Accumulation of defective viral genomes in peripheral blood mononuclear cells of human immunodeficiency virus type 1-infected individuals

Human immunodeficiency virus type 1 (HIV-1) genomes present in peripheral blood mononuclear cells (PBMCs) of infected persons or in lymphocytes infected in vitro were studied by long-distance PCR (LD-PCR) using primers localized in the HIV-1 long terminal repeats. The full-length 9-kb DNA was the only LD-PCR product obtained in peripheral and cord blood lymphocytes from seronegative donors infected in vitro. However, a high proportion (27% to 66%) of distinct populations of extensively deleted HIV-1 genomes of variable size was detected in PBMCs of 15 of 16 HIV-1-infected persons. Physical mapping of defective genomes showed that the frequency of deletions is proportional to their proximity to the central part of HIV-1 genome, which is consistent with a deletion mechanism involving a single polymerase jump during reverse transcription. Sequencing of deletion junctions revealed the presence of short direct repeats of three or four nucleotides. The number of defective HIV-1 genomes decreased after in vitro activation of PBMCs. Persistence of full-length and deleted genomes in in vitro activated PBMCs correlated with isolation of an infectious virus. Our results represent the first quantitative assessment of intragenomic rearrangements in HIV-1 genomes in PBMCs of infected persons and demonstrate that, in contrast to in vitro infection, defective genomes accumulate in PBMCs of infected persons.

Insulin analogues: new agents for improving glycemic control

For years, it has been recognized that "reasonable" control of blood glucose levels reduces the acute complications of diabetes mellitus. Recent studies have conclusively shown that strict glycemic control reduces the appearance and progression of chronic complications. Thus, strict glycemic control is the most salient goal of insulin therapy. Insulin regimens that closely mimic physiologic insulin secretory patterns have been inadequate because of limitations imposed by the pharmacokinetic profiles of commercially available preparations. The newer insulin analogues, both rapid-acting and long-acting, have more appropriate pharmacokinetic profiles. Lispro (Humalog) is the first human insulin analogue to be approved in the United States. Its pharmacokinetic and pharmacodynamic profile makes it amenable for use before meals. The search for long-acting and hepatospecific analogues continues.

Genetic control of infection of primary macrophages with T-cell-tropic strains of HIV-1

Human immunodeficiency virus type 1 (HIV-1) NDK, a Zairian subtype D virus highly cytopathic for CD4-positive lymphocytes, and the prototype subtype B virus HIV-1 LAV are about 10(4) and 10(5) times more infectious, respectively, for T lymphocytes than for blood-derived macrophages (BDM). Recombinant viruses derived from HIV-1 LAV and HIV-1 NDK were used to determine the genetic control and the step of the virus/cell cycle responsible for infection of BDM with T-cell-tropic viruses. We found that recombinants bearing the envelope glycoprotein of HIV-1 NDK are able to enter more efficiently into BDM than recombinants with HIV-1 LAV envelope glycoprotein. We also found that a genetic region outside of the env gene is responsible for production of HIV-1 NDK infectious progeny from BDM. This region consists of the vif gene and the C- and N-terminal portions of pol and vpr genes, respectively. Our results suggest that productive infection of primary macrophages with T-cell-tropic strains of HIV-1 is determined by two different genetic mechanisms: one effective at the virus/cell entry, controlled by the env gene, and the second after entry, controlled by genes vif and vpr. In comparison with HIV-1 LAV, HIV-1 NDK has been able to more easily overcome both restriction mechanisms.

Fusogenic determinants of highly cytopathic subtype D Zairian isolate HIV-1 NDK

Phenotypic characterization of subtype B strains of human immunodeficiency virus type 1 (HIV-1) indicates that the major determinants of their cytopathogenicity and tropism are contained in the gene coding for the envelope glycoprotein gp120, namely in its variable regions V1, V2, and V3. Recombinant viruses derived from HIV-1 LAV, the subtype B prototype virus, and HIV-1 NDK, the Zairian subtype D virus highly cytopathic for CD4-positive lymphocytes, were used to elucidate genetic control of fusogenic functions in subtype D viruses. Our data demonstrate that multigenic determination of fusogenic properties is more complex in the subtype D than in clade B viruses. Variability in three regions of HIV-1 NDK genome correlated with formation of large syncytia. These regions consisted of the matrix protein, the C-terminal portion of vpr up to the C1 region of gp120, and the V1-V3 regions of gp120. Variability in the envelope glycoprotein but not in other regions of the HIV-1 genome was related to enhanced resistance of HIV-1 NDK to treatment of target cells with OKT4-A anti-CD4 MAb. Therefore, a different genetic control affects two aspects of HIV-1 fusogenicity: (i) variability in the envelope glycoprotein itself is sufficient to influence a virus-to-cell fusion at the virus/cell entry, and (ii) a more complex genetic function including genes of matrix protein and envelope glycoprotein is related to variability of cell-to-cell fusion during formation of syncytium.

