INTRODUCTION:Islatravir (ISL) is a nucleoside reverse transcriptase translocation inhibitor (NRTTI) with robust antiretroviral activity. The efficacy of ISL administered for post-exposure prophylaxis (PEP) was evaluated in a simian immunodeficiency virus (SIV) rhesus macaque intravenous (IV) challenge model. METHODS:Twelve rhesus macaques were challenged with SIVmac251 via IV administration. After 24 hours, six animals received ISL 3.9 mg/kg (the minimum effective dose that gives maximal protection) and six animals were untreated controls. In stage 1, treated animals received 4 weekly oral doses of ISL and were monitored for SIV infection for 7 weeks after the last dose. In stage 2, uninfected, treated animals from stage 1 were challenged similarly; 24 hours after challenge, 3 weekly oral doses of ISL 3.9 mg/kg were initiated. The treated animals were monitored for 7 weeks, as in stage 1. Uninfected, treated animals (from stage 2) entered stage 3. In stage 3, the animals were challenged as in stage 2; 24 hours after challenge, 2 weekly oral doses of ISL 3.9 mg/kg were initiated. The treated animals were monitored for 7 weeks, as before. Finally, in stage 4, uninfected, treated animals were challenged using IV administration and 24 hours later were treated with a single oral dose of ISL 3.9 mg/kg and monitored for 7 weeks. Infection was monitored through plasma viral RNA and proviral DNA amplification. Virus-specific antibody responses were measured using a commercial assay. ISL concentrations in plasma and ISL triphosphate (ISL-TP) levels in peripheral blood mononuclear cells were measured longitudinally. RESULTS:All untreated controls were viraemic 7 days after SIVmac251 IV challenge. All six ISL-treated animals were completely protected in stages 1-3 (Fisher exact test p = 0.0022). In stage 4, two of six ISL-treated animals became infected with wild-type SIVmac251: viraemia was observed at days 14 and 49 in the two animals (Fisher exact test p = 0.06). Both animals had unquantifiable ISL-TP on the day viraemia was observed. CONCLUSIONS:Two weekly oral doses of ISL 3.9 mg/kg, administered 24 hours post IV SIV exposure, prevents infection of rhesus macaques. These results support further investigation of a long-acting oral NRTTI for PEP.

Pattern recognition receptors (PRRs) protect against microbial invasion by de-tecting specific molecular patterns found in pathogens and initiating an immune response. Although microbial-derived PRR ligands have been extensively charac-terized, the contribution and relevance of endogenous ligands to PRR activation remains overlooked. Here, we characterize the landscape of endogenous ligands that engage RIG-I-like receptors (RLRs) upon infection by different RNA viruses. In each infection, several RNAs transcribed by RNA polymerase III (Pol3) specif-ically engaged RLRs, particularly the family of Y RNAs. Sensing of Y RNAs was dependent on their mimicking of viral secondary structure and their 5'-triphos-phate extremity. Further, we found that HIV-1 triggered a VPR-dependent down -regulation of RNA triphosphatase DUSP11 in vitro and in vivo, inducing a tran-scriptome-wide change of cellular RNA 5'-triphosphorylation that licenses Y RNA immunogenicity. Overall, our work uncovers the contribution of endoge-nous RNAs to antiviral immunity and demonstrates the importance of this pathway in HIV-1 infection.

Several antiretroviral agents do not efficiently enter the CNS, and independent evolution of HIV-1 viral variants in the CNS and plasma can occur. We used single-genome amplification (SGA) in cross-sectional and longitudinal analyses to uniquely define both the identity and relative proportions of drug resistance mutations (DRMs) on individual HIV-1 polymerase genomes in the cerebrospinal fluid (CSF) and plasma in individuals with incomplete viral suppression and known neurocognitive status. Statistically significant differences in the ratio of DRMs in the CSF and plasma were readily found in those on nonsuppressive cART, and overrepresentation of DRMs in the CNS can occur. Although questions about the clinical significance of DRM discordance remain, in the quest for viral eradication, it is important to recognize that a significant, dynamic, compartment-based DRM ratio imbalance can exist, as it has the potential to go unnoticed in the setting of standard clinical drug resistance testing.

