Effect of immunization on HTLV-I infection in rabbits

Microorganisms-derived antigens for preventive anti-cancer vaccines

Cancer prevention is one of the aim with the highest priority in order to reduce the burden of cancer diagnosis and treatment on individuals as well as on healthcare systems. To this aim, vaccines represent the most efficient primary cancer prevention strategy. Indeed, anti-cancer immunological memory elicited by preventive vaccines might promptly expand and prevent tumor from progressing. Antigens derived from microorganisms (MoAs), represent the obvious target for developing highly effective preventive vaccines for virus-induced cancers. In this respect, the drastic reduction in cancer incidence following HBV and HPV preventive vaccines are the paradigmatic example of such evidence. More recently, experimental evidences suggest that MoAs may represent a "natural" anti-cancer preventive vaccination or can be exploited for developing vaccines to prevent cancers presenting highly homologous tumor-associated antigens (TAAs) (e.g. molecular mimicry). The present review describes the different preventive anti-cancer vaccines based on antigens derived from pathogens at the different stages of development.

The Past, Present, and Future of a Human T-Cell Leukemia Virus Type 1 Vaccine

Human T-cell leukemia virus type 1 (HTLV-1) is an oncogenic human retrovirus which causes a lifelong infection. An estimated 5-10 million persons are infected with HTLV-1 worldwide - a number which is likely higher due to lack of reliable epidemiological data. Most infected individuals remain asymptomatic; however, a portion of HTLV-1-positive individuals will develop an aggressive CD4+ T-cell malignancy called adult T-cell leukemia/lymphoma (ATL), or a progressive neurodegenerative disease known as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Few treatment options exist for HAM/TSP outside of palliative care and ATL carries an especially poor prognosis given the heterogeneity of the disease and lack of effective long-term treatments. In addition, the risk of HTLV-1 disease development increases substantially if the virus is acquired early in life. Currently, there is no realistic cure for HTLV-1 infection nor any reliable measure to prevent HTLV-1-mediated disease development. The severity of HTLV-1-associated diseases (ATL, HAM/TSP) and limited treatment options highlights the need for development of a preventative vaccine or new therapeutic interventions. This review will highlight past HTLV-1 vaccine development efforts, the current molecular tools and animal models which might be useful in vaccine development, and the future possibilities of an effective HTLV-1 vaccine.

A role for an HTLV-1 vaccine?

HTLV-1 is a global infection with 5-20 million infected individuals. Although only a minority of infected individuals develop myelopathy, lymphoproliferative malignancy, or inflammatory disorders, infection is associated with immunosuppression and shorter survival. Transmission of HTLV-1 is through contaminated blood or needles, mother-to-child exposure through breast-feeding, and sexual intercourse. HTLV-1 is a delta retrovirus that expresses immunogenic Gag, Envelope, TAX, and Hbz proteins. Neutralizing antibodies have been identified directed against the surface envelope protein, and cytotoxic T-cell epitopes within TAX have been characterized. Thus far, there have been few investigations of vaccines directed against each of these proteins, with limited responses, thus far. However, with new technologies developed in the last few years, a renewed investigation is warranted in search for a safe and effective HTLV-1 vaccine.

Molecular determinants of human T-lymphotropic virus type 1 transmission and spread

Human T-lymphotrophic virus type-1 (HTLV-1) infects approximately 15 to 20 million people worldwide, with endemic areas in Japan, the Caribbean, and Africa. The virus is spread through contact with bodily fluids containing infected cells, most often from mother to child through breast milk or via blood transfusion. After prolonged latency periods, approximately 3 to 5% of HTLV-1 infected individuals will develop either adult T-cell leukemia/lymphoma (ATL), or other lymphocyte-mediated disorders such as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The genome of this complex retrovirus contains typical gag, pol, and env genes, but also unique nonstructural proteins encoded from the pX region. These nonstructural genes encode the Tax and Rex regulatory proteins, as well as novel proteins essential for viral spread in vivo such as, p30, p12, p13 and the antisense encoded HBZ. While progress has been made in the understanding of viral determinants of cell transformation and host immune responses, host and viral determinants of HTLV-1 transmission and spread during the early phases of infection are unclear. Improvements in the molecular tools to test these viral determinants in cellular and animal models have provided new insights into the early events of HTLV-1 infection. This review will focus on studies that test HTLV-1 determinants in context to full length infectious clones of the virus providing insights into the mechanisms of transmission and spread of HTLV-1.

