Transient early post-inoculation anti-retroviral treatment facilitates controlled infection with sparing of CD4+ T cells in gut-associated lymphoid tissues in SIVmac239-infected rhesus macaques, but not resistance to rechallenge.

Like human immunodeficiency virus infection of humans, infection of rhesus macaques with pathogenic simian immunodeficiency virus (SIV) strains typically results in persistent progressive infection, leading to clinically significant immunosuppression. In previous studies, we administered short term anti-retroviral treatment, shortly after intravenous inoculation with SIVsmE660, in an effort to allow immunologic sensitization under conditions not characterized by overwhelming cytopathic infection compromising the developing immune response. We showed that such treatment allowed control of off treatment viremia and was associated with resistance to rechallenge. Control of off treatment viremia was associated, at least in part, with CD8+ lymphocytes, based on in vivo CD8 depletion studies. In the present study, six rhesus macaques were infected intravenously with 100 MID50 of SIVmac239; four then received 30 days of treatment with tenofovir 9-[2-(R)-(phosphonomethoxy)propyl]adenine (PMPA); 20-30 mg/kg, subcutaneously) starting 24 hours post-inoculation. Tenofovir-treated animals showed low (<500 copy Eq/ml) or undetectable (<100 copy Eq/ml) plasma SIV RNA levels during treatment, with undetectable plasma viremia following discontinuation of treatment. Plasma SIV RNA remained <100 copy Eq/ml, even after depletion of CD8+ lymphocytes, 6 weeks after discontinuation of tenofovir treatment. In contrast to untreated infected control animals that showed substantial depletion of CD4+ T cells from gut-associated lymphoid tissues (GALT), tenofovir-treated animals showed sparing of GALT CD4+ T cells both during the treatment period and in the off treatment follow-up period. However, in contrast to earlier results with animals infected with SIVsmE660, in the present study, the animals did not develop readily measurable cellular anti-SIV immune responses, and did not resist homologous rechallenge with SIVmac239, administered 44 weeks after the initial infection. Differences in the animals and virus strains employed may in part account for the differences in results observed. Comparative analysis of virologic and immunologic parameters in this model system may provide important insights for understanding the basis of effective immunologic control of SIV infection.

Whole inactivated SIV virion vaccines with functional envelope glycoproteins: safety, immunogenicity, and activity against intrarectal challenge.

A novel type of whole inactivated simian immunodeficiency virus (SIV) virion vaccine immunogen with functional envelope glycoproteins was evaluated, without adjuvant, in rhesus macaques. Immunogens included purified inactivated virions of SIVmac239, a designed mutant of SIVmac239 with gp120 carbohydrate attachment sites deleted (SIVmac239 g4,5), and SIVmneE11S. The vaccines were noninfectious, safe, and immunogenic, inducing antibody responses and cellular responses, including responses by CD8+ lymphocytes. Interpretation of protective efficacy following intrarectal challenge was complicated by incomplete take of the challenge in some SIV naïve controls.

Role of CD8(+) lymphocytes in control of simian immunodeficiency virus infection and resistance to rechallenge after transient early antiretroviral treatment.

Transient antiretroviral treatment with tenofovir, (R)-9-(2-phosphonylmethoxypropyl)adenine, begun shortly after inoculation of rhesus macaques with the highly pathogenic simian immunodeficiency virus (SIV) isolate SIVsmE660, facilitated the development of SIV-specific lymphoproliferative responses and sustained effective control of the infection following drug discontinuation. Animals that controlled plasma viremia following transient postinoculation treatment showed substantial resistance to subsequent intravenous rechallenge with homologous (SIVsmE660) and highly heterologous (SIVmac239) SIV isolates, up to more than 1 year later, despite the absence of measurable neutralizing antibody. In some instances, resistance to rechallenge was observed despite the absence of detectable SIV-specific binding antibody and in the face of SIV lymphoproliferative responses that were low or undetectable at the time of challenge. In vivo monoclonal antibody depletion experiments demonstrated a critical role for CD8(+) lymphocytes in the control of viral replication; plasma viremia rose by as much as five log units after depletion of CD8(+) cells and returned to predepletion levels (as low as <100 copy Eq/ml) as circulating CD8(+) cells were restored. The extent of host control of replication of highly pathogenic SIV strains and the level of resistance to heterologous rechallenge achieved following transient postinoculation treatment compared favorably to the results seen after SIVsmE660 and SIVmac239 challenge with many vaccine strategies. This impressive control of viral replication was observed despite comparatively modest measured immune responses, less than those often achieved with vaccination regimens. The results help establish the underlying feasibility of efforts to develop vaccines for the prevention of AIDS, although the exact nature of the protective host responses involved remains to be elucidated.

