TMPRSS2 is a functional receptor for human coronavirus HKU1

Four endemic seasonal human coronaviruses causing common colds circulate worldwide: HKU1, 229E, NL63 and OC43 (ref. 1). After binding to cellular receptors, coronavirus spike proteins are primed for fusion by transmembrane serine protease 2 (TMPRSS2) or endosomal cathepsins2-9. NL63 uses angiotensin-converting enzyme 2 as a receptor10, whereas 229E uses human aminopeptidase-N11. HKU1 and OC43 spikes bind cells through 9-O-acetylated sialic acid, but their protein receptors remain unknown12. Here we show that TMPRSS2 is a functional receptor for HKU1. TMPRSS2 triggers HKU1 spike-mediated cell-cell fusion and pseudovirus infection. Catalytically inactive TMPRSS2 mutants do not cleave HKU1 spike but allow pseudovirus infection. Furthermore, TMPRSS2 binds with high affinity to the HKU1 receptor binding domain (Kd 334 and 137 nM for HKU1A and HKU1B genotypes) but not to SARS-CoV-2. Conserved amino acids in the HKU1 receptor binding domain are essential for binding to TMPRSS2 and pseudovirus infection. Newly designed anti-TMPRSS2 nanobodies potently inhibit HKU1 spike attachment to TMPRSS2, fusion and pseudovirus infection. The nanobodies also reduce infection of primary human bronchial cells by an authentic HKU1 virus. Our findings illustrate the various evolution strategies of coronaviruses, which use TMPRSS2 to either directly bind to target cells or prime their spike for membrane fusion and entry.

Fusogenicity and neutralization sensitivity of the SARS-CoV-2 Delta sublineage AY.4.2

BACKGROUND

SARS-CoV-2 lineages are continuously evolving. As of December 2021, the AY.4.2 Delta sub-lineage represented 20 % of sequenced strains in the UK and had been detected in dozens of countries. It has since then been supplanted by Omicron. The AY.4.2 spike displays three additional mutations (T95I, Y145H and A222V) in the N-terminal domain when compared to the original Delta variant (B.1.617.2) and remains poorly characterized.

METHODS

We compared the Delta and the AY.4.2 spikes, by assessing their binding to antibodies and ACE2 and their fusogenicity. We studied the sensitivity of an authentic AY.4.2 viral isolate to neutralizing antibodies.

FINDINGS

The AY.4.2 spike exhibited similar binding to all the antibodies and sera tested, and similar fusogenicity and binding to ACE2 than the ancestral Delta spike. The AY.4.2 virus was slightly less sensitive than Delta to neutralization by a panel of monoclonal antibodies; noticeably, the anti-RBD Imdevimab showed incomplete neutralization. Sensitivity of AY.4.2 to sera from vaccinated individuals was reduced by 1.3 to 3-fold, when compared to Delta.

INTERPRETATION

Our results suggest that mutations in the NTD remotely impair the efficacy of anti-RBD antibodies. The spread of AY.4.2 was not due to major changes in spike fusogenicity or ACE2 binding, but more likely to a partially reduced neutralization sensitivity.

FUNDING

The work was funded by Institut Pasteur, Fondation pour la Recherche Médicale, Urgence COVID-19 Fundraising Campaign of Institut Pasteur, ANRS, the Vaccine Research Institute, Labex IBEID, ANR/FRM Flash Covid PROTEO-SARS-CoV-2 and IDISCOVR.

Considerable escape of SARS-CoV-2 Omicron to antibody neutralization

The SARS-CoV-2 Omicron variant was first identified in November 2021 in Botswana and South Africa^1-3. It has since spread to many countries and is expected to rapidly become dominant worldwide. The lineage is characterized by the presence of around 32 mutations in spike-located mostly in the N-terminal domain and the receptor-binding domain-that may enhance viral fitness and enable antibody evasion. Here we isolated an infectious Omicron virus in Belgium from a traveller returning from Egypt. We examined its sensitivity to nine monoclonal antibodies that have been clinically approved or are in development⁴, and to antibodies present in 115 serum samples from COVID-19 vaccine recipients or individuals who have recovered from COVID-19. Omicron was completely or partially resistant to neutralization by all monoclonal antibodies tested. Sera from recipients of the Pfizer or AstraZeneca vaccine, sampled five months after complete vaccination, barely inhibited Omicron. Sera from COVID-19-convalescent patients collected 6 or 12 months after symptoms displayed low or no neutralizing activity against Omicron. Administration of a booster Pfizer dose as well as vaccination of previously infected individuals generated an anti-Omicron neutralizing response, with titres 6-fold to 23-fold lower against Omicron compared with those against Delta. Thus, Omicron escapes most therapeutic monoclonal antibodies and, to a large extent, vaccine-elicited antibodies. However, Omicron is neutralized by antibodies generated by a booster vaccine dose.

