<i>M. tuberculosis</i> antigen-specific T-cell function in breast milk of HIV-infected mothers

Abstract Objective Breast milk (BM) is a mucosal compartment containing T cells, however, little is known regarding BM T-cell functional capacity or role in infant immunity. We hypothesized that BM T cells have M. tuberculosis (Mtb)-specific Th1 responses that are compartment-specific and differ from peripheral blood (PB) responses. Methods HIV-infected mothers and their infants were enrolled in a randomized clinical trial of isoniazid to prevent Mtb infection in Kisumu, Kenya. Maternal BM and PB were collected at 6–10 weeks postpartum. Cells were stimulated with Mtb whole cell lysate and controls. We measured frequencies of T cells expressing CD4 and CD8 and intracellular cytokines IFN-γ, IL-2, and TNF-α. Results Among 12 mothers with >1000 CD3+ cells evaluable, 33% had Mtb-specific IFNγ responses, 66% had Mtb-specific IL2 responses, 66% had Mtb-specific TNF responses, and 25% had combined IFNγ, IL2, and TNF responses. The most common Mtb-specific CD4 cytokine profile was IFNγ-IL2+TNF+ (66%) and the most common CD8 profile was IFNγ+IL2-TNF+ (58%). When compared to PB profiles (N=25), BM had higher polyfunctional CD4 cells expressing IFNγ-IL2+TNF+ (median 0.11 BM vs 0.0 PB, p=.005) and lower frequencies of IFNγ+IL2-TNF− CD4 cells (median 0.0 BM vs 0.03 PB, p=.002). CD8 cells in BM had higher frequencies of IFNγ+IL2-TNF+ cells compared to PB (median 0.05 BM vs 0.0 PB, p=.0002). Conclusions Our data demonstrate the presence of Mtb antigen-specific Th1 cells in BM with cytokine profiles distinct from PB responses. Defining BM Mtb-specific immune responses may inform novel vaccine strategies. Studies are ongoing to examine correlations between maternal BM and PB Mtb-specific T-cell responses and infant responses to BCG vaccination.