Under what circumstances need to be tested for HIV drug resistance

  HIV resistance is one of the important reasons leading to the failure of AIDS antiretroviral therapy. In the 2020 edition of the “National AIDS Testing Technical Specifications”, the content of HIV drug resistance testing continues to be included. What should we know about HIV drug resistance testing?
  What is AIDS drug
  , also known as the AIDS virus (HIV) drug, refers to genetic variation caused by HIV, reduced susceptibility to antiviral inhibition or insensitive phenomenon.
  Where does AIDS resistance come from?
  (1) Direct infection. When the infected strain is a drug-resistant strain of HIV, primary drug resistance, also known as transmissible drug resistance, occurs.
  (2) Drug selection. HIV is a virus that replicates quickly and is very easy to mutate. In the absence of antiviral drugs, HIV resistant mutants will appear randomly, but they have no replication advantage and will not accumulate in the body; during antiviral treatment, when the drug concentration is When insufficient, HIV replication cannot be completely inhibited, and the replication advantages of HIV drug-resistant mutant strains will appear, and then the drug-resistant mutant strains will gradually accumulate and increase, resulting in secondary drug resistance, also known as acquired drug resistance.
  How to detect AIDS resistance
  (1) Genotype testing. Through sequencing or gene chip hybridization and other methods, detect whether there are drug resistance-related mutations in the HIV genome. Genotype testing usually uses sequencing. The testing process is as follows: using HIV genomic RNA as a template, reverse transcription PCR amplifies the target gene fragment, sequencing to obtain the HIV gene sequence, and comparing it with the wild-type sequence to determine whether there is a resistance-related gene Mutations, and then correlate the degree of resistance through the algorithm of the resistance database. The sample type can be plasma and dried blood spots. The sequencing method usually adopts the Sanger sequencing method. With the development of sequencing technology, the deep sequencing method has gradually begun to be used.
  (2) Phenotypic testing. Also known as in vitro drug susceptibility test, it is expressed as 50% inhibitory concentration (IC50). The IC50 of the tested strain and the wild-type strain is compared, and the degree of resistance is evaluated by Fold change (FC). The virus to be tested can be a virus directly isolated and cultured from the PBMC of the infected person, or a recombinant virus containing the HIV gene of the infected person.
  Generally speaking, the operation of genotype testing is simpler and the testing cycle is short, so it is used more clinically, but phenotyping testing has more advantages for the detection of drug resistance against complex mutations and new drugs.
  How to look at the results of genotype resistance testing
  (1) The expression method of resistance mutations. Drug resistance mutations are changes in the nucleotide sequence of HIV genes, but they are expressed in terms of amino acid changes. The format is as follows: amino acid of wild virus strain + position of amino acid + amino acid after mutation, such as K103N, which is the 103rd of HIV reverse transcriptase. The amino acid at position mutated from lysine (K) to asparagine (N).
  (2) Drug resistance interpretation system. Refers to a database with an algorithm for the degree of resistance, through which the results of the resistance mutation can be converted into the degree of resistance. For example, in the widely used Stanford HIVdb drug resistance interpretation system, the resistance of the K103N mutation is highly resistant to nevirapine (NVP) and efavirenz (EFV).
  Precautions for HIV drug resistance testing
  (1) Timing of testing. Because HIV is very susceptible to mutation, when drug-resistant patients stop or discontinue treatment, when there is no antiviral drug in the body, the replication advantage of the wild strain appears and gradually accumulates, and finally drug resistance will not be detected. Therefore, the best time for drug resistance testing is when the patient is undergoing antiviral treatment, or within one month of interruption of treatment.
  (2) Be wary of cross-contamination between samples. During the detection process, blank and negative controls need to be set, and cross-contamination should be eliminated through sequence evolutionary tree analysis.
  (3) When no drug-resistant mutations are detected, the existence of a low proportion of drug-resistant strains cannot be ruled out. This is because when the proportion of drug-resistant strains in the individual virus quasispecies is less than 10% to 20%, its existence is usually not detected by the Sanger sequencing method.