Preventive and therapeutic strategies for bovine leukemia virus: lessons for HTLV

Bovine leukemia virus (BLV) is a retrovirus closely related to the human T-lymphotropic virus type 1 (HTLV-1). BLV is a major animal health problem worldwide causing important economic losses. A series of attempts were developed to reduce prevalence, chiefly by eradication of infected cattle, segregation of BLV-free animals and vaccination. Although having been instrumental in regions such as the EU, these strategies were unsuccessful elsewhere mainly due to economic costs, management restrictions and lack of an efficient vaccine. This review, which summarizes the different attempts previously developed to decrease seroprevalence of BLV, may be informative for management of HTLV-1 infection. We also propose a new approach based on competitive infection with virus deletants aiming at reducing proviral loads.

Human T Lymphotropic Virus Type 1 (HTLV-1): Molecular Biology and Oncogenesis

Human T lymphotropic viruses (HTLVs) are complex deltaretroviruses that do not contain a proto-oncogene in their genome, yet are capable of transforming primary T lymphocytes both in vitro and in vivo. There are four known strains of HTLV including HTLV type 1 (HTLV-1), HTLV-2, HTLV-3 and HTLV-4. HTLV-1 is primarily associated with adult T cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-2 is rarely pathogenic and is sporadically associated with neurological disorders. There have been no diseases associated with HTLV-3 or HTLV-4 to date. Due to the difference in the disease manifestation between HTLV-1 and HTLV-2, a clear understanding of their individual pathobiologies and the role of various viral proteins in transformation should provide insights into better prognosis and prevention strategies. In this review, we aim to summarize the data accumulated so far in the transformation and pathogenesis of HTLV-1, focusing on the viral Tax and HBZ and citing appropriate comparisons to HTLV-2.

Mouse models of human T lymphotropic virus type-1-associated adult T-cell leukemia/lymphoma

Human T-lymphotropic virus type-1 (HTLV-1), the first human retrovirus discovered, is the causative agent of adult T-cell leukemia/lymphoma (ATL) and a number of lymphocyte-mediated inflammatory conditions including HTLV-1-associated myelopathy/tropical spastic paraparesis. Development of animal models to study the pathogenesis of HTLV-1-associated diseases has been problematic. Mechanisms of early infection and cell-to-cell transmission can be studied in rabbits and nonhuman primates, but lesion development and reagents are limited in these species. The mouse provides a cost-effective, highly reproducible model in which to study factors related to lymphoma development and the preclinical efficacy of potential therapies against ATL. The ability to manipulate transgenic mice has provided important insight into viral genes responsible for lymphocyte transformation. Expansion of various strains of immunodeficient mice has accelerated the testing of drugs and targeted therapy against ATL. This review compares various mouse models to illustrate recent advances in the understanding of HTLV-1-associated ATL development and how improvements in these models are critical to the future development of targeted therapies against this aggressive T-cell lymphoma.

Animal models for human T-lymphotropic virus type 1 (HTLV-1) infection and transformation

Over the past 25 years, animal models of human T-lymphotropic virus type 1 (HTLV-1) infection and transformation have provided critical knowledge about viral and host factors in adult T-cell leukemia/lymphoma (ATL). The virus consistently infects rabbits, some non-human primates, and to a lesser extent rats. In addition to providing fundamental concepts in viral transmission and immune responses against HTLV-1 infection, these models have provided new information about the role of viral proteins in carcinogenesis. Mice and rats, in particular immunodeficient strains, are useful models to assess immunologic parameters mediating tumor outgrowth and therapeutic invention strategies against lymphoma. Genetically altered mice including both transgenic and knockout mice offer important models to test the role of specific viral and host genes in the development of HTLV-1-associated lymphoma. Novel approaches in genetic manipulation of both HTLV-1 and animal models are available to address the complex questions that remain about viral-mediated mechanisms of cell transformation and disease. Current progress in the understanding of the molecular events of HTLV-1 infection and transformation suggests that answers to these questions are approachable using animal models of HTLV-1-associated lymphoma.

