Although many HIV cure strategies seek to expand HIV-specific CD8 + T cells to control the virus, all are likely to fail if cellular exhaustion is not prevented. A loss in stem-like memory properties (i.e., the ability to proliferate and generate secondary effector cells) is a key feature of exhaustion; little is known, however, about how these properties are regulated in human virus–specific CD8 + T cells. We found that virus-specific CD8 + T cells from humans and nonhuman primates naturally controlling HIV/SIV infection express more of the transcription factor TCF-1 than noncontrollers. HIV-specific CD8 + T cell TCF-1 expression correlated with memory marker expression and expansion capacity and declined with antigenic stimulation. CRISPR-Cas9 editing of TCF-1 in human primary T cells demonstrated a direct role in regulating expansion capacity. Collectively, these data suggest that TCF-1 contributes to the regulation of the stem-like memory property of secondary expansion capacity of HIV-specific CD8 + T cells, and they provide a rationale for exploring the enhancement of this pathway in T cell–based therapeutic strategies for HIV.

Retroviral long terminal repeats (LTRs) contain elements responsible for the control of proviral transcription and gene expression. Molecular clones of the LTR region of a number of avian retroviruses have been isolated, and DNA sequence analysis of these clones reveals the existence of a related, but heterogenous, family of LTRs. To examine the functional significance of the observed sequence differences, we have directly tested the abilities of several different avian retrovirus LTRs to act as promoters and enhancers of mRNA transcription. Our results indicate that large differences in LTR transcriptional activity exist and that these differences in gene expression directly correlate with LTR enhancer activity. In particular, we show that the LTR of Fujinami sarcoma virus is intermediate in both transcriptional and enhancer activity when compared with the very active LTRs of the exogenous viruses RAV-2 and Schmidt-Ruppin B and the much less active LTRs of the endogenous virus RAV-0 and its provirus ev-2. These results suggest that LTR enhancer activity may be the primary determinant of avian retroviral LTR transcriptional activity and, hence, oncogenic potential.

Quiescence is a hallmark of CD4 + T cells latently infected with HIV-1. While reversing this quiescence is an effective approach to reactivate latent HIV from T cells in culture, it can cause deleterious cytokine dysregulation in patients. As a key regulator of T-cell quiescence, FOXO1 promotes latency and suppresses productive HIV infection. We report that in resting T cells, FOXO1 inhibition impaired autophagy and induced ER stress, thereby activating two associated transcription factors: activating transcription factor 4 (ATF4) and nuclear factor of activated T cells (NFAT). Both factors associate with HIV chromatin and were for HIV reactivation. Indeed, inhibition of PKR-like endoplasmic reticulum kinase (PERK), an ER stress sensor that can mediate the induction of ATF4, and calcineurin, a calcium-dependent regulator of NFAT, synergistically suppressed HIV reactivation induced by FOXO1 inhibition. Thus, our studies uncover a link between FOXO1, ER stress, and HIV infection that could be therapeutically exploited to selectively reverse T-cell quiescence and reduce the size of the latent viral reservoir.

On May 6, 2022, a powerful outbreak of monkeypox virus (MPXV) had been reported outside of Africa, with many continuing new cases being reported around the world. Analysis of mutations among the two different lineages present in the 2021 and 2022 outbreaks revealed the presence of G->A mutations occurring in the 5′GpA context, indicative of APOBEC3 cytosine deaminase activity. By using a sensitive PCR (3D-PCR) method allowing differential amplification of ATrich DNA, we demonstrate that G->A hypermutated MPXV genomes can be recovered experimentally from APOBEC3 transfection followed by MPXV infection. Here, among the 7 human APOBEC3 cytidine deaminases (A3A-A3C, A3DE, A3F-A3H), only APOBEC3F was capable of extensively deaminating cytidine residues in MPXV genomes. Hyperedited genomes were also recovered in ~42% of analyzed patients, indicating that editing is part of the natural cycle of MPXV infection. Moreover, we demonstrate that substantial repair of these mutations occurs. Upon selection, corrected G->A mutations escaping drift loss contribute to the MPXV evolution observed in the current epidemics. Thus, stochastic or transient overexpression of APOBEC3F gene exposes the MPXV genome to a broad spectrum of mutations that may be modeling the mutational landscape after multiple cycles of viral replication.