Development of RNA-based approaches to stem cell gene therapy for HIV
Despite significant advances in treatment and prevention programs, HIV infection with progression to Acquired Immunodeficiency Syndrome (AIDS) is still prevalent in California. The CDC Estimates >56,000 new cases of HIV infection each year in the US with over 148,000 cumulative cases reported in California alone (as of 2009). Multi-drug therapy has been helpful in reducing the severity of disease and prolonging lifespan but sixteen of every one hundred HIV patients will eventually fail to control the virus after attempting at least 2 drug treatment regimens. The Centers for Disease Control (CDC) recently estimated the lifetime cost of medical care for AIDS to be in excess of $600,000 per patient, over 85% of which is attributable to prescription drug costs. Additionally, medication non-compliance, intolerance of drugs due to side effects and the development of resistant strains of virus are all complicating factors in obtaining consistent clinical benefit with lifelong drug therapy. Therefore, there is a need to provide a longer lasting, cost effective therapy for this disease. Our project builds on prior work from our laboratories in which genetically engineered blood stem cells were transplanted into HIV patients and shown to give rise to gene-marked peripheral blood cells that last for up to 2 years. These cells may protect HIV patients from progression to AIDS if they are present in sufficient numbers. Our therapeutic candidate is a gene modified human blood stem cell carrying multiple anti-HIV molecules that prevent virus infection, replication and spread and a gene that allows us to chemically “enrich” the number of disease resistant cells present in a patient’s blood. The anti-HIV molecules are made of ribonucleic acid (RNA) and were developed and tested in our laboratories. We have already conducted a first generation stem cell therapy clinical trial to test these molecules with promising results. We now propose to refine and further develop this treatment with second generation RNA molecules and gene transfer procedures that will improve the number of disease resistant cells in the blood of HIV patients. We will develop an animal model system to test newer, more efficient anti-HIV molecules and a drug treatment method to enhance the number of HIV resistant stem cells circulating in the blood of patients that receive gene modified blood stem cells. At the end of the proposed experiments, we expect to have selected the most efficient combination of RNA molecules and drug selection strategy to provide a sufficient number of disease resistant cells in the peripheral blood to prevent progression to clinical immunodeficiency (AIDS).
California has ~14% of all cases of AIDS in the U.S., and this translates into a medical and fiscal burden larger than any other state except NY. Antiviral chemotherapy accounts for approximately 85% of AIDS-related medical costs, and federal and state law requires that in California the AIDS Drug Assistance Program (ADAP) be the payer of last resort for these medications. Antiretroviral drugs currently cost about $12,000 per year and account for about $350 million of the California AIDS Drug Assistance Plan's budget. The Governor's spending plan (2009-09 Budget Act) called for $418M to support this program, with funds from several sources including federal (Ryan White Care Act), from an ADAP Rebate Fund, and from the California State General Fund. The ADAP Rebate Fund consists of monies paid to the state by the manufacturers of the drugs provided to the HIV/AIDS clients under the program. The ADAP budget has grown by ~15% yearly for several years, and based on an Legislative Analyst's Office (LAO) review, the problem faced is that, as the case load is increasing, support from the Rebate Fund is decreasing. It is projected by LAO that from a level of $80.3 million at end 2008, the Fund will decrease to $24M by the end of 2010. The General Fund currently provides $96.3M to the ADAP budget, and it is projected that as the ADAP Rebate Fund shrinks, the shortfall will have to be met by increases from the General Fund by 2012. The alternative, as noted by LOA, is to implement cost-cutting measures that would likely increase the barriers to receiving care for some patients, impacting the health of some HIV/AIDS patients and increasing the associated public health risks.
Our goal in the first year of the grant has been to establish a mouse model for HIV infection using hematopoietic stem and progenitor cells (HSPC) from healthy adult donors and to create a series of novel RNA-based vectors that will provide resistance to HIV infection in the progeny of these cells. Dr. DiGiusto's group has successfully demonstrated the ability to reliably engrafted mice with human immune system cells derived from adult HSPC. Among the engrafted cells are CD4+ T-cells and monocytes, the target cells for HIV infection. We have also demonstrated that we can expand the number of HSPC from each donor and maintain their ability to support engraftment of the mice with human T-cells and monocytes. This means that we are able to make a large number of mice with which to screen genetic therapies for HIV. During this period, Dr. Rossi's group has created a 5 new anti-HIV viral vectors that can be used to genetically modify HSPC and impart HIV resistance to the T-cells and monocytes that are derived from these HSPC. Assays performed in culture dishes indicate that 3 of these vectors are very potent HIV inhibitors. Addionally, the vectors contain a gene that will allow us to selectively enrich for those HSPC that carry the gene under specific culture conditions. Thus, we can produce a population highly enriched for disease resistant HSPC. We are now beginning testing of anti-HIV vectors in our mouse model to establish which would be the best for moving towards clinical trials. The ultimate goal of the study is to define the best clinical candidate and we on track for meeting that goal within the timeframe of the grant.
In the second year of the CIRM ETR2-01771 project entitled “Development of RNA-based approaches to stem cell gene therapy for HIV” we have made significant progress in the development of a robust animal model of human hematopoietic stem and progenitor cell (HSPC) engraftment, completed the cloning and in vitro testing of the candidate second generation anti-HIV lentiviral vectors and begun testing HIV infectivity of humanized NSG mice. Additionally, we have initiated transplantation of NSG mice with gene modified HSPC to evaluate the level of gene modified CD4+ T-cells and monocytes in vivo. This work will culminate in HIV challenge assays in the final year of the grant and selection of the second generation candidate therapeutic to be used in our clinical development program.
We are working on a cure for HIV using blood stem cell transplantation of HIV-infected individuals. We have completed the development of a second generation of anti-HIV genes with potent anti-viral activity and reduced toxicity from our first generation products. We have demonstrated that we can modify adult human blood stem cells with these vectors and that macrophage and T-cell progeny of these modified cells are resistant to HIV infection and spread. We are currently screening the genes to identify the next drug development candidate using a humanized mouse model developed in our laboratory. The completion of these experiments will allow us to immediately move towards clinical testing. This approach to HIV therapy is likley to replace drug therapy and may result in a functional or sterilizing cure for HIV.
During the final reporting period for this grant we have completed in vivo testing of our second generation anti-HIV constructs. We have identified a construct (SGLV4) that has an improved safety profile compared to our first generation vectors (less toxic) and superior anti-HIV activity including inhibition of viral replication and protection of CD4+ T-cells and monocytes as demosntrated in our in vivo animal model system. The use of this vector to genetically modify heamtopoietic stem cells may lead to a functional cure for HIV through the provision of an HIV-resistant immune system that will clear virus through normal immune mediated mechanisms. We will move this vector construct into pre-clinical development testing as funds become available through CIRM or other sources (NIH).
- Stem Cells Transl Med (2014) Enhanced Genetic Modification of Adult Growth Factor Mobilized Peripheral Blood Hematopoietic Stem and Progenitor Cells With Rapamycin. (PubMed: 25107584)
- Expert Opin Biol Ther (2013) Combinatorial RNA-based gene therapy for the treatment of HIV/AIDS. (PubMed: 23394377)
- Cytotherapy (2012) Current translational and clinical practices in hematopoietic cell and gene therapy. (PubMed: 22799276)
- Hum Gene Ther (2012) Endogenous MCM7 MicroRNA Cluster as a Novel Platform to Multiplex Small Interfering and Nucleolar RNAs for Combinational HIV-1 Gene Therapy. (PubMed: 22834872)