Christine E. Nickerson

Bio: Christine E. Nickerson is an academic researcher from Beth Israel Deaconess Medical Center. The author has contributed to research in topics: CTL* & Simian immunodeficiency virus. The author has an hindex of 13, co-authored 14 publications receiving 2163 citations.

Control of Viremia and Prevention of Clinical AIDS in Rhesus Monkeys by Cytokine-Augmented DNA Vaccination

Abstract: With accumulating evidence indicating the importance of cytotoxic T lymphocytes (CTLs) in containing human immunodeficiency virus-1 (HIV-1) replication in infected individuals, strategies are being pursued to elicit virus-specific CTLs with prototype HIV-1 vaccines. Here, we report the protective efficacy of vaccine-elicited immune responses against a pathogenic SHIV-89.6P challenge in rhesus monkeys. Immune responses were elicited by DNA vaccines expressing SIVmac239 Gag and HIV-1 89.6P Env, augmented by the administration of the purified fusion protein IL-2/Ig, consisting of interleukin-2 (IL-2) and the Fc portion of immunoglobulin G (IgG), or a plasmid encoding IL-2/Ig. After SHIV-89.6P infection, sham-vaccinated monkeys developed weak CTL responses, rapid loss of CD4+ T cells, no virus-specific CD4+ T cell responses, high setpoint viral loads, significant clinical disease progression, and death in half of the animals by day 140 after challenge. In contrast, all monkeys that received the DNA vaccines augmented with IL-2/Ig were infected, but demonstrated potent secondary CTL responses, stable CD4+ T cell counts, preserved virus-specific CD4+ T cell responses, low to undetectable setpoint viral loads, and no evidence of clinical disease or mortality by day 140 after challenge.

Emergence of CTL coincides with clearance of virus during primary simian immunodeficiency virus infection in rhesus monkeys.

Abstract: The CTL response was characterized during primary SIV/macaque (SIVmac) infection of rhesus monkeys to assess its role in containing early viral replication using both an epitope-specific functional and an MHC class I/peptide tetramer-binding assay. The rapid expansion of a single dominant viral epitope-specific CTL population to 1.3–8.3% of circulating CD8+ peripheral blood and 0.3–1.3% of lymph node CD8+ T cells was observed, peaking at day 13 following infection. A subsequent decrease in number of these cells was then demonstrated. Interestingly, the percent of tetramer-binding CD8+ T cells detected in the lymph nodes of all evaluated animals was smaller than the percent detected in PBL. These epitope-specific CD8+ T cells expressed cell surface molecules associated with memory and activation. Early clearance of SIVmac occurred coincident with the emergence of the CTL response, suggesting that CTL may be important in containing virus replication. A higher percent of annexin V-binding cells was detected in the tetramer+ CD8+ T cells (range, from 33% to 75%) than in the remaining CD8+ T cells (range, from 3.3% to 15%) at the time of maximum CTL expansion in all evaluated animals. This finding indicates that the decrease of CTL occurred as a result of the death of these cells rather than their anatomic redistribution. These studies provide strong evidence for the importance of CTL in containing AIDS virus replication.

Augmentation of immune responses to HIV-1 and simian immunodeficiency virus DNA vaccines by IL-2/Ig plasmid administration in rhesus monkeys

Abstract: The potential utility of plasmid DNA as an HIV-1 vaccination modality currently is an area of active investigation. However, recent studies have raised doubts as to whether plasmid DNA alone will elicit immune responses of sufficient magnitude to protect against pathogenic AIDS virus challenges. We therefore investigated whether DNA vaccine-elicited immune responses in rhesus monkeys could be augmented by using either an IL-2/Ig fusion protein or a plasmid expressing IL-2/Ig. Sixteen monkeys, divided into four experimental groups, were immunized with (i) sham plasmid, (ii) HIV-1 Env 89.6P and simian immunodeficiency virus mac239 Gag DNA vaccines alone, (iii) these DNA vaccines and IL-2/Ig protein, or (iv) these DNA vaccines and IL-2/Ig plasmid. The administration of both IL-2/Ig protein and IL-2/Ig plasmid induced a significant and sustained in vivo activation of peripheral T cells in the vaccinated monkeys. The monkeys that received IL-2/Ig plasmid generated 30-fold higher Env-specific antibody titers and 5-fold higher Gag-specific, tetramer-positive CD8+ T cell levels than the monkeys receiving the DNA vaccines alone. IL-2/Ig protein also augmented the vaccine-elicited immune responses, but less effectively than IL-2/Ig plasmid. Augmentation of the immune responses by IL-2/Ig was evident after the primary immunization and increased with subsequent boost immunizations. These results demonstrate that the administration of IL-2/Ig plasmid can substantially augment vaccine-elicited humoral and cellular immune responses in higher primates.