New approach for generation of neutralizing antibody against human T-cell leukaemia virus type-I (HTLV-I) using phage clones

We have screened a phage peptide library to address whether clones binding to a monoclonal antibody (mAb) could be isolated and if the selected phage particles would be able to elicit an in vivo immune response against the original antigen. A phage peptide library, consisting of seven random amino acids inserted in the minor coat protein (pIII), was screened for specific binding to a rat mAb LAT-27, which is capable of neutralizing human T-cell leukaemia virus type-I (HTLV-I) by binding to its envelope gp46 epitope, (amino acids LPHSNL). Total 37 clones were selected from the library and one clone named 4-2-22 was tested for its immunogenicity in three rabbits. The all rabbit immune sera showed strong binding activity to a gp46 peptide carrying the neutralization sequence, stained gp46-expressing cells and neutralized HTLV-I in vitro as determined by cell fusion inhibition assay. These results show that the selected phage clone was capable of mimicking the epitope recognized by a HTLV-I neutralizing mAb, and it can be used as an immunogen to induce protective immune response against HTLV-I. Thus, the present methodology could be one of the approaches to develop vaccines against infectious agents in a simple and inexpensive way.

Neutralizing human monoclonal antibodies to conformational epitopes of human T-cell lymphotropic virus type 1 and 2 gp46

Ten human monoclonal antibodies derived from peripheral B cells of a patient with human T-cell lymphotropic virus (HTLV)-associated myelopathy are described. One monoclonal antibody recognized a linear epitope within the carboxy-terminal 43 amino acids of HTLV gp21, and two monoclonal antibodies recognized linear epitopes within HTLV type 1 (HTLV-1) gp46. The remaining seven monoclonal antibodies recognized denaturation-sensitive epitopes within HTLV-1 gp46 that were expressed on the surfaces of infected cells. Two of these antibodies also bound to viable HTLV-2 infected cells and immunoprecipitated HTLV-2 gp46. Virus neutralization was determined by syncytium inhibition assays. Eight monoclonal antibodies, including all seven that recognized denaturation-sensitive epitopes within HTLV-1 gp46, possessed significant virus neutralization activity. By competitive inhibition analysis it was determined that these antibodies recognized at least four distinct conformational epitopes within HTLV-1 gp46. These findings indicate the importance of conformational epitopes within HTLV-1 gp46 in mediating a neutralizing antibody response to HTLV infection.

Cervicovaginal synthesis of IgG antibodies to the immunodominant 175-199 domain of the surface glycoprotein gp46 of human T-cell leukemia virus type I

Paired sera, saliva and cervicovaginal secretions from 17 HTLV-I-infected women (19-75 yr) were tested for total IgA and IgG, for IgA and IgG to the immunodominant region gp46/175-Pro-199, for serum IgG to the neutralizing domains gp46/ 190-Pro-199 and gp46/190-Ser-199, or for tax-rex proviral HTLV-DNA. Serum antibodies to gp46/ 175-Pro-199 were detected more frequently in the IgG (13/17) than in the IgA (5/17) isotypes. The majority (8/12) of anti-gp46/175-Pro-199-positive sera reacted also to gp46/190-Pro-199 or to gp46/ 190-Ser-199, demonstrating their neutralizing properties. In saliva, antibodies to gp46/175-Pro-199 were not generally detected. In cervicovaginal secretions, IgG to gp46/175-Pro-199, but not IgA, were detected in 6/15 (40%) patients. The mean specific activity of IgG to gp46/175-Pro-199 showed a trend to be higher in cervicovaginal secretions (218 +/- 109) than in sera (14 +/- 4). Furthermore, in all patients with cervicovaginal IgG to gp46/175-Pro-199, the cervicogaginal/serum ratio (19 +/- 6) of anti-gp46 IgG specific activities were markedly above 1. HTLV-DNA was detected in 4/17 salivas, and in 3/15 cervicovaginal secretions, all from patients demonstrating cervicovaginal synthesis of IgG to gp46/175-Pro-199. In conclusion, IgG to gp46/175-Pro-199 in cervicovaginal secretions, when present, appear to be produced primarily locally because of local HTLV-I excretion. Since anti-gp46/175-Pro-199 antibodies usually support reactivities to neutralizing domains, their presence could be relevant for limiting HTLV-I transmission via cervicovaginal secretions.

