Detection of the human T cell lymphoma virus p19 in cells of some patients with cutaneous T cell lymphoma and leukemia using a monoclonal antibody.

A monoclonal antibody specific for the internal p19 protein of a type-C retrovirus (HTLV) isolated from human neoplastic T cells has been developed. Its specificity has been shown by radioimmune precipitation and by affinity chromatography of iodinated HTLV proteins. By indirect immune fluorescence this antibody recognizes only HTLV-producing cells. Examination of cells from patients with cutaneous T cell lymphomas and leukemias and with other types of lymphomas and leukemias indicated that HTLV p19 expression is rare. The monoclonal antibody will be useful in determining the natural reservoir of HTLV, possibly in a subset of mature T cell neoplasias.

Natural antibodies to the human T cell lymphoma virus in patients with cutaneous T cell lymphomas.

Sera from patients with cutaneous T cell lymphoma and leukemia were screened for the presence of natural antibody to the human T cell lymphoma (leukemia) virus, HTLVCR, using a solid-phase radioimmunoassay. Sera from two patients, including patient CR, from whose cultured T lymphoblastic cell line (HUT102), the retrovirus HTLVCR was isolated, reacted specifically with proteins of HTLVCR. Serum from patient CR also reacted specifically with proteins of HTLVMB, an independent but highly related retroviral isolate from a patient with Sezary T cell leukemia. The specificity for HTLVCR proteins was demonstrated by solid-phase immunocompetition assays and competition radioimmunoprecipitation assays. Analysis of radioimmunoprecipitates indicated that the natural antibodies were directed against HTLVCR core proteins with molecular weights of 24,000 and 19,000 (p24 and p19). Whereas the serum reactivities for HTLVCR proteins were shown to be highly specific, additional reactivities seen against proteins of animal retroviruses including GaLV, SSV, FeLV, and BaEV were clearly shown not to be viral specific but rather were due to reactivity with cellular antigens contaminating the viral preparations or with related antigens present in fetal calf serum. These results demonstrating natural antibodies to HTLVCR provide the first evidence for a specific antibody response to a retrovirus in humans.

Fidelity of HIV-1 reverse transcriptase.

The human immunodeficiency virus type 1 (HIV-1) shows extensive genetic variation and undergoes rapid evolution. The fidelity of purified HIV-1 reverse transcriptase was measured during DNA polymerization in vitro by means of three different assays. Reverse transcriptase from HIV-1 introduced base-substitution errors in DNA from the bacteriophage phi X174 amber3 at estimated frequencies of 1/2000 to 1/4000. Analyses of misincorporation rates opposite a single template adenine residue showed that HIV-1 reverse transcriptase catalyzed nucleotide mismatches with a specificity of A:C much greater than A:G greater than A:A. The high error rate of HIV-1 reverse transcriptase in vitro translates to approximately five to ten errors per HIV-1 genome per round of replication in vivo. This high error rate suggests that misincorporation by HIV-1 reverse transcriptase is, at least in part, responsible for the hypermutability of the AIDS virus. The specificity of misincorporation may provide a basis for the systematic construction of antiviral nucleosides.

Seroprevalence and epidemiological correlates of HTLV-I infection in U.S. blood donors.

Screening for human T-lymphotropic virus type I (HTLV-I) antibodies was performed on sera from 39,898 blood donors at eight blood centers in geographically distinct areas of the United States. Ten donors (0.025 percent) showed evidence of HTLV-I seropositivity by enzyme immunoassays; this was confirmed by protein immunoblot and radioimmunoprecipitation. Seroprevalence rates ranged from 0 to 0.10 percent at the locations sampled, with HTLV-I antibodies found predominantly in donors from the southeastern and southwestern United States. Matched case-control interviews and laboratory studies were performed on five seropositive women and two seropositive men who participated in an identity-linked collection of sera from a subset of 33,893 donors at six of the eight blood centers. Four of the women and both men are black; one woman is Caucasian. Four of the seven seropositive individuals admitted to prior intravenous drug abuse or sexual contact with an intravenous drug user. Sexual contact with native inhabitants of an HTLV-I endemic area was the only identified risk factor for one male. The distribution of HTLV-I antibodies in this U.S. blood donor sample corroborates the previously reported epidemiology of this agent and suggests that additional donor screening measures, including the testing of donated blood for HTLV-I markers, may be necessary to prevent the spread of HTLV-I to transfusion recipients.

