DEBATE ON HIV ENVELOPE AS A T CELL IMMUNOGEN HAS BEEN GAG-GED Viv Peut Kent Laboratory, University of Melbourne, Australia
WHY ENVELOPE? Env subject to both humoral and cellular immune responses Perhaps multiple rounds of mutation would be required for effective immune escape May result in virus with reduced fitness Lower viral fitness = Lower viral load (VL) - slower progression to disease - reduced transmission rates
VERY UNFIT VIRUS
HOWEVER... Gag has recently been shown to elicit a more effective CD8 T cell response in humans. Broad Env-specific CTL responses correlated with higher levels of viremia. (Kiepiela et al., Nat Med 2007) Gag-specific CD8 T cell clones more efficient than Envspecific CD8 T cells in limiting viral replication in vitro. (Chen, Walker, 4th IAS Conference, Sydney, 2007) Gag presented much earlier than other HIV proteins. (Sacha et al., J Immunol, 2007)
OUTLINE OF TALK What is VL outcome of macaques responding to Env vs those responding to Gag? X4-SHIV trial analyzed What is the pattern of immune escape at Env compared to Gag? Kinetics of escape Diversity of escape motifs What is effect of therapeutic immunization with only Gag vs all SIV proteins? R5-SIVmac251 study Viral load Immunodominance
THE SHIVmn229 TRIAL IN 30 PIGTAIL MACAQUES Vaccination SHIV DNA and fowlpoxvirus vaccines expressing Gag and Env (De Rose et al., J Virol, 2007) - HIV-1 Env truncated - no induction of neutralizing antibodies (NAb) Challenge Heterologous X4-utilising SHIV mn229 Env-specific T cell epitope identification Eight Env-specific CD8 T cell epitopes mapped in 10 animals identified by Intracellular cytokine staining (ICS)
Viral Load (log 10 copies/ml plasma) CD4 Lymphocytes (%) 8 7 6 5 4 3 40 30 20 10 VL AND CD4 LEVELS - ENV vs GAG A. Env CD8 T Cell Responders vs Non Responders Non responders 0 5 10 15 20 B. Responders 0 0 5 10 15 20 Weeks Post Challenge
Viral Load (log 10 copies/ml plasma) CD4 Lymphocytes (%) 8 7 6 5 4 3 40 30 20 10 VL AND CD4 LEVELS - ENV vs GAG A. 0 5 10 15 20 B. Env CD8 T Cell Responders vs Non Responders Non responders Responders 40 30 20 10 8 7 6 5 4 3 C. Gag CD8 T Cell Responders vs Non Responders 0 5 10 15 20 D. Non responders Responders p = 0.01 p = 0.02 0 0 5 10 15 20 Weeks Post Challenge 0 0 5 10 15 20
Poster #PO8-08
KINETICS OF ESCAPE - ENV vs GAG Gag vs Env epitope escape kinetics 100 80 % Wild Type Virus 60 40 20 6349 NL9 5350 NL9 6349 SP9 6167 SP9 5350 SP9 6279 RY8 6259 RY8 4253 AF9 4296 KW9 4246 KP9 4292 KP9 Env Gag 0 0 1 2 3 4 5 6 7 8 9 10 11 Weeks Post Challenge p = 0.04
NUMBER OF MUTANT QUASISPECIES - ENV vs GAG 4 p = 0.03 I7S9 C8 G1R8 I7 Number of Total Mutant Quasispecies at week 8 post infection 3 2 1 0 Epitope KP9 Animal ID 4246 (#) clones (10) R2 R2 2aa R1 H8 del KP9 4292 (9) AF9 4253 (28) KW9 4296 (23) G1 R3 RY8 6259 (12) G3 R3 T5 RY8 6279 (23) N1 S9 S9 E8 SP9 5350 (16) N6 R8 I6 SP9 6167 (11) GI S9 SP9 6349 (14) 5aa del G4 N3 NL9 5350 (15) E4 NL9 6349 (11) Gag Epitopes Env Epitopes