Human T-lymphotropic virus type I excretion and specific antibody response in paired saliva and cervicovaginal secretions

Paired sera, salivas, and cervicovaginal secretions from 17 HTLV-I-infected women (10-75 years) were evaluated for total IgA, IgG, IgM, for IgA and IgG to whole HTLV-I lysate, for albumin, and for tax-rex proviral HTLV-DNA. IgG to HTLV-I were constantly detected, with much higher titers in serum (mean titer: 97,800) than in saliva (53) or in cervicovaginal secretions (216). IgA to HTLV-I were detected in only 12 (70%) sera, 6 (35%) salivas, and 8 (53%) cervicovaginal secretions, with higher titers in serum (75) than in saliva (8). Using the relative coefficient of excretion by reference to albumin, as well as the comparison of specific activities, the HTLV-I-specific IgG appeared primarily originating from serum, whereas IgA to HTLV-I were primarily locally produced. Salivary synthesis of IgG to HTLV-I occurred in both patients with a sicca syndrome attesting salivary glands impairment. Local excretions of total IgA, IgG, and IgM evaluated in body fluids were normal. HTLV DNA was detected in 4 (24%) salivas and in 3 (20%) cervicovaginal secretions, always in patients demonstrating local synthesis of HTLV-I-specific IgA or IgG. HTLV-I excretion elicits a weak local immune response to HTLV-I in saliva as well as in cervicovaginal secretions, which could be relevant for HTLV-I transmission via body fluids.

An HTLV-I/II vaccine: from animal models to clinical trials?

A human T-lymphotropic virus type I/II (HTLV-I/II) vaccine is necessary in view of two etiologically related, life-threatening diseases, namely, adult T-cell leukemia/lymphoma and tropical spastic paraparesis/HTLV-I-associated myelopathy. When the risk of developing autoimmune diseases such as uveitis, polymyositis, and arthritis is included, one can estimate the life-long risk of infected individuals to develop an HTLV associated pathology as approximately 10%. The populations at risk are, in a large majority, from developing countries but the epidemic of HTLV-II infection in intravenous drug users (IVDU) represents a possible reservoir for dissemination in the general population. The number of HTLV-I-infected individuals (15 to 25 million), together with the severity of associated disease, justifies the development of a vaccine. Different vaccine preparations have been developed, using mostly recombinant pox and adenoviruses, but DNA plasmid technology will soon become a feasible approach. Various animal models exist for experimental viral infections, involving rats, rabbits, or monkeys, but up to now, neither hematological nor neurological disorders have been induced by HTLV infection in such animal models. For long-term protection from HTLV-I-associated diseases, vaccination should induce both neutralizing antibodies and specific cell-mediated immunity. This will require the incorporation of both env and gag coding sequences in the vaccine preparations. Preventive clinical trials may involve different cohorts of seronegative young girls from endemic areas prior to sexual activity and IVDU in the industrialized world. In parallel, one should consider therapeutic vaccine trials in HTLV-I-positive mothers and IVDU to protect them against disease development. The observed rate of seroconversion in these different cohorts makes such trials feasible.

