Protective Immunity to HIV: What Animal Models of HIV Infection Can and Cannot Teach Us

1. Protective Immunity to HIV: What Animal Models of HIV Infection Can and Cannot Teach Us Models of Protective Immunity to HIV XVI International AIDS Conference August 13 – 18, 2006 Toronto, Canada Ruth Ruprecht, M.D., Ph.D.Dana-Farber Cancer Institute Harvard Medical School, Boston

2. What Are the Correlates of Protection?

3. What Are the Correlates of Protection? Λ Immune

4. Vaccine-induced Protection Could be Due to… • acquired immunity

5. Vaccine-induced Protection Could be Due to… • acquired immunity • innate immunity

6. Vaccine-induced Protection Could be Due to… • acquired immunity • innate immunity • both acquired and innate immunity

7. Vaccine-induced Protection Could be Due to… • acquired immunity • innate immunity • both acquired and innate immunity • viral interference (in the case of live attenuated SIV or SHIV)

8. Passive Immunization = Tool to Assess Correlates of Protection

9. Because rhesus monkeys are outbred and twin gestations are very rare, adoptive transfer of immune T cells is not feasible.Only the humoral arm of the immune system can be tested by passive immunization.

10. Passive Immunization: Cross-clade Protection

11. SIVmac239 HXBc2 HIV1157i env HIV1157i TM SHIV-1157i tat vif rev vpx gag vpu nef vpr LTR pol 1157i env LTR TM gp120 gp41 SHIV­1157ip: Summary • built from the SHIV-vpu+ backbone • env was derived from an HIV clade C strain, HIV1157i, a primary R5 strain isolated from a six-month old Zambian infant who was HIV positive at birth • replicates in rhesus macaque PBMC • uses only CCR5 as coreceptor • was adapted to rhesus monkeys by rapid animal-to-animal passage in five animals • results in high peak viral RNA levels and persistent infection in infant and adult macaques • was titrated orally in neonatal rhesus monkeys • shows signs of pathogenicity in rhesus macaques: persistent viremia, depletion of memory T cells, loss of absolute numbers of CD4+ T cells, AIDS, thrombocytopenia

12. Experimental Design oral SHIV-1157ip control (n=4) 4 100 weeks 0 1 2 oral SHIV-1157ip mAbs mAbs treatment with 4x mAbs i.v. (n=4) 1hr d8 0 1 2 4 100 weeks

13. Passive Immunization: 1h Post-Exposure Prophylaxis RPj-9 RTj-9 RWk-9 Week 40 7 RZk-9 RPk-9 RSj-9 5 RTk-9 log plasma viral RNA load RVj-9 (copies/ml) 3 1 0 30 60 90 Weeks after inoculation

14. The Correlates of Immune Protection • The human anti-HIV mAbs used in the quadruple combination completely protected monkeys against mucosal virus challenge. • These nmAbs, which recognize conserved epitopes and are active across clades, were the sole immune protective mechanism.

15. Epitope Specificity IgG1b12 : anti - CD4 binding site(b12)2G12 : complex epitope on gp120 dependent on correct N-linked glycosylation2F5 : linear gp41 epitope, ELDKWA 4E10 : linear gp41 epitope, NWFDIT

16. Correlates of Immune Protection IgG1b12 : anti - CD4 binding site(b12)2G12 : complex epitope on gp120 dependent on correct N-linked glycosylation2F5 : linear gp41 epitope, ELDKWA 4E10 : linear gp41 epitope, NWFDIT

17. Causes of Immune Protection IgG1b12 : anti - CD4 binding site(b12)2G12 : complex epitope on gp120 dependent on correct N-linked glycosylation2F5 : linear gp41 epitope, ELDKWA 4E10 : linear gp41 epitope, NWFDIT

18. Protective Epitopes IgG1b12 : anti - CD4 binding site(b12)2G12 : complex epitope on gp120 dependent on correct N-linked glycosylation2F5 : linear gp41 epitope, ELDKWA 4E10 : linear gp41 epitope, NWFDIT

19. Passive immunization with nmAbs is a tool to identify protective epitopes

20. AIDS Vaccine Development and Challenge Viruses in Primates – Getting Real

21. In order to be as predictive as possible, vaccine efficacy studies in non-human primate models should reflect the biology of HIV-1 transmission among humans as closely as possible.

22. HIV-1 Transmission Among Humans • 90% of all HIV-1 transmissions occur via mucosal exposure; this includes sexual transmission and mother-to-child transmission • mucosal HIV-1 transmission involves R5 viruses almost exclusively, even if the source person harbors predominantly X4R5 and X4 strains • recently transmitted strains of HIV-1 may be more sensitive to neutralization and encode shorter Env molecules than quasispecies that predominate in the source person (shown for clade C)1 1 Derdeyn et al., Science 2004; 303:2019-22; Li et al., J Virol 2006; 80:5211-8

23. Vaccine Challenge Studies in Primates: Getting Real… • mucosal route (intrarectal, intravaginal, oral) • R5-tropic virus • repeated low-dose vs. standard high-dose challenges • neutralization-sensitive virus • virus lacking overwhelming, acute pathogenicity • heterologous virus (with regard to vaccine)

