Biological mechanisms underpinning the development of long COVID

As COVID-19 evolves from a pandemic to an endemic disease, the already staggering number of people that have been or will be infected with SARS-CoV-2 is only destined to increase, and the majority of humanity will be infected. It is well understood that COVID-19, like many other viral infections, leaves a significant fraction of the infected with prolonged consequences. Continued high number of SARS-CoV-2 infections, viral evolution with escape from post-infection and vaccinal immunity, and reinfections heighten the potential impact of Long COVID. Hence, the impact of COVID-19 on human health will be seen for years to come until more effective vaccines and pharmaceutical treatments become available. To that effect, it is imperative that the mechanisms underlying the clinical manifestations of Long COVID be elucidated. In this article, we provide an in-depth analysis of the evidence on several potential mechanisms of Long COVID and discuss their relevance to its pathogenesis.

Monkeypox (Mpox) requires continued surveillance, vaccines, therapeutics and mitigating strategies

The widespread outbreak of the monkeypox virus (MPXV) recognized in 2022 poses new challenges for public healthcare systems worldwide. With more than 86,000 people infected, there is concern that MPXV may become endemic outside of its original geographical area leading to repeated human spillover infections or continue to be spread person-to-person. Fortunately, classical public health measures (e.g., isolation, contact tracing and quarantine) and vaccination have blunted the spread of the virus, but cases are continuing to be reported in 28 countries in March 2023. We describe here the vaccines and drugs available for the prevention and treatment of MPXV infections. However, although their efficacy against monkeypox (mpox) has been established in animal models, little is known about their efficacy in the current outbreak setting. The continuing opportunity for transmission raises concerns about the potential for evolution of the virus and for expansion beyond the current risk groups. The priorities for action are clear: 1) more data on the efficacy of vaccines and drugs in infected humans must be gathered; 2) global collaborations are necessary to ensure that government authorities work with the private sector in developed and low and middle income countries (LMICs) to provide the availability of treatments and vaccines, especially in historically endemic/enzootic areas; 3) diagnostic and surveillance capacity must be increased to identify areas and populations where the virus is present and may seed resurgence; 4) those at high risk of severe outcomes (e.g., immunocompromised, untreated HIV, pregnant women, and inflammatory skin conditions) must be informed of the risk of infection and be protected from community transmission of MPXV; 5) engagement with the hardest hit communities in a non-stigmatizing way is needed to increase the understanding and acceptance of public health measures; and 6) repositories of monkeypox clinical samples, including blood, fluids, tissues and lesion material must be established for researchers. This MPXV outbreak is a warning that pandemic preparedness plans need additional coordination and resources. We must prepare for continuing transmission, resurgence, and repeated spillovers of MPXV.

Long COVID: a review and proposed visualization of the complexity of long COVID

Post-Acute Sequelae of Severe Acute Respiratory Syndrome Coronavirus - 2 (SARS-CoV-2) infection, or Long COVID, is a prevailing second pandemic with nearly 100 million affected individuals globally and counting. We propose a visual description of the complexity of Long COVID and its pathogenesis that can be used by researchers, clinicians, and public health officials to guide the global effort toward an improved understanding of Long COVID and the eventual mechanism-based provision of care to afflicted patients. The proposed visualization or framework for Long COVID should be an evidence-based, dynamic, modular, and systems-level approach to the condition. Furthermore, with further research such a framework could establish the strength of the relationships between pre-existing conditions (or risk factors), biological mechanisms, and resulting clinical phenotypes and outcomes of Long COVID. Notwithstanding the significant contribution that disparities in access to care and social determinants of health have on outcomes and disease course of long COVID, our model focuses primarily on biological mechanisms. Accordingly, the proposed visualization sets out to guide scientific, clinical, and public health efforts to better understand and abrogate the health burden imposed by long COVID.

2019 meeting of the global virus network

The Global Virus Network (GVN) was established in 2011 to strengthen research and responses to emerging viral causes of human disease and to prepare against new viral pandemics. There are now 52 GVN Centers of Excellence and 9 Affiliate laboratories in 32 countries. The 11th International GVN meeting was held from June 9-11, 2019 in Barcelona, Spain and was jointly organized with the Spanish Society of Virology. A common theme throughout the meeting was globalization and climate change. This report highlights the recent accomplishments of GVN researchers in several important areas of medical virology, including severe virus epidemics, anticipation and preparedness for changing disease dynamics, host-pathogen interactions, zoonotic virus infections, ethical preparedness for epidemics and pandemics, one health and antivirals.

2018 international meeting of the Global Virus Network

The Global Virus Network (GVN) was established in 2011 to strengthen research and responses to emerging viral causes of human disease and to prepare against new viral pandemics. There are now 45 GVN Centers of Excellence and 7 Affiliate laboratories in 29 countries. The 10th International GVN meeting was held from November 28–30, 2018 in Veyrier du Lac, France and was co-hosted by the two GVN Centers of Excellence, the Mérieux Foundation and the University of Veterinary Medicine Hannover (TiHo). The theme of this 10th International GVN meeting was “Eradication and control of (re-) emerging viruses”. This report highlights the recent accomplishments of GVN researchers in several important areas of medical virology, including strategies for the eradication of smallpox, measles, polio, SARS and vector-borne or zoonotic infections, emergence and intervention strategies for retroviruses and arboviruses, preparedness for outbreaks of Filo- and other hemophilic viruses, pathogenesis, impact and prevention of respiratory viruses, as well as, viruses affecting the central and peripheral nervous system. Also threats in crisis settings like refugee camps were presented.

Identification and application of self-binding zipper-like sequences in SARS-CoV spike protein

Self-binding peptides containing zipper-like sequences, such as the Leu/Ile zipper sequence within the coiled coil regions of proteins and the cross-β spine steric zippers within the amyloid-like fibrils, could bind to the protein-of-origin through homophilic sequence-specific zipper motifs. These self-binding sequences represent opportunities for the development of biochemical tools and/or therapeutics. Here, we report on the identification of a putative self-binding β-zipper-forming peptide within the severe acute respiratory syndrome-associated coronavirus spike (S) protein and its application in viral detection. Peptide array scanning of overlapping peptides covering the entire length of S protein identified 34 putative self-binding peptides of six clusters, five of which contained octapeptide core consensus sequences. The Cluster I consensus octapeptide sequence GINITNFR was predicted by the Eisenberg’s 3D profile method to have high amyloid-like fibrillation potential through steric β-zipper formation. Peptide C6 containing the Cluster I consensus sequence was shown to oligomerize and form amyloid-like fibrils. Taking advantage of this, C6 was further applied to detect the S protein expression in vitro by fluorescence staining. Meanwhile, the coiled-coil-forming Leu/Ile heptad repeat sequences within the S protein were under-represented during peptide array scanning, in agreement with that long peptide lengths were required to attain high helix-mediated interaction avidity. The data suggest that short β-zipper-like self-binding peptides within the S protein could be identified through combining the peptide scanning and predictive methods, and could be exploited as biochemical detection reagents for viral infection.