Protection of Macaca nemestrina from disease following pathogenic simian immunodeficiency virus (SIV) challenge: utilization of SIV nucleocapsid mutant DNA vaccines with and without an SIV protein boost.

Molecular clones were constructed that express nucleocapsid (NC) deletion mutant simian immunodeficiency viruses (SIVs) that are replication defective but capable of completing virtually all of the steps of a single viral infection cycle. These steps include production of particles that are viral RNA deficient yet contain a full complement of processed viral proteins. The mutant particles are ultrastructurally indistinguishable from wild-type virus. Similar to a live attenuated vaccine, this approach should allow immunological presentation of a full range of viral epitopes, without the safety risks of replicating virus. A total of 11 Macaca nemestrina macaques were inoculated with NC mutant SIV expressing DNA, intramuscularly (i.m.) in one study and i.m. and subcutaneously in another study. Six control animals received vector DNA lacking SIV sequences. Only modest and inconsistent humoral responses and no cellular immune responses were observed prior to challenge. Following intravenous challenge with 20 animal infectious doses of the pathogenic SIV(Mne) in a long-term study, all control animals became infected and three of four animals developed progressive SIV disease leading to death. All 11 NC mutant SIV DNA-immunized animals became infected following challenge but typically showed decreased initial peak plasma SIV RNA levels compared to those of control animals (P = 0.0007). In the long-term study, most of the immunized animals had low or undetectable postacute levels of plasma SIV RNA, and no CD4(+) T-cell depletion or clinical evidence of progressive disease, over more than 2 years of observation. Although a subset of immunized and control animals were boosted with SIV(Mne) proteins, no apparent protective benefit was observed. Immunization of macaques with DNA that codes for replication-defective but structurally complete virions appears to protect from or at least delay the onset of AIDS after infection with a pathogenic immunodeficiency virus. With further optimization, this may be a promising approach for vaccine development.

Mucosal challenge of Macaca nemestrina with simian immunodeficiency virus (SIV) following SIV nucleocapsid mutant DNA vaccination.

A simian immunodeficiency virus (SIV)(Mne) DNA clone was constructed that produces viruses containing a four amino acid deletion in the second zinc finger of the nucleocapsid (NC) domain of the Gag polyprotein. Viruses produced from this clone, although non-infectious both in vitro and in vivo, complete a majority of the steps in a single retroviral infection cycle. Eight pig-tailed macaques (Macaca nemestrina) were inoculated intramuscularly and subcutaneously three times over the course of 24 weeks with the NC mutant expressing DNA. These macaques, and four controls, were then challenged mucosally (intrarectally) with the homologous virus (SIV Mne CL E11S) and monitored for evidence of infection and clinical disease. Prior to challenge, a measurable humoral immune response was noted in four of eight immunized macaques. After challenge, all 12 macaques became infected, although four immunized animals greatly restricted their viral replication, and one immunized animal that controlled replication remains antibody negative. No disease has been evidence during the 46-week period of monitoring after challenge.

Containment of simian immunodeficiency virus infection: cellular immune responses and protection from rechallenge following transient postinoculation antiretroviral treatment.

