Cytotoxic T-cell abundance and virus load in human immunodeficiency virus type 1 and human T-cell leukaemia virus type 1.

The correlation between virus load and specific cytotoxic T-lymphocyte (CTL) frequency during the chronic phase in human immunodeficiency virus type 1 (HIV-1) infection has been found to be negative in cross-sectional studies. We report here that, in infection with the related retrovirus human T-cell leukaemia virus type 1 (HTLV-1), the correlation is positive in asymptomatic carriers and zero in patients with the associated inflammatory disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). We demonstrate that the direction of the correlation may depend on the efficacy of the CTL response using mathematical models. We conclude that the CTL response is effective in asymptomatic carriers of HTLV-1, but ineffective in patients with HAM/TSP. Virus-mediated impairment of specific CTL production in HIV-1 infection can account for the negative correlation observed.     

Cytotoxic T-cell antagonism in HIV-1

The cytotoxic T-cell (CTL) response to human immunodeficiency virus Type 1 (HIV-1) is vigorous and sustained, but despite this, the virus persists. Natural variation arising within CTL epitopes may affect CTL recognition of infected targets and allow viral escape. Some of these variant epitopes appear to engage T-cell receptors but fail to activate the CTL normally. This can interfere with recognition of the unmutated epitope — a phenomenon known as T-cell antagonism. We discuss the evidence for this in HIV-1 using CTL and epitope variants derived from infected donors, and discuss its possible relevancein vivo.     

In vivo cellular tropism of human T-cell leukemia virus type 1.

To establish the phenotype of human T-cell leukemia virus type 1 (HTLV-1)-infected cells in peripheral blood, the polymerase chain reaction was used to detect and quantitate viral DNA in subpopulations of leukocytes obtained from patients with tropical spastic paraparesis and asymptomatic carriers. HTLV-1 could not be detected in peripheral blood mononuclear cells thoroughly depleted of T lymphocytes (E- CD3-), nor could it be detected in highly enriched populations of B lymphocytes (E- CD19+), monocytes (E- CD14+), or natural killer cells (E- CD16+). T lymphocytes were strongly positive for HTLV-1, and fractionation of this population revealed that 90 to 99% of the HTLV-1 DNA segregated with the CD4+ CD8- and CD45RO+ subsets. No difference between the cell type distribution of HTLV-1 in the asymptomatic carrier and the subjects with tropical spastic paraparesis was evident. Southern hybridization of genomic DNA prepared from the peripheral blood of HTLV-1 carriers indicated that up to 10% of circulating leukocytes may carry the HTLV-1 provirus.     

Adult T-cell leukemia-lymphoma.

Adult T-cell leukemia-lymphoma, an aggressive T-cell leukemia, is characterized by the presence in the peripheral blood of malignant T cells that have highly indented or lobulated nuclei. Phenotypically the cells are usually helper T cells, but functionally they behave as suppressor cells. Patients have skin and lung involvement, hepatosplenomegaly, moderate lymphadenopathy sparing the mediastinum, and various metabolic abnormalities such as hypercalcemia. The clinical course may be chronic or acute, usually followed by a rapidly progressive terminal course. Adult T-cell leukemia-lymphoma is now known to be caused by human T-cell lymphotropic virus type I, which has been identified in the cells of patients with the disease.     

The Mlvi-1 locus involved in the induction of rat T-cell lymphomas and the pvt-1/Mis-1 locus are identical.

Mlvi-1 defines a locus of proviral integration in rat thymomas induced by Moloney murine leukemia virus. pvt-1/Mis-1 represents an independently identified locus which becomes rearranged either by chromosomal translocation in murine plasmacytomas or by provirus insertion in retrovirus-induced murine and rat thymic lymphomas. Although it had been claimed that pvt-1/Mis-1 and Mlvi-1 represent two different loci, we present here evidence showing that they are identical. This finding demonstrates the need for rigorous characterization of any newly identified common regions of integration in retrovirus-induced neoplasms.     

Identification of a T-cell epitope adjacent to neutralization antigenic site 1 of poliovirus type 1.

Proliferative T-cell responses to poliovirus in various strains of mice have been analyzed by using either killed purified virus or capsid protein VP1 synthetic peptides. Following immunization of mice with inactivated poliovirus type 1 (PV1), a specific proliferative response of their lymph node CD4+ T cells was obtained after in vitro stimulation with purified virus. In mice immunized with PV1, PV2, or PV3, a strong cross-reactivity of the T-cell responses was observed after in vitro stimulation with heterologous viruses. By using various strategies, a dominant T-cell epitope was identified in the amino acid 103 to 115 region of capsid polypeptide VP1, close by the C3 neutralization epitope. The T-cell response to VP1 amino acids 103 to 115 is H-2 restricted: H-2d mice are responders, whereas H-2k and H-2b mice do not respond to this T-cell epitope. Immunization of BALB/c (H-2d) mice with the uncoupled p86-115 peptide, which represents VP1 amino acids 86 to 115 and contains both the T-cell epitope and the C3 neutralization epitope, induced poliovirus-specific B- and T-cell responses. Moreover, these mice developed poliovirus neutralizing antibodies.     