Reduction of simian-human immunodeficiency virus 89.6P viremia in rhesus monkeys by recombinant modified vaccinia virus Ankara vaccination.

Abstract: Since cytotoxic T lymphocytes (CTLs) are critical for controlling human immunodeficiency virus type 1 (HIV-1) replication in infected individuals, candidate HIV-1 vaccines should elicit virus-specific CTL responses. In this report, we study the immune responses elicited in rhesus monkeys by a recombinant poxvirus vaccine and the degree of protection afforded against a pathogenic simian-human immunodeficiency virus SHIV-89.6P challenge. Immunization with recombinant modified vaccinia virus Ankara (MVA) vectors expressing SIVmac239 gag-pol and HIV-1 89.6 env elicited potent Gag-specific CTL responses but no detectable SHIV-specific neutralizing antibody (NAb) responses. Following intravenous SHIV-89.6P challenge, sham-vaccinated monkeys developed low-frequency CTL responses, low-titer NAb responses, rapid loss of CD4+ T lymphocytes, high-setpoint viral RNA levels, and significant clinical disease progression and death in half of the animals by day 168 postchallenge. In contrast, the recombinant MVA-vaccinated monkeys demonstrated high-frequency secondary CTL responses, high-titer secondary SHIV-89.6-specific NAb responses, rapid emergence of SHIV-89.6P-specific NAb responses, partial preservation of CD4+ T lymphocytes, reduced setpoint viral RNA levels, and no evidence of clinical disease or mortality by day 168 postchallenge. There was a statistically significant correlation between levels of vaccine-elicited CTL responses prior to challenge and the control of viremia following challenge. These results demonstrate that immune responses elicited by live recombinant vectors, although unable to provide sterilizing immunity, can control viremia and prevent disease progression following a highly pathogenic AIDS virus challenge.

Immunization with a modified vaccinia virus expressing simian immunodeficiency virus (SIV) Gag-Pol primes for an anamnestic Gag-specific cytotoxic T-lymphocyte response and is associated with reduction of viremia after SIV challenge.

