Elizabeth M. Benson

Role of the Mitogen-Activated Protein Kinase Signaling Pathway in the Regulation of Human Melanocytic Antigen Expression

Heterogeneous expression of melanocytic antigens occurs frequently in melanomas and represents a potent barrier to immunotherapy. We previously showed that coordinated losses of several melanocytic antigens are generally attributable to down-regulation of antigen gene expression rather than irreversible mutation. Treatment of melanoma cells with mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitors blocks ERK activation and increases steady-state levels of mRNAs and corresponding protein expression for the melanocytic antigens Melan-A/MART-1, gp100, and tyrosinase. Although the degree of MEK inhibitor enhancement of antigen expression varied among different cell lines irrespective of their antigen expression status, all showed detectable responses. Notably, the antigen-enhancing effects of the MEK inhibitors could not be attributed to the master melanocytic regulator MITF-M. Because MAPK pathway activation via constitutively active mutant forms of BRAF is common in melanomas, correlation between BRAF function and antigen expression was investigated. No simple correlation of endogenous BRAF mutational status and antigen levels was observed, but transient overexpression of V600E BRAF increased ERK activation and reduced Melan-A/MART-1 levels in antigen-positive cell lines. These data indicate that whereas multiple factors may regulate antigen expression in melanomas, enhancement of MAPK signaling can act as a negative influence. Blocking such signaling with MEK inhibitors accordingly augments antigen levels, thereby enhancing Melan-A/MART-1–specific cytotoxic T-cell responses to antigen-negative cells following MEK inhibition treatment. Consequently, MAPK inhibition may assist targeting of melanomas for immunotherapy. (Mol Cancer Res 2006;4(10):779–92)

Increased frequency of CCR-5 Δ32 heterozygotes among long-term non-progressors with HIV-1 infection

Background:The β-chemokine receptor CCR-5 is used as a coreceptor by macrophage-tropic strains of HIV-1 to gain entry into CD4+ cells. Objective:To determine the effect of a common 32 base-pair deletion mutation in the CCR-5 gene (CCR-5 Δ32) on progression of HIV infection to AIDS, and to assess the level of heterozygosity for this mutation in a well-defined group of long-term non-progressors (LTNP). Participants:Sixty-four HIV-1-infected LTNP (CD4+ T lymphocyte count > 500 × 106/l after 8 years) were compared with 95 individuals infected within a similar period (1983–1986) but who had rapidly progressed to AIDS and death, and with a further 120 HIV-positive individuals with CD4+ counts < 500 × 106/l. Methods:The presence of the CCR-5 Δ32 mutation was assessed using polymerase chain reaction with primers spanning the 32 base-pair deletion. CD4+ and CD8+ counts, plasma HIV-1 RNA, p24 antigen and β2-microglobulin levels in LTNP carrying the CCR-5 Δ32 mutation were compared with LTNP lacking the mutation. Results:A marked increase in the frequency of CCR-5 Δ32 heterozygosity was found among LTNP (35.9%) compared with rapid progressors (12.6%; P = 0.0005) and patients selected on the basis of a CD4+ T-cell count < 500 × 106/l (12.5%; P = 0.0004). LTNP heterozygous for CCR-5 Δ32 had a significantly higher CD8+ T-cell count than those without the mutation (1218 versus 972 × 106/l; P = 0.044). No significant correlation was observed between heterozygosity and CD4 count, viral load, p24 antigen or β2-microglobulin within the LTNP group. Conclusions:This study provides the strongest evidence to date for the importance of a single copy of the CCR-5 Δ32 mutation in long-term non-progression of HIV infection, which may involve, in part, CD8+ T lymphocytes.To determine the effect of a common 32 base-pair deletion mutation in the CCR-5gene (CCR-5 Δ32) on progression of HIV infection to AIDS, and to assess the level of heterozygosity for this mutation in a well-defined group of long-term non-progressors (LTNP).