Allogeneic bone marrow transplantation for childhood acute lymphoblastic leukemia in second remission: factors predictive of survival, relapse and graft-versus-host disease

Between 1983 and 1993, 42 patients with acute lymphoblastic leukemia (ALL) in second complete remission (CR) underwent an allogeneic HLA-identical bone marrow transplant (BMT; there was one family mismatched graft). The conditioning regimens varied, consisting of cyclophosphamide (CY) and total body irradiation (TBI; n = 10); CY, TBI, Ara C, VP-16 (n = 11); TBI, Ara C, melphalan (n = 20) (TAM) or other (n = 1). Cyclosporine A (CsA) (n = 15) or CsA and methotrexate (MTX) (n = 24) were the main regimens for prophylaxis of graft-versus-host disease (GVHD). Nineteen of 42 patients are alive in CR ranging from 1 to 72 months after BMT with a median follow-up of 36 months. The 4-year actuarial survival rate was 53%. The actuarial relapse rate was 17%. Twenty three patients died: 4 patients of leukemic relapse, 9 of infection, 2 of acute GVHD, 2 of multiorgan failure after chronic GVHD, 2 of a secondary tumour and 4 patients died of other causes. Several pre- and post-transplant characteristics were analyzed to determine predictive factors for survival, relapse and GVHD. The relapse rate was significantly influenced by the type of conditioning regimen with no relapse in the TBI, Ara C, melphalan group. The analysis of long-term sequelae shows that there are no severe complications in this last group. Our results confirm that allogeneic BMT can lead to long-term survival for children with ALL in second CR and suggest an advantage of using the TAM conditioning regimen in the eradication of the leukemic disease.

Restriction of HIV-1 replication in intestinal cells is genetically controlled by the gag-pol region of the HIV-1 genome

The human colon epithelial line HT29 represents a semipermisive cellular system for human immunodeficiency virus type 1 (HIV-1). It could be productively infected with HIV-1 NDK, a Zairian virus isolate highly cytopathic for CD4 positive lymphocytes, whereas infection with the prototype virus HIV-1 LAV was nonproductive. Recombinant viruses derived from HIV-1 LAV and HIV-1 NDK were used to determine the genetic control, step of virus/cell cycle, and molecular mechanism responsible for productive versus nonproductive infection of intestinal cells. Both parental viruses and all recombinants retrotranscribed their genomes with a similar kinetics and were able to complete HIV-1 DNA synthesis, HIV-1 LAV provirus present in preintegration complexes could be rescued by cocultivation with T-lymphocytes. However, it was aborted during prolonged cultivation of HT29 cells. Our results suggest that (i) gag/pol region of HIV-1 genome (fragment BssHII255-EcoRI4183) genetically controlled productive infection of intestinal cells and that (ii) the difference between productive and abortive infection occurred before synthesis of HIV-1 mRNA, at the integration level.

Neutralizing antibodies against highly cytopathic Zairian human immunodeficiency type-1 virus (HIV-1) NDK are present in sera outside Africa

The prototype virus HIV-1 LAV and highly cytopathic Zairian virus HIV-1 NDK belong to the genetic subtypes B and D and represent low and highly cytopathic phenotypes, respectively. Their neutralization pattern and serotype were studied with respect to differences in their genotypes and phenotypes. Sera from HIV-1-infected persons living in four geographically distant areas, Philadelphia (USA), Ribeirao Preto (Brazil), Marseille (France) and Kinshasa (Zaire), were tested for the presence of type-specific and group-specific cross-reacting neutralizing antibodies against HIV-1 LAV and HIV-1 NDK in a continuous cell line MT4. The majority of type-specific antibodies were directed against HIV-1 LAV in Philadelphia, Ribeirao Preto and Marseille, and against HIV-1 NDK in Kinshasa. However, some sera with an HIV-1 NDK type-specific neutralization pattern were also found in Philadelphia, Ribeirao Preto and Marseille. These results indicate that strains with an HIV-1 NDK-like serotype could be found outside Africa. The presence of type-specific neutralizing antibodies against HIV-1 NDK in sera from North and South America and Europe should be taken into account during attempts to serotype HIV as well as in the course of selection of HIV-1 candidate strains for an AIDS vaccine.