Abstract: Evidence for a critical role of cytotoxic T lymphocytes (CTLs) in the containment of human immunodeficiency virus (HIV) infection (16, 23, 36, 39) has led to a consensus among those attempting to develop an AIDS vaccine that such a vaccine should generate CTL in addition to broadly neutralizing antibodies (26). An additional hurdle for an AIDS vaccine is the long-term maintenance of levels of CTL and antibody that will be necessary for protection (26). Both effector CTL and neutralizing antibodies induced by vaccination tend to be transient. Therefore, it may not be feasible to maintain immune responses essential for preventing infection. The importance of the magnitude of the vaccine-elicited memory and postinfection anamnestic immune responses thus become a critical issue in developing an AIDS vaccine. At present, viable vaccine strategies that might effectively stimulate CTL include viral vectors, peptides, and DNA immunization (26). Viral vectors under investigation include adenovirus (10, 48), alphaviruses such as Semliki Forest virus (8, 35) and Venezuelan equine encephalitis virus (11), poliovirus replicons (23), and various poxviruses (12, 21, 29, 30, 34, 43). Among these approaches, use of the poxviruses is a particularly promising vaccine strategy to express viral proteins. Studies with conventional New York Board of Health vaccinia virus demonstrated that priming with a vaccinia virus recombinant expressing simian immunodeficiency virus (SIV) envelope and/or core proteins, followed by boosting the antibody response with recombinant envelope protein, provided protection against a homologous SIV challenge with a biologically cloned strain of limited pathogenicity (SIVmne/E11S) (20). However this approach provided only partial protection against a more pathogenic and heterogeneous SIV challenge (SIVmne) (44) and blunting of viremia in macaques challenged with the highly pathogenic SIVmac251 (2). Since there are side effects associated with using conventional vaccinia viruses that become potentially life threatening when used in immunocompromised individuals (34), the use of attenuated poxviruses is an attractive alternative (20, 34, 43). A number of attenuated poxvirus strains have been developed as vaccine vectors: the avipoxviruses (43), canarypox virus, fowlpox virus, and the attenuated vaccinia virus derivatives, NYVAC (43), and modified vaccinia virus Ankara (MVA) (13, 32, 34, 43). The attenuated poxviruses appear to be safe in immunosuppressed animals (30), although their bases for attenuation differ. Thus, the avipoxviruses are genetically quite distinct from vaccinia viruses and do not complete an entire replication cycle in mammalian cells. NYVAC is a genetically engineered derivative of the Copenhagen strain with deletion of host range genes (43). MVA is a spontaneously derived attenuated variant of the Ankara strain that has multiple deletions in host range genes and genes involved in suppressing vaccinia virus-elicited immune responses (29, 30, 34). Perhaps due to these latter deletions, MVA appears to be as immunogenic as wild-type vaccinia virus strains, despite limited replication in mammalian cells (5, 9, 13, 32). In addition, MVA has an excellent safety record in humans, having been used without incident as a smallpox vaccine in approximately 100,000 individuals (30). Each of these attenuated poxvirus vectors has been evaluated in primate models and has shown some degree of efficacy (1, 4, 7, 14, 19, 22, 24, 37, 49, 50, 54). In previous studies, we explored the use of MVA as a viral vector to express SIV antigens and have evaluated its efficacy in the SIVsm-macaque model (19). The SIV-macaque model is a highly relevant system in which to evaluate the efficacy of partially protective vaccines since it provides valid disease endpoints. In addition, the level at which plasma viremia stabilizes after primary infection (or viral set point) is a highly significant prognostic surrogate for the rate of disease progression in both HIV infection (31) and SIV infection (19, 52, 55). While the SIV-HIV (SHIV) chimeras provide a system to evaluate the role of envelope-specific immune response in vaccine protection, there is no particular advantage to the use of SHIV in evaluating Gag-Pol-specific immunity. Indeed, the pathogenesis of SIV infection of macaques more closely models the pathogenesis of human AIDS (18) than the rapid CD4+ T-cell depletion observed with the pathogenic SHIVs (21, 28, 51). Prior immunization with MVA expressing the SIVsmH4 Gag-Pol and Env followed by boosting with whole inactivated SIV particles, administered without adjuvant, resulted in significant modulation of viremia and disease progression in macaques subsequently challenged with pathogenic SIVsmE660 (19). Two of these MVA-SIV vaccinees have maintained low viremia and normal CD4+ T-lymphocyte numbers throughout the 4 years since challenge, analogous to HIV type 1-infected clinical long-term nonprogressor humans (12, 42). The recent development of technology for measuring effector CTL by flow cytometric analyses of CD8+ T lymphocytes that bind specific peptide epitope-major histocompatibility complex (MHC) class I tetrameric complexes (3) has revolutionized the ability to quantitate CTL responses in SIV-infected macaques (24, 25). This technology is particularly useful for evaluation of CTL responses in recombinant vaccinia virus-immunized macaques since the background cytolysis that is seen in functional CTL assays with the use of vaccinia virus expression of viral proteins in target cells can be avoided. In a previous study we used tetramer technology to evaluate the ability of an MVA recombinant expressing SIV Gag-Pol to elicit CTL (50). In the present study, we evaluated immunogenicity of this recombinant through two subsequent boosts and evaluated the efficacy following intravenous challenge with pathogenic, uncloned, SIVsmE660.

Effector and memory T-cell differentiation: implications for vaccine development

Abstract: Recent work shows that after stimulation with antigen, CD4+ and CD8+ T cells embark on a programme of proliferation that is closely linked with the acquisition of effector functions and leads ultimately to memory-cell formation. Here, we discuss the signals required for commitment to this programme of development and the factors that might influence its progression. Models of the pathways of effector and memory T-cell differentiation are discussed, and we highlight the implications of this new understanding for the optimization of vaccine strategies.

Viral Persistence Alters CD8 T-Cell Immunodominance and Tissue Distribution and Results in Distinct Stages of Functional Impairment

Abstract: Chronic viral infections often result in ineffective CD8 T-cell responses due to functional exhaustion or physical deletion of virus-specific T cells. However, how persisting virus impacts various CD8 T-cell effector functions and influences other aspects of CD8 T-cell dynamics, such as immunodominance and tissue distribution, remains largely unknown. Using different strains of lymphocytic choriomeningitis virus (LCMV), we compared responses to the same CD8 T-cell epitopes during acute or chronic infection. Persistent infection led to a disruption of the normal immunodominance hierarchy of CD8 T-cell responses seen following acute infection and dramatically altered the tissue distribution of LCMV-specific CD8 T cells in lymphoid and nonlymphoid tissues. Most importantly, CD8 T-cell functional impairment occurred in a hierarchical fashion in chronically infected mice. Production of interleukin 2 and the ability to lyse target cells in vitro were the first functions compromised, followed by the ability to make tumor necrosis factor alpha, while gamma interferon production was most resistant to functional exhaustion. Antigen appeared to be the driving force for this loss of function, since a strong correlation existed between the viral load and the level of exhaustion. Further, epitopes presented at higher levels in vivo resulted in physical deletion, while those presented at lower levels induced functional exhaustion. A model is proposed in which antigen levels drive the hierarchical loss of different CD8 T-cell effector functions during chronic infection, leading to distinct stages of functional impairment and eventually to physical deletion of virus-specific T cells. These results have implications for the study of human chronic infections, where similar T-cell deletion and functional dysregulation has been observed.

