seeding by 65% compared to untreated cells. Extrapolation of our data to the clinical situation suggests that coagulation activation, and subsequent increase in circulating Fn monomer, may enhance platelet adhesion to circulating tumor cells and thereby facilitate metastatic spread.

The application of high-throughput screening to novel lead discovery

The ability to discover new lead compounds for novel therapeutic targets is a pivotal step in drug discovery programmes. High-throughput screening (HTS) utilises a number of platforms for the rapid screening of novel targets to accelerate this process. Key issues in HTS include assay configuration and the ability of a high-throughput screen to predict drug-target interactions accurately. This review highlights a number of issues in the HTS process and describes three key target areas that are likely to be sources of novel, therapeutically important drugs. Particular emphasis is placed on the mechanistic basis of drug-target interactions that are of prime importance in the design of HTS approaches. Critical aspects of information management related to HTS are summarised.

Effect of passive range of motion on intracranial pressure in neurosurgical patients

PURPOSE

A prospective patient study was done to evaluate the effect of passive range of motion (PROM) on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) in neurosurgical patients.

MATERIALS AND METHODS

Twelve adult patients admitted to the neurological-neurosurgical intensive care unit of a community teaching hospital were enrolled in the study. The study patients all required ICP monitoring and they underwent a total of 20 PROM sessions. Six patients (10 PROM sessions) were mechanically ventilated, and six patients (10 PROM sessions) were breathing spontaneously. Mean arterial pressure (MAP), heart rate (HR), respiratory rate (RR), and ICP were measured at baseline and at 1-minute intervals during the physical therapy session. CPP was calculated as the difference between MAP and ICP.

RESULTS

No significant changes were detected in MAP, ICP, HR, or RR during the study period. Calculated CPP remained unchanged. Mean duration of PROM intervention was 7 +/- 1 minute. Mean Glasgow Coma Scale (GCS) for mechanically ventilated patients was 7 +/- 1.3 and for spontaneously breathing patients 13 +/- 0.8.

CONCLUSION

PROM results in no significant changes in ICP or CPP in stable, neurosurgical patients in the absence of intracranial hypertension.

Purification of insect vitellogenin and vitellin by gel-immobilized ferric chelate

Vitellogenin and vitellin of Manduca sexta and some other insect species were purified by immobilized metal ion affinity chromatography. Ferric ion was chosen as the immobilized metal ion. Agarose-bound carboxymethylpicolylamine was used as the chelating adsorbent for the ferric ion. Vitellogenin and vitellin, both phosphorylated lipoproteins, were shown to bind specifically to the iron. The general applicability of immobilized ferric ion affinity chromatography for the purification of insect vitellogenin and vitellin is suggested.

Bacteriophage lambda DNA packaging: a mutant terminase that is independent of integration host factor

Lambda+ is able to grow in Escherichia coli cells lacking integration host factor (IHF), producing a burst of approximately 25% that produced in IHF+ cells. In vitro, however, we find that the lambda DNA packaging enzyme terminase is strongly dependent on IHF in both cos cleavage reactions and DNA packaging reactions. The cos59 mutation renders lambda dependent on IHF in vivo. The cos59 mutation is a deletion of 3 base pairs at the XmnI site in the cohesive end site (cos) of lambda. Variants of lambda cos59 that were able to grow in the absence of IHF were isolated and found to carry a mutation, called ms1, in the Nu1 gene, which codes for the small subunit of terminase. The Nu1ms1 mutation results in a change of the 40th amino acid of the Nu1 gene product from leucine to phenylalanine. The Nu1ms1 terminase was independent of IHF in packaging reactions in vitro. The results indicate that the mutation either renders terminase: (1) able to utilize some host protein other than IHF, or (2) totally independent of host factors.