Expression of int-2 oncogene in Kaposi's sarcoma lesions.

Fibroblast growth factors (FGFs), such as basic FGF, have been implicated in the growth of Kaposi's sarcoma (KS) cells in vitro. In the evaluation of the expression of the various genes of the different members of the FGF family and their receptors in fresh KS tissue specimens, int-2 was found to be expressed in more than half of the KS tumors examined. Using reverse transcription PCR, the expression of int-2 was detected in 21 of 38 (55.2%) fresh KS biopsy specimens. In contrast, int-2 mRNA transcripts were not found in normal appearing skin from the same patients except in one sample which was obtained from an AIDS patient with disseminated KS lesions. Sequence data confirmed that the amplified sequences were derived from int-2 mRNA with proper splicing. In addition, 12 nucleic acid alterations were identified in eight out of nine KS tumor samples sequenced. Using immunohistochemical methods, int-2 protein was detected in some of the spindle-shaped tumor cells surrounding the abnormal endothelial-lined vascular slits histologically characteristic of KS. Int-2 specific immunostaining was shown to be present in both the nuclei and cytoplasm of these spindle cells but was more pronounced in the nuclei. Neither amplification nor gross rearrangement of the int-2 gene was detected in KS lesions by Southern blot analysis. These results suggest that the expression of int-2 may play a role in the pathogenesis KS by stimulating local angiogenesis and cell proliferation.

Cell-mediated inhibition of tumor colony formation in agarose by resting and interleukin 2-stimulated human lymphocytes.

Human nonadherent peripheral blood mononuclear cells (PBMC) isolated from nonimmunized donors were preincubated for 18 h in medium alone or medium containing the lymphokine interleukin 2 and subsequently cocultured with tumor cells derived from malignant tumor cell lines or from fresh human tumors. The cell suspensions were subsequently inoculated into agarose; 14 days later, new tumor colony formation was determined. Although the different tumor cells displayed a wide range of sensitivity to the PBMC, in each instance, the number of colonies formed by the tumor cells exposed to the PBMC was consistently reduced relative to that of control cells. The inhibitory effect on the colony-forming cells was especially pronounced with PBMC preincubated with interleukin-2 and was dependent on the ratio of tumor cells to PBMC in the culture. This assay system provides an alternative to the standard 51Cr release assays in assessing the immunomodulatory effects of lymphokines and in quantitating the cytolytic or cytostatic activity of various effector cells against neoplastic stem cells from established cell lines and from heterogeneous cell preparations derived from fresh human tumors.

A phase I and clinical pharmacology study of intravenously administered carminomycin in cancer patients in the United States.

Carminomycin (CMN) was administered i.v. to 44 patients with a variety of nonhematological cancers every 4 weeks at doses of 15, 20, 22.5, and 25 mg/sq m. Granulocytopenia was the dose-limiting toxicity. The median granulocyte count for previously untreated patients receiving 22.5 mg/sq m was 0.962 cells/microliters, and for previously treated patients receiving 20 mg/sq m it was 0.420 cell/microliters. Moderate to severe phlebitis was associated with drug administration in 50% of cases. Nausea, vomiting, and alopecia were mild. Three of nine patients who received a total CMN dose of greater than or equal to 100 mg/sq m (mean, 132 mg/sq m) developed unexplained decreases in radionuclide cardiac ejection fraction, with one patient developing decreased QRS amplitude and congestive heart failure at a total dose of 160 mg/sq m. CMN is rapidly metabolized to carminomycinol. The elimination half-lives of CMN and carminomycinol are 6 to 10 and 50 hr, respectively. CMN was found to be a more potent inhibitor of human granulocyte-macrophage colony-forming units than was carminomycinol. Objective partial responses were seen in two of seven previously untreated patients with non-small cell lung cancer and one of three patients with squamous cell carcinoma of the head and neck previously untreated with chemotherapy.

Quantitative assay of human T-cell leukemia/lymphoma virus transformation.