2016 International meeting of the Global Virus Network

The Global Virus Network (GVN) was established in 2011 in order to strengthen research and responses to current viral causes of human disease and to prepare against new viral pandemic threats. There are now 38 GVN Centers of Excellence and 6 Affiliate laboratories in 24 countries. GVN scientists meet annually to learn about each other's current research, address collaborative priorities and plan future programs. The 2016 meeting was held from October 23–25 in Hokkaido, Japan, in partnership with the Japanese Society for Virology, the National Institute of Infectious Diseases of Japan and the Research Center for Zoonosis Control of Hokkaido University. This report highlights the accomplishments of GVN researchers in many priority areas of medical virology, including the current Zika epidemic, infections by human papillomavirus, influenza, Ebola, Lassa, dengue, HIV, hepatitis C, and chikungunya viruses, and the development of improved diagnostics and new vaccines.

•

The GVN is an international research network comprised of 38 Centers of Excellence and 6 Affiliates in 24 countries.

•

The 2016 Global Virus Network (GVN) Meeting was held in Sapporo, Japan from October 23–25.

•

New data were presented on all various aspects of medical virology, therapy, and vaccines were presented.

•

International collaboration is needed to develop effective viral vaccines and therapeutics.

•

The 2017 international GVN meeting will be held on September 25–28 in Melbourne, Australia.

Trimeric HIV Env provides epitope occlusion mediated by hypervariable loops

Hypervariable loops of HIV-1 Env protein gp120 are speculated to play roles in the conformational transition of Env to the receptor binding-induced metastable state. Structural analysis of full-length Env-based immunogens, containing the entire V2 loop, displayed tighter association between gp120 subunits, resulting in a smaller trimeric diameter than constructs lacking V2. A prominent basal quaternary location of V2 and V3′ that challenges previous reports would facilitate gp41-independent gp120-gp120 interactions and suggests a quaternary mechanism of epitope occlusion facilitated by hypervariable loops. Deletion of V2 resulted in dramatic exposure of basal, membrane-proximal gp41 epitopes, consistent with its predicted basal location. The structural features of HIV-1 Env characterized here provide grounds for a paradigm shift in loop exposure and epitope occlusion, while providing substantive rationale for epitope display required for elicitation of broadly neutralizing antibodies, as well as substantiating previous pertinent literature disregarded in recent reports.

Anti-human immunodeficiency virus type 1 agent alpha-hydroxy glycineamide enters the target cells via a mechanism of passive diffusion

OBJECTIVES

Alpha-hydroxy glycineamide (αHGA) is the active antiviral metabolite of tri-peptide glycyl-prolyl-glycine-amide (GPG-NH2 ). αHGA inhibits the replication of HIV-1 in vitro by interfering with the capsid formation. It has also an effect on viral gp160 envelope protein. Since drug transport is an important aspect of drug function, we investigated the mechanism of [(14) C] αHGA uptake by a human T cell line.

METHODS

H9 cells were incubated with defined amounts of radiolabelled αHGA for definite time durations. After harvesting the cells and removal of radiolabelled material, the radioactivity associated with the cells was assayed. Experiments were also designed to address the effect of metabolic inhibitors, temperature and extra unlabelled compound as potential competitor on the cellular uptake of αHGA.

KEY FINDINGS

Uptake of αHGA into H9 cells was time- and dose-dependent. The uptake properties showed a low temperature dependency (Q10  < 2). Moreover the uptake was not inhibited by increasing concentrations of cold competitors. There was no effect on cellular uptake of αHGA by known metabolic inhibitors, NaN3 and NaF.

CONCLUSIONS

Kinetic analysis of compound uptake, metabolic inhibition studies, saturation studies and the Q10 value of αHGA uptake indicate that the compound enters H9 cells by a mechanism of passive diffusion.

122 Peptide Inhibitors of HIV

No abstract provided.

Therapeutic DNA vaccination using in vivo electroporation followed by standard of care therapy in patients with genotype 1 chronic hepatitis C

Clearance of infections caused by the hepatitis C virus (HCV) correlates with HCV-specific T cell function. We therefore evaluated therapeutic vaccination in 12 patients with chronic HCV infection. Eight patients also underwent a subsequent standard-of-care (SOC) therapy with pegylated interferon (IFN) and ribavirin. The phase I/IIa clinical trial was performed in treatment naive HCV genotype 1 patients, receiving four monthly vaccinations in the deltoid muscles with 167, 500, or 1,500 μg codon-optimized HCV nonstructural (NS) 3/4A-expressing DNA vaccine delivered by in vivo electroporation (EP). Enrollment was done with 2 weeks interval between patients for safety reasons. Treatment was safe and well tolerated. The vaccinations significantly improved IFN-γ-producing responses to HCV NS3 during the first 6 weeks of therapy. Five patients experienced 2-10 weeks 0.6-2.4 log10 reduction in serum HCV RNA. Six out of eight patients starting SOC therapy within 1-30 months after the last vaccine dose were cured. This first-in-man therapeutic HCV DNA vaccine study with the vaccine delivered by in vivo EP shows transient effects in patients with chronic HCV genotype 1 infection. The interesting result noted after SOC therapy suggests that therapeutic vaccination can be explored in a combination with SOC treatment.

HIV inhibition by CD4 and CCR5-derived glycopeptides

We have previously proposed a method by which natural antibodies can be redirected toward a known pathogen. We could show that CD4-derived peptides coupled to the galα1,3gal sugar moiety, a specificity held by natural antibodies, were able to neutralize HIV. Importantly, the antibody-peptide-antigen complexes activated the innate immune system through the Fc parts of the natural antibody. We now tested these peptides for their effectiveness on primary isolates and included sequence variations to increase their binding affinity. In addition, we evaluated three new CCR5-derived peptides. All peptides were tested for neutralization of six primary HIV-1 isolates. When testing three of the previously published glycopeptides we found that 10 to 100 times higher concentrations were needed to achieve the same neutralization of primary isolates. We found that the modifications of the CD4 glycopeptides modestly improved the neutralization of HIV-1. The modified CD4 and the CCR5 glycopeptides neutralized HIV-1 strains from different patients and of different subtypes. Notably, the combination of CD4 and CCR5 glycopeptides enhanced the neutralization potential as compared to the single peptides. A combination of CD4- and CCR5-galα1,3gal-linked peptides redirected natural antibodies to neutralize primary isolates of HIV-1, although less efficiently than laboratory-adapted strains. This might represent a new and valuable tool to block the entry of HIV into susceptible cells.

