HIV is driven to low levels on HAART therapy but is not cured. While infectious spread is prevented by drugs, it does nothing to purge the latent reservoir (LR) or persistent reservoir (PR) that provide viruses for relapse of infection when HAART is removed. It has been said that there is no present likelihood for a sterilizing cure for HIV, and that a 'functional cure' should attract our focus as a more suitable and attainable goal. An alternative approach with potential for functional cure exploits a vulnerable step in the life cycle of HIV: the virus requires CD4 binding to enter the cell. Whereas mutations of gp120 that escape MHC presentation or antibody binding may thwart the immune reaction without affecting infectivity, any mutation of viral gp120 that blocks CD4 binding will destroy virus infectivity. T cells expressing chimeric antigen receptors (CARs) through gene modification ('designer T cells', dTc) can be redirected to kill virus-infected cells. A CD4 based anti-HIV CAR (CD4-TCR ) was previously prepared that redirects CTL to kill HIV gp120+ cells in an MHC non-restricted fashion. However, clinical trials of adoptive transfer of autologous CD4 designer T cells failed to control viral infection, despite a persistent fraction of designer T cells in recipents one year after infusion. The mechanisms of failure were proposed to include: activation induced cell death (AICD), deficiencies of signals and cytokines, regulatory T cell suppression, and heightened susceptibility of designer T cells to HIV infection. Many of these suppositions were addressed in the preliminary data for this proposal that were obtained under prior NIH R21 funding. In response, we created a CAR enhanced for potency in T cell activation via a 2-signal format that provides co-stimulatory signal (e.g., CD28; Signal 2) to create 2nd generation (gen) designer T cells. Our preliminary studies indicate high cytotoxic potency against infected targets and superiority of this construct in key aspects to justify a renewed clinical test of this modalit, including potentially the exposure and targeting of latently infected cells.
Aims for this study include 1. Complete characterization of a 2nd gen agent in anticipation of a clinical application, 2. 'Infection-proof' the dTc with siRNA against CCR5 and viral Tat/Rev to create a 3rd gen dTc; 3. Conduct in vivo correlate studies in a humanized mouse model to demonstrate resistance to infection of the new dTc and improved effectiveness in HIV suppression; and 4. Continuing research and development for still more advanced, 4th generation, agents for later clinical development, if needed. Anticipated results from these new products would justify new clinical trials for dTc in HIV/AIDS. The intention of the dTc first use will be to administer during HAART to establish a proof-of-principle in terms of eliminating the Persistent Reservoir and reducing residual viremia. This compartment is always gp120+. If HAART is then withdrawn, observation of a continued suppression would be tantamount to a 'functional cure', eliminating cells from the Latent Reservoir as they reactivate. We have shown with an in vitro model that dTc-secreted cytokine can also induce latent cells to re-express viral proteins, rendering them vulnerable to elimination, raising the prospect of a 'sterilizing cure'. Whether a cure is functional or sterilizng, it would be the most significant advance in HIV treatment since HAART.
A ''functional cure'' of HIV/AIDS may be possible through new types of anti-HIV T cell constructions (designer T cells; dTc) that effectively target virus-producing cells and that render the anti-HIV designer T cells themselves resistant to infection. This dTc agent is predicted to eliminate residual virus while patients are on HAART and to maintain suppression of viremia after HAART withdrawal by eliminating reactivating latent cells before virus spread. This research builds on a prior clinical trial by identifying potential limitations of that trial agent and devising specific solutions to obtain an improved therapeutic result.
|MacLean, Andrew G; Walker, Edith; Sahu, Gautam K et al. (2014) A novel real-time CTL assay to measure designer T-cell function against HIV Env(+) cells. J Med Primatol 43:341-8|
|Sahu, Gautam K; Sango, Kaori; Selliah, Nithianandan et al. (2013) Anti-HIV designer T cells progressively eradicate a latently infected cell line by sequentially inducing HIV reactivation then killing the newly gp120-positive cells. Virology 446:268-75|