Vaccination of rabbits with recombinant vaccinia virus carrying the envelope gene of human T-cell lymphotropic virus type I

Two groups of 3 rabbits each were immunized with either recombinant vaccinia virus, WR-SFB5env, carrying the human T-cell lymphotropic virus type I (HTLV-I) env gene at the site of the hemagglutinin gene of the WR strain, or control vaccinia virus, HA-WR, lacking the functional hemagglutinin gene. All 6 rabbits responded with anti-vaccinia virus antibodies. WR-SFB5env elicited anti-HTLV-I env antibodies but no vesicular stomatitis virus (HTLV-I) pseudotype neutralizing antibodies in all 3 rabbits. After 10 weeks, the animals were challenged by transfusion of blood from an HTLV-I-infected rabbit. Two of the 3 vaccinated rabbits and all 3 control rabbits became infected with HTLV-I, as indicated by seroconversion and detection of HTLV-I proviral sequences by polymerase chain reaction. The rabbit that had been protected from initial challenge became infected with HTLV-I upon rechallenge 12 weeks after the first challenge. In view of the proven prophylactic effect of passive immunization against HTLV-I, our vaccine trial failed because WR-SFB5env was incapable of inducing neutralizing antibodies against HTLV-I in the immunized animals. It remains to be studied whether cell-mediated immunity such as antibody-dependent cellular cytotoxicity was involved in the temporary protection of I vaccinated rabbit.

Induction of antibody responses that neutralize human T-cell leukemia virus type I infection in vitro and in vivo by peptide immunization

In order to define neutralization regions on the envelope antigen of human T-cell leukemia virus type I (HTLV-I), we have generated a number of new anti-envelope gp46 monoclonal antibodies from rats and mice. Epitopes recognized by new monoclonal antibodies which could neutralize HTLV-I in syncytium and transformation inhibition assays were localized to sequences in gp46 from amino acids 186 to 193, 190 to 195, 191 to 195, 191 to 196, and 194 to 199. Ovalbumin-conjugated synthetic gp46 peptides containing these neutralization epitopes, pep190-199 (a synthetic gp46 peptide containing amino acids 190 to 199) and pep180-204, but not pep185-194 or pep194-203, could give rise to HTLV-I-neutralizing antibody responses in rabbits. These immune or nonimmune rabbits were then challenged with HTLV-I by intravenous inoculation with 5 x 10(7) live HTLV-I-producing ILT-8M2 cells. By a PCR assay, it was revealed that HTLV-I provirus was detected in peripheral blood lymphocytes from nonimmune and pep288-312-immunized rabbits, whereas the provirus was not detected in peripheral blood lymphocytes from pep190-199- and pep180-204-immunized rabbits over an extended period. These results suggest that the induction of anti-gp46 neutralizing antibody responses by immunization with synthetic peptides has the potential to protect animals against HTLV-I infection in vivo.

Identification of novel neutralization-inducing regions of the human T cell lymphotropic virus type I envelope glycoproteins with human HTLV-I-seropositive sera

The humoral immune response in sera from 30 human T cell lymphotropic virus type I (HTLV-I)-positive individuals from Martinique in the French West Indies was studied. The subjects were subdivided into those suffering from TSP/HAM and those being asymptomatic. In general, TSP/HAM patient sera seemed to contain more virus-specific antibodies than did the sera from the asymptomatic subjects. Three of the 13 TSP/HAM sera and 1 of the 17 asymptomatic sera contained HTLV-I-specific IgM antibodies, whereas 6 and 5 sera, respectively, contained IgA antibodies. By correlating the ability of patient sera to inhibit HTLV-I-induced syncytia with their antibody reactivity in ELISA to 42 synthetic peptides, together corresponding to the entire envelope glycoprotein of HTLV-I, a number of putative neutralizing domains were identified. Eight synthetic peptides representing the regions with the highest coefficient of correlation between neutralizing titer and ELISA reactivity were employed to specifically adsorb potentially neutralizing antibodies, and were also used directly, without sera, in the syncytium-neutralizing test. By those techniques, three novel and two previously described domains that seemed to contain neutralizing epitopes were identified. Two of the novel neutralizing sites resided in the external glycoprotein (gp46) and were contained within amino acids 53-75 and 287-311, respectively, and one was located in the transmembrane glycoprotein (gp21) within amino acids 346-368. Our findings may have implications for the rational design of subunit vaccines for prevention of and/or alteration of the clinical outcome of HTLV-I-related diseases.