Considerable escape of SARS-CoV-2 Omicron to antibody neutralization

The SARS-CoV-2 Omicron variant was first identified in November 2021 in Botswana and South Africa^1-3. It has since then spread to many countries and is expected to rapidly become dominant worldwide. The lineage is characterized by the presence of about 32 mutations in the spike, located mostly in the N-terminal domain (NTD) and the receptor binding domain (RBD), which may enhance viral fitness and allow antibody evasion. Here, we isolated an infectious Omicron virus in Belgium, from a traveller returning from Egypt. We examined its sensitivity to 9 monoclonal antibodies (mAbs) clinically approved or in development⁴, and to antibodies present in 115 sera from COVID-19 vaccine recipients or convalescent individuals. Omicron was totally or partially resistant to neutralization by all mAbs tested. Sera from Pfizer or AstraZeneca vaccine recipients, sampled 5 months after complete vaccination, barely inhibited Omicron. Sera from COVID-19 convalescent patients collected 6 or 12 months post symptoms displayed low or no neutralizing activity against Omicron. Administration of a booster Pfizer dose as well as vaccination of previously infected individuals generated an anti-Omicron neutralizing response, with titers 6 to 23 fold lower against Omicron than against Delta. Thus, Omicron escapes most therapeutic monoclonal antibodies and to a large extent vaccine-elicited antibodies. Omicron remains however neutralized by antibodies generated by a booster vaccine dose.

SARS-CoV-2 Alpha, Beta, and Delta variants display enhanced Spike-mediated syncytia formation

Severe COVID‐19 is characterized by lung abnormalities, including the presence of syncytial pneumocytes. Syncytia form when SARS‐CoV‐2 spike protein expressed on the surface of infected cells interacts with the ACE2 receptor on neighboring cells. The syncytia forming potential of spike variant proteins remain poorly characterized. Here, we first assessed Alpha (B.1.1.7) and Beta (B.1.351) spread and fusion in cell cultures, compared with the ancestral D614G strain. Alpha and Beta replicated similarly to D614G strain in Vero, Caco‐2, Calu‐3, and primary airway cells. However, Alpha and Beta formed larger and more numerous syncytia. Variant spike proteins displayed higher ACE2 affinity compared with D614G. Alpha, Beta, and D614G fusion was similarly inhibited by interferon‐induced transmembrane proteins (IFITMs). Individual mutations present in Alpha and Beta spikes modified fusogenicity, binding to ACE2 or recognition by monoclonal antibodies. We further show that Delta spike also triggers faster fusion relative to D614G. Thus, SARS‐CoV‐2 emerging variants display enhanced syncytia formation.

Abstract 2871: The Nanoprimer: a nanoparticle designed to transiently occupy the mononuclear phagocytic system in order to increase nanomedicine-based treatments efficacy

Introduction: Most nanomedicines are currently limited in their efficacy due to a sub-optimal biodistribution/accumulation in the target tissues. A large part of the administered dose remains useless due to the high rate of clearance by the mononuclear phagocytic system (mainly by Kupffer cells in liver). We designed a new approach based on the use of an engineered, biocompatible nanoparticle–the Nanoprimer–that is administered before the nanomedicine in order to transiently and specifically occupy the liver clearance pathways responsible for sub-optimal therapeutic bioavailability. The Nanoprimer's effect is only based on its specific physico-chemical properties, there is no active principal ingredient encapsulated in it. Here we demonstrate the ability of the Nanoprimer to redefine the bioavailability and efficacy of nanomedicines loaded with small molecules or nucleic acid. We evaluated the biodistribution and the safety of the Nanoprimer alone and of an irinotecan loaded liposome combined with the Nanoprimer.