The in vitro transformation of normal T-lymphocytes by human T-cell leukemia/lymphoma virus (HTLV-I) is possible utilizing cocultivation techniques. We now report on a quantitative assay for HTLV-I transformation. Transformed cell lines were produced by cocultivation of either preactivated (phytohemagglutinin and T-cell growth factor) or nonactivated peripheral blood mononuclear cells with an equal number of lethally irradiated HTLV-I-positive donor cells (MT-2). After 14 days in liquid culture, transformed cells were plated in a 2-layer soft agarose system with or without T-cell growth factor (TCGF). Colony formation among 50 normal controls was observed at varying efficiencies with a mean number of 179 colonies (range, 6-599) in the presence of TCGF (up to a 2-log difference). The day 14 T-cell cultures demonstrated relatively low colony-forming efficiencies (less than or equal to 0.1%) and enhanced colony formation in the presence of TCGF. Day 14 after cocultivation was chosen for this assay based on a dose-response relationship between colony formation and the virus-positive donor cell inoculum and the known kinetics of colony growth of normal activated T-cells. An analysis of individual colonies indicated that they were of target cell origin and HTLV-I positive. Recombinant beta-interferon in increasing concentrations caused a decrease in colony formation as measured in this assay. Long-term cell cultures (2-18 months) showed higher colony-forming efficiencies (up to 1.0%) which were not enhanced by TCGF. The ability to quantitatively evaluate transformation via colony counts will provide an opportunity to study differences in transforming efficiencies attributable to varying target cells, donor cells, or blocking factors such as interferons, drugs, or anti-HTLV-I antibodies.

Mechlorethamine, vincristine, and procarbazine chemotherapy for recurrent high-grade glioma in adults: a phase II study.

We undertook a phase II study of combination chemotherapy with mechlorethamine (nitrogen mustard) 6 mg/m2 intravenously day 1 and day 8, vincristine 2 mg intravenously day 1 and day 8, and procarbazine 100 mg/m2 orally days 1 through 14 (MOP) in adults with recurrent high-grade glioma. There were 31 patients entered and 27 patients assessable for response. The median age was 49 years old. All patients had prior maximal radiotherapy, and eight had previous chemotherapy. Responses were determined based on clinical and computed tomographic (CT) scan/magnetic resonance imaging (MRI) criteria. The response rate (partial response [PR] plus objective qualitative response [OQR] plus complete response [CR]) was 52% with one CR. The response rate was higher in patients with anaplastic astrocytoma as compared with glioblastoma multiforme (P less than .05). The median duration of response was 42 weeks. Median survival for all assessable patients was 30 weeks, and for responders, it was 60 weeks. Response was correlated with ability to decrease dexamethasone doses and improved performance status. Toxicity was mainly hematologic with leukopenia being common. There was one treatment-related death from listeria meningitis, and two patients developed Pneumocystis carinii pneumonia. There were three episodes of neutropenic fever. We conclude that MOP is active and merits further investigation in adult high-grade glioma.

Prognostic significance of K-ras codon 12 mutations in patients with resected stage I and II non-small-cell lung cancer.

PURPOSE: The aim of this study was to investigate the prognostic importance of codon 12 K-ras mutations in patients with early-stage non-small-cell lung cancer (NSCLC). PATIENTS AND METHODS: We identified 260 patients with surgically resected stage I (n = 193) and stage II (n = 67) NSCLC with at least a 5-year follow-up. We performed polymerase chain reaction analysis of DNA obtained from paraffin-embedded NSCLC tissue, using mutation-specific probes for codon 12 K-ras. RESULTS: K-ras mutations were detected in 35 of 213 assessable specimens (16.4%). K-ras mutations were detected in 27 of 93 adenocarcinomas (29.0%), one of 61 squamous cell carcinomas (1.6%), five of 39 large-cell carcinomas (12.8%), and two of 20 adenosquamous carcinomas (10%) (P = .001). G to T transversions accounted for 71% of the mutations. There was no statistically significant difference in overall survival for all patients with K-ras mutations (median survival, 39 months) compared with patients without K-ras mutations (median survival, 53 months; P = .33). There was no statistically significant difference in overall or disease-free survival for subgroups with stage I disease, adenocarcinoma, or non-squamous cell carcinoma or for specific amino acid substitutions. The median survival time for stage II patients with K-ras mutations was 13 months, compared with 38 months for patients without K-ras mutations (P = .03). CONCLUSION: Codon 12 K-ras mutations were more common in adenocarcinomas than in squamous cell carcinomas. For the subgroup with stage II NSCLC, there was a statistically significant adverse effect on survival for the presence of K-ras mutations. However, when the entire group was considered, the presence of K-ras mutations was not of prognostic significance in this cohort of patients with resected early-stage NSCLC.