PURPOSE OF REVIEWTo discuss the potential role of islatravir (ISL), a novel reverse transcriptase translocation inhibitor, in the treatment and prevention of human immunodeficiency virus type 1 (HIV-1) infection.RECENT FINDINGSIslatravir (4'-ethynyl-2-fluoro-2'-deoxyadenosine, MK-8591) is a long-acting first-in-class nucleoside reverse transcriptase translocation inhibitor with the potential for versatile dosing routes and dosing intervals. It demonstrated robust antiviral activity when dosed once daily and once weekly in HIV-1-infected individuals and SIV-infected rhesus macaques. In clinical trials of ISL in combination with doravirine and lamivudine, daily oral administration resulted in high levels of virologic suppression in HIV-infected individuals. In preclinical studies, ISL dosed orally once-weekly as preexposure prophylaxis (PrEP), protected rhesus macaques against SHIV infection via the mucosal route in the low-dose rectal challenge model. Most recently, data in healthy HIV-1-uninfected individuals demonstrated the feasibility of formulating of ISL as an implant. In these studies, levels of intracellular ISL-triphosphate were consistent with the potential for a once-yearly implantable administration of ISL as PrEP.SUMMARYIslatravir is a promising new agent for both the treatment and prevention of HIV-1 infection.

Objective: Toll-like receptor-3 agonist Poly-ICLC has been known to activate immune cells and induce HIV replication in pre-clinical experiments. In this study we investigated if Poly-ICLC could be used for disrupting HIV latency while simultaneously enhancing innate immune responses. Design: This was a randomized, placebo-controlled, double-blinded trial in aviremic, cART-treated HIV-infected subjects. Participants (n = 15) were randomized 3:1 to receive two consecutive daily doses of Poly-ICLC (1.4 mg subcutaneously) vs. placebo. Subjects were observed for adverse events, immune activation, and viral replication. Methods: Besides primary outcomes of safety and tolerability, several longitudinal immune parameters were evaluated including immune cell phenotype and function via flowcytometry, ELISA, and transcriptional profiling. PCR assays for plasma HIV-1 RNA, CD4+ T cell-associated HIV-1 RNA, and proviral DNA were performed to measure HIV reservoirs and latency. Results: Poly-ICLC was overall safe and well-tolerated. Poly-ICLC-related adverse events were Grade 1/2, with the exception of one Grade 3 neutropenia which was short-lived. Mild Injection site reactions were observed in nearly all participants in the Poly-ICLC arm. Transcriptional analyses revealed upregulation of innate immune pathways in PBMCs following Poly-ICLC treatment, including strong interferon signaling accompanied by transient increases in circulating IP-10 (CXCL10) levels. These responses generally peaked by 24–48 h after the first injection and returned to baseline by day 8. CD4+ T cell number and phenotype were unchanged, plasma viral control was maintained and no significant effect on HIV reservoirs was observed. Conclusions: These finding suggest that Poly-ICLC could be safely used for inducing transient innate immune responses in treated HIV+ subjects indicating promise as an adjuvant for HIV therapeutic vaccines. Trial Registration: www.ClinicalTrials.gov, identifier: NCT02071095.

Upon completion of this chapter, the reader should be able to • Demonstrate and apply knowledge about established and evolving science describing HIV virology, both in the cell and in the host. • Effectively counsel and educate patients and their communities regarding HIV treatment.

