Inverse relationship between constitutive gamma interferon production and human T-cell lymphoma/leukemia virus expression in cultured T lymphocytes

Unique features and clinical importance of acute alloreactive immune responses

Allogeneic stem cell transplantation (allo-SCT) can cure some patients with hematopoietic malignancy, but this relies on the development of a donor T cell alloreactive immune response. T cell activity in the first 2 weeks after allo-SCT is crucial in determining outcome, despite the clinical effects of the early alloreactive immune response often not appearing until later. However, the effect of the allogeneic environment on T cells is difficult to study at this time point due to the effects of profound lymphopenia. We approached this problem by comparing T cells at week 2 after allograft to T cells from autograft patients. Allograft T cells were present in small numbers but displayed intense proliferation with spontaneous cytokine production. Oligoclonal expansions at week 2 came to represent a substantial fraction of the established T cell pool and were recruited into tissues affected by graft-versus-host disease. Transcriptional analysis uncovered a range of potential targets for immune manipulation, including OX40L, TWEAK, and CD70. These findings reveal that recognition of alloantigen drives naive T cells toward a unique phenotype. Moreover, they demonstrate that early clonal T cell responses are recruited to sites of subsequent tissue damage and provide a range of targets for potential therapeutic immunomodulation.

Alloreactive response T cells at 2 weeks after allo-SCT displayed intense proliferation with spontaneous cytokine production, and were recruited into tissues affected by GvHD.

Class I–unrestricted noncytotoxic anti–HTLV-I activity of CD8+ T cells

Although it is widely believed that viral clearance is mediated principally by the destruction of infected cells by cytotoxic T cells, noncytolytic antiviral activity of CD8+ T cells may play a role in preventing the progression to disease in infections with immunodeficiency viruses and hepatitis B virus. We demonstrate here that (1) replication of human T-lymphotropic virus type I (HTLV-I) is more readily detected from CD8+ T-cell–depleted (CD8−) peripheral blood mononuclear cells (PBMCs) of healthy HTLV-I carriers than from unfractionated PBMCs, (2) cocultures of CD8− PBMCs with autologous or allogeneic CD8+ T cells suppressed HTLV-I replication, and (3) CD8+ T-cell anti-HTLV-I activity is not abrogated intrans-well cultures in which CD8+ cells are separated from CD8− PBMCs by a permeable membrane filter. These results suggest that class I-unrestricted noncytolytic anti–HTLV-I activity is mediated, at least in part by a soluble factor(s), and may play a role in the pathogenesis of HTLV-I infection.

Class I–unrestricted noncytotoxic anti–HTLV-I activity of CD8+ T cells

Although it is widely believed that viral clearance is mediated principally by the destruction of infected cells by cytotoxic T cells, noncytolytic antiviral activity of CD8+ T cells may play a role in preventing the progression to disease in infections with immunodeficiency viruses and hepatitis B virus. We demonstrate here that (1) replication of human T-lymphotropic virus type I (HTLV-I) is more readily detected from CD8+ T-cell–depleted (CD8−) peripheral blood mononuclear cells (PBMCs) of healthy HTLV-I carriers than from unfractionated PBMCs, (2) cocultures of CD8− PBMCs with autologous or allogeneic CD8+ T cells suppressed HTLV-I replication, and (3) CD8+ T-cell anti-HTLV-I activity is not abrogated intrans-well cultures in which CD8+ cells are separated from CD8− PBMCs by a permeable membrane filter. These results suggest that class I-unrestricted noncytolytic anti–HTLV-I activity is mediated, at least in part by a soluble factor(s), and may play a role in the pathogenesis of HTLV-I infection.

Benign monoclonal T cell proliferation in HTLV-I infection

A spectrum of carrier states in human T lymphotropic virus type-I (HTLV-I) infection is proposed. The suspected process of clonal selection of HTLV-I infected cells results in the spectrum of nonfatal states from polyclonal to monoclonal virus integration. This idea is based on the discovery that monoclonal proviral HTLV-I DNA was detected in the fresh peripheral blood lymphocytes from some patients with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a nonfatal chronic neurological disorder.

Suppressive effects of interferons on the production and release of human T-lymphotropic virus type-I (HTLV-I)

The effects of human alpha-, beta-, or gamma-interferon (IFN) on the replication and production of human T-lymphotrophic virus type-I (HTLV-I) were investigated in a human T-cell line, MT-2. Virus transmission and production estimated by syncytium formation and HTLV-I-associated reverse transcriptase (RT) activity were strongly suppressed in the presence of alpha- and beta-IFN, but not gamma-IFN. However, the expression of virus specific proteins gp46 but not p19, p24, p28, p36, and gp68 was affected with IFNs as revealed by Western blotting analysis. Electron microscopic observations showed that some of the HTLV-I particles were trapped in the intracellular vacuoles in the presence of high doses of alpha- or beta-IFN. Continuous supply of IFNs appeared to be essential for the constant suppression of RT activity. These results suggest that alpha- and beta-IFN do not inhibit HTLV-I gene expression strikingly but suppress processing or assembly of virus proteins and/or releasing of virions in the late phase of maturation.

