Maria Caterina Sirianni

T-cell homeostasis alteration in HIV-1 infected subjects with low CD4 T-cell count despite undetectable virus load during HAART.

Objective:To investigate the pathogenesis of low CD4 T-cell count in subjects who are immunological non responders (InR) to HAART. Design:Thirty-five HIV-positive subjects on HAART for at least 1 year, all with undetectable HIV-1 RNA, were studied. Patients were defined as InR according to a CD4 cell increase < 20% from CD4 cell baseline or CD4 cell count < 200/μl; subjects with a CD4 T-cell increase > 20% from baseline and a CD4 cell count > 200/μl were defined as immunological responders (IR). We performed a comprehensive study to characterize the immune response of InR. Methods:The immunological phenotype of peripheral blood mononuclear cells, thymic naive T cells, T-cell receptor Vβ repertoire, serum concentration of interleukin (IL)-7, the expression of IL-7Rα on naive and memory CD4 and CD8 T cells, and regulatory T cells (Treg) were studied. Results:In InR a significant reduction (P < 0.0001) of naive and thymic naive CD4 T cells was associated with a reduced expression of IL-7Rα in both cell subsets, with an increased serum concentration of IL-7 was observed. Furthermore, an increased immune activation with a reduced Treg frequency and increased number of expansions of Vβ families was observed. Conclusions:The reduced expression of IL-7Rα associated with the persistent immune activation and the alteration of Treg frequencies in part explains the low level of CD4 T cells observed in InR.

Pathogenesis of the natural killer cell deficiency in AIDS

Deficiency in natural killer (NK) cell activity is a common feature of acquired immune deficiency syndrome (AIDS). This is part of a general immune dysfunction in AIDS and may lead to progression of the disease, since NK cells are known to be involved in protection against tumors and against viral infections. The lack of immunological surveillance by NK cells of the growth of pathogens that activate the HIV-1 tat infectivity gene may also favor progression to AIDS. The pathogenesis of NK cell deficiency in AIDS is not known. Previous studies have shown that NK cells from AIDS patients are able to bind but not to lyse the target cell line K562. This results from an inability to rearrange the cytoskeleton microtubular (MT) system and to release the natural killer cytotoxic factor (NKCF). This report by Maria Caterina Sirianni and colleagues evaluates the possible mechanisms leading to this NK cell deficiency.

NK cell activity controls human herpesvirus 8 latent infection and is restored upon highly active antiretroviral therapy in AIDS patients with regressing Kaposi's sarcoma.

Kaposis sarcoma (KS) develops upon reactivation of human herpesvirus 8 (HHV8) infection and virus dissemination to blood and tissue cells, including endothelial and KS spindle cells where the virus is mostly present in a latent form. However, this may likely require the presence of compromised host immune responses and/or the evasion of infected cells from the host immune response.In this regard, mechanisms of evasion of productively infected cells from both CTL and NK cell responses, and resistance of latently infected cells from specific CTL, have already been shown. Here we show that cells which are latently infected by HHV8 are indeed efficiently lysed by NK cells from individuals with a normal immune response. Notably, NK cell‐mediated immunity was found to be significantly reduced in AIDS patients with progressing KS as compared to both HIV‐negative patients with indolent classic KS or normal blood donors. However, it was restored after treatment with the highly active antiretroviral therapy (HAART) in AIDS‐KS patients, that showed regression and clearance of HHV8 from PBMC. By contrast, AIDS‐KS patients with a more aggressive disease and no clinicalresponse had persistent HHV8 viremia associated with reduced NK cell cytotoxicity. These results suggest a key role for NK cells in the control of HHV8 latent infection, KS development, and in disease remission upon HAART.