Methods: Quantitative evaluation of the Nanoprimer's biodistribution was performed by mass spectrometry. Safety profile of the Nanoprimer was evaluated in vitro (cell viability, cytokines/interleukins expression profile, complement activation, phagoburst and phagotest on different cell lines) and in vivo, in mice, by a follow up of body weight and clinical signs, histological observations of liver, spleen and lungs and blood parameters titration, after the injection of a maximized dose of Nanoprimer. The impact of the Nanoprimer on the bioavailability and biodistribution of nanomedicines loaded with irinotecan or nucleic acids (mRNA / SiRNA) was evaluated by HPLC and fluorescence quantification, respectively. Finally, the impact of the Nanoprimer on treatment was evaluated using nanomedicines encapsulating human erythropoietin (hEPO) mRNA, Factor VII (FVII) siRNA or irinotecan.

Results: The Nanoprimer presents a rapid accumulation within liver and spleen. The Nanoprimer was well tolerated with no sign of toxicity observed using therapeutic dosage. The administration of the Nanoprimer increases systemic bioavailability of different type of nanomedicines and enhances their accumulation in target tissues. This improved bioavailability is correlated with an increased secretion of hEPO by 30%, for mRNA-loaded nanomedicines, an increased silencing of FVII by 50%, for siRNA-loaded nanomedicines, and an increased anti-tumor efficacy by 50%, for irinotecan-loaded nanomedicines.

Here, we showed the safe profile of the Nanoprimer and its ability to increase the treatment outcomes for different nature of nanomedicines. The separation of the functions ensuring the efficacy of a treatment into two distinct objects opens perspectives for designing future nanomedicines and a shift in the therapeutic paradigm.

Citation Format: Julie Devalliere, Laurence Poul, Audrey Darmon, Oceane Jibault, Maxime Bergere, Francis Mpambani, Nell Saunders, Marion Paolini, Robert Langer, Matthieu Germain. The Nanoprimer: a nanoparticle designed to transiently occupy the mononuclear phagocytic system in order to increase nanomedicine-based treatments efficacy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2871.

Genome-Wide Association Studies for Methane Production in Dairy Cattle

Genomic selection has been proposed for the mitigation of methane (CH₄) emissions by cattle because there is considerable variability in CH₄ emissions between individuals fed on the same diet. The genome-wide association study (GWAS) represents an important tool for the detection of candidate genes, haplotypes or single nucleotide polymorphisms (SNP) markers related to characteristics of economic interest. The present study included information for 280 cows in three dairy production systems in Mexico: 1) Dual Purpose (n = 100), 2) Specialized Tropical Dairy (n = 76), 3) Familiar Production System (n = 104). Concentrations of CH₄ in a breath of individual cows at the time of milking (MEIm) were estimated through a system of infrared sensors. After quality control analyses, 21,958 SNPs were included. Associations of markers were made using a linear regression model, corrected with principal component analyses. In total, 46 SNPs were identified as significant for CH₄ production. Several SNPs associated with CH₄ production were found at regions previously described for quantitative trait loci of composition characteristics of meat, milk fatty acids and characteristics related to feed intake. It was concluded that the SNPs identified could be used in genomic selection programs in developing countries and combined with other datasets for global selection.

Does the diurnal pattern of enteric methane emissions from dairy cows change over time?

Diet manipulation and genetic selection are two important mitigation strategies for reducing enteric methane (CH4) emissions from ruminant livestock. The aim of this study was to assess whether the diurnal pattern of CH4 emissions from individual dairy cows changes over time when cows are fed on diets varying in forage composition. Emissions of CH4 from 36 cows were measured during milking in an automatic (robotic) milking station in three consecutive feeding periods, for a total of 84 days. In Periods 1 and 2, the 36 cows were fed a high-forage partial mixed ration (PMR) containing 75% forage, with either a high grass silage or high maize silage content. In Period 3, cows were fed a commercial PMR containing 69% forage. Cows were offered PMR ad libitum plus concentrates during milking and CH4 emitted by individual cows was sampled during 8662 milkings. A linear mixed model was used to assess differences among cows, feeding periods and time of day. Considerable variation was observed among cows in daily mean and diurnal patterns of CH4 emissions. On average, cows produced less CH4 when fed on the commercial PMR in feeding Period 3 than when the same cows were fed on high-forage diets in feeding Periods 1 and 2. The average diurnal pattern for CH4 emissions did not significantly change between feeding periods and as lactation progressed. Emissions of CH4 were positively associated with dry matter (DM) intake and forage DM intake. It is concluded that if the management of feed allocation remains constant then the diurnal pattern of CH4 emissions from dairy cows will not necessarily alter over time. A change in diet composition may bring about an increase or decrease in absolute emissions over a 24-h period without significantly changing the diurnal pattern unless management of feed allocation changes. These findings are important for CH4 monitoring techniques that involve taking measurements over short periods within a day rather than complete 24-h observations.

