Degeneracy and Repertoire of the Human HIV-1 Gag p1777–85 CTL Response

Abstract

CD8+ CTL responses are important for the control of HIV-1 infection. The immunodominant HLA-A2-restricted Gag epitope, SLYNTVATL (SL9), is considered to be a poor immunogen because reactivity to it is rare in acute infection despite its paradoxical dominance in patients with chronic infection. We have previously reported SL9 to be a help-independent epitope in that it primes highly activated CTLs ex vivo from CD8+ T cells of seronegative healthy donors. These CTLs produce sufficient cytokines for extended autocrine proliferation but are sensitive to activation-induced cell death, which may cause them to be eliminated by a proinflammatory cytokine storm. Here we identified an agonist variant of the SL9 peptide, p41 (SLYNTVAAL), by screening a large synthetic combinatorial nonapeptide library with ex vivo-primed SL9-specific T cells. p41 invariably immunized SL9-cross-reactive CTLs from other donors ex vivo and H-2Db β2m double knockout mice expressing a chimeric HLA-A*0201/H2-Db MHC class I molecule. Parallel human T cell cultures showed p41-specific CTLs to be less fastidious than SL9-CTLs in the level of costimulation required from APCs and the need for exogenous IL-2 to proliferate (help dependent). TCR sequencing revealed that the same clonotype can develop into either help-independent or help-dependent CTLs depending on the peptide used to activate the precursor CD8+ T cells. Although Ag-experienced SL9-T cells from two patients were also sensitive to IL-2-mediated cell death upon restimulation in vitro, the loss of SL9 T cells was minimized with p41. This study suggests that agonist sequences can replace aberrantly immunogenic native epitopes for the rational design of vaccines targeting HIV-1.

Minor viral and host genetic polymorphisms can dramatically impact the biologic outcome of an epitope-specific CD8 T-cell response

“…However, it is important that sequence selection is based on a comprehensive approach that will enable the identification of optimal antigens, either alone or in combination, for incorporation into vaccines delivered in the setting of both host and viral heterogeneity. 51 In conclusion, we have shown that minor genetic differences in viral epitopes and host restriction elements can dramatically affect CD8 T-cell immunity with profound implications for the biologic outcome of HIV infection. These findings indicate that, in addition to the identification of optimal antigens, rational vaccine design should also incorporate a comprehensive approach to epitope sequence selection guided by detailed analyses of the downstream consequences of immunization.…”

Immune Activation in the Pathogenesis of Treated Chronic HIV Disease: A Workshop Summary

“…Landay noted the importance of microbial translocation in immune activation through the TLR-4 pathway and in inducing proinflammatory cytokines. 49 He suggested the possibility of a common pathway of the proinflammatory cytokines driving immune activation characterized by HLA-DR and CD38 coexpressed on CD4 and CD8 T cells.…”

Availability of a Diversely Avid CD8+ T Cell Repertoire Specific for the Subdominant HLA-A2-Restricted HIV-1 Gag p2419–27 Epitope

“…HLA typing was possible for 280 of these samples, of which 121 were HLA-A2 ϩ . OLP21 (PRTLNAWVKVVEEKAP, p24 [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] ) was recognized by 24 subjects, with most of this reactivity (14 of 24) likely directed against the HLA-B*1503-restricted VKV VEEKAF epitope frequently seen in HLA-B*1503-expressing subjects (21). Reactivity to the nonameric TV9 peptide was confirmed in one of two HLA-A2 ϩ HLA-B*1503 Ϫ samples tested that reacted to OLP21 (L8 47, 500 sfc/10 6 PBMCs; Fig.…”

“…Positively selected CD8 ϩ T cells (Dynabeads; Dynal Biotech) were primed with irradiated (4000 cGy) peptidepulsed or transduced DCs at a T cell-DC ratio of 5:1 in 48-well or 96-well cluster plates. Cells were cultured in complete medium containing 10 ng/ml IL-7 (Genzyme) and restimulated every 7-10 days with autologous monocytes pulsed with peptides or transduced DCs (24,25). IL-2 (20 U/ml) was added 1 and 4 days poststimulation.…”

“…With this approach, we have shown that CTLs to the HLA-A2-restricted immunodominant SL9 epitope in Gag p17 [77][78][79][80][81][82][83][84][85] are aberrantly sensitive to cytokine-mediated activation-induced cell death in vitro. At the same time, these T cells are capable of producing sufficient autocrine factors to support prolonged periods of proliferation (24,25). These characteristics provide a plausible explanation for the paucity of circulating SL9-specific CD8 ϩ T cell reactivity during the proinflammatory acute phase of infection, as well as its paradoxical dominance during the CD4-diminished chronic phase of infection (18,26,27).…”