Circulating spindle cells : correlation with human herpesvirus-8 (HHV-8) infection and Kaposi's sarcoma

Vol 349 • January 25, 1997 255 cultures with the endothelial cell marker VE-cadherin and the tissue-macrophage marker PAM-1 (40–60% in KS patients and 0·5–6% in controls) (table). 4 weeks later, culture were examined for HHV-8 DNA sequences by nested PCR. None of the control cultures was positive, whereas HHV-8 was detected in all T-KS and AIDS-KS cases and in 11/14 cultures derived from patients with C-KS (table). HHV-8 was also detected in the patient with C-KS after bleomycin therapy. Our results indicate that an expansion of circulating KS-like cells or their progenitors is present in all forms of KS; KS-derived cultures are infected by HHV-8; and the presence of HHV-8 in these cells correlates with KS. Since these cells are capable of chemotaxis and can induce KS-like lesion formation in nude mice, our data suggest that they may localise into tissues, transmit HHV-8 infection to neighbour cells, and participate in the formation of KS lesions.

Modulation of human natural killer activity by vasoactive intestinal peptide (VIP) family. VIP, glucagon and GHRF specifically inhibit NK activity

Vasoactive intestinal polypeptide (VIP) is a neuropeptide, which also modulates some immune functions. Natural killer (NK) cell activity was already found to be diminished by VIP. In the present paper we report that VIP is able to decrease NK cell activity of human large granular lymphocytes (LGL), showing maximal inhibition at doses ranging from 10(-8) to 10(-6) M. Some neuropeptides, belonging to the VIP family (secretin, glucagon, peptide histidine isoleucine, PHI and human growth hormone releasing factor, GHRF), were also tested. Among these peptides, secretin and PHI were shown to be uneffective on NK cell activity whereas glucagon and GHRF were inhibitory. The D50 of GHRF was similar to that of VIP (10(-9) M), the D50 of glucagon was 10(-8) M. A recently synthesized VIP-antagonist (4Cl-D-Phe6-Leu17) was then used to assess its ability to reverse the VIP-mediated inhibition of NK activity. The antagonist was able to completely reverse the inhibitory effect of VIP on NK activity. The VIP-antagonist was also able to reverse the inhibitory effect of glucagon and GHRF, even though to a lesser extent than for VIP. Our data provide a new physiological observation regarding the functional activity of LGL, supporting the presence of a receptor for VIP on human LGL with NK activity.

Idiopathic CD4+ Lymphocytopenia May Be due to Decreased Bone Marrow Clonogenic Capability

Background: Idiopathic CD4+ lymphocytopenia is defined by a stable decrease of CD4+ T cells in the absence of any known cause of immune deficiency. The mechanisms responsible for the immunological impairment are still unknown, but a regenerative failure of hematopoietic stem/progenitor cells has been hypothesized. Methods: We evaluated in the bone marrow (BM) of 5 patients with idiopathic CD4+ lymphocytopenia the phenotype of BM progenitor cells, their differentiation capacity with colony-forming cells and long-term culture-initiating cell assays, in parallel with the spontaneous IL-7 production in the patient sera. Results: Compared with controls, a regenerative failure of hematopoietic stem cells has been observed, both in ‘committed’ and in ‘uncommitted’ progenitor cells, despite high IL-7 serum levels. The percentage of phenotypically primitive CD34+CD38–DR+ cells (this includes the lymphoid precursor cells) was decreased, suggesting an involvement of the more primitive BM compartment in the de novo T cell generation. Conclusions: Despite the low number of patients, due to the low incidence of the disease, the decrease of primitive precursors sustains the possibility that diminished stem cell precursors might contribute to the development of CD4+ T cell depletion.

Deficiency of natural killer activity, but not of natural killer binding, in patients with lymphoadenopathy syndrome positive for antibodies to HTLV-III

Blood lymphocytes (BL) of eleven patients with lymphoadenopathy syndrome (LAS) were studied for natural killer (NK) activity against the K562 cell line (using both the standard 51Cr release assay and the single-cell cytotoxicity assay on poly-L-lysine-coated coverslips) and for surface phenotype (employing OKT4, OKT8 and Leu7 monoclonal antibodies). A significant reduction in NK activity and in NK active cells was detected, while the percentage of target binding cells was not affected. Furthermore, the OKT4/OKT8 ratio was found to be inverted, and the Leu7+ subpopulation expanded. The patients had high titers of anti-HTLV-III antibodies. This study indicates that defective NK activity in LAS is secondary to an abnormality in the lytic event itself and not in target binding.

