1. 1 ARV Drug Resistance HAIVN Harvard Medical School AIDS Initiative in Vietnam

2. 2 Learning Objectives By the end of this session, participants should be able to: Explain how HIV develops resistance Describe the factors that increase the risk of developing HIV resistance Outline the types of resistance tests Explain data about resistance in Vietnam

3. 3 HIV Life Cycle HIV is a “retrovirus” Replication occurs from RNA to DNA using “reverse transcriptase” enzyme The DNA created is then integrated into host cell genome (T lymphocyte) New HIV viruses are then produced using this DNA complex

4. 4 HIV - Life Cycle & ARV Drugs Protease Inhibitors (9) Fusion/Entry Inhibitors (2) Integration Inhibitors (1) Reverse Transcriptase Inhibitors (11) Source:wires.wiley.com-2010

5. 5 HIV Drug Resistance: Introduction HIV reverse transcriptase is very prone to errors resulting in mutations HIV mutations occur naturally during HIV replication Mutations in the virus can cause resistance HIV is “resistant” to a drug if it keeps multiplying while patients are taking the drug

6. 6 How Does HIV Develop Resistance? (1) Administration of ARVs in an insufficiently potent manner exerts reproductive pressure that selects for resistant strains Only resistant strains continue to reproduce, which then become the majority strain of HIV in that patient

7. 7 How Does HIV Develop Resistance? (2)

8. 8 How Does HIV Develop Resistance? (3) Changes of drug concentration in blood during treatment

9. 9 How Does HIV Develop Resistance? (4) Insufficient drug level Viral replication in the presence of drug Resistant virus Poor adherence Social/personal issues Regimen issues Toxicities Poor potency Wrong dose Host genetics Poor absorption Rapid clearance Poor activation Drug interactions

10. 10 Resistance Testing: Types of Resistance Tests Genotypic testing: look for specific mutations that could cause drug resistance Phenotypic testing: measure ability of a patient’s virus to grow in different concentrations of ARV

11. 11 Genotypic Testing: Limitations (1) Patient must be taking ARV at time the test is done Test only detects mutations present in ≥ 20% of circulating virus Viral load must be ≥ 1,000 copies/ml

12. 12 Genotypic Testing: Limitations (2) Reversion to Wild-Type Virus After Discontinuing ARV

13. 13 Genotypic Testing: Genetic Code (1) The genetic code of the sample virus is compared to the wild type The genetic code is a long chain of molecules called nucleotides Each group of 3 nucleotides (called a codon), defines a particular amino acid used to build a new virus

14. 14 Genotypic Testing: Genetic Code (2) Codon Nucleotide Amino acid AAA ATG AGC LysMet Ser Genetic Code

15. 15 Genotypic Testing: Mutation (1) Mutations are described by a combination of letters and numbers, i.e.: M184V = 3TC resistance M (Methionine): name for the amino acid in the wild type virus 184: identifies the position of the codon V (Valine): name for the “changed” amino acid in the mutant sample

16. 16 Genotypic Testing: Mutation (2) Codon 184 Mutation Codon 184 Nucleotide Amino acid AAA ATG AGC AAA GTG AGC LysMet Ser LysVal Ser Mutation

17. 17 Genotypic Testing: Disadvantages Resistance test are not available everywhere Expensive Work better when viral load is higher Results can be difficult to understand

18. 18 Resistance Concepts (1): Genetic Barrier Low genetic barrierHigh genetic barrier High level resistance with one mutation: NVP, EFV: K103N 3TC: M184V ≥3 mutations needed to develop high level resistance to most PIs Genetic barrier is number of mutations required to confer resistance to a drug

19. 19 Resistance Concepts (2): Cross- Resistance A mutant version of HIV is resistant to more than one drug Cross-resistance within classes is common Resistance to one NNRTI means resistance to other NNRTIs (NVP and EFV) Resistance to one NRTI can indicate resistance to other NRTI (3TC and FTC) Use the results of resistance testing to choose second-line drugs

20. 20 HIV Drug Resistance in Vietnam

21. 21 Treatment Experienced and ARV Resistance (1) 248 patients in 11 PEPFAR-supported clinics: suspected treatment failure on first line therapy or history of suboptimal ARV treatment June - December 2007 Viral Load: 148/248 (59.7%) detectable Genotype results available on 136 patients Mutations found in 121/136 (89%) patients Giang LT, AIDS Conference 2008

22. 22 Treatment Experienced and ARV Resistance (2) Mutations% NRTI95.9 M184V77.6 TAMS (> 1)71.7 TAMS (> 3)49.1 K65R9.4 Q151M7.8 NNRTI88.4 PI8.3

23. Treatment Experienced and ARV Resistance (3) ARV Resistance High level (%) NRTI 3TC76.3 AZT37.3 d4T34.2 ABC32.5 DDI31.4 TDF0.8 NNRTI85.2 PI0

24. 24 When to Do Resistance Testing Patient currently taking ARV with good adherence for at least 6 months Evidence for treatment failure Viral load testing done first and result > 1,000 More than one 2nd-line ARV regimen available Indications for ordering test in Vietnam: all criteria should be met

25. 25 Case Study

26. 26 Key Points Resistance develops in the setting of an inadequately suppressive ARV therapy For the patient who is failing therapy: check adherence issues first Testing for HIV resistance to ARVs is an important component of clinical care Resistance assays can assist the clinician in selecting a maximally effective 2 nd -line ARV regimen

27. 27 Thank You Questions?