GPG-NH2 acts via the metabolite alphaHGA to target HIV-1 Env to the ER-associated protein degradation pathway

Background

The synthetic peptide glycyl-prolyl-glycine amide (GPG-NH₂) was previously shown to abolish the ability of HIV-1 particles to fuse with the target cells, by reducing the content of the viral envelope glycoprotein (Env) in progeny HIV-1 particles. The loss of Env was found to result from GPG-NH₂ targeting the Env precursor protein gp160 to the ER-associated protein degradation (ERAD) pathway during its maturation. However, the anti-viral effect of GPG-NH₂ has been shown to be mediated by its metabolite α-hydroxy-glycineamide (αHGA), which is produced in the presence of fetal bovine serum, but not human serum. In accordance, we wanted to investigate whether the targeting of gp160 to the ERAD pathway by GPG-NH₂ was attributed to its metabolite αHGA.

Results

In the presence of fetal bovine serum, GPG-NH₂, its intermediary metabolite glycine amide (G-NH₂), and final metabolite αHGA all induced the degradation of gp160 through the ERAD pathway. However, when fetal bovine serum was replaced with human serum only αHGA showed an effect on gp160, and this activity was further shown to be completely independent of serum. This indicated that GPG-NH₂ acts as a pro-drug, which was supported by the observation that it had to be added earlier to the cell cultures than αHGA to induce the degradation of gp160. Furthermore, the substantial reduction of Env incorporation into HIV-1 particles that occurs during GPG-NH₂ treatment was also achieved by treating HIV-1 infected cells with αHGA.

Conclusions

The previously observed specificity of GPG-NH₂ towards gp160 in HIV-1 infected cells, resulting in the production of Env (gp120/gp41) deficient fusion incompetent HIV-1 particles, was most probably due to the action of the GPG-NH₂ metabolite αHGA.

A historical reflection on the discovery of human retroviruses

The discovery of HIV-1 as the cause of AIDS was one of the major scientific achievements during the last century. Here the events leading to this discovery are reviewed with particular attention to priority and actual contributions by those involved. Since I would argue that discovering HIV was dependent on the previous discovery of the first human retrovirus HTLV-I, the history of this discovery is also re-examined. The first human retroviruses (HTLV-I) was first reported by Robert C. Gallo and coworkers in 1980 and reconfirmed by Yorio Hinuma and coworkers in 1981. These discoveries were in turn dependent on the previous discovery by Gallo and coworkers in 1976 of interleukin 2 or T-cell growth factor as it was called then. HTLV-II was described by Gallo's group in 1982. A human retrovirus distinct from HTLV-I and HTLV-II in that it was shown to have the morphology of a lentivirus was in my mind described for the first time by Luc Montagnier in an oral presentation at Cold Spring Harbor in September of 1983. This virus was isolated from a patient with lymphadenopathy using the protocol previously described for HTLV by Gallo. The first peer reviewed paper by Montagnier's group of such a retrovirus, isolated from two siblings of whom one with AIDS, appeared in Lancet in April of 1984. However, the proof that a new human retrovirus (HIV-1) was the cause of AIDS was first established in four publications by Gallo's group in the May 4^th issue of Science in 1984.

Isolation and characterization of a small antiretroviral molecule affecting HIV-1 capsid morphology

Background

Formation of an HIV-1 particle with a conical core structure is a prerequisite for the subsequent infectivity of the virus particle. We have previously described that glycineamide (G-NH₂) when added to the culture medium of infected cells induces non-infectious HIV-1 particles with aberrant core structures.

Results

Here we demonstrate that it is not G-NH₂ itself but a metabolite thereof that displays antiviral activity. We show that conversion of G-NH₂ to its antiviral metabolite is catalyzed by an enzyme present in bovine and porcine but surprisingly not in human serum. Structure determination by NMR suggested that the active G-NH₂ metabolite was α-hydroxy-glycineamide (α-HGA). Chemically synthesized α-HGA inhibited HIV-1 replication to the same degree as G-NH₂, unlike a number of other synthesized analogues of G-NH₂ which had no effect on HIV-1 replication. Comparisons by capillary electrophoresis and HPLC of the metabolite with the chemically synthesized α-HGA further confirmed that the antiviral G-NH₂-metabolite indeed was α-HGA.

Conclusion

α-HGA has an unusually simple structure and a novel mechanism of antiviral action. Thus, α-HGA could be a lead for new antiviral substances belonging to a new class of anti-HIV drugs, i.e. capsid assembly inhibitors.

Characterization of the invariable residue 51 mutations of human immunodeficiency virus type 1 capsid protein on in vitro CA assembly and infectivity

BACKGROUND

The mature HIV-1 conical core formation proceeds through highly regulated protease cleavage of the Gag precursor, which ultimately leads to substantial rearrangements of the capsid (CAp24) molecule involving both inter- and intra-molecular contacts of the CAp24 molecules. In this aspect, Asp51 which is located in the N-terminal domain of HIV-1 CAp24 plays an important role by forming a salt-bridge with the free imino terminus Pro1 following proteolytic cleavage and liberation of the CAp24 protein from the Pr55Gag precursor. Thus, previous substitution mutation of Asp51 to alanine (D51A) has shown to be lethal and that this invariable residue was found essential for tube formation in vitro, virus replication and virus capsid formation.

RESULTS

We extended the above investigation by introducing three different D51 substitution mutations (D51N, D51E, and D51Q) into both prokaryotic and eukaryotic expression systems and studied their effects on in vitro capsid assembly and virus infectivity. Two substitution mutations (D51E and D51N) had no substantial effect on in vitro capsid assembly, yet they impaired viral infectivity and particle production. In contrast, the D51Q mutant was defective both for in vitro capsid assembly and for virus replication in cell culture.

CONCLUSION

These results show that substitutions of D51 with glutamate, glutamine, or asparagine, three amino acid residues that are structurally related to aspartate, could partially rescue both in vitro capsid assembly and intra-cellular CAp24 production but not replication of the virus in cultured cells.

