Background: Most laboratory assays measure HIV-specific CD8 T-cell responses to consensus sequences from lab-adapted HIV virus. However the CTL response to laboratory HIV-1 strains may become irrelevant because of the emergence of viral variants in response to selection pressure by CTL. In this study we evaluated the lytic ability of HIVIIIB-responding CD8 T-cell lines and clones from seropositive subjects against primary CD4 T cells infected with autologous HIV virus.
CTL Response to Lab-Adapted HIVIIIB Virus Is not Predictive of Autologous Virus Recognition|
S. K. Lee*, Z. Xu, J. Lieberman, and P. Shankar
Harvard Med. Sch., Boston, MA
Methods: PBMCs from 3 HIV-infected subjects were stimulated with IIIB-infected autologous primary CD4 T cells. After overnight culture, the responding IFN-gamma-secreting cells were selected immunomagnetically and cloned or cultured for 10-14 days before testing in cytotoxicity assays against primary CD4 T cell targets uniformly infected with HIVIIIB or autologous virus.
Results: A cell line from a CDC stage A subject recognized both HIVIIIB and autologous virus-infected target cells, whereas cell lines from CDC stage B and C subjects recognized HIVIIIB-infected, but not autologous virus-infected targets. Even in the stage A subject, 4 of 6 CTL clones that were generated from the IFN-gamma selected cells responding to HIVIIIB failed to recognize autologous virus-infected targets. The 6 clones, directed against gag (4 clones), gp120 (1 clone), or RT (1 clone), were all able to lyse HIVIIIB-infected targets. We identified the epitopes recognized by the clones and sequenced the patientís current infecting viral strain to identify mutations within or in the flanking regions of the recognized epitopes. The epitopes mapped to HIV gag p24 VKNWMTETLLVQNANPDCKT (aa: 181-200), HIV gag p17 LRPGGKKKYKLKHIV (aa: 21-35), HIV gp120 HACVPTDPNPQEVVLVNVTE (aa: 72-91) and HIV RT YTAFTIPSI (aa: 127-135) respectively. Sequencing of the patientís pro-virus revealed point mutations in the p17 gag, env and pol epitopes but not in the p24 gag epitope. However, a mutation in the p24 epitope flanking region was identified.
Conclusions: Autologous virus-infected targets provide a simple but powerful tool to evaluate the in vivo relevance of CTL responses identified by conventional laboratory assays. HIV-specific CD8 T cells that recognize laboratory strain virus persist even when they are no longer capable of responding to the patientís evolving virus. Lack of CTL recognition of autologous virus-infected primary cells can be traced to mutation of the epitopic or, in some cases, flanking sequences.