PB2 residue 473 contributes to the mammalian virulence of H7N9 avian influenza virus by modulating viral polymerase activity via ANP32A.

Since the first human infection reported in 2013, H7N9 avian influenza virus (AIV) has been regarded as a serious threat to human health. In this study, we sought to identify the virulence determinant of the H7N9 virus in mammalian hosts. By comparing the virulence of the SH/4664 H7N9 virus, a non-virulent H9N2 virus, and various H7N9-H9N2 hybrid viruses in infected mice, we first pinpointed PB2 as the primary viral factor accounting for the difference between H7N9 and H9N2 in mammalian virulence. We further analyzed the in vivo effects of individually mutating H7N9 PB2 residues different from the closely related H9N2 virus and consequently found residue 473, alongside the well-known residue 627, to be critical for the virulence of the H7N9 virus in mice and the activity of its reconstituted viral polymerase in mammalian cells. The importance of PB2-473 was further strengthened by studying reverse H7N9 substitutions in the H9N2 background. Finally, we surprisingly found that species-specific usage of ANP32A, a family member of host factors connecting with the PB2-627 polymorphism, mediates the contribution of PB2 473 residue to the mammalian adaption of AIV polymerase, as the attenuating effect of PB2 M473T on the viral polymerase activity and viral growth of the H7N9 virus could be efficiently complemented by co-expression of chicken ANP32A but not mouse ANP32A and ANP32B. Together, our studies uncovered the PB2 473 residue as a novel viral host range determinant of AIVs via species-specific co-opting of the ANP32 host factor to support viral polymerase activity.IMPORTANCEThe H7N9 avian influenza virus has been considered to have the potential to cause the next pandemic since the first case of human infection reported in 2013. In this study, we identified PB2 residue 473 as a new determinant of mouse virulence and mammalian adaptation of the viral polymerase of the H7N9 virus and its non-pathogenic H9N2 counterparts. We further demonstrated that the variation in PB2-473 is functionally linked to differential co-opting of the host ANP32A protein in supporting viral polymerase activity, which is analogous to the well-known PB2-627 polymorphism, albeit the two PB2 positions are spatially distant. By providing new mechanistic insight into the PB2-mediated host range determination of influenza A viruses, our study implicated the potential existence of multiple PB2-ANP32 interfaces that could be targets for developing new antivirals against the H7N9 virus as well as other mammalian-adapted influenza viruses.

A randomized, double-blind, placebo-controlled phase I trial of inhalation treatment of recombinant TFF2-IFN protein: A multifunctional candidate for the treatment of COVID-19.

Background and Objectives: Coronavirus disease 2019 (COVID-19) has caused global pandemics in the last 3 years, and the development of new therapeutics is urgently needed. This study aimed to assess the safety, tolerated, and prolonged retention of recombinant protein trefoil factor 2 (TFF2)- interferon (IFN) in the respiratory tract of healthy volunteers. Methods: We conducted a randomized, double-blind, placebo-controlled, single-dose, dose-escalation phase I study to evaluate safety, tolerability, pharmacokinetics (PK), and cytokine responses after administration of recombinant TFF2-IFN proteins. Healthy volunteers were informed, enrolled, and randomized into four groups with a dose escalation of 0.2, 1, 2, and 4 mg and then inhaled the investigation product or placebo. Thirty-two eligible participants were finally enrolled; eight were assigned to the placebo group and 24 to the TFF2-IFN group, with six participants per group. Data were collected from 19 November 2021, to 4 January 2022. Results: All 32 participants completed the study. Of the participants who received the recombinant TFF2-IFN protein, 41.7% (10/24) reported 11 adverse events (AEs) during treatment and 62.5% (5/8) of those who received a placebo reported six AEs. Sixteen of the 17 AEs were grade 1. Only one grade 3 AE occurred in the placebo group and no worse event occurred as a serious adverse event. The pharmacokinetics was analyzed for times and concentrations of the investigation products in 0.2, 1, 2, and 4 mg groups in 24 recipients of TFF2-IFN, and the results showed that TFF2-IFN was retained in the lung for at least 6-8 h. Only the highest dose group (4 mg) had a transient detectable concentration in serum, while all other dose groups had a level below the lower limit of quantification. Conclusion: In this study, the recombinant TFF2-IFN protein was a well-tolerated and safe therapeutic when administered by nebulization, characterized by prolonged retention in the respiratory tract, which would be greatly beneficial in combating respiratory viral infection. Systematic Review Registration: [http://www.chictr.org.cn], identifier [ChiCTR2000035633].

