Monthly Archives: July 2010

Hopping rabbits herald breakthrough in tissue engineering

A team of NIH-funded scientists and veterinarians at Columbia University, the University of Missouri, Clemson University, and the Medical University of South Carolina, have this week announced a significant advance in tissue engineering, for the first time they have used cutting–edge tissue engineering technology to produced a moving joint, in this case the hip, in rabbits.  A press release on the NIH website discusses the work in some detail, and those with a subscription can read the original research article in the Lancet.  This is not the first paper to describe the production of bone or cartilage using tissue engineering, but it is the first time that the two tissues have been regenerated together to produce a moveable joint, and represents a significant step forward in terms of the complexity of tissue that can now be engineered.

Rabbits are a popular experimental model for the study of bone repair and regeneration; the structure of their bones is very similar to that seen in larger animals including humans, for example unlike some smaller rodents they have structures known as  Haversian canals that affect bone growth and repair, while their size allows more complex surgery than is possible with smaller rodents.

Tissue engineering techniques we have discussed previously, such as the artificial lung, involved seeding a scaffold, were created by stripping cells from donor tissue, seeding with stem cells, and then allowing the cells to grow in vitro to produce a functioning organ. The technique reported this week differs in that the scaffold was made from an artificial bio-polymer, and rather than implant stem cells into the scaffold and growing the tissue in vitro, they coated the scaffolds with the growth factor known as TGFβ3 and then implanted it into the rabbits. TGFβ3 attracts bone and cartilage precursor cells to the scaffold, where they multiply and after a few weeks have formed a functioning joint.  When they compared scaffolds coated with TGFβ3 to bare scaffolds, they observed that more precursor cells were recruited to the scaffold when TGFβ3 was present, and that the rabbits transplanted with TGFβ3-coated scaffolds moved more easily when assessed one to two months after surgery, indeed the joints were able to support the weight of the rabbits without any limping.

Rabbits play an important role in medical research. Image courtesy of Understanding Animal Research.

This technique is significantly simpler than those approaches that require stem cell seeding and in vitro growth prior to transplant, and might be especially useful for younger hip transplant patients, individuals aged 65 or younger. Younger patients would be expected to recover more quickly, have fewer co-morbidities that would be aggravated by staying in bed for a prolonged time to allow the tissue to regenerate, and would benefit more from not having to have hip operations every 10-15 years as is currently the case with metal hip joints.  For more elderly patients metal hip joints are likely to remain the best option.

So does this technique replace that used in the tissue engineering studies we have previously discussed? Well, the answer is no, for some applications either approach might work, but for others, for example the artery and lung transplants, the tissue needs to be capable of functioning immediately following transplant. One aspect that is being evaluated elsewhere is the use of biopolymer scaffolds, which are being used with stem cells to produce replacement blood vessels, and may provide a more flexible and reliable alternative to the use of decellularized tissue.

It’s an interesting development, and one that again highlights how quickly things are happening in the field of tissue engineering. Of course it will be some time before clinical trials in humans start, before then this technique must be evaluated in a larger animal, probably a pig, to determine whether tissue regeneration on the scaffold is rapid and effective enough in a model of comparable sizes to humans. Only if these tests are successful will this technique warrant evaluation in a human clinical trial.

Paul Browne

Microbicide gel cuts HIV infection rates…thank the monkeys!

There was exciting news on Monday when it was announced at an international AIDS conference in Vienna that microbicide gel had dramatically reduced the transmission of HIV in a Phase 2 clinical trial involving 889 women in South Africa.  If confirmed by  larger phase 3 trials this gel will offer millions of women a way to protect themselves against this dread disease that blights communities around the world.

Dr Abdool Karim explains how to use a microbicide gel applicator. Image courtesy of CAPRISA.

Unlike previous microbicide gels that failed to offer significant protection against HIV infection this gel included the anti-retroviral drug tenofovir. Regular readers of this blog may recognize tenofovir, it was discussed in an article on the role of non-human primate research in developing HIV prophylaxis by virologist Dr. Koen Van Rompay that we posted last year.  Dr. Van Rompay’s article looked at the use of oral tenofovir in pre- and post-exposure prophylaxis rather than its use in a microbicide gel.

