Substitution of hiv type-1 non-B env genes in C2, a subtype B cassette system, results in functional chimeric viruses

Env gene glycoprotein products are essential to viral infectivity and important targets for a host's humoral and cellular immune responses. We have reported the construction of C2, an effective env gene cassetting system for assessing biological properties of HIV-1 subtype B env gene glycoprotein products within a constant genetic background (Zheng NN and Daniels RS: AIDS Res Hum Retroviruses 2001;17:1501-7506). Here we report the ability of C2 to produce chimeric subtype A, C, D, A/E, F, and J HIV-1 and studies of the viruses' biological properties. Virus RNAs were extracted and full-length env genes rescued by RT-PCR. Expression-competent env genes were cloned into the C2 cassette and chimeric recombinant viruses produced by transfecting 293T cells. For each subtype, X4 viruses yielded higher TCID(50) than R5 viruses and the TCID(50) of chimeric viruses were either the same as or lower than their parental viruses. The limited coreceptor usage of R5-tropic parent viruses was retained in the chimeric viruses. Generally, with the exception of the subtype C virus (SE12808), the X4-tropic parental viruses utilized CXCR4 and a wide range of additional coreceptors, while their respective chimeric viruses retained CXCR4 usage but showed a more limited range in respect of other coreceptors. The replication rates of non-B subtype chimeric viruses were generally lower (1.5- to 13.6-fold) than their respective parental viruses with the exception of C2-92UG029, an X4-tropic subtype A chimeric virus. This study demonstrates that C2 is a functional cassette capable of producing infectious chimeric viruses to allow study of the biological phenotypes and functions of HIV-1 subtype B and non-B subtype glycoproteins.