Severe combined immunodeficiencies, primary T-cell defects and DiGeorge syndrome in humans: characterization by monoclonal antibodies and natural killer cell activity.

Peripheral blood mononuclear cells from three patients with severe combined immunodeficiency (SCID), three with SCID whether B cell positive or with pure T-cell defect, and two with DiGeorge syndrome were analyzed with a panel of monoclonal antibodies against immature and mature T-cell subsets. Natural killer (NK) cells were enumerated by the use of the HNK-1 monoclonal antibody. NK activity against the K562 and MOLT 4 cell lines was also investigated. According to the monoclonal antibodies profile and the NK activity, patients could be divided into three groups. Patients with classical SCID had no detectable circulating T cells as well as NK cells and activity, probably due to an early block in stem cell differentiation. Patients affected by SCID with B cells or pure T cell defect showed a decrease in lymphocytes with mature phenotypes but prothymocytes or immature thymocytes circulated in peripheral blood. Children with DiGeorge syndrome had a decrease in mature thymocytes and, in this study, NK cells were normal. These data help to clarify both the preeminent immunologic features of SCID and related syndromes and the character of NK cells.

Distribution of the natural killer-related receptor for HLA-C during highly active antiretroviral therapy for human immunodeficiency virus infection.

Receptors interacting with Major Histocompatibility Complex class I molecules have been initially found on the surface of human natural killer (NK) cells, where they deliver inhibitory signals to the lysis, being thus defined killer inhibitory receptors (KIR). Subsequently, they were detected also on the surface of T-CD8(+) lymphocytes and are particularly expanded during human immunodeficiency virus (HIV) infection, where they downregulate HIV-specific cytolysis. The expression of KIR recognizing human leukocyte antigen-C alleles was assessed in HIV-infected patients, undergoing highly active antiretroviral therapy (HAART). To this end, the combined expression of CD16/CD56, of CD3 and CD8 as well as of KIR (CD158a and CD158b) surface molecules was analyzed on peripheral blood mononuclear cells by monoclonal antibodies, and flow cytometry. An increase of CD3(+)CD8(+)CD158b(+) cells was found after 6 months of HAART. This finding may have implications for the regulation of T-cell mediated cytolysis during HAART.

Treatment of Kaposi's sarcoma--an update.

Kaposis sarcoma (KS) is an angioproliferative disease of multifactorial origin arising in different clinic-epidemiologic forms, which show the same histopathological features. It generally starts as a hyperplastic reactive-inflammatory and angiogenic process, which may evolve into monomorphic nodules of KS cells that can be clonal (late-stage lesions) and resemble a true sarcoma. Infection with the human herpesvirus 8, cytokine- and angiogenic factor-induced growth together with an immuno-dysregulated state represent fundamental conditions for the development of this tumor. Several local therapies are used to eradicate early and confined skin lesions, whereas widely disseminated, progressive or symptomatic disease requires a more aggressive treatment. Although different chemotherapeutic agents have been used to treat aggressive KS, the growing understanding of the pathogenetic factors participating in KS development has provided a strong rationale for using less- or non-cytotoxic agents that block the mechanisms involved in KS pathogenesis. The angiogenic nature of KS makes it particularly suitable for using therapies based on anti-angiogenic agents. Of note on this goal, recent studies indicate that the highly active anti-retroviral therapy, including at least one human immunodeficiency virus (HIV) protease inhibitor (PI), is associated with a dramatic decrease in the incidence of AIDS-KS and with a regression of KS in treated individuals. Consistent with this, results from preclinical studies indicate that PIs have potent and direct anti-angiogenic and anti-KS activities, suggesting that they should be further investigated, alone or combined with other therapies, as a novel treatment for KS in both HIV seropositive or seronegative individuals.