24. Vaccine Challenge Studies in Primates: Getting Real… • mucosal route (intrarectal, intravaginal, oral) • R5-tropic virus • repeated low-dose vs. standard high-dose challenges • neutralization-sensitive virus • virus lacking overwhelming, acute pathogenicity • heterologous virus (with regard to vaccine)

25. Mucosal Challenge in Primates: Virus Dose Matters… • The standard single high-dose virus challenge, designed to yield > 95% chance of infecting unvaccinated controls, does not reflect the HIV-1 inocula during sexual transmission • High-dose challenge may overrun host defenses and set the bar for achieving protection too high

26. Repeated Low-dose Challenge: Lowering the Hurdle • Example: using an R5 SHIV, Kim et al.1 performed weekly intravaginal challenges at low doses (10 TCID) in monkeys. Group 1 received the vaginal microbicide CAP 15 min prior to each virus inoculation; controls remained untreated. Whereas all controls became systemically infected after 3 to 4 weekly exposures, 3 out of 4 monkeys given CAP microbi-cide remained uninfected after 12 exposures (p = 0.015). • CAP microbicide efficacy was 66% when tested against a single high-dose virus challenge; when tested against repeated low-dose challenges, efficacy was 92%. 1J Med Primatol 2006; 35: 210-6 CAP = cellulose acetate phthalate.

27. Vaccine Challenge Studies in Primates: Getting Real… • mucosal route (intrarectal, intravaginal, oral) • R5-tropic virus • repeated low-dose vs. standard high-dose challenges • neutralization-sensitive virus • virus lacking overwhelming, acute pathogenicity • heterologous virus (with regard to vaccine)

28. Neutralization Sensitivity: Avoid “Stealth” Envelopes • Late-stage viruses that have undergone multiple rounds of neutralizing antibody (nAb) selection followed by repeated escape develop more compact, hard-to-neutralize envelopes. • Using viruses with such impenetrable envelopes in primates may set the bar for achieving vaccine protection unrealistically high. • Neutralization resistance is an issue for SIVmac239 and primary SIVmac251 grown in rhesus monkey PBMC. • Essentially, nAb-based vaccines cannot be evaluated for efficacy with these challenge strains.

29. Vaccine Challenge Studies in Primates: Getting Real… • mucosal route (intrarectal, intravaginal, oral) • R5-tropic virus • repeated low-dose vs. standard high-dose challenges • neutralization-sensitive virus • virus lacking overwhelming, acute pathogenicity • heterologous virus (with regard to vaccine)

30. The chance of a human AIDS vaccine recipient to be exposed to an HIV-1 strain that exactly matches his/her vaccine approaches zero…

31. Heterologous Virus Challenge: Reflecting Viral Complexity in Real Life Given the many HIV-1 quasispecies and their increasing divergence with time, human AIDS vaccine recipients will not encounter viruses exactly matched to their vaccine. Vaccine efficacy testing in primates should reflect this reality. Exactly matching vaccine and challenge virus may overestimate the potential of new vaccines and raise unjustified expectations.Success with homologous virus challenges may also stimulate the development of vaccine strategies that yield highly protective but only narrowly focused immune responses that fail to protect against divergent viruses.

32. SHIV Challenges: Closer to the Real Thing • SHIV chimeras allow efficacy testing of HIV-1 Env-based vaccines. • SHIV chimeras allow testing of neutralizing antibodies isolated from HIV-1-infected individuals. • As such, vaccine development could be significantly accelerated because primate-tested reagents can be directly used in clinical trials. • In contrast, SIV challenges only allow the evaluation of active or passive immunization concepts but not the actual vaccines or antibodies intended for human use.

33. Summary • AIDS vaccine efficacy studies in primate models should focus on mucosal challenge with R5 strains • SHIVs have the added advantage of directly testing anti-HIV-1 Env responses • SHIVs allow development of passive immunization with human anti-HIV-1 Env nmAbs in primates • Challenge viruses should encode neutralization- sensitive, primary envelopes

34. Summary, continued • To reflect HIV heterogeneity, vaccine and challenge virus should not exactly match. Ideally, primate vaccine efficacy studies should employ fully hetero-logous virus, rather than one differing in env only. • Replacing single high-dose viral challenges with repeated low-dose mucosal exposures has shown promise. • Ultimately, efficacy data generated in primate models need to be compared directly to phase III clinical vaccine trials for validation.

35. Acknowledgements DFCI / Harvard Medical School Ruijiang Song Robert Rasmussen Agnès Chenine Mila Ayash-Rashkovsky Lauren Goins Ricky Grisson Pei-lin Li Chantelle McCann Saied Mirshahidi Helena Ong Claudia Ruprecht Ela Shai-Kobiler Tao Wang James Whitney W. Xu L.-Y. Yeh Beth-Israel Deaconess Medical Center Lisa Cavacini Marshall Posner Institute of Applied Microbiology, Vienna, Austria Hermann Katinger Gabriela Stiegler Centers for Disease Control W. Evan Secor Memorial Sloan-Kettering Cancer Center Ting Chao Chou Yerkes National Primate Research Center Harold McClure† James Else Elizabeth Strobert University of Nebraska Charles Wood H. Zhang Univ. Teaching Hospital, Lusaka, Zambia Ganapati Bhat Chipepo Kankasa University of Washington Shiu-lok Hu Patricia Polacino NIAID HIV-RAD P01: Nancy Miller Harvard School of Public Health Janet Andersen