Efficacy of ACL injury risk screening methods in identifying high-risk landing patterns during a sport-specific task

Screening methods sensitive to movement strategies that increase anterior cruciate ligament (ACL) loads are likely to be effective in identifying athletes at-risk of ACL injury. Current ACL injury risk screening methods are yet to be evaluated for their ability to identify athletes' who exhibit high-risk lower limb mechanics during sport-specific maneuvers associated with ACL injury occurrences. The purpose of this study was to examine the efficacy of two ACL injury risk screening methods in identifying high-risk lower limb mechanics during a sport-specific landing task. Thirty-two female athletes were screened using the Landing Error Scoring System (LESS) and Tuck Jump Assessment. Participants' also completed a sport-specific landing task, during which three-dimensional kinematic and kinetic data were collected. One-dimensional statistical parametric mapping was used to examine the relationships between screening method scores, and the three-dimensional hip and knee joint rotation and moment data from the sport-specific landing. Higher LESS scores were associated with reduced knee flexion from 30 to 57 ms after initial contact (P = 0.003) during the sport-specific landing; however, no additional relationships were found. These findings suggest the LESS and Tuck Jump Assessment may have minimal applicability in identifying athletes' who exhibit high-risk landing postures in the sport-specific task examined.

Predictors of Unintentional Injuries in Paediatric Immigrants in Ontario

BACKGROUND: Unintentional injury is a frequent reason for emergency department visits and is the leading cause of death for Canadian children. Injury is associated with a number of socio-demographic variables but it is not known whether being an immigrant changes this risk.

OBJECTIVES: To examine the association between family immigrant status and unintentional injury; and to test this relationship within immigrants by refugee status.

DESIGN/METHODS: Retrospective population-based cross-sectional study of children ages 0 to 14 years residing in Ontario, Canada from 2008 to 2012, using linked health administrative databases and Citizenship and Immigration Canada’s Permanent Resident Database. The main exposure was immigration status (immigrant or child of an immigrant vs. Canadian born). Secondary exposure was refugee status. Main outcome measure was unintentional injury events (emergency department visits, hospitaliza-tions, deaths), annualized. Data were analyzed using Poisson regression models to estimate risk ratios (RR) for unintentional injuries.

RESULTS: There were 11 464 317 injuries per year. Non-immigrant children sustained 12051 injuries/100 000 and immigrants had 6837 injuries/100 000, annually. In adjusted models, immigrants had a significantly lower risk of injury compared with non-immigrant children (RR 0.60; 95% confidence interval [CI] 0.57, 0.63). Overall, the most materially deprived neighbourhood quintile was associated with a higher rate of injury (RR 1.13; 95% CI 1.07, 1.02, quintile 5 vs. 1) whereas within immigrants, material deprivation was associated with a lower rate of injury (RR 0.96; 95% CI 0.94, 0.98, quintile 5 vs. 1). Other predictors of injury included age (0 to 4 years: RR 0.84; 95% CI 0.81, 0.88; 5 to 9 years: RR 0.70; 95% CI 0.67, 0.73), male sex (RR 1.30; 95% CI 1.26, 1.35), and rural residence (RR 1.50; 95% CI 1.43, 1.57). Injury rates were lower in immigrants across all types of unintentional injuries. Within immigrants, refugees had a higher risk of injury compared with non-refugees (RR 1.12; 95% CI 1.10, 1.14). This risk was particularly high for motor vehicle accidents (RR = 1.58; 95% CI 1.46, 1.71) and scald burns (RR 1.23; 95% CI 1.11, 1.35).

CONCLUSION: Risk of unintentional injury is lower among immigrants compared with Canadian-born children. These findings support a healthy immigrant effect. Socioeconomic status has a different effect on injury risk in immigrant and non-immigrant populations, suggesting alternative causal pathways for injuries in immigrants. Risk of unintentional injury is higher in refugees versus non-refugee immigrants, highlighting a population in need of targeted injury prevention strategies.

