Selective side-chain modification of cysteine and arginine residues blocks pathogenic activity of HIV-1-Tat functional peptides.

Extracellular Tat protein of HIV-1 activates virus replication in HIV-infected cells and induces a variety of host factors in the uninfected cells, some of which play a critical role in the progression of HIV infection. The cysteine-rich and arginine-rich basic domains represent key components of the HIV-Tat protein for pathogenic effects of the full-length Tat protein and, therefore, could be ideal candidates for the development of a therapeutic AIDS vaccine. The present study describes selective modifications of the side-chain functional groups of cysteine and arginine amino acids of these HIV-Tat peptides to minimize the pathogenic effects of these peptides while maintaining natural peptide linkages. Modification of cysteine by introducing either a methyl or t-butyl group in the free sulfhydryl group and replacing the guanidine group with a urea linkage in the side chain of arginine in the cysteine-rich and arginine-rich Tat peptide sequences completely blocked the ability of these peptides to induce HIV replication, chemokine receptor CCR-5 expression, and NF-kappaB activity in monocytes. Such modifications also inhibited angiogenesis and migration of Kaposi's sarcoma cells normally induced by Tat peptides. Such chemical modifications of the cysteine-rich and arginine-rich peptides did not affect their reactivity with antibodies against the full-length Tat protein. With an estimated 40 million HIV-positive individuals worldwide and approximately 4 million new infections emerging every year, a synthetic subunit HIV-Tat vaccine comprised of functionally inactive Tat domains could provide a safe, effective, and economical therapeutic vaccine to reduce the progression of HIV disease.

Mechanisms for macrophage-mediated HIV-1 induction.

Viral latency is a long-term pathogenic condition in patients infected with HIV-1. Low but sustained virus replication in chronically infected cells can be activated by stimulation with proinflammatory cytokines such as TNF-alpha, IL-1 beta, or other host factors. However, the precise mechanism by which cellular activation induces latently infected cells to produce virions has remained unclear. In the present report, we present evidence that activation of HIV-1 replication in latently infected U1 or ACH2 cells by human macrophages is mediated by a rapid nuclear localization of NF-kappaB p50/p65 dimer with concomitant increased expression of proinflammatory cytokines. Multiplexed RT-PCR amplification of mRNA isolated from cocultures of macrophages and U1 and ACH2 cells showed significant induction of IL-1beta, IL-6, IL-8, TNF-alpha, and TGF-beta expression within 3 h of coincubation. Fixation of macrophages, U-1, or ACH2 cells with paraformaldehyde before coculture completely abrogated the induction of NF-kappaB subunits and HIV-1 replication, suggesting that cooperative interaction between the two cell types is an essential process for cellular activation. Pretreatment of macrophage-U1 or macrophage-ACH2 cocultures with neutralizing anti-TNF-alpha Ab down-regulated the replication of HIV-1. In addition, pretreatment of macrophage-U1 or macrophage-ACH2 cocultures with the NF-kappaB inhibitor (E)3-[(4-methylphenyl)sulfonyl]-2-propenenitrile (BAY 11-7082) prevented the induction of cytokine expression, indicating a pivotal role of NF-kappaB-mediated signaling in the reactivation of HIV-1 in latently infected cells by macrophages. These results provide a mechanism by which macrophages induce HIV-1 replication in latently infected cells.

Secretory leukocyte protease inhibitor binds to annexin II, a cofactor for macrophage HIV-1 infection.

The distribution of secretory leukocyte protease inhibitor (SLPI) at entry portals indicates its involvement in defending the host from pathogens, consistent with the ability of SLPI to inhibit human immunodeficiency virus (HIV)-1 infection by an unknown mechanism. We now demonstrate that SLPI binds to the membrane of human macrophages through the phospholipid-binding protein, annexin II. Based on the recent identification of human cell membrane phosphatidylserine (PS) in the outer coat of HIV-1, we define a novel role for annexin II, a PS-binding moiety, as a cellular cofactor supporting macrophage HIV-1 infection. Moreover, this HIV-1 PS interaction with annexin II can be disrupted by SLPI or other annexin II-specific inhibitors. The PS-annexin II connection may represent a new target to prevent HIV-1 infection.

Conversion of peripheral CD4+CD25- naive T cells to CD4+CD25+ regulatory T cells by TGF-beta induction of transcription factor Foxp3.

CD4+CD25+ regulatory T cells (Treg) are instrumental in the maintenance of immunological tolerance. One critical question is whether Treg can only be generated in the thymus or can differentiate from peripheral CD4+CD25- naive T cells. In this paper, we present novel evidence that conversion of naive peripheral CD4+CD25- T cells into anergic/suppressor cells that are CD25+, CD45RB-/low and intracellular CTLA-4+ can be achieved through costimulation with T cell receptors (TCRs) and transforming growth factor beta (TGF-beta). Although transcription factor Foxp3 has been shown recently to be associated with the development of Treg, the physiological inducers for Foxp3 gene expression remain a mystery. TGF-beta induced Foxp3 gene expression in TCR-challenged CD4+CD25- naive T cells, which mediated their transition toward a regulatory T cell phenotype with potent immunosuppressive potential. These converted anergic/suppressor cells are not only unresponsive to TCR stimulation and produce neither T helper cell 1 nor T helper cell 2 cytokines but they also express TGF-beta and inhibit normal T cell proliferation in vitro. More importantly, in an ovalbumin peptide TCR transgenic adoptive transfer model, TGF-beta-converted transgenic CD4+CD25+ suppressor cells proliferated in response to immunization and inhibited antigen-specific naive CD4+ T cell expansion in vivo. Finally, in a murine asthma model, coadministration of these TGF-beta-induced suppressor T cells prevented house dust mite-induced allergic pathogenesis in lungs.