Cross-presentation by dendritic cells of tumor antigen expressed in apoptotic recombinant canarypox virus-infected dendritic cells

We have investigated the possible usefulness of recombinant canarypox virus (ALVAC) encoding the melanoma-associated Ag, Melan-A/MART-1 (MART-1), in cancer immunotherapy, using a dendritic cell (DC)-based approach. ALVAC MART-1-infected DC express, and are able to process and present, the Ag coded by the viral vector. One consistent feature of infection by ALVAC is that these viruses induce apoptosis, and we show cross-presentation of Ag when uninfected DC are cocultured with ALVAC MART-1-infected DC. Uptake of apoptotic virally infected DC by uninfected DC and subsequent expression of tumor Ag in the latter were verified by flow cytometry analysis, image cytometry, and confocal microscopy. Functional activity was monitored in vitro by the stimulation of a MART-1-specific cytotoxic T cell clone. Heightened efficiency in Ag presentation is evidenced in the 2- to 3-fold increase in IFN-gamma production by the T cell clone, as compared with the ALVAC-infected DC alone. Cocultures of ALVAC MART-1-infected and uninfected DC are able to induce MART-1-specific T cell immune responses, as assessed by HLA class I/peptide tetramer binding, IFN-gamma ELISPOT assays, and cytotoxicity tests. Overall, our data indicate that DC infected with recombinant canarypox viruses may represent an efficient presentation platform for tumor Ags, which can be exploited in clinical studies.

A canarypox vector-expressing cytomegalovirus (CMV) phosphoprotein 65 induces long-lasting cytotoxic T cell responses in human CMV-seronegative subjects

The major matrix phosphoprotein 65 (pp65) of cytomegalovirus (CMV) is an important target of HLA-restricted cytotoxic T cells (CTL) after natural infection. A canarypox-CMV pp65 recombinant was studied for its ability to induce CMV pp65-specific CTL, helper T lymphocytes, and antibodies in a phase I clinical trial. Twenty-one CMV-seronegative adult volunteers were randomized to receive immunizations at months 0, 1, 3, and 6 with either canarypox-CMV pp65 or placebo. In canarypox-CMV pp65-immunized subjects, pp65-specific CTL were elicited after only 2 vaccinations and were present at months 12 and 26 in all subjects tested. Cell-depletion studies indicated that the CTL were phenotype CD8(+). Peripheral blood mononuclear cells proliferated in response to stimulation with purified pp65, and antibodies specific for pp65 also were detected. Canarypox-CMV pp65 is the first recombinant vaccine to elicit CMV-specific CTL responses, which suggests the potential usefulness of this approach in preventing disease caused by CMV.

Mature dendritic cells infected with canarypox virus elicit strong anti-human immunodeficiency virus CD8+ and CD4+ T-cell responses from chronically infected individuals

Recombinant canarypox virus vectors containing human immunodeficiency virus type 1 (HIV-1) sequences are promising vaccine candidates, as they replicate poorly in human cells. However, when delivered intramuscularly the vaccines have induced inconsistent and in some cases transient antigen-specific cytotoxic T-cell (CTL) responses in seronegative volunteers. An attractive way to enhance these responses would be to target canarypox virus to professional antigen-presenting cells such as dendritic cells (DCs). We studied (i) the interaction between canarypox virus and DCs and (ii) the T-cell responses induced by DCs infected with canarypox virus vectors containing HIV-1 genes. Mature and not immature DCs resisted the cytopathic effects of canarypox virus and elicited strong effector CD8+ T-cell responses from chronically infected HIV+ individuals, e.g., cytolysis, and secretion of gamma interferon (IFN-gamma) and beta-chemokines. Furthermore, canarypox virus-infected DCs were >30-fold more efficient than monocytes and induced responses that were comparable to those induced by vaccinia virus vectors or peptides. Addition of exogenous cytokines was not necessary to elicit CD8+ effector cells, although the presence of CD4+ T cells was required for their expansion and maintenance. Most strikingly, canarypox virus-infected DCs were directly able to stimulate HIV-specific, IFN-gamma-secreting CD4 helper responses from bulk as well as purified CD4+ T cells. Therefore, these results suggest that targeting canarypox virus vectors to mature DCs could potentially elicit both anti-HIV CD8+ and CD4+ helper responses in vivo.