Replication-incompetent adenoviral vaccine vector elicits effective anti-immunodeficiency-virus immunity.

Abstract: Recent studies of human immunodeficiency virus type 1 (HIV-1) infection in humans and of simian immunodeficiency virus (SIV) in rhesus monkeys have shown that resolution of the acute viral infection and control of the subsequent persistent infection are mediated by the antiviral cellular immune response. We comparatively assessed several vaccine vector delivery systems-three formulations of a plasmid DNA vector, the modified vaccinia Ankara (MVA) virus, and a replication incompetent adenovirus type 5 (Ad5) vector-expressing the SIV gag protein for their ability to elicit such immune responses in monkeys. The vaccines were tested either as a single modality or in combined modality regimens. Here we show that the most effective responses were elicited by a replication-incompetent Ad5 vector, used either alone or as a booster inoculation after priming with a DNA vector. After challenge with a pathogenic HIV-SIV hybrid virus (SHIV), the animals immunized with Ad5 vector exhibited the most pronounced attenuation of the virus infection. The replication-defective adenovirus is a promising vaccine vector for development of an HIV-1 vaccine.

Control of a mucosal challenge and prevention of AIDS by a multiprotein DNA/MVA vaccine.

Abstract: Heterologous prime/boost regimens have the potential for raising high levels of immune responses. Here we report that DNA priming followed by a recombinant modified vaccinia Ankara (rMVA) booster controlled a highly pathogenic immunodeficiency virus challenge in a rhesus macaque model. Both the DNA and rMVA components of the vaccine expressed multiple immunodeficiency virus proteins. Two DNA inoculations at 0 and 8 weeks and a single rMVA booster at 24 weeks effectively controlled an intrarectal challenge administered 7 months after the booster. These findings provide hope that a relatively simple multiprotein DNA/MVA vaccine can help to control the acquired immune deficiency syndrome epidemic.

Profound early control of highly pathogenic SIV by an effector memory T-cell vaccine

Abstract: The acquired immunodeficiency syndrome (AIDS)-causing lentiviruses human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) effectively evade host immunity and, once established, infections with these viruses are only rarely controlled by immunological mechanisms. However, the initial establishment of infection in the first few days after mucosal exposure, before viral dissemination and massive replication, may be more vulnerable to immune control. Here we report that SIV vaccines that include rhesus cytomegalovirus (RhCMV) vectors establish indefinitely persistent, high-frequency, SIV-specific effector memory T-cell (T(EM)) responses at potential sites of SIV replication in rhesus macaques and stringently control highly pathogenic SIV(MAC239) infection early after mucosal challenge. Thirteen of twenty-four rhesus macaques receiving either RhCMV vectors alone or RhCMV vectors followed by adenovirus 5 (Ad5) vectors (versus 0 of 9 DNA/Ad5-vaccinated rhesus macaques) manifested early complete control of SIV (undetectable plasma virus), and in twelve of these thirteen animals we observed long-term (≥1 year) protection. This was characterized by: occasional blips of plasma viraemia that ultimately waned; predominantly undetectable cell-associated viral load in blood and lymph node mononuclear cells; no depletion of effector-site CD4(+) memory T cells; no induction or boosting of SIV Env-specific antibodies; and induction and then loss of T-cell responses to an SIV protein (Vif) not included in the RhCMV vectors. Protection correlated with the magnitude of the peak SIV-specific CD8(+) T-cell responses in the vaccine phase, and occurred without anamnestic T-cell responses. Remarkably, long-term RhCMV vector-associated SIV control was insensitive to either CD8(+) or CD4(+) lymphocyte depletion and, at necropsy, cell-associated SIV was only occasionally measurable at the limit of detection with ultrasensitive assays, observations that indicate the possibility of eventual viral clearance. Thus, persistent vectors such as CMV and their associated T(EM) responses might significantly contribute to an efficacious HIV/AIDS vaccine.