A Novel Autocrine Pathway of Tumor Escape from Immune Recognition: Melanoma Cell Lines Produce a Soluble Protein That Diminishes Expression of the Gene Encoding the Melanocyte Lineage Melan-A/MART-1 Antigen Through Down-Modulation of Its Promoter

We have observed that malignant melanoma cells produce a soluble protein factor(s), which down-regulates melanocyte lineage Melan-A/MART-1 Ag expression by melanoma cells with concomitant loss of recognition by Melan-A/MART-1-specific T cells. This down-modulation of Melan-A/MART-1 expression, which we refer to as “Ag silencing,” is mediated via its minimal promoter, whereas the promoter for the restricting Ag-presenting HLA-A2 molecule is not affected. Significantly, this Ag silencing is reversible, as removal of factor-containing supernatants from Melan-A/MART-1-expressing cells results in up-regulation of the promoter for the gene encoding this Ag, and renewed expression of the protein. We have evaluated over 20 known factors, none of which accounts for the Ag-silencing activity of the melanoma cell culture supernatants. The existence of this autocrine pathway provides an additional novel explanation for melanoma tumor progression in vivo in the presence of CTL specific for this melanocyte lineage Ag. These observations may have important implications for Melan-A/MART-1-specific CTL-mediated immunotherapy of melanoma tumors.

Assessment of male CVID patients for mutations in the Btk gene: how many have been misdiagnosed?

The presentation of hypogammaglobulinaemia in young males without a family history of immunodeficiency can pose a diagnostic problem. In the past, the presence of B‐cells has suggested a diagnosis of common variable immunodeficiency (CVID), although genotypic analysis has now clarified that individuals with B cells may have mutations in their Btk gene. In order to address the issue of how many male individuals with a clinical diagnosis of CVID do in fact have mutations in the Btk gene, we analysed a group of 24 male patients. Single‐strand conformation polymorphism (SSCP) analysis was used to screen the patient cohort for mutations in the Btk gene. Given the size of the Btk gene, the number of patients in the cohort and the amount of available DNA, multiplex PCR reactions were utilized to span the 19 exons and promoter region of the gene. Where abnormal migration patterns were observed with multiplex PCR reactions, in nine of the 24 patients, the individual Btk gene fragments were re‐amplified and analysed again by SSCP. Following this analysis, four patients continued to demonstrate abnormal SSCP migration patterns. However, direct sequencing of the relevant Btk gene fragments for these four CVID patients revealed a mutation in only one patient. The mutation was the previously described polymorphism at position 2031 of Btk gene within exon 18. These results indicate that caution should be taken with the application of SSCP analysis to mutation detection. While it has a role to play in screening large patient cohorts, direct sequencing is a necessary adjunct to such analysis. Finally, the clinical diagnosis of CVID in this cohort successfully excluded males with Btk mutations.

Therapeutic Vaccination with p24-VLP and Zidovudine Augments HIV-Specific Cytotoxic T Lymphocyte Activity in Asymptomatic HIV-Infected Individuals

This study evaluates the impact of therapeutic vaccination with p24-VLP and zidovudine on the induction or maintenance of HIV-specific cytotoxic lymphocyte activity in a cohort of asymptomatic patients with CD4 counts greater than 400 cells/microl. In a dummy, randomized, phase II clinical trial of the therapeutic vaccine, participants were randomized to one of three arms for 6 months: p24-VLP (500 microg) in alum monthly plus zidovudine 200 mg tds, alum adjuvant plus zidovudine, or p24-VLP plus placebo. Subjects were studied for a total of 52 weeks from baseline. Monitoring included viral load, CD4 and CD8 counts, markers of immune activation, delayed-type hypersensitivity (DTH) skin testing, and cytotoxic T lymphocyte (CTL) measurement. The nine subjects who received p24-VLP and zidovudine had an augmentation and/or broadening of their CTL response compared with baseline (p = 0.004). The eight subjects receiving p24-VLP and seven subjects receiving zidovudine did not have a statistically significant increase or broadening of CTL activity. The augmentation of the CTL response in the subjects who received p24-VLP and zidovudine was not associated with a decline in viral load or an increase in CD8 counts. This study suggests that HIV-specific CTL activity can be augmented in HIV-infected individuals receiving p24-VLP and zidovudine, supporting the hypothesis of therapeutic vaccination in the presence of antiretroviral therapy.