Expression of HTLV-I antigen in cultured peripheral blood mononuclear cells from patients with HTLV-I associated myelopathy

The HTLV-I antigen (Ag) was detected in short-term cultured peripheral blood mononuclear cells (PBMNC) from 44% of patients with HTLV-I-associated myelopathy (HAM), using the indirect immunofluorescence method. The HTLV-I Ag-positive cells accounted for less than 4% of cultured PBMNC in all but one case. The kinetics and mechanism of HTLV-I Ag expression in cultured cells were these studied in this individual with about 20% positive cells. HTLV-I Ag was 0.3% at 6 h after the culture and the number of positive cells increased to 9.3% at 48 h. The sera from HAM patients had a suppressive effect on the expression of HTLV-I Ag in the cultured cells. This suppression was more potent in sera from patients with a high than with low antibody titer. There were no correlations between the HTLV-I Ag expression in cultured cells and the various clinical and laboratory findings, in each case.

Interferons and autoimmunity

Autoimmunity can be accelerated in several genetically prone murine models and can even be induced in normal mice by treatment with interferon (IFN) or IFN-inducers. Several cases of IFN-induced autoimmune disease in humans also have been observed; however, more striking is the fact that some of the clinical manifestations in autoimmune diseases and many of the immunological aberrations can be mediated or enhanced by IFN. The finding of high levels of circulating IFN in many patients may be highly significant in that respect, and the characterization of the predominant type of IFN as an unusual acid-labile IFN-alpha may indicate an infectious etiologic agent in autoimmunity, since this peculiar IFN was mostly associated with viral infections in vivo or in vitro. The induction of MHC class II antigens on previously HLA-DR or Ia negative cells appears to be caused primarily by IFN-gamma and may have a central role in the pathogenesis of autoimmunity in susceptible individuals. Such aberrant HLA-DR expression on nonlymphoid cells can be detected early in the disease in the target organs of many varied autoimmune conditions and may trigger a cascade of self-directed, uncontrolled immune response in conjunction with other factors.

Human T-lymphoblastoid cell lines with high and low abilities to produce interferon-gamma constitutively and their susceptibilities to interferon

A human T-lymphoblastoid cell line, TCL-Fuj, produces large amounts of interferon (IFN)-gamma constitutively. A variant cell line, 2M, was derived from it. Both cell lines express similar surface antigen markers, but differ in surface morphology. Compared with the parent TCL-Fuj cell line, 2M produced less IFN-gamma constitutively but more in response to IFN inducers. The IFNs produced constitutively and on stimulation with inducers were analyzed by SDS-polyacrylamide gel electrophoresis. In TCL-Fuj cells, the constitutive and induced IFNs consisted of the same molecular species (22K and 39K). In 2M cells, smaller IFNs were produced constitutively (18K and 32K) and induction resulted in a marked increase of 22K molecules. These two cell lines also differed in sensitivity to the antiviral activity of IFN. Other T-lymphoblastoid cell lines, HPB-ALL and TCL-Fuj 4 cells, which did not produce IFN-gamma were permissive for vesicular stomatitis virus (VSV) replication; its growth was markedly suppressed by IFN-gamma and -alpha. TCL-Fuj cells were also permissive for VSV, but were not susceptible to the antiviral effect of the IFNs. In contrast, in 2M cells the multiplication of VSV was restricted; the viral yield was further reduced by the IFNs and increased by treatment with anti-human IFN-gamma serum. Several clonal cell lines derived from TCL-Fuj and 2M cells had characteristics similar to the respective parent cell lines. The growth of both cell lines was not affected by IFN-gamma or by -alpha. The separation of antiviral and anti-proliferative susceptibilities was peculiar to 2M cells unlike other cell lines.

Immortalization of human T lymphocytes by HTLV-I: phenotypic characteristics of target cells and kinetics of virus integration and expression

In-vitro infection of normal human lymphocytes with HTLV-I (human T-cell lymphotropic retrovirus type I) has been carried out to study the target cell specificity and the kinetics of infection. Cord blood (CBL) and adult peripheral blood lymphocytes (PBL) have been co-cultivated with irradiated HTLV-I donor cells (MT2 and C91PL lines). Established ('immortalized') HTLV-I positive cell lines were obtained only from CBL: in comparison with PBL, a less mature phenotype of T-cell subsets and a lower interferon-gamma production was evidenced in CBL. A progressive variation of differentiation antigen representation and of exogenous T-cell growth factor (TCGF, interleukin-2, IL-2) medium concentration was observed with increasing time from infection. The four established lines obtained showed a predominant T3+, T4+, T8-, Tac+ phenotype and a reduced TCGF requirement. Studies on kinetics of HTLV-I infection showed that p19 and p24 viral antigens became expressed after a lag phase of 5 weeks. DNA Southern blot analysis indicated that a shift from polyclonal to monoclonal pattern of proviral integration occurred with time of culture, both complete and defective copies being transmitted from donor to recipient cells.