Canarypox virus-induced maturation of dendritic cells is mediated by apoptotic cell death and tumor necrosis factor alpha secretion

Recombinant avipox viruses are being widely evaluated as vaccines. To address how these viruses, which replicate poorly in mammalian cells, might be immunogenic, we studied how canarypox virus (ALVAC) interacts with primate antigen-presenting dendritic cells (DCs). When human and rhesus macaque monocyte-derived DCs were exposed to recombinant ALVAC, immature DCs were most susceptible to infection. However, many of the infected cells underwent apoptotic cell death, and dying infected cells were engulfed by uninfected DCs. Furthermore, a subset of DCs matured in the ALVAC-exposed DC cultures. DC maturation coincided with tumor necrosis factor alpha (TNF-alpha) secretion and was significantly blocked in the presence of anti-TNF-alpha antibodies. Interestingly, inhibition of apoptosis with a caspase 3 inhibitor also reduced some of the maturation induced by exposure to ALVAC. This indicates that both TNF-alpha and the presence of primarily apoptotic cells contributed to DC maturation. Therefore, infection of immature primate DCs with ALVAC results in apoptotic death of infected cells, which can be internalized by noninfected DCs driving DC maturation in the presence of the TNF-alpha secreted concomitantly by exposed cells. This suggests an important mechanism that may influence the immunogenicity of avipox virus vectors.

Paucity of functional T-cell memory to melanoma antigens in healthy donors and melanoma patients

The functional characteristics of CD8+ T cells specific for melanoma antigens (MAs) have often been defined after in vitro culture using nonprofessional antigen-presenting cells. We have examined CD8+ T-cell immunity to MAs and a viral antigen (influenza) in uncultured T cells of healthy donors and melanoma patients using autologous, mature, monocyte-derived dendritic cells (DCs) pulsed with peptide antigens and viral vectors. Antigen-specific IFN-gamma-producing T cells reactive with HLA-A*0201-restricted peptides from four melanoma antigens (MelanA/MART-1, MAGE-3, tyrosinase, and gp100) were detected only at low frequencies (<30 per 2 x 10(5) peripheral blood mononuclear cells for each of the MAs) from HLA-A2.1-positive healthy donors (n = 12) and patients with stages III/IV melanoma (n = 8). Detection of MA-specific, but not influenza matrix peptide (Flu-MP)-specific, T cells required a high concentration (10 microg/ml) of the peptide in this assay. Furthermore, these T cells did not recognize endogenously processed antigen on tumor cell lines or cells infected with viral vectors capable of expressing MAs. The use of autologous, mature DCs led to a significant increase in the number of Flu-MP, but not MA-specific, T cells in 16-h ELISPOT assays for both melanoma patients and healthy donors. In 1-week cocultures with DCs pulsed with 10 microg/ml peptide, MelanA/MART-1-specific T cells did not readily proliferate or differentiate into lytic effectors, in contrast to strong influenza-specific lytic responses. Therefore, despite distinct memory responses to influenza antigens, melanoma patients and healthy controls have a paucity of MA-reactive memory T cells, failing to rapidly generate IFN-gamma-secreting lytic effectors in short-term assays, even when stimulated by DCs.

Cytotoxic T lymphocyte (CTL) responses to human cytomegalovirus pp65, IE1-Exon4, gB, pp150, and pp28 in healthy individuals: reevaluation of prevalence of IE1-specific CTLs

The prevalence of human cytomegalovirus (HCMV) pp65-, pp150-, IE1-exon4-, gB- and pp28-specific cytotoxic T lymphocyte (CTL) responses was compared among 34 healthy individuals, grouped by neutralizing antibody titers. Moderately and highly seropositive donors showed predominantly pp65- and IE1-exon4-specific CTL responses (92% and 76% of the donors, respectively), with similar precursor frequencies in the 2 donors tested. In addition, highly seropositive and a few moderately seropositive donors showed CTL responses to gB and pp150 (33% and 30% of the donors, respectively). No individual recognized pp28 as a target in the CTL assay. Phenotypic analysis revealed a mixed effector population of CD4+ and CD8+ (1 donor) or only CD8+ cells for pp65-specific effectors (2 donors). IE1-exon4- and pp150-specific effectors were CD8+ (2 donors and 1 donor, respectively), whereas gB-specific CTLs were CD4+ (1 donor). These data may help to design a cellular immunity-based vaccine effective against HCMV diseases.

