Curing AIDS With Engineereed Stem Cells

Scientists from the UC Davis Health Science HIV team have demonstrated in a proof of principle study the safety and efficacy of transplanting HIV-resistant stem cells into mice.  If this protocol can be replicated in humans, it could signal a way to completely block HIV infection in human patients.

The human immunodeficiency virus (HIV) is a retrovirus.  The retroviruses contain an RNA genome, but once they infect the host cell, the RNA genome serves as a template for the synthesis of a DNA copy of the RNA genome.  The enzyme that performs this task is reverse transcriptase.  The DNA copy of the genome is inserted into the genome of the host cell.  This means that when the host cell divides, the viral DNA is passed to all of its progeny.

HIV infection causes acquired immunodeficiency syndrome (AIDS).  AIDS is characterized by a progressive shutdown of the immune system, which leads to life-threatening infections and cancers.  HIV infection occurs through the transfer of bodily fluids, such as semen, blood, vaginal fluid, saliva, or breast milk.  Sexual transmission, transmission from breast milk, contaminated needles, or from an infected mother to her baby at birth are the four main modes of transmission.  HIV screening of blood products has largely eliminated HIV transmission from blood products.

Since the discovery of AIDS in 1981, more than 25 million people have died from it, and even though antiretroviral treatments have decreased AIDS deaths and new infections, there were still probably at least 2.5 million new cases of AIDS in 2009.

HIV destroys the immune response by infecting helper T cells (CD4+ cells).  HIV can also infect dendritic cell and macrophages.  The mass die off of T helper cells prevents them from mediating cell-mediated immunity, and this makes the patient more susceptible to opportunistic infections.  People with untreated HIV infections usually develop AIDS and die from opportunistic infections or tumors.  Without antiretroviral treatment, someone with AIDS usually dies within a year.

In order to make HIV-resistant blood cell-making stem cells, Joseph Anderson and his co-workers engineered stem cells with three different genes.  First, they introduced into the stem cells, a human/macaque TRIM5 isoform.  In order to understand the significance of this gene, we must understand HIV more deeply.  When a retrovirus enters a host cell, it must “uncoat,” which simply means that the protein coating that surrounds the virus’ genome must be removed so that the reverse transcriptase can convert the RNA genome into a DNA copy.  Macaques are very widespread Old Word nonhuman primates that are immune the infection by HIV.  The reason for the immunity of these animals to HIV infection is that they possess in their cells a form of the TRIM5 protein that binds to bits of the HIV coat proteins and interferes with the uncoating process.  This prevents successful reverse transcription and transport of the viral DNA to the nucleus.  Therefore, the expression of the macaque version of TRIM5 is these blood-making stem cells rendered them resistant to HIV infection.

Secondly, the blood-making stem cells were given a gene that expresses a short hairpin RNA (shRNA).  These shRNAs can bind to the mRNAs are particular genes that prevent their expression.  In this case, the shRNA that was introduced into the blood-making stem cells prevented the production of the CCR5 gene product.  CCR5 is one of the cell surface proteins that HIV uses to gain entry into host cells.  Therefore, these blood-making stem cells will make blood cells that lacked the target for HIV infection.

Third, cells were engineered with a “TAR decoy.”  TAR is a site in the HIV genome that is bound by the HIV-encoded proteins Tat.  Tat binding to TAR activates expression of HIV genes.  However, by introducing TAR sites into the cells, Tat proteins inordinately bind to these non-functional TAR sites and not to the viral TAR site.  This will inactivate any HIV particles that happen to infect these cells.  With all these factors introduced into them, these blood-making stem cells and their progeny are completely resistant to HIV infection.

Introduction of these engineered stem cells into mice allowed these mice to resist infection even after experimental infection with HIV.  In the words of the lead author of this paper, Joseph Anderson, “After we challenged transplanted mice with live HIV, we demonstrated that the cells with HIV-resistant genes were protected from infection and survived in the face of a viral challenge, maintaining normal human CD4 levels.”  Remember the CD4 cells are the class of T cells that are specifically targeted by HIV, although the virus can infect other cell types too.

Anderson continued: “We actually saw an expansion of resistant cells after the viral challenge, because other cells which were not resistant were being killed off, and only the resistant cells remained, which took over the immune system and maintained normal CD4 levels.”  Anderson’s optimism, however, does not end there:  “We envision this as a potential functional cure for patients infected with HIV giving them the ability to maintain a normal immune system through genetic resistance.”  Anderson is an assistant professor of internal medicine and a stem cell researcher at the UC Davis Institute for Regenerative Cures.

This study confirms the safety and efficacy of this protocol, and validates the potential of this treatment for human HIV patients.  A grant application has been submitted by Anderson and his team for human clinical trials, and they are also pursuing regulatory approval for clinical trials.

Richard Pollard, the chief of infectious diseases at UC Davis (and a co-author on the study), said: “This research represents an important step in our fight against HIV/AIDS.  Clinical trials could give us the critical information we need to determine whether our approach truly represents a functional cure for a terrible disease that has affected millions and millions of people.”