Classic Kaposi's sarcoma associated with human herpesvirus 8 infection in a 13-year-old male: a case report.

PURPOSE: Classic Kaposi's sarcoma (KS) is rare in children. Although its etiology is not fully understood, human herpesvirus 8 (HHV-8) is present in the angiogenic lesions. We report an HIV-negative, 13-year-old patient of Sicilian descent with HHV-8-associated classic KS to facilitate the diagnosis and treatment of this entity in children. EXPERIMENTAL DESIGN: DNA was extracted from the skin specimen of the patient and analyzed via PCR assay and Southern blot hybridization for HHV-8 DNA. The amplified HHV-8 DNA was cloned, sequenced, and compared with the prototype HHV-8-KS330/BAM. RESULTS: The patient presented with purpuric lesions on the distal lower extremities and the tip of his nose, associated with thrombocytopenia and leukopenia, suggesting an immune-mediated cytopenia. While on prednisone, he developed marked vascular proliferation in the groins. Biopsy of the skin lesions showed KS, and HHV-8 was detected in the tissues by PCR. Sequence analysis of the amplified DNA was homologous to the prototype HHV-8-KS330/BAM. His HHV-8 strain was the A subgroup, the type associated with Mediterranean classic KS. Stopping prednisone and treatment with IFN-alpha and IgG resulted in regression of the groin lesions. CONCLUSIONS: This report emphasizes the importance of recognizing classic KS in children and avoiding immunosuppressive therapies in indolent classic KS. The diagnostic and therapeutic strategies were effective and well tolerated.

Transmission of human T-lymphotropic virus types I and II by blood transfusion. A retrospective study of recipients of blood components (1983 through 1988). The American Red Cross HTLV-I/II Collaborative Study Group.

We studied results of a "lookback" program involving laboratory testing and interviews of 133 recipients of prior donations from blood donors seropositive for human T-lymphotropic virus types I and II (HTLV-I/II) identified at 28 American Red Cross blood centers. The study was designed to explore the natural course of posttransfusion HTLV-I/II infection among individuals who received blood components from donors subsequently identified as being HTLV-I/II seropositive. Seventeen recipients were seropositive, an apparent transmission rate of 12.8%. Red blood cells and platelets were the implicated components, and red blood cells that were less than 6 days old had a transmission efficiency of 80%. Virus typing enabled documentation of primary and secondary transfusion transmission of HTLV-I and HTLV-II, including the direct transmission of HTLV-II by a donor with a history of intravenous drug use. We conclude that transfusion transmission of HTLV-I/II to approximately 700 recipients per year occurred in the United States before routine donor testing began in 1988.

HIV-1 infection and modulation of cytokine and growth factor expression in Kaposi's sarcoma-derived cells in vitro.

OBJECTIVES: HIV-1 transcripts have been detected in AIDS-related Kaposi's sarcoma (KS) tissues within the factor XIIIa + dermal dendrocytes present in the tumor. Various cytokines and growth factors have been shown to influence the growth of KS-derived cells in vitro. HIV-1 preferentially infects CD4+ cells and has also been found to infect some CD4- cells in vitro. The susceptibility of cultured KS cells in vitro to infection with HIV-1 and the expression of interleukin (IL)-1 beta, IL-6 and basic fibroblast growth factor (bFGF) after exposure to HIV-1 was examined. METHODS: The susceptibility of two different KS-derived cell cultures to HIV-1 infection was examined by the expression of p24 antigen, detection of proviral sequence and electron microscopy. The expression of IL-1 beta, IL-6 and bFGF was detected by enzyme-linked immunosorbent assay and reverse transcriptase polymerase chain reaction. RESULTS: KS-derived cells can be infected by HIV-1 in vitro. Both KS-derived cells were found to express CD4 mRNA. The expression of IL-1 beta and IL-6 was increased, whereas the expression of bFGF was not stimulated after exposure of KS cells to HIV-1. CONCLUSION: These experiments describe the in vitro infection of KS-derived cells by HIV-1 and the expression of various cytokines and growth factor following infection. The increased production of cytokines observed following such infection may be involved in the pathogenesis of AIDS-related KS.

Maintenance of CD4+ cells by thymopentin in asymptomatic HIV-infected subjects: results of a double-blind, placebo-controlled study.

