Promises and pitfalls in the reconstitution of immunity in patients who have HIV-1 infection

Structured Treatment Interruptions and Low Doses of IL-2 in Patients with Primary HIV Infection. Inflammatory, Virological and Immunological Outcomes

BACKGROUND

Interventions during primary HIV infection (PHI) can modify the clinical course during the chronic phase. The long-term effect of structured treatment interruptions (STI) followed by low doses of interleukin-2 (IL-2) in treated PHI patients is unknown.

METHODS

Twelve PHI patients with viral load (VL) <20 copies/mL, CD4 cells >500 cells/mm3, and CD4/CD8 ratio >1, on antiretroviral therapy (ART) initiated within the first 90 days of infection and continued for at least 12 months were included. They underwent four STI and were then allocated (week 0 of the study) to ART alone or ART plus low doses of IL-2. ART was stopped once VL <20 copies/mL ('final stop'). Primary endpoints were VL<3000 copies/mL and CD4 cells >500 cells/mm3 at 48 weeks; secondary endpoints were immune activation, inflammatory markers until 48 weeks and the time before resuming ART (CD4 <350 cells/mm3 or AIDS) after 'final stop', compared between groups.

RESULTS

Ten out of 12 patients were males, median age was 35 years and the main risk was men-who-have-sex-with-men. Only one out of 12 patients (in the STI group) maintained VL<3000 copies/mL and CD4 cells >500 cells/mm3 without ART at 48 weeks. All other virological and immunological parameters were comparable between groups at week 0, 'final stop' and week 48. However, the proportion of CD8-CD38+ cells, tumor necrosis factor and srIL-2 were higher in the IL-2 group at 'final stop' and week 24. All these differences vanished during follow-up. At 5 years after the final stop 3 out of 6 patients in the IL-2 group and 6 out of 6 patients in the STI group have resumed ART (P = 0.19).

CONCLUSIONS

STI and IL-2 failed to achieve virological control after ART interruption. STI were not deleterious in long-term follow-up, an important issue for eradication and functional cure trials.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02300623.

Growth hormone enhances thymic function in HIV-1-infected adults

Growth hormone (GH) is an underappreciated but important regulator of T cell development that can reverse age-related declines in thymopoiesis in rodents. Here, we report findings of a prospective randomized study examining the effects of GH on the immune system of HIV-1-infected adults. GH treatment was associated with increased thymic mass. In addition, GH treatment enhanced thymic output, as measured by both the frequency of T cell receptor rearrangement excision circles in circulating T cells and the numbers of circulating naive and total CD4(+) T cells. These findings provide compelling evidence that GH induces de novo T cell production and may, accordingly, facilitate CD4(+) T cell recovery in HIV-1-infected adults. Further, these randomized, prospective data have shown that thymic involution can be pharmacologically reversed in humans, suggesting that immune-based therapies could be used to enhance thymopoiesis in immunodeficient individuals.

Enhancing therapeutic vaccination by blocking PD-1-mediated inhibitory signals during chronic infection

Therapeutic vaccination is a potentially promising strategy to enhance T cell immunity and viral control in chronically infected individuals. However, therapeutic vaccination approaches have fallen short of expectations, and effective boosting of antiviral T cell responses has not always been observed. One of the principal reasons for the limited success of therapeutic vaccination is that virus-specific T cells become functionally exhausted during chronic infections. We now provide a novel strategy for enhancing the efficacy of therapeutic vaccines. In this study, we show that blocking programmed death (PD)-1/PD-L1 inhibitory signals on exhausted CD8⁺ T cells, in combination with therapeutic vaccination, synergistically enhances functional CD8⁺ T cell responses and improves viral control in mice chronically infected with lymphocytic choriomeningitis virus. This combinatorial therapeutic vaccination was effective even in the absence of CD4⁺ T cell help. Thus, our study defines a potent new approach to augment the efficacy of therapeutic vaccination by blocking negative signals. Such an approach may have broad applications in developing treatment strategies for chronic infections in general, and perhaps also for tumors.

