Strong HIV-1-specific T cell responses in HIV-1-exposed uninfected infants and neonates revealed after regulatory T cell removal

Abstract

Background: In utero transmission of HIV-1 occurs on average in only 3%-15% of HIV-1-exposed neonates born to mothers not on antiretroviral drug therapy. Thus, despite potential exposure, the majority of infants remain uninfected. Weak HIV-1-specific T-cell responses have been detected in children exposed to HIV-1, and potentially contribute to protection against infection. We, and others, have recently shown that the removal of CD4(+) CD25(+) T-regulatory (Treg) cells can reveal strong HIV-1 specific T-cell responses in some HIV-1 infected adults. Here, we hypothesized that Treg cells could suppress HIV-1-specific immune responses in young children.

Methodology/principal findings: We studied two cohorts of children. The first group included HIV-1-exposed-uninfected (EU) as well as unexposed (UNEX) neonates. The second group comprised HIV-1-infected and HIV-1-EU children. We quantified the frequency of Treg cells, T-cell activation, and cell-mediated immune responses. We detected high levels of CD4(+) CD25(+) CD127(-) Treg cells and low levels of CD4(+) and CD8(+) T cell activation in the cord blood of the EU neonates. We observed HIV-1-specific T cell immune responses in all of the children exposed to the virus. These T-cell responses were not seen in the cord blood of control HIV-1 unexposed neonates. Moreover, the depletion of CD4(+) CD25(+) Treg cells from the cord blood of EU newborns strikingly augmented both CD4(+) and CD8(+) HIV-1-specific immune responses.

Conclusions/significance: This study provides new evidence that EU infants can mount strong HIV-1-specific T cell responses, and that in utero CD4(+) CD25(+) T-regulatory cells may be contributing to the lack of vertical transmission by reducing T cell activation.

Figure 1

CD4⁺ and CD8⁺ T cell immune responses were measured by cytokine flow cytometry. A) Gating strategy for the identification of polyfunctional IFN-gamma/TNF-alpha CD8⁺ T cell responses. B) Shown are representative data for the unstimulated and HIV-gag-specific response from subject PB-INF-4 after an 18 h in vitro stimulation.

Figure 2. CD8⁺ IFN-gamma T-cell immune responses to HIV-1 Gag (A) and Nef (B) peptide pools as well as SEB (C) in the cord blood of unexposed neonates (CB-UNEX; n = 4), HIV-1-exposed uninfected neonates (CB-EU; n = 6), and in the peripheral blood of HIV-1-exposed-uninfected infants (PB-EU 7 mo; n = 9) and young children (PB-EU 20 mo; n = 7), and in HIV-1-infected infants (PB-INF 7 mo; n = 5) and young children (PB-INF 25 mo; n = 5). Each group is represented by a different symbol.

Figure 3

Polyfunctional CD8⁺ T cell immune responses to the HIV-1 Gag peptide pool were detected by cytokine flow cytometry. Responses were measured in the cord blood of unexposed neonates (CB-UNEX; n = 4), HIV-1-exposed uninfected neonates (CB-EU; n = 6), and in the peripheral blood of HIV-1-exposed-uninfected infants (PB-EU 7 mo; n = 9) and young children (PB-EU 20 mo; n = 7), and in HIV-1-infected infants (PB-INF 7 mo; n = 5) and young children (PB-INF 25 mo; n = 5). Each group is represented by a different symbol.

Figure 4. Augmented CD8⁺ HIV-1 immune responses to Gag peptide pools in exposed uninfected neonatal cord blood upon the removal of CD4⁺CD25⁺ Treg cells. A) IFN-gamma production by undepleted whole cord blood and peripheral blood mononuclear cells (MNCs) derived CD8⁺ T-cells (open white symbols) and CD25-depleted MNCs derived CD8⁺ T-cells (closed black symbols) is depicted. B) Flow cytometry plots from an exposed uninfected neonate (Patient 30) representing HIV-1-Gag-induced IFN- gamma production in non-CD25-depleted CBMC derived CD8⁺ T-cells and CD25-depleted CBMC derived CD8⁺ T-cells.

Figure 5

Augmented CD4⁺ HIV-1 immune responses to Gag peptide pools in exposed uninfected neonatal cord blood upon the removal of CD4⁺CD25⁺ Treg cells. A) IL-2 production by undepleted whole cord blood and peripheral blood mononuclear cells (MNCs) derived CD4⁺ T-cells (open white symbols) and CD25-depleted MNCs derived CD4⁺ T-cells (closed black symbols) is depicted. B) Flow cytometry plots from an exposed uninfected neonate (Patient 63) representing HIV-1 Gag induced IL-2 production in undepleted whole CBMC derived CD4⁺ T-cells and CD25-depleted CBMC derived CD4⁺ T-cells.