Strong human immunodeficiency virus (HIV)-specific CD4+ T cell responses in a cohort of chronically infected patients are associated with interruptions in anti-HIV chemotherapy

Virus-specific CD4+ T-helper cell function is important in controlling human immunodeficiency virus (HIV) infection but is impaired in patients with progressive HIV disease. It has been reported that after highly active antiretroviral therapy (HAART), HIV-specific lymphoproliferative responses remain absent, whereas responses to non-HIV microbial antigens are restored. However, in analyzing immune responses in a cohort of chronically infected adults on HAART, we observed strong HIV-specific CD4+ T cell responses of Th-1 phenotype in 11 of 22 patients. The magnitude and frequency of HIV-specific lymphoproliferative responses was strongly associated with previous interruptions in HAART (P=.001). In contrast, the magnitude of CD8+ T cell responses to HIV Gag, Pol, Env, and Nef was similar in patients who had and those who had not interrupted HAART. We conclude that (1) a significant proportion of chronically HIV-infected patients on HAART can generate strong HIV-specific CD4+ and CD8+ T cell immunity and (2) transient interruptions in antiviral treatment may prime or boost HIV-specific CD4+ T-helper responses.

Vaccinia virus inhibits the maturation of human dendritic cells: a novel mechanism of immune evasion

Vaccinia virus employs multiple mechanisms to evade the immune system, yet is highly immunogenic. We studied the interaction between vaccinia and human dendritic cells (DCs), potent APCs. DCs develop from precursor cells in two stages: an immature stage in which Ag uptake and processing occur, and a mature stage in which there is up-regulation of costimulatory and HLA molecules and efficient T cell activation. Vaccinia virus undergoes an abortive replication in both stages of DCs and induces apoptotic cell death. Furthermore, maturation of immature DCs and consequently T cell activation are inhibited. Obstruction of DC maturation may constitute a novel mechanism by which vaccinia attempts to evade the immune response.

A canarypox vector expressing cytomegalovirus (CMV) glycoprotein B primes for antibody responses to a live attenuated CMV vaccine (Towne)

To develop a vaccine against cytomegalovirus (CMV), a canarypox virus (ALVAC) expressing CMV glycoprotein (gB) was evaluated alone or in combination with a live, attenuated CMV vaccine (Towne). Three doses of 106.5 TCID50 of ALVAC-CMV(gB) induced very low neutralizing or ELISA antibodies in most seronegative adults. However, to determine whether ALVAC-CMV(gB) could prime for antibody responses, 20 seronegative adults randomly received either 106.8 TCID50 of ALVAC-CMV(gB) or 106.8 TCID50 of ALVAC-RG, expressing the rabies glycoprotein, administered at 0 and 1 month, with all subjects receiving a dose of 103.5 pfu of the Towne vaccine at 90 days. For subjects primed with ALVAC-CMV(gB), neutralizing titers and ELISA antibodies to CMV(gB) developed sooner, were much higher, and persisted longer than for subjects primed with ALVAC-RG. All vaccines were well tolerated. These results demonstrate that ALVAC-CMV(gB) primes the immune system and suggest a combined-vaccine strategy to induce potentially protective levels of neutralizing antibodies.