BROAD vs NARROW RESPONSE Compare Gag and Env - specific CD8 T cell responses elicited by a Gag, Env, Pol and accessory proteins combined (OPAL All) vaccination with a Gag-alone vaccination (OPAL Gag). Overlapping Peptide-pulsed Autologous Leukocytes (Kent et al., Poster, #P09-06)
OPAL - WHAT IS INVOLVED 18 ml blood draw PBMC Pulse PBMC with Overlapping 15mer peptides (ALL or GAG) 1 h at 37 o C IV infuse PBMC back into same animal Vaccinated or Infected Pigtail Macaque IFNγ BEFORE treatment 10 5 10 4 10 3 10 2 0 ABCDEFGHIJKLMNO EFGHIJKLMNOPQRS IJKLMNOPQRSTUV MNOPQRSTUVWXYZ Experimental Design * 36 pigtail macaques * Infected with SIVmac251 * Treated with antiretrovirals (Tenofovir, FTC) * Immunised with - Gag peptide 10 - All SIV peptides (including Gag) 4 - Controls * Recrudescence of VL studied 2 weeks AFTER treatment CD8 CD4 0 CD8 CD4 10 5 10 3 Intracellular IFNγ Assay 0 10 2 10 3 10 4 10 5 0 10 2 10 3 10 4 10 5
7 6 5 Viral Load (by Treatment Group) ΔVL = 0.93 log 10 (p = 0.01) Control OPAL All OPAL Gag 4 3 0 4 8 12 16 20 24 28 32 36 Week post SIV infection
GAG-SPECIFIC CD8 T CELL REPONSES IFNγ Gag responses - OPAL Gag 7 6 5 4 3 2 1 7 6 5 4 3 2 1 Gag responses - OPAL All 0 6804 8012 8020 8244 8454 8673 8873 9196 0 1.3731 8240 8251 8680 8682 9020 9021 9175 Animal ID At same dose of Gag in both groups, why are Gag responses reduced in the OPAL All group???
NEVER THE TWAIN SHALL MEET - Gag OR Env but rarely both Week 12 post infection in the ALL group SIV Gag-specific CD8 T cell (% IFNγ+ cells) Including 2 extreme Env-specific responses SIV Env-specific CD8 T cell (% IFNγ+ cells) Excluding 2 extreme Env-specific responses
DOMINANCE?
DOMINANCE? COMPETITION?
IN A NUT SHELL Characteristics Maintain lower viremia Gag Env
IN A NUT SHELL Characteristics Gag Env Maintain lower viremia Early and rapid CD8 T cell escape (Gag-specific CTL exerts vigorous selection pressure)
IN A NUT SHELL Characteristics Gag Env Maintain lower viremia Early and rapid CD8 T cell escape (Gag-specific CTL exerts vigorous selection pressure) Low diversity of escape mutants (Gag more constrained in its mutational manoeuvres )
IN A NUT SHELL Characteristics Gag Env Maintain lower viremia Early and rapid CD8 T cell escape (Gag-specific CTL exerts vigorous selection pressure) Low diversity of escape mutants (Gag more constrained in its mutational manoeuvres ) Strong response regardless of other CD8 T cell responses (broadest multi-protein responses may not always be the most useful)
FUTURE WORK Are a subset of HIV Env-specific T cell responses helpful? Prevent Env responses dominating Gag responses T cell mapping and escape studies in SIV Env Explore the relationships between CD8 T cell escape, NAb escape and N-linked glycosylation sites. (Peut et al., Poster #P03-06)
ACKNOWLEDGEMENTS Stephen Kent and all the lab and macaque facility staff M. Davenport & J. Petravic University of NSW Scholarships AChSHM GlaxoSmithKline Univ Melbourne AIDS Vaccine 07 NHMRC NIH Australian-Thai HIV Vaccine consortium