Antigen-specific T-cell hybrids: I. Ovalbumin binding T-cell hybrid

Somatic cell hybrids were prepared between BW 5147 AKR T lymphoma cells and thymus-derived suppressor lymphocytes obtained from ovalbumin (OVA)-immunized, urea-denatured-ovalbumin (UD-OVA)-treated, suppressed BDF1 female mice. These T-cell hybrids express parental constitutive enzymes and differentiation antigens. Of the four hybrid lines developed, Hybrid 49A (Hyb 49A) has exhibited antigen-specific binding of OVA-coated syngeneic erythrocytes which is inhibited by preincubation in soluble OVA. This hybrid also interacts with self epitopes expressed on syngeneic erythrocytes. Antigen-specific rosette formation by Hyb 49A is not inhibited by preincubation in soluble keyhole limpet hemocyanin or normal mouse serum. This line and its agar-derived subclones have maintained their antigen-specific activity for 9 months and will provide extensive homogeneous quantities of T-cell products for molecular analysis.     

Ephrin-B1 is critical in T-cell development

Eph kinases are the largest family of receptor tyrosine kinases, and their ligands, ephrins (EFNs), are also cell surface molecules. In this study, we investigated the role of EFNB1 and the Ephs it interacts with (collectively called EFNB1 receptors) in mouse T-cell development. In the thymus, CD8 single positive (SP) and CD4CD8 double positive (DP) cells expressed high levels of EFNB1 and EFNB1 receptors, whereas CD4 SP cells had moderate expression of both. Soluble EFNB1-Fc in fetal thymus organ culture caused significant subpopulation ratio skew, with increased CD4 SP and CD8 SP and decreased DP percentage, while the cellularity of the thymus remained constant. Moreover, in EFNB1-treated fetal thymus organ culture, CD117(+), CD25(+), DP, CD4 SP, and CD8 SP cells all had significantly enhanced proliferation history, according to bromodeoxyuridine uptake. In vitro culture of isolated thymocytes revealed that EFNB1-Fc on solid-phase protected thymocytes from anti-CD3-induced apoptosis, with concomitant augmentation of several antiapoptotic factors, particularly in CD4 SP and CD8 SP cells; on the other hand, soluble EFNB1-Fc promoted anti-CD3-induced apoptosis, as was the case in vivo. This study reveals that EFNB1 and EFNB1 receptors are critical in thymocyte development.     

Human T-cell leukemia virus type 1 Tax transactivates the human proliferating cell nuclear antigen promoter.

The human T-cell leukemia virus type 1 (HTLV-1) transforming protein, Tax, is a potent transactivator of both viral and cellular gene expression. The ability of Tax to transform cells is believed to depend on its transactivation of cellular-growth-regulatory genes. Expression of proliferating cell nuclear antigen (PCNA) is intimately linked to cell growth and DNA replication and repair. By testing a series of PCNA promoter deletion constructs, we have demonstrated that the PCNA promoter can be transactivated by Tax. The smallest construct that was activated did not include the ATF/CRE binding site at nucleotide -50, and mutations in the ATF/CRE element in the context of a larger promoter were still activated by Tax. In addition, a Tax mutant that is defective for activation of the CRE pathway retained the ability to activate the -397 promoter construct. When a series of linker scanner mutations that span the region from nucleotide -45 to -7 were assayed, mutations in and around a repeat sequence were found to abolish Tax transactivation. Multimerized copies of either half of the repeat were Tax responsive. A single protein complex was shown to bind specifically to the Tax-responsive region, and the binding of this complex was enhanced in the presence of Tax. These results demonstrate that the PCNA promoter contains a Tax-responsive element located between nucleotides -45 and -7 whose sequence is different from those of other, previously identified Tax-responsive elements. The ability of Tax to activate the PCNA promoter may play an important role in cellular transformation by HTLV-1.     

T-cell specific rearrangement of T-cell receptor beta transgenes in mice.

To study rearrangement of T cell receptor (TCR) genes, transgenic mice were generated with a TCR beta minilocus in germline configuration, containing three V beta, two D beta, fourteen J beta and two C beta gene segments and the TCR beta enhancer. Using the polymerase chain reaction as an analytical tool both partial DJ as well as complete VDJ rearrangements were seen, indicating that the minilocus contained all sequence elements required for rearrangment. Rearrangements of minilocus gene segments were restricted to T cells in the thymus and the periphery and did not occur in B cells. V beta 8.3 and V beta 5 sequences encoded by the minilocus were expressed on the surface of peripheral T cells at high frequencies. Transgenic mice with TCR minilocus genes will be a useful system to identify DNA sequence elements required for regulation of rearrangement in vivo.