Comparison of H7N9 and H9N2 influenza infections in mouse model unravels the importance of early innate immune response in host protection.

The outcome of infection with influenza A virus is determined by a complex virus-host interaction. A new H7N9 virus of avian origin crossed the species barrier to infect humans, causing high mortality and emerged as a potential pandemic threat. The mechanisms underlying the virulence and pathogenicity of H7N9 virus remains elusive. H7N9 virus originated from a genetic assortment that involved the avian H9N2 virus, which was the donor of the six internal genes. Unlike the H7N9 virus, the H9N2 virus caused only mild phenotype in infected mice. In this study, we used the mouse infection model to dissect the difference in the host response between the H7N9 and H9N2 viruses. Through analyzing transcriptomics of infected lungs, we surprisingly found that the H9N2 infection elicited an earlier induction of innate immunity than H7N9 infection. This finding was further corroborated by an immunohistochemical study demonstrating earlier recruitment of macrophage to the H9N2-infected lung than the H7N9-infected lung, which could occur as early as 6 hours post infection. In contrast, H7N9 infection was characterized by a late, strong lung CD8+ T cell response that is more robust than H9N2 infection. The different pattern of immune response may underlie more severe lung pathology caused by H7N9 infection compared to H9N2 infection. Finally, we could show that co-infection of the H9N2 virus protected mice from the challenge of both H7N9 and PR8 viruses, thereby strengthening the importance of the induction of an early innate immunity in the host's defense against influenza infection. Collectively, our study unraveled a previously unidentified difference in host response between H7N9 and H9N2 infection and shed new insight on how virus-host interaction shapes the in vivo outcome of influenza infection.

Neutralization mechanism of a human antibody with pan-coronavirus reactivity including SARS-CoV-2.

Frequent outbreaks of coronaviruses underscore the need for antivirals and vaccines that can counter a broad range of coronavirus types. We isolated a human antibody named 76E1 from a COVID-19 convalescent patient, and report that it has broad-range neutralizing activity against multiple α- and ß-coronaviruses, including the SARS-CoV-2 variants. 76E1 also binds its epitope in peptides from γ- and δ-coronaviruses. 76E1 cross-protects against SARS-CoV-2 and HCoV-OC43 infection in both prophylactic and therapeutic murine animal models. Structural and functional studies revealed that 76E1 targets a unique epitope within the spike protein that comprises the highly conserved S2' site and the fusion peptide. The epitope that 76E1 binds is partially buried in the structure of the SARS-CoV-2 spike trimer in the prefusion state, but is exposed when the spike protein binds to ACE2. This observation suggests that 76E1 binds to the epitope at an intermediate state of the spike trimer during the transition from the prefusion to the postfusion state, thereby blocking membrane fusion and viral entry. We hope that the identification of this crucial epitope, which can be recognized by 76E1, will guide epitope-based design of next-generation pan-coronavirus vaccines and antivirals.

SARS-CoV-2 RNA elements share human sequence identity and upregulate hyaluronan via NamiRNA-enhancer network.

BACKGROUND: Since late 2019, SARS-CoV-2 infection has resulted in COVID-19 accompanied by diverse clinical manifestations. However, the underlying mechanism of how SARS-CoV-2 interacts with host and develops multiple symptoms is largely unexplored. METHODS: Bioinformatics analysis determined the sequence similarity between SARS-CoV-2 and human genomes. Diverse fragments of SARS-CoV-2 genome containing Human Identical Sequences (HIS) were cloned into the lentiviral vector. HEK293T, MRC5 and HUVEC were infected with laboratory-packaged lentivirus or transfected with plasmids or antagomirs for HIS. Quantitative RT-PCR and chromatin immunoprecipitation assay detected gene expression and H3K27ac enrichment, respectively. UV-Vis spectroscopy assessed the interaction between HIS and their target locus. Enzyme-linked immunosorbent assay evaluated the hyaluronan (HA) levels of culture supernatant and plasma of COVID-19 patients. FINDINGS: Five short sequences (24-27 nt length) sharing identity between SARS-CoV-2 and human genome were identified. These RNA elements were highly conserved in primates. The genomic fragments containing HIS were predicted to form hairpin structures in silico similar to miRNA precursors. HIS may function through direct genomic interaction leading to activation of host enhancers, and upregulation of adjacent and distant genes, including cytokine genes and hyaluronan synthase 2 (HAS2). HIS antagomirs and Cas13d-mediated HIS degradation reduced HAS2 expression. Severe COVID-19 patients displayed decreased lymphocytes and elevated D-dimer, and C-reactive proteins, as well as increased plasma hyaluronan. Hymecromone inhibited hyaluronan production in vitro, and thus could be further investigated as a therapeutic option for preventing severe outcome in COVID-19 patients. INTERPRETATION: HIS of SARS-CoV-2 could promote COVID-19 progression by upregulating hyaluronan, providing novel targets for treatment. FUNDING: The National Key R&D Program of China (2018YFC1005004), Major Special Projects of Basic Research of Shanghai Science and Technology Commission (18JC1411101), and the National Natural Science Foundation of China (31872814, 32000505).

