Miroslav Malkovsky

Heat shock proteins, tumor immunogenicity and antigen presentation: an integrated view

A broad range of studies has established that heat shock proteins (Hsps) potentially play a role in tumor immunosurveillance. Here, Andrew Wells and Miroslav Malkovsky highlight recent data that demonstrate a causal relationship between the expression of Hsps and tumor immunogenicity, and suggest several mechanisms by which Hsps might influence the capacity of a tumor to induce an immune response.

The role of dendritic cells in the initiation of immune responses to contact sensitizers: I. In vivo exposure to antigen

Twenty-four hours after skin painting mice with picryl chloride (PIC) there was a four- to fivefold increase in the numbers of dendritic cells (DC) isolated from the lymph nodes. These DC initiated primary proliferative and cytotoxic responses when added to cultures of normal syngeneic lymph node cells. The proliferative response was enhanced when the donors of the responding lymph node cells were sensitized with the same antigen. Contact sensitivity developed in syngeneic mice injected into the footpads with 30,000-50,000 DC from lymph nodes of mice painted with picryl chloride 1 day previously. Thus, 1 day after skin painting mice, there were dendritic cells in the draining lymph nodes which were able both to initiate primary stimulation of lymphocytes in vitro and to sensitize recipient mice to give specific delayed hypersensitivity reactions.

Endogenous release of interferon-gamma and diminished response of peripheral blood mononuclear cells to antigenic stimulation

The capacity of T lymphocytes to proliferate in response to stimulation and the amount of representative lymphokines produced in vitro often correlate with the immunocompetence of patients. However, direct and indirect measurement of endogenous interferon-gamma (IFN-gamma) brings some evidence that decreased in vitro production of IFN-gamma by T lymphocytes is associated with increased concentrations in vivo. The data indicate that both a functional inhibition of IFN-gamma and its continuous presence at high levels may result in hyporesponsiveness or unresponsiveness of immune cells. A possible role of IFN-gamma in the induction of tolerance is discussed.

Cutting Edge: TGF-β1 and IL-15 Induce FOXP3+ γδ Regulatory T Cells in the Presence of Antigen Stimulation

Several subsets of αβ regulatory T cells (Tregs) have been described and studied intensively, but the potential regulatory role of γδ T cells remains largely unclear. Lymphocytes expressing γδ TCR are involved in both innate and adaptive immune responses, and their major adult human peripheral blood subset (Vγ9Vδ2) displays a broad reactivity against microbial agents and tumors. In this study we report that γδ T lymphocytes with regulatory functions (Vδ2 Tregs) are induced in vitro in the presence of specific Ag stimulation and cytokines (TGF-β1 and IL-15). These cells express FOXP3 and, similarly as αβ Tregs, suppress the proliferation of anti-CD3/anti-CD28 stimulated-PBMC. Phenotypic and functional analyses of Vδ2 Tregs will very likely improve our understanding about the role of γδ T cells in the pathogenesis of autoimmune, infectious, and neoplastic diseases.

γδ T lymphocyte responses to HIV

Natural immunity may be involved in controlling viral spread in hosts infected with HIV. A panel of γδ T cell receptor‐positive lymphocyte clones was isolated from the peripheral blood of healthy HIV− donors and tested for anti‐HIV cytotoxic responses. Twelve of 30 (40%) Vγ9+Vδ2+ T cell clones, but none of seven Vδ1+ T cell clones, displayed lytic activity against HIV‐infected cells. The Vγ9+/Vδ2+ clones cytotoxic for HIV‐infected cells also lysed Daudi cells. However, not all Vγ9+/Vδ2+ clones which lysed Daudi targets had the capacity to lyse HIV‐infected cells. Some of the γδ T cell clones were also investigated for potential proliferative responses to HIV‐infected cells. One Vγ9+/Vδ2+ T cell clone (ME8‐7) and one Vδ1+ T cell clone (ME18‐2) demonstrated proliferative responses toward HIV‐infected cells. Another Vγ9+/Vδ2+ clone (VM39) proliferated in response to cell‐free HIV. Taken together, these results provide direct evidence of anti‐HIV γδ T cell responses in healthy, HIV− persons.

Gamma/delta T lymphocytes in viral Infections

T lymphocyte progenitors differentiate into two distinct T cell lineages. Although the αβ and γδ T cell lineages resemble each other phenotypically and functionally, there are some striking differences. Some γδ T cells recognize, similarly to αβ T cells, peptides presented by major histocompatibility complex (MHC) proteins or MHC‐like molecules. However, there are γδ T cells that recognize MHC molecules in a fundamentally different manner in comparison with αβ T cells. Also in contrast to aLβ T lymphocytes, many γδ T cells are capable of recognizing nonpeptide antigens. Most responses of γδ T cells appear to be directed against microbial pathogenic agents including bacteria, parasites, and viruses. In particular, the potent cytotoxic responses of γδ T cells against cells infected with, for example, herpesviruses or lentiviruses may be essential for the overall antiviral defense of vertebrates. The analysis of antiviral immunosurveillance by γδ T cells is crucial for understanding the unique biological role of this lymphocyte subset.