BACKGROUND:MK-8591 (4'-ethynyl-2-fluoro-2'-deoxyadenosine [EFdA]) is a novel reverse transcriptase-translocation inhibitor.METHODS:We assessed MK-8591 as preexposure prophylaxis in the rhesus macaque model of intrarectal challenge with simian/human immunodeficiency virus (SHIV). In study 1, 8 rhesus macaques received 3.9 mg/kg of MK-8591 orally on day 0 and once weekly for the next 14 weeks. Eight controls were treated with vehicle. All rhesus macaques were challenged with SHIV109CP3 on day 6 and weekly for up to 12 challenges or until infection was confirmed. The dose of MK-8591 was reduced to 1.3 and 0.43 mg/kg/week in study 2 and further to 0.1 and 0.025 mg/kg/week in study 3. In studies 2 and 3, each dose was given up to 6 times once weekly, and animals were challenged 4 times once weekly with SHIV109CP3.RESULTS:Control macaques were infected after a median of 1 challenge (range, 1-4 challenges). All treated animals in studies 1 and 2 were protected, consistent with a 41.5-fold lower risk of infection (P < .0001, by the log-rank test). In study 3, at a 0.1-mg/kg dose, 2 rhesus macaques became infected, consistent with a 7.2-fold lower risk of infection (P = .0003, by the log-rank test). The 0.025-mg/kg dose offered no protection.CONCLUSIONS:These data support MK-8591's potential as a preexposure prophylaxis agent.

Pattern recognition receptors (PRRs) protect against host invasion by detecting specific molecular patterns found in pathogens and initiating an immune response. While microbial-derived PRR ligands have been extensively characterized, the contribution and relevance of endogenous ligands to PRR activation during viral infection remain overlooked. In this work, we characterize the landscape of endogenous ligands that engage RIG-I-like receptors (RLRs) upon infection by a positive-sense RNA virus, a negative-sense RNA virus or a retrovirus. We found that several endogenous RNAs transcribed by RNA polymerase 3 (Pol3) specifically engage RLRs, and in particular the family of small non-coding repeats Y-RNAs, which presents the highest affinity as RIG-I ligands. We show that this recognition is dependent on Y-RNA mimicking viral secondary structure and its 5’-triphosphate extremity. Further, we found that HIV-1 infection triggers a VPR-dependent downregulation of RNA triphosphatase DUSP11 in vitro and in vivo , leading to an increase of Y-RNA 5’-triphosphorylation that enables their immunogenicity. Importantly, we show that altering DUSP11 expression is sufficient to induce a type-I interferon and T cell activation transcriptional program associated with HIV-1 infection. Overall, our work uncovers the critical contribution of endogenous repeat RNAs ligands to antiviral immunity and demonstrates the role of this pathway in HIV-1 infection.

Background: Cabotegravir (GSK1265744) is an integrase strand transfer inhibitor in development as a long-acting (LA) intramuscular injectable suspension for HIV-1 pre-exposure prophylaxis (PrEP). Objective: We report participant outcomes from the phase IIa ECLAIR study related to tolerability, acceptability, and satisfaction of cabotegravir LA. Methods: The ECLAIR study (ClinicalTrials.gov identifier, NCT02076178) was a randomized, placebo-controlled study in healthy men not at high risk of acquiring HIV-1. Participants were randomized (5:1) to once-daily oral cabotegravir 30 mg or placebo tablets for 4 weeks, followed by gluteal intramuscular injections of cabotegravir LA 800 mg or saline placebo every 12 weeks. The primary objective was to evaluate the safety of cabotegravir LA over three injection cycles (to Week 41). Secondary objectives assessed the tolerability, satisfaction, and acceptability of cabotegravir LA. Results: Among 115 participants who received injections in the cabotegravir (n = 94) and placebo (n = 21) groups, 93% (n = 87) and 95% (n = 20) completed the injection phase, respectively. Injection intolerability led to withdrawal in 4 participants (4%) receiving cabotegravir LA. The most frequently reported Grade ≥2 adverse event was injection-site pain. Most participants (74% [n = 67]) receiving consecutive injections favored cabotegravir LA vs oral cabotegravir. Most participants were satisfied with cabotegravir LA (75% [n = 64]), were willing to continue (79% [n = 68]), and would recommend (87% [n = 75]) the therapy. Conclusions: While Grade ≥2 injection-site pain was common, most participants reported overall satisfaction with and preference for cabotegravir LA, with few discontinuations due to injection intolerance. These findings support investigation of cabotegravir LA as an alternative to daily oral PrEP regimens.