Correlation Between Early Plasma Interleukin 37 Responses With Low Inflammatory Cytokine Levels and Benign Clinical Outcomes in Severe Acute Respiratory Syndrome Coronavirus 2 Infection.

BACKGROUND: The immune protective mechanisms during severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection remain to be deciphered for the development of an effective intervention approach. METHODS: We examined early responses of interleukin 37 (IL-37), a powerful anti-inflammatory cytokine, in 254 SARS-CoV-2-infected patients before any clinical intervention and determined its correlation with clinical prognosis. RESULTS: Our results demonstrated that SARS-CoV-2 infection causes elevation of plasma IL-37. Higher early IL-37 responses were correlated with earlier viral RNA negative conversion, chest computed tomographic improvement, and cough relief, consequently resulted in earlier hospital discharge. Further assays showed that higher IL-37 was associated with lower interleukin 6 and interleukin 8 (IL-8) and higher interferon α responses and facilitated biochemical homeostasis. Low IL-37 responses predicted severe clinical prognosis in combination with IL-8 and C-reactive protein. In addition, we observed that IL-37 administration was able to attenuate lung inflammation and alleviate respiratory tissue damage in human angiotensin-converting enzyme 2-transgenic mice infected with SARS-CoV-2. CONCLUSIONS: Overall, we found that IL-37 plays a protective role by antagonizing inflammatory responses while retaining type I interferon, thereby maintaining the functionalities of vital organs. IL-37, IL-8, and C-reactive protein might be formulated as a precise prediction model for screening severe clinical cases and have good value in clinical practice.

CD160 Plays a Protective Role During Chronic Infection by Enhancing Both Functionalities and Proliferative Capacity of CD8+ T Cells.

The understanding of protective immunity during HIV infection remains elusive. Here we showed that CD160 defines a polyfunctional and proliferative CD8+ T cell subset with a protective role during chronic HIV-1 infection. CD160+ CD8+ T cells derived from HIV+ patients correlated with slow progressions both in a cross-sectional study and in a 60-month longitudinal cohort, displaying enhanced cytotoxicity and proliferative capacity in response to HIV Gag stimulation; triggering CD160 promoted their functionalities through MEK-ERK and PI3K-AKT pathways. These observations were corroborated by studying chronic lymphocytic choriomeningitis virus (LCMV) infection in mice. The genetic ablation of CD160 severely impaired LCMV-specific CD8+ T cell functionalities and thereby resulted in loss of virus control. Interestingly, transcriptional profiling showed multiple costimulatory and survival pathways likely to be involved in CD160+ T cell development. Our data demonstrated that CD160 acts as a costimulatory molecule positively regulating CD8+ T cells during chronic viral infections, thus representing a potential target for immune intervention.

An open-label, randomized trial of the combination of IFN-κ plus TFF2 with standard care in the treatment of patients with moderate COVID-19.