Lectin-mediated effects on HIV type 1 infection in vitro

Lectins with specificity for terminal mannose residues and anti-mannan antibodies neutralize HIV-1 infection in vitro. This is assumed to be caused by binding of the agents to the viral glycoproteins. In this study we show that one such agent, the Galanthus nivalis lectin (GNA), also blocks infection at the target cell level. To explore the effect of GNA on HIV infection we used the two HIV-1 isolates LAV and NDK, representing in the first case a prototype virus and in the latter case a highly cytopathic virus, which spreads preferentially via cell-to-cell contact. MT-4 cells were used as target cells and infection was determined from the occurrence of syncytia. Cell-to-cell infection was studied with CEM cells persistently infected with the two virus isolates. GNA, at concentrations in the nanogram per milliliter range, neutralized the HIV-1 isolates LAV, NDK, and MN as well as HIV-2ROD. Pretreatment of cells with the lectin, before addition of virus, or of infected cells, also blocked infection. This effect was more pronounced with HIV-1NDK than with HIV-1LAV. Mannosidase treatment of the target cells abolished the GNA effect on HIV-1NDK infection. It is concluded that GNA inhibits infection of several HIV isolates. It neutralizes infection by binding to the virion but also blocks infection at the target cell level. The latter effect may be different for different virus isolates. Mannosyl residuals at the cell surface are targets for GNA modulation of infection with the cytopathic HIV-1NDK. These do not represent essential virus receptors.

Lectin effects on HIV-1 infectivity

Lectins with specificity for terminal mannose residues and anti-mannan antibodies are assumed to neutralize HIV-1 by binding to the viral glycoproteins. In this report we demonstrate that one such agents, the lectin from Galanthus nivalis (GNA), blocks infection also at the target cell level.

Production and simple purification of a protein encoded by part of the gag gene of HIV-1 in the Escherichia coli HB101F+ expression system inducible by lactose and isopropyl-beta-D-thiogalactopyranoside

The development of the Escherichia coli expression system, which was prepared by transferring the F' episome from strain 71/18 to a highly to a transformable F- strain HB101, is described. These new HB101 (F+) cells, which produced high levels of lac repressor, were capable of taking up lactose and grew under strict selection conditions. A relatively simple two-step purification of part of a protein (M(r) 27,000) encoded by the gag gene of HIV-1 in this expression system is described. The supernatant prepared by removal of cell debris was precipitated by 30% saturation of ammonium sulphate. The protein spectrum was characterized by gel electrophoresis, immunoblotting and ion-exchange titration curves. Optimum separation was achieved using a strong anion exchanger (Mono Q) at pH 8.0. The purified protein did not cross-react with antibodies to E. coli.

Progress in the prevention of cytomegalovirus infection after allogeneic bone marrow transplantation

There has been substantial progress in preventing and treating CMV infection. Prophylaxis with CMV screened blood products, IVIG and antiviral drugs (high dose acyclovir and/or Ganciclovir) considerably reduce the incidence of CMV disease and nearly eliminate CMV pneumonia after allogeneic BMT.

Binding of human immunodeficiency virus type-1 (HIV-1) to partially purified membrane vesicles of lymphoblastoid cell line CEM

Binding of human immunodeficiency virus type 1 (HIV-1) to membrane of its target cells was studied by a quantitative and non-isotopic method called the viral membrane trapping method (VMTM). Membranes prepared from the CD4 positive lymphoblastoid cell line CEM and adsorbed to a solid support retained the ability to bind HIV-1. Similar results were obtained by Western dot blot and ELISA modification of VMTM, when membrane fraction was bound to nitrocellulose or polystyrene, respectively. In ELISA modification, viral association with 1 microgram of membranes coated on 96-well microplate was linear within a range of 3.75 micrograms to 60 micrograms of p24gag protein. The use of anti-CD4 mAbs, OKT4A and 13B8.2, identified CD4 molecule as a major HIV-1 binding component of membrane fraction. The procedure will allow the study of virus binding to this and to other possible additional receptor(s).

