HIV Specific T Cell Priming Figure 5. Strong and broad HIV-specific CD4 T cell responses exist in acute infection which quickly diminish. (A and B) Fresh CD8- depleted PBMCs from 12 adult individuals with documented primary HIV infection (PHI) were screened for HIV Gag-specific CD4 responses by IFNc Elispot using a pool of overlapping peptides spanning all HIV proteins and corresponding to Clade B consensus sequence 2001. Subjects were assessed at baseline (BL) before institution of any antiviral therapy and 1 month, 3 months and 6 months after BL. Data represent total HIV-specific CD4 T cells responses (A) as well as responses to individual gene products (B). Grey circles: subjects treated with HAART; white circles: individuals who remained without therapy. Horizontal black bars: median values. (C) This decline can also be demonstrated by intracellular cytokine staining and affects both IFNc- and IL-2-secreting CD4+ T cells. Fresh PBMCs from an adult individual with acute HIV infection were stimulated with medium alone, the same HIV Gag as above or a CMV lysate, in the presence of anti-CD28 and anti-CD49 stimulating antibodies and submitted to intracellular cytokine staining after six hour incubation. Similar experiments were performed 12, 24 and 36 weeks after BL. These results are representative of three separate subjects. Numbers in quadrants: percentage of cytokine-producing CD4+ T cells. doi:10.1371/journal.pone.0004256.g005 in HIV-infected individuals. The majority of the in vitro primed T cell responses that we observed were CD4+ T helper cells recognizing epitopes within Env (gp120SU, gp41TM, p24CA, p17MA), and Pol (RT and IN). The majority of the CD4+ T cell responses and all of the CD8+ T cell responses we observed in our priming targeted the same antigenic regions that had previously been documented in acutely and/or chronically HIV-infected subjects[19,31,36,46,47]. Individuals with acute or long term nonprogressive infection have a strong HIV-specific T cell ex vivo proliferative capacity, whereas this effector function seems to be absent in chronically infected individuals with high level of viremia [1,2,3]. The changes in functionality and phenotype of HIV- specific CD4+ T cells are a consequence of high levels of antigens [40]. The persistence of CD4+ T cells with defective proliferation suggests a dysfunction possibly due to impaired development of IL- 2 producing central memory T cells [48,49]. In contrast, the T cells activated in our in vitro priming are polyfunctional memory T cells, capable of secreting IL-2, IFN-c, MIP-1b and TNF-a in response to stimulation. In addition, the HIV-specific T cells had the ability to recognize and proliferate in response to stimulation with both infectious and AT-2 HIV-1. A number of the in vitro primed CD4+ T cell responses were towards peptides that had not previously been documented to elicit responses in the studies of infected individuals. When we investigated a cohort of acute/recent HIV-infected subjects, we detected responses to 4 of the 5 novel epitopes within env and pol that we found in our in vitro priming. Novel CD4+ T cell responses to the env gp41 peptides AVLSIVNRVRQGYSPLSF and LELDKWASLWNWFNITNW were seen in a couple of the donors used for priming. When we re-examined the CD4+ T cell responses of acute HIV-infected subjects for responses against these epitopes we were able to detect responses targeting the AVLSIVNRVRQGYSPLSF peptide. However, CD4+ T cell responses against this epitope waned as the infection progressed PLoS ONE | www.plosone.org 9 January 2009 | Volume 4 | Issue 1 | e4256