July 23, 2010
This blog entry is the fourth in a series of reports on a few of the scientific abstracts submitted for presentation on the subject of "HIV Controllers (HCs)" and "Long Term Nonprogressors (LTNPs) -- a small minority of HIV-positive people who control the virus in as-of-yet unexplained ways -- to the XVIII International AIDS Conference in Vienna.
This blog entry wraps up my series of reports highlighting several abstracts presented at the XVIII AIDS Conference in Vienna on the most recent studies of "HIV Controllers (HCs)" and "Long Term Nonprogressors (LTNPs)" -- a unique group of HIV-positive individuals whose immune systems or genetic make-up contribute to remarkable suppression of the virus without aid of antiretroviral medications.
Clinical research studies of our community are relatively recent when compared to the 30 year-long HIV/AIDS epidemic. For example, the earliest study of LTNPs was inspired in 1993, when Dr. Mark Connors (head of the HIV-Specific Immunity Section of the National Institute of Allergy and Infectious Diseases -- NIAID) recognized that several participants involved in a separate study under his direction "had this inexplicable level of control of HIV." [Source: "Insights from People Who Keep HIV in Check," NIAID Discovery News, Spring 2008 Issue]. Since that time, many institutions, scientists and study volunteers have brought all of us closer to understanding how we keep this virus at bay. In time, the answers will come, I just know they will!
Abstracts can be accessed on the conference site.
THPE0005: Vpu-Specific ADCC Antibodies Efficiently Kill HIV-Infected Cells: Implications for ADCC-Inducing HIV Vaccines
M. Navis1, G. Isitman1, S. Kent1,2, I. Stratov1,2,3
1University of Melbourne, Department of Microbiology and Immunology, Melbourne, Australia, 2Melbourne Sexual Health Clinic, Melbourne, Australia, 3Burnet Institute, Melbourne, Australia
Background: "Antibody dependent cellular cytotoxicity (ADCC) is a potentially effective but under-explored adaptive immune response to HIV. These special antibodies have been associated with protection from SIV disease in macaques and delayed progressive HIV infection in humans. The ability of purified ADCC antibodies (without neutralizing capacity) to kill HIV-infected cells has not been previously studied but is likely to generate new HIV vaccine leads."
Methods: "We selected serum from a slow progressing HIV-infected subject from a cohort of 80 ART-naive patients. IgG antibodies were isolated with use of a protein A and G Sephadex column and then loaded onto a cyanogen bromide activated sepharose column with a bound Vpu peptide to purify Vpu-specific antibodies. The ADCC activity of the panels of purified antibodies (was) assessed by ICS-based and killing-based (ADCVI) ADCC assays. In addition, ADCC activity was examined in the serum of 40 patients from the cohort in both assays."
Results: "We mapped an ADCC epitope to the Vpu protein and then purified Vpu-specific ADCC antibodies over columns -- these purified ADCC antibodies retained efficient activation of IFNg-expression and degranulation by NK cells. Furthermore, these purified Vpu-specific ADCC antibodies killed up to 60% of HIV-infected cells, comparable to the killing activity of the source patient serum. This level of killing of HIV infected cells was greater than serum across the vast majority of the ART-naive cohort."
Conclusions: "We show here that HIV-specific antibodies mediating ADCC activity can successfully be purified. Remarkably, ADCC antibodies to the regulatory HIV protein Vpu, not classically thought of as a humoral vaccine target, can efficiently kill HIV infected cells. These antibodies will help define the utility of HIV-specific ADCC responses and open up a novel avenue towards vaccination against HIV."
ADCC: Antibody-Dependent Cell-Mediated Cytotoxicity is a mechanism of cell-mediated immunity whereby an effector cell of the immune system actively lyses a target cell that has been bound by specific antibodies. It is one of the mechanisms through which antibodies, as part of the humoral immune response, can act to limit and contain infection. Classical ADCC is mediated by natural killer (NK) cells; neutrophils and eosinophils can also mediate ADCC.
Antibody: Antibodies (also known as immunoglobulins, abbreviated Ig) are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacteria and viruses.
Epitope: An epitope, also known as antigenic determinant, is the part of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells.
IFNg (Interferon-gamma, IFNγ) is a dimerized soluble cytokine that is the only member of the type II class of interferons. In humans, the IFNγ protein is encoded by the IFNG gene.
Immunoglobulin G (IgG) are antibody molecules.
Natural Killer cells (NK) are a type of cytotoxic lymphocyte that constitutes a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses. They kill cells by releasing small cytoplasmic granules of proteins called perforin and granzyme that cause the target cell to die by apoptosis.
Vpu is a HIV gene. Vpu stands for "Viral Protein U." Vpu is involved in viral budding, enhancing virion release from the cell by counteracting BST2 (also known as tetherin). It can be found in HIV-1 but not in HIV-2. [Source: Wikipedia.org].
