Background In the USA, most HIV-1 infected children are on antiretroviral drug regimens, with many individuals surviving through adolescence and into adulthood. disease progression in straight contamination is usually associated with significantly higher levels of CD4+ TEMRA (CCR7?CDeb45RA+) cells. Introduction Numerous studies have sought to determine an association between the control of HIV-1 viremia and magnitude of the HIV-1 specific immune response , , , , . The results have been inconsistent. The qualitative characteristics of the HIV-1-specific T cell response have become the focus of intense study and it has been suggested that the failure 64849-39-4 IC50 of these responses to control viremia is usually due to a failure of these cells to fully differentiate . In contrast to other chronic viral infections such as CMV, HIV-1 contamination appears to result in a maturational block in the generation of the HIV-1-specific T cell responses with skewing toward an effector memory, TEM, phenotype . This seems to result in an overall decrease in the frequency of fully differentiated effector memory, TEMRA, cells , . We have previously shown that the frequency and complete figures of CD8+ HIV-specific TEMRA cells in early HIV-1 RDX contamination negatively correlate with the future viral weight set point . As CD4+ T cells are also known to be important in the control of HIV-1 viremia, , , , , , 64849-39-4 IC50 , , , , we sought to determine whether modifications in CD4+ T cell subpopulations were associated with disease progression. We selected to study a populace of vertically infected children, and categorized them into two progression groups based on CD4% values using revised guidelines published by the CDC in 1994 , subjects with no immune suppression (LTS-NS; CD4%25%), and subjects with severe immune suppression (LTS-SS; CD4%15%). Surprisingly, we found striking differences in the differentiation phenotype of CD4+ T cells between the two groups. Results Subject Cohort Characteristics We analyzed peripheral blood samples from 58 children and adolescents with vertically acquired HIV-1. As explained in Materials and Methods, these subjects were divided into two groups of immunological progression based on CDC guidelines. The characteristics of both groups are explained in Table 1. Table 1 Patient cohort characteristics. As the children were 64849-39-4 IC50 categorized according to percentage CD4+ T cell count, it was not amazing to find a statistically significant difference in the viral lots between the two groups. Of particular notice, all of the patients experienced some level of ongoing viral replication, as none of them managed consistently undetectable viral lots. The LTS-NS group contained more African-Americans than the LTS-SS group, but this did not reach significance. The LTS-SS group was slightly older than the LTS-NS group, but again this did not reach significance. There were no significant differences in treatment regimen or adherence levels between the two clinical groups. Comparison of Differentiation Information of Bulk and HIV-1-specific CD8+ T cells Between Progression Groups We first characterized the HIV-1-specific CD8+ T cell populace in the two groups. We hypothesized that there would be more fully differentiated CD8+ TEMRA cells in the LTS-NS subjects compared to LTS-SS subjects, both in the total CD8+ T cell populace and in Gag-specific CD8+ T cells, as has been observed from studies from adult HIV-1 infected cohorts , . We performed 64849-39-4 IC50 surface staining and intracellular cytokine staining on 17 LTS-NS subjects and 15 LTS-SS subjects, stimulating PBMC with single Gag peptides. Surface staining of the total CD8+ T cell populace revealed a significantly higher frequency of na?ve T cells (CCR7+ CD45RA+) in LTS-NS subjects (p?=?0.0066). We observed a 64849-39-4 IC50 pattern towards higher levels of TEM (CCR7?CD45RA?) cells in the LTS-SS group although this was not significant (p?=?0.2). There was no difference in the levels of TCM (CCR7+.