The application of a pCR technique for the detection of immunoglobulin heavy chain gene rearrangements in fresh or paraffin-embedded skin tissue

Summary Although detection of a clonal sequence of the heavy chain gene of immunoglobulin by the polymerase chain reaction (PCR) is frequently used to assess lymphoid infiltrates in skin biopsy specimens, there are no data on the sensitivity and specificity of this test in detecting clonal B cell populations. Having refined a PCR technique for the detection of immunoglobulin heavy chain (IgH) gene rearrangement in both fresh and formalin‐fixed, paraffin‐embedded skin samples, we undertook to define the role of this assay in the diagnostic setting. Thirty‐one cases of cutaneous B cell lymphoma (CBCL), 19 cases of B cell pseudolymphoma (lymphocytoma cutis), 34 cases of benign lymphocytic infiltrates of the skin and one case of cutaneous T cell lymphoma (CTCL) were studied using the polymerase chain reaction assay. All biopsies were formalin‐fixed, paraffin‐embedded skin sections apart from 13 of the 31 CBCL specimens which were fresh skin specimens. DNA from the framework region 3 (FR3) sequence of the IgH genes was amplified to ascertain the presence of a clonal IgH gene rearrangement. The findings were correlated with histological and immunophenotyping results on all samples. The assay performed with 73% sensitivity and 100% specificity, comparable to results obtained examining fresh lymphoid tissue specimens from patients with B cell tumours. The results indicate that this technique is a useful tool in the work up of suspected CBCL and in differentiating between CBCL and mixed lymphocytic infiltrates, a clearly important distinction with regards to prognosis and treatment.

Enhancement of Human Melanoma Antigen Expression by IFN-β

Although many immunotherapeutic investigations have focused on improving the effector limb of the antitumor response, few studies have addressed preventing the loss of tumor-associated Ag (TAA) expression, associated with immune escape by tumors. We found that TAA loss from human melanomas usually results from reversible gene down-regulation, rather than gene deletion or mutation. Previously, we showed that inhibitors of MAPK-signaling pathways up-regulate TAA expression in melanoma cell lines. We have now identified IFN-β as an additional stimulus to TAA expression, including Melan-A/MART-1, gp100, and MAGE-A1. IFN-β (but neither IFN-α nor IFN-γ) augmented both protein and mRNA expression of melanocytic TAA in 15 melanoma lines (irrespective of initial Ag-expression levels). Treatment of low Ag melanoma lines with IFN-β increased expression of melanocyte-lineage Ags, inducing susceptibility to lysis by specific CTLs. Treatment with IFN-β also enhances expression of class I HLA molecules, thereby inducing both nominal TAA and the presenting HLA molecule. Data from fluorescent cellular reporter systems demonstrated that IFN-β triggers promoter activation, resulting in augmentation of Ag expression. In addition to enhancing TAA expression in melanomas, IFN-β also stimulated expression of the melanocytic Ag gp100 in cells of other neural crest-derived tumor lines (gliomas) and certain unrelated tumors. Because IFN-β is already approved for human clinical use in other contexts, it may prove useful as a cotreatment for augmenting tumor Ag expression during immunotherapy.

Tracking membrane and secretory immunoglobulin α heavy chain mRNA variation during B-cell differentiation by real-time quantitative polymerase chain reaction