My Comments: This is an extremely important finding, with definite attributes toward a novel vaccine approach. Antibodies (naturally programmed to identify and neutralize invading antigens, not just HIV) were isolated from the serum (a component of the blood) of a "slow progressor" (clinical data for this individual was not provided in the abstract). The antibodies were purified (by a process I don't understand) to recognize only a specific gene of HIV (Vpu). The antibody-dependent cell-mediated cytotoxicity (the quality of being toxic to cells) activity of the purified antibodies were assessed in order to verify their function (by definition, to actively destroy an infected cell that has been identified and bound by an antibody) and confirmed by the team. The ADCC was then "mapped" to the HIV gene (Vpu). The team discovered that the purified HIV-specific ADCC antibodies killed up to 60% of HIV-infected cells! In fact, they also found that the magnitude of the killing capability in the purified ADCC was greater than what was already present in the serum of a majority of the treatment-naive donors in the cohort. Wow.
THPE0010: High Frequencies of Circulating HIV-Specific Memory B-Cells in the Blood of Infected Individuals
K. Kunz1, S. Reiche2, Y. Dwai1, B. Bieniek3, I. Krznaric4, B.M. Bussmann2, C. Jassoy1
1University of Leipzig, University Clinics, Institute of Virology, Leipzig, Germany, 2University of Leipzig, Translational Centre for Regenerative Medicine, Leipzig, Germany, 3PraxisCityOst, Berlin, Germany, 4Medical Practice Dupke/Carganico/Baumgarten, Berlin, Germany
Background: "A prospective HIV vaccine should induce long-lasting immunity. Analysis of the immunologic B-cell memory in natural HIV infection may provide information on how to achieve that goal."
Methods: "Memory B-cell responses to Env/gp120, gp41, Gag/p24, reverse transcriptase, and Nef as well als influenza nucleoprotein (NP), tetanus toxoid and Epstein-Barr virus (EBV) capsid antigen p23/p18 were quantified in the peripheral blood of HIV+ subjects with CD4+ T-cell counts above 350/µl."
Results: "A broad spectrum of circulating HIV-specific memory B-cells capable to differentiate into plasma cells in vitro was present in the majority of infected individuals. Memory B-cell responses to HIV proteins were comparable to or more vigorous than those to non-HIV proteins. Gag and Env-specific memory B-cells were particularly frequent."
Conclusions: "The peripheral blood of HIV-infected individuals with CD4+ T-cell counts above 350/µl contains high frequencies of circulating HIV-specific memory B-cells capable to differentiate into antibody-secreting plasma cells. This reflects potent activation of the B-cell system by natural HIV infection and suggests that induction of vigorous long-lasting HIV-specific B-cell responses by a vaccine might be feasible."
Memory B cells are a B cell subtype that are formed following primary infection. In wake of first (primary response) infection involving a particular antigen, the responding naive (ones which have never been exposed to the antigen) cells proliferate to produce a colony of cells, most of which differentiate into the plasma cells, also called effector B cells (which produce the antibodies) and clear away with the resolution of infection, and the rest persist as the memory cells that can survive for years, or even a lifetime).
Env: Env is a viral protein that serves to form the viral envelope.
gp120: Exposed on the surface of the viral envelope, the glycoprotein gp120 binds to the CD4 receptor on any target cell that has such a receptor, particularly the helper T-cell.
gp41: The glycoprotein gp41 is non-covalently bound to gp120, and provides the second step by which HIV enters the cell. It is originally buried within the viral envelope, but when gp120 binds to a CD4 receptor, gp120 changes its conformation causing gp41 to become exposed, where it can assist in fusion with the host cell.
Gag/p24, Gag: proteins are encoded by the gag gene, and provide structural elements of the virus; p24 makes up the viral capsid. (When a Western blot test is used to detect HIV infection, p24 is one of the three major proteins tested for, along with gp120/gp160 and gp41.)
Nef (Negative Regulatory Factor) is a protein expressed by primate lentiviruses. These include human immunodeficiency viruses (HIV-1 and HIV-2) and simian immunodeficiency virus (SIV). Nef is one of many pathogen-expressed proteins, known as virulence factors, which function to manipulate the host's cellular machinery and thus allow infection, survival or replication of the pathogen. Nef stands for "Negative Factor."
Reverse Transcriptase: Reverse transcriptase creates single stranded DNA from an RNA template. (The process of reverse transcription is extremely error-prone and it is during this step that mutations may occur. Such mutations may cause drug resistance.) [Source: Wikipedia.org].