Neutralizing antibody to vesicular stomatitis virus (HTLV-I) pseudotype in infants born to seropositive mothers

Breast feeding is the major route of mother-to-child transmission of human T-cell leukemia virus type I (HTLV-I). Our experiments with rabbits have shown that passive immunization is capable of blocking cell-to-cell infection of HTLV-I by blood transfusion or breast feeding. In this study, sera were collected serially from 3 infants born to seropositive mothers and were tested for the presence of neutralizing antibody to vesicular stomatitis virus (HTLV-I) pseudotype as well as antibodies to viral structural proteins. There was a good correlation between neutralizing and viral antibody titers, both of which were detectable until 3-6 months after birth. Whether maternally transmitted neutralizing antibody is protective against perinatal infection of HTLV-I remains to be studied.

Characterization of a B-cell immunodominant epitope of human T-lymphotropic virus type 1 (HTLV-I) envelope gp46

The immune response elicited by a synthetic peptide derived from an immunodominant external envelope region (Env-5, amino acids 242-257) of human T-lymphotropic virus type 1 (HTLV-I) was tested in a rabbit model of HTLV-I infection. The synthetic peptide elicited a strong antibody response to the HTLV-I envelope protein gp46; however, these antibodies failed to inhibit HTLV-I-mediated cell fusion. Immunized rabbits were not protected from HTLV-I infection as determined by seroconversion to viral core proteins by immunoblot, HTLV-I p24 antigen detection in lymphocyte cultures and polymerase chain reaction for the HTLV-I provirus in lymphocyte DNA. Env-5 peptide immunization failed to induce T-cell lymphocyte proliferative responses in rabbits, but induced antibody responses in T-cell deficient Balb c nu/nu mice suggesting that the antigenic determinant represented by the Env-5 peptide is primarily a B-cell epitope. These results further define an immunodominant epitope of the HTLV-I envelope protein and suggest that potential synthetic peptide vaccines against HTLV-I infection must contain multiple antigens that induce both humoral and cellular immune reactivity.

Neutralizing activity of human antibodies against the structural protein of human T-cell lymphotropic virus type I

We have identified and mapped the regions responsible for neutralization in the human T-cell leukemia virus type I (HTLV-I) structural proteins by using region-specific human antibodies derived from seropositive blood donors. We have obtained 18 kinds of region-specific antibody (2 in the p19 gag, 10 in the gp46 env and 6 in the gp21 env proteins) from seropositive human plasma by means of an affinity column coupled with the synthetic peptides corresponding to the antigenic regions of the HTLV-I structural proteins. These antibodies were highly specific in ELISA using synthetic peptides as an antigen. Subsequently, we examined the neutralizing activity expressed by the inhibition of virion-induced syncytium formation by region specific antibodies. Twelve of 16 antibodies derived from the env protein were able to inhibit syncytium formation induced by co-cultivation of 8C cells with HTLV-I antigen-positive T cells. The antibodies derived from the p19 gag protein and the seronegative plasma used as the control showed no significant activity. The sequences recognized by the 10 neutralizing antibodies were sites corresponding to amino acids 20 to 49, 89 to 115, 136 to 160, 175 to 199, 213 to 236, 235 to 254, 277 to 292, 332 to 352, 350 to 386, 382 to 403, 426 to 448 and 458 to 488 from the amino terminal of the env protein. These observations suggest that the neutralizing epitopes were widely distributed in the env proteins of HTLV-I.

