Michael Palm Basic Science, Vaccines & Prevention Project Weblog

Peptide-Pulsed Blood as an Immunization Strategy

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

Control of Viremia and Prevention of AIDS following Immunotherapy of SIV-Infected Macaques with Peptide-Pulsed Blood

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.

Souping Up Therapeutic Vaccines

Two new papers in the advance online section of the Journal of Experimental Medicine report that blocking immunosuppressive signals can give therapeutic immunization a boost. The studies follow on from work covered on the blog previously in which the IL-10/IL-10 receptor and PD-1/PD-L1 signaling pathways were identified as key contributors to viral persistence in the mouse model of chronic infection with lymphocytic choriomeningitis virus (LCMV).

In the first paper, David Brooks and colleagues from Mike Oldstone’s laboratory at Scripps show that combining DNA vaccination with an antibody blocking the IL-10 receptor leads to improved LCMV-specific CD4 and CD8 T cell function and accelerated clearance of the virus from chronically infected mice. In the second paper, Sang-Jun Ha and a team from Rafi Ahmed’s lab at Emory University report that immunization with a vaccinia vector encoding a single CD8 T cell epitope from LCMV also accelerates viral clearance when combined with an antibody blocking PD-L1 (the ligand for the molecule PD-1). The vaccine had no effect when given alone. In addition, these researchers demonstrate an effect of the vaccine plus PD-L1 blockade in mice transiently depleted of CD4 T cells, suggesting that the approach might have an impact in settings of CD4 T cell deficiency.

Both groups conclude by citing each other’s work and noting that, taken together, the results indicate that immunosuppressive signaling in chronic infection may explain the disappointing results of most therapeutic vaccination studies conducted to date. The authors also argue that their data point toward new strategies for boosting the impact of therapeutic immunization. In the hopeful closing words of Brooks et al: “a similar dual immunotherapeutic adjuvant/vaccination strategy that alleviates immunosuppressive signals while boosting immunity may stimulate effective, long-term, immune-mediated control of persistent viral infections in humans, and may also be an adjuvant for primary vaccination.”

The Journal of Experimental Medicine
Published online 10 March 2008
doi:10.1084/jem.20071948

BRIEF DEFINITIVE REPORT

IL-10 blockade facilitates DNA vaccine-induced T cell responses and enhances clearance of persistent virus infection

David G. Brooks1, Andrew M. Lee1, Heidi Elsaesser1, Dorian B. McGavern1, and Michael B.A. Oldstone1,2

1 Viral-Immunobiology Laboratory, Department of Molecular and Integrative Neuroscience, and 2 Department of Infectology, The Scripps Research Institute, La Jolla, CA 92037

Therapeutic vaccination is a potentially powerful strategy to establish immune control and eradicate persistent viral infections. Large and multifunctional antiviral T cell responses are associated with control of viral persistence; however, for reasons that were mostly unclear, current therapeutic vaccination approaches to restore T cell immunity and control viral infection have been ineffective. Herein, we confirmed that neutralization of the immunosuppressive factor interleukin (IL)-10 stimulated T cell responses and improved control of established persistent lymphocytic choriomeningitis virus (LCMV) infection. Importantly, blockade of IL-10 also allowed an otherwise ineffective therapeutic DNA vaccine to further stimulate antiviral immunity, thereby increasing T cell responses and enhancing clearance of persistent LCMV replication. We therefore propose that a reason that current therapeutic vaccination strategies fail to resurrect/sustain T cell responses is because they do not alleviate the immunosuppressive environment. Consequently, blocking key suppressive factors could render ineffective vaccines more efficient at improving T cell immunity, and thereby allow immune-mediated control of persistent viral infection.

The Journal of Experimental Medicine
Published online 10 March 2008
doi:10.1084/jem.20071949

ARTICLE

Enhancing therapeutic vaccination by blocking PD-1–mediated inhibitory signals during chronic infection

Sang-Jun Ha1, Scott N. Mueller1, E. John Wherry1, Daniel L. Barber1, Rachael D. Aubert1, Arlene H. Sharpe2, Gordon J. Freeman3, and Rafi Ahmed1

1 Emory Vaccine Center and Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322
2 Department of Pathology, Harvard Medical School and Brigham and Women's Hospital, 3 Department of Medical Oncology, Dana-Farber Cancer Institute, Department of Medicine, Harvard Medical School, Boston, MA 02115

Therapeutic vaccination is a potentially promising strategy to enhance T cell immunity and viral control in chronically infected individuals. However, therapeutic vaccination approaches have fallen short of expectations, and effective boosting of antiviral T cell responses has not always been observed. One of the principal reasons for the limited success of therapeutic vaccination is that virus-specific T cells become functionally exhausted during chronic infections. We now provide a novel strategy for enhancing the efficacy of therapeutic vaccines. In this study, we show that blocking programmed death (PD)-1/PD-L1 inhibitory signals on exhausted CD8+ T cells, in combination with therapeutic vaccination, synergistically enhances functional CD8+ T cell responses and improves viral control in mice chronically infected with lymphocytic choriomeningitis virus. This combinatorial therapeutic vaccination was effective even in the absence of CD4+ T cell help. Thus, our study defines a potent new approach to augment the efficacy of therapeutic vaccination by blocking negative signals. Such an approach may have broad applications in developing treatment strategies for chronic infections in general, and perhaps also for tumors.

Provenge: An Approvable Therapeutic Vaccine?

The idea that vaccines might be used as therapies in some settings was first proposed by Robert Koch more than a century ago. But despite much study, there remains very little data suggesting any efficacy of vaccination against an established disease. The only approved uses of vaccines that might be considered vaguely therapeutic are rabies and smallpox when given very quickly after exposure  (for a great overview on therapeutic vaccination see this presentation by Mike Lederman). Now, according to recent releases from a company called Dendreon, it appears that the US Food and Drug Administration may be on the verge of approving a therapeutic vaccine for prostrate cancer called Provenge. To quote from yesterday's press release from Dendreon:

"Dendreon recently held a pre-BLA meeting with the FDA to review safety and efficacy data from its two completed Phase 3 clinical trials of PROVENGE, D9901 and D9902A, in men with asymptomatic, metastatic, advanced prostate cancer. In these discussions, the FDA agreed that the survival benefit observed in the D9901 study in conjunction with the supportive data obtained from study D9902A and the absence of significant toxicity in both studies is sufficient to serve as the clinical basis of a BLA submission for PROVENGE. As a result of that meeting, Dendreon recently announced plans to submit a BLA to the FDA in 2006 to market PROVENGE for the treatment of men with asymptomatic, metastatic, androgen-independent prostate cancer."

A BLA is a Biologics License Application, the equivalent of a New Drug Application or NDA for biological products like vaccines and cytokine therapies. While unfortunately this does not mean that therapeutic vaccines for HIV are right around the corner, it does offer some hope that the immune system can be prodded into exerting useful therapeutic effects and may address the most commonly cited reason for pessimism about prospects for therapeutic vaccines: the lack of an effective precedent .

Thanks to Daniel Raymond, Policy Director for the Harm Reduction Coalition and presider over the Hepatitis C Harm Reduction Project blog, for alerting me to this release.