The Tax protein of the human T-cell leukemia virus type I (HTLV-I) serves as a potent transcriptional activator of its own long terminal repeat as well as select cellular genes, including interleukin-2 and the alpha subunit of the interleukin-2 receptor. Tax activation of these two growth-related genes appears to involve the induced nuclear expression of DNA-binding proteins that specifically engage related kappa B enhancer elements present in the 5' regulatory regions of these genes. In human T cells, kappa B enhancer-binding activity has been discerned as an unexpectedly large family of UV cross-linked nucleoprotein adducts, termed p50, p55, p75, and p85. The protein components of each of these DNA-protein adducts have been shown to share structural similarity with the v-rel oncogene product. The p55 adduct is composed of the 50-kDa subunit of NF-kappa B derived from a 105-kDa precursor polypeptide, while the p50 adduct contains a smaller protein that is closely related to NF-kappa B p50. The p75 adduct contains the 65-kDa subunit of NF-kappa B, while the p85 adduct is composed of the human c-rel proto-oncogene product. We now demonstrate that HTLV-I Tax, in the absence of other viral pX gene products, is capable of inducing the nuclear expression of all four of these kappa B-binding proteins in human T cells, with most marked effects involving c-Rel and NF-kappa B p65. Tax induction of the nuclear expression of c-Rel and NF-kappa B p50 is regulated, at least in part, at a pretranslational level involving increases in c-rel and NF-kappa B p105 mRNA expression. To study the pattern of expression of these kappa B-specific proteins in cells infected with the whole HTLV-I, seven cloned HTLV-I-infected T-cell lines were established from the peripheral blood of patients with adult T-cell leukemia. Of note, only three of these seven cell lines produced Tax, and c-rel mRNA and nuclear protein expression was confined to these three cell lines. In contrast, NF-kappa B p50 and NF-kappa B p65 were constitutively expressed in the nuclei of all seven of the HTLV-I-infected cell lines, even in the absence of detectable Tax or other viral gene expression. These findings raise the possibility of an alternate, Tax-independent pathway for the induced nuclear expression of NF-kappa B p50 and NF-kappa B p65 following HTLV-I infection.

Leukemic cells in the peripheral blood of a patient with adult T cell leukemia (ATL), which expressed the Tac antigen/interleukin 2 (IL2) receptor, were investigated in vitro for autocrine growth by IL 2. The cells showed spontaneous proliferation in mitogen-free medium. The spontaneous proliferation of the cells was inhibited by monoclonal anti- IL 2 or anti-Tac antibody. These cells were found to produce messenger RNA for IL 2 and secrete IL 2 during short-term culture in the same medium. Recombinant IL 2 and IL 2 secreted by the cells enhanced the proliferation of the cells in a dose-dependent manner when added to the initial culture. These findings demonstrate that an autocrine mechanism by IL 2 is involved in the proliferation of ATL cells during short-term culture.

The HLA types of peripheral blood lymphocytes (PBL) of 36 adult T-cell leukemia/lymphoma (ATLL) patients were examined and compared with those of 45 healthy relatives of these patients, and with those of 10 non-ATLL families including 80 healthy members. Thirty-one percent of ATLL patients showed either a gain or a loss of HLA antigens determined by the presence of alien HLA antigens or the absence of inherent HLA antigens deduced from familial haplotype analysis. The antigen specificity of HLA gained or lost was variable and differed from case to case among ATLL patients. Although the gain of HLA was detected only in ATLL patients, the loss of HLA was found both in ATLL patients and in asymptomatic healthy relatives. The rate of HLA loss in ATLL patients (8.4%) and their relatives (17.8%) was much higher than in relatives of non-ATLL patients (1.1%). The HLA gain and loss revealed in the PBL of ATLL patients were confirmed by altered HLA phenotypes in the cloned T and B cells established from ATLL patients. Our results suggest that latently infecting HTLV-I may induce altered HLA phenotypes in T and B cells, primarily with loss of HLA antigens in a population of asymptomatic virus carriers, and secondarily with a gain of HLA antigens after the development of ATLL.