The challenges of HIV vaccine development and testing

A vaccine against HIV remains the best hope for bringing the epidemic under control. An intensive global effort is underway to develop such a vaccine; however, the challenges are considerable. Several new vaccine technologies that have been developed and shown promise in animal models are now being tested in early phase safety trials in humans. Because there is no laboratory assay that will predict whether an HIV vaccine can protect humans from infection, clinical trials involving thousands of volunteers will need to be conducted to determine the efficacy of HIV vaccines. These trials need to take place in the developing countries that bear the burden of the epidemic, requiring a substantial amount of infrastructure development and capacity building.

ELISPOT cell rescue

The enzyme-linked immunospot (ELISPOT) assay is a highly sensitive and reproducible method for quantifying T cell-mediated immune responses, and has been used to measure antigen-specific responses post-vaccination. While there are several advantages of the ELISPOT assay for use in field settings for large-scale vaccination trials, blood draw volumes are often limited, and the number of antigen-specific responses that can be measured is constrained by the limited cell number. We reasoned that it should be possible to salvage and rescue viable cells from a completed ELISPOT assay post-incubation, to use for further experimentation. Here, we show that cells rescued from an ELISPOT plate after assay are viable, and may be used in a second cytokine-producing assay, in a proliferation assay, or to provide a source of DNA for genetic studies such as human leukocyte antigen (HLA) typing. Rescue of cells after an ELISPOT assay will be particularly useful for increasing sample utility and maximizing data collection from T cell assays in vaccine trials.

Magnetic resonance imaging of activated proliferating rhesus macaque T cells labeled with superparamagnetic monocrystalline iron oxide nanoparticles

Imaging of adoptively transferred cells in vivo by magnetic resonance imaging (MRI) could provide important information on disease-related patterns of lymphocyte homing in nonhuman primate models of AIDS. As a preliminary study to assess the feasibility of visualizing activated rhesus T cells by MRI, anti-CD3/CD28-expanded CD4+ T lymphocytes were labeled in vitro with monocrystalline iron oxide nanoparticles (MION). Intracellular incorporation of MION was determined by transmission electron microscopy (TEM) and inductively coupled plasma mass spectrography (ICP-MS). Pretreatment with colchicine did not affect MION labeling, suggesting that cellular uptake of MION occurred by adsorptive pinocytosis or receptor-mediated endocytosis. TEM analysis revealed that MION were intracellularly compartmentalized exclusively in the cytoplasm and did not cause any measurable physiologic effects on T-cell function, including viability, proliferation, synthesis of select cytokines (interleukin [IL]-2, IL-4, IL-6, IL-10, tumor necrosis factor-alpha, and interferon-gamma), activation antigens (CD25 and CD69), adhesion molecules (alpha4beta7 and CD49d), and susceptibility to in vitro infection with simian immunodeficiency virus mac239. A sensitivity of 0.05% (1 MION-labeled T cell in 2000 unlabeled cells) could be achieved using T2-weighted gradient echo imaging. Furthermore, under these experimental conditions, the MRI signal did not decrease in proliferating MION-labeled CD4+ T cells over a period of 120 hours. These results indicate that intracellular labeling with MION can be a useful technique for noninvasively monitoring trafficking patterns of adoptively transferred leukocyte subsets in real-time by MRI in nonhuman primate models of AIDS.