Technology for mobility in SCI 10 years from now

OBJECTIVES

To identify technological advances and that are likely to have a great impact on the quality of life and participation in individuals with spinal cord injury (SCI).

METHODS

In this paper we use the International Classification of Function to frame a discussion on how technology is likely to impact SCI in 10 years. In addition, we discuss the implication of technological advances on future research.

RESULTS/CONCLUSION

Although technology advances are exciting, a large challenge for the research community will be how to effectively apply and deploy this technology. Advances occurring in the next 10 years that reduce cost of technology may be more important to the population with SCI than brand new technologies. Social context is everything. As a research community we must advocate for better systems of care. Advocating now for better care will lead to a world in 2020 that is ready to adopt new technologies that are truly transformative.

Increased haematopoietic progenitor cells are associated with poor outcome in patients with metastatic renal cancer treated with sunitinib

BACKGROUND

Haematopoietic progenitor cells (HPCs) are present in blood in metastatic renal cell cancer (mRCC). We investigate their expression in mRCC patients treated with sunitinib and correlate their expression with plasma growth factor levels [insulin-like growth factor (IGF)-1].

METHODS

Circulating HPCs (CD34(+)/CD45(+)) and plasma IGF-1 levels were measured at specific sequential time points (0, 6, 18 and 28 weeks) in 43 untreated mRCC patients receiving sunitinib (50 mg for 28 days followed by 14-day off treatment). Univariate and multivariate analysis assessed the prognostic significance of HPCs and IGF-1.

RESULTS

HPCs levels were raised in 40 of 43 (93%) of patients. IGF-1 levels were raised in 9 of 43 patients (21%). Univariate and multivariate analysis revealed that high HPCs before treatment were associated with a significantly shorter overall survival (hazard ratio 3.3, 95% confidence interval 1.23-8.8, P=0.01), which was not the case for IGF-1 levels. Both HPC and IGF-1 levels fell with sunitinib (61% and 14% fall, respectively, P <0.05 for both). A positive correlation between the falls in HPC and IGF-1 occurred (P<0.001).

CONCLUSIONS

HPCs are over expressed in the peripheral blood in the majority of patients with mRCC. Higher levels are associated with poor prognosis. A concurrent fall in HPCs and growth factor expression (IGF-1) with sunitinib occurs.

White sponge nevus presenting as genital lesions in a 28-year-old female

A case is presented of white plaques occurring predominantly on the vulvar mucosa of a 28-year-old female diagnosed as white sponge nevus (WSN). WSN is a rare, autosomal dominant disorder involving mucous membranes. It predominantly affects the oral mucosa; however, it has been reported to rarely involve extraoral mucosal sites. In this case, histology and family history were key features leading to the correct diagnosis. WSN is an extremely rare cause of vulvar leukoplakia, yet it is important to recognize to allow for appropriate genetic counseling of this autosomal dominant disorder and to avoid misdiagnosis and the potential for subsequent exposure to ineffective treatment modalities.

Identification and characterization of Cor33p, a novel protein implicated in tolerance towards oxidative stress in Candida albicans

We applied two-dimensional gel electrophoresis to identify downstream effectors of CPH1 and EFG1 under hypha-inducing conditions in Candida albicans. Among the proteins that were expressed in wild-type cells but were strongly downregulated in a cph1Delta/efg1Delta double mutant in alpha-minimal essential medium at 37 degrees C, we could identify not-yet-characterized proteins, including Cor33-1p and Cor33-2p. The two proteins are almost identical (97% identity) and represent products of allelic isoforms of the same gene. Cor33p is highly similar to Cip1p from Candida sp. but lacks any significant homology to proteins from Saccharomyces cerevisiae. Strikingly, both proteins share homology with phenylcoumaran benzylic ether reductases and isoflavone reductases from plants. For other hypha-inducing media, like yeast-peptone-dextrose (YPD) plus serum at 37 degrees C, we could not detect any transcription for COR33 in wild-type cells, indicating that Cor33p is not hypha specific. In contrast, we found a strong induction for COR33 when cells were treated with 5 mM hydrogen peroxide. However, under oxidative conditions, transcription of COR33 was not dependent on EFG1, indicating that other regulatory factors are involved. In fact, upregulation depends on CAP1 at least, as transcript levels were clearly reduced in a Deltacap1 mutant strain under oxidative conditions. Unlike in wild-type cells, transcription of COR33 in a tsa1Delta mutant can be induced by treatment with 0.1 mM hydrogen peroxide. This suggests a functional link between COR33 and thiol-specific antioxidant-like proteins that are important in the oxidative-stress response in yeasts. Concordantly, cor33Delta deletion mutants show retarded growth on YPD plates supplemented with hydrogen peroxide, indicating that COR33 in general is implicated in conferring tolerance toward oxidative stress on Candida albicans.

