RNA interference is a naturally occurring means to block the function of genes in our body. We propose that RNA interference can be used to block HIV-1 infection and its reproduction within the body. When RNA interference is introduced into a stem cell, its blocking activity will be present throughout the lifetime of the stem cell, theoretically the lifespan of a human being. Thus, in theory an effective stem cell RNA interference therapy will require only a single treatment as opposed to the current lifetime administration of anti-HIV-1 drugs often accompanied by serious side effects. In nature, some individuals carry a genetic mutation that renders them resistant to HIV-1 infection. This mutation prevents HIV-1 from attaching to the white blood cells. Our RNA interference approach will be to mimic this natural situation by blocking the activity of this “co-receptor” within infected individuals by creating a new blood system that carries the RNA interference therapy. This therapy will be developed as a combination with other gene therapeutic reagents to protect the new blood system from HIV infection.
The need for novel approaches to the treatment of HIV infection has never been greater, because new infections continue to occur at undiminished rates, in California and across the nation, despite decades of prevention efforts. Moreover, the number of people living with HIV is rising steadily, thanks to improved management of HIV infection. As a result, California, which ranks second in the nation in diagnosed cases of HIV infection, behind only New York, has identified 67,500 men, women, and children who carry the virus. (Estimates of the number of Californians who are infected but have yet to be diagnosed range as high as 33,513.) Not all of the state’s HIV-positive residents are currently on therapy, but eventually virtually all of them will be—and many of them will receive their drugs through government-supported programs. In addition, the longer these infected individuals live, the more likely they are to avail themselves of a range of support services that the state pays for. The drugs themselves, which are routinely administered in combination, are initially effective in suppressing viral replication in infected individuals, but their potency diminishes over time, even as the toxic effects of therapy accumulate.
California, which is supporting the nation’s second-highest case-load of HIV-positive individuals, can expect to see that number grow at a rate of 5,000-7,000 a year for the foreseeable future. The cost of providing life-sustaining medications and social services to this burgeoning population will also continue to rise, not arithmetically but exponentially—because as increasing numbers of infected individuals fail standard drug regimens, it will be necessary to shift them to newer, more expensive treatments, and as the side effects of therapy become more manifest, it will be necessary to prescribe drugs to combat those toxicities, adding to the overall drug burden for patients and the overall cost of drug therapy for the state.
In such circumstances, the prospect of stem-cell based therapy that will require “only a single treatment” is especially compelling. In theory, RNA interference might effectively cure individuals infected with HIV, by blocking the ports through which the virus enters CD4 cells and destroys the body’s immune system. And even if RNA interference proves only partially effective in blocking viral entry, it could significantly suppress viremia while sparing patients the toxicities associated with drug therapy. This would be a boon to infected individuals, but it would also be a benefit to uninfected Californians, because reductions in viremia in infected individuals translate into a reduction in the community burden of HIV infection—and that, in turn, reduces the overall rate of new infections statewide.
The applicant proposes to develop and test a stem cell-based treatment strategy for HIV-infection, with the potential to provide long-term protection or a ‘functional cure’. The applicant proposes to make use of RNA interference as a means of blocking expression of CCR5, a key co-receptor used by HIV-1 to gain entry into host cells. The RNA interference approach is proposed to mimic the effects of a naturally occurring mutation in humans that renders individuals resistant to HIV-1 infection. The applicant will develop and optimize methods to transduce autologous hematopoietic progenitor stem cells (HPSC) with a viral vector delivering a specific interfering short hairpin RNA (shRNA) designed to block production of CCR5. In addition, since combination treatment strategies are often more effective than monotherapy, the applicant proposes to add a second inhibitory component to the vector, a gene encoding an inhibitor of virus-cell fusion. Thus their primary therapeutic candidate is the combination of shRNA-mediated CCR5 inhibition and fusion inhibitor in one vector. Mobilized autologous stem cells will be transduced with this vector ex vivo and the engineered cells will then be transplanted intravenously after myeloablative chemotherapy. The applicant will test the primary therapeutic candidate in tissue culture systems in vitro and then assess both safety and efficacy in in vivo models. Additional plans include optimization of HPSC mobilization procedures; assessment and optimization of conditioning regimens; automation of cell processing procedures; production of Good Manufacturing Practice (GMP) grade therapeutic vector; validation of assays to support the clinical trial; and selection of the patient population. The primary goal is to file an Investigational New Drug (IND) application in order to conduct a pilot safety and tolerability trial in humans.
Reviewers were in agreement that this is a strong proposal based (a) on the scientific rationale, strengthened by validated targets and substantial preliminary proof-of-concept data; (b) the outstanding team which has both research and development experience; and (c) significant unmet medical need.
