Short communication: no evidence of occult SHIV infection as demonstrated by CD8+ cell depletion after chemoprophylaxis-induced protection from mucosal infection in rhesus macaques

Short communication: Viremic control is independent of repeated low-dose SHIVSF162p3 exposures

The repeat low-dose virus challenge model is commonly used in nonhuman primate studies of HIV transmission and biomedical preventions. For some viruses or challenge routes, it is uncertain whether the repeated exposure design might induce virus-directed innate or adaptive immunity that could affect infection or viremic outcomes. Retrospective cohorts of male Indian rhesus (n=40) and female pigtail (n=46) macaques enrolled in repeat low-dose rectal or vaginal SHIV(SF162p3) challenge studies, respectively, were studied to compare the relationship between the number of previous exposures and peak plasma SHIV RNA levels or viral load area under the curve (AUC), surrogate markers of viral control. Repeated mucosal exposures of 10 or 50 TCID50 of virus for rectal and vaginal exposures, respectively, were performed. Virus levels were measured by quantitative reverse-transcriptase real-time PCR. The cumulative number of SHIV(SF162p3) exposures did not correlate with observed peak virus levels or with AUC in rectally challenged rhesus macaques [peak: rho (ρ)=0.04, p=0.8; AUC: ρ=0.33, p=0.06] or vaginally challenged pigtail macaques (peak: ρ=-0.09, p=0.7; AUC: ρ=0.11, p=0.6). Infections in these models occur independently of exposure history and provide assurance that neither inoculation route nor number of exposures required for infection correlates with postinfection viremia. These data also indicate that both the vaginal and rectal repeated low-dose virus exposure models using SHIV(SF162p3) provide a reliable system for nonhuman primate studies.

Susceptibility to repeated, low-dose, rectal SHIVSF162P3 challenge is independent of TRIM5 genotype in rhesus macaques

Infections following repeated, low-dose (RLD), mucal S(H)IV exposures of macaques are used to model sexual HIV exposures for biomedical prevention testing. Different susceptibilities among animals can complicate study designs. In rhesus macaques, TRIM5 alleles Q, CypA, and TFP are resistance factors for infection with some S(H)IV strains, but not for SIVmac239 due to its capsid properties. SIVmac239-derived SHIVSF162P3 has been demonstrated to reproducibly infect mucosally in vaginal and rectal RLD models. To further test the suitability of SHIVSF162P3 for RLD models, we studied the influence of the TRIM5 genotype on susceptibility to rectal RLD infection and on plasma viremia by analyzing 43 male Indian rhesus macaques from control arms of completed studies. The median number of exposures required for infection was three (Q/Q, n=4) (TRIM5 alleles, number of macaques, respectively), four (Q/CypA, n=7), three (TFP/Q, n=15), three (TFP/TFP, n=15), and two (TFP/CypA, n=2); TRIM5(CypA/CypA) was not represented in our study. Median peak viremia (log10 viral copies/ml) in infected animals was 7.4 (Q/Q, n=4), 7.2 (Q/CypA, n=6), 7.3 (TFP/Q, n=13), 7.1 (TFP/TFP, n=15), and 6.5 (TFP/CypA; n=2). Neither susceptibility nor peak viremia was significantly different (log rank test, Kruskal-Wallis test, respectively). Rhesus macaques' susceptibility to RLD SHIVSF162P3 is independent of the TRIM5 TFP, CypA, and Q alleles, with the limitation that the power to detect any impact of CypA/CypA and TFP/CypA genotypes was nonexistent or low, due to absence or infrequency, respectively. The finding that TRIM5 alleles do not restrict mucosal infection or ensuing replication rates suggests that SHIVSF162P3 is indeed suitable for RLD experimentation.

Reduced inflammation and CD4 loss in acute SHIV infection during oral pre-exposure prophylaxis

BACKGROUND

The impact of pre-exposure prophylaxis (PrEP) with antiretrovirals on breakthrough HIV or SHIV infection is not fully documented. We addressed the hypothesis that SHIV(SF162P3) infection despite active PrEP results in altered early immune parameters, compared with untreated infection.

METHODS

Eleven rhesus macaques were infected during repeated, rectal, low-dose SHIV(SF162P3) exposures while receiving concurrent oral PrEP (Truvada [n = 2] or GS7340 [n = 4]) or as untreated controls (n = 5). We measured SHIV RNA, inflammatory cytokines, CD4 cells, and SHIV-specific and memory T cells until 20 weeks after peak viremia.

RESULTS

SHIV infection during PrEP resulted in 100-fold lower peak viremia and lower IL-15, IL-18, and IL-1Ra levels, compared with controls (P < .05; Wilcoxon rank-sum test). Unlike controls, PrEP-treated macaques showed no significant CD4 cell count reduction during acute infection and developed more SHIV-specific central memory T cells, relative to controls. After in vivo CD8 cell depletion, viral load increased to similar levels, indicating that CD8 cells were critical for viral control in both groups.