To better understand the viral and host factors involved in the establishment of persistent productive infection by primate lentiviruses, we varied the time of initiation and duration of postinoculation antiretroviral treatment with tenofovir (9-[2-(R)-(phosphonomethoxy)propyl]adenine) while performing intensive virologic and immunologic monitoring in rhesus macaques, inoculated intravenously with simian immunodeficiency virus SIVsmE660. Postinoculation treatment did not block the initial infection, but we identified treatment regimens that prevented the establishment of persistent productive infection, as judged by the absence of measurable plasma viremia following drug discontinuation. While immune responses were heterogeneous, animals in which treatment resulted in prevention of persistent productive infection showed a higher frequency and higher levels of SIV-specific lymphocyte proliferative responses during the treatment period compared to control animals, despite the absence of either detectable plasma viremia or seroconversion. Animals protected from the initial establishment of persistent productive infection were also relatively or completely protected from subsequent homologous rechallenge. Even postinoculation treatment regimens that did not prevent establishment of persistent infection resulted in downmodulation of the level of plasma viremia following treatment cessation, compared to the viremia seen in untreated control animals, animals treated with regimens known to be ineffective, or the cumulative experience with the natural history of plasma viremia following infection with SIVsmE660. The results suggest that the host may be able to effectively control SIV infection if the initial exposure occurs under favorable conditions of low viral burden and in the absence of ongoing high level cytopathic infection of responding cells. These findings may be particularly important in relation to prospects for control of primate lentiviruses in the settings of both prophylactic and therapeutic vaccination for prevention of AIDS.

Chemical inactivation of retroviral infectivity by targeting nucleocapsid protein zinc fingers: a candidate SIV vaccine.

Although most viral vaccines used in humans have been composed of live attenuated viruses or whole killed viral particles, the latter approach has received little attention in research on experimental primate immunodeficiency virus vaccines. Inactivation procedures involving heat or formalin appear to adversely affect the viral envelope proteins. Recently we have inactivated human immunodeficiency virus type 1 (HIV-1) with the compound 2,2'-dithiodipyridine (Aldrithiol-2, Aldrich, Milwaukee, WI), which inactivates infectivity of retroviruses by covalently modifying the nucleocapsid zinc finger motifs. HIV-1 inactivated with Aldrithiol-2 retained the conformational and functional integrity of the viral and virion-associated cellular proteins on the viral membrane. We have extended our studies of zinc finger targeted inactivation to simian immunodeficiency virus (SIV) and evaluated the feasibility of applying the procedures to large scale (>30 l) production and purification of the primate immunodeficiency viruses. There was no detectable residual infectivity of SIV after treatment with 1 mM Aldrithiol-2 (>5 logs inactivation). Treatment with Aldrithiol-2 resulted in extensive reaction with the nucleocapsid protein of treated virus, as shown by immunoblot and high-performance liquid chromatography (HPLC) analysis. As expected, the virion gp120SU appeared to be completely unreactive with Aldrithiol-2. Sucrose gradient purification and concentration procedures resulted in little loss of viral infectivity or virion-associated gp120SU. When tested in a gp120-CD4 dependent cell binding assay, the inactivated virus bound to cells comparably to the untreated virus. Analysis of gp120-CD4 mediated postbinding fusion events showed that the inactivated virus could induce CD4-dependent fusion with efficiencies similar to the untreated virus. Inactivation and processing of primate immunodeficiency viruses by methods described here results in highly concentrated virus preparations that retain their envelope proteins in a native configuration. These inactivated virus preparations should be useful in whole killed-particle vaccine experiments as well as laboratory reagents to prepare antisera, including monoclonal antibodies, and to study noninfective virion-cell interactions.

CD4(+) T-lymphocyte depletion in human lymphoid tissue ex vivo is not induced by noninfectious human immunodeficiency virus type 1 virions.

We tested infectious human immunodeficiency virus type 1 (HIV-1), noninfectious but conformationally authentic inactivated whole HIV-1 virions, and purified gp120 for the ability to induce depletion of CD4(+) T cells in human lymphoid tissues ex vivo. Infectious CXCR4-tropic HIV-1, but not matched inactivated virions or gp120, mediated CD4(+) T-cell depletion, consistent with mechanisms requiring productive infection.