This study aimed to identify patients' physical and psychosocial experiences of an investigational long-acting injectable PrEP product to aid in the development of patient and provider education materials. Twenty-eight participants of a Phase 2 safety, tolerability, and acceptability study of long-acting integrase inhibitor cabotegravir (CAB-LA) were interviewed on their physical and psychosocial experiences of the injections. Five themes emerged through a framework analysis on these interview transcripts: (1) injection-related pain is highly variable across individuals; (2) pain is more impactful after the injections than during; (3) patient anxiety is critical, but does not determine the experience of injections and decreases over time; (4) intimacy and awkwardness of gluteal injections impacts patients' experiences; (5) patient education and care strategies can mitigate the above factors. These findings can inform further sociobehavioral research within Phase 3 efficacy trials of CAB-LA, as well as patient education and provider guidance for future injectable PrEP products.

Using 5′ rapid amplification of cDNA ends, Illumina MiSeq, and basic flow cytometry, we systematically analyzed the expressed B cell receptor (BCR) repertoire in 14 healthy adult PBMCs, 5 HIV-1+ adult PBMCs, 5 cord blood samples, and 3 HIS-CD4/B mice, examining the full-length variable region of μ, γ, α, κ, and λ chains for V-gene usage, somatic hypermutation (SHM), and CDR3 length. Adding to the known repertoire of healthy adults, Illumina MiSeq consistently detected small fractions of reads with high mutation frequencies including hypermutated μ reads, and reads with long CDR3s. Additionally, the less studied IgA repertoire displayed similar characteristics to that of IgG. Compared to healthy adults, the five HIV-1 chronically infected adults displayed elevated mutation frequencies for all μ, γ, α, κ, and λ chains examined and slightly longer CDR3 lengths for γ, α, and λ. To evaluate the reconstituted human BCR sequences in a humanized mouse model, we analyzed cord blood and HIS-CD4/B mice, which all lacked the typical SHM seen in the adult reference. Furthermore, MiSeq revealed identical unmutated IgM sequences derived from separate cell aliquots, thus for the first time demonstrating rare clonal members of unmutated IgM B cells by sequencing.

Introduction: Human Immunodeficiency Virus (HIV) is a chronic infection that depletes the immune system of essential components causing those infected to be at risk for multiple life-threatening infections. Worldwide, millions live with this infection, the vast majority attributable to HIV-1. Transmission persists with hundreds of thousands of new infections reported yearly. Implementation of combination antiretroviral therapy (cART) has been effective in improving outcomes and decreasing transmission. Newer co-formulated agents have provided simpler medication regimens, fewer side effects, and, in some cases, a higher barrier to the emergence of medication resistance.Areas covered: Here, we review trials of cabotegravir (CAB) as treatment of HIV-1 infection and its potential use as pre-exposure prophylaxis (PrEP) in high risk individuals, including issues around oral lead in and potential resistance emergence.Expert opinion: CAB is efficacious when used in combination therapy orally or given intramuscularly every 4 to 8weeks. Its availability in a long-acting injectable formulation (CAB-LA) makes it a valuable, novel drug to treat HIV-1 infection when combined with long-acting injectable rilpivirine (RPV-LA). Moreover, pre-clinical and early Phase 2a studies support its testing as monotherapy as PrEP. Studies are underway comparing the efficacy of every 8week CAB-LA to tenofovir disoproxil fumarate/emtricitabine (TDF/FTC).

