Year 4 + NCE

Infection with HIV-1 requires entry of the virus into cells by binding to a receptor protein called CCR5. Persons with a natural mutation in the gene encoding CCR5 (CCR532) are protected from HIV-1 infection and AIDS. Everyone has two copies of this gene, one inherited from their mother and one from their father. People with both copies of CCR5 mutated (CCR532/ CCR532) are highly resistant to becoming infected with HIV-1. If only one copy is abnormal (CCR5/ CCR532), infection with HIV can occur but progression of the infection to AIDS is delayed. The only clear cure of HIV-1 infection occurred in a patient with leukemia who received a blood stem cell transplant from a tissue-matched donor whose cells carried the double mutation CCR532/CCR532. After transplantation, this patient was able to stop all anti-HIV medicine, the immune system improved, and the level of HIV-1 in the blood dropped to undetectable levels. Even after more than 6 years off anti-HIV medicine, the patient is considered cured, as there is no evidence of an active HIV-1 infection.

This Disease Team proposed to treat blood stem cells from an HIV-1 infected person with a protein that can mutate the CCR5 gene, and then transplant these same cells back into the patient. The idea was to try and reproduce the effects of the CCR532 mutation by providing a renewable and long-lasting source of these HIV-1 resistant cells. This approach gets around the need to find a stem cell donor who happens to carry the CCR532/ CCR532 double mutation and is a suitable “perfect match” for tissue transplant. The proteins that will be used in this treatment are called Zinc Finger Nucleases (ZFNs). Preliminary results in mice transplanted with ZFN-treated blood stem cells showed that the modified cells are functional and produce CCR5 mutant progeny cells – including CD4 T cells that are the natural target of HIV-1. Importantly, after HIV-1 infection, the mice demonstrated reduced viral loads, maintenance of CD4 T cells in peripheral tissues, and a powerful survival advantage for the CCR5-negative cells [Holt et al., Nature Biotechnology 2010; 28: 839-47]. These data supported the development of this ZFN approach to treat HIV-1 infected patients by first isolating the subjects own blood stem cells, modifying them using CCR5-specific ZFNs, and then re-infusing them back into the patient to thereby reconstitute the immune system with CCR5-mutant, HIV-1 resistant cells. The Disease Team assembled to accomplish this goal has expertise in stem cell technology [City of Hope], HIV-1 infection in pre-clinical mouse models [University of Southern California], and in ZFN-based clinical trial development [Sangamo BioSciences].

The Disease Team developed a new method for delivering the ZFNs to the blood stem cells using messenger RNA (mRNA, or SB-728mR). Using a process called electroporation, a technique that involves exposing a mixture of the blood stem cells and the SB-728mR to a transient electrical field, efficient mutation of the CCR5 gene was achieved. This method was tested in mice and again showed evidence of protection from HIV-1. Electroporation of SB-728mR was then moved into clinical-scale manufacturing to support our proposed clinical trial. In Year 4 of the study, the Disease Team completed studies demonstrating the safety of these modified blood stem cells, and obtained the required federal and local approvals to initiate the first-in-human testing of the CCR5-modified blood stem cell therapy. The Phase I clinical trial, which is sponsored by City of Hope and funded by Sangamo BioSciences and CIRM under its Strategic Partnership funding mechanism, is planned to start accrual in the fourth quarter of 2014.