rose: Hi everyone sorry about that - I couldn't see the chat on my computer but it is fixed now
rick: morning Rose and weklcome to the OmniChat
kathy admin: Thanks, Rose. CAn we start off with a question?
rose: Of course
kathy admin: students? question, anyone?
phoebe lee: As for the vaccines targeting anthrax is not that effective, and that HIV can undergo mutation so quick, how could that vaccines for HIV-1 be effective to those 3 types of responses?
rose: Mutation is a major problem is designing a vaccine for HIV - we need to produce different vaccines for different parts of the world, and also put in as much of the genetic sequence as we can safely include.
mary: Can you talk a bit about how the fowlpox works to boost the HIV vaccine?
rose: The vaccine strategy we are using is to include some of the HIV sequence in two different vectors - one is a DNA plasmid, which will initiate the cellular immune response, which will then be boosted using the same HIV sequences expressed by a recombinant fowl pox virus
mary: So the sequences used are the same in the 2 vectors?
rose: Yes this gives the prime and boost effect. Both vectors will express the HIV genes (at relatively low levels) and these antigens will stimulate T cell responses.
amy: What geographic trends have you seen in HIV-1 mutations that make it necessary to design different vaccines for different parts of the world?
rose: In Australia we have predominantly clade B virus, so our first vaccine will be a clade B sequence for the HIV genes. This is fine for Australia and other Western countries that have this virus, but to test the vaccine in countries with higher prevalence or newer epidemics we need to use the predominant circulating strain. In our case this will be and A/E vaccine for the pahse II trials in Thailand next year.
samiran: are there any retroviruses known that have a low mutagenesis rate? are there any known retroviral mismatch repair genes etc. known that could be introduced into the HIV genome?
rose: Well I am not a virologist, but I understand all retroviruses, and othe RNA viruses that use a reverse transptase or an RNA dependent RNA polymerase all lack proof reading capacity, and so have high error rate. It is an interesting idea to include an enzyme that could fix these errors artificially, but you would actually have to infect peopl with the recombinant virus, and I dont think many people would be too keen to try this as a treatment strategy.
mary: Which strain(s) does the CCRV deletion seem to be most associated with in LTNPs, and does this appear to be a fairly recent evolutionary stage?
mary: CCR-5, I meant---
rose: Most infections with HIV are caused by a CCR5 using strain, which then later mutates to be able to use other co-receptors. The mutation in CCR5 appears to slow decrease progression in people who are heterozygous, and often prevent infection in people who are homozygous for the deltion. There does not seem to be any effect of the clade of virus, but it is interesting that the deletion is relativley recent, and appears to have arisn in the middle ages. It is not found in Africans, but is a caucasion mutation.
phoebe lee: refering to the recombinant virus, as there are species share the same gene w/ human genome, will that be possible to have trial in those "rats" prior to ppl? and for cats also carry HIV (somehow) can we investigate those genome as reference?
rose: One of the difficulties of HIV research is the species specificity of the virus. HIV really only infects human, chimps and othe primates. There is no good animal model, so some people use the mouse immunodeficency virus, or the feline virus as models. The closest model we have used is the simian human hybrid virus infection of macaques, which although not perfect does cause HIV like disease.
amy: About CCR5 again, are there any known adverse side effects of the CCR5 deletion? Does CCR5 have other known functions?
phoebe lee: there is a small group of ppl that are genetically HIV resistant, is there any possibility to have their allele clone to other infected individuals and see the effects?
rose: Those that are resistant to HIV generally have mutations in the CCR5 genes are described below. Some drug companies are designing molecules to block HIV binding to CCR5, as these individuals obviously can get by without at functioning CCR5 molecule as there is a lot of redunancy in the chemokine receptors and their ligands.
kathy han: Delta-32 homozygosity for the CCR-5 gene doesn't always prevent HIV infection. In this case, the virus can presumably infect independently of the presence of a functional CCR-5 coreceptor?
rose: Yes the virus is able to use one of the minor co-receptors if there is no CCR5 present.
samiran: how about cell to cell transfer by syncytia? can this mechanism of infection sustain a HIV population even if neutralizing antibodies can be devised?
rose: Syncytia formation is usually a function of virus that arises later in the course of disease progression to utilise the CXCR4 receptor. If you could elicit neutrliasing antibody that would prevent the spread of the CCR5 using virus that is usually found early after infection this might prevent the establishment of chronic infection. However as you know neutralising antibodies are difficult to elicit with HIV gp120, and the virus soon mutates to escape from this selective pressure.
