1. Design and Use of HIV-1 Reference Strains for Standardized Assessments of Vaccine-Elicited Neutralizing Antibody Responses David C. Montefiori, Ph.D. Laboratory for AIDS Vaccine Research & Development Duke University Medical Center Durham, NC monte@duke.edu

2. Standardization of HIV-1 Reference Strains HIV-1 exhibits an extraordinary degree of genetic variability that has given rise to multiple genetic subtypes and circulating recombinant forms (CRFs) of the virus. Information on the neutralization properties of each major genetic subtype and CRFs will inform vaccine design and will facilitate standardized assessments of vaccine-elicited neutralizing antibody responses.

3. The choice of target viruses has a significant influence on the outcome and interpretation of assay results The Need for HIV-1 Reference Strains

4. Overall neutralization-sensitivity Average High Low V3 & CD4i sensitive Where most vaccine-elicited responses are now TCLA & some 1 o isolates Relative abundance SPECTRUM OF NEUTRALIZATION-SENSITIVITIES Desired reference strains Where they need to be

5. How to Measure HIV-1 Vaccine-Elicited Neutralizing Antibody Responses An effective neutralizing antibody response will need to overcome the genetic variability, structural complexity and many neutralization escape mechanisms of the HIV-1 envelope glycoproteins. These same properties of the virus need to be part of the plan when assessing vaccine-elicited neutralizing antibody responses.

6. Compare new immunogens based on the potency and breadth of neutralizing antibody responses Prioritize the advancement of candidate vaccine Identify small but significant improvements in immunogen design Facilitate assay standardization and GCLP assay validation for clinical trials Inform new vaccine designs Need for Standard Panels of HIV-1 Reference Strains

7. Composition of Standard Virus Panels 12 viruses from acute/early sexually acquired infections per panel Not unusually sensitive or resistant to neutralization Genetically and antigenically diverse R5 biologic phenotype Molecularly cloned Env pseudotyped viruses are required for stability, reproducibility, improved GCLP and subsequent epitope analysis Grouping by clade – rational for this purpose: 6 major genetic subtypes: over 90% viruses Clades A, B, C, D, E (CRF01), A/G (CRF02) Need additional panels corresponding to vaccine trial sites Address key scientific questions relating to optimal panel composition and the possible need to modify initial panels to improve their correlative value.

8. Multi-Tiered Approach to Assessing Vaccine-Elicited NAb Responses Tier 1: Vaccine strain(s) and neutralization-sensitive strains not included in the vaccine. Tier 2: Panel of heterologous viruses matching the genetic subtype(s) of the vaccine; 12 viruses per panel. May include additional strains from vaccine trial sites Tier 3: Multi-clade panel comprised of six tier 2 viruses of each genetic subtype, excluding the genetic subtype(s) evaluated in Tier 2. May include additional strains from the proposed vaccine trial site. 12 viruses from each clade J. Virol. 79:10103-10107 (2005)

9. Scientific Issues to Address Effect of possible genetic drift – compare recent vs. older isolates Early/acute transmitted isolates vs chronic isolates Clonal viruses vs. virus swarms Plasma viruses vs PBMC coculture viruses Mother-to-child transmission (vaginal, breast milk viruses) Env pseudoviruses vs full-length molecular clones Effect of virus produced in non-lymphoid cells such as 293T compared to primary T- cells Impact of genetically engineered cell lines as target cells What is threshold bar for meaningful neutralization?

10. Full-length functional Env plasmids – recently donated to the NIH AIDS Research & Reference Reagent Program (B panel cat. #11227; C panel cat. #11326) Sexually acquired, acute/early infections R5 biologic phenotype Neutralization phenotypes represent primary isolates Genetically and antigenically diverse – sequences deposited in Genbank Well-characterized e.g., N-glycans, V-regions, MAb epitopes Transmissions M-M, F-M, M-F Initial Panels of 12 Clade B and 12 Clade C HIV-1 Reference Strains J. Virol. 79:10108-10125 (2005) – Clade B panel J. Virol., in press (2006) – Clade C panel

11. Emphasis on assays with Tier 2/Tier 3 viruses. Consider the magnitude (e.g., ID50 titer, % neutralization) and breadth (coverage) of the response. Exceed the minimum bar in the Vax004 phase III trial (~10% coverage for 50-80% neutralization; 0% coverage for >80% neutralization). These parameters are only part of a decision pathway that includes other immune responses. Decision Pathway for Prioritizing NAb-Based Vaccine Candidates

12. COMENTARY: Mascola, J. R., P. D'Souza, P. Gilbert, B. Hahn, N. L. Haigwood, L. Morris, C. J. Petropoulos, V. R. Polonis, M. Sarzotti-Kelsoe, and D. C. Montefiori. 2005. Recommendations for the design and use of standard virus panels to assess the neutralizing antibody response elicited by candidate human immunodeficiency virus type 1 vaccines. J. Virol. 79:10103-10107. CLADE B REFERENCE PANEL: Li, M., F. Gao, J.R. Mascola, L. Stamatatos, V.R. Polonis, M. Koutsoukos, G. Voss, P. Goepfert, P. Gilbert, K.M. Greene, M. Bilska, D.L. Kothe, J.F. Salazar-Gonzalez, X. Wei, J.M. Decker, B.H. Hahn, and D.C. Montefiori. 2005. Human immunodeficiency virus type 1 env clones from acute and early subtype B infections for standardized assessments of vaccine-elicited neutralizing antibodies. J. Virol., 79:10108-10125. CLADE C REFERENCE PANEL: Li, M,. J.F. Salazar-Gonzalez, C.A. Derdeyn, L. Morris, C. Williamson, J.E. Robinson, J.M. Decker, Y. Li, M.G. Salazar, V.R. Polonis, K. Mlisana, S.A. Karim, K. Hong, K.M. Greene, M. Bilska, J.T. Zhou, S. Allen, E. Chomba, J. Mulenga, C. Vwalika, F. Gao, M. Zhang, B.T.M. Korber, E. Hunter, B.H. Hahn, and D.C. Montefiori. 2006. Genetic and neutralization properties of acute and early subtype C human immunodeficiency virus type 1 molecular env clones from heterosexually acquired infections in southern Africa. J. Virol., in press. ADDITIONAL PANELS: Brown, B. K., J. M. Darden, S. Tovanabutra, T. Oblander, J. Frost, E. Sanders-Buell, M. S. DeSouza, D. L. Birx, F. E. McCutchan, and V. R. Polonis. 2005. Biologic and genetic characterization of a panel of 60 human immunodeficiency virus type 1 (HIV-1) isolates, representing clades A, B, C, D, CRF01_AE, and CRF02_AG, for the development and assessment of candidate vaccines. J. Virol. 79:6089-6101. REFERENCES

13. Dr. Montefioris laboratory is funded by: Division of AIDS/NIAID/NIH: Primate Core Immunology Laboratory for AIDS Vaccine Research and Development (PCIL) HIV Vaccine Trials Network (HVTN) Center for HIV/AIDS Vaccine Immunology (CHAVI) Bill & Melinda Gates Foundation: Collaboration for AIDS Vaccine Discovery (CAVD)