Maternal transmission of HTLV-1 other than through breast milk: discrepancy between the polymerase chain reaction positivity of cord blood samples for HTLV-1 and the subsequent seropositivity of individuals

We used a nested polymerase chain reaction (PCR) to diagnose HTLV-1 carriers. The DNA isolated from the nuclear extract obtained from frozen whole blood was found appropriate for PCR study both qualitatively and quantitatively. The use of freshly frozen whole blood made the field work much easier, and the use of a nuclear extraction procedure allowed DNA isolation in just 4 microcentrifuge tubes. We could not attain sufficient sensitivity to detect a single molecule with single-step PCR, but nested PCR was confirmed to detect a single molecule/reaction. All samples of the seropositive group including 94 blood donors, 66 mothers, and 13 children were positive in the nested PCR, while none of the seronegative group, including 198 blood donors and 285 children, was positive. Although 18/717 (2.5%) cord blood samples obtained from babies born to carrier mothers were PCR-positive, none of 5 formula-fed children tested who had been PCR-positive in the cord blood gave evidence of infection later on. Furthermore, all of 4 seropositive infected children who were formula-fed had been PCR-negative in their cord blood. The results are not consistent with intrauterine infection, but suggest the presence of a perinatal or postnatal infection route other than through breast milk.

Persistent infection of rabbits with bovine immunodeficiency-like virus

Chronic infection of rabbits was induced by a single intraperitoneal injection of bovine immunodeficiency-like virus (BIV)-infected cells. Ten BIV-infected animals were monitored serologically for up to 2 years. Results of serologic and virus rescue assays indicated that all animals became infected and demonstrated a rapid and sustained BIV-specific humoral response. BIV was rescued by cocultivation from spleen, lymph nodes, and peripheral blood leukocytes of infected animals. Viral DNA in immune tissues was confirmed by polymerase chain reaction amplification of BIV sequences. These data and specific immunohistochemical staining of mononuclear cells of the spleen for BIV antigen suggest that the infection is targeted to immune system cells.

Inhibitory effect of maternal antibody on mother-to-child transmission of human T-lymphotropic virus type I. The Mother-to-Child Transmission Study Group

In order to evaluate the protective role of the maternal antibody against mother-to-child transmission of HTLV-I, we followed a total of 780 children born to HTLV-I carrier mothers by investigating the level of anti-HTLV-I antibody transferred in utero, decline of the maternal antibody and seroconversion in post-natal life. The anti-HTLV-I antibody was positively detected within the first 3-6 months of life and declined at 6-12 months after birth in all children. After the maternal antibody declined, seroconversion occurred in some of the children following either breast feeding or bottle feeding. The seroconversion rates of short-term (less than or equal to 6 months) and long-term (greater than or equal to 7 months) breast feeders were 4.4% (4/90 cases) and 14.4% (20/139 cases), and the rate of bottle feeders was 5.7% (9/158 cases). Long-term breast feeding yielded more seroconverters than short-term breast feeding; 14.4% (20/139 cases) vs. 4.4% (4/90 cases), RR = 3.68, p = 0.018. The seroconversion rate of short-term breast feeders was nearly equal to that of bottle feeders; 4.4% (4/90 cases) vs. 5.7% (9/158 cases), RR = 0.770, p = 0.471. When neonatal lymphocytes were cultured with breast milk cells of HTLV-I carrier mothers, the in vitro infection of HTLV-I was inhibited by the addition of HTLV-I-seropositive cord-blood plasma. Our results suggest that the maternal antibody may inhibit HTLV-I infection by short-term breast feeding but not by long-term breast feeding after decline of the maternal antibody.

Expression of HTLV-I envelope protein fused to hydrophobic amino-terminal peptide of baculovirus polyhedrin in insect cells and its application for serological assays

The envelope of human T-cell leukemia virus type I (HTLV-I) consists of two glycoproteins gp46 and p20E. Recombinant envelope proteins were produced by using an expression vector derived from insect baculovirus, Bombyx mori nuclear polyhedrosis virus. Polyhedrin fusion proteins C182, N147, and N287 contained whole region p20E, C-terminal half of gp46, and almost whole region gp46, respectively. N147 and N287 were suggested to be processed forms resulting from internal cleavage by cellular enzymes. In cultured cells and the insect larvae, C182 and N147 were produced abundantly enough to be purified to homogeneity; however, N287 was produced poorly and not purified. The purified proteins were recognized by HTLV-I-infected human sera and shown to be highly specific antigens for blood screening systems.