Surviving Sepsis and the acute medicine - critical care interface

Critical care is now a well established specialty in the UK. The rapid development of acute medicine across the country has many similarities to the development of critical care in the 1960's. How these two specialties interface will be an important issue in the way acute hospitals deliver care over the next few years. The Surviving Sepsis Campaign resuscitation care bundle is a useful tool to help develop this interface.

Genotyping of measles and mumps virus strains using amplification refractory mutation system analysis combined with enzyme immunoassay: a simple method for outbreak investigations

A simple method, based on a modification of the amplification refractory mutation system (ARMS), for genotyping outbreak strains of measles and mumps viruses and detecting these in a simple enzyme immunoassay (EIA) is described. Fifty-three measles strains circulating at the time of an outbreak in London in 2000 and 26 strains circulating at the time of a mumps outbreak in Accrington, UK, in 1999 were investigated. All strains were genotyped by direct sequencing. ARMS primers were then designed to amplify the outbreak strain. The ARMS-EIA for measles and mumps detected all 36 measles outbreak strains as genotype D6, and all 15 mumps outbreak strains as genotype F, respectively. The sensitivity and specificity of both the measles D6 and Mumps F genotype ARMS EIA was 100% compared with direct sequencing. The results show that ARMS-EIA can be used as a rapid alternative to genotyping by direct sequence analysis in outbreak situations.

The molecular epidemiology of tuberculosis in inner London

The study used DNA fingerprint typing (spoligotyping and Heminested-lnverse-PCR) of Mycobacterium tuberculosis from all culture-confirmed inner London patients over a 12-month period to describe transmission. The methodology was evaluated by comparison with standard IS6110 typing and by examining its ability to identify known household clusters of cases. Isolates sharing indistinguishable typing patterns using both techniques were defined as clustered. Clusters were investigated to identify epidemiological links. The methodology showed good discriminatory power and identified known household clusters of cases. Of 694 culture-confirmed cases, 563 (81%) were typed. Eleven (2%) were due to laboratory cross-contamination and were excluded. Of the remaining 552 isolates 148 (27%) were clustered. Multivariate analysis indicated that clustering was more common in those with pulmonary smear positive disease (P < 0.02); those born in the United Kingdom (P < 0.0003) and in patients living in south London (P = 0.02). There was also a trend towards clustering being more common in those not known to have HIV infection (P = 0.051). The results suggest that in inner London, recent local transmission makes an important contribution to notification rates.

Up-regulation of p21(WAF1/CIP1) by histone deacetylase inhibitors reduces their cytotoxicity

Histone deacetylase inhibitors show promise as chemotherapeutic agents and have been demonstrated to block proliferation in a wide range of tumor cell lines. Much of this antiproliferative effect has been ascribed to the up-regulated expression of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1). In this article, we report that p21 expression was up-regulated by relatively low doses of the histone deacetylase inhibitor azelaic bishydroxamic acid (ABHA) and correlated with a proliferative arrest. Higher doses of ABHA were cytotoxic. Cells that did not up-regulate p21 expression were hypersensitive to killing by ABHA and died via apoptosis, whereas up-regulation of p21 correlated with reduced sensitivity and a block in the apoptotic mechanism, and these cells seemed to die by necrosis. Using isogenic p21(+/+) and p21(-/-) cell lines and direct inhibition of caspase activity, we demonstrate that the reduced sensitivity to killing by ABHA is a consequence of inhibition of apoptosis by up-regulated p21 expression. These data indicate the enormous potential of therapeutic strategies that bypass the cytoprotective effect of p21 and act on the same molecular targets as the histone deacetylase inhibitors.