Inactivation of human immunodeficiency virus type 1 infectivity with preservation of conformational and functional integrity of virion surface proteins.

Whole inactivated viral particles have been successfully used as vaccines for some viruses, but procedures historically used for inactivation can denature virion proteins. Results have been inconsistent, with enhancement of disease rather than protection seen in some notable instances following vaccination. We used the compound 2,2'-dithiodipyridine (aldrithiol-2; AT-2) to covalently modify the essential zinc fingers in the nucleocapsid (NC) protein of human immunodeficiency virus type 1 (HIV-1) or simian immunodeficiency virus (SIV) virions, thereby inactivating infectivity. The inactivated virus was not detectably infectious in vitro (up to 5 log units of inactivation). However, in contrast to virions inactivated by conventional methods such as heat or formalin treatment, viral and host cell-derived proteins on virion surfaces retained conformational and functional integrity. Thus, immunoprecipitation of AT-2-treated virions was comparable to precipitation of matched untreated virus, even when using antibodies to conformational determinants on gp120. AT-2 inactivated virions bound to CD4(+) target cells and mediated virus-induced, CD4-dependent "fusion from without" comparably to native virions. However, viral entry assays demonstrated that the viral life cycle of AT-2-treated virions was arrested before initiation of reverse transcription. The major histocompatibility complex (MHC) class II molecules on the surface of AT-2-treated virions produced from MHC class II-expressing cells retained the ability to support class II-dependent, superantigen-triggered proliferative responses by resting T lymphocytes. These findings indicate that inactivation via this method results in elimination of infectivity with preservation of conformational and functional integrity of virion surface proteins, including both virally encoded determinants and proteins derived from the host cells in which the virus was produced. Such inactivated virions should provide a promising candidate vaccine antigen and a useful reagent for experimentally probing the postulated involvement of virion surface proteins in indirect mechanisms of HIV-1 pathogenesis.

The extent of early viral replication is a critical determinant of the natural history of simian immunodeficiency virus infection.

Different patterns of viral replication correlate with the natural history of disease progression in humans and macaques infected with human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV), respectively. However, the viral and host factors influencing these patterns of viral replication in vivo are poorly understood. We intensively studied viral replication in macaques receiving identical inocula of SIV. Marked differences in viral replication patterns were apparent within the first week following inoculation, a time prior to the development of measurable specific immune effector responses to viral antigens. Plasma viral RNA levels measured on day 7 postinoculation correlated with levels measured in the postacute phase of infection. Differences in the susceptibility of host cells from different animals to in vitro SIV infection correlated with the permissiveness of the animals for early in vivo viral replication and hence with the postacute set point level of plasma viremia. These results suggest that host factors that exert their effects prior to full development of specific immune responses are critical in establishing the in vivo viral replication pattern and associated clinical course in subjects infected with SIV and, by extension, with HIV-1.

HLA class II on HIV particles is functional in superantigen presentation to human T cells: implications for HIV pathogenesis.

The mechanisms of immune suppression by the human immunodeficiency virus, HIV-1, are more complex than simple helper T cell deletion via infection and viral-induced lysis. Since the recent description of cellular proteins associated with HIV suggests that these proteins may be active in viral pathogenesis, the nature of HLA class II gene product carried on HIV, one of the most abundant of the human components carried with the virus, was examined. HIV bearing HLA-DR was shown to act with bacterial superantigen, staphylococcal enterotoxin A (SEA), to stimulate highly purified human T lymphocytes. T cell stimulation by wild-type HIV was shown by both induction of proliferation and by production of the cytokine interleukin 2 (IL-2). In contrast, HIV produced from mutant cells lacking class II genes were unable to cooperate with SEA to activate T cells. Neither whole HIV nor several proteins purified from HIV (gp120, gp41, p24, p7, and p6) exhibited superantigen-like activity in this system. HLA-DR-bearing HIV could, in the continued presence of SEA, induce T cell apoptosis, as detected by nuclear fragmentation and morphological criteria. These data indicate that human cellular proteins associated with HIV may be biologically active, and these proteins should be considered in mechanisms of viral pathogenicity and immunogenicity.