So did the research on preventing SIV transmission in monkeys influence the decision to use tenofovir in this microbicide gel? You betcha! In the first report of a Phase 1 trial of this tenofovir-containing microbicide gel published in 2006 (1) the authors state that the success of tenofovir in preventing SIV infection on monkeys – the same research discussed by Dr. Van Rompay – was a deciding factor when they took this gel into clinical trials.

‘Tenofovir gel, 9-[(R)-9-(2-phosphonylmethoxyprophyl) propyl]adenine monohydrate, a nucleotide reverse transcriptase inhibitor, has demonstrated ability to inhibit retroviral replication in animals and humans, and it has been well tolerated when used orally, as tenofovir disoproxil fumarate, (tenofovir DF; Viread) [16–20]. Tenofovir DF has been approved for treatment of HIV-1 infection and is increasingly used as part of therapeutic regimens for HIV-positive individuals [21]. Tenofovir has been proven to be effective in blocking the transmission of SIV in animal models when given as pre- or postexposure prophylaxis systemically or when applied as an intravaginal gel [22–25]. Tenofovir bisphosphate, the active intracellular moiety, has a very long intracellular half-life (> 72 h), which could allow for more convenient, coitally independent intravaginal use [26]. Given the data showing animal protection with tenofovir gel, and the extensive human safety data with oral tenofovir in HIV-positive patients, the HIV Prevention Trials Network (HPTN) decided to assess the safety and tolerability of tenofovir gel in HIV-negative and HIV-positive women and their male sexual partners (HPTN 050).’

The above passage also mentions that they tested whether the microbicide gel containing tenofovir could prevent vaginal SIV transmission in monkeys*, and the finding that it could drove their subsequent decision to take the gel into clinical trials.  This was an important decision, a review of HIV microbicide gels published in the journal Science (2) two years ago pointed out the failure to evaluate other microbicide gels in monkey models of HIV transmission allowed these gels to proceed into clinical trials where they subsequently failed.  It is notable that the microbicide PRO 2000, also evaluated in monkeys, is the only other microbicide to demonstrate an ability (albeit less dramatic) to prevent HIV infection in clinical trials.

So what now? Well the tenofovir containing gel will go on into larger phase 3 trials to further evaluate its ability to prevent HIV infection in women. In the meantime following a study showing that it can prevent the transmission of rectal SIV transmission in macaques (3) this gel is now in phase 1 safety trials in men.

This is welcome news after years of disappointment, and further evidence that where HIV is concerned there can be no shortcuts; all therapies whether microbicide gels or vaccines must be thoroughly evaluated in stringent animal models before being taken to human clinical trials. Perhaps now we can start to turn realism into optimism.

In other news this week, Americans for Medical progress have announced the 2010 Michael D. Hayre Fellows in Public Outreach. Neuroscientists Elizabeth Burnett and Scott Dobrin will use the fellowship grant to develop their project “Speaking Honestly – Animal Research Education (SHARE)”, which is designed to guide educators in leading classroom discussions on the humane use of animals in research in an engaging and interactive manner. We wish them the very best as they follow in the footsteps of the first Hayre fellow, Speaking of Research founder Tom Holder.

* Unfortunately this study was never published in the scientific literature, this is something that sometimes happens with pre-clinical studies performed by biotechnology and pharmaceutical companies…usually because they wish to keep the work confidential for commercial reasons…and is a source of great frustration to people like me who write about this work!

Paul Browne

1)      Mayer K.H. et al. “Safety and tolerability of tenofovir vaginal gel in abstinent and sexually active HIV-infected and uninfected women.” AIDS. volume 20(4), pages 543-551 (2006), DOI:10.1097/01.aids.0000210608.70762.c3.

2)      Grant R.M. “Whither or wither microbicides?”  Science. Volume 321(5888), pages 532-534 (2008), PubMed Central:PMC2835691.

3)      Cranage M. et al. “Prevention of SIV Rectal Transmission and Priming of T Cell Responses in Macaques after Local Pre-exposure Application of Tenofovir Gel” PLoS Med. Volume 5(8):e157(2008) DOI:10.1371/journal.pmed.0050157

Shots without jabs: The future of vaccination.

