A quantitative approach for measuring the reservoir of latent HIV-1 proviruses

A stable latent reservoir for HIV-1 in resting CD4⁺ T cells is the principal barrier to a cure^1–3. Curative strategies that target the reservoir are being tested^4,5 and require accurate, scalable reservoir assays. The reservoir was defined with quantitative viral outgrowth assays for cells that release infectious virus after one round of T cell activation¹. However, these quantitative outgrowth assays and newer assays for cells that produce viral RNA after activation⁶ may underestimate the reservoir size because one round of activation does not induce all proviruses⁷. Many studies rely on simple assays based on polymerase chain reaction to detect proviral DNA regardless of transcriptional status, but the clinical relevance of these assays is unclear, as the vast majority of proviruses are defective^7–9. Here we describe a more accurate method of measuring the HIV-1 reservoir that separately quantifies intact and defective proviruses. We show that the dynamics of cells that carry intact and defective proviruses are different in vitro and in vivo. These findings have implications for targeting the intact proviruses that are a barrier to curing HIV infection.