Changes in frequency of HIV-1-specific cytotoxic T cell precursors and circulating effectors after combination antiretroviral therapy in children

Combination antiretroviral therapy has had a major role in reducing human immunodeficiency virus type 1 (HIV-1) plasma viral loads in HIV-1-infected adults but a variable effect in infants, in whom complete viral suppression appears to be less readily achieved. In adults, after the reduction in plasma viremia, there is a decrease in the numbers of circulating cytotoxic T cell (CTL) effectors and precursors in the majority of patients. This longitudinal study assessed the effect of combination drug therapy on the frequency of HIV-1-specific CTL responses in 8 HIV-1-infected children. Following treatment, the frequency of HIV-1-specific CTL responses initially increased, especially in children with incomplete viral suppression but with increasing CD4+ cell counts. In children with complete viral suppression, the frequency of HIV-1-specific CTL responses decreased, suggesting that viral replication is required to maintain CTL responses in the systemic circulation.

A recombinant vaccinia virus based ELISPOT assay detects high frequencies of Pol-specific CD8 T cells in HIV-1-positive individuals

OBJECTIVES

HIV-1-specific CD8 T cells are considered to be critical in anti-HIV responses. It is important to quantify these cells and to determine their antigenic targets. Here quantification of interferon (IFN)-gamma secreting, virus-specific cells was achieved with an enzyme linked immuno spot (ELISPOT) assay.

METHODS

Peripheral blood mononuclear cells (PBMC) were infected with recombinant vaccinia vectors expressing HIV-1 genes (gag, pol, env or nef) and added to wells precoated with anti-IFN-gamma monoclonal antibodies. Spot forming cells (SFC), i.e. antigen-specific T cells were detected 24 h later by the addition of biotinylated anti-IFN-gamma monoclonal antibodies, followed by avidin-bound biotinylated horseradish peroxidase.

RESULTS

In a cohort of 19 patients, of whom 15 were on highly active antiretroviral therapy, 18 had primed T cells directed against one or more HIV-1 antigens (P < 0.0001). Pol-specific T cells routinely dominated the CD8 response with frequencies up to 2000 SFC per 10(6) PBMC. In HLA A*0201-positive patients, the vaccinia vectors detected much higher frequencies of SFC than haplotype-restricted peptides. Elimination of CD8 T cells resulted in > 90% loss of antigen-specific SFC when vaccinia virus was used as a vector. The number of CD8 SFC exceeded the number of memory cells detected in limiting dilution assays by > 1 log10, whereas a correlation was found between the frequency of effector cells detected by both ELISPOT and MHC class I peptide tetramer assays.

CONCLUSIONS

Vaccinia virus vectors used in ELISPOT assays are useful for determining the frequency and specificity of CD8 T cells for individual HIV-1 gene products. The dominance of cytolytic T lymphocytes (CTL) recognizing pol proteins suggests that this antigen should be considered in vaccine strategies.

Induction of immune responses to HIV-1 by canarypox virus (ALVAC) HIV-1 and gp120 SF-2 recombinant vaccines in uninfected volunteers. NIAID AIDS Vaccine Evaluation Group

OBJECTIVE

To determine the ability of live attenuated canarypox virus expressing HIV antigens to induce CD8+ cytotoxic T-cell responses and to prime for neutralizing antibody responses to boosting with purified recombinant gp120 subunit vaccine.

DESIGN

A prospective, double-blind, randomized, immunogenicity and safety study was conducted in healthy adults at low risk for acquiring HIV infection and who were seronegative for HIV.

METHODS

CD8+ cytotoxic T-cells directed against Env or Gag expressing target cells were measured after live recombinant canarypox-HIV-1 vaccine priming (vaccine given at days 0, 7, 14 and 21). Neutralizing antibodies were measured after subunit boosting (vaccine given at days 28 and 84).

RESULTS

CD8+ CTL were induced in 64% of volunteers by the live recombinant canarypox-HIV-1 vaccine. All volunteers who received two doses of subunit vaccine after live recombinant canarypox priming developed neutralizing antibodies directed against laboratory strains of HIV-1 and seven out of eight volunteers tested developed neutralizing antibodies to the primary isolate, BZ167, but to none of eight other primary isolates. Unprimed controls had low or absent neutralizing antibodies after two doses of subunit vaccine.

