Epitope specificity of T cells induced by chemo-vaccination.

<p><b>A</b>: T cell specificities in PrEP-protected macaques 4284 and 35451 change rapidly during SHIV exposures and PrEP, while they remain more consistent in infected control macaque AG94, and in 4284 after infection. T cell specificities were determined by IFNγ-ELISPOT with 14 peptide pools represented by the indicated colors. The pie charts depict percentages of contributions to the T cell response. Arrows indicate time point of virus exposures, adjacent numbers indicate how many exposures were given. Seroconversion is recorded by “Y”; numbers indicates the study week of seroconversion. <b>B</b>: T cells induced by chemo-vaccination appear focused on epitopes derived from the <i>pol</i> region. IFNγ-ELISPOT responses to 14 peptide pools were combined for the indicated gene products; their contribution to the response (all 14 peptide pools) was calculated. All IFNγ-ELISPOT results from week 1–41 are depicted. N refers to number of macaques in the 4 specified groups. P-values were obtained by unpaired, two-sided student's t-tests comparing all results before infection (12 time-points from 3 chemo-vaccinated macaques, filled circles and open diamonds combined) to those after infection (56 time-points from 5 macaques in control or PrEP-infected groups, open circles and filled triangles combined).</p

Cytokine production of CD4⁺ and CD8⁺ T cells induced by chemo-vaccination.

<p>Intracellular production of IFNγ, IL-2, MIP-1β, or TNFα was measured by flow cytometry after in-vitro incubation of freeze-thawed cells with the two dominant peptide pools as determined by previous IFNγ-ELISPOT. We gated on CD3⁺ and CD69⁺ (<b>A, B</b>), or on CD3⁺, CD69⁺, and CD4⁺ or CD8⁺ (<b>C</b>), and determined the number of cells with intracellular production of any of the factors, regardless of whether they simultaneously produced the remaining 3 factors. “Any” refers to cells producing any of the indicated factors, not necessarily all simultaneously. Samples from infected controls or infected PrEP-treated macaques were from peak viremia or 6 weeks thereafter, whenever available. Such samples are not shown for CD4/CD8 analysis, because CD4⁺ cells significantly decline depending on the stage of SHIV infection. (<b>B</b>) Representative example of results obtained with cells from macaque 34912 before its infection, without stimulation (“no stim.”), with the two dominant peptide pools, or with SEB for polyclonal stimulation.</p

Experimental Design.

<p>SHIV-specific T cells were measured during the indicated experimental procedures. Arrows indicate repeated viral exposures, horizontal lines depict intermittent, oral PrEP. PrEP consisted of human-equivalent doses of oral Truvada. Each virus exposure was flanked by a waning drug dose of 7 days prior, and one drug dose administered 2 hours after exposure, as a model for intermittent PrEP use in humans. Bolded rectangles highlight final outcomes of SHIV challenges. Numbers in lower right corners refer to macaque identifications (IDs).</p

Chemo-vaccination effect.

<p>SHIV-specific T cells are induced in two PrEP-protected macaques during PrEP and virus exposures. PrEP protected four macaques from infection during 14 SHIV exposures in weeks 1–14 (<b>A</b> and <b>B</b>), while two became infected despite PrEP (<b>C</b>); three macaques were controls (<b>D</b>). SHIV-specific T cells were determined by IFNγ-ELISPOT. The black bars represent the number of specific T cells as a sum of responses to 14 SHIV-derived peptide pools for antigenic simulation, measured in SFU (spot forming units, left axis). Grey lines depict plasma viremia (right axes). The graphs represent data from individual macaques, their identification codes are bolded. The dotted lines are cut-off values for positive T cell responses. Two PrEP-protected macaques (35451 (<b>A</b>), 4284 (<b>B</b>)) showed signs of chemo-vaccination. During re-challenge with 14 SHIV exposures in weeks 42–55, additional PrEP protected macaques 35451 and 33756 (<b>A</b>). Chemo-vaccinated macaques 4284 and 33246 were not protected from SHIV infection (<b>B</b>). Throughout the study, anti-SHIV antibodies were determined every 6 weeks (weeks 1–41) or 4 weeks (weeks 42–69). “Y” indicates time of seroconversion.</p