BACKGROUND: Epidemic outbreaks caused by SARS-CoV-2 are worsening around the world, and there are no target drugs to treat COVID-19. IFN-κ inhibits the replication of SARS-CoV-2; and TFF2 is a small secreted polypeptide that promotes the repair of mucosal injury and reduces the inflammatory responses. We used the synergistic effect of both proteins to treat COVID-19. METHODS: We conducted an open-label, randomized, clinical trial involving patients with moderate COVID-19. Patients were assigned in a 1:1 ratio to receive either aerosol inhalation treatment with IFN-κ and TFF2 every 24 h for six consecutive dosages in addition to standard care (experimental group) or standard care alone (control group). The primary endpoint was the time until a viral RNA negative conversion for SARS-CoV-2 in all clinical samples. The secondary clinical endpoint was the time of CT imaging improvement. Data analysis was performed per protocol. This study was registered with chictr.org.cn, ChiCTR2000030262. FINDINGS: Between March 23 and May 23 of 2020, 86 COVID-19 patients with symptoms of moderate illness were recruited, and 6 patients were excluded due to not matching the inclusion criteria (patients with pneumonia through chest radiography). Among the remaining 80 patients, 40 patients were assigned to experimental group, and the others were assigned to control group to only receive standard care. Efficacy and safety were evaluated for both groups. The time of viral RNA negative conversion in experimental group (Mean, 3·80 days, 95% CI 2·07-5·53), was significantly shorter than that in control group (7·40 days, 95% CI 4·57 to 10·23) (p = 0.031), and difference between means was 3·60 days. The percentage of patients in experimental group with reversion to negative viral RNA was significantly increased compared with control group on all sampling days (every day during the 12-day observation period) (p = 0·037). For the secondary endpoint, the experimental group had a significantly shorter time until improvement was seen by CT (Mean 6·21 days, N = 38/40, 95% CI 5·11-7·31) than that in control group (8·76 days, N = 34/40, 95% CI 7·57-9·96) (p = 0.002), and difference between means was 2·55 days. No discomfort or complications during aerosol inhalation were reported to the nurses by any experimental patients. INTERPRETATION: In conclusion, we found that aerosol inhalation of IFN-κ plus TFF2 in combination with standard care is safe and superior to standard care alone in shortening the time up to viral RNA negative conversion in all clinical samples. In addition, the patients in experimental group had a significantly shortened CT imaging improvement time than those in control group. This study suggested that this combination treatment is able to facilitate clinical improvement (negative for virus, improvement by CT, reduced hospitalization stay) and thereby result in an early release from the hospital. These data support the need for exploration with a large-scale trial of IFN-κ plus TFF2 to treat COVID-19. FUNDING: Funding was provided by the National Natural Science Foundation of China, National Major Project for Control and Prevention of Infectious Disease in China, Shanghai Science and Technology Commission, Shanghai Municipal Health Commission.

Self-Assembly M2e-Based Peptide Nanovaccine Confers Broad Protection Against Influenza Viruses.

The extracellular domain of influenza M2 protein (M2e) is highly conserved and is a promising target for development of universal influenza vaccines. Here, we synthesized a peptide vaccine consisting of M2e epitope linked to a fibrillizing peptide, which could self-assemble into nanoparticle in physiological salt solutions. When administrated into mice without additional adjuvant, the influenza A M2e epitope-bearing nanoparticles induced antibodies against M2e of different influenza subtypes. Comparing with other M2e-based vaccine, these M2e nanoparticles did not induce immune response against the fibrillizing peptide, demonstrating minimal immunogenicity of vaccine carrier. Furthermore, vaccination with M2e-based nanoparticles did not only protect mice against homologous challenge of influenza PR8 H1N1 virus, but also provide protection against heterologous challenge of highly pathogenic avian influenza H7N9 virus. These results indicated that M2e-based self-assembled nanoparticle vaccine is safe and can elicit cross-protection, therefore is a promising candidate of universal influenza vaccines.

A novel biparatopic hybrid antibody-ACE2 fusion that blocks SARS-CoV-2 infection: implications for therapy.

In the absence of a proven effective vaccine preventing infection by SARS-CoV-2, or a proven drug to treat COVID-19, the positive results of passive immune therapy using convalescent serum provide a strong lead. We have developed a new class of tetravalent, biparatopic therapy, 89C8-ACE2. It combines the specificity of a monoclonal antibody (89C8) that recognizes the relatively conserved N-terminal domain of the viral Spike (S) glycoprotein, and the ectodomain of ACE2, which binds to the receptor-binding domain of S. This molecule shows exceptional performance in vitro, inhibiting the interaction of recombinant S1 to ACE2 and transduction of ACE2-overexpressing cells by S-pseudotyped lentivirus with IC50s substantially below 100 pM, and with potency approximately 100-fold greater than ACE2-Fc itself. Moreover, 89C8-ACE2 was able to neutralize authentic viral infection in a standard 96-h co-incubation assay at low nanomolar concentrations, making this class of molecule a promising lead for therapeutic applications.

A clinical pilot study on the safety and efficacy of aerosol inhalation treatment of IFN-κ plus TFF2 in patients with moderate COVID-19.