Primary transcripts for all Ig heavy chain isotypes are alternatively processed to encode either secreted or membrane forms of the same antibody and, in plasma cells, a shift towards the secreted form occurs. In principle, measuring the relative quantities of secreted and membrane forms for a particular isotype could monitor B‐cell plasmacytoid differentiation. Ratios of α heavy chain mRNA secreted (αs) to membrane (αm) form were assessed by quantitative reverse transcriptase–polymerase chain reaction (RT‐PCR; TaqMan) using an IgA plasma cell line (NCI‐H929), a surface IgA+ line (Dakiki) and human tonsillar B cells. While NCI‐H929 cells showed the highest αs : αm ratio as expected, αs mRNA predominated for all unstimulated B cells and Dakiki cells. Treatment of B cells and Dakiki cells with IL‐2 and IL‐10 resulted in a further progression towards the αs form, correlating with increased human plasma cell antigen‐1 (HPC1) mRNA levels. However, α mRNA processing and HPC1 expression were independently regulated, as IFN‐γ treatment suppressed HPC1 levels while increasing αs : αm ratios. Cytokine‐mediated increases in the αs : αm ratio resulted from strongly enhanced levels of αs with relatively constant αm values. Differentiation‐related changes in mRNA processing can thus be tracked by automated quantitative PCR.

Mutational screening of the CD40 ligand (CD40L) gene in patients with X linked hyper-IgM syndrome (XHIM) and determination of carrier status in female relatives.

Aims: To analyse the gene encoding the CD40 ligand (CD40L) in 11 Australian patients from 10 unrelated families with the X linked hyper-IgM (XHIM) phenotype. Methods: The CD40L gene was screened for mutations using direct sequencing of exon specific polymerase chain reaction (PCR) products. Results: Ten mutations were identified. Seven of these mutations have been described previously, whereas three new nonsense mutations were identified, namely: E108X (c.322G>T), G167X (c.499G>T), and C218X (c.654C>A). Ten of 15 female family members revealed both a mutated allele and a normal allele, indicating that they were XHIM carriers. Conclusion: The 10 mutations (including the three new ones) identified in this study reflect the heterogeneity of the CD40L gene, and indicate the need for accurate and reliable molecular testing of those patients suspected of XHIM.

Interleukin 12-Augmented T Cell Proliferation of Peripheral Blood Mononuclear Cells from HIV-Seropositive Individuals Is Associated with Interleukin 12 Receptor β2 Upregulation

Interleukin 12 (IL-12) production is believed to be impaired in individuals with HIV infection and this impairment manifests early in disease, when the CD4(+) cell counts are within normal values. The reduced antigen-specific and mitogen-stimulated T cell-proliferative responses that occur in HIV infection can be corrected by the addition of recombinant human interleukin 12 (rhIL-12). As the IL-12 receptor (IL-12R) is central to the IL-12 signaling pathway, we examined whether the augmentation of antigen-specific proliferation of HIV(+) peripheral blood mononuclear cells (PBMCs) related to altered IL-12R expression. rhIL-12 augmented antigen-specific proliferation of HIV(+) PBMCs but not of HIV(-) PBMCs. Examination of resting PBMCs from HIV(+) and HIV(-) donors showed that neither of these populations expressed IL-12R beta 1 or IL-12R beta 2 chains on their cell surface as detected by flow cytometry. However, examination of mRNA showed that both IL-12R beta 1 and IL-12R beta 2 mRNAs were markedly reduced in HIV(+) PBMCs when compared with HIV(-) PBMCs. After mitogen activation there was an increase in IL-12R beta 1 expression on the cell surface of HIV(+) and HIV(-) PBMCs and this level was not altered by coculture with rhIL-12 or interferon gamma (IFN-gamma). However, coculture of phytohemagglutinin (PHA)-activated HIV(+) or HIV(-) PBMCs with rhIL-12 (but not IFN-gamma) increased IL-12R beta 2 expression on the cell surface of both populations. Examination at the message level showed a correction of IL-12R beta 1 to normal levels with activation that was further enhanced by rhIL-12 coculture for both the HIV(+) and HIV(-) PBMCs. However, although the level of IL-12R beta 2 for the HIV(+) PBMCs was normalized by PHA, rhIL-12 caused a further augmentation. This information provides a strong link between IL-12R upregulation, and the significant improvement in antigen-specific HIV-proliferative responses seen with the addition of rhIL-12. It also reveals that the dysfunction in IL-12R expression seen in cells from HIV(+) patients occurs at the transcriptional level. In addition, we provide further evidence that IL-12R beta 1 and IL-12R beta 2 regulation in human PBMCs is independent of IFN-gamma.