CONCLUSIONS

The live canarypox vector was safe, stimulated cytotoxic T-cells and primed for a vigorous neutralizing antibody response upon boosting with subunit gp120 vaccine. This vaccine combination should be evaluated further for inducing protection against HIV infection.

Replication-defective canarypox (ALVAC) vectors effectively activate anti-human immunodeficiency virus-1 cytotoxic T lymphocytes present in infected patients: implications for antigen-specific immunotherapy

In the attempt to develop immunotherapeutic strategies for acquired immunodeficiency syndrome capable of activating effector cells in an antigen-specific manner while maintaining the broadest possible T-cell repertoire, we evaluated two canarypox (ALVAC)-based vectors for their capacity to induce ex vivo activation/expansion of human immunodeficiency virus (HIV)-specific CD8+ cytotoxic lymphocyte precursors (CTLp) obtained from HIV-1-infected donors. These two vectors, vCP205 encoding HIV-1 gp120 + TM (28 amino acid transmembrane anchor sequence) in addition to Gag/protease and vCP300 encoding gp120 + Gag/protease as well as Nef and Pol CTL determinants, are pancytotropic but replication incompetent in mammalian cells. Bulk peripheral blood mononuclear cells (PBMCs) or enriched CD8+ T cells were stimulated for 10 days with autologous ALVAC-infected PBMCs in the presence of different cytokine combinations (interleukin-2 [IL-2], IL-4, IL-7, and IL-12). Activation by ALVAC constructs was highly antigen-specific, because vCP205 elicited only Env and Gag CTL, whereas vCP300 elicited broader reactivities against Env, Gag, Pol, and Nef determinants. The ALVAC activation of CTLp was IL-2 dependent and enhanced by the addition of IL-7, whereas IL-4 and IL-12 failed to augment cytotoxic reactivities elicited by these constructs. The expansion of enriched CD8+ T cells after activation with vCP300 was higher in patients with CD4 counts greater than 400 cells/microL. Two rounds of in vitro stimulation (IVS) with vCP300 resulted in nearly an eightfold expansion of CD8+ lymphocytes over a 25-day period. After the second IVS, an average 3.2-fold increase among the different antigen-specific CTL frequencies was achieved. These studies clearly show that HIV-recombinant ALVAC vectors represent powerful polyvalent antigenic stimuli for activation and expansion of the CD8 lymphocyte response that occurs as a result of HIV infection.

Attenuated vaccinia virus-circumsporozoite protein recombinants confer protection against rodent malaria

NYVAC-based vaccinia virus recombinants expressing the circumsporozoite protein (CSP) were evaluated in the Plasmodium berghei rodent malaria model system. Immunization of mice with a NYVAC-based CSP recombinant elicited a high level of protection (60 to 100%). Protection did not correlate with CS repeat-specific antibody responses and was abrogated by in vivo CD8+ T-cell depletion. Protection was not enhanced by modification of the subcellular localization of CSP. These results suggest the potential of poxvirus-based vectors for the development of vaccine candidates for human malaria.

Safety and immunogenicity of recombinants based on the genetically-engineered vaccinia strain, NYVAC

NYVAC-based recombinants expressing pertinent immunogens from equine influenza virus (EIV), pseudorabies virus (PRV), Japanese encephalitis virus (JEV) and human immunodeficiency virus (HIV) were used to evaluate the safety and immunogenicity of this vector. Administration of either NYVAC recombinants or parenteral virus to mice, horses and swine was well tolerated with no notable local or systemic reactivities. Further, despite a highly attenuated phenotype, NYVAC was found to function effectively as an immunization vehicle capable of eliciting both humoral and cell-mediated immune responses.

Induction of cytotoxic T lymphocytes by recombinant canarypox (ALVAC) and attenuated vaccinia (NYVAC) viruses expressing the HIV-1 envelope glycoprotein

Successful immunization against many viruses, including retroviruses such as HIV-1, is thought to depend upon the roles of both antibody and cytotoxic T-lymphocyte responses. With safety a major concern, we developed two poxvirus recombinants expressing the envelope glycoprotein of HIV-1 IIIB. Canarypox (ALVaC), which is not known to replicate in mammalian cells, and a highly attenuated vaccinia (NYVAC) virus deleted of 18 open reading frames associated with virulence and host range were used as vectors. Upon inoculation into BALB/c mice, both the ALVAC and NYVAC recombinants were capable of inducing antibody responses to HIV gp120 and provoking remarkable levels of primary and memory Thy1.2+, CD4-, CD8+ cytotoxic T-lymphocyte responses to the hypervariable V3 loop of the HIV-1 envelope glycoprotein.

