TWiV 459: Polio turns over a new leaf

The TWiV team reviews the first FDA approved gene therapy, accidental exposure to poliovirus type 2 in a manufacturing plant, and production of a candidate poliovirus vaccine in plants.

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The $475,000 drug

KymriahThe US Food and Drug Administration recently approved the first gene therapy, Kymriah, to treat B-cell acute lymphoblastic leukemia. It uses a lentivirus to modify the patient’s T cells to kill tumor cells.

Acute lymphoblastic leukemia, or ALL, is caused by uncontrolled growth of B cells, which normally produce antibodies to fight off infections. It is the most common cancer in children. The uncontrolled production of these cells by the bone marrow causes a shortage of blood cell production, leading to fever, increased risk of infection, and anemia. These B cells have on their surfaces a protein called B19 – which is the key to understanding how Kymriah works.

The therapy begins with drawing blood from the patient, from which T cells are purified. These T cells are then infected with a lentivirus vector that encodes the gene for a chimeric antigen receptor (CAR) that recognizes the B19 protein. The CAR protein is synthetic – it doesn’t exist in any cell. The extracellular domain consists of a single-chain antibody directed against the B19 protein (pictured). The cytoplasmic domain of the protein contains sequences that stimulate the T cells to proliferate.

After the T cells are infected with the CAR-encoding lentivirus, they are infused back into the patient. Upon encountering a B cell producing B19, the T cells bind to the protein and kill the cells, thus eliminating the cancer.

Kymriah was licensed by the FDA after testing showed it was effective, leading to remission of cancers in the majority of children treated. But the price tag is steep – $475,000 for a treatment, and other similar drugs in the pipeline could be even more expensive. The drug makers justify the high price by arguing that it reflects the value to the patient – it saves their lives.

But vaccines also save lives, and they cost much less than Kymriah. The difference, of course, is that vaccines are given to millions of people. Kymriah, in contrast, would be given to thousands in the US.

In other words, the high cost of Kymriah reflects the need of drug companies to recoup their high investment in developing and testing the drug – not the value to the patient.  Rather than spinning a false story about the value of a drug to a patient, the drug companies should be honest about the pricing of their products. No wonder the public has a negative image of the industry.

TWiV 350: Viral gene therapy with Katherine High

On episode #350 of the science show This Week in Virology, Vincent speaks with Katherine High about her career and her work on using viral gene therapy to treat inherited disorders.

This episode is drawn from one of twenty-six video interviews with leading scientists who have made significant contributions to the field of virology, part of the new edition of the textbook Principles of Virology.

You can find TWiV #350 at

TWiV 326: Giving HIV a flat tyr

On episode #326 of the science show This Week in Virology, the sternutating TWiVers discuss preventing infection of cells and animals by a soluble CD4-CCR5 molecule that binds to HIV-1 virus particles.

You can find TWiV #326 at

TWiV 214: This is your brain on polyomavirus

On episode #214 of the science show This Week in Virology, Vincent, Alan, and Kathy discuss how coagulation factor X binding to adenovirus activates the innate immune system, and a novel polyomavirus associated with brain tumors in raccoons.

You can find TWiV #214 at

TWiV 102: Catch me if you can in Munich

Hosts: Vincent Racaniello, Andrew BakerKarl-Klaus ConzelmannPeter Palese, and Katharina Eisenächer

Episode #102 of the podcast This Week in Virology is a conversation about the RNA sensor RIG-I, adenovirus gene therapy, a universal influenza vaccine, and rabies virus, recorded in Munich, Germany at the SFB455 symposium ‘Viral offense and immune defense’.

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Weekly Science Picks

Katharina – Deutsches Museum
Vincent – HHMI holiday lectures on science (thanks Judi!)

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TWiV 88: A bug fix, an AIDS treatment, and an undead retrovirus

Hosts: Vincent Racaniello, Alan Dove, and Marc Pelletier

On episode #88 of the podcast This Week in Virology, Vincent, Alan, and Marc discuss using a virus for beetle control, RNA based gene therapy for AIDS, and reconstitution of a endogenous human retrovirus.