Mutation in the loop C-terminal to the cyclophilin A binding site of HIV-1 capsid protein disrupts proper virus assembly and infectivity

We have studied the effects associated with two single amino acid substitution mutations in HIV-1 capsid (CA), the E98A and E187G. Both amino acids are well conserved among all major HIV-1 subtypes. HIV-1 infectivity is critically dependent on proper CA cone formation and mutations in CA are lethal when they inhibit CA assembly by destabilizing the intra and/or inter molecular CA contacts, which ultimately abrogate viral replication. Glu98, which is located on a surface of a flexible cyclophilin A binding loop is not involved in any intra-molecular contacts with other CA residues. In contrast, Glu187 has extensive intra-molecular contacts with eight other CA residues. Additionally, Glu187 has been shown to form a salt-bridge with Arg18 of another N-terminal CA monomer in a N-C dimer. However, despite proper virus release, glycoprotein incorporation and Gag processing, electron microscopy analysis revealed that, in contrast to the E187G mutant, only the E98A particles had aberrant core morphology that resulted in loss of infectivity.

Orally active antiviral tripeptide glycyl-prolyl-glycinamide is activated by CD26 (dipeptidyl peptidase IV) before transport across the intestinal epithelium

The tripeptide amide glycyl-prolyl-glycinamide (GPG-amide) is a new antiretroviral drug candidate, but its absorption mechanism is unknown. In this investigation, the transport and metabolism of GPG-amide were studied in a model of the human intestinal epithelium, Caco-2 cell monolayers. The results show that when the tripeptide amide came into contact with the apical enterocyte membrane, it was degraded by CD26 (dipeptidyl peptidase IV) to glycylproline and the antiretrovirally active metabolite glycinamide. Glycinamide retained antiretroviral activity in vitro after transport through the Caco-2 cell monolayers. The transport of glycinamide across Caco-2 cell monolayers occurred via passive diffusion with an apparent permeability coefficient of about 2 x 10(-6) cm s(-1), which suggests that it is absorbed by the oral route in sufficient amounts to be considered for oral administration. In conclusion, the tripeptide GPG-amide acts as a prodrug that is activated by CD26 to release the orally active antiretroviral compound glycinamide.

Glycine-amide is an active metabolite of the antiretroviral tripeptide glycyl-prolyl-glycine-amide

The chemically modified tripeptide glycyl-prolyl-glycine-amide (GPG-NH(2)) inhibits replication of human immunodeficiency virus (HIV) type 1 (HIV-1) in vitro, probably by interfering with capsid formation. The aim of the present study was to determine whether the metabolites glycyl-proline (GP-OH), glycine (G-OH), prolyl-glycine-amide (PG-NH(2)), proline (P-OH), and glycine-amide (G-NH(2)) from proteolytic cleavage may inhibit the replication of HIV-1 in vitro. PG-NH(2) has previously been shown to have a modest effect on HIV-1 replication. In the present study we show that G-NH(2) exhibits a pronounced inhibitory effect on HIV-1. This effect was not due to a decrease in cell proliferation or viability and could not be shown for herpes simplex virus type 1. The G-NH(2) concentration that inhibited virus replication by 50% (IC(50)) was equimolar to that of GPG-NH(2) and ranged from 3 to 41 microM. Transmission electron microscopy revealed that the effect of G-NH(2) on HIV-1 morphology was equivalent to that of GPG-NH(2) and showed disarranged capsid structures, indicating interference with capsid formation. Serial passage of HIV-infected cells with G-NH(2) for more than 20 subcultivations did not decrease the susceptibility to the compound. The results from this study suggest that GPG-NH(2) might act as a prodrug and that G-NH(2) is an active antiretroviral metabolite.

Selected amino acid substitutions in the C-terminal region of human immunodeficiency virus type 1 capsid protein affect virus assembly and release

The capsid protein (CA or p24) of human immunodeficiency virus type 1 (HIV-1) plays a major role both early and late in the virus replication cycle. Many studies have suggested that the C-terminal domain of this protein is involved in dimerization and proper assembly of the viral core. Point mutations were introduced in two conserved sites of this region and their effects on viral protein expression, particle assembly and infectivity were studied. Eight different mutants (L205A+P207A, L205A, P207A, 223GPG225AAA, G223A, P224A, G225A and V221G) of the infectious clone pNL4-3 were constructed. Most substitutions had no substantial effect on HIV-1 protein synthesis, yet they impaired viral infectivity and particle production. The two mutants P207A and V221G also had a profound effect on Gag–Pol protein processing in HeLa–tat cells. However, these results were cell line-specific and Gag–Pol processing of P207A was not affected in 293T cells. In HeLa–tat cells, no virus particles were detected with the P207A mutation, whereas the other mutant virus particles were heterogeneous in size and morphology. None of the mutants showed normal, mature, conical core structures in HeLa–tat cells. These results indicate that the two conserved sequences in the C-terminal CA domain are essential for proper morphogenesis and infectivity of HIV-1 particles.

Obligatory involvement of CD26/dipeptidyl peptidase IV in the activation of the antiretroviral tripeptide glycylprolylglycinamide (GPG-NH2)

GPG-NH2 and G-NH2 are highly selective antiretroviral agents in cell culture, and both compounds inhibit HIV replication in CEM cell cultures to an equal extent (50% effective concentration: approximately 30 microM). The lymphocyte surface glycoprotein marker CD26, which is identical to dipeptidyl peptidase IV, efficiently converted GPG-NH2 to G-NH2 releasing the dipeptide GP-OH. The closely related QPG-NH2 derivative was also inhibitory to HIV, presumably by the dipeptidyl peptidase IV (DPP IV)-catalyzed release of G-NH2. In contrast, the cyclic pQPG-NH2 derivative in which the glutamine at the amino terminal position of QPG-NH2 was replaced by pyroglutamine and which is resistant to cleavage by purified CD26, was devoid of antiviral activity. CD26 is abundantly expressed on a variety of HIV target cells and is also present in serum of bovine, murine and human origin. The CD26/DPP IV enzymatic activity in serum and in cell suspensions could be efficiently inhibited by the CD26/DPP IV inhibitor L-isoleucinepyrrolidine (IlePyr) with 50% inhibitory concentrations ranging between 20 and 100 microM. When combined in HIV-1-infected cell cultures, IlePyr and Diprotin A (DP-A), another CD26/DPP IV inhibitor, abrogated the antiviral activity of GPG-NH2 but not of G-NH2. Therefore, it was concluded that the anti-HIV drug GPG-NH2 is not active as such, but rather behaves as a prodrug that must be obligatorily cleaved by CD26/DPP IV to G-NH2 to exert its antiretroviral activity. This is the first demonstration of a lymphocyte activation/differentiation marker (i.e. CD26) that plays a direct regulatory and indispensable role in the eventual antiretroviral activity of small synthetic molecules such as the antiretroviral (pro)drug GPG-NH2.