NYVAC: a highly attenuated strain of vaccinia virus

A highly attenuated vaccinia virus strain, NYVAC (vP866), was derived from a plaque-cloned isolate of the Copenhagen vaccine strain by the precise deletion of 18 open reading frames (ORFs) from the viral genome. Among the ORFs deleted from NYVAC (vP866) are two genes involved in nucleotide metabolism, the thymidine kinase (ORF J2R) and the large subunit of the ribonucleotide reductase (ORF I4L); the gene encoding the viral hemagglutinin (ORF A56R); the remnant (ORF A26L) of a highly expressed gene responsible for the formation of A-type inclusion bodies; the disrupted gene (ORFs B13R/B14R) normally encoding a serine protease inhibitor; and a block of 12 ORFs bounded by two known viral host range regulatory functions (ORFs C7L through K1L). Within this block a secretory protein (ORF N1L) implicated in viral virulence and a functional complement 4b binding protein (ORF C3L) are encoded. The ORFs were deleted in a manner which prevents the synthesis of undesirable novel gene products. The attenuation characteristics of the derived NYVAC strain were compared in in vitro and in vivo studies with those of the Western Reserve (WR) laboratory strain, the New York City Board of Health vaccine strain (Wyeth), the parental plaque-cloned isolate (VC-2) of the Copenhagen vaccine strain used to derive NYVAC, and the avipox virus canarypox (ALVAC), which is naturally restricted for replication to avian species. The NYVAC strain was demonstrated to be highly attenuated by the following criteria: (a) no detectable induration or ulceration at the site of inoculation on rabbit skin; (b) rapid clearance of infectious virus from the intradermal site of inoculation on rabbit skin; (c) absence of testicular inflammation in nude mice; (d) greatly reduced virulence as demonstrated by the results of intracranial challenge of both 3-week-old or newborn mice; (e) greatly reduced pathogenicity and failure to disseminate in immunodeficient (nude or cyclophosphamide treated) mice; and (f) dramatically reduced ability to replicate on a variety of human tissue culture cells. Despite these highly attenuated characteristics, the NYVAC strain, as a vector, retains the ability to induce strong immune responses to extrinsic antigens.

Dietary nucleotide effects upon immune function in infants

Nucleotide (NT) nitrogen, a component of nonprotein nitrogen, accounts for approximately 0.1% to 0.15% of the total nitrogen content of human milk. The results of studies in animals indicate that dietary NTs may be required for maintenance of normal immune function. Thirty-seven healthy term infants were either breast-fed (n = 9) or fed SMA formula supplemented with 33 mg of NTs per liter (n = 13, NT+) or standard SMA formula (n = 15; NT-). At 2 months of age, natural killer cell percent cytotoxicity was significantly higher in the breast-fed and NT+ groups compared with the NT- group (41.7 +/- 4.7, 32.2 +/- 3.4, 21.7 +/- 2.2%, respectively). Interleukin-2 production by stimulated mononuclear cells was higher in the NT+ compared with the NT- group at 2 months of age (0.90 +/- 0.28 U/mL, 0.27 +/- 0.11 U/mL, respectively); neither formula-fed group differed significantly from the breast-fed group. Rate of growth and incidence and severity of infections did not differ significantly among dietary groups. Nucleotides may be a component of human milk that contributes to the enhanced immunity of the breast-fed infant.