HIV Drug Maraviroc Reduces Graft-Versus-Host Disease In Stem Cell Transplant Patients

A drug called maraviroc is normally used to treat Human Immunodeficiency Virus (HIV) infections, but work at the University of Pennsylvania suggests that maraviroc redirects the trafficking of immune cells. The significance of these results are profound for transplant patients, since a drug like maraviroc can potentially reduce the incidence of graft-versus-host disease in cancer patients who have received allogeneic (from someone else) stem cell transplantation (ASCT). This research, which was conducted at the Perelman School of Medicine at the University of Pennsylvania, was presented at the 53rd American Society of Hematology Annual Meeting.

Graft-versus-host disease or GvHD occurs as complication after a stem cell or bone marrow transplant. During GvHD, the newly transplanted cells recognize the recipient’s body as foreign and mount an attack against it. Acute cases of GvHD usually occur within the first 3 months after the transplant. Chronic GvHD usually starts more than 3 months after the transplant. GvHD rates vary from 30 – 40% among related bone marrow or stem cells donors and from 60 – 80% between unrelated donors and recipients. The greater the degree of immunological mismatches between the donor and the recipient, the greater the risk of GvHD. After a transplant, the recipient usually takes a battery of drugs that suppress the immune system. These drug treatments help reduce the chances or severity of GvHD.

Standard treatments for GvHD suppress the immune system. Commonly used medicines include methotrexate, cyclosporine, tacrolimus, sirolimus, ATG (Antithymocyte globulin), and alemtuzumab either alone or in combination. High-dose corticosteroids are the most effective treatment for acute GVHD. Antibodies to T cells and other medicines are given to patients who do not respond to steroids. Chronic GvHD treatments include prednisone, (a steroid) with or without cyclosporine. Other treatments include mycophenolate mofetil (CellCept), sirolimus (Rapamycin), and tacrolimus (Prograf). These treatments, if given during the course of the stem cell or bone marrow transplant, reduce but do not eliminate the risk of developing GvHD.

In the current trial, treatment with maraviroc dramatically reduced the incidence of GvHD in organs where it is most dangerous (liver, GI tract, lung, skin — without compromising the immune system and leaving patients more vulnerable to severe infections.

Assistant professor in the division of Hematology-Oncology and a member of the Hematologic Malignancies Research Program at Penn’s Abramson Cancer Center, Ran Reshef, commented: “There hasn’t been a change to the standard of care for GvHD since the late 1980s, so we’re very excited about these results, which exceeded our expectations. Until now, we thought that only extreme suppression of the immune system can get rid of GvHD, but in this approach we are not killing immune cells or suppressing their activity, we are just preventing them from moving into certain sensitive organs that they could harm.”

Reshef and colleagues presented results showing that maraviroc is safe and feasible in stem cell transplant patients who have received stem cells from a healthy donor. A brief course of the drug led to a 73% reduction in severe GvHD in the first six months after transplant, compared with a matched control group treated at Penn during the same time period (6% who received maraviroc developed severe GvHD vs. 22% of other patients receiving standard drug regimens).

Reshef explained, “Just like in real estate, immune responses are all about location, location, location. Cells of the immune system don’t move around the body in a random way. There is a very distinct and well-orchestrated process whereby cells express particular receptors on their surface that allows them to respond to small proteins called chemokines. The chemokines direct the immune cells to specific organs, where they are needed, or in the case of GvHD, to where they cause damage.”

Thirty-eight patients with blood cancers, including acute myeloid leukemia, myelodysplastic syndrome, lymphoma, myelofibrosis, and others, enrolled in the phase I/II trial. All patients received the standard GvHD prevention drugs tacrolimus and methotrexate, plus a 33-day course of maraviroc that began two days before transplant. In the first 100 days after transplant, none of the patients treated with maraviroc developed GvHD in the gut or liver. By contrast, 12.5% of patients in the control group developed GvHD in the gut and 8.3 percent developed it in the liver within 100 days of their transplant.

The differential impact of maraviroc on those organs indicates that the drug is working as expected, by limiting the movement of T lymphocytes to specific organs in the body. Maraviroc works by blocking the CCR5 receptor on the surfaces of lymphocytes. This prevents the lymphocytes from trafficking to certain organs. Maraviroc did not affect GvHD rates in the skin, which might mean that the CCR5 receptor is more important for sending lymphocytes into the liver and the gut than the skin.

After 180 days, the benefit of maraviroc appeared to be partially sustained in patients and the cumulative incidence of gut GvHD rose to 8.8% and the rates of liver GvHD rose only to 2.9%. The cumulative incidence of GvHD in the control group, however, remained higher, at 28.4% for gut and 14.8% for liver GvHD. Based on these data, the research team plans to try a longer treatment regimen with maraviroc to see if longer exposures to maraviroc can its protective effect.

Additionally, maraviroc treatment appeared to neither increase treatment-related toxicities nor alter the relapse rate of their underlying disease. Clearly this drug shows promise for limiting the devastating effects of GvHD in stem transplant patients.