No cross-resistance or selection of HIV-1 resistant mutants in vitro to the antiretroviral tripeptide glycyl-prolyl-glycine-amide

The chemically modified tripeptide glycyl-prolyl-glycine-amide (GPG-NH(2)) inhibits replication of HIV-1 in vitro, probably by interfering with capsid formation. This study was aimed at determining cross-resistance between antiretroviral drugs and GPG-NH(2), and whether resistance to GPG-NH(2) can be induced in vitro. Fifty-five clinical HIV-1 isolates with different resistance-related mutations were tested for susceptibility to GPG-NH(2). No correlation between NRTI-, NNRTI- or PI-resistance and efficacy of GPG-NH(2) was found, indicating the lack of cross-resistance. Serial passages were performed with GPG-NH(2), and with lamivudine, and genotypic or phenotypic changes were determined. Resistance to lamivudine was detected after six passages. No resistance to GPG-NH(2) was generated after 30 passages in two parallel series. However, one mutation (T107I) in the p24 gene was detected in both series, but this mutation was not associated with decreased sensitivity to GPG-NH(2).

Intracellular high mobility group B1 protein (HMGB1) represses HIV-1 LTR-directed transcription in a promoter- and cell-specific manner

We investigated whether the high mobility group B 1 (HMGB1), an abundant nuclear protein in all mammalian cells, affects HIV-1 transcription. Intracellular expression of human HMGB1 repressed HIV-1 gene expression in epithelial cells. This inhibitory effect of HMGB1 was caused by repression of long terminal repeat (LTR)-mediated transcription. Other viral promoters/enhancers, including simian virus 40 or cytomegalovirus, were not inhibited by HMGB1. In addition, HMGB1 inhibition of HIV-1 subtype C expression was dependent on the number of NF kappa B sites in the LTR region. The inhibitory effect of HMGB1 on viral gene expression observed in HeLa cells was confirmed by an upregulation of viral replication in the presence of antisense HMGB1 in monocytic cells. In contrast to what was found in HeLa cells and monocytic cells, endogenous HMGB1 expression did not affect HIV-1 replication in unstimulated Jurkat cells. Thus, intracellular HMGB1 affects HIV-1 LTR-directed transcription in a promoter- and cell-specific manner.

Tripeptide interference with human immunodeficiency virus type 1 morphogenesis

Capsid assembly during virus replication is a potential target for antiviral therapy. The Gag polyprotein is the main structural component of retroviral particles, and in human immunodeficiency virus type 1 (HIV-1), it contains the sequences for the matrix, capsid, nucleocapsid, and several small polypeptides. Here, we report that at a concentration of 100 micro M, 7 of 83 tripeptide amides from the carboxyl-terminal sequence of the HIV-1 capsid protein p24 suppressed HIV-1 replication (>80%). The three most potent tripeptides, glycyl-prolyl-glycine-amide (GPG-NH(2)), alanyl-leucyl-glycine-amide (ALG-NH(2)), and arginyl-glutaminyl-glycine-amide (RQG-NH(2)), were found to interact with p24. With electron microscopy, disarranged core structures of HIV-1 progeny were extensively observed when the cells were treated with GPG-NH(2) and ALG-NH(2). Furthermore, nodular structures of approximately the same size as the broad end of HIV-1 conical capsids were observed at the plasma membranes of treated cells only, possibly indicating an arrest of the budding process. Corresponding tripeptides with nonamidated carboxyl termini were not biologically active and did not interact with p24.

MCEF, the newest member of the AF4 family of transcription factors involved in leukemia, is a positive transcription elongation factor-b-associated protein

Positive transcription elongation factor-b (P-TEFb) contains CDK9 and cyclin T(1). P-TEFb was affinity purified from a stably transfected cell line that expresses epitope-tagged CDK9, and proteins that appeared to be specifically bound were sequenced. In addition to CDK9, previously identified isoforms of cyclin T (including T(1), T(2A) and T(2B)), HSP90 and CDC37, this analysis identified a novel protein named MCEF. Cloning of its cognate cDNA revealed that MCEF is the newest member of the AF4 family of transcription factors involved in acute lymphoblastic leukemia. MCEF RNA was expressed in all human tissues examined, and antisera directed against recombinant MCEF specifically immunoprecipitated P-TEFb. Ectopic expression of MCEF did not activate HIV-1 replication, and tethering of MCEF to a promoter did not activate transcription.

Smaller amounts of antiretroviral drugs are needed when combined with an active ribozyme against HIV-1

We have tested for combined anti-HIV-1 effects of a hammerhead ribozyme and antiretroviral drugs and the possibility of reducing the drug burden of patients on highly active antiretroviral therapy (HAART). The antiretroviral compounds used represent the three groups in HAART: nucleoside analogue reverse-transcriptase inhibitors, nonnucleoside reverse-transcriptase inhibitors, and protease inhibitors. A human T cell line (HUT78), stably expressing a hammerhead ribozyme targeted to nef (hhRz.nef(9016-9029)), was infected with HIV-1(SF2) in the presence of a single drug. The combined effects on HIV-1 replication were measured by p24 antigen determinations over a 2-week period. In the presence of the ribozyme, smaller amounts of antiretroviral drugs were required to reduce the HIV-1 p24 levels equally as much as when only drugs were present. The results support a strategy of combining ribozyme gene therapy with HAART to improve the long-term outcome of anti-HIV-1 therapy.

Upstream stimulating factor affects human immunodeficiency virus type 1 (HIV-1) long terminal repeat-directed transcription in a cell-specific manner, independently of the HIV-1 subtype and the core-negative regulatory element

Human immunodeficiency virus type 1 (HIV-1) is classified into subtypes on the basis of phylogenetic analysis of sequence differences. Inter- and intra-subtype polymorphism extends throughout the genome, including the long terminal repeat (LTR). In this study, the importance of the upstream stimulating factor (USF)-binding site (E-box) in the core-negative regulatory element (NRE) of the LTR of HIV-1 subtypes A, B, C, D, E and G was investigated. In vivo, USF was found to repress transcription directed from representative HIV-1 LTR sequences of all the subtypes tested in an epithelial cell line, yet activate the same transcription in a T-cell line. Mutation of the core-NRE USF site of the representative subtype B LTR did not affect the cell-specific, subtype-independent, dual role of USF. In vitro binding assays showed that recombinant USF(43) interacts with the core-NRE from subtypes B and C, but not A, D, E or G. Thus, USF affects LTR-directed transcription in a cell-specific manner, independently of both the HIV-1 subtype from which the LTR was derived and the core-NRE USF site sequences.