This episode is sponsored by Data Robotics Inc. Use the promotion code TWIVPOD to receive $75-$500 off a Drobo.

To enter a drawing to receive 50% off the manufacturers suggested retail price of a Drobo S or FS at, fill out the questionnaire here.

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Weekly Science Picks

Marc Apple iPad as a tool for writing, with Papers, Pages, and GoodReader
AlanThe Bacterium and the Bacteriophage
Naturally Obsessed (thanks, Sharon!)

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TWiV 71: Please Mr. Postman

Hosts: Vincent Racaniello, Dickson Despommier, Alan Dove, and Rich Condit

Vincent, Dickson, Alan, and Rich answer listener questions about maternal infection and fetal injury, viral gene therapy, eyeglasses and influenza, filtering prions from blood, eradication of rinderpest, Tamiflu resistance of H1N1 influenza, bacteriophages and the human microbiome, H1N1 vaccine recalls, human tumor viruses, RNA interference, and junk DNA.

This episode is sponsored by Data Robotics Inc. Use the promotion code VINCENT to receive $50 off a Drobo or $100 off a Drobo S.

Win a free Drobo S! Contest rules here.

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Dickson and Alan NSF/AAAS Science and Engineering Visualization Challenge
Rich Foundation by Issac Asimov
Vincent Natural Obsessions by Natalie Angier

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Clinical benefit of lentiviral gene therapy in two patients with a rare neurologic disease

aldX-linked adrenoleukodystrophy (ALD) is a rare neurologic disease caused by a defect in a gene required for normal ABCD1 transporter function. The lack of this function leads to progressive demyelination, severe neurologic disease and death in males, often in childhood. ALD disease progression can be controlled by allogeneic hematopoietic cell transplantation (HCT) in those patients for whom bone marrow donors can be found. This unusual correction occurs because bone marrow-derived monocyte-macrophages are known to migrate into the central nervous system and form functional microglial cells. These corrected microglial cells provide the patients with cells with normal ABCD1 transporter activity and allow normal myelin function.

Two patients with progressive ALD with no available allogeneic HCT donors were recently treated by lentiviral-mediated gene therapy. A lentiviral vector containing the normal ABCD1 transporter gene coding sequence was integrated into the patients’ own marrow derived hematopoietic stem cells after transduction of defective viral particles into the cells ex vivo. The gene-corrected cells were then re-infused into the patients. Myeloablation of the patients’ own marrow was required (as it is in allogeneic HCT treatment) since the gene-corrected cells have no growth advantage over resident patient cells. In addition, the treatment is necessary to provide marrow space for the new gene-corrected cells.

In both of the treated patients, seven and seven and a half years old, there was significant gene transfer and expression of the corrected ABCD1 protein expressed in transplanted myelomonocytes, the population from which the corrected brain glial cells arise. More importantly, brain MRIs from the two patients (left image) showed no progression of demyelinating lesions than in untreated patients (right image). The clinical neurologic status of one patient improved and, in the other, the patient’s disease was stabilized. Untreated patients usually deteriorate in neurologic function when their disease becomes active.

In all HCT gene therapy, stable integration with viruses is required since expansion of specific hematopoietic cell lineages, (here of monocyte-macrophages), are needed to provide adequate numbers of new corrected cells after extensive cell division. Lentiglobin gene transfer (HIV-based) permits integration of transferred genes into quiescent cells (many hematopoietic stem cells are non-dividing) that must be stably transduced for gene therapy with HCT to be successful. By contrast, a property of previously utilized oncoretroviral or gammaretroviral transfer (largely MLV-based) in human gene therapy is that cell division is necessary for viral integration. Consequently gene transfer into HCT is much less efficient.

The clinical benefit provided by this first reported trial of successful lentiviral gene therapy using hematopoietic stem cells in neurologic disease may provide an impetus for similar approaches to treating other neurological diseases.