OBJECTIVE: To assess the efficacy and safety of thymopentin in HIV-infected patients who had not yet developed AIDS. DESIGN: Patients were stratified into asymptomatic or symptomatic groups and randomized to receive either thymopentin (50 mg) or placebo, subcutaneously, double-blind for 24 or 52 weeks, three times a week. SETTING: Patients were enrolled at three sites (two hospital clinics and one private practice). PATIENTS: Of 91 HIV-seropositive patients (52 asymptomatic and 39 symptomatic) from whom HIV could be isolated from peripheral blood, 45 were enrolled for 24 weeks and 46 for 52 weeks of double-blind evaluation. MAIN OUTCOME MEASURES: Virological, immunological and clinical evaluations were performed before and during treatment. RESULTS: Thymopentin-treated asymptomatic patients had more CD4+ cells, as demonstrated by a greater area under the percentage CD4+ cells curve (P = 0.03) and a shorter median time to a 20% increase in percentage of CD4+ cells (P = 0.04) in the first 24 weeks, with similar trends in the 52-week study. By 24 weeks no asymptomatic thymopentin-treated and two placebo-treated patients (9.1%, Kaplan-Meier estimate) had progressed to constitutional symptoms (P = 0.12; two-tailed Wilcoxon-Gehan test), with only one further progression in a placebo-treated patient in the subset followed for 52 weeks. Symptomatic patients receiving thymopentin or placebo were similar in both CD4+ cell levels and disease progression (two progressions to AIDS in each group). No serious adverse effects attributable to thymopentin were observed. CONCLUSIONS: These results, if confirmed, indicate that thymopentin, by maintaining CD4+ cells, could slow or arrest immune decline and consequent disease progression at the asymptomatic stage of HIV infection.

A phase II study of recombinant interleukin-2 with or without recombinant interferon-beta in non-Hodgkin's lymphoma. A study of the Cancer and Leukemia Group B.

Interleukin-2 (IL-2) and interferon-beta (IFN-beta) have demonstrated activity against lymphoid malignancies, presumably mediated by the augmentation of lymphokine-activated killer (LAK) cell and natural killer (NK) cell activity. There is in vitro and in vivo evidence to suggest that the combination of IL-2 and IFN-beta is synergistic. The Cancer and Leukemia Group B (CALGB) conducted a randomized phase II trial of IL-2 with or without IFN-beta in 49 patients with relapsed or refractory non-Hodgkin's lymphoma (NHL). Overall toxicity was severe, with 17 patients experiencing life-threatening toxicity. Three patients had treatment-related deaths. Responses were noted in seven patients (17%). There were no meaningful differences between treatment arms in toxicity profile, response rate, or modulation of in vivo NK and LAK activity. We conclude that IL-2 with or without IFN-beta is not effective therapy for NHL in the doses and schedule used in this study.

Leukemias associated with human T-cell lymphotropic virus type I in a non-endemic region.

Human T lymphotropic virus type 1 (HTLV-I) is a retrovirus which is prevalent in southern Japan, the Caribbean Basin, and Africa. Recent seroprevalence studies in the United States suggest that there are about 50,000 infected individuals. The identification of 5 individuals with HTLV-I-associated leukemia/lymphoma referred to our center with relatively limited screening methods suggests that these disorders are more common than currently appreciated. Though 99% of infected individuals remain asymptomatic, this virus may cause immunosuppression, lymphomas, or myelopathy. The lymphomas have been classified as acute or chronic forms of adult T cell leukemia-lymphoma (ATLL). Acute ATLL is a T cell form of non-Hodgkin's lymphoma in an HTLV-I-infected individual with leukemia, skin infiltration, or hypercalcemia. This disorder is poorly responsive to chemotherapy and all patients should be referred for experimental protocols. Chronic ATLL is an insidious disease characterized by lymphadenopathy, skin infiltration of less than 10% of the body surface, and/or atypical lymphocytes with highly convoluted nuclei which include 1 to 10% of the nucleated cells in the peripheral blood, but no visceral involvement or hypercalcemia. The prognosis of these patients is not clearly defined. All individuals with mature T lymphocytic malignancies should be evaluated with HTLV-I-specific assays. The most sensitive and specific assays available include the enzyme linked immunoadsorbent antibody assay (ELISA) and the polymerase chain DNA amplification reaction assay. With improved laboratory techniques and greater awareness of the characteristics of this disease by clinicians, it is likely that the natural history of HTLV-I infection will be better defined, and improvements in therapeutic management will be developed.