The tripeptide glycyl-prolyl-glycine amide does not affect the early steps of the human immunodeficiency virus type 1 replication

OBJECTIVE

To determine whether the peptide glycyl-prolyl-glycine amide (GPG-NH2) corresponding to a conserved motif in the tip of the third hypervariable region of gp120 affected the early events in the human immunodeficiency virus type 1 (HIV-1) replication.

DESIGN/METHODS

Glycyl-prolyl-glycine amide was tested for its effect on HIV-1 adsorption, co-receptor usage, proviral DNA synthesis, messenger RNA (mRNA) synthesis and splicing, translation, tat/TAR transactivation, and virus protease activity.

RESULTS

Glycyl-prolyl-glycine amide did not appear to affect the early events of the virus replication. HIV-1 having glycine-leucine-glycine instead of GPG in the V3 loop and the mutants deleted of the GPG motif were still inhibited by the peptide. Glycyl-prolyl-glycine-NH2 had no discernible effect on any of the other steps in the virus replication cycle tested. The only effect observed was an increased sodium dodecyl sulfate polyacrylamide amide gel electrophoresis mobility of gp160/120 at high concentrations of GPG-NH2.

CONCLUSIONS

The tripeptide GPG-NH2 is a nontoxic compound that inhibits the replication of HIV-1 by an apparently new mode of action.

The nontoxic tripeptide glycyl-prolyl-glycine amide inhibits the replication of human immunodeficiency virus type 1

OBJECTIVE

To determine whether short peptides corresponding to the RGPGR motif of the V3 loop of gp 120 have anti-human immunodeficiency virus type 1 (anti-HIV-1) activity.

DESIGN/METHODS

Short peptides were tested against the HIV-1 laboratory strains and clinical isolates.

RESULTS

The tripeptide glycyl-prolyl-glycine amide (GPG-NH2) inhibited the replication of both laboratory strains and 47 clinical isolates, including 19 strains that were resistant to other drugs or that were from patients with failing therapy. The 50% inhibitory concentrations values were 2.7 to 37 microM. Phenotypic change of two isolates from nonsyncytia-inducing to syncytia-inducing did not change their sensitivity to GPG-NH2. The tripeptide added to the antiviral effect of both zidovudine and ritonavir.

CONCLUSIONS

The tripeptide GPG-NH2 is a nontoxic compound that inhibits the replication of HIV-1 by an apparently new mode of action. Glycyl-prolyl-glycine-NH2 might prove useful by itself or as a lead compound for the treatment of drug-resistant HIV-1. Glycyl-prolyl-glycine-NH2 is currently undergoing phase I/II human clinical trials in Sweden.

Real-time monitoring of cytomegalovirus infections after stem cell transplantation using the TaqMan polymerase chain reaction assays

BACKGROUND

Real-time monitoring of cytomegalovirus (CMV) infections in transplant patients demands a rapid and high-throughput CMV DNA quantification method.

METHODS

TaqMan polymerase chain reaction assays based on CMV immediate early protein exon 4 and glycoprotein B were developed and were compared with a COBAS AMPLICOR CMV MONITOR (CMM) test for quantifying CMV DNA in peripheral blood leukocytes from seven stem cell transplant patients having received antiviral treatment.

RESULTS

There was a good correlation between the TaqMan assays and the CMM test for CMV DNA quantification. The throughput of the TaqMan assays was, however, about 3 times higher than that of the CMM test. The CMV DNA dynamics patterns determined by the TaqMan polymerase chain reaction were well in line with the outcome of the antiviral therapy.

CONCLUSIONS

The TaqMan assays may potentially serve as a useful tool for rapid quantification of CMV infections in stem cell transplant patients.

Deletion of the GPG motif in the HIV type 1 V3 loop does not abrogate infection in all cells

The three amino acids glycine, proline, and glycine (GPG) constitute a conserved motif at the center of the V3 loop of HIV-1 surface glycoprotein 120. It has been indicated that deletion of this GPG motif is lethal for viral infectivity and abrogates the ability of the virus to form syncytia. In the present work, we studied the effects of GPG deletion on viral infectivity, cell tropism, syncytium formation, and initiation of apoptosis by constructing a mutant provirus based on the infectious clone pBRu-2. Successful infection and replication of GPG-deleted virus were detected in MT-2 cells, although the mutant virus showed lower infectivity. Infection could also be observed in the C8166, C91-PL, Molt-3, and THP-1 cell lines, and in PBMC-derived dendritic cells (DCs), but not in CEM-SS, HUT78, H9, Jurkat, and U937 cell lines or in PBMCs. Mutant virus also induced syncytia and apoptosis in the MT-2 cells. An intact GPG motif is probably necessary for unimpaired induction of fusion in some HIV-1-permissive cells. However, once the virus enters the cells, the GPG sequence does not seem to be indispensable for syncytium formation or apoptosis induction in MT-2 cells. Our data also imply that cell surface molecules other than CD4 and CXCR4 may be involved in entry of the GPG-deleted virus.

Long terminal repeat promoter/enhancer activity of different subtypes of HIV type 1

Transcription of the HIV-1 provirus genome is regulated by a complex interplay between viral regulatory proteins and cellular transcription factors that interact with the viral long terminal repeat (LTR) region of HIV-1. However, several cellular transcription factors have been identified that can interact with the HIV-1 LTR; the significance of all of these factors is not clearly understood. In this study we have characterized the LTR region of different subtypes of HIV-1 with regard to nucleotide sequence and promoter activity. The LTR regions of HIV-1 from peripheral blood mononuclear cells of 29 infected individuals originating from 10 different geographical regions were sequenced and further analyzed for promoter/enhancer activity in transient transfection of HeLa cells, in the context of a reporter gene and in the context of the complete virus genome. We found several subtype-specific LTR sequences of the various HIV-1 strains, such as an insertion that created a potential third NF-kappaB site in the LTR of the subtype C strains. The USF-binding site in the NRE also contained subtype-specific sequences. Interestingly, the promoter/enhancer activities of the subtype C LTRs were higher than the activities of the other subtypes analyzed here (subtypes A, B, D, E, and G), suggesting that the potential third NF-kappaB site may confer higher LTR activity or that the subtype C NRE may be less potent. Thus, our data suggest that genetic diversity of the LTR may result in HIV-1 subtypes with different replicative properties.

