Mechanisms of HIV non-progression; robust and sustained CD4+ T-cell proliferative responses to p24 antigen correlate with control of viraemia and lack of disease progression after long-term transfusion-acquired HIV-1 infection

Dyer, Wayne B; Zaunders, John J; Yuan, Fang Fang; Wang, Bin; Learmont, Jennifer C; Geczy, Andrew F; Saksena, Nitin K; McPhee, Dale A; Gorry, Paul R; Sullivan, John S

To determine why strong Gag CTL may have contained viral replication in some, but failed in others, we mapped the breadth of the Gag CTL response over time in patients with at least moderate CLT responses to whole Gag antigens. Pools of overlapping 15-mer Gag peptides were used to test sequential PBMC spanning the study period by ELISPOT. The composition of each peptide pool, and examples of responses to these are shown in Figures 4 and 5 , indicating the relevant HLA-specific epitopes contained in peptides at the intersection of positive pools. Figure 4 demonstrates a broad strong response by C53's PBMC to multiple immunodominant epitopes, contrasted in Figure 5 by the restricted response from C122 to only two immunodominant epitopes. The sequential analysis revealed relatively high stability in the repertoire of Gag responses over the past 10 years in most subjects (Additional file 2). Relevant epitopes at intersecting positive peptide pools were then confirmed using individual peptides ( Figure 6 ). This data demonstrates that retention of broadly reactive Gag CTL was associated with ongoing non-progression (C49, C64, and C53), while restriction toward a narrow CTL specificity was observed in patients that eventually lost control of viraemia (C122 and possibly C13). The SBBC non-progressors C49 and C64 had responses to several Gag epitopes, and although Gag responses were moderate to weak in C64, this needs to be viewed in the context of Pol CTL dominance in the SBBC. A strong but Immunovirological status of the surviving non-progressors, showing T cell counts; viral RNA copies/ml plasma (data generated from the Roche Amplicore standard assay, limit of detection 400, and Ultrasensitive assay, limit of detection 50, plotted sepa-rately); T cell proliferative responses to recombinant HIV-1 p24 (stimulation index; significant responses >3, defined by the broken line); and IFNγ responses (ELISPOT) by CTL against autologous BCL expressing HIV-1 antigens after infection with recombinant vaccinia Figure 1 Immunovirological status of the surviving non-progressors, showing T cell counts; viral RNA copies/ml plasma (data generated from the Roche Amplicore standard assay, limit of detection 400, and Ultrasensitive assay, limit of detection 50, plotted separately); T cell proliferative responses to recombinant HIV-1 p24 (stimulation index; significant responses >3, defined by the broken line); and IFNγ responses (ELISPOT) by CTL against autologous BCL expressing HIV-1 antigens after infection with recombinant vaccinia. *SBBC member. Immunovirological status of the former non-progressors (same parameters as in figure 1) Figure 2 Immunovirological status of the former non-progressors (same parameters as in figure 1 ). Initiation of antiretroviral therapy is defined by an arrow in the viral load panels. Other reasons for loss of non-progressor status are summarised in Additional file 1. restricted Gag response was also seen in C18, but these Gag responses were likely to be secondary in controlling viraemia, as suggested by the kinetics of Pol CTL in response to a spike in viraemia ( Figure 3 ). Pol CTL recognition was confirmed by subsequent analysis of responses to peptide pools derived from the full set of Pol overlapping 15-mer peptides. Moderate to strong responses to multiple pools containing epitopes in the reverse transcriptase protein were detected in SBBC members C49, C64, C18, C54, but weakly in C98 (data not shown). C18 also responded