HIV-1 infection abolishes CD4 biosynthesis but not CD4 mRNA.

In order to improve understanding of how HIV-1 infection down-modulates cell surface membrane expression of CD4, we have measured several parameters of CD4 expression in the human tumor T-cell lines CEM and MOLT-4 at different times after infection. Three independent HIV-1 isolates were used including one that encodes a truncated nef protein and another that appeared to be noncytolytic against CEM. The level of CD4 mRNA, the rate of biosynthesis of CD4 protein, and the percentage of CD4-positive cells were measured. With each viral isolate it was found that infection led to a specific and almost complete inhibition of CD4 protein biosynthesis. This substantially exceeded, at every time point after infection, a concomitant reduction in CD4 mRNA. Hence an inhibition of translation probably accounts for much of the decline in the rate of CD4 biosynthesis. This implicates a novel selective translational inhibition of host gene expression by HIV-1 as a factor in the disappearance of surface membrane CD4 from infected cultures.

HTLV-I DNA sequences in CNS tissue of a patient with tropical spastic paraparesis and HTLV-I-associated myelopathy.

Human T cell lymphotrophic virus type I (HTLV-I) is the etiologic agent of adult T cell lymphoma/leukemia (ATLL) and tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM). We studied an HTLV-I-seropositive, white man diagnosed in 1977 with ATLL and 10 years later, 6 months prior to his death, with TSP/HAM. Sections of brain, spinal cord, and visceral tissues were examined histologically, immunohistochemically, by in situ hybridization, and by the polymerase chain reaction (PCR). PCR amplification of a region of the polymerase (pol) gene of HTLV-I from visceral tissue demonstrated the presence of proviral HTLV-I DNA in paraffin-embedded sections from the liver and in DNA extracted from frozen sections of kidney and spleen, but failed to demonstrate viral sequences in paraffin sections of the lung and a lymph node. PCR analysis of CNS tissue demonstrated viral sequences in regions of the brain including frozen samples from cerebellum and cerebral cortex and paraffin sections of the thoracic spinal cord, but failed to detect proviral DNA in sections from a region in the lumbar cord. These results map the distribution of HTLV-I DNA sequences in the CNS of a patient with TSP/HAM for 3 months.

Synergy, activity and tolerability of zidovudine and interferon-alpha in patients with symptomatic HIV-1 infection: AIDS Clincal Trial Group 068.

Thirty-four subjects with symptomatic HIV-1 infection, p24 antigenaemia, and CD4 cell counts > 200/mm3 were randomly assigned to receive treatment with either zidovudine (ZDV) orally, interferon-alpha (IFN-alpha) subcutaneously, or both at respective low (200 mg ZDV/ 2 million international units IFN-alpha (MIU)), middle (400 mg/4 MIU) or high (600 mg/6 MIU) daily dose levels for 12 weeks. Thereafter, all patients received combination therapy at the initially assigned dose level to a total of 96 weeks. This design permitted analysis by the combination index (CI) method, which demonstrated antiretroviral synergy between ZDV and IFN-alpha with respect to p24 antigen suppression. Over the first 12 weeks, combination therapy was acceptably tolerated, more so than IFN-alpha monotherapy, and it was significantly more active in suppressing antigenaemia than either of the monotherapies. Similarly, the high-dose combination was the most active dose level over weeks 12 to 96. Combination ZDV/IFN-alpha at the optimal dose level defined by this trial merits further study. In addition, the CI design strategy employed here may be useful for the investigation of new antiretroviral combinations.

Multiple sclerosis, retroviruses, and PCR. The HTLV-MS Working Group.

Previously reported serologic and polymerase chain reaction (PCR)-based findings have suggested an association between the human retrovirus, HTLV-I, and multiple sclerosis (MS). Due to the inherent ability of PCR to produce false-positive results, we developed a set of physical and procedural safeguards to minimize the possibility of molecular carryover. These were applied as part of a blinded, large-scale, multipopulation, multiplex PCR-based study designed to examine this issue of association. Our results do not support the hypothesis that HTLV-I, which plays a role in the pathogenesis of an encephalomyeloneuropathy, HTLV-II, or closely related agents are associated with MS. A concomitant review of the current literature supports this view.