No association of HIV type 1 long terminal repeat sequence pattern with long-term nonprogression and in vivo viral replication levels in European subjects

The HIV-1 long terminal repeat (LTR) promotes and modulates proviral transcription in the infected cell. It has been suggested that truncations and even point mutations in functional sites of the LTR are associated with low viral replication and attenuated pathogenesis in HIV-1-infected long-term nonprogressors (LTNPs). We performed a detailed analysis of LTR sequences from proviral DNA of 21 Italian and Swedish, well-characterized LTNPs and of 15 progressor patients. No truncation was found and no correlation was identified between specific LTR mutations and disease progression. We also failed to find a significant correlation between phylogenetic distance and clinical status. Although HIV-1 LTR interpatient heterogeneity among LTNPs and subjects with HIV-1 RNA levels <500 copies/ml tended to be lower, no sequence mutation was correlated with in vivo viral loads. Our results suggest that HIV-1 LTR defects are rare among Italian and Swedish LTNPs.

HIV-1 nef mutations and clinical long-term nonprogression. A molecular epidemiology study

OBJECTIVES

To analyze HIV-1 nef gene mutations in a cohort of Italian and Swedish long-term nonprogressors (LTNP) and to investigate whether particular amino acid substitutions are associated with LTNP.

STUDY DESIGN/METHODS

nef alleles from 21 LTNP and 8 progressor controls were amplified by polymerase chain reaction (PCR) and sequenced. The amino acid sequences were compared with the previously reported sequences of 16 North American LTNP and of 28 patients with progressive infection.

RESULTS

An untruncated intact open reading frame was observed as major sequence in all LTNP and controls. None of the amino acid substitutions in known biologically functional sites was linked to LTNP. A valine/isoleucine at the variable position 11 was associated with both European (P = .0001) and American (P = .001) LTNP. The interpatient nef variation was lower among European LTNP (P = .002) than in European progressor controls.

CONCLUSIONS

Nef amino acid heterogeneity is lower among LTNP, probably reflecting the lower HIV-1 replication rate. Nef gene defects appear uncommon in both Swedish and Italian LTNP, although the presence of a valine/isoleucine at position 11 is statistically associated with a lower probability to progress to disease.

Increased serum concentrations of interleukin-2 receptor in the first trimester in women who later developed severe preeclampsia

BACKGROUND

To determine the concentration of cytokines having an immunomodulating effect in the first trimester in women who subsequently developed preeclampsia.

METHODS

The serum concentrations of IL-10, TNFalpha, IL-6 and IL-2R were determined in ten women who later developed severe preeclampsia and in ten healthy controls. The groups were compared with the Mann-Whitney U test.

RESULTS

The IL-2R concentration was significantly higher in the women who later developed preeclampsia than in normal patients (p = 0.028). No significant differences were detected between the groups with respect to the other evaluated cytokines.

CONCLUSION

Elevated IL-2R concentrations in maternal serum as early as in the first trimester may be a sign of immunological maladaptation and might be associated with a disturbance of trophoblastic invasion.

Nonsynonymous mutations within the human immunodeficiency virus type 1 p17 gene are clustered to sequences binding to the host human leukocyte antigen class I molecules

We have analyzed the relation between intrapatient variabilities of the p17 gene and the location of known host p17 cytotoxic T lymphocyte (CTL) epitopes in five patients infected with human immunodeficiency virus type 1 (HIV-1). All patients were typed with respect to the human leukocyte antigen (HLA) class I type. One to seven previously fine-mapped p17 CTL epitopes corresponded to the HLA class I restriction elements of each patient. An average of 28+/-16% of the p17 gene of each patient encoded CTL epitopes corresponding to the HLA restriction elements of the host. Twenty full-length p17 gene clones were sequenced from each patient. The intrapatient homology between the p17 sequences ranged from 96.4 to 98.9%. The interpatient homology between the consensus sequences of each patient ranged from 83.1 to 91.6%. A total of 246 nucleotide differences within the 100 p17 clones was noted. Fifteen (16%) of 96 synonymous substitutions were found within host CTL epitopes, whereas 72 (48%) of 150 nonsynonymous nucleotide changes were found within CTL epitopes corresponding to the HLA restriction elements of the host (p < 0.0001; Fisher's exact test). Subsequently, variable residues indicating the evolution of at least two major p17 species (i.e., >20% of the clones) were determined to be more common at positions contained within these CTL epitopes (p < 0.01). The present data suggest that the evolution of the p17 gene is influenced by contact areas with the host HLA class I molecules.

Quantification of HIV-1 proviral DNA from peripheral blood mononuclear cells using a high throughput four-competitor competitive PCR

A multiple competitor PCR (mcPCR) was developed to quantify HIV-1 proviral DNA from peripheral blood mononuclear cells (PBMC). DNA extracted from a mixture of HIV infected PBMC and four size-mutated DNA competitors were co-amplified. The Cy5-fluorescence labelled PCR products were denatured by heating, separated using an automated DNA sequencer and quantified by a fragment analysis computer software. An internal standard was generated by plotting the peak areas of the four competitors against their inputs. Based on the internal standard, HIV sample DNA was quantified by extrapolating the corresponding signal. The linear range of the mcPCR was three log wide and the quantitation limit was about 20 copies of HIV DNA/10(6) PBMC. Using the mcPCR, HIV DNA was quantified from 14 long-term non progressors (LTNP) and 14 patients with advanced disease. A significantly lower copy number of HIV DNA was obtained in the LTNP (p = 0.018). These data suggest that the mcPCR is sensitive, reliable and especially useful for HIV DNA quantification of a large number of clinical samples.

Differences in humoral responses to the p24 antigen between Ethiopian and Swedish human immunodeficiency virus type 1-infected patients may suggest influences from a T-helper 2-like phenotype

The levels of human immunodeficiency virus type 1 p24 antibodies and p24 antigen among 256 Ethiopians and Africans and 86 Swedes were compared. The elevated levels of total anti-p24 immunoglobulin G (IgG) and anti-p24 IgG4 among the Ethiopian and African patients suggest influences from T-helper-cell type 2-like responses.