Reviewers concurred that there is strong scientific rationale for this proposal and that targeting HPSC for gene therapy approaches has a strong theoretical advantage over other approaches that target terminally differentiated effector memory T-cells. There was also agreement that the use of a combination gene therapy targeting two different viral mechanisms is a good idea and adds strength, although one reviewer commented that there is the possibility that some of the patients who will be candidates for this approach may carry virus that is resistant to the virus-cell fusion inhibitor. The reviewers pointed out that there is good supportive data validating the choice of targets, based on proven anti-retroviral efficacy of small molecule antagonists. The observation that loss of CCR5 cell surface expression due to a naturally occurring mutation confers resistance to infection provides further supportive evidence. One reviewer noted that a substantial fraction of patients with advanced HIV disease carry CXCR4-using as opposed to CCR5-using virus, and hence would be unaffected by CCR5 inhibition, which strengthens the rationale for adding a second inhibitor with a different mechanism.
There was agreement among reviewers that there is a significant unmet medical need and that if successful, this approach could have substantial positive impact on patients by reducing or eliminating the need for lifetime administration of relatively toxic anti-HIV-1 drugs that often have serious side effects. Reviewers differed in their assessment regarding how widely applicable this approach is likely to be. One reviewer commented that it would provide a potentially safer, easier, less expensive and more effective way to manage HIV viral load in infected patients and could reduce the overall need for using antiviral therapy, which would, in turn, reduce the development of drug-resistant strains. Another reviewer expressed the view that although the treatment will likely find a significant niche, the complexity, cost and potential toxicity of the approach will likely limit its use, even if successful.
The proposal was bolstered by the inclusion of substantial preliminary proof-of-concept data from the applicant, much of it generated by the team of investigators represented on this proposal. These data demonstrate inhibition of CCR5 expression using the shRNA approach, with resultant inhibition of HIV-1 infection in vitro, although some reviewers pointed out that the magnitude of this inhibition was relatively modest and will need optimization. One reviewer expressed some concern that the shRNA-mediated downregulation of CCR5 expression may diminish over time. Synergistic anti-HIV effects with the combination vector have also been demonstrated in vitro. Thus, although some additional optimization of activity may be needed, the preliminary data were considered to be robust and sufficiently mature such that the goal of submitting an IND within four years was thought to be achievable.
The reviewers agreed that the preclinical research and development plan is strong and well thought-out, and outlines the steps needed to establish a manufacturing process as well as to evaluate safety and efficacy in preclinical models in vivo. Reviewers were mixed in their opinions regarding the proposed preclinical model studies. In regard to safety, one reviewer noted that in face of the risk of insertional mutagenesis leading to leukemia in addition to general problems concerning safety and cytotoxicity, special and ample attention is given to well described preclinical model studies. Other reviewers questioned whether the proposed large animal studies would be required for the IND or not, suggesting that they might represent an unnecessary prolongation of the timeline. One reviewer commented that the amount of effort devoted to proof-of-concept studies in a mouse model could be re-evaluated since it may not be a necessary element in the critical path towards obtaining an IND. Despite these comments, reviewers concurred that the plan addresses all necessary preclinical and validation studies that will be needed to file the IND. Given that this group has experience in this area, they are well aware of the steps that must be taken, which was viewed as a strength. Reviewers generally agreed that the timeline is appropriate and achievable, although one reviewer expressed a small concern that because of the large number of variables, optimization of the transduction conditions may take longer than anticipated. The review panel discussed the proposed cascade of eligible patients for clinical trials. One reviewer suggested that to increase the likelihood of getting IND approval, it might be best to start with patients that have advanced disease with concomitant AIDS-related malignancy, thus demanding the use of the most aggressive myeloablative approach. Under these circumstances, engraftment of therapeutic HPSC is most likely. Then, having demonstrated proof-of-concept, the applicant could move to less sick patients. Overall, the proposed development plan was thought to be logical and achievable and the timeline includes meaningful milestones.
Reviewers stated that the resources and investigators are outstanding and the team is superb, both scientifically and in therapy development. The Disease Team comprises a collaboration between two complementary groups, one academic and one corporate. Each brings unique expertise to the project, with the academic group providing scientific know-how and proof of concept and the corporate group providing expertise in biologics development and commercialization. The team leaders are accomplished, highly productive investigators with a demonstrated track record in the field of HIV research, gene therapy, and/or clinical drug development. Key members of this team made the initial scientific observations leading to their hypothesis and demonstrated proof of concept in tissue culture and relevant models. A subset of the team has direct experience with a gene therapy trial in humans. The clinical team has extensive experience treating HIV patients with standard therapeutic approaches, enabling them to define appropriate patient eligibility criteria, stopping rules and clinical study endpoints. An appropriate research team that includes a highly talented and committed group of collaborators has been assembled to meet the evolving needs of the proposed project. The principal investigator has built up a rich and well-considered network of collaborations and resources and there is no doubt that the environment will be sufficient for this task.
In summary, the consensus opinion of the review panel was that this is a well written, well thought out proposal, with strong scientific rationale and a high probability of success. They also agreed that there is a medical need and that, if successful, this approach would provide considerable benefit to patients.
- John Rasko
- John Wagner
- Rainer Storb