Aqueous humor cytokine profile in patients with chronic uveitis.

There is increasing evidence that cytokines play an important role in the pathogenesis of uveitis. The aim of this study was to determine the presence of cytokines in the aqueous humor (AH) of patients with chronic idiopathic uveitis (CU). Patients with uveitis (n=10) were compared to those undergoing cataract surgery (n=1) for non-inflammatory eye diseases. ELISA's for the detection of cytokines (IL-1, IL-2, IL-6, TNF-α) in aqueous humor were developed that allowed the measurement of multiple cytokines present in low concentrations. Interleukin-6 was found to be elevated in the aqueous humor of two patients (20%) with CU, but in none of the controls. Interleukin-1-α, Interleukin-2 and TNF-α were not detected in the AH of patients or controls. TGF-ß was detected in the aqueous of all patients and controls, using a bioassay.

Interleukin-2 suppresses activated macrophage intracellular killing activity by inducing macrophages to secrete TGF-beta.

Phorbol myristate acetate (PMA) treatment of an EL-4 thymoma cell line (EL-4FARRAR) induced secretion of a factor that inhibited intracellular killing of Leishmania major amastigotes by activated macrophages. Analysis of the cytokines produced by EL-4 cells after PMA stimulation identified interleukin-2 (IL-2, 2500 U/ml), IL-4 (1280 U/ml), interferon-gamma (IFN-gamma; 100 U/ml), and granulocyte-macrophage colony-stimulating factor (GM-CSF; 50 U/ml). Neither tumor necrosis factor nor transforming growth factor beta (TGF-beta) was detected. Each of the cytokines present in EL-4 fluids was assessed for capacity to activate macrophages for destruction of parasites or to suppress intracellular killing. IFN-gamma and GM-CSF both activated macrophages to kill Leishmania; IL-2 and IL-4 had no activity for induction of this antimicrobial effector function. IL-2 and IL-4 were tested for their capacity to inhibit lymphokine- or IFN-gamma-induced destruction of L. major by macrophages: IL-4 was ineffective, but IL-2 markedly suppressed the activation of macrophages for intracellular killing. Addition of > or = 10 U/ml of IL-2 at the time of infection, or up to 4 h before, blocked up to 100% of the capacity of activated macrophages to kill intracellular amastigotes. Immunoaffinity treatment of EL-4 fluids with anti-IL-2 antibody resulted in > 80% reduction in suppression of intracellular killing. The suppressive effects of IL-2 were not direct, but mediated by TGF-beta. IL-2 induced resident peritoneal macrophages to secrete > 5000 pg/ml TGF-beta 1, a quantity that is > 500-fold higher than constitutive background levels (20-40 pg/ml) and is sufficient to block intracellular killing activities. This increase in secretion of TGF-beta was not dependent increases in TGF-beta 1 mRNA. Treatment of cultures with EL-4 fluids or recombinant IL-2 in the presence of antibody to TGF-beta 1 blocked the suppressive activity of both. Thus, IL-2 was the major suppressor factor in EL-4 fluids, and it acted indirectly through the induction and autocrine action of TGF-beta.

Determining confidence limits for drug potency in immunoassay.

Nonlinear models have frequently been used to characterize dose-response data obtained from biological assays. The effect of a bioactive agent is observed and the model allows prediction of the dose required to obtain the observed effect (the 'inverse prediction'). The precision of this estimate is important in potency determination. Here, a general method is presented for calculating the inverse confidence intervals for estimates of dose potencies obtained from nonlinear models often used to describe these tests. The approach is demonstrated with application of data sets to the negative exponential and four-parameter logistic regression models. Necessary theory is presented and followed by detailed discussion in which estimation strategies are explained and intermediate quantities calculated.