Identification of cross-reactive antigenic target regions for HIV type 1-specific antibody-dependent cellular cytotoxicity

Monkey-derived hyperimmune antisera against 40 peptides, together representing the entire envelope gp120 of HIV-1LAI, were used to map antibody-dependent cellular cytotoxicity (ADCC) target regions. Four regions corresponding to amino acids 65-126, 152-230, 248-330, and 445-466 were found to contain epitopes inducing ADCC activity not only against HIV-1LAI-infected cells but also against cells infected with HIV-1SF2 and clinical isolates of HIV-1. When comparing seroreactivity to the individual peptides with ADCC titers none of the regions seemed to be dominant. These results thus describe cross-reactive regions involved in the functional immunity against HIV-1 gp120.

mtDNA variation indicates Mongolia may have been the source for the founding population for the New World

mtDNA RFLP variation was analyzed in 42 Mongolians from Ulan Bator. All four founding lineage types (A [4.76%], B [2.38%], C [11.9%], and D [19.04%]) identified by Torroni and colleagues were detected. Seven of the nine founding lineage types proposed by Bailliet and colleagues and Merriwether and Ferrell were detected (A2 [4.76%], B [2.38%], C1 [11.9%], D1 [7.14%], D2 [11.9%], X6 [16.7%], and X7 [9.5%]). Sixty-four percent of these 42 individuals had "Amerindian founding lineage" haplotypes. A survey of 24 restriction sites yielded 16 polymorphic sites and 21 different haplotypes. The presence of all four of the founding lineages identified by the Torroni group (and seven of Merriwether and Ferrell's nine founding lineages), combined with Mongolia's location with respect to the Bering Strait, indicates that Mongolia is a potential location for the origin of the founders of the New World. Since lineage B, which is widely distributed in the New World, is absent in Siberia, we conclude that Mongolia or a geographic location common to both contemporary Mongolians and American aboriginals is the more likely origin of the founders of the New World.

A novel ribozyme target site located in the HIV-1 nef open reading frame

We have tested the sequence UUC CAG UCA GAC CU, at position 9016--9029 within the HIV-1(SF2) nef open reading frame, for accessibility to antisense and hammerhead ribozyme attack. The accessibility was first studied using a phosphorothioate-modified 14-nt DNA oligo (complementary to the nef9016--9029 site). A dose-dependent repression of HIV-1(SF2) growth was observed in human peripheral blood mononuclear cells after exogenous administration of the oligo to the cell culture medium. A hammerhead ribozyme with a 6+7-nt antisense specificity for the nef9016--9029 site (hhRz.nef9016--9029) was constructed and transfected into the human T-cell line HUT78. Again, a dose-dependent repression of virus growth was observed when different individual clones expressing hhRz.nef9016--9029 were infected with HIV-1(SF2). A complete abrogation of virus production was observed after infection with a low (0.5 TCID50) HIV-1 titer. Increasing doses (2.5 and 12.5 TCID50) of HIV-1 virus yielded a low production (10(3)-fold reduced) of virus particles in most cases; but a complete, or close to complete, abrogation was observed even in individual cultures infected with the highest dose. Presence of proviral pol and gag sequences in hhRz.nef9016--9029-expressing HUT78 clones was assayed, using PCR. Interestingly, since no pol and gag PCR products could be detected, the results strongly indicated that the hammerhead ribozyme was already acting on the infecting HIV RNA before its reverse transcription and integration as proviral DNA. In summary, the results obtained in this study support the nef9016--9029 site as a strong new candidate for ribozymal gene therapy against HIV-1 infection.

Acyclovir treatment of relapsing-remitting multiple sclerosis. A randomized, placebo-controlled, double-blind study

Acyclovir treatment was used in a randomized, double-blind, placebo-controlled clinical trial with parallel groups to test the hypothesis that herpes virus infections are involved in the pathogenesis of multiple sclerosis (MS). Sixty patients with the relapsing-remitting form of MS were randomized to either oral treatment with 800 mg acyclovir or placebo tablets three times daily for 2 years. The clinical effect was investigated by an extensive test battery consisting of neurological examinations, neuro-ophthalmological and neuropsychological tests, and evoked potentials. Results were based on "intent-to-treat" data and the primary outcome measure was the exacerbation rate. In the acyclovir group (n = 30), 62 exacerbations were recorded during the treatment period, yielding an annual exacerbation rate of 1.03. The placebo group (n = 30) had 94 exacerbations and an annual exacerbation rate of 1.57. Thus, 34% fewer exacerbations were encountered during acyclovir treatment. This difference in exacerbation rate between the treatment groups was not significant (P = 0.083). However, this trend to a lower disease activity in acyclovir-treated patients was supported in subsequent data analysis. If the patients were grouped according to exacerbation frequencies, i.e. into low (0-2), medium (3-5) and high (6-8) rate groups, the difference between acyclovir and placebo treatment was significant (P = 0.017). Moreover, in a subgroup of the population with a duration of the disease of at least 2 years providing an exacerbation rate base-line before entry, individual differences in exacerbation rates were compared between the 2-year pre-study period and the study period in acyclovir-treated (n = 19) and placebo (n = 20) patients and acyclovir-treated patients showed a significant reduction of exacerbations (P = 0.024). Otherwise, neurological parameters were essentially unaffected by acyclovir treatment and there were no convincing signs of reduced neurological deterioration in the acyclovir group. This study indicates that acyclovir treatment might inhibit the triggering of MS exacerbations and thus suggests that acyclovir-susceptible viruses might be involved in the pathogenesis of MS. This possibility warrants further investigation.

Characterization of an antigen shared by human thymic epithelium and human T cell leukemia virus p19 Gag protein

The molecular basis for cross-reactive antibody binding to human T cell leukemia virus type I (HTLV-I) p19 core protein and human thymic epithelium has been defined with two monoclonal antibodies (mAbs), 12/1-2 and 13B12, raised to HTLV-I p19. The mAb 12/1-2 has previously been shown to react with HTLV-I p19, HTLV-II p22, and antigens of normal human thymic epithelium, placenta, and foreskin, whereas mAb 13B12 binds only to the carboxyl terminus of HTLV-I p19. In the present study, mAb 12/1-2 bound to a subset of Triton X-100-insoluble intermediate filaments in human thymic epithelium also recognized by antikeratin antibodies AE1 and AE3. The mAb 12/1-2 also reacted in Western blot assays with proteins of 54, 46, and 40 kDa present in extracts of human thymic epithelium and with hexameric peptides containing overlapping sequences of HTLV-I p19 with the amino acids IPP (amino acids 117-119). In contrast, the HTLV-I-specific mAb 13B12 did not bind to human thymic epithelium and reacted with a single hexameric peptide containing the carboxy-terminal HTLV-I p19 sequence IPPPYV (amino acids 117-122). Binding of mAb 12/1-2 to thymic epithelium could be inhibited by adsorption with peptide SP-79 containing a C-terminal sequence (amino acids 112-125) of p19. The crossreactive IPP site is within a region of p19 that has been previously shown to be highly immunogenic in HTLV-I-infected individuals and that is also encoded by genes or mRNA of human cytokeratin 17, keratin 4, epidermal cytokeratin 2, and 50-kDa type I epidermal keratin. Thus, our studies define the sequence of a cross-reactive antigen on HTLV-I p19 that is also associated with keratin intermediate filaments from human thymic epithelium and other normal human tissues and that could serve as a focus of an autoimmune response during HTLV-I infection.