Don't usually post on weekends but I think this team of Australian researchers deserves recognition for particularly inspired use of the NIH AIDS Reagent Program. While the wider vaccine field wrestles with the challenges of inducing broad and high magnitude T cell responses, this team from Stephen Kent's lab has developed a strategy where multiple peptides obtained from the reagent program are simply mixed with unfractionated peripheral blood mononuclear cels (PBMC) and reinfused:
"All isolated PBMC (on average 24 million cells) were suspended in 0.5 ml of normal saline to which either a pool of 125 SIVmac239 Gag peptides or 823 peptides spanning all SIVmac239 proteins (Gag, Pol, Env, Nef, Vif, Tat, Rev, Vpr, Vpx) were added at 10 µg/ml of each peptide within the pool. Peptides were 15mers overlapping by 11 amino acids at >80% purity kindly provided by the NIH AIDS reagent repository program (catalog numbers 6204, 6443, 6883, 6448-50, 6407, 8762, 6205)."
Using this approach as an immunization strategy in a relatively large study of SIV-infected pigtailed macaques, they induced high-magnitude SIV-specific CD4 and CD8 T cell responses which were associated with durable viral load reductions of close to 1 log compared to controls after cessation of antiretroviral therapy. These are among the best results reported from therapeutic immunization in the SIV model. The viral load data was independently verified in a blinded analysis by Jeff Lison and Michael Piatak from the National Cancer Institute. Kent has now formed a company to develop the approach for human use under the acronym OPAL. According to the discussion section of the paper, the approach may even be viable using whole blood instead of PBMC. Although it would not be ideal in terms of practicality, it is tempting to wonder if this type of approach could be evaluated as a preventive vaccine strategy, particularly given recent data suggesting the importance of inducing a broad response to multiple epitopes in Gag.
The study also offers an opportunity to salute the NIH AIDS Reagent Program itself; when talking to HIV researchers, the program is consistently complimented for the services it provides. At the moment the program website is promoting the biannual feedback campaign, any researchers interested in providing input can fill out a brief online survey (the closing date is tomorrow, May 4).
PLoS Pathog 4(5): e1000055. doi:10.1371/journal.ppat.1000055
Robert De Rose1, Caroline S. Fernandez1, Miranda Z. Smith1, C. Jane Batten1, Sheilajen Alcântara1, Vivienne Peut1, Erik Rollman1, Liyen Loh1, Rosemarie D. Mason1, Kim Wilson2, Matthew G. Law3, Amanda J. Handley1,4¤, Stephen J. Kent1
1 Department of Microbiology and Immunology, University of Melbourne, Parkville, Victoria, Australia2 National Serology Reference Laboratory, Fitzroy, Victoria, Australia3 National Centre for HIV Epidemiology and Clinical Research, University of New South Wales, Sydney, New South Wales, Australia4 Opal Therapeutics Pty Ltd, Melbourne, Victoria, Australia
Abstract
Effective immunotherapies for HIV are needed. Drug therapies are life-long with significant toxicities. Dendritic-cell based immunotherapy approaches are promising but impractical for widespread use. A simple immunotherapy, reinfusing fresh autologous blood cells exposed to overlapping SIV peptides for 1 hour ex vivo, was assessed for the control of SIVmac251 replication in 36 pigtail macaques. An initial set of four immunizations was administered under antiretroviral cover and a booster set of three immunizations administered 6 months later. Vaccinated animals were randomized to receive Gag peptides alone or peptides spanning all nine SIV proteins. High-level, SIV-specific CD4 and CD8 T-cell immunity was induced following immunization, both during antiretroviral cover and without. Virus levels were durably ~10-fold lower for 1 year in immunized animals compared to controls, and a significant delay in AIDS-related mortality resulted. Broader immunity resulted following immunizations with peptides spanning all nine SIV proteins, but the responses to Gag were weaker in comparison to animals only immunized with Gag. No difference in viral outcome occurred in animals immunized with all SIV proteins compared to animals immunized against Gag alone. Peptide-pulsed blood cells are an immunogenic and effective immunotherapy in SIV-infected macaques. Our results suggest Gag alone is an effective antigen for T-cell immunotherapy. Fresh blood cells pulsed with overlapping Gag peptides is proceeding into trials in HIV-infected humans.
The concept is such a simple one that (in retrospect) I'm surprised we haven't seen it used before. It is a brute-force approach to generating a broadly-diverse T cell response. It lacks some elegance but who cars about elegance, if it works.
The use of 15mers is a little interesting. Though this is standard technique for stimulating CTL, 15mers are well above the optimum size for CTL recognition (they want to see 9- or 10mers). The advantage of 15mers, of course, is that you don't need as many; you can span the proteome with fewer 15mers than 10mers. It's believed (and has been shown in some cases) that the stimulation in this case comes not from the 15mers but from very small amount of contamination with shorter peptides. Here they used peptides that were >80% pure, and probably much of the remaining <20% encompass the range of shorter nested peptides within that. Using 10mers or 9mers might even induce better responses for CTL. (Or it might be worse, for various reasons.)
The other advantage of 15mers is that this is close to optimium size for CD4 responses, so they can trigger both forms of resposne with the same set of peptides.
There are still a lot of issues to resolve, but it's new and exciting direction.
Posted by: Ian | May 04, 2008 at 09:01 AM