Blocking HIV-1 infection with intrakines

Abstract

Later this year, IntraVec Inc. – a company created by Wake Forest University (WFU, Winston-Salem, NC, USA) – will begin clinical trials of a new therapy to boost immune function in people infected with HIV. The treatment was developed by Dr Si-Yi Chen (Baylor School of Medicine, Houston, TX, USA) while he was working at WFU, and uses intrakines (intracellular chemokines) to block the expression of chemokine co-receptors at the cell surface of macrophages and T cells.The CCR-5 chemokine co-receptor is vital to macrophage-tropic HIV-1 (M-tropic HIV-1) infection of lymphocytes and macrophages, and people who do not express this co-receptor are resistant to HIV-1 infection. Chen and colleagues mimic this natural pattern of resistance using a modified chemokine CCR-5 ligand – the regulated upon-activation, normal T-expressed and secreted ligand (RANTES) to produce an intrakine (RANTES-K). The intrakine is targeted at the endoplasmic reticulum (ER), where an intracellular retention signal expressed at its C-terminus ensures that it remains in the ER. Once in the ER, explains Chen, ‘the intrakine binds newly synthesized receptors and prevents their transport to the cell surface.’ (Fig. 1Fig. 1). This process prevents M-tropic HIV-1 binding to the cell.Figure 1By preventing the transport of newly synthesized CCR-5 co-receptors, the regulated upon-activation, normal T-expressed and secreted ligand intrakine (RANTES-K) prevents macrophage-tropic HIV-1 binding. Figure kindly provided by Dr S-Y. Chen, Baylor College of Medicine, Houston, TX, USA.View Large Image | Download PowerPoint SlideBoth T-tropic and M-tropic viruses can co-exist in one individual: T-tropic HIV-1 is usually found in the later stages of infection and is a sign of progression to AIDS, whereas the M-tropic form is most prevalent shortly after infection. To provide maximal protection against HIV-1, the team has also developed an intrakine (modified stromal cell-derived factor – SDF-K) to block expression of CXCR-4, the principal co-receptor needed for HIV infection of T cells. A bicistronic vector (pCMV-S-K/R-K) with an internal ribosome entry sequence mediates co-expression of RANTES-K and SDF-K (Ref. 1xGenetic co-inactivation of macrophage- and T-tropic HIV-1 chemokine coreceptors CCR-5 and CXCR-4 by intrakines. Bai, X. et al. Gene Ther. 1998; 5: 984–994Crossref | PubMedSee all ReferencesRef. 1). Once transduced, lymphocytes appear unaffected by the process, apart from their ability to resist both M- and T-tropic HIV-1 infection; the cells proliferate normally, possess normal cell-surface markers (CD3, CD4 and CCR2), and respond normally to antigen and mitogen stimulation.Chen believes that the combination of co-inactivation of the principal co-receptors involved in HIV infection with currently available chemotherapy is a promising therapeutic strategy for HIV-1 infection. In practice, Chen explains, ‘a retroviral or other vector will be used to transduce patients’ T cells or stem cells ex vivo in order to make them immune to HIV-1 infection and to restore immune functions to the patient. Although this genetic approach may have long-term effects, repeat treatments are likely to be needed.’The intrakine approach has a number of advantages over current HIV therapies: ‘Most antiretroviral therapies seek to block viral replication after the host cell has been infected – targeting viral components that frequently mutate. In contrast, IntraVec’s approach seeks to prevent infection of HIV-susceptible immune cells by inactivating conserved cellular proteins critical for HIV infection,’ explains Chen. The new therapy should therefore be less likely to cause HIV mutation. In addition, he hopes that intrakine therapy will avoid or minimize some of the problems associated with direct administration of chemokines, such as short half-life and inflammatory effects, although the forthcoming clinical trials will answer these questions. ‘The first clinical trial is designed to test the safety of the infusion of intrakine-transduced T-cells and the survival advantage of the transduced T-cells versus control-transduced T-cells,’ says Chen.Although Chen is now working at the Center for Cell and Gene Therapy at Baylor College of Medicine, he will continue to collaborate with IntraVec on the development of intrakine-based therapies. He will also continue pre-clinical research into another strategy to combat both HIV and cancer. In this approach, normal cells, such as lymphocytes, are transduced to produce Pseudomonas toxins coupled to a targeting antibody. For HIV, the toxin is coupled to an antibody against the HIV glycoprotein gp120, whereas for breast and ovarian cancer, the toxin is coupled to an antibody against HER2 – an oncoprotein that is often overproduced in these types of tumours. ‘Since normal cells do not express or only express very low levels of HER2 or HIV-1 gp120, the anti-HER2- or anti-HIV-1 gp120–Pseudomonas-toxins secreted from the transduced cells cannot bind and destroy normal cells,’ explains Chen.