BACKGROUND: The outbreak of a new coronavirus (SARS-CoV-2) poses a great challenge to global public health. New and effective intervention strategies are urgently needed to combat the disease. METHODS: We conducted an open-label, non-randomized, clinical trial involving moderate COVID-19 patients according to study protocol. Patients were assigned in a 1:2 ratio to receive either aerosol inhalation treatment with IFN-κ and TFF2, every 48 h for three consecutive dosages, in addition to standard treatment (experimental group), or standard treatment alone (control group). The end point was the time to discharge from the hospital. This study is registered with chictr.org.cn, ChiCTR2000030262. FINDINGS: A total of thirty-three eligible COVID-19 patients were enrolled from February 1, 2020 to April 6, 2020, eleven were assigned to the IFN-κ plus TFF2 group, and twenty-two to the control group. Safety and efficacy were evaluated for both groups. No treatment-associated severe adverse effects (SAE) were observed in the group treated with aerosol inhalation of IFN-κ plus TFF2, and no significant differences in the safety evaluations were observed between experimental and control groups. CT imaging was performed in all patients with the median improvement time of 5.0 days (IQR 3.0-9.0) in the experimental group versus 8.5 days (IQR 3.0-17.0) in the control group (p<0.05). In addition, the experimental group had a significant shorten median time in cough relief (4.5 days [IQR 2.0-7.0]) than the control group did (10.0 days [IQR 6.0-21.0])(p<0.005), in viral RNA reversion of 6.0 days (IQR 2.0-13.0) in the experimental group vs 9.5 days (IQR 3.0-23.0) in the control group (p < 0.05), and in the median hospitalization stays of 12.0 days (IQR 7.0-20.0) in the experimental group vs 15.0 days (IQR 10.0-25.0) in the control group (p<0.001), respectively. INTERPRETATION: Aerosol inhalation of IFN-κ plus TFF2 is a safe treatment and is likely to significantly facilitate clinical improvement, including cough relief, CT imaging improvement, and viral RNA reversion, thereby achieves an early release from hospitalization. These data support to explore a scale-up trial with IFN-κ plus TFF2. FUNDING: National Major Project for Control and Prevention of Infectious Disease in China, Shanghai Science and Technology Commission, Shanghai Municipal Health Commission.

IFN-κ suppresses the replication of influenza A viruses through the IFNAR-MAPK-Fos-CHD6 axis.

Type I interferons (IFNs) are the first line of defense against viral infection. Using a mouse model of influenza A virus infection, we found that IFN-κ was one of the earliest responding type I IFNs after infection with H9N2, a low-pathogenic avian influenza A virus, whereas this early induction did not occur upon infection with the epidemic-causing H7N9 virus. IFN-κ efficiently suppressed the replication of various influenza viruses in cultured human lung cells, and chromodomain helicase DNA binding protein 6 (CHD6) was the major effector for the antiviral activity of IFN-κ, but not for that of IFN-α or IFN-ß. The induction of CHD6 required both of the type I IFN receptor subunits IFNAR1 and IFNAR2, the mitogen-activated protein kinase (MAPK) p38, and the transcription factor c-Fos but was independent of signal transducer and activator of transcription 1 (STAT1) activity. In addition, we showed that pretreatment with IFN-κ protected mice from lethal influenza viral challenge. Together, our findings identify an IFN-κ-specific pathway that constrains influenza A virus and provide evidence that IFN-κ may have potential as a preventative and therapeutic agent against influenza A virus.

Both haemagglutinin-specific antibody and T cell responses induced by a chimpanzee adenoviral vaccine confer protection against influenza H7N9 viral challenge.

Since 2013, the outbreak or sporadic infection of a new reassortant H7N9 influenza virus in China has resulted in hundreds of deaths and thousands of illnesses. An H7N9 vaccine is urgently needed, as a licensed human vaccine against H7N9 influenza is currently not available. Here, we developed a recombinant adenovirus-based vaccine, AdC68-H7HA, by cloning the H7N9 haemagglutinin (HA) gene into the chimpanzee adenoviral vector AdC68. The efficacy of AdC68-H7HA was evaluated in mice as well as guinea pigs. For comparison, an H7N9 DNA vaccine based on HA was also generated and tested in mice and guinea pigs. The results demonstrated that both AdC68-H7HA and the DNA vaccine prime-adenovirus boost regimen induced potent immune responses in animals and completely protected mice from lethal H7N9 influenza viral challenge. A post-immunization serum transfer experiment showed that antibody responses could completely protect against lethal challenge, while a T cell depletion experiment indicated that HA-specific CD8+ T cells responses also contributed to protection. Therefore, both HA-specific humoral immunity and cellular immunity play important roles in the protection. These data suggest that the chimpanzee adenovirus expressing HA is a promising vaccine candidate for H7N9 virus or other influenza viral subtypes.