My Comments: I'm curious to know the clinical data of the participants in this cohort -- duration of infection, viral loads, treatment experienced or treatment naive -- as it's unclear to me what is meant by the term "natural HIV infection." It's very interesting, though, that the Memory B-cell responses to HIV proteins Gag and Env were "particularly more frequent" and "more vigorous" in some of the samples from individuals who register >350 CD4 counts. These findings prompt me to wonder if these responses decline if one's CD4 count drops below 350 and whether the response lost with antiretroviral therapy. Even so, I like reading sentences that infer that a vaccine capable of inducing a "vigorous long-lasting HIV-specific B-cell response" might be "feasible." Go, Germany!
THPE0029: No Major Differences in the Functional Profile of HIV-Specific Immune Responses Comparing HIV-Exposed Seronegative and HIV-Infected Individuals
C. Restrepo1, N.I. Rallón1, J. del Romero2, C. Rodríguez2, V. Hernando2, M. López1, A. Peris1, V. Soriano1, J.M. Benito1
1Infectious Diseases Department, Hospital Carlos III, Madrid, Spain, 2Centro Sanitario Sandoval, Madrid, Spain
Background: "HIV-specific T-cell responses are frequently seen in exposed seronegative individuals (ESN). Herein, the functional profile of HIV-specific T-cells was assessed in ESN individuals by simultaneously measuring MIP1α, IFNγ, IL-2 and TNFα in response to overlapping HIV peptides."
Methods: "5 ESN and 6 HIV+ individuals were examined. ESN had a prior history of low-level exposure to HIV as result of stable high risk heterosexual relationship with an HIV-infected patient who kept undetectable viremia on HAART, and depicted a detectable HIV-specific T-cell response using IFNγ. Polychromatic flow cytometry was used for the simultaneous assessment of MIP1α, IFNγ, TNFα and IL-2 production by HIV-specific CD4+ and CD8+ T-cells."
Results: "Of 5 ESN, 3 (60%) had detectable CD4+ T-cell responses and 1 (20%) had detectable CD8+ T-cell responses. The hierarchy of the CD4+ response in ESN was as follows: MIP1α-IFNγ-IL2-TNFα+, MIP1α-IFNγ+IL2-TNFα+ and MIP1α-IFNγ-IL2+TNFα subsets. Overall, TNFα dominated the HIV-specific CD4+ response in both HIV+ and ESN followed by IFNγ, although IL-2 also contributed in some extent in ESN. In both groups the CD4+ T-cell response was dominated by monofunctional cells and in lesser extent by bi-functional cells."
"In the only ESN individual who presented CD8+ T-cell response, the hierarchy of this response was as follows: MIP1α-IFNγ+IL2-TNFα, MIP1α-IFNγ-IL2+TNFα, MIP1α+IFNγ+IL2-TNFα, MIP1α-IFNγ-IL2-TNFα+ subsets. All cytokines in ESN individual contributed to this response, being IFNγ the biggest contributor. Although monofunctional subsets dominated the CD8+ T-cell response in this individual, there was also contribution by bi-functional cells. This profile was quite similar to the group of HIV+ subjects."
Conclusions: "In ESN individuals with detectable HIV-specific immune response and a low level of exposure to virus, the functional profile of immune cells is quite similar to that found in HIV+ individuals. Further longitudinal studies are warranted to ascertain the potential role of this response in resistance to HIV infection."
ESN: Exposed Seronegative.
My Comments: I've been fascinated for years by the extraordinary story of "ESNs" -- and the studies conducted on women who have been exposed repeatedly to HIV yet who resist infection -- small cohorts in Nairobi, Kenya ["Pumwani Cohort"] and Gambia, South Africa. The fact that comparisons are being drawn between ESNs and HCs/LTNPs is quite remarkable! (This riveting topic is the subject of a satellite session at the upcoming AIDS Vaccine Conference in Atlanta, Georgia -- "Exposed uninfected and HIV controllers: models for preventive and therapeutic vaccines?": September 28, 2010). (The earliest paper published on ESNs: "T cell response towards HIV in infected individuals with and without zidovudine therapy, and in HIVexposed sexual partners" Ranki A, Mattinen S, Yarchoan R, Broder S, Ghrayeb J,Lahdevirta J, et al; For the ESN Study Group (Japan, Italy, France): AIDS 1989; 3:63-69.) [Source: http://journals.lww.com/aidsonline/fulltext/2009/01140/the__immunologic_advantage__of_hiv_exposed.2.aspx]
This has been an interesting endeavor and I've learned many things. I hope you have, too. By the way, I don't have a biomedical background and started on a relatively clean slate with all of the science just 6 years ago, right after I enrolled into my first clinical research study. Next week will mark the 18th anniversary of my diagnosis, and it's a privilege to share this time with you.
This blog series is dedicated to all of the wonderful members of the HIV Controller/LTNP community who have blessed my life!
In solidarity and hope,
Read more of Life as an Elite Controller, Loreen Willenberg's blog, at TheBody.com.