Evidence that membrane proteins of rhabdomyosarcoma cell line RD bind human immunodeficiency virus type 1 (HIV-1)

Membrane proteins (MP) obtained from the human mesenchymal rhabdomyosarcoma cell line RD were coated on 96-well polystyrene microplates and tested for their ability to bind human immunodeficiency virus type 1 (HIV-1). The virus bound to MP was detected by solid phase assay. Anti-human CD4 monoclonal antibodies directed against the HIV-1 gp120 binding site of the CD4 receptor did not inhibit viral binding to MP. HIV-1 specific polypeptides were recovered from coated MP to microplates by a modification of the solid phase immunoisolation technique and shown by immunoblotting analysis using a high titer of biotinylated human anti-HIV-1 IgG. Together these findings provide evidence that HIV-1 binding to RD cell surfaces can proceed via a mechanism other than those mediated by the CD4 receptor.

A PC-based on-line system for physiological in vivo and in vitro experiments

A PC-based system for data acquisition, control of experiments and analysis of physiological signals has been developed. The system has a flexibility that makes it useful for many different types of study, e.g. hemodynamics, electrophysiology and in vitro studies of organ contractile functions. The experimental set-up is specified in a number of tables, which can be modified with a table editor. The specifications can be stored in file and used for other experiments with an identical experimental set-up. The recording of data can be done either intermittently or continuously, and the intermittent recordings are initiated automatically at predefined times, or manually. With a tape recorder utility, data can be recorded during an experiment and analyzed at a later time. The signal analysis module has a high degree of flexibility, achieved by parameters defining preprocessing, heartbeat detection, heartbeat selection and analysis. Data is presented on the display in three types of window, showing phasic signals, derived parameters in trend graphs and derived parameters in numerical form. Data is saved on disk in two types of file: sampled raw data or derived parameters (ASCII file). An Ethernet-based network is used to send data to a VAX cluster, where it is further processed in RS/1 or the BIOLAB analysis program. The source code has been written in Ada, and the compiler generated a 32-bit code, which facilitated the development of a large program with large data buffers.

Characterization of HIV1-PAR, a macrophage-tropic strain: cell tropism, virus/cell entry and nucleotide sequence of the envelope glycoprotein

The HIV1-PAR strain, isolated from the cerebrospinal fluid of an HIV1-seropositive man suffering from encephalopathy, replicated well in cord blood lymphocytes, poorly in peripheral blood mononuclear cells, and to different levels in blood-derived macrophage (BDM) cultures prepared from different blood donors. In marked contrast to its replication in primocultures, it did not grow in CEM and U937 cell lines. HIV1-PAR production in BDM was inhibited by more than 90% after treatment with OKT4A or 13B8.2 monoclonal antibodies (mAb) binding to adjacent epitopes of the D1 domain of the CD4 molecules. A lower but significant inhibitory effect was observed after BDM treatment with BL4 and OKT4 mAb, directed to the D2 and D3 domain of the CD4 molecule, respectively. The entire HIV1-PAR envelope glycoprotein gene was amplified by polymerase chain reaction and sequenced. The deduced amino acid sequence of HIV1-PAR gp160 revealed the presence of 847 amino acids and 86% homology with the HIV1 LAV virus prototype. An alignment of the amino acid sequence of the envelope glycoprotein of HIV1-PAR and HIV1-LAV showed that the differences were mostly clustered within the five variable regions. Five CD4-binding domains, the gp120/gp41 cleavage site, the putative gp41 fusion domain and 21 out of the 22 cysteine residues were conserved in both isolates. The results further confirm the macrophage-tropic character of the HIV1-PAR virus.

The human immunodeficiency virus (HIV) gag gene product p18 is responsible for enhanced fusogenicity and host range tropism of the highly cytopathic HIV-1-NDK strain

Formation of large syncytia and rapid cell killing are characteristics of the Zairian human immunodeficiency virus type 1 isolate HIV-1-NDK, which is highly cytopathic for CD4+ lymphocytes in comparison with the HIV-1-LAV prototype. Chimeric viruses containing different combinations of HIV-1-NDK genetic determinants corresponding to the splice donor, the packaging signal, and the coding sequence of the p18gag protein together with the HIV-1-NDK EcoRI5278-XhoI8401 fragment were obtained by polymerase chain reaction-directed recombination. Phenotypic analysis of recombinant viruses indicated that 75 amino acids from the N-terminal part of HIV-1-NDK p18gag protein together with the HIV-1-NDK envelope glycoprotein are responsible for enhanced fusogenicity of HIV-1-NDK in CD4+ lymphocytes as well as for enhanced infectivity of HIV-1-NDK in some CD4- cells lines. The HIV-1-NDK splice donor/packaging sequence and the sequence encoding the gag protein p25 were not important for the variation observed in HIV-1 fusogenicity.