Risk of HIV infection is high in Chinese MSM, with an annual HIV incidence ranging from 3.41 to 13.7/100 person-years. Tenofovir-based PrEP is effective in preventing HIV transmission in MSM. This study evaluates the epidemiological impact and cost-effectiveness of implementing PrEP in Chinese MSM over the next two decades. A compartmental model for HIV was used to forecast the impact of PrEP on number of infections, deaths, and disability-adjusted life years (DALY) averted. We also provide an estimate of the incremental cost-effectiveness ratio (ICER) and the cost per DALY averted of the intervention. Without PrEP, there will be 1.1–3.0 million new infections and 0.7–2.3 million HIV-related deaths in the next two decades. Moderate PrEP coverage (50%) would prevent 0.17–0.32 million new HIV infections. At Truvada’s current price in China, daily oral PrEP costs $46,813–52,008 per DALY averted and is not cost-effective; on-demand Truvada reduces ICER to $25,057–27,838 per DALY averted, marginally cost-effective; daily generic tenofovir-based regimens further reduce ICER to $3675–8963, wholly cost-effective. The cost of daily oral Truvada PrEP regimen would need to be reduced by half to achieve cost-effectiveness and realize the public health good of preventing hundreds of thousands of HIV infections among MSM in China.

Purpose of review4-Ethynyl-2-fluoro-2-deoxyadenosine (EFdA) is a nucleoside reverse transcriptase inhibitor (NRTI) with a novel mechanism of action, unique structure, and amongst NRTIs, unparalleled anti-HIV-1 activity. We will summarize its structure and function, antiviral activity, resistance profile, and potential as an antiretroviral for use in the treatment and preexposure prophylaxis of HIV-1 infection.Recent findingsEFdA is active against wild-type (EC50 as low as 50pmol/l) and most highly NRTI-resistant viruses. The active metabolite, EFdA-triphosphate, has been shown to have a prolonged intracellular half-life in human and rhesus (Rh) blood cells. As a result, single drug doses tested in simian immunodeficiency virus mac(251)-infected Rh macaques and HIV-1-infected individuals exhibited robust antiviral activity of 7-10 days duration. Preclinical studies of EFdA as preexposure prophylaxis in the Rh macaque/simian/human immunodeficiency virus low-dose intrarectal challenge model have shown complete protection when given in clinically relevant doses.SummaryEFdA is a novel antiretroviral with activity against both wild-type and NRTI-resistant viruses. As a result of the prolonged intracellular half-life of its active moiety, it is amenable to flexibility in dosing of at least daily to weekly and perhaps longer.

Background Cabotegravir (GSK1265744) is an HIV-1 integrase strand transfer inhibitor with potent antiviral activity and a long half-life when administered by injection that prevented simian-HIV infection upon repeat intrarectal challenge in male macaques. We aimed to assess the safety, tolerability, and pharmacokinetics of long-acting cabotegravir injections in healthy men not at high risk of HIV-1 infection.Methods We did this multicentre, double-blind, randomised, placebo-controlled, phase 2a trial at ten sites in the USA. Healthy men (aged 18-65 years) deemed not at high risk of acquiring HIV-1 at screening were randomly assigned (5: 1), via computer-generated central randomisation schedules, to receive cabotegravir or placebo. Participants received oral cabotegravir 30 mg tablets or matching placebo once daily during a 4 week oral lead-in phase, followed by a 1 week washout period and, after safety assessment, three intramuscular injections of long-acting cabotegravir 800 mg or saline placebo at 12 week intervals. Study site staff and participants were masked to treatment assignment from enrolment through week 41 (time of the last injection). The primary endpoint was safety and tolerability from the first injection (week 5) to 12 weeks after the last injection. We did analysis in the safety population, defined as all individuals enrolled in the study who received at least one dose of the study drug. This study is registered with ClinicalTrials.gov identifier, NCT02076178.Findings Between March 27, 2014, and Feb 23, 2016, we randomly assigned 127 participants to receive cabotegravir (n=106) or placebo (n=21); 126 (99%) participants comprised the safety population. Most participants were men who have sex with men (MSM; n=106 [83%]) and white (n=71 [56%]). 87 (82%) participants in the cabotegravir group and 20 (95%) participants in the placebo group completed the injection phase. Adverse events (n=7 [7%]) and injection intolerability (n=4 [4%]) were the main reasons for withdrawal in the cabotegravir group. The frequency of grade 2 or higher adverse events was higher in participants in the long-acting cabotegravir group (n=75 [80%]) than in those in the placebo group (n=10 [48%]; p=0.0049), mostly due to injection-site pain (n=55 [59%]). No significant differences were noted in concomitant medications, laboratory abnormalities, electrocardiogram, and vital sign assessments. Geometric mean trough plasma concentrations were 0.302 mu g/mL (95% CI 0.237-0.385), 0.331 mu g/mL (0.253-0.435), and 0.387 mu g/mL (0.296-0.505) for injections one, two, and three, respectively, indicating lower than predicted exposure. The geometric mean apparent terminal phase half-life estimated after the third injection was 40 days. Two (2%) MSM acquired HIV-1 infection, one in the placebo group during the injection phase and one in the cabotegravir group 24 weeks after the final injection when cabotegravir exposure was well below the protein-binding-adjusted 90% inhibitory concentration.Interpretation Despite high incidence of transient, mild-to-moderate injection-site reactions, long-acting cabotegravir was well tolerated with an acceptable safety profile. Pharmacokinetic data suggest that 800 mg administered every 12 weeks is a suboptimal regimen; alternative dosing strategies are being investigated. Our findings support further investigation of long-acting injectable cabotegravir as an alternative to orally administered pre-exposure prophylaxis regimens.