phoebe lee: as ppl of HIV resistance, can mutation to CCR5 be induced to those infected and hence further reproduction of the virion can be stopped and treatment can be performed? also, instead of targeting CCR5 and T cell binding, how bout that reverse transcriptase?
rose: I dont think mutating a functioning human gene would be seen as an attractive treatment strategy. Rather competition for binding with a synthetic ligand that binds CCR5 but does not signal or internalise the receptor is possible. There are currently many effective drugs that target the reverse transcriptase, including the nucleoside analogues such as AZT and the non nuceosides such as nevirapine. These drugs are now usually used in combination with a protease inhibitor, which targets another enzyme critical in the viral life cycle.
delia: i have heard about linear expression elements (LEE) to rapidly design a DNA vaccine. Can you comment on this and is this applicable for HIV vaccines?
amy: If drug companies come up with a molecule that will prevent HIV binding to CCR5, do you think infection with HIV would be prevented for a time in most innoculated people for, then rise again after viruses using other coreceptors become more prevalent?
rose: Yes because of the high inherent mutation rate of the virus, I think it would quickly mutate to use another co-receptor. I think if these drugs are to be effective they would have to be used in combination with the other drugs that target other parts of the viral life cycle.
rose: Re the question about linear expression elements, I do not have any experience with designing a vaccine using this system. How do you think this might improve the current DNA vaccines?
phoebe lee: in fact that targeting viral life cycle could be effective for a period of time with combination of other drug uses, but shouldn't the genome of the virus is lethal as high inherent mutation presence?
delia: it was cited as one of the promises in a bioinformatics seminar i attended, but the speaker did not elaborate.
rose: Combination drugs are often able to completely control viral replication, so there is very litlle replication occurring, and so greatly reduced chance of mutations being selected. Theoretically if people wer able to keep with these complex regimens that often cause quite nasty side effects, they wouldn't ever progress to AIDS
rose: On the DNA plasmid question, there have been many recent developments in DNA delivery technology that has really increased the immunogenicity of the inserted gene of interest. Some such as the CpG sequences we are using, increase the immune response by targetting the innate immune response via the toll-like receptors, and so amplify the induction of the specific cellular immune response
kathy admin: We have a few minutes left; perhaps Rose can field just one or two more brief questions, before we end this session...
amy: I'm curious whether infants infected with HIV-1 progress faster, slower, or at the same rate as adults? Is there a trend, or is it too variable?
phoebe lee: is there any common weakness and strength in vaccines on targeting HIV according to the responses on infected ppl?
rose: There are two major patterns in infants - one group prgresses very fast, and without treatment often dies before 12 months of age. This often occurs in developing countries were there are other issues of nutrition and lots of environmental pathogens. The second pattrn is to have a fairly similar rate of progression as adults, with a similar rate of T cell decline, and so they live until about 10 or 12 without treatment. Of course in Australia now all babies will be treated from birth, and in fact we dont see many babies even getting infected now, and those that do are living long and fairly normal lives.
rick: Rose - on behalf of us all, we thank you for your time and skill in answering questions in this unusual way. I did prove to be a very effective chat session and one which everyone will have benefitted from greatly. For your interest, you have just been chatting with students and professors from Portugal, USA, Taiwan, UK, Philippines and of course Australia. There will be three more 'special guest' chats this week (see Activity#3 for times) and you are of course welcome to drop in if you so wish. Once again thanks for joining in with VSG.
rose: In response to Phoebe's question yes I think there may be different responses in people who are resistant compared to those who have become chronically infected, and we probably want to target the former. Andrew McMichael's group in Oxford has developed a vaccine that they are now testing in nairobi, where they have included T cell epitopes defined in the population of resistant sex workers in an attempt to mimic the succesfful immune responses.
rose: Thanks to everyone - it was very interesting.
kathy admin: Thank you so much, Rose. We've really enjoyed this most informative session. Please do stay in touch.
amy: Thanks for taking the time to share your expertise with us, Dr. Ffrench. You've taught me a lot in a short time.
mary: Thank you very much for sharing your busy day and your great knowledge with us.
rose: No problems. I will have a look at the questions posted ealier and try to answer any of those I have missed this morning.
phoebe lee: Thanks very much for answering all these question :)
Have a great day Rose
samiran: thank you very much - the discussion was enlightening
kathy admin: Bye Rose! The rest of you are welcome to continue chatting... or working on your projects. I've got to zip across to the other side of town to meet rick now... catch you all later...
delia: thank you so much for this unusual but enjoyyable experience, Dr. Ffrench, and the rest of us here. Good day, have to log out now. will be back later. Have a great day, everyone!
|
