Compartment-specific HIV-1 resting T-cell reservoirs

Abstract

A proof-of-concept study recently assessed the efficiency of a standard clinical dose of valproic acid in order selectively to induce the expression of HIV-1 latent proviral genome, and potentially to deplete HIV from the blood resting CD4 T-cell reservoir [1]. The efficacy of this purge of the CD4 T-cell reservoir by valproic acid has been hypothesized to be tissue compartment specific [2]. We conducted a study on HIV-1 T-cell reservoirs in the blood and breast milk of nine HIV-1-infected women. Using an exquisitely sensitive HIV-1 antigen enzyme-linked immunospot (ELISPOT) assay combined with the quantitation of HIV-1 DNA by real time polymerase chain reaction (see Fig. 1), we were able to demonstrate a 17 times higher capacity of HIV-1 latently infected CD4 T cells to enter the replicative cycle after ex-vivo activation, in breast milk compared with blood [3]. The study is important not only for understanding the possible mechanisms of HIV-1 transmission by breastfeeding, but also for anticipating the feasibility of an HIV cure by treatments aimed at depleting the HIV-1 proviral reservoirs.Fig. 1: Characterization of resting T-cell reservoir in blood and breast milk. (a) Isolation of resting CD4 T cells from blood and breast milk samples. (b) Quantification of the HIV-1 DNA and enumeration of HIV-1 antigen-secreting cells after CD4 T-cell polyclonal activation. ELISPOT, Enzyme-linked immunospot; PCR, polymerase chain reaction.First, our HIV-1 antigen ELISPOT assay is at least as sensitive and considerably less time consuming and labour intensive than the limiting-dilution culture of resting CD4 T cells after ex-vivo activation, as used in the study by Lehrman et al. [1]. Major points concerning our approach consist of the combination of: (i) an efficient method of resting CD4 T-cell isolation; (ii) the conservation of CD4 T-cell functions; and (iii) an exquisitely sensitive ELISPOT assay (with the capacity to detect a single HIV-1 antigen-producing cell among 1 × 106 CD4 T lymphocytes) [4]. As it can be applied to other compartments than blood, the HIV-1 antigen ELISPOT assay may become the technique of choice for further studies on the compartmentalization of the HIV-1 resting CD4 T-cell reservoirs. Second, our study demonstrates a strong compartmentalization of the HIV-1 latently infected CD4 T-cell reservoir at least in the mammary gland, because HIV-1-infected resting CD4 T cells can replicate HIV-1 after ex-vivo activation more extensively in breast milk than in blood. Compartmentalization of the viral reservoir is not an academic fantasy. For example, a strong genotypic and phenotypic compartmentalization of cell-free as well as cell-associated HIV-1 has been observed in the blood and seminal reservoirs after an intensification and stimulatory HIV-1 eradication protocol [5]. As suggested by Routy [2], the enumeration and assessment of functional capacities of resting CD4 T cells to enter a replicative cycle in peripheral blood may not necessarily reflect what happens in other anatomical or tissue compartments, such as seminal fluid, cervicovaginal secretions, central nervous system or breast milk. In our ultimate goal of finding a cure for HIV, this compartmentalization should be taken into account in further clinical trials on valproic acid or related compounds aimed at purging the HIV-1 proviral reservoir. The authors declare that they have no conflict of interest. Sponsorship: This work was supported by the Agence Nationale de Recherches sur le SIDA (ANRS), as part of the project ANRS 1271 (contract 2004-010).