Polyinosinic-polycytidylic acid complexed with poly-L-lysine and carboxymethylcellulose in combination with interleukin 2 in patients with cancer: clinical and immunological effects.

We have performed a phase IB study of polyinosinic-polycytidylic acid complexed with poly-L-lysine and carboxymethylcellulose (poly-ICLC) in combination with interleukin 2 (IL-2) in 25 patients with a variety of cancers. Patients received weekly or biweekly poly-ICLC by i.m. injection, at doses ranging from 0.01 to 1.0 mg/m2, for 1 month. This was followed by 2 months of outpatient therapy with biweekly i.m. poly-ICLC in combination with IL-2 (3 x 10(6) units/m2) given i.v. by 24-h continuous infusion twice weekly, using a portable infusion pump. No objective tumor responses were observed. Toxicity was moderate at all poly-ICLC doses tested and increased only slightly following the addition of IL-2. No increases in peripheral blood natural killer (NK) activity were observed after treatment with poly-ICLC alone. However, high dose poly-ICLC (greater than or equal to 0.3 mg/m2) in combination with IL-2 resulted in NK activity greater than that seen using the same dose of IL-2 in combination with lower poly-ICLC doses. Increases in the number and percentage of CD56+ cells were evident only after initiation of IL-2 therapy and were unaffected by the poly-ICLC dose. In the majority of patients, these increases were preferentially associated with the subset of CD56+ cells coexpressing CD8, while the CD56+/CD16+ population was elevated to a lesser extent. Moderate increases in serum neopterin levels and 2',5'-oligoadenylate synthetase activity in peripheral blood mononuclear cells were noted at 72 h following initial treatment with 1.0 mg/m2 poly-ICLC. No induction of alpha or gamma interferon was detected. This study shows that the addition of poly-ICLC to a well tolerated IL-2 regimen can significantly enhance NK activity. Poly-ICLC can be used to enhance IL-2-induced NK lytic activity without increases in the dose and, therefore, the toxicity of IL-2 treatment.

A trial of recombinant human interleukin-1 in patients with severe refractory aplastic anaemia.

We report here the effects of in vivo administration of recombinant interleukin-1 alpha (rIL-1 alpha) to patients with severe, idiopathic aplastic anaemia. Four patients who were refractory to immunosuppressive therapy and were not bone marrow transplantation candidates received daily doses of 0.03 microgram/kg and 0.10 microgram/kg intravenously as 5 d courses. No significant changes in either peripheral blood counts or bone marrow cellularity were observed at either dose during or following therapy. Two patients showed increased numbers of bone marrow progenitor colonies. Lymphocyte phenotyping demonstrated an elevated percentage of CD8+/DR+ activated suppressor T lymphocytes prior to therapy. After rIL-1 alpha administration, the percentage of CD8+/DR+ cells was reduced or returned to normal in all patients. Significant side-effects included fever, rigours, fatigue, headache and nausea. Transient hypotension was observed at both doses in all patients. These results suggest that while rIL-1 alpha can be safely administered, no significant haematologic improvement was observed in patients with severe aplastic anaemia.

Intraperitoneal lymphokine-activated killer cell/interleukin-2 therapy in patients with intra-abdominal cancer: immunologic considerations.

Lymphokine-activated killer (LAK) cells and interleukin-2 (IL-2) were administered by the ip route to patients with intra-abdominal malignancies. Pharmacokinetic studies of IL-2 revealed 10- to 100-fold higher concentrations of IL-2 in peritoneal fluid versus serum. Ip levels of IL-2 were maintained well above those required to generate and maintain LAK cells in vitro. LAK cell activity was detectable in the peritoneal fluid for the duration of each treatment cycle and did not disappear until IL-2 was discontinued. Detection of interferon-gamma (IFN-gamma) in the peritoneal fluid of all patients was consistent with production in situ by activated lymphocytes. In some patients, low but detectable levels of IFN-gamma were also found in the serum. In vivo activation of monocytes in the peritoneal fluid as measured by in vitro production of hydrogen peroxide was documented in the majority of patients. Neither interleukin-1 nor tumor necrosis factor-alpha was detected in the peritoneal fluid. We found no correlation between the presence or levels of IL-2, IFN-gamma, or LAK cell lytic activity in peritoneal fluid or serum and response or nonresponse to therapy.