CONCLUSIONS

PrEP with antiretrovirals has beneficial effects on early SHIV infection even when infection is not prevented. Although long-term immune control could not be examined in this SHIV infection model, our results suggest that PrEP results in improved early disease parameters in breakthrough infections.

Estimates of human immunodeficiency virus incidence among female sex workers in north central Nigeria: implications for HIV clinical trials

We estimated the HIV incidence among commercial female sex workers (FSWs) in north central Nigeria using bimodal methodology. Using a cross-sectional study design, a total of 900 active FSWs between the ages of 18 and 35 years were recruited from 52 brothels within Nasarawa State, Nigeria. A rapid test algorithm was used to determine their HIV status. The BED IgG-Capture enzyme immunoassay (CEIA) was applied on the HIV-seropositive samples to detect recent HIV-1 infection for the estimation of incidence among those with HIV infection. Of the 900 FSWs tested, 335 (37.2%) were found to be positive for HIV. Of these, 63 showed evidence of recent infection. Using two third-generation BED analysis approaches that account for false-recent rate, an annualized adjusted HIV incidence of 11.97% (95% CI: 8.51-15.43%) and 12.36% (95% CI: 8.18-16.34%) was observed; difference P>0.05. In addition, 875 (97.2%) of the FSWs readily agreed to participate in HIV clinical trials. We have developed the expertise and infrastructure necessary for clinical trial investigations in sub-Saharan Africa. We have recorded a high proportion of recent HIV infections among FSWs in Nigeria and also provided an enabling environment for future studies of HIV prevention methods.

T cell chemo-vaccination effects after repeated mucosal SHIV exposures and oral pre-exposure prophylaxis

Pre-exposure prophylaxis (PrEP) with anti-viral drugs is currently in clinical trials for the prevention of HIV infection. Induction of adaptive immune responses to virus exposures during anti-viral drug administration, i.e., a "chemo-vaccination" effect, could contribute to PrEP efficacy. To study possible chemo-vaccination, we monitored humoral and cellular immune responses in nine rhesus macaques undergoing up to 14 weekly, low-dose SHIV(SF162P3) rectal exposures. Six macaques concurrently received PrEP with intermittent, oral Truvada; three were no-PrEP controls. PrEP protected 4 macaques from infection. Two of the four showed evidence of chemo-vaccination, because they developed anti-SHIV CD4(+) and CD8(+) T cells; SHIV-specific antibodies were not detected. Control macaques showed no anti-SHIV immune responses before infection. Chemo-vaccination-induced T cell responses were robust (up to 3,940 SFU/10(6) PBMCs), predominantly central memory cells, short-lived (≤22 weeks), and appeared intermittently and with changing specificities. The two chemo-vaccinated macaques were virus-challenged again after 28 weeks of rest, after T cell responses had waned. One macaque was not protected from infection. The other macaque concurrently received additional PrEP. It remained uninfected and T cell responses were boosted during the additional virus exposures. In summary, we document and characterize PrEP-induced T cell chemo-vaccination. Although not protective after subsiding in one macaque, chemo-vaccination-induced T cells warrant more comprehensive analysis during peak responses for their ability to prevent or to control infections after additional exposures. Our findings highlight the importance of monitoring these responses in clinical PrEP trials and suggest that a combination of vaccines and PrEP potentially might enhance efficacy.

Yet another ten stories on antiviral drug discovery (part D): paradigms, paradoxes, and paraductions

This review article presents the fourth part (part D) in the series of stories on antiviral drug discovery. The stories told in part D focus on: (i) the cyclotriazadisulfonamide compounds; (ii) the {5-[(4-bromophenylmethyl]-2-phenyl-5H-imidazo[4,5-c]pyridine} compounds; (iii) (1H,3H-thiazolo[3,4-a]benzimidazole) derivatives; (iv) T-705 (6-fluoro-3-hydroxy-2-pyrazinecarboxamide) and (v) its structurally closely related analogue pyrazine 2-carboxamide (pyrazinamide); (vi) new strategies for the treatment of hemorrhagic fever virus infections, including, as the most imminent, (vii) dengue fever, (viii) the veterinary use of acyclic nucleoside phosphonates; (ix) the potential (off-label) use of cidofovir in the treatment of papillomatosis, particularly RRP (recurrent respiratory papillomatosis); and (x) finally, the prophylactic use of tenofovir to prevent HIV infections.