Enhancement of gp120-specific immune responses by genetic vaccination with the human immunodeficiency virus type 1 envelope gene fused to the gene coding for soluble CTLA4

DNA vaccines exploit the inherent abilities of professional antigen-presenting cells to prime the immune system and to elicit immunity against diverse pathogens. In this study, we explored the possibility of augmenting human immunodeficiency virus type 1 gp120-specific immune responses by a DNA vaccine coding for a fusion protein, CTLA4:gp120, in mice. In vitro binding studies revealed that secreted CTLA4:gp120 protein induced a mean florescence intensity shift, when incubated with Raji B cells, indicating its binding to B7 proteins on Raji B cells. Importantly, we instituted three different vaccination regimens to test the efficacy of DNA vaccines encoding gp120 and CTLA4:gp120 in the induction of both cellular (CD8(+)) and antibody responses. Each of the vaccination regimens incorporated a single intramuscular (i.m.) injection of the DNA vaccines to prime the immune system, followed by two booster injections. The i.m.-i.m.-i.m. regimen induced only modest levels of gp120-specific CD8(+) T cells, but the antibody response by CTLA4:gp120 DNA was nearly 16-fold higher than that induced by gp120 DNA. In contrast, using the i.m.-subcutaneous (s.c.)-i.m. regimen, it was found that gp120 and CTLA4:gp120 DNAs were capable of inducing significant levels of gp120-specific CD8(+) T cells (3.5 and 11%), with antibody titers showing a modest twofold increase for CTLA4:gp120 DNA. In the i.m.-gene gun (g.g.)-g.g. regimen, the mice immunized with gp120 and CTLA4:gp120 harbored gp120-specific CD8(+) T cells at frequencies of 0.9 and 2.9%, with the latter showing an eightfold increase in antibody titers. Thus, covalent antigen modification and the routes of genetic vaccination have the potential to modulate antigen-specific immune responses in mice.

Analysis of the helper virus in murine retrovirus-induced immunodeficiency syndrome: evidence for immunoselection of the dominant and subdominant CTL epitopes of the BM5 ecotropic virus

In genetically susceptible strains, such as C57BL/6 (B6) mice, LP-BM5 causes murine AIDS (MAIDS). LP-BM5 is a complex mixture of murine leukemia viruses (MuLV) that includes replication competent ecotropic (BM5eco) and mink cell focus inducing (MCF), and replication defective (BM5d) MuLV. At present, for the BM5eco virus, sequence information on only the gag region is available. In this paper, we describe for the first time the sequencing of the entire BM5eco viral genome as well as analysis of homology with two other previously sequenced and well-characterized MuLVs, Emv-11 and Emv-2, the latter constituting the parental virus for BM5eco. We propose that the detailed sequence comparisons herein provide cogent evidence that BM5eco utilizes variations in cytotoxic T lymphocytes (CTL) epitopes as an immune escape mechanism. This CTL evasion mechanism may contribute substantially to the underlying prototypic susceptibility of B6 mice to LP-BM5-induced MAIDS.

Kunjin virus replicon vectors for human immunodeficiency virus vaccine development

We have previously demonstrated the ability of the vaccine vectors based on replicon RNA of the Australian flavivirus Kunjin (KUN) to induce protective antiviral and anticancer CD8+ T-cell responses using murine polyepitope as a model immunogen (I. Anraku, T. J. Harvey, R. Linedale, J. Gardner, D. Harrich, A. Suhrbier, and A. A. Khromykh, J. Virol. 76:3791-3799, 2002). Here we showed that immunization of BALB/c mice with KUN replicons encoding HIV-1 Gag antigen resulted in induction of both Gag-specific antibody and protective Gag-specific CD8+ T-cell responses. Two immunizations with KUNgag replicons in the form of virus-like particles (VLPs) induced anti-Gag antibodies with titers of > or =1:10,000. Immunization with KUNgag replicons delivered as plasmid DNA, naked RNA, or VLPs induced potent Gag-specific CD8+ T-cell responses, with one immunization of KUNgag VLPs inducing 4.5-fold-more CD8+ T cells than the number induced after immunization with recombinant vaccinia virus carrying the gag gene (rVVgag). Two immunizations with KUNgag VLPs also provided significant protection against challenge with rVVgag. Importantly, KUN replicon VLP vaccinations induced long-lasting immune responses with CD8+ T cells able to secrete gamma interferon and to mediate protection 6 to 10 months after immunization. These results illustrate the potential value of the KUN replicon vectors for human immunodeficiency virus vaccine design.