Cartier N, Hacein-Bey-Abina S, Bartholomae CC, Veres G, Schmidt M, Kutschera I, Vidaud M, Abel U, Dal-Cortivo L, Caccavelli L, Mahlaoui N, Kiermer V, Mittelstaedt D, Bellesme C, Lahlou N, Lefrère F, Blanche S, Audit M, Payen E, Leboulch P, l’Homme B, Bougnères P, Von Kalle C, Fischer A, Cavazzana-Calvo M, & Aubourg P (2009). Hematopoietic stem cell gene therapy with a lentiviral vector in X-linked adrenoleukodystrophy. Science (New York, N.Y.), 326 (5954), 818-23 PMID: 19892975

Anti-HIV ribozyme: an alternative to HAART?

hdv_ribozymeThe treatment of AIDS patients with a combination of three or four antiviral drugs is known as HAART, or highly active antiretroviral therapy. Combination therapy has been effective for long-term control of infection, and represents one of the high points in AIDS research. The downside of HAART is that strict adherence to daily therapy must be maintained, and toxicity and viral resistance are continuing problems. Is there an alternative for AIDS patients?

The results of a phase 2 gene therapy trial suggest that gene therapy with an anti-HIV ribozyme could control HIV-1 replication in AIDS patients. A ribozyme is an enzyme made of RNA, not protein. Examples include the group I intron of Tetrahymena thermophila (the first ribozyme discovered), RNAse P of bacteria, group II self-splicing introns, and the hepatitis delta ribozyme. They differ widely in size, sequence, and mechanism of catalysis. They can cleave their own phosphodiester bonds, or those of other RNAs – which is why they are being explored as antiviral and antitumor agents.

The ribozyme used in the phase 2 study, which targets two overlapping open reading frames of HIV-1, was previously shown to inhibit viral replication in cultured cells. The ribozyme was incorporated into a retrovirus vector, which was then used to infect peripheral blood CD34+ stem cells that had been obtained from each patient. The stem cells were placed in culture, infected with the ribozyme-containing retrovirus, and then the cells were injected intravenously back into each patient. A total of 38 patients received cells that had been infected with the ribozyme-containing retrovirus, while 36 patients received cells that had been infected with a control retrovirus. Six months later, HAART therapy was halted for 4 weeks, to allow increased reproduction of HIV-1. The idea was that the virus would kill lymphocytes that lack the ribozyme, and that ribozyme-expressing immune cells would expand in number.

The treatment regimen was well-tolerated by all patients, and no adverse side effects were observed. The levels of HIV-1 in the blood of patients who received the ribozmye-expressing cells were consistently lower than patients in the control group. Lymphocytes of the CD4+ class – the kind infected by HIV-1 – were also more numerous in the blood of ribozyme-treated patients. These observations demonstrate that a single-dose gene therapy approach has great potential for treating AIDS.

Curiously, no viral mutants emerged in the patients that were resistant to the ribozyme. Nor had such mutations been previously observed in cell culture studies. Why such resistance mutations have not been described is a mystery – a single base change in the region of HIV-1 targeted by the ribozyme should be sufficient to prevent cleavage and inactivation of the viral genome. Because this region of the HIV-1 genome is highly conserved, mutations might produce less fit viruses which cannot compete with ribozyme-sensitive viruses.

Ronald T Mitsuyasu, Thomas C Merigan, Andrew Carr, Jerome A Zack, Mark A Winters, Cassy Workman, Mark Bloch, Jacob Lalezari, Stephen Becker, Lorna Thornton, Bisher Akil, Homayoon Khanlou, Robert Finlayson, Robert McFarlane, Don E Smith, Roger Garsia, David Ma, Matthew Law, John M Murray, Christof von Kalle, Julie A Ely, Sharon M Patino, Alison E Knop, Philip Wong, Alison V Todd, Margaret Haughton, Caroline Fuery, Janet L Macpherson, Geoff P Symonds, Louise A Evans, Susan M Pond, David A Cooper (2009). Phase 2 gene therapy trial of an anti-HIV ribozyme in autologous CD34+ cells Nature Medicine DOI: 10.1038/nm.1932