Establishment of a human B cell line that proliferates in response to B cell growth factor.

A human B cell line which shows a marked dose dependence on B cell growth factor (BCGF) when cultured in less than or equal to 2% serum has been established. Human B lymphocytes were obtained from peripheral blood of normal donors and cultured in the presence of anti-IgM (mu chain specific) and BCGF. Frequent refeedings with fresh medium containing BCGF and anti-IgM led to the establishment of a long term cultured human B cell line, HAB-40. Phenotyping of HAB-40 revealed that the cell population consisted predominantly of IgM-bearing (72%) and B1 (100%) positive cells. This B cell line consistently secreted IgM and IgG when co-cultured in the presence of PMA, anti-IgM and beta or gamma interferon (IFN). Also, it was Epstein-Barr virus nuclear antigen (EBNA) positive (100%). HAB-40 cells have been successfully maintained in the presence of BCGF without anti-IgM for over a year. Removal of BCGF led to the rapid loss of viable cells in cultures containing less than 2% serum. HAB-40 cells in microassays exhibited a marked dose-dependent incorporation of [3H]thymidine in response to BCGF in the absence of any exogenous stimulants such as anti-IgM or Staphylococcus aureus Cowan I (SAC). Recombinant interleukin 2 (IL-2) failed to augment the [3H]thymidine uptake by these B cells despite the low density expression of Tac antigen (IL-2 receptor) on their cell surface, or even when the cells were stimulated with phorbol myristate acetate (PMA) to express higher density of Tac antigen (48%). HAB-40 cells could be maintained in BCGF which was partially purified to deplete it of other contaminating proteins. None of the seven well established EBNA-positive human B cell lines nor two chronic B lymphocytic leukemia (B-CLL) cell lines that were tested showed BCGF dependence. The same BCGF-active chromatographic fractions that were active on HAB-40 cells also stimulated BCL1 and normal human B cells stimulated with anti-IgM. In the presence of less than or equal to 2% serum proteins this cell line provides a simple, reproducible assay for BCGF even in the presence of contaminant IL-2.

Relationship of the clinical response and binding of recombinant interferon alpha in patients with lymphoproliferative diseases.

Patients with hairy cell leukemia (HCL) and chronic lymphocytic leukemia (CLL) were treated with recombinant interferon alpha A (rIFN-alpha A). The binding of iodinated recombinant interferon-alpha to baseline samples of peripheral blood mononuclear cells (PBMCs) from the leukemia patients was compared with clinical responsiveness to rIFN-alpha A. HCL patients (8/10) responded to rIFN-alpha A therapy, whereas none (0/10) of the CLL patients studied responded. The PBMCs from the eight responsive HCL patients bound approximately twice as much iodinated interferon as the PBMCs from nonresponsive CLL patients. This difference was due to more high-affinity receptors per cell with no difference in the affinity of the interferon-receptor interaction. However, because PBMCs from HCL patients were larger than PBMCs from CLL patients, the cell surface receptor density was similar. The leukemic cells from one of the two nonresponsive HCL patients bound iodinated interferon similarly to the cells from the responsive HCL patients, whereas the leukemic cells from the other nonresponsive HCL patient bound considerably less. The rapidity of response of the HCL patients did not correlate with the level of binding of iodinated interferon. Our results suggest that the absolute number of interferon receptors per cell may be only one of several important parameters in the response to rIFN-alpha A therapy, and that the responsiveness of a particular lymphoproliferative disease or a particular patient to rIFN-alpha A therapy cannot be predicted or explained solely by the degree of interaction between IFN and its cell surface receptor.