CD8+ cell depletion accelerates HIV-1 immunopathology in humanized mice

Stable engraftment of human lymphoid tissue in NOD/scid-IL-2Rgammacnull mice after CD34+ hematopoietic stem cell reconstitution permits the evaluation of ongoing HIV-1 infection for weeks to months. We demonstrate that HIV-1-infected rodents develop virus-specific cellular immune responses. CD8+ cell depletion, 2 or 5-7 wk after viral infection, resulted in a significant increase of HIV-1 load, robust immune cell activation, and cytopathology in lymphoid tissues but preserved CD4/CD8 double-positive thymic T cell pools. Human CD8+ cells reappeared in circulation as early as 2-3 wk. These data support a role of CD8+ cells in viral surveillance and the relevance of this humanized mouse model for the studies of HIV-1 pathobiology and virus-specific immunity.

Repeated rectal SHIVSF162P3 exposures do not consistently induce sustained T cell responses prior to systemic infection in the repeat-low dose preclinical macaque model

The macaque model of repeated SHIV exposures is increasingly used as a preclinical tool to evaluate biomedical HIV intervention strategies. It is unclear whether multiple virus exposures induce immune responses in macaques, as documented in uninfected individuals repeatedly exposed to HIV. We here address whether repeated, rectal SHIV(SF162P3) exposures lead to systemic T cell activation in 12 rhesus macaques, and whether this is associated with increased infection resistance. Eight macaques became systemically infected after 2-7 exposures, three macaques were less susceptible (infection after 10-12 exposures), and one macaque remained uninfected after 14 exposures. PBMCs were retrospectively monitored for increases in T cell activation by analyzing the proportion of CD8(+) T cells, recently activated or proliferated T cells (markers CD38, Ki67), a marker for cytotoxicity (granzyme B), or T cell-produced plasma cytokines (IFN-gamma, RANTES, IL-2). Repeated virus exposures did not induce sustained, potent, or diverse T cell responses prior to systemic infection. Some changes occurred in the analyzed parameters during repeated virus exposures, but similar T cell activities were also observed in five SHIV-unexposed control macaques. Thus, we found no evidence that delayed infection or resistance to infection was associated with systemic, long-lasting, protective T cell responses to repeated rectal virus exposures. Our results provide further insights into the repeat exposure macaque model. We find that this model can be used for testing biomedical prevention strategies without concern of eliciting a systemic vaccination effect.

Evaluation of the lymphocyte trafficking drug FTY720 in SHIVSF162P3-infected rhesus macaques

OBJECTIVES

FTY720 causes retention of lymphocytes in lymphatic tissues. Previous studies revealed that FTY720 can decrease or eliminate chronic viral infections of mice. We address here whether therapeutic use of FTY720 in simian human immunodeficiency virus (SHIV)-infected rhesus macaques could also decrease viraemia.

METHODS

FTY720 was administered intravenously to three SHIV(SF162P3)-infected macaques at 39, 7 or 6 weeks of infection; three control macaques (47, 48 or 6 weeks of infection) did not receive drug. FTY720 was given at 0.004 mg/kg on days 0, 1, 2, 14, 15 and 16, followed by 0.1 mg/kg on days 28, 29, 30, 42, 43 and 44. Blood was collected seven times throughout and four times during 47 days of follow-up.

RESULTS

Only the 0.1 mg/kg dose resulted in a reduction in mean blood CD4+ T cells and B cells (to 33% and 27% of pre-drug levels, P=0.0024 and 0.003, respectively). FTY720 treatment did not lead to significant deviations from the natural pattern of viral control. Plasma viraemia progressed from a range of 10(4)-10(2) copies/mL before treatment to 10(4)-temporarily undetectable levels on the last day of treatment. SHIV(SF162P3) was not eliminated, however, as plasma viraemia and proviral DNA persisted during the follow-up. No significant alterations in T cell activity were noted throughout the drug course.

CONCLUSIONS

FTY720 administration had no detectable therapeutic effect at the doses and schedules outlined here, although blood CD4+ T cells and B cells were effectively reduced. Future work might reveal whether FTY720 could be beneficial in more pathogenic SHIV, simian immunodeficiency virus or HIV infections.

Vaccines, virucides and drugs against HIV/AIDS: hopes and optimisms for the future

More than 25 million lives have been claimed by AIDS and 33.2 million people are estimated to have HIV, the majority of which are living in the underdeveloped countries. Failed tests on vaccines, virucides and complete virus eradication have caused scientists to refocus on the basic questions of what makes an effective HIV immune response. The "gloom" over disappointing research results on vaccine development and virucides "threatens to overshadow more positive" HIV/AIDS-related news, such as findings that male circumcision might reduce the likelihood of HIV transmission and that giving antiretroviral drugs to "high-risk" HIV-negative people (pre-exposure prophylaxis) could help protect them from infection. Something like pre-exposure prophylaxis has a good chance of becoming available before we have a 100% efficacious vaccine. The future in the field of HIV/AIDS will be much brighter if global research is appropriately coordinated and sufficient funds are available.