Antiviral reactivities of γδ T cells

Abstract The complex antiviral immune mechanisms involve both adaptive and innate reactions mediated by γδ T lymphocytes, whose unique immunosurveillance contributions are analyzed here in different clinical and experimental settings. It is beyond any doubt that the fast, potent, cytotoxic as well as non-cytolytic antiviral activities of γδ T cells are critical in protecting the host against diverse viral pathogens.

Drug-Induced Expansion and Differentiation of Vγ9Vδ2 T Cells In Vivo: The Role of Exogenous IL-2

Human Vγ9Vδ2 T cells recognize nonpeptidic Ags generated by the 1-deoxy-d-xylulose 5-phosphate (many eubacteria, algae, plants, and Apicomplexa) and mevalonate (eukaryotes, archaebacteria, and certain eubacteria) pathways of isoprenoid synthesis. The potent Vγ9Vδ2 T cell reactivity 1) against certain cancer cells or 2) induced by infectious agents indicates that therapeutic augmentations of Vγ9Vδ2 T cell activities may be clinically beneficial. The functional characteristics of Vγ9Vδ2 T cells from Macaca fascicularis (cynomolgus monkey) are very similar to those from Homo sapiens. We have found that the i.v. administration of nitrogen-containing bisphosphonate or pyrophosphomonoester drugs into cynomolgus monkeys combined with s.c. low-dose (6 × 105 U/animal) IL-2 induces a large pool of CD27+ and CD27− effector/memory T cells in the peripheral blood of treated animals. The administration of these drugs in the absence of IL-2 is substantially less effective, indicating the importance of additional exogenous costimuli. Shortly after the costimulatory IL-2 treatment, only γδ (but not αβ) T cells expressed the CD69 activation marker, indicating that Vγ9Vδ2 T lymphocytes are more responsive to low-dose IL-2 than αβ T cells. Up to 100-fold increases in the numbers of peripheral blood Vγ9Vδ2 T cells were observed in animals receiving the γδ stimulatory drug plus IL-2. Moreover, the expanded Vγ9Vδ2 T cells were potent Th1 effectors capable of releasing large amounts of IFN-γ. These results may be relevant for designing novel (or modifying current) immunotherapeutic trials with nitrogen-containing bisphosphonate or pyrophosphomonoester drugs.

FUNCTIONAL GAMMA DELTA T-LYMPHOCYTE DEFECT ASSOCIATED WITH HUMAN IMMUNODEFICIENCY VIRUS INFECTIONS

BackgroundAntiviral cellular immune responses may influence immunological homeostasis in HIV-infected persons. Recent data indicate that Vγ9/Vδ2 T lymphocytes display potent cytotoxic activities against human cells infected with certain viruses including HIV. Understanding the role of γδ T cells in the course of HIV infection may be helpful for designing novel treatment strategies for HIV-associated disorders.Materials and MethodsThe constitutive recognition of Daudi cells and monoethyl pyrophosphate (Etpp) by peripheral blood Vγ9/Vδ2 T cells was assessed using a proliferation assay. The cytotoxicity of Daudi-stimulated lymphocyte populations was measured by chromium release assays. The HIV infectivity for γδ T cell clones was determined by measuring the levels of HTV p24 in cell supernatants. The effect of in vitro HIV-infection on cytokine mRNA production by γδ T cell clones was assessed by PCR.ResultsThe constitutive proliferative responses of peripheral blood Vγ9/Vδ2 T cells and the lytic functions of Daudi-expanded lymphoid cells from HTV+ persons were substantially diminished in comparison with those of HlV-seronegative persons. These alterations were present in asymptomatic HIV+ persons prior to substantial αβ CD4+ T cell loss. Productive fflV infection of γδ T cells in vitro had no measurable effect either on their proliferative response to Daudi stimuli or on the expression of cytokine mRNAs for IFN-γ, IL-2, IL-4, IL-5, IL-6, IL-10, and IL-13.ConclusionsThe constitutive responsiveness of Vγ9/Vδ2 T lymphocytes to Daudi and Etpp is severely altered in HIV+ persons. HTV infection of γδ T cells in vitro does not substantially change their cytokine expression or antigenic response.

NEUTRALISATION OF HIV ISOLATES BY ANTI-IDIOTYPIC ANTIBODIES WHICH MIMIC THE T4 (CD4) EPITOPE: A POTENTIAL AIDS VACCINE

Polyclonal anti-idiotypic antibodies were raised in mice against anti-Leu3a, a mouse monoclonal anti-human T4 (CD4) antibody that blocks the in-vitro binding of human immunodeficiency virus (HIV) to the CD4 molecule. The anti-idiotypes recognized anti-Leu3a but not OKT4, an anti-human T4 antibody that does not inhibit HIV binding to CD4. The anti-idiotypes specifically reacted with the HIV envelope glycoprotein in solid-phase immunoassays. More importantly, the anti-idiotypes neutralised three distinct isolates of HIV-1 and one isolate of HIV-2 in a syncytial inhibition assay. These results have implications for a potential AIDS vaccine of anti-CD4 preparations to induce an anti-idiotypic response with the capacity to bind HIV at its receptor site.