Vaccines make a crucial contribution to public health, saving hundreds of millions of people from deadly or debilitating diseases every year, but it’s also fair to say that getting your shots is not the most pleasant of experiences. It’s not just a question of short term discomfort, many people suffer from needle phobias that can prevent them from getting necessary vaccination, and wherever you have used used hypodermic needles there is always the question of safe disposal of this biohazardous waste and the risk of needle stick injury. Now research conducted on mice and pigs at Emory University and the Georgia Institute of Technology shows that there may be a safer and less painful way to administer vaccines (1).

Dissolving polymer microneedle patch for vaccine delivery. Image Courtesy of the Georgia Institute of Technology.

The new vaccine patch uses an array of one hundred tiny needles to deliver the vaccine painlessly into the skin, but the clever part is that having done so the needles, which are made from a polymer material known to be safe for clinical use, dissolve within a few minutes so there is no hazardous sharps waste to be disposed of.  This is a significant advantage over previous microneedle patches that used metal or silicon needles. The vaccine is also injected in a solid form which makes it stable and less likely to break down in storage, an important consideration for clinics in developing nations and remote areas of the world.

So how do they know it works? Well they first had to make sure that the needles could deliver the vaccine into skin without breaking, and then quickly dissolve. The team led by Sean Sullivan assessed this using skin obtained from freshly slaughtered pigs, because pig skin is very similar to human skin in thickness and structure, and found that the microneedles delivered the vaccine successfully and then quickly dissolved.

Microneedles immediately after application of the patch to pig skin. Image courtesy of Georgia Institute of Technology.

Of course delivering a vaccine into the skin is not enough, you have to know if that vaccine will stimulate the desired response from the immune system. The team needed to assess whether the vaccine patch could provoke an immune response that is strong enough to protect against subsequent infection, and this is something that can only be properly done in a living animal.  When the vaccine patch was used to immunize mice with an influenza virus vaccine it provoked a robust and sustained response from the immune system, one that was in fact better than that observed with traditional intramuscular injection. Furthermore the vaccine patch immunized mice survived when infected with influenza virus three months after immunization, whereas all non-immunized control mice died.

Microneedles dissolving one minute after application of patch to pig skin. Image courtesy of Georgia Institute of Technology.

Vaccine patches promise a safe, painless and cheap alternative to vaccination via hypodermic needle, and as someone who likes to keep their shots up to date I’m hoping that this new method will succeed in human trials and soon be available in the clinic.

Paul Browne

1)      Sullivan S.P. et al. “Dissolving polymer microneedle patches for influenza vaccination”  Nature Medicine, Published Online 18 July 2010 DOI:10.1038/nm.2182

Now the Oscar for Best Biomedical Research

A cutting edge procedure performed by Dr. Noel Fitzpatrick (star of the BBC’s new show The Bionic Vet) provided Oscar a new way to walk around, which means that he will not need to be euthanized. This video caught my attention and still is exciting to watch. I decided to look into the story behind the bionic surgery success story.

Here’s a quick timeline

Regards

Andrea Knipe

Animal Research – Interview Technique

I would like to share an old news debate on animal research between Simon Festing (Chief Executive of Understanding Animal Research) and Nicky Gordon (Dr. Hadwen Trust):

There is much that can be learned from Simon’s interview technique.

  • Have information on the benefits of animal research readily to hand – Simon looked ready to list 100’s of examples, bolstering his argument
  • Use recent examples – such as Herceptin – prevents others accusing scientists of only looking to decades gone
  • Interject if necessary, but keep it short – Simon’s counter-point at 2:25 effectively destroys Vicky’s argument
  • Although “millions of people can’t be wrong” is not a good argument, pointing to the weight of expert scientific opinion behind animal research is!

Scientists and other university officials around the world are going to need to become more confident with talking about the benefits of animal research rather than using their limited time in the news condemning extremists. Condemning extremists is important – but it is made more effective by pointing to the damage they do to lifesaving medical science.

Regards

Tom