Distinctive pattern of infection and replication of HIV1 strains in blood-derived macrophages

The macrophage-tropic virus HIV1-PAR, isolated from cerebrospinal fluid of HIV1-seropositive man, induced cytopathic effect accompanied by different magnitude of the virus production in blood-derived macrophages (BDM) obtained from different donors. HIV1-PAR-specific RNA was detected by in situ hybridization in 15 and 66% of BDM producing low and high levels of virus, respectively. In contrast with HIV1-PAR, infection of BDM with two laboratory strains adapted to T-cell lines, HIV1-LAV prototype and HIV1-NDK, a Zairian virus that is highly cytopathic for T-lymphocytes, resulted in a low production of HIV1 p24gag in culture fluid. Expression of HIV1-LAV and HIV1-NDK RNA was detected by in situ hybridization in a maximum of 1% of macrophages. Only HIV1-NDK, and not HIV1-LAV, induced ultrastructural alterations in BDM. In contrast with a striking difference in the production of macrophage-tropic and T-lymphotropic viruses, no significant differences were found in the proportion of macrophages containing retrotranscribed genomes of HIV1-. HIV1 DNA was detected by in situ hybridization in 93, 100, and 80% of macrophages infected with HIV1-PAR, HIV1-LAV, and HIV1-NDK, respectively. A higher level of HIV1 DNA was detected by polymerase chain reaction in the BDM infected with HIV1-PAR than in that infected with HIV1-LAV and HIV1-NDK. The results indicate that both macrophage-tropic as well as T-lymphotropic viruses can enter and retrotranscribe their genomes in a vast majority of macrophages.

Inhibition of HIV by an anti-HIV protease synthetic peptide blocks an early step of viral replication

The processing of the human immunodeficiency virus (HIV) gag and gag-pol precursor proteins by the virus-encoded protease is an essential step in maturation of infectious virus particles. Like most retroviral proteases, the HIV protease belongs to the aspartyl-protease family and can be inhibited by specific inhibitors. Twenty-four synthetic peptides known to be inhibitors of human renin were tested for inhibition of HIV replication in tissue cultures. One of them, a synthetic peptide analogue, SR41476, which has been shown to be a specific inhibitor of purified recombinant HIV1 protease in vitro, totally blocked infection with different isolates including the HIV1 LAV prototype, the highly cytopathic Zairian isolate HIV1 NDK, and HIV2 ROD, both in primary blood lymphocytes (PBL) and in the lymphoid cell lines MT4 and CEM, for at least 3 weeks. It also significantly reduced virus replication in chronically infected CEM cells, without any effect on cell proliferation. Radioimmunoprecipitation assay revealed that the inhibitor blocked processing of polyprotein precursors p55 gag and p40 gag into a mature form of gag proteins, p25 and p18. Synthetic peptide analogue SR 41476, when added before infection, efficiently inhibited formation of HIV DNA provirus and successfully suppressed synthesis of HIV-specific proteins. These results imply that the HIV protease inhibitor not only inhibited virus maturation in the late phase of the HIV replication cycle, but also interfered in the early phase, before the provirus was formed. This mechanism of antiviral activity provides new possibilities and strategies for AIDS chemotherapy.

Central nervous system involvement in Leber congenital amaurosis

Sixteen patients with ocular criteria of Leber congenital amaurosis (LCA) were studied. Neurological examination was normal in 11 of 16 patients. The electroencephalogram was normal in six of eight patients, while two had nonspecific theta slowing. Computerized tomography of the brain was normal in two of five; hypoplasia of the cerebellar vermis was seen in one, and mild to moderate ventriculomegaly was seen in two of five. Six patients underwent the verbal subtests of the Wechsler Intelligence Scale and a detailed battery of neuropsychological tests. Subtests dependent on early environmental influences were most severely affected, while culture-free subtests showed average or well above average performance. These results strongly support the hypothesis that children with LCA may be capable of normal cognitive functioning, although they perform poorly on standard IQ tests. This is related to their early environmental and sensory deprivation, rather than to a primary central nervous system dysfunction.

