'Possible' Resistance: Comparison of 'Possible' Resistance Results Derived from a Genotyping Report versus the IC50 Virtual Phenotype

摘要

HIV resistance testing employs either genotyping or phenotyping methods or a hybrid method known as Virtual Phenotyping. Phenotyping assays purify the virus's nucleic acids, convert them into cDNA and clone a portion of the cDNA into a reporter vector that permits the determination of the concentration at which 50% of the virus is inhibited by each drug (IC50). In genotyping, the virus is sequenced and mutations identified. Interpretation of the relevance of a mutation is determined by software that classifies certain mutations as either primary or secondary mutations or by using a relational database (Virtual Phenotype). Primary mutations are defined as causing resistance while secondary mutations facilitate the "fitness" of the virus. Generally, multiple secondary mutations are necessary to cause resistance of a virus. Rules based software provides the interpretation of mutation p atterns t hus e asing t he b urden o n non-expert clinical personnel. In the Virtual Phenotyping relational database, sequences of isolates that have had the phenotyping result generated are linked. This linkage permits a virtual phenotype to be generated using only the sequence data from a new specimen. Sometimes the resistance results of a rules based interpretation is neither "none" or "high," but rather "possible". In this study, HIV rules based resistance test results from 3 months were analyzed against the Virtual Phenotyping result to determine whether any drug classes or specific drugs tended to g enerate more "possible" results. In addition, variances were determined between the IC50 for the virtual phenotype for these "possible" results. The graph below demonstrates some of our findings. The first 6 drugs are protease inhibitors and demonstrate the greatest standard deviation but correlate closely to the cutoff for the development of resistance (designated as 0) compared to the nucleoside reverse transcriptase inhibitors and finally the non-nucleoside reverse transcriptase inhibitors. Nucleoside reverse transcriptase inhibitors had the most "possible" results while the nonnucleoside : inhibitors had the fewest.