| Summary: | <p>Abstract</p> <p>Background</p> <p>Transmission of human immunodeficiency virus type 1 (HIV-1) through breast-feeding may involve both cell-free and cell-associated virus. This latter viral reservoir remains, however, to be fully explored. CD4<sup>+ </sup>T cell-associated virus production in breast milk was therefore investigated.</p> <p>Methods</p> <p>The <it>ex vivo </it>spontaneous production of HIV-1 antigen and HIV-1 RNA by CD4<sup>+ </sup>T cells was measured in paired blood and breast milk samples from 15 HIV-1 infected women treated or not with antiretroviral drugs. Spontaneous antigen secreting cells (HIV-1-AgSCs) from breast milk and blood were enumerated by an ELISpot assay, and cell-associated HIV-1 RNA was quantified by real-time PCR in supernatants of CD4<sup>+ </sup>T cells cultured for 18 hours without addition of polyclonal activators.</p> <p>Results</p> <p>Among the CD4<sup>+ </sup>T cells present in breast milk, memory cells expressing high levels of cell-surface activation markers were predominant. Spontaneous HIV-1-AgSCs were detected and enumerated in the breast milk of all 15 women, with a median number of 13.0 and 9.5 HIV-1- AgSCs/106 CD4<sup>+ </sup>T cells in aviremic (n = 7) and viremic (n = 8) women, respectively. Cell- associated HIV-1 RNA was detected in cell-free supernatants from 4/7 aviremic and 5/8 viremic individuals at median levels of 190 and 245 copies/ml, respectively.</p> <p>Conclusions</p> <p>Activated CD4<sup>+ </sup>T cells producing HIV-1 are detected in the breast milk of untreated individuals as well as those receiving highly active antiretroviral therapy. This finding strongly suggests that HIV-1 replication occurs in latently infected CD4<sup>+ </sup>T cells that, upon spontaneous activation, revert to productively infected cells. These cells might be responsible for a residual breast milk transmission despite maternal highly active antiretroviral therapy.</p>
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