Prevention and treatment of CMV infection after allogeneic bone marrow transplant

CMV infection is the major infectious complication following bone marrow transplantation. It is most often related to reactivation of latent infection in patients who were CMV seropositive before BMT. The incidence and severity have recently been modified by the use of preventive and curative treatments. Prevention of CMV infection with the transfusion of seronegative blood products is useful only when donor and recipient are seronegative. High-dose acyclovir has been shown effective in one randomized study. A multicenter study is currently being performed in Europe to confirm this result. Intravenous gammaglobulins seemed to lower the number of patients who incur interstitial pneumonitis but not the incidence of viremia. They also decreased the incidence of gram-negative sepsis and severe GVH and improved survival. The treatment is based on the use of gancyclovir. Several studies show that gancyclovir is more effective in asymptomatic patients with viral isolation from blood or bronchoalveolar lavage. The addition to gancyclovir of high-dose gammaglobulin improves survival in symptomatic patients with interstitial pneumonitis. This progress in the prevention and treatment of CMV infection has improved the overall results of allogeneic bone marrow transplantation.

HIV-1 infectivity of human carcinoma cell lines lacking CD4 receptors

Human immunodeficiency virus type 1 (HIV-1) prototype, HIV1 LAV, and a Zairian virus HIV1 NDK, an isolate highly cytopathic for CD4+ lymphocytes, were used to infect eleven different CD4 negative non-lymphoid human cell lines. Eight of the lines were derived from carcinomas wherein human papillomavirus was thought to have been etiologic. All these cell lines lacked CD4 receptor and CD4 specific mRNA. After cocultivation with sensitive CEM cells, HIV-1 LAV was rescued from six infected cell lines and HIV-1 NDK from nine. Shedding of free virus into the culture medium was observed in three cell lines infected by HIV-1 NDK and in only one cell line infected by HIV-1 LAV. The infectibility of CD4 negative cell lines indicates that both HIV-1 strains were able to use a CD4 independent mechanism to infect the cells; however, HIV-1 NDK showed the higher efficiency of infection. This virus was also able to overcome the intracellular block of viral reproduction. These results suggest that a broader spectrum of cell types of non-lymphoid origin lacking the CD4 receptor can serve as a viral reservoir. In some cases they are direct producers of infectious HIV-1 particles. This suggests, that in addition to immunosuppressive mechanisms, HIV-1 could play a more direct role in induction of neoplastic changes.

Structural variability of env and gag gene products from a highly cytopathic strain of HIV-1

The glycoprotein precursor of the highly cytopathic Zairian virus HIV1-NDK synthesized in CEM leukemic cells displayed a molecular mass of 140 kDa (gp140) as compared to the 160 kDa of gp160 of HIV1-LAV prototype strain. This precursor was cleaved to produce a smaller than prototype extra-cellular envelope glycoprotein (gp100) and a transmembrane component with a usual size (gp41). Immunoprecipitates from tunicamycin-treated infected cells demonstrated the presence of a non-glycosylated precursor of 100 kDa for HIV1-LAV prototype strain and 90 kDa for HIV1-NDK. Digestion of labeled precipitates with a mixture of endoglycosidase F and glycopeptidase F reduced the size of HIV1-LAV gp160 and gp120 to 100 and 60 kDa, respectively, while HIV1-NDK gp140 and gp100, after treatment with the same enzymes, displayed an apparent molecular mass of 90 kDa and 55 kDa, respectively. From these data we conclude that HIV1-LAV gp120 and HIV1-NDK gp100 differ both in their proteic moiety (60 kDa and 55 kDa, respectively) and in their carbohydrate moiety (60 kDa and 45 kDa, respectively). These differences could not be deduced from the available gene sequences of the two viruses. A chimeric virus containing the first 124 amino acid residues of the envelope glycoprotein coded by HIV1-LAV sequence and the rest by HIV1-NDK displayed normal size envelope glycoproteins, demonstrating the involvement of this N-terminal sequence in the alteration of the molecular mass characteristic of HIV1-NDK gp140 and gp100. Finally, characterization of the gag gene products from both strains demonstrated that HIV1-NDK p18 and p15 have a slower electrophoretic mobility as compared to its HIV1-LAV counterparts. Therefore, structural properties of HIV1-NDK env and gag products, reflected by their unusual electrophoretic mobilities, may be responsible for HIV1-NDK biological properties.