FIG. 3.

Immunization with MVA-SIVsmH4 recombinants is associated with preservation of central memory CD4⁺ T lymphocytes following SIVsmE660 challenge. (A) Flow cytometric gating strategy for identification of naïve (CD28^high CD95^low), central memory (CD28^high CD95^high), and effector memory (CD28^low CD95^high) CD4⁺ T cells is shown for a representative macaque from the control group (H387) and a long-term-surviving macaque with sustained control of viremia vaccinated with MVA-Env (H422). Profiles are shown for samples collected prior to challenge, 4 and 20 weeks post-SIV challenge, and time of death (H387) or 472 weeks postchallenge (H422). As indicated by the percentages of central and effector memory CD4⁺ T cells, progressive loss of these populations was observed in the control macaque. In contrast, these populations were preserved in the vaccinated macaque with sustained control of viremia. (B) Bar graphs depicting mean cell numbers of total (left), central memory (center), or effector memory (right) CD4⁺ T cells in PBMC samples of the various groups for 1 week (white) prechallenge and 4 weeks (black) and 20 weeks (gray) postchallenge show loss of central and effector memory cells in the control macaques and significantly better preservation of these cells in each of the three vaccinated groups. (C) Better preservation of mean central memory and effector memory CD4⁺ T cells in macaques showing sustained control (SC) of viremia compared to those with partial control (PC). (D) A significant inverse correlation of peak viremia was observed with the percentage of CD4⁺ T cells remaining at 4 weeks (P < 0.0383) and 20 weeks (P < 0.0162) postchallenge.