Research advances in evaluation and measurement techniques of latent human immunodeficiency virus reservoirs

: Latent reservoir (LR) of HIV is the cells (such as CD4(+)T cell) where HIV is able to hide. These cellular reservoirs are located throughout the body, including the spleen, lymph nodes, gastrointestinal lymphoid tissues, and become the major obstacle to cure HIV infection. To truly cure patients, a new strategy "shock and kill" was put forward by scientists, which is to shock HIV-infected cells out of hidden reservoirs in the body and then kill them. Quantitatively evaluating the size of long-lived LR is essential to this strategy. This paper reviews assays that measure the magnitude of the latent HIV reservoir, including Alu-gag PCR, quantitative viral outgrowth assay (Q-VOA) and tat/rev induced limiting dilution assay(TILDA). Alu-gag PCR can differentiate the integrated and un-integrated HIV DNA, however, it cannot distinguish defective virus from competent virus, leading to overestimate the real size of LR. Q-VOA is based on cell culture, and is the golden standard for measuring the LR since it provides a definitive minimal estimate of reservoir size. Its disadvantages are being more costly, large amount of blood sample required, and underestimating the true size, which was resulted from particles being not released after one round of stimulation. TILDA measures cells with inducible msRNA as these transcripts are absent in latently infected cells but induced upon viral reactivation. It requires small blood sample size, does not need extraction of viral nucleic acids, can be completed in 2 d and covers a wide dynamic range of reservoir sizes, but has the disadvantage of overestimating the true size of LR.