Dietary nucleotide effects upon murine natural killer cell activity and macrophage activation

Weanling mice fed chow or chow plus water supplemented with 3.5 mg of nucleotides per 100 ml of water for 6 weeks exhibited increased natural killer cell (NK) activity and lower macrophage activation compared to mice fed chow plus nonsupplemented water. In a dose-response study, NK activity, macrophage activation and spleen weight (as a percentage of body weight) were higher in mice fed up to 0.035% w/w nucleotides, however macrophage activation was decreased by feeding over 0.35% w/w compared to those receiving basal purified diet (BPD). Nucleotides in human milk may affect the immune response in breast-fed infants.

Dimethyl sulfoxide-induced inhibition of the immunosuppressive activity of cultured Friend erythroleukemia cells

Two Friend leukemia virus-induced tumor cell lines lost their immunosuppressive properties in vitro when treated with dimethyl sulfoxide (DMSO), a known cellular differentiation agent. Incubation of the cell lines, GM 979 and GM 86, with DMSO for 4 days or longer, inhibited their ability to suppress the antibody forming capacity of normal murine spleen cells immunized in vitro with sheep red blood cells. Suppression of the inhibitory capability of the tumor cell lines by DMSO was time dependent. Three days incubation caused only slight, if any, inhibition, while a shorter period of treatment had no effect. Inhibition of the immunosuppressive properties of the tumor cell lines was not due to a decrease in tumor cell viability. The development of previously reported metabolic alterations in the treated cells, such as increased hemoglobin synthesis and other physicochemical alterations, paralleled cellular differentiation, and loss of immunosuppressive properties.

Mechanism of glucocorticoid action on murine natural killer cell activity

With the use of an in vitro model system, the mode of action of glucocorticoids on murine natural killer (NK) cell-mediated cytotoxicity of tumor cells was investigated. Of the steroids tested, only the glucocorticoids notably suppressed NK activity. Glucocorticoids were not toxic to the NK effector cell since inhibitors of protein synthesis protected NK activity from the suppressive action of glucocorticoids. Glucocorticoid-treated C57BL/6J spleen cells, although suppressed in NK activity, were unable to suppress the NK activity of normal syngeneic spleen cell cultures. Similarly, the supernatants of glucocorticoid-treated cultures were also unable to suppress normal NK activity. Thus a role for suppressor cell activity or soluble suppressive factors was excluded. Results of analyses of the NK activity of Percoll-fractionated glucocorticoid-treated C3H/HeN (nu/nu) spleen cells at the single-cell level demonstrated that NK effector cells could efficiently bind to YAC-1 lymphoma cells but were incapable of inducing cytolysis. Moreover, the production of NK cytotoxicity factor(s) in tumor cell-stimulated nude mouse spleen cell cultures was severely depressed after glucocorticoid treatment. The results of these studies suggest that glucocorticoids suppress murine NK activity by acting directly on the NK effector cells, possibly by inhibiting the formation or release of specific effector molecules that are cytotoxic to NK-sensitive tumor cells.

Direct suppression of natural killer activity in human peripheral blood leukocyte cultures by glucocorticoids and its modulation by interferon

In vitro treatment of human peripheral blood leukocytes for 18 to 24 hr with physiological concentrations of glucocorticoids resulted in a marked decrease (up to 90%) in natural killer (NK) activity. The effect on NK activity was both dose and time dependent and was specific for glucocorticoids. Glucocorticoids had no effect when added directly to the 4-hr 51Cr release cytotoxicity assay, nor did they alter the susceptibility of K562 cells to NK-mediated cytolysis. Glucocorticoid-induced inhibition occurred in Percoll-fractionated peripheral blood leukocytes enriched for NK activity. Viabilities of steroid-treated and untreated cultures were similar. Mixing experiments failed to demonstrate the involvement of suppressor activity in the inhibition. Purified cloned human leukocyte interferon subtype A and inducers of interferon enhanced NK activity in the presence of glucocorticoid, although the levels of enhancement were lower than those produced by these agents in the absence of the steroid. Thus, glucocorticoids appear to suppress human NK activity by interacting directly with the NK effector cell, and our results obtained with physiological concentrations of these steroids suggest that they may play an important role in regulating NK activity in vivo. Additionally, these findings suggest a possible means for overriding this immunosuppressive side effect of glucocorticoid therapy by simultaneous treatment with interferon.