Immune Activation Influences SAMHD1 Expression and Vpx-mediated SAMHD1 Degradation during Chronic HIV-1 Infection.

SAMHD1 restricts human immunodeficiency virus type 1 (HIV-1) replication in myeloid cells and CD4+ T cells, while Vpx can mediate SAMHD1 degradation to promote HIV-1 replication. Although the restriction mechanisms of SAMHD1 have been well-described, SAMHD1 expression and Vpx-mediated SAMHD1 degradation during chronic HIV-1 infection were poorly understood. Flow cytometric analysis was used to directly visualize ex vivo, and after in vitro SIV-Vpx treatment, SAMHD1 expression in CD4+ T cells and monocytes. Here we report activated CD4+ T cells without SAMHD1 expression were severely reduced, and SAMHD1 in CD4+ T cells became susceptible to SIV-Vpx mediated degradation during chronic HIV-1 infection, which was absent from uninfected donors. These alterations were irreversible, even after long-term fully suppressive antiretroviral treatment. Although SAMHD1 expression in CD4+ T cells and monocytes was not found to correlate with plasma viral load, Vpx-mediated SAMHD1 degradation was associated with indicators of immune activation. In vitro assays further revealed that T-cell activation and an upregulated IFN-I pathway contributed to these altered SAMHD1 properties. These findings provide insight into how immune activation during HIV-1 infection leads to irreparable aberrations in restriction factors and in subsequent viral evasion from host antiviral defenses.

IFN-stimulated gene LY6E in monocytes regulates the CD14/TLR4 pathway but inadequately restrains the hyperactivation of monocytes during chronic HIV-1 infection.

Owing to ongoing recognition of pathogen-associated molecular patterns, immune activation and upregulation of IFN-stimulated genes (ISGs) are sustained in the chronically infected host. Albeit most ISGs are important effectors for containing viral replication, some might exert compensatory immune suppression to limit pathological dysfunctions, although the mechanisms are not fully understood. In this study, we report that the ISG lymphocyte Ag 6 complex, locus E (LY6E) is a negative immune regulator of monocytes. LY6E in monocytes negatively modulated CD14 expression and subsequently dampened the responsiveness to LPS stimulation in vitro. In the setting of chronic HIV infection, the upregulation of LY6E was correlated with reduced CD14 level on monocytes; however, the immunosuppressive effect of LY6E was not adequate to remedy the hyperresponsiveness of activated monocytes. Taken together, the regulatory LY6E pathway in monocytes represents one of negative feedback mechanisms that counterbalance monocyte activation, which might be caused by LPS translocation through the compromised gastrointestinal tract during persistent HIV-1 infection and may serve as a potential target for immune intervention.

MCPIP1 restricts HIV infection and is rapidly degraded in activated CD4+ T cells.

HIV-1 primarily infects activated CD4+ T cells and macrophages. Quiescent CD4+ T cells, however, possess cellular factors that limit HIV-1 infection at different postentry steps of the viral life cycle. Here, we show that the previously reported immune regulator monocyte chemotactic protein-induced protein 1 (MCPIP1) restricts HIV-1 production in CD4+ T cells. While the ectopic expression of MCPIP1 in cell lines abolished the production of HIV-1, silencing of MCPIP1 enhanced HIV-1 production. Subsequent analysis indicated that MCPIP1 imposes its restriction by decreasing the steady levels of viral mRNA species through its RNase domain. Remarkably, common T-cell stimuli induced the rapid degradation of MCPIP1 in both T-cell lines and quiescent human CD4+ T cells. Lastly, blocking the proteosomal degradation of MCPIP1 by MG132 abrogated HIV-1 production in phorbol 12-myristate 13-acetate/ionomycin-stimulated human CD4+ T cells isolated from healthy donors. Overall, MCPIP1 poses a potent barrier against HIV-1 infection at a posttranscriptional stage. Although the observed HIV restriction conferred by MCPIP1 does not seem to be overcome by any viral protein, it is removed during cellular stimulation. These findings provide insights into the mechanisms of cellular activation-mediated HIV-1 production in CD4+ T cells.