To the Editors: Antiretroviral agents as preexposure prophylaxis (PrEP) against HIV-1 infection are a recent and welcome addition to the prevention toolbox. Clinical trials have shown tenofovir disoproxil fumarate/emtrcitabine (TDF/FTC) as PrEP to be safe and associated with substantial reductions (44%–86%) in the rates of HIV-1 acquisition in men who have sex with men (MSM) and transgender women,1–4 heterosexual HIV-discordant couples,5 and high-risk heterosexual men and women.6 In July 2012, the U.S. Food and Drug Administration approved the use of TDF/FTC as PrEP in combination with safer sex practices to reduce the risk of sexually acquired HIV-1. Important lessons of PrEP use have emerged from clinical trials. Efficacy is highly dependent on adherence.7 Self-reported adherence, however, is of limited positive predictive utility. Indeed, objective measures of adherence (eg, drug levels in plasma and peripheral blood mononuclear cells) proved critical to study interpretation. For instance, in clinical trials, individuals randomized to active treatment who acquired HIV-1 infection had low or undetectable tenofovir (TFV) levels in plasma or TFV-diphosphate (TFV-DP) in peripheral blood mononuclear cells2,8,9 indicating poor adherence. Because of the relatively short half-life of TFV in blood plasma, however, this metric indicates the timing of the last dose and not longer-term adherence.10 The measurement of TFV-DP in red blood cells using dried blood spot (DBS) technology11 and TFV in hair samples12 indicates cumulative dosing and longer-term use and has proven valuable in interpreting subsequent open-label studies. In this article, we present a case report of a young MSM in an HIV-serodiscordant relationship who was prescribed PrEP and, despite reportedly high-level adherence, became infected with HIV-1. This 26-year-old MSM had been tested for HIV-1 infection routinely and deemed to be uninfected in January 2013, October 2013, and March 2015. Immediately before being prescribed TDF/FTC as PrEP in December 2015, a fourth-generation combination antigen/antibody (Ag/Ab) test was nonreactive and an HIV-RNA level was undetectable, consistent with his uninfected status. He was circumcised and had a history of treated urethral gonorrhea in September 2014. Of note, his regular partner had consistent virologic suppression on 3-drug antiretroviral therapy that had been initiated 4 years previously during acute infection. The patient was prescribed a 90-day supply of PrEP with 1 refill which was commenced on January 1, 2016. He was seen on February 2, 2016 and was adherent by history and tolerating TDF/FTC. He presented on May 3, 2016, 5 months after PrEP initiation, for routine HIV-1 testing reporting excellent adherence to the prescribed regimen. He reported insertive condomless anal intercourse (ICAI) and receptive condomless anal intercourse with his regular partner and 2 separate episodes of ICAI with 2 different partners of unknown HIV status, 11 and 5.5 weeks before presentation. Results of HIV-1 testing are shown in Table 1. The reactive fourth-generation HIV test with a nonreactive HIV-1/2 Multispot and reactive qualitative testing for HIV-1 RNA by nucleic acid amplification test suggested recent HIV-1 infection. Supplemental tests were performed, as were tests for levels of plasma HIV-1 RNA and CD4+ T cells and results reported 2 weeks thereafter (Table 1). The results were consistent with extremely low levels of HIV-1 viremia and immune system preservation without seroconversion, and the treatment regimen was intensified with the addition of dolutegravir 50 mg daily to TDF/FTC on May 26, 2016. On June 7, the patient was reevaluated. To confirm the subject's self-reports of excellent adherence with his prescribed PrEP regimen, TFV and TFV-DP levels were measured in hair and DBS, respectively (Table 1). Results were consistent with high-level (eg, daily) adherence over the preceding 6–8 weeks,11,13 both prior and subsequent to the first indications of seroconversion.11,13TABLE 1.: Summary of Pertinent Laboratory ResultsSince the patient's HIV-1 RNA level had been persistently below the level of detection, resistance testing on the virus in the plasma could not be performed. A GenoSure Archive test (Monogram), which derives HIV-1 sequences from cell-associated DNA, was sent on June 7 and failed to provide a result. On June 9, 2016, retesting revealed a reactive Bio-Rad GS HIV Combo Ag/Ab assay with both qualitative and quantitative HIV-1 RNA determinations being nondetectable. The Multispot HIV-1/2 Rapid test remained nonreactive (Table 1). By the current HIV testing algorithm, these results were reported as "no laboratory evidence of HIV infection," despite the persistently reactive combo assay. To determine whether the patient's partner was the source of infection, we amplified and sequenced the V3 loop of env, reverse transcriptase, protease, and integrase coding regions from HIV-1 viral DNA extracted from isolated CD4+ T cells from blood drawn on both patient and partner on June 9th (Supplemental Digital Content Fig. 1, https://links.lww.com/QAI/B76). Of note, the viral burden was extremely low in the newly infected patient, approximately 33.0 copies/106 CD4+ T cells on average that is orders of magnitude lower than typical viral loads among untreated individuals during early infection.14 Amplification of these coding regions proved challenging, and few sequences were available for comparison to those of his partner. However, phylograms demonstrated conclusively that the 2 individuals were infected with different viruses, as viral populations clearly segregate from each other (Supplemental Digital Content Fig. 1, https://links.lww.com/QAI/B76) and from additional viruses similarly analyzed. Infection despite high-level adherence to TDF and FTC suggested acquisition of a virus resistant to the components of PrEP. Genotyping of the reverse transcriptase coding region on single genomes derived by limiting dilution polymerase chain reaction revealed linked mutations at K65R and M184V, resistance-conferring mutations to TDF and FTC, respectively,15 and additional mutations to nonnucleoside reverse transcriptase inhibitors, specifically K103S, E138Q, and Y188L15 (Table 1, Supplemental Digital Content Table 1, https://links.lww.com/QAI/B76). This individual was likely infected with a multidrug-resistant (MDR) virus, as the nonnucleoside reverse transcriptase inhibitor–associated resistance mutations would not have evolved under pressure by TDF/FTC alone. However, given that sampling was not performed at the time of infection, the possibility of evolution of resistance under pressure by TDF and FTC cannot be completely ruled out. Given that the patient harbored HIV-1 resistant to both TDF and FTC, coformulated cobicistat-boosted darunavir was subsequently added to the patient's treatment regimen to ensure continued and prolonged virologic suppression. This is the second reported case of the acquisition of an MDR HIV-1 variant in an apparently adherent individual on TDF/FTC-based PrEP.16 In both cases, the patients reported excellent adherence confirmed by objective measurements of TDF use. However, these measurements could not be performed at the exact time of infection in both cases, so we can only extrapolate that adherence around the time of HIV acquisition was adequate. As the number and risk of sexual exposures were highest with the patient's regular partner, the question of transmissibility from an HIV-infected individual with an undetectable viral load was raised. Our patient's regular partner had achieved consistent virologic suppression on antiretroviral therapy for approximately 4 years. In this case, it was critical that we documented that the suppressed regular partner was not the source of the new HIV-1 infection in our index patient. The patient reported only ICAI with nonregular partners, and although ICAI carries a much lower of HIV acquisition than RCAI (11 versus 138 HIV-1 infections per 10,000 exposures), this case does demonstrate the importance of counseling MSM as to the per-act probability of HIV-1 acquisition.17 For our patient, repeated testing with the fourth-generation Ag/Ab combination test was reactive. As HIV-RNA levels were either barely or nondetectable, the presence of antibodies to HIV-1 was suggested, although the confirmatory immunoassay (Multispot HIV-1/2) remained repeatedly nonreactive over 5 weeks. Delayed seroconversion may be observed in those administered combination antiretroviral therapy during acute infection18 and in one other case report of an individual becoming HIV infected during repeated courses of postexposure prophylaxis with TDF/FTC.19 Essential to this case is that the combination of the reactive fourth-generation combination Ag/Ab test and the qualitative nucleic acid amplification test established the diagnosis of HIV infection. These findings highlight the importance of using sensitive HIV tests in the context of PrEP delivery.20 In summary, newly acquired HIV-1 infection in patients being treated with PrEP and with evidence of adequate adherence as assessed through objective measures is rare. To date, there have been 2 such cases of acquisition of MDR HIV-1 and a recent report of infection with wild-type HIV-1 in an MSM with repeated exposures through CAI,21 despite more than 86,000 people using PrEP in the United States. Such cases may pose clinical and laboratory challenges. Although sensitive fourth-generation tests were sufficient to detect infection in this case, subsequent recommended confirmatory testing following the 2014 Centers for Disease Control/Association of Public Health Laboratories HIV testing algorithm proved challenging. The limitations of testing in the face of a low viral burden may complicate testing efficacy. Objective adherence testing in this case proved useful. However, despite the high effectiveness of TDF/FTC as PrEP in highly adherent individuals, the level of protection, if any, against infection by circulating viruses resistant to both medications is not known. Although the transmission of MDR HIV-1 has fallen over the past decade,22,23 this case, as well as the "Toronto case," highlights the importance of awareness of the potential risk of MDR HIV-1 viral transmission despite PrEP use. Surveillance for drug resistance among people who become infected after receiving PrEP is needed to evaluate whether these cases will remain rare.

Objective:We evaluated the effectiveness of cabotegravir (CAB; GSK1265744 or GSK744) long acting as preexposure prophylaxis (PrEP) against intravenous simian immunodeficiency virus (SIV) challenge in a model that mimics blood transfusions based on the per-act probability of infection. Design:CAB long acting is an integrase strand transfer inhibitor formulated as a 200 mg/ml injectable nanoparticle suspension that is an effective PrEP agent against rectal and vaginal simian/human immunodeficiency virus transmission in macaques. Methods:Three groups of rhesus macaques (n = 8 per group) were injected intramuscularly with CAB long acting and challenged intravenously with 17 animal infectious dose 50% SIVmac251 on week 2. Group 1 was injected with 50 mg/kg on week 0 and 4 to evaluate the protective efficacy of the CAB long-acting dose used in macaque studies mimicking sexual transmission. Group 2 was injected with 50 mg/kg on week 0 to evaluate the necessity of the second injection of CAB long acting for protection against intravenous challenge. Group 3 was injected with 25 mg/kg on week 0 and 50 mg/kg on week 4 to correlate CAB plasma concentrations at the time of challenge with protection. Five additional macaques remained untreated as controls. Results:CAB long acting was highly protective with 21 of the 24 CAB long-acting-treated macaques remaining aviremic, resulting in 88% protection. The plasma CAB concentration at the time of virus challenge appeared to be more important for protection than sustaining therapeutic plasma concentrations with the second CAB long acting injection